Merge remote-tracking branch 'origin/sos' into spec-0.6

beacon_node/db/src/stores/beacon_block_store.rs

@@ -1,6 +1,6 @@
 use super::BLOCKS_DB_COLUMN as DB_COLUMN;
 use super::{ClientDB, DBError};
-use ssz::decode;
+use ssz::Decode;
 use std::sync::Arc;
 use types::{BeaconBlock, Hash256, Slot};
 
@@ -30,7 +30,7 @@ impl<T: ClientDB> BeaconBlockStore<T> {
         match self.get(&hash)? {
             None => Ok(None),
             Some(ssz) => {
-                let block = decode::<BeaconBlock>(&ssz).map_err(|_| DBError {
+                let block = BeaconBlock::from_ssz_bytes(&ssz).map_err(|_| DBError {
                     message: "Bad BeaconBlock SSZ.".to_string(),
                 })?;
                 Ok(Some(block))

beacon_node/db/src/stores/beacon_state_store.rs

@@ -1,6 +1,6 @@
 use super::STATES_DB_COLUMN as DB_COLUMN;
 use super::{ClientDB, DBError};
-use ssz::decode;
+use ssz::Decode;
 use std::sync::Arc;
 use types::{BeaconState, EthSpec, Hash256};
 
@@ -26,7 +26,7 @@ impl<T: ClientDB> BeaconStateStore<T> {
         match self.get(&hash)? {
             None => Ok(None),
             Some(ssz) => {
-                let state = decode::<BeaconState<E>>(&ssz).map_err(|_| DBError {
+                let state = BeaconState::from_ssz_bytes(&ssz).map_err(|_| DBError {
                     message: "Bad State SSZ.".to_string(),
                 })?;
                 Ok(Some(state))

beacon_node/db/src/stores/validator_store.rs

@@ -4,7 +4,7 @@ use self::bytes::{BufMut, BytesMut};
 use super::VALIDATOR_DB_COLUMN as DB_COLUMN;
 use super::{ClientDB, DBError};
 use bls::PublicKey;
-use ssz::{decode, ssz_encode};
+use ssz::{Decode, Encode};
 use std::sync::Arc;
 
 #[derive(Debug, PartialEq)]
@@ -55,7 +55,7 @@ impl<T: ClientDB> ValidatorStore<T> {
         public_key: &PublicKey,
     ) -> Result<(), ValidatorStoreError> {
         let key = self.get_db_key_for_index(&KeyPrefixes::PublicKey, index);
-        let val = ssz_encode(public_key);
+        let val = public_key.as_ssz_bytes();
         self.db
             .put(DB_COLUMN, &key[..], &val[..])
             .map_err(ValidatorStoreError::from)
@@ -69,7 +69,7 @@ impl<T: ClientDB> ValidatorStore<T> {
         let val = self.db.get(DB_COLUMN, &key[..])?;
         match val {
             None => Ok(None),
-            Some(val) => match decode::<PublicKey>(&val) {
+            Some(val) => match PublicKey::from_ssz_bytes(&val) {
                 Ok(key) => Ok(Some(key)),
                 Err(_) => Err(ValidatorStoreError::DecodeError),
             },
@@ -125,7 +125,7 @@ mod tests {
             .unwrap()
             .unwrap();
 
-        assert_eq!(public_key_at_index, ssz_encode(&public_key));
+        assert_eq!(public_key_at_index, public_key.as_ssz_bytes());
     }
 
     #[test]
@@ -139,7 +139,7 @@ mod tests {
         db.put(
             DB_COLUMN,
             &store.get_db_key_for_index(&KeyPrefixes::PublicKey, index)[..],
-            &ssz_encode(&public_key)[..],
+            &public_key.as_ssz_bytes(),
         )
         .unwrap();
 
@@ -157,7 +157,7 @@ mod tests {
         db.put(
             DB_COLUMN,
             &store.get_db_key_for_index(&KeyPrefixes::PublicKey, 3)[..],
-            &ssz_encode(&public_key)[..],
+            &public_key.as_ssz_bytes(),
         )
         .unwrap();
 

beacon_node/eth2-libp2p/src/behaviour.rs

@@ -13,7 +13,7 @@ use libp2p::{
     NetworkBehaviour, PeerId,
 };
 use slog::{debug, o, trace, warn};
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError, Encode};
 use types::{Attestation, BeaconBlock};
 use types::{Topic, TopicHash};
 
@@ -49,7 +49,7 @@ impl<TSubstream: AsyncRead + AsyncWrite> NetworkBehaviourEventProcess<GossipsubE
             GossipsubEvent::Message(gs_msg) => {
                 trace!(self.log, "Received GossipEvent"; "msg" => format!("{:?}", gs_msg));
 
-                let pubsub_message = match PubsubMessage::ssz_decode(&gs_msg.data, 0) {
+                let pubsub_message = match PubsubMessage::from_ssz_bytes(&gs_msg.data) {
                     //TODO: Punish peer on error
                     Err(e) => {
                         warn!(
@@ -59,7 +59,7 @@ impl<TSubstream: AsyncRead + AsyncWrite> NetworkBehaviourEventProcess<GossipsubE
                         );
                         return;
                     }
-                    Ok((msg, _index)) => msg,
+                    Ok(msg) => msg,
                 };
 
                 self.events.push(BehaviourEvent::GossipMessage {
@@ -197,34 +197,59 @@ pub enum PubsubMessage {
 }
 
 //TODO: Correctly encode/decode enums. Prefixing with integer for now.
-impl Encodable for PubsubMessage {
-    fn ssz_append(&self, s: &mut SszStream) {
+impl Encode for PubsubMessage {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        let offset = <u32 as Encode>::ssz_fixed_len() + <Vec<u8> as Encode>::ssz_fixed_len();
+
+        let mut encoder = ssz::SszEncoder::container(buf, offset);
+
         match self {
             PubsubMessage::Block(block_gossip) => {
-                0u32.ssz_append(s);
-                block_gossip.ssz_append(s);
+                encoder.append(&0_u32);
+
+                // Encode the gossip as a Vec<u8>;
+                encoder.append(&block_gossip.as_ssz_bytes());
             }
             PubsubMessage::Attestation(attestation_gossip) => {
-                1u32.ssz_append(s);
-                attestation_gossip.ssz_append(s);
+                encoder.append(&1_u32);
+
+                // Encode the gossip as a Vec<u8>;
+                encoder.append(&attestation_gossip.as_ssz_bytes());
             }
         }
+
+        encoder.finalize();
     }
 }
 
-impl Decodable for PubsubMessage {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        let (id, index) = u32::ssz_decode(bytes, index)?;
+impl Decode for PubsubMessage {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
+        let mut builder = ssz::SszDecoderBuilder::new(&bytes);
+
+        builder.register_type::<u32>()?;
+        builder.register_type::<Vec<u8>>()?;
+
+        let mut decoder = builder.build()?;
+
+        let id: u32 = decoder.decode_next()?;
+        let body: Vec<u8> = decoder.decode_next()?;
+
         match id {
-            0 => {
-                let (block, index) = BeaconBlock::ssz_decode(bytes, index)?;
-                Ok((PubsubMessage::Block(block), index))
-            }
-            1 => {
-                let (attestation, index) = Attestation::ssz_decode(bytes, index)?;
-                Ok((PubsubMessage::Attestation(attestation), index))
-            }
-            _ => Err(DecodeError::Invalid),
+            0 => Ok(PubsubMessage::Block(BeaconBlock::from_ssz_bytes(&body)?)),
+            1 => Ok(PubsubMessage::Attestation(Attestation::from_ssz_bytes(
+                &body,
+            )?)),
+            _ => Err(DecodeError::BytesInvalid(
+                "Invalid PubsubMessage id".to_string(),
+            )),
         }
     }
 }
@@ -240,9 +265,7 @@ mod test {
 
         let encoded = ssz_encode(&original);
 
-        println!("{:?}", encoded);
-
-        let (decoded, _i) = PubsubMessage::ssz_decode(&encoded, 0).unwrap();
+        let decoded = PubsubMessage::from_ssz_bytes(&encoded).unwrap();
 
         assert_eq!(original, decoded);
     }

beacon_node/eth2-libp2p/src/rpc/methods.rs

@@ -1,5 +1,6 @@
-use ssz::{Decodable, DecodeError, Encodable, SszStream};
-/// Available RPC methods types and ids.
+//!Available RPC methods types and ids.
+
+use ssz::{impl_decode_via_from, impl_encode_via_from};
 use ssz_derive::{Decode, Encode};
 use types::{BeaconBlockBody, BeaconBlockHeader, Epoch, Hash256, Slot};
 
@@ -149,19 +150,8 @@ impl Into<u64> for GoodbyeReason {
     }
 }
 
-impl Encodable for GoodbyeReason {
-    fn ssz_append(&self, s: &mut SszStream) {
-        let id: u64 = (*self).clone().into();
-        id.ssz_append(s);
-    }
-}
-
-impl Decodable for GoodbyeReason {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        let (id, index) = u64::ssz_decode(bytes, index)?;
-        Ok((Self::from(id), index))
-    }
-}
+impl_encode_via_from!(GoodbyeReason, u64);
+impl_decode_via_from!(GoodbyeReason, u64);
 
 /// Request a number of beacon block roots from a peer.
 #[derive(Encode, Decode, Clone, Debug, PartialEq)]

beacon_node/eth2-libp2p/src/rpc/protocol.rs

@@ -1,6 +1,6 @@
 use super::methods::*;
 use libp2p::core::{upgrade, InboundUpgrade, OutboundUpgrade, UpgradeInfo};
-use ssz::{ssz_encode, Decodable, DecodeError as SSZDecodeError, Encodable, SszStream};
+use ssz::{impl_decode_via_from, impl_encode_via_from, ssz_encode, Decode, Encode};
 use std::hash::{Hash, Hasher};
 use std::io;
 use std::iter;
@@ -72,18 +72,8 @@ impl Into<u64> for RequestId {
     }
 }
 
-impl Encodable for RequestId {
-    fn ssz_append(&self, s: &mut SszStream) {
-        self.0.ssz_append(s);
-    }
-}
-
-impl Decodable for RequestId {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), SSZDecodeError> {
-        let (id, index) = u64::ssz_decode(bytes, index)?;
-        Ok((Self::from(id), index))
-    }
-}
+impl_encode_via_from!(RequestId, u64);
+impl_decode_via_from!(RequestId, u64);
 
 /// The RPC types which are sent/received in this protocol.
 #[derive(Debug, Clone)]
@@ -125,42 +115,40 @@ where
     }
 }
 
+// NOTE!
+//
+// This code has not been tested, it is a placeholder until we can update to the new libp2p
+// spec.
 fn decode(packet: Vec<u8>) -> Result<RPCEvent, DecodeError> {
-    // decode the header of the rpc
-    // request/response
-    let (request, index) = bool::ssz_decode(&packet, 0)?;
-    let (id, index) = RequestId::ssz_decode(&packet, index)?;
-    let (method_id, index) = u16::ssz_decode(&packet, index)?;
+    let mut builder = ssz::SszDecoderBuilder::new(&packet);
+
+    builder.register_type::<bool>()?;
+    builder.register_type::<RequestId>()?;
+    builder.register_type::<u16>()?;
+    builder.register_type::<Vec<u8>>()?;
+
+    let mut decoder = builder.build()?;
+
+    let request: bool = decoder.decode_next()?;
+    let id: RequestId = decoder.decode_next()?;
+    let method_id: u16 = decoder.decode_next()?;
+    let bytes: Vec<u8> = decoder.decode_next()?;
 
     if request {
         let body = match RPCMethod::from(method_id) {
-            RPCMethod::Hello => {
-                let (hello_body, _index) = HelloMessage::ssz_decode(&packet, index)?;
-                RPCRequest::Hello(hello_body)
-            }
-            RPCMethod::Goodbye => {
-                let (goodbye_reason, _index) = GoodbyeReason::ssz_decode(&packet, index)?;
-                RPCRequest::Goodbye(goodbye_reason)
-            }
+            RPCMethod::Hello => RPCRequest::Hello(HelloMessage::from_ssz_bytes(&bytes)?),
+            RPCMethod::Goodbye => RPCRequest::Goodbye(GoodbyeReason::from_ssz_bytes(&bytes)?),
             RPCMethod::BeaconBlockRoots => {
-                let (block_roots_request, _index) =
-                    BeaconBlockRootsRequest::ssz_decode(&packet, index)?;
-                RPCRequest::BeaconBlockRoots(block_roots_request)
+                RPCRequest::BeaconBlockRoots(BeaconBlockRootsRequest::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::BeaconBlockHeaders => {
-                let (block_headers_request, _index) =
-                    BeaconBlockHeadersRequest::ssz_decode(&packet, index)?;
-                RPCRequest::BeaconBlockHeaders(block_headers_request)
+                RPCRequest::BeaconBlockHeaders(BeaconBlockHeadersRequest::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::BeaconBlockBodies => {
-                let (block_bodies_request, _index) =
-                    BeaconBlockBodiesRequest::ssz_decode(&packet, index)?;
-                RPCRequest::BeaconBlockBodies(block_bodies_request)
+                RPCRequest::BeaconBlockBodies(BeaconBlockBodiesRequest::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::BeaconChainState => {
-                let (chain_state_request, _index) =
-                    BeaconChainStateRequest::ssz_decode(&packet, index)?;
-                RPCRequest::BeaconChainState(chain_state_request)
+                RPCRequest::BeaconChainState(BeaconChainStateRequest::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::Unknown => return Err(DecodeError::UnknownRPCMethod),
         };
@@ -174,29 +162,24 @@ fn decode(packet: Vec<u8>) -> Result<RPCEvent, DecodeError> {
     // we have received a response
     else {
         let result = match RPCMethod::from(method_id) {
-            RPCMethod::Hello => {
-                let (body, _index) = HelloMessage::ssz_decode(&packet, index)?;
-                RPCResponse::Hello(body)
-            }
-            RPCMethod::Goodbye => unreachable!("Should never receive a goodbye response"),
+            RPCMethod::Hello => RPCResponse::Hello(HelloMessage::from_ssz_bytes(&bytes)?),
             RPCMethod::BeaconBlockRoots => {
-                let (body, _index) = BeaconBlockRootsResponse::ssz_decode(&packet, index)?;
-                RPCResponse::BeaconBlockRoots(body)
+                RPCResponse::BeaconBlockRoots(BeaconBlockRootsResponse::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::BeaconBlockHeaders => {
-                let (body, _index) = BeaconBlockHeadersResponse::ssz_decode(&packet, index)?;
-                RPCResponse::BeaconBlockHeaders(body)
+                RPCResponse::BeaconBlockHeaders(BeaconBlockHeadersResponse::from_ssz_bytes(&bytes)?)
             }
             RPCMethod::BeaconBlockBodies => {
-                let (body, _index) = BeaconBlockBodiesResponse::ssz_decode(&packet, index)?;
-                RPCResponse::BeaconBlockBodies(body)
+                RPCResponse::BeaconBlockBodies(BeaconBlockBodiesResponse::from_ssz_bytes(&packet)?)
             }
             RPCMethod::BeaconChainState => {
-                let (body, _index) = BeaconChainStateResponse::ssz_decode(&packet, index)?;
-                RPCResponse::BeaconChainState(body)
+                RPCResponse::BeaconChainState(BeaconChainStateResponse::from_ssz_bytes(&packet)?)
             }
+            // We should never receive a goodbye response; it is invalid.
+            RPCMethod::Goodbye => return Err(DecodeError::UnknownRPCMethod),
             RPCMethod::Unknown => return Err(DecodeError::UnknownRPCMethod),
         };
+
         Ok(RPCEvent::Response {
             id,
             method_id,
@@ -220,35 +203,51 @@ where
     }
 }
 
-impl Encodable for RPCEvent {
-    fn ssz_append(&self, s: &mut SszStream) {
+impl Encode for RPCEvent {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    // NOTE!
+    //
+    // This code has not been tested, it is a placeholder until we can update to the new libp2p
+    // spec.
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        let offset = <bool as Encode>::ssz_fixed_len()
+            + <u16 as Encode>::ssz_fixed_len()
+            + <Vec<u8> as Encode>::ssz_fixed_len();
+
+        let mut encoder = ssz::SszEncoder::container(buf, offset);
+
         match self {
             RPCEvent::Request {
                 id,
                 method_id,
                 body,
             } => {
-                s.append(&true);
-                s.append(id);
-                s.append(method_id);
+                encoder.append(&true);
+                encoder.append(id);
+                encoder.append(method_id);
+
+                // Encode the `body` as a `Vec<u8>`.
                 match body {
                     RPCRequest::Hello(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                     RPCRequest::Goodbye(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                     RPCRequest::BeaconBlockRoots(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                     RPCRequest::BeaconBlockHeaders(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                     RPCRequest::BeaconBlockBodies(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                     RPCRequest::BeaconChainState(body) => {
-                        s.append(body);
+                        encoder.append(&body.as_ssz_bytes());
                     }
                 }
             }
@@ -257,28 +256,32 @@ impl Encodable for RPCEvent {
                 method_id,
                 result,
             } => {
-                s.append(&false);
-                s.append(id);
-                s.append(method_id);
+                encoder.append(&true);
+                encoder.append(id);
+                encoder.append(method_id);
+
                 match result {
                     RPCResponse::Hello(response) => {
-                        s.append(response);
+                        encoder.append(&response.as_ssz_bytes());
                     }
                     RPCResponse::BeaconBlockRoots(response) => {
-                        s.append(response);
+                        encoder.append(&response.as_ssz_bytes());
                     }
                     RPCResponse::BeaconBlockHeaders(response) => {
-                        s.append(response);
+                        encoder.append(&response.as_ssz_bytes());
                     }
                     RPCResponse::BeaconBlockBodies(response) => {
-                        s.append(response);
+                        encoder.append(&response.as_ssz_bytes());
                     }
                     RPCResponse::BeaconChainState(response) => {
-                        s.append(response);
+                        encoder.append(&response.as_ssz_bytes());
                     }
                 }
             }
         }
+
+        // Finalize the encoder, writing to `buf`.
+        encoder.finalize();
     }
 }
 

beacon_node/rpc/src/attestation.rs

@@ -7,7 +7,7 @@ use protos::services::{
 };
 use protos::services_grpc::AttestationService;
 use slog::{error, info, trace, warn};
-use ssz::{ssz_encode, Decodable};
+use ssz::{ssz_encode, Decode};
 use std::sync::Arc;
 use types::{Attestation, EthSpec};
 
@@ -110,8 +110,8 @@ impl<E: EthSpec> AttestationService for AttestationServiceInstance<E> {
         let mut resp = PublishAttestationResponse::new();
         let ssz_serialized_attestation = req.get_attestation().get_ssz();
 
-        let attestation = match Attestation::ssz_decode(ssz_serialized_attestation, 0) {
-            Ok((v, _index)) => v,
+        let attestation = match Attestation::from_ssz_bytes(ssz_serialized_attestation) {
+            Ok(v) => v,
             Err(_) => {
                 let log_clone = self.log.clone();
                 let f = sink

beacon_node/rpc/src/beacon_block.rs

@@ -11,7 +11,7 @@ use protos::services::{
 use protos::services_grpc::BeaconBlockService;
 use slog::Logger;
 use slog::{error, info, trace, warn};
-use ssz::{ssz_encode, Decodable};
+use ssz::{ssz_encode, Decode};
 use std::sync::Arc;
 use types::{BeaconBlock, EthSpec, Signature, Slot};
 
@@ -35,8 +35,8 @@ impl<E: EthSpec> BeaconBlockService for BeaconBlockServiceInstance<E> {
         // decode the request
         // TODO: requested slot currently unused, see: https://github.com/sigp/lighthouse/issues/336
         let _requested_slot = Slot::from(req.get_slot());
-        let randao_reveal = match Signature::ssz_decode(req.get_randao_reveal(), 0) {
-            Ok((reveal, _index)) => reveal,
+        let randao_reveal = match Signature::from_ssz_bytes(req.get_randao_reveal()) {
+            Ok(reveal) => reveal,
             Err(_) => {
                 // decode error, incorrect signature
                 let log_clone = self.log.clone();
@@ -91,8 +91,8 @@ impl<E: EthSpec> BeaconBlockService for BeaconBlockServiceInstance<E> {
 
         let ssz_serialized_block = req.get_block().get_ssz();
 
-        match BeaconBlock::ssz_decode(ssz_serialized_block, 0) {
-            Ok((block, _i)) => {
+        match BeaconBlock::from_ssz_bytes(ssz_serialized_block) {
+            Ok(block) => {
                 match self.chain.process_block(block.clone()) {
                     Ok(outcome) => {
                         if outcome.sucessfully_processed() {

beacon_node/rpc/src/validator.rs

@@ -5,7 +5,7 @@ use grpcio::{RpcContext, RpcStatus, RpcStatusCode, UnarySink};
 use protos::services::{ActiveValidator, GetDutiesRequest, GetDutiesResponse, ValidatorDuty};
 use protos::services_grpc::ValidatorService;
 use slog::{trace, warn};
-use ssz::decode;
+use ssz::Decode;
 use std::sync::Arc;
 use types::{Epoch, EthSpec, RelativeEpoch};
 
@@ -74,7 +74,7 @@ impl<E: EthSpec> ValidatorService for ValidatorServiceInstance<E> {
         for validator_pk in validators.get_public_keys() {
             let mut active_validator = ActiveValidator::new();
 
-            let public_key = match decode::<PublicKey>(validator_pk) {
+            let public_key = match PublicKey::from_ssz_bytes(validator_pk) {
                 Ok(v) => v,
                 Err(_) => {
                     let log_clone = self.log.clone();

eth2/README.md

@@ -30,7 +30,7 @@ Rust crates containing logic common across the Lighthouse project.
 	- [`ssz`](utils/ssz/): an implementation of the SimpleSerialize 
 	    serialization/deserialization protocol used by Eth 2.0.
 	- [`ssz_derive`](utils/ssz_derive/): provides procedural macros for
-		deriving SSZ `Encodable`, `Decodable`, and `TreeHash` methods.
+		deriving SSZ `Encode`, `Decode`, and `TreeHash` methods.
 	- [`swap_or_not_shuffle`](utils/swap_or_not_shuffle/): a list-shuffling
 		method which is slow, but allows for a subset of indices to be shuffled.
 	- [`test_random_derive`](utils/test_random_derive/): provides procedural

eth2/types/src/beacon_state.rs

@@ -3,12 +3,13 @@ use self::exit_cache::ExitCache;
 use crate::test_utils::TestRandom;
 use crate::*;
 use cached_tree_hash::{Error as TreeHashCacheError, TreeHashCache};
+use hashing::hash;
 use int_to_bytes::int_to_bytes32;
 use pubkey_cache::PubkeyCache;
 
 use fixed_len_vec::{typenum::Unsigned, FixedLenVec};
 use serde_derive::{Deserialize, Serialize};
-use ssz::{hash, ssz_encode};
+use ssz::ssz_encode;
 use ssz_derive::{Decode, Encode};
 use test_random_derive::TestRandom;
 use tree_hash::TreeHash;

eth2/types/src/slot_epoch.rs

@@ -15,7 +15,7 @@ use crate::test_utils::TestRandom;
 use rand::RngCore;
 use serde_derive::{Deserialize, Serialize};
 use slog;
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError, Encode};
 use std::cmp::{Ord, Ordering};
 use std::fmt;
 use std::hash::{Hash, Hasher};
@@ -145,11 +145,13 @@ mod epoch_tests {
     #[test]
     fn max_epoch_ssz() {
         let max_epoch = Epoch::max_value();
-        let mut ssz = SszStream::new();
-        ssz.append(&max_epoch);
-        let encoded = ssz.drain();
-        assert_eq!(&encoded, &[255, 255, 255, 255, 255, 255, 255, 255]);
-        let (decoded, _i): (Epoch, usize) = <_>::ssz_decode(&encoded, 0).unwrap();
-        assert_eq!(max_epoch, decoded);
+        assert_eq!(
+            &max_epoch.as_ssz_bytes(),
+            &[255, 255, 255, 255, 255, 255, 255, 255]
+        );
+        assert_eq!(
+            max_epoch,
+            Epoch::from_ssz_bytes(&max_epoch.as_ssz_bytes()).unwrap()
+        );
     }
 }

eth2/types/src/slot_epoch_macros.rs

@@ -192,17 +192,31 @@ macro_rules! impl_display {
 
 macro_rules! impl_ssz {
     ($type: ident) => {
-        impl Encodable for $type {
-            fn ssz_append(&self, s: &mut SszStream) {
-                s.append(&self.0);
+        impl Encode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                <u64 as Encode>::is_ssz_fixed_len()
+            }
+
+            fn ssz_fixed_len() -> usize {
+                <u64 as Encode>::ssz_fixed_len()
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                self.0.ssz_append(buf)
             }
         }
 
-        impl Decodable for $type {
-            fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-                let (value, i) = <_>::ssz_decode(bytes, i)?;
+        impl Decode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                <u64 as Decode>::is_ssz_fixed_len()
+            }
 
-                Ok(($type(value), i))
+            fn ssz_fixed_len() -> usize {
+                <u64 as Decode>::ssz_fixed_len()
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+                Ok($type(u64::from_ssz_bytes(bytes)?))
             }
         }
 

eth2/types/src/slot_height.rs

@@ -3,7 +3,7 @@ use crate::test_utils::TestRandom;
 
 use rand::RngCore;
 use serde_derive::Serialize;
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError, Encode};
 use std::cmp::{Ord, Ordering};
 use std::fmt;
 use std::hash::{Hash, Hasher};

eth2/types/src/test_utils/macros.rs

@@ -5,13 +5,13 @@ macro_rules! ssz_tests {
         #[test]
         pub fn test_ssz_round_trip() {
             use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
-            use ssz::{ssz_encode, Decodable};
+            use ssz::{ssz_encode, Decode};
 
             let mut rng = XorShiftRng::from_seed([42; 16]);
             let original = $type::random_for_test(&mut rng);
 
             let bytes = ssz_encode(&original);
-            let (decoded, _): ($type, usize) = <_>::ssz_decode(&bytes, 0).unwrap();
+            let decoded = $type::from_ssz_bytes(&bytes).unwrap();
 
             assert_eq!(original, decoded);
         }

eth2/utils/bls/src/aggregate_signature.rs

@@ -1,4 +1,4 @@
-use super::{AggregatePublicKey, Signature, BLS_AGG_SIG_BYTE_SIZE};
+use super::*;
 use bls_aggregates::{
     AggregatePublicKey as RawAggregatePublicKey, AggregateSignature as RawAggregateSignature,
 };
@@ -6,7 +6,7 @@ use cached_tree_hash::cached_tree_hash_ssz_encoding_as_vector;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::{encode as hex_encode, HexVisitor};
-use ssz::{decode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{Decode, DecodeError};
 use tree_hash::tree_hash_ssz_encoding_as_vector;
 
 /// A BLS aggregate signature.
@@ -99,8 +99,12 @@ impl AggregateSignature {
     pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
         for byte in bytes {
             if *byte != 0 {
-                let sig =
-                    RawAggregateSignature::from_bytes(&bytes).map_err(|_| DecodeError::Invalid)?;
+                let sig = RawAggregateSignature::from_bytes(&bytes).map_err(|_| {
+                    DecodeError::BytesInvalid(
+                        format!("Invalid AggregateSignature bytes: {:?}", bytes).to_string(),
+                    )
+                })?;
+
                 return Ok(Self {
                     aggregate_signature: sig,
                     is_empty: false,
@@ -127,22 +131,11 @@ impl AggregateSignature {
     }
 }
 
-impl Encodable for AggregateSignature {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.as_bytes());
-    }
-}
-
-impl Decodable for AggregateSignature {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_AGG_SIG_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
-        }
-        let agg_sig = AggregateSignature::from_bytes(&bytes[i..(i + BLS_AGG_SIG_BYTE_SIZE)])
-            .map_err(|_| DecodeError::Invalid)?;
-        Ok((agg_sig, i + BLS_AGG_SIG_BYTE_SIZE))
-    }
-}
+impl_ssz!(
+    AggregateSignature,
+    BLS_AGG_SIG_BYTE_SIZE,
+    "AggregateSignature"
+);
 
 impl Serialize for AggregateSignature {
     /// Serde serialization is compliant the Ethereum YAML test format.
@@ -161,8 +154,9 @@ impl<'de> Deserialize<'de> for AggregateSignature {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let agg_sig = decode(&bytes[..])
+        let agg_sig = AggregateSignature::from_ssz_bytes(&bytes)
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
+
         Ok(agg_sig)
     }
 }
@@ -174,7 +168,7 @@ cached_tree_hash_ssz_encoding_as_vector!(AggregateSignature, 96);
 mod tests {
     use super::super::{Keypair, Signature};
     use super::*;
-    use ssz::{decode, ssz_encode};
+    use ssz::Encode;
 
     #[test]
     pub fn test_ssz_round_trip() {
@@ -183,8 +177,8 @@ mod tests {
         let mut original = AggregateSignature::new();
         original.add(&Signature::new(&[42, 42], 0, &keypair.sk));
 
-        let bytes = ssz_encode(&original);
-        let decoded = decode::<AggregateSignature>(&bytes).unwrap();
+        let bytes = original.as_ssz_bytes();
+        let decoded = AggregateSignature::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/bls/src/fake_aggregate_signature.rs

@@ -3,7 +3,7 @@ use cached_tree_hash::cached_tree_hash_ssz_encoding_as_vector;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::{encode as hex_encode, PrefixedHexVisitor};
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError};
 use tree_hash::tree_hash_ssz_encoding_as_vector;
 
 /// A BLS aggregate signature.
@@ -57,28 +57,32 @@ impl FakeAggregateSignature {
     ) -> bool {
         true
     }
-}
 
-impl Encodable for FakeAggregateSignature {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.bytes);
-    }
-}
-
-impl Decodable for FakeAggregateSignature {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_AGG_SIG_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
+    /// Convert bytes to fake BLS aggregate signature
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        if bytes.len() != BLS_AGG_SIG_BYTE_SIZE {
+            Err(DecodeError::InvalidByteLength {
+                len: bytes.len(),
+                expected: BLS_AGG_SIG_BYTE_SIZE,
+            })
+        } else {
+            Ok(Self {
+                bytes: bytes.to_vec(),
+            })
         }
-        Ok((
-            FakeAggregateSignature {
-                bytes: bytes[i..(i + BLS_AGG_SIG_BYTE_SIZE)].to_vec(),
-            },
-            i + BLS_AGG_SIG_BYTE_SIZE,
-        ))
+    }
+
+    pub fn as_bytes(&self) -> Vec<u8> {
+        self.bytes.clone()
     }
 }
 
+impl_ssz!(
+    FakeAggregateSignature,
+    BLS_AGG_SIG_BYTE_SIZE,
+    "FakeAggregateSignature"
+);
+
 impl Serialize for FakeAggregateSignature {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
@@ -94,7 +98,7 @@ impl<'de> Deserialize<'de> for FakeAggregateSignature {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(PrefixedHexVisitor)?;
-        let (obj, _) = <_>::ssz_decode(&bytes[..], 0)
+        let obj = <_>::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
         Ok(obj)
     }
@@ -117,7 +121,7 @@ mod tests {
         original.add(&Signature::new(&[42, 42], 0, &keypair.sk));
 
         let bytes = ssz_encode(&original);
-        let (decoded, _) = FakeAggregateSignature::ssz_decode(&bytes, 0).unwrap();
+        let decoded = FakeAggregateSignature::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/bls/src/fake_signature.rs

@@ -4,7 +4,7 @@ use hex::encode as hex_encode;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::HexVisitor;
-use ssz::{ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError};
 use tree_hash::tree_hash_ssz_encoding_as_vector;
 
 /// A single BLS signature.
@@ -49,31 +49,31 @@ impl FakeSignature {
         true
     }
 
+    /// Convert bytes to fake BLS Signature
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        if bytes.len() != BLS_SIG_BYTE_SIZE {
+            Err(DecodeError::InvalidByteLength {
+                len: bytes.len(),
+                expected: BLS_SIG_BYTE_SIZE,
+            })
+        } else {
+            Ok(Self {
+                bytes: bytes.to_vec(),
+            })
+        }
+    }
+
+    pub fn as_bytes(&self) -> Vec<u8> {
+        self.bytes.clone()
+    }
+
     /// Returns a new empty signature.
     pub fn empty_signature() -> Self {
         FakeSignature::zero()
     }
 }
 
-impl Encodable for FakeSignature {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.bytes);
-    }
-}
-
-impl Decodable for FakeSignature {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_SIG_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
-        }
-        Ok((
-            FakeSignature {
-                bytes: bytes[i..(i + BLS_SIG_BYTE_SIZE)].to_vec(),
-            },
-            i + BLS_SIG_BYTE_SIZE,
-        ))
-    }
-}
+impl_ssz!(FakeSignature, BLS_SIG_BYTE_SIZE, "FakeSignature");
 
 tree_hash_ssz_encoding_as_vector!(FakeSignature);
 cached_tree_hash_ssz_encoding_as_vector!(FakeSignature, 96);
@@ -93,7 +93,7 @@ impl<'de> Deserialize<'de> for FakeSignature {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let (pubkey, _) = <_>::ssz_decode(&bytes[..], 0)
+        let pubkey = <_>::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
         Ok(pubkey)
     }
@@ -112,7 +112,7 @@ mod tests {
         let original = FakeSignature::new(&[42, 42], 0, &keypair.sk);
 
         let bytes = ssz_encode(&original);
-        let (decoded, _) = FakeSignature::ssz_decode(&bytes, 0).unwrap();
+        let decoded = FakeSignature::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/bls/src/lib.rs

@@ -1,6 +1,8 @@
 extern crate bls_aggregates;
 extern crate ssz;
 
+#[macro_use]
+mod macros;
 mod aggregate_public_key;
 mod keypair;
 mod public_key;

eth2/utils/bls/src/macros.rs

@@ -0,0 +1,38 @@
+macro_rules! impl_ssz {
+    ($type: ident, $byte_size: expr, $item_str: expr) => {
+        impl ssz::Encode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $byte_size
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                buf.append(&mut self.as_bytes())
+            }
+        }
+
+        impl ssz::Decode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $byte_size
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+                let len = bytes.len();
+                let expected = <Self as ssz::Decode>::ssz_fixed_len();
+
+                if len != expected {
+                    Err(ssz::DecodeError::InvalidByteLength { len, expected })
+                } else {
+                    $type::from_bytes(bytes)
+                }
+            }
+        }
+    };
+}

eth2/utils/bls/src/public_key.rs

@@ -4,7 +4,7 @@ use cached_tree_hash::cached_tree_hash_ssz_encoding_as_vector;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::{encode as hex_encode, HexVisitor};
-use ssz::{decode, ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError};
 use std::default;
 use std::fmt;
 use std::hash::{Hash, Hasher};
@@ -27,9 +27,19 @@ impl PublicKey {
         &self.0
     }
 
+    /// Returns the underlying point as compressed bytes.
+    ///
+    /// Identical to `self.as_uncompressed_bytes()`.
+    fn as_bytes(&self) -> Vec<u8> {
+        self.as_raw().as_bytes()
+    }
+
     /// Converts compressed bytes to PublicKey
     pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
-        let pubkey = RawPublicKey::from_bytes(&bytes).map_err(|_| DecodeError::Invalid)?;
+        let pubkey = RawPublicKey::from_bytes(&bytes).map_err(|_| {
+            DecodeError::BytesInvalid(format!("Invalid PublicKey bytes: {:?}", bytes).to_string())
+        })?;
+
         Ok(PublicKey(pubkey))
     }
 
@@ -40,8 +50,9 @@ impl PublicKey {
 
     /// Converts (x, y) bytes to PublicKey
     pub fn from_uncompressed_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
-        let pubkey =
-            RawPublicKey::from_uncompressed_bytes(&bytes).map_err(|_| DecodeError::Invalid)?;
+        let pubkey = RawPublicKey::from_uncompressed_bytes(&bytes).map_err(|_| {
+            DecodeError::BytesInvalid("Invalid PublicKey uncompressed bytes.".to_string())
+        })?;
         Ok(PublicKey(pubkey))
     }
 
@@ -68,22 +79,7 @@ impl default::Default for PublicKey {
     }
 }
 
-impl Encodable for PublicKey {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.0.as_bytes());
-    }
-}
-
-impl Decodable for PublicKey {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_PUBLIC_KEY_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
-        }
-        let raw_sig = RawPublicKey::from_bytes(&bytes[i..(i + BLS_PUBLIC_KEY_BYTE_SIZE)])
-            .map_err(|_| DecodeError::TooShort)?;
-        Ok((PublicKey(raw_sig), i + BLS_PUBLIC_KEY_BYTE_SIZE))
-    }
-}
+impl_ssz!(PublicKey, BLS_PUBLIC_KEY_BYTE_SIZE, "PublicKey");
 
 impl Serialize for PublicKey {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -100,7 +96,7 @@ impl<'de> Deserialize<'de> for PublicKey {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let pubkey = decode(&bytes[..])
+        let pubkey = Self::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid pubkey ({:?})", e)))?;
         Ok(pubkey)
     }
@@ -139,7 +135,7 @@ mod tests {
         let original = PublicKey::from_secret_key(&sk);
 
         let bytes = ssz_encode(&original);
-        let (decoded, _) = PublicKey::ssz_decode(&bytes, 0).unwrap();
+        let decoded = PublicKey::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/bls/src/secret_key.rs

@@ -1,10 +1,10 @@
 use super::BLS_SECRET_KEY_BYTE_SIZE;
-use bls_aggregates::{DecodeError as BlsDecodeError, SecretKey as RawSecretKey};
+use bls_aggregates::SecretKey as RawSecretKey;
 use hex::encode as hex_encode;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::HexVisitor;
-use ssz::{decode, ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError};
 use tree_hash::tree_hash_ssz_encoding_as_vector;
 
 /// A single BLS signature.
@@ -19,11 +19,21 @@ impl SecretKey {
         SecretKey(RawSecretKey::random())
     }
 
+    /// Returns the underlying point as compressed bytes.
+    fn as_bytes(&self) -> Vec<u8> {
+        self.as_raw().as_bytes()
+    }
+
     /// Instantiate a SecretKey from existing bytes.
     ///
     /// Note: this is _not_ SSZ decoding.
-    pub fn from_bytes(bytes: &[u8]) -> Result<SecretKey, BlsDecodeError> {
-        Ok(SecretKey(RawSecretKey::from_bytes(bytes)?))
+    pub fn from_bytes(bytes: &[u8]) -> Result<SecretKey, DecodeError> {
+        Ok(SecretKey(RawSecretKey::from_bytes(bytes).map_err(|e| {
+            DecodeError::BytesInvalid(format!(
+                "Invalid SecretKey bytes: {:?} Error: {:?}",
+                bytes, e
+            ))
+        })?))
     }
 
     /// Returns the underlying secret key.
@@ -32,22 +42,7 @@ impl SecretKey {
     }
 }
 
-impl Encodable for SecretKey {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.0.as_bytes());
-    }
-}
-
-impl Decodable for SecretKey {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_SECRET_KEY_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
-        }
-        let raw_sig = RawSecretKey::from_bytes(&bytes[i..(i + BLS_SECRET_KEY_BYTE_SIZE)])
-            .map_err(|_| DecodeError::TooShort)?;
-        Ok((SecretKey(raw_sig), i + BLS_SECRET_KEY_BYTE_SIZE))
-    }
-}
+impl_ssz!(SecretKey, BLS_SECRET_KEY_BYTE_SIZE, "SecretKey");
 
 impl Serialize for SecretKey {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -64,7 +59,7 @@ impl<'de> Deserialize<'de> for SecretKey {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let secret_key = decode::<SecretKey>(&bytes[..])
+        let secret_key = SecretKey::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
         Ok(secret_key)
     }
@@ -84,7 +79,7 @@ mod tests {
                 .unwrap();
 
         let bytes = ssz_encode(&original);
-        let (decoded, _) = SecretKey::ssz_decode(&bytes, 0).unwrap();
+        let decoded = SecretKey::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/bls/src/signature.rs

@@ -5,7 +5,7 @@ use hex::encode as hex_encode;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::HexVisitor;
-use ssz::{decode, ssz_encode, Decodable, DecodeError, Encodable, SszStream};
+use ssz::{ssz_encode, Decode, DecodeError};
 use tree_hash::tree_hash_ssz_encoding_as_vector;
 
 /// A single BLS signature.
@@ -83,8 +83,11 @@ impl Signature {
     pub fn from_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
         for byte in bytes {
             if *byte != 0 {
-                let raw_signature =
-                    RawSignature::from_bytes(&bytes).map_err(|_| DecodeError::Invalid)?;
+                let raw_signature = RawSignature::from_bytes(&bytes).map_err(|_| {
+                    DecodeError::BytesInvalid(
+                        format!("Invalid Signature bytes: {:?}", bytes).to_string(),
+                    )
+                })?;
                 return Ok(Signature {
                     signature: raw_signature,
                     is_empty: false,
@@ -100,21 +103,7 @@ impl Signature {
     }
 }
 
-impl Encodable for Signature {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(&self.as_bytes());
-    }
-}
-
-impl Decodable for Signature {
-    fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() - i < BLS_SIG_BYTE_SIZE {
-            return Err(DecodeError::TooShort);
-        }
-        let signature = Signature::from_bytes(&bytes[i..(i + BLS_SIG_BYTE_SIZE)])?;
-        Ok((signature, i + BLS_SIG_BYTE_SIZE))
-    }
-}
+impl_ssz!(Signature, BLS_SIG_BYTE_SIZE, "Signature");
 
 tree_hash_ssz_encoding_as_vector!(Signature);
 cached_tree_hash_ssz_encoding_as_vector!(Signature, 96);
@@ -136,7 +125,7 @@ impl<'de> Deserialize<'de> for Signature {
         D: Deserializer<'de>,
     {
         let bytes = deserializer.deserialize_str(HexVisitor)?;
-        let signature = decode(&bytes[..])
+        let signature = Self::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
         Ok(signature)
     }
@@ -156,7 +145,7 @@ mod tests {
         let original = Signature::new(&[42, 42], 0, &keypair.sk);
 
         let bytes = ssz_encode(&original);
-        let decoded = decode::<Signature>(&bytes).unwrap();
+        let decoded = Signature::from_ssz_bytes(&bytes).unwrap();
 
         assert_eq!(original, decoded);
     }

eth2/utils/boolean-bitfield/src/lib.rs

@@ -7,7 +7,7 @@ use cached_tree_hash::cached_tree_hash_bytes_as_list;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
 use serde_hex::{encode, PrefixedHexVisitor};
-use ssz::{Decodable, Encodable};
+use ssz::{Decode, Encode};
 use std::cmp;
 use std::default;
 
@@ -194,29 +194,23 @@ impl std::ops::BitOr for BooleanBitfield {
     }
 }
 
-impl Encodable for BooleanBitfield {
-    // ssz_append encodes Self according to the `ssz` spec.
-    fn ssz_append(&self, s: &mut ssz::SszStream) {
-        s.append_vec(&self.to_bytes())
+impl Encode for BooleanBitfield {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        buf.append(&mut self.to_bytes())
     }
 }
 
-impl Decodable for BooleanBitfield {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), ssz::DecodeError> {
-        let len = ssz::decode::decode_length(bytes, index, ssz::LENGTH_BYTES)?;
-        if (ssz::LENGTH_BYTES + len) > bytes.len() {
-            return Err(ssz::DecodeError::TooShort);
-        }
+impl Decode for BooleanBitfield {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
 
-        if len == 0 {
-            Ok((BooleanBitfield::new(), index + ssz::LENGTH_BYTES))
-        } else {
-            let bytes = &bytes[(index + 4)..(index + len + 4)];
-            let field = BooleanBitfield::from_bytes(bytes);
-
-            let index = index + ssz::LENGTH_BYTES + len;
-            Ok((field, index))
-        }
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
+        Ok(BooleanBitfield::from_bytes(bytes))
     }
 }
 
@@ -277,7 +271,7 @@ cached_tree_hash_bytes_as_list!(BooleanBitfield);
 mod tests {
     use super::*;
     use serde_yaml;
-    use ssz::{decode, ssz_encode, SszStream};
+    use ssz::ssz_encode;
     use tree_hash::TreeHash;
 
     #[test]
@@ -452,30 +446,17 @@ mod tests {
     #[test]
     fn test_ssz_encode() {
         let field = create_test_bitfield();
-        let mut stream = SszStream::new();
-        stream.append(&field);
-        assert_eq!(stream.drain(), vec![2, 0, 0, 0, 0b0000_0011, 0b1000_0111]);
+        assert_eq!(field.as_ssz_bytes(), vec![0b0000_0011, 0b1000_0111]);
 
         let field = BooleanBitfield::from_elem(18, true);
-        let mut stream = SszStream::new();
-        stream.append(&field);
         assert_eq!(
-            stream.drain(),
-            vec![3, 0, 0, 0, 0b0000_0011, 0b1111_1111, 0b1111_1111]
+            field.as_ssz_bytes(),
+            vec![0b0000_0011, 0b1111_1111, 0b1111_1111]
         );
 
         let mut b = BooleanBitfield::new();
         b.set(1, true);
-        assert_eq!(
-            ssz_encode(&b),
-            vec![
-                0b0000_0001,
-                0b0000_0000,
-                0b0000_0000,
-                0b0000_0000,
-                0b0000_0010
-            ]
-        );
+        assert_eq!(ssz_encode(&b), vec![0b0000_0010]);
     }
 
     fn create_test_bitfield() -> BooleanBitfield {
@@ -491,13 +472,13 @@ mod tests {
 
     #[test]
     fn test_ssz_decode() {
-        let encoded = vec![2, 0, 0, 0, 0b0000_0011, 0b1000_0111];
-        let field = decode::<BooleanBitfield>(&encoded).unwrap();
+        let encoded = vec![0b0000_0011, 0b1000_0111];
+        let field = BooleanBitfield::from_ssz_bytes(&encoded).unwrap();
         let expected = create_test_bitfield();
         assert_eq!(field, expected);
 
-        let encoded = vec![3, 0, 0, 0, 255, 255, 3];
-        let field = decode::<BooleanBitfield>(&encoded).unwrap();
+        let encoded = vec![255, 255, 3];
+        let field = BooleanBitfield::from_ssz_bytes(&encoded).unwrap();
         let expected = BooleanBitfield::from_bytes(&[255, 255, 3]);
         assert_eq!(field, expected);
     }
@@ -527,7 +508,7 @@ mod tests {
     fn test_ssz_round_trip() {
         let original = BooleanBitfield::from_bytes(&vec![18; 12][..]);
         let ssz = ssz_encode(&original);
-        let decoded = decode::<BooleanBitfield>(&ssz).unwrap();
+        let decoded = BooleanBitfield::from_ssz_bytes(&ssz).unwrap();
         assert_eq!(original, decoded);
     }
 

eth2/utils/fixed_len_vec/src/impls.rs

@@ -1,7 +1,4 @@
 use super::*;
-// use cached_tree_hash::CachedTreeHash;
-// use ssz::{Decodable, Encodable};
-// use tree_hash::TreeHash;
 
 impl<T, N: Unsigned> tree_hash::TreeHash for FixedLenVec<T, N>
 where
@@ -51,20 +48,93 @@ where
     }
 }
 
-impl<T, N: Unsigned> ssz::Encodable for FixedLenVec<T, N>
+impl<T, N: Unsigned> ssz::Encode for FixedLenVec<T, N>
 where
-    T: ssz::Encodable,
+    T: ssz::Encode,
 {
-    fn ssz_append(&self, s: &mut ssz::SszStream) {
-        s.append_vec(&self.vec)
+    fn is_ssz_fixed_len() -> bool {
+        true
+    }
+
+    fn ssz_fixed_len() -> usize {
+        if <Self as ssz::Encode>::is_ssz_fixed_len() {
+            T::ssz_fixed_len() * N::to_usize()
+        } else {
+            ssz::BYTES_PER_LENGTH_OFFSET
+        }
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        if T::is_ssz_fixed_len() {
+            buf.reserve(T::ssz_fixed_len() * self.len());
+
+            for item in &self.vec {
+                item.ssz_append(buf);
+            }
+        } else {
+            let mut encoder = ssz::SszEncoder::list(buf, self.len() * ssz::BYTES_PER_LENGTH_OFFSET);
+
+            for item in &self.vec {
+                encoder.append(item);
+            }
+
+            encoder.finalize();
+        }
     }
 }
 
-impl<T, N: Unsigned> ssz::Decodable for FixedLenVec<T, N>
+impl<T, N: Unsigned> ssz::Decode for FixedLenVec<T, N>
 where
-    T: ssz::Decodable + Default,
+    T: ssz::Decode + Default,
 {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), ssz::DecodeError> {
-        ssz::decode_ssz_list(bytes, index).and_then(|(vec, i)| Ok((vec.into(), i)))
+    fn is_ssz_fixed_len() -> bool {
+        T::is_ssz_fixed_len()
+    }
+
+    fn ssz_fixed_len() -> usize {
+        if <Self as ssz::Decode>::is_ssz_fixed_len() {
+            T::ssz_fixed_len() * N::to_usize()
+        } else {
+            ssz::BYTES_PER_LENGTH_OFFSET
+        }
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
+        if bytes.len() == 0 {
+            Ok(FixedLenVec::from(vec![]))
+        } else if T::is_ssz_fixed_len() {
+            bytes
+                .chunks(T::ssz_fixed_len())
+                .map(|chunk| T::from_ssz_bytes(chunk))
+                .collect::<Result<Vec<T>, _>>()
+                .and_then(|vec| Ok(vec.into()))
+        } else {
+            ssz::decode_list_of_variable_length_items(bytes).and_then(|vec| Ok(vec.into()))
+        }
+    }
+}
+
+#[cfg(test)]
+mod ssz_tests {
+    use super::*;
+    use ssz::*;
+    use typenum::*;
+
+    #[test]
+    fn encode() {
+        let vec: FixedLenVec<u16, U2> = vec![0; 2].into();
+        assert_eq!(vec.as_ssz_bytes(), vec![0, 0, 0, 0]);
+        assert_eq!(<FixedLenVec<u16, U2> as Encode>::ssz_fixed_len(), 4);
+    }
+
+    fn round_trip<T: Encode + Decode + std::fmt::Debug + PartialEq>(item: T) {
+        let encoded = &item.as_ssz_bytes();
+        assert_eq!(T::from_ssz_bytes(&encoded), Ok(item));
+    }
+
+    #[test]
+    fn u16_len_8() {
+        round_trip::<FixedLenVec<u16, U8>>(vec![42; 8].into());
+        round_trip::<FixedLenVec<u16, U8>>(vec![0; 8].into());
     }
 }

eth2/utils/fixed_len_vec/src/lib.rs

@@ -9,10 +9,7 @@ pub use typenum;
 mod impls;
 
 #[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
-pub struct FixedLenVec<T, N>
-where
-    N: Unsigned,
-{
+pub struct FixedLenVec<T, N> {
     vec: Vec<T>,
     _phantom: PhantomData<N>,
 }

eth2/utils/ssz/Cargo.toml

@@ -4,6 +4,14 @@ version = "0.1.0"
 authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
 
+[[bench]]
+name = "benches"
+harness = false
+
+[dev-dependencies]
+criterion = "0.2"
+ssz_derive = { path = "../ssz_derive" }
+
 [dependencies]
 bytes = "0.4.9"
 ethereum-types = "0.5"

eth2/utils/ssz/README.md

@@ -38,8 +38,8 @@ spec is decided.*\
   + [bytes v0.4.9](#bytes-v049)
   + [ethereum-types](#ethereum-types)
 * [Interface](#interface)
-  + [Encodable](#encodable)
-  + [Decodable](#decodable)
+  + [Encode](#encodable)
+  + [Decode](#decodable)
   + [SszStream](#sszstream)
     - [new()](#new)
     - [append(&mut self, value: &E) -> &mut Self](#appendmut-self-value-e---mut-self)
@@ -299,24 +299,24 @@ Github: [ https://github.com/paritytech/primitives ](https://github.com/parityte
 
 ## Interface
 
-### Encodable
+### Encode
 
-A type is **Encodable** if it has a valid ``ssz_append`` function. This is
+A type is **Encode** if it has a valid ``ssz_append`` function. This is
 used to ensure that the object/type can be serialized.
 
 ```rust
-pub trait Encodable {
+pub trait Encode {
     fn ssz_append(&self, s: &mut SszStream);
 }
 ```
 
-### Decodable
+### Decode
 
-A type is **Decodable** if it has a valid ``ssz_decode`` function. This is
+A type is **Decode** if it has a valid ``ssz_decode`` function. This is
 used to ensure the object is deserializable.
 
 ```rust
-pub trait Decodable: Sized {
+pub trait Decode: Sized {
     fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError>;
 }
 ```
@@ -342,7 +342,7 @@ Appends a value that can be encoded into the stream.
 
 | Parameter | Description                              |
 |:---------:|:-----------------------------------------|
-| ``value`` | Encodable value to append to the stream. |
+| ``value`` | Encode value to append to the stream. |
 
 **Example**
 
@@ -371,7 +371,7 @@ Appends some vector (list) of encodable values to the stream.
 
 | Parameter | Description                                   |
 |:---------:|:----------------------------------------------|
-|  ``vec``  | Vector of Encodable objects to be serialized. |
+|  ``vec``  | Vector of Encode objects to be serialized. |
 
 **Example**
 

eth2/utils/ssz/benches/benches.rs

@@ -0,0 +1,80 @@
+#[macro_use]
+extern crate criterion;
+
+use criterion::black_box;
+use criterion::{Benchmark, Criterion};
+use ssz::{Decode, Encode};
+use ssz_derive::{Decode, Encode};
+
+#[derive(Clone, Copy, Encode, Decode)]
+pub struct FixedLen {
+    a: u64,
+    b: u64,
+    c: u64,
+    d: u64,
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let n = 8196;
+
+    let vec: Vec<u64> = vec![4242; 8196];
+    c.bench(
+        &format!("vec_of_{}_u64", n),
+        Benchmark::new("as_ssz_bytes", move |b| {
+            b.iter_with_setup(|| vec.clone(), |vec| black_box(vec.as_ssz_bytes()))
+        })
+        .sample_size(100),
+    );
+
+    let vec: Vec<u64> = vec![4242; 8196];
+    let bytes = vec.as_ssz_bytes();
+    c.bench(
+        &format!("vec_of_{}_u64", n),
+        Benchmark::new("from_ssz_bytes", move |b| {
+            b.iter_with_setup(
+                || bytes.clone(),
+                |bytes| {
+                    let vec: Vec<u64> = Vec::from_ssz_bytes(&bytes).unwrap();
+                    black_box(vec)
+                },
+            )
+        })
+        .sample_size(100),
+    );
+
+    let fixed_len = FixedLen {
+        a: 42,
+        b: 42,
+        c: 42,
+        d: 42,
+    };
+    let fixed_len_vec: Vec<FixedLen> = vec![fixed_len; 8196];
+
+    let vec = fixed_len_vec.clone();
+    c.bench(
+        &format!("vec_of_{}_struct", n),
+        Benchmark::new("as_ssz_bytes", move |b| {
+            b.iter_with_setup(|| vec.clone(), |vec| black_box(vec.as_ssz_bytes()))
+        })
+        .sample_size(100),
+    );
+
+    let vec = fixed_len_vec.clone();
+    let bytes = vec.as_ssz_bytes();
+    c.bench(
+        &format!("vec_of_{}_struct", n),
+        Benchmark::new("from_ssz_bytes", move |b| {
+            b.iter_with_setup(
+                || bytes.clone(),
+                |bytes| {
+                    let vec: Vec<u64> = Vec::from_ssz_bytes(&bytes).unwrap();
+                    black_box(vec)
+                },
+            )
+        })
+        .sample_size(100),
+    );
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

eth2/utils/ssz/examples/large_list.rs

@@ -0,0 +1,16 @@
+//! Encode and decode a list many times.
+//!
+//! Useful for `cargo flamegraph`.
+
+use ssz::{Decode, Encode};
+
+fn main() {
+    let vec: Vec<u64> = vec![4242; 8196];
+
+    let output: Vec<Vec<u64>> = (0..40_000)
+        .into_iter()
+        .map(|_| Vec::from_ssz_bytes(&vec.as_ssz_bytes()).unwrap())
+        .collect();
+
+    println!("{}", output.len());
+}

eth2/utils/ssz/examples/large_list_of_structs.rs

@@ -0,0 +1,32 @@
+//! Encode and decode a list many times.
+//!
+//! Useful for `cargo flamegraph`.
+
+use ssz::{Decode, Encode};
+use ssz_derive::{Decode, Encode};
+
+#[derive(Clone, Copy, Encode, Decode)]
+pub struct FixedLen {
+    a: u64,
+    b: u64,
+    c: u64,
+    d: u64,
+}
+
+fn main() {
+    let fixed_len = FixedLen {
+        a: 42,
+        b: 42,
+        c: 42,
+        d: 42,
+    };
+
+    let vec: Vec<FixedLen> = vec![fixed_len; 8196];
+
+    let output: Vec<Vec<u64>> = (0..40_000)
+        .into_iter()
+        .map(|_| Vec::from_ssz_bytes(&vec.as_ssz_bytes()).unwrap())
+        .collect();
+
+    println!("{}", output.len());
+}

eth2/utils/ssz/examples/struct_definition.rs

@@ -0,0 +1,66 @@
+use ssz::{Decode, DecodeError, Encode, SszDecoderBuilder, SszEncoder};
+
+#[derive(Debug, PartialEq)]
+pub struct Foo {
+    a: u16,
+    b: Vec<u8>,
+    c: u16,
+}
+
+impl Encode for Foo {
+    fn is_ssz_fixed_len() -> bool {
+        <u16 as Encode>::is_ssz_fixed_len() && <Vec<u16> as Encode>::is_ssz_fixed_len()
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        let offset = <u16 as Encode>::ssz_fixed_len()
+            + <Vec<u16> as Encode>::ssz_fixed_len()
+            + <u16 as Encode>::ssz_fixed_len();
+
+        let mut encoder = SszEncoder::container(buf, offset);
+
+        encoder.append(&self.a);
+        encoder.append(&self.b);
+        encoder.append(&self.c);
+
+        encoder.finalize();
+    }
+}
+
+impl Decode for Foo {
+    fn is_ssz_fixed_len() -> bool {
+        <u16 as Decode>::is_ssz_fixed_len() && <Vec<u16> as Decode>::is_ssz_fixed_len()
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        let mut builder = SszDecoderBuilder::new(bytes);
+
+        builder.register_type::<u16>()?;
+        builder.register_type::<Vec<u8>>()?;
+        builder.register_type::<u16>()?;
+
+        let mut decoder = builder.build()?;
+
+        Ok(Self {
+            a: decoder.decode_next()?,
+            b: decoder.decode_next()?,
+            c: decoder.decode_next()?,
+        })
+    }
+}
+
+fn main() {
+    let foo = Foo {
+        a: 42,
+        b: vec![0, 1, 2, 3],
+        c: 11,
+    };
+
+    let bytes = vec![42, 0, 8, 0, 0, 0, 11, 0, 0, 1, 2, 3];
+
+    assert_eq!(foo.as_ssz_bytes(), bytes);
+
+    let decoded_foo = Foo::from_ssz_bytes(&bytes).unwrap();
+
+    assert_eq!(foo, decoded_foo);
+}

eth2/utils/ssz/src/decode.rs

@@ -1,215 +1,248 @@
-use super::LENGTH_BYTES;
+use super::*;
 
+pub mod impls;
+
+/// Returned when SSZ decoding fails.
 #[derive(Debug, PartialEq)]
 pub enum DecodeError {
-    TooShort,
-    TooLong,
-    Invalid,
+    /// The bytes supplied were too short to be decoded into the specified type.
+    InvalidByteLength { len: usize, expected: usize },
+    /// The given bytes were too short to be read as a length prefix.
+    InvalidLengthPrefix { len: usize, expected: usize },
+    /// A length offset pointed to a byte that was out-of-bounds (OOB).
+    ///
+    /// A bytes may be OOB for the following reasons:
+    ///
+    /// - It is `>= bytes.len()`.
+    /// - When decoding variable length items, the 1st offset points "backwards" into the fixed
+    /// length items (i.e., `length[0] < BYTES_PER_LENGTH_OFFSET`).
+    /// - When decoding variable-length items, the `n`'th offset was less than the `n-1`'th offset.
+    OutOfBoundsByte { i: usize },
+    /// The given bytes were invalid for some application-level reason.
+    BytesInvalid(String),
 }
 
-pub trait Decodable: Sized {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError>;
-}
-
-/// Decode the given bytes for the given type
+/// Provides SSZ decoding (de-serialization) via the `from_ssz_bytes(&bytes)` method.
 ///
-/// The single ssz encoded value/container/list will be decoded as the given type,
-/// by recursively calling `ssz_decode`.
-/// Check on totality for underflowing the length of bytes and overflow checks done per container
-pub fn decode<T>(ssz_bytes: &[u8]) -> Result<(T), DecodeError>
-where
-    T: Decodable,
-{
-    let (decoded, i): (T, usize) = match T::ssz_decode(ssz_bytes, 0) {
-        Err(e) => return Err(e),
-        Ok(v) => v,
-    };
+/// See `examples/` for manual implementations or the crate root for implementations using
+/// `#[derive(Decode)]`.
+pub trait Decode: Sized {
+    /// Returns `true` if this object has a fixed-length.
+    ///
+    /// I.e., there are no variable length items in this object or any of it's contained objects.
+    fn is_ssz_fixed_len() -> bool;
 
-    if i < ssz_bytes.len() {
-        return Err(DecodeError::TooLong);
+    /// The number of bytes this object occupies in the fixed-length portion of the SSZ bytes.
+    ///
+    /// By default, this is set to `BYTES_PER_LENGTH_OFFSET` which is suitable for variable length
+    /// objects, but not fixed-length objects. Fixed-length objects _must_ return a value which
+    /// represents their length.
+    fn ssz_fixed_len() -> usize {
+        BYTES_PER_LENGTH_OFFSET
     }
 
-    Ok(decoded)
+    /// Attempts to decode `Self` from `bytes`, returning a `DecodeError` on failure.
+    ///
+    /// The supplied bytes must be the exact length required to decode `Self`, excess bytes will
+    /// result in an error.
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError>;
 }
 
-/// Decode a vector (list) of encoded bytes.
+#[derive(Copy, Clone, Debug)]
+pub struct Offset {
+    position: usize,
+    offset: usize,
+}
+
+/// Builds an `SszDecoder`.
 ///
-/// Each element in the list will be decoded and placed into the vector.
-pub fn decode_ssz_list<T>(ssz_bytes: &[u8], index: usize) -> Result<(Vec<T>, usize), DecodeError>
-where
-    T: Decodable,
-{
-    if index + LENGTH_BYTES > ssz_bytes.len() {
-        return Err(DecodeError::TooShort);
-    };
-
-    // get the length
-    let serialized_length = match decode_length(ssz_bytes, index, LENGTH_BYTES) {
-        Err(v) => return Err(v),
-        Ok(v) => v,
-    };
-
-    let final_len: usize = index + LENGTH_BYTES + serialized_length;
-
-    if final_len > ssz_bytes.len() {
-        return Err(DecodeError::TooShort);
-    };
-
-    let mut tmp_index = index + LENGTH_BYTES;
-    let mut res_vec: Vec<T> = Vec::new();
-
-    while tmp_index < final_len {
-        match T::ssz_decode(ssz_bytes, tmp_index) {
-            Err(v) => return Err(v),
-            Ok(v) => {
-                tmp_index = v.1;
-                res_vec.push(v.0);
-            }
-        };
-    }
-
-    Ok((res_vec, final_len))
+/// The purpose of this struct is to split some SSZ bytes into individual slices. The builder is
+/// then converted into a `SszDecoder` which decodes those values into object instances.
+///
+/// See [`SszDecoder`](struct.SszDecoder.html) for usage examples.
+pub struct SszDecoderBuilder<'a> {
+    bytes: &'a [u8],
+    items: Vec<&'a [u8]>,
+    offsets: Vec<Offset>,
+    items_index: usize,
 }
 
-/// Given some number of bytes, interpret the first four
-/// bytes as a 32-bit little-endian integer and return the
-/// result.
-pub fn decode_length(
-    bytes: &[u8],
-    index: usize,
-    length_bytes: usize,
-) -> Result<usize, DecodeError> {
-    if bytes.len() < index + length_bytes {
-        return Err(DecodeError::TooShort);
-    };
-    let mut len: usize = 0;
-    for (i, byte) in bytes
-        .iter()
-        .enumerate()
-        .take(index + length_bytes)
-        .skip(index)
-    {
-        let offset = (i - index) * 8;
-        len |= (*byte as usize) << offset;
-    }
-    Ok(len)
-}
-
-#[cfg(test)]
-mod tests {
-    use super::super::encode::*;
-    use super::*;
-
-    #[test]
-    fn test_ssz_decode_length() {
-        let decoded = decode_length(&vec![1, 0, 0, 0], 0, LENGTH_BYTES);
-        assert_eq!(decoded.unwrap(), 1);
-
-        let decoded = decode_length(&vec![0, 1, 0, 0], 0, LENGTH_BYTES);
-        assert_eq!(decoded.unwrap(), 256);
-
-        let decoded = decode_length(&vec![255, 1, 0, 0], 0, LENGTH_BYTES);
-        assert_eq!(decoded.unwrap(), 511);
-
-        let decoded = decode_length(&vec![255, 255, 255, 255], 0, LENGTH_BYTES);
-        assert_eq!(decoded.unwrap(), 4294967295);
-    }
-
-    #[test]
-    fn test_encode_decode_length() {
-        let params: Vec<usize> = vec![
-            0,
-            1,
-            2,
-            3,
-            7,
-            8,
-            16,
-            2 ^ 8,
-            2 ^ 8 + 1,
-            2 ^ 16,
-            2 ^ 16 + 1,
-            2 ^ 24,
-            2 ^ 24 + 1,
-            2 ^ 32,
-        ];
-        for i in params {
-            let decoded = decode_length(&encode_length(i, LENGTH_BYTES), 0, LENGTH_BYTES).unwrap();
-            assert_eq!(i, decoded);
+impl<'a> SszDecoderBuilder<'a> {
+    /// Instantiate a new builder that should build a `SszDecoder` over the given `bytes` which
+    /// are assumed to be the SSZ encoding of some object.
+    pub fn new(bytes: &'a [u8]) -> Self {
+        Self {
+            bytes,
+            items: vec![],
+            offsets: vec![],
+            items_index: 0,
         }
     }
 
-    #[test]
-    fn test_encode_decode_ssz_list() {
-        let test_vec: Vec<u16> = vec![256; 12];
-        let mut stream = SszStream::new();
-        stream.append_vec(&test_vec);
-        let ssz = stream.drain();
+    /// Declares that some type `T` is the next item in `bytes`.
+    pub fn register_type<T: Decode>(&mut self) -> Result<(), DecodeError> {
+        if T::is_ssz_fixed_len() {
+            let start = self.items_index;
+            self.items_index += T::ssz_fixed_len();
 
-        // u16
-        let decoded: (Vec<u16>, usize) = decode_ssz_list(&ssz, 0).unwrap();
+            let slice = self.bytes.get(start..self.items_index).ok_or_else(|| {
+                DecodeError::InvalidByteLength {
+                    len: self.bytes.len(),
+                    expected: self.items_index,
+                }
+            })?;
 
-        assert_eq!(decoded.0, test_vec);
-        assert_eq!(decoded.1, LENGTH_BYTES + (12 * 2));
+            self.items.push(slice);
+        } else {
+            let offset = read_offset(&self.bytes[self.items_index..])?;
+
+            let previous_offset = self
+                .offsets
+                .last()
+                .and_then(|o| Some(o.offset))
+                .unwrap_or_else(|| BYTES_PER_LENGTH_OFFSET);
+
+            if previous_offset > offset {
+                return Err(DecodeError::OutOfBoundsByte { i: offset });
+            } else if offset > self.bytes.len() {
+                return Err(DecodeError::OutOfBoundsByte { i: offset });
+            }
+
+            self.offsets.push(Offset {
+                position: self.items.len(),
+                offset,
+            });
+
+            // Push an empty slice into items; it will be replaced later.
+            self.items.push(&[]);
+
+            self.items_index += BYTES_PER_LENGTH_OFFSET;
+        }
+
+        Ok(())
     }
 
-    #[test]
-    fn test_decode_ssz_list() {
-        // u16
-        let v: Vec<u16> = vec![10, 10, 10, 10];
-        let decoded: (Vec<u16>, usize) =
-            decode_ssz_list(&vec![8, 0, 0, 0, 10, 0, 10, 0, 10, 0, 10, 0], 0).unwrap();
+    fn finalize(&mut self) -> Result<(), DecodeError> {
+        if !self.offsets.is_empty() {
+            // Check to ensure the first offset points to the byte immediately following the
+            // fixed-length bytes.
+            if self.offsets[0].offset != self.items_index {
+                return Err(DecodeError::OutOfBoundsByte {
+                    i: self.offsets[0].offset,
+                });
+            }
 
-        assert_eq!(decoded.0, v);
-        assert_eq!(decoded.1, LENGTH_BYTES + (4 * 2));
+            // Iterate through each pair of offsets, grabbing the slice between each of the offsets.
+            for pair in self.offsets.windows(2) {
+                let a = pair[0];
+                let b = pair[1];
 
-        // u32
-        let v: Vec<u32> = vec![10, 10, 10, 10];
-        let decoded: (Vec<u32>, usize) = decode_ssz_list(
-            &vec![
-                16, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 00,
-            ],
-            0,
-        )
-        .unwrap();
-        assert_eq!(decoded.0, v);
-        assert_eq!(decoded.1, 20);
+                self.items[a.position] = &self.bytes[a.offset..b.offset];
+            }
 
-        // u64
-        let v: Vec<u64> = vec![10, 10, 10, 10];
-        let decoded: (Vec<u64>, usize) = decode_ssz_list(
-            &vec![
-                32, 0, 0, 0, 10, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0, 0, 0, 0,
-                0, 0, 10, 0, 0, 0, 0, 0, 0, 0,
-            ],
-            0,
-        )
-        .unwrap();
-        assert_eq!(decoded.0, v);
-        assert_eq!(decoded.1, LENGTH_BYTES + (8 * 4));
+            // Handle the last offset, pushing a slice from it's start through to the end of
+            // `self.bytes`.
+            if let Some(last) = self.offsets.last() {
+                self.items[last.position] = &self.bytes[last.offset..]
+            }
+        } else {
+            // If the container is fixed-length, ensure there are no excess bytes.
+            if self.items_index != self.bytes.len() {
+                return Err(DecodeError::InvalidByteLength {
+                    len: self.bytes.len(),
+                    expected: self.items_index,
+                });
+            }
+        }
 
-        // Check that it can accept index
-        let v: Vec<usize> = vec![15, 15, 15, 15];
-        let offset = 10;
-        let decoded: (Vec<usize>, usize) = decode_ssz_list(
-            &vec![
-                0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 32, 0, 0, 0, 15, 0, 0, 0, 0, 0, 0, 0, 15, 0, 0, 0, 0,
-                0, 0, 0, 15, 0, 0, 0, 0, 0, 0, 0, 15, 0, 0, 0, 0, 0, 0, 0,
-            ],
-            offset,
-        )
-        .unwrap();
-        assert_eq!(decoded.0, v);
-        assert_eq!(decoded.1, offset + LENGTH_BYTES + (8 * 4));
+        Ok(())
+    }
 
-        // Check that length > bytes throws error
-        let decoded: Result<(Vec<usize>, usize), DecodeError> =
-            decode_ssz_list(&vec![32, 0, 0, 0, 15, 0, 0, 0, 0, 0, 0, 0], 0);
-        assert_eq!(decoded, Err(DecodeError::TooShort));
+    /// Finalizes the builder, returning a `SszDecoder` that may be used to instantiate objects.
+    pub fn build(mut self) -> Result<SszDecoder<'a>, DecodeError> {
+        self.finalize()?;
 
-        // Check that incorrect index throws error
-        let decoded: Result<(Vec<usize>, usize), DecodeError> =
-            decode_ssz_list(&vec![15, 0, 0, 0, 0, 0, 0, 0], 16);
-        assert_eq!(decoded, Err(DecodeError::TooShort));
+        Ok(SszDecoder { items: self.items })
+    }
+}
+
+/// Decodes some slices of SSZ into object instances. Should be instantiated using
+/// [`SszDecoderBuilder`](struct.SszDecoderBuilder.html).
+///
+/// ## Example
+///
+/// ```rust
+/// use ssz_derive::{Encode, Decode};
+/// use ssz::{Decode, Encode, SszDecoder, SszDecoderBuilder};
+///
+/// #[derive(PartialEq, Debug, Encode, Decode)]
+/// struct Foo {
+///     a: u64,
+///     b: Vec<u16>,
+/// }
+///
+/// fn main() {
+///     let foo = Foo {
+///         a: 42,
+///         b: vec![1, 3, 3, 7]
+///     };
+///
+///     let bytes = foo.as_ssz_bytes();
+///
+///     let mut builder = SszDecoderBuilder::new(&bytes);
+///
+///     builder.register_type::<u64>().unwrap();
+///     builder.register_type::<Vec<u16>>().unwrap();
+///
+///     let mut decoder = builder.build().unwrap();
+///
+///     let decoded_foo = Foo {
+///         a: decoder.decode_next().unwrap(),
+///         b: decoder.decode_next().unwrap(),
+///     };
+///
+///     assert_eq!(foo, decoded_foo);
+/// }
+///
+/// ```
+pub struct SszDecoder<'a> {
+    items: Vec<&'a [u8]>,
+}
+
+impl<'a> SszDecoder<'a> {
+    /// Decodes the next item.
+    ///
+    /// # Panics
+    ///
+    /// Panics when attempting to decode more items than actually exist.
+    pub fn decode_next<T: Decode>(&mut self) -> Result<T, DecodeError> {
+        T::from_ssz_bytes(self.items.remove(0))
+    }
+}
+
+/// Reads a `BYTES_PER_LENGTH_OFFSET`-byte length from `bytes`, where `bytes.len() >=
+/// BYTES_PER_LENGTH_OFFSET`.
+fn read_offset(bytes: &[u8]) -> Result<usize, DecodeError> {
+    decode_offset(bytes.get(0..BYTES_PER_LENGTH_OFFSET).ok_or_else(|| {
+        DecodeError::InvalidLengthPrefix {
+            len: bytes.len(),
+            expected: BYTES_PER_LENGTH_OFFSET,
+        }
+    })?)
+}
+
+/// Decode bytes as a little-endian usize, returning an `Err` if `bytes.len() !=
+/// BYTES_PER_LENGTH_OFFSET`.
+fn decode_offset(bytes: &[u8]) -> Result<usize, DecodeError> {
+    let len = bytes.len();
+    let expected = BYTES_PER_LENGTH_OFFSET;
+
+    if len != expected {
+        Err(DecodeError::InvalidLengthPrefix { len, expected })
+    } else {
+        let mut array: [u8; BYTES_PER_LENGTH_OFFSET] = std::default::Default::default();
+        array.clone_from_slice(bytes);
+
+        Ok(u32::from_le_bytes(array) as usize)
     }
 }

eth2/utils/ssz/src/decode/impls.rs

@@ -0,0 +1,422 @@
+use super::*;
+use ethereum_types::H256;
+
+macro_rules! impl_decodable_for_uint {
+    ($type: ident, $bit_size: expr) => {
+        impl Decode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $bit_size / 8
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+                let len = bytes.len();
+                let expected = <Self as Decode>::ssz_fixed_len();
+
+                if len != expected {
+                    Err(DecodeError::InvalidByteLength { len, expected })
+                } else {
+                    let mut array: [u8; $bit_size / 8] = std::default::Default::default();
+                    array.clone_from_slice(bytes);
+
+                    Ok(Self::from_le_bytes(array))
+                }
+            }
+        }
+    };
+}
+
+impl_decodable_for_uint!(u8, 8);
+impl_decodable_for_uint!(u16, 16);
+impl_decodable_for_uint!(u32, 32);
+impl_decodable_for_uint!(u64, 64);
+impl_decodable_for_uint!(usize, 64);
+
+impl Decode for bool {
+    fn is_ssz_fixed_len() -> bool {
+        true
+    }
+
+    fn ssz_fixed_len() -> usize {
+        1
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        let len = bytes.len();
+        let expected = <Self as Decode>::ssz_fixed_len();
+
+        if len != expected {
+            Err(DecodeError::InvalidByteLength { len, expected })
+        } else {
+            match bytes[0] {
+                0b0000_0000 => Ok(false),
+                0b0000_0001 => Ok(true),
+                _ => {
+                    return Err(DecodeError::BytesInvalid(
+                        format!("Out-of-range for boolean: {}", bytes[0]).to_string(),
+                    ))
+                }
+            }
+        }
+    }
+}
+
+impl Decode for H256 {
+    fn is_ssz_fixed_len() -> bool {
+        true
+    }
+
+    fn ssz_fixed_len() -> usize {
+        32
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        let len = bytes.len();
+        let expected = <Self as Decode>::ssz_fixed_len();
+
+        if len != expected {
+            Err(DecodeError::InvalidByteLength { len, expected })
+        } else {
+            Ok(H256::from_slice(bytes))
+        }
+    }
+}
+
+macro_rules! impl_decodable_for_u8_array {
+    ($len: expr) => {
+        impl Decode for [u8; $len] {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $len
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+                let len = bytes.len();
+                let expected = <Self as Decode>::ssz_fixed_len();
+
+                if len != expected {
+                    Err(DecodeError::InvalidByteLength { len, expected })
+                } else {
+                    let mut array: [u8; $len] = [0; $len];
+                    array.copy_from_slice(&bytes[..]);
+
+                    Ok(array)
+                }
+            }
+        }
+    };
+}
+
+impl_decodable_for_u8_array!(4);
+
+impl<T: Decode> Decode for Vec<T> {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
+        if bytes.len() == 0 {
+            Ok(vec![])
+        } else if T::is_ssz_fixed_len() {
+            bytes
+                .chunks(T::ssz_fixed_len())
+                .map(|chunk| T::from_ssz_bytes(chunk))
+                .collect()
+        } else {
+            decode_list_of_variable_length_items(bytes)
+        }
+    }
+}
+
+/// Decodes `bytes` as if it were a list of variable-length items.
+///
+/// The `ssz::SszDecoder` can also perform this functionality, however it it significantly faster
+/// as it is optimized to read same-typed items whilst `ssz::SszDecoder` supports reading items of
+/// differing types.
+pub fn decode_list_of_variable_length_items<T: Decode>(
+    bytes: &[u8],
+) -> Result<Vec<T>, DecodeError> {
+    let mut next_variable_byte = read_offset(bytes)?;
+
+    // The value of the first offset must not point back into the same bytes that defined
+    // it.
+    if next_variable_byte < BYTES_PER_LENGTH_OFFSET {
+        return Err(DecodeError::OutOfBoundsByte {
+            i: next_variable_byte,
+        });
+    }
+
+    let num_items = next_variable_byte / BYTES_PER_LENGTH_OFFSET;
+
+    // The fixed-length section must be a clean multiple of `BYTES_PER_LENGTH_OFFSET`.
+    if next_variable_byte != num_items * BYTES_PER_LENGTH_OFFSET {
+        return Err(DecodeError::InvalidByteLength {
+            len: next_variable_byte,
+            expected: num_items * BYTES_PER_LENGTH_OFFSET,
+        });
+    }
+
+    let mut values = Vec::with_capacity(num_items);
+    for i in 1..=num_items {
+        let slice_option = if i == num_items {
+            bytes.get(next_variable_byte..)
+        } else {
+            let offset = read_offset(&bytes[(i * BYTES_PER_LENGTH_OFFSET)..])?;
+
+            let start = next_variable_byte;
+            next_variable_byte = offset;
+
+            bytes.get(start..next_variable_byte)
+        };
+
+        let slice = slice_option.ok_or_else(|| DecodeError::OutOfBoundsByte {
+            i: next_variable_byte,
+        })?;
+
+        values.push(T::from_ssz_bytes(slice)?);
+    }
+
+    Ok(values)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Note: decoding of valid bytes is generally tested "indirectly" in the `/tests` dir, by
+    // encoding then decoding the element.
+
+    #[test]
+    fn invalid_u8_array_4() {
+        assert_eq!(
+            <[u8; 4]>::from_ssz_bytes(&[0; 3]),
+            Err(DecodeError::InvalidByteLength {
+                len: 3,
+                expected: 4
+            })
+        );
+
+        assert_eq!(
+            <[u8; 4]>::from_ssz_bytes(&[0; 5]),
+            Err(DecodeError::InvalidByteLength {
+                len: 5,
+                expected: 4
+            })
+        );
+    }
+
+    #[test]
+    fn invalid_bool() {
+        assert_eq!(
+            bool::from_ssz_bytes(&[0; 2]),
+            Err(DecodeError::InvalidByteLength {
+                len: 2,
+                expected: 1
+            })
+        );
+
+        assert_eq!(
+            bool::from_ssz_bytes(&[]),
+            Err(DecodeError::InvalidByteLength {
+                len: 0,
+                expected: 1
+            })
+        );
+
+        if let Err(DecodeError::BytesInvalid(_)) = bool::from_ssz_bytes(&[2]) {
+            // Success.
+        } else {
+            panic!("Did not return error on invalid bool val")
+        }
+    }
+
+    #[test]
+    fn invalid_h256() {
+        assert_eq!(
+            H256::from_ssz_bytes(&[0; 33]),
+            Err(DecodeError::InvalidByteLength {
+                len: 33,
+                expected: 32
+            })
+        );
+
+        assert_eq!(
+            H256::from_ssz_bytes(&[0; 31]),
+            Err(DecodeError::InvalidByteLength {
+                len: 31,
+                expected: 32
+            })
+        );
+    }
+
+    #[test]
+    fn first_length_points_backwards() {
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[0, 0, 0, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 0 })
+        );
+
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[1, 0, 0, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 1 })
+        );
+
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[2, 0, 0, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 2 })
+        );
+
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[3, 0, 0, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 3 })
+        );
+    }
+
+    #[test]
+    fn lengths_are_decreasing() {
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[12, 0, 0, 0, 14, 0, 0, 0, 12, 0, 0, 0, 1, 0, 1, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 12 })
+        );
+    }
+
+    #[test]
+    fn awkward_fixed_lenth_portion() {
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[10, 0, 0, 0, 10, 0, 0, 0, 0, 0]),
+            Err(DecodeError::InvalidByteLength {
+                len: 10,
+                expected: 8
+            })
+        );
+    }
+
+    #[test]
+    fn length_out_of_bounds() {
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[5, 0, 0, 0]),
+            Err(DecodeError::InvalidByteLength {
+                len: 5,
+                expected: 4
+            })
+        );
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[8, 0, 0, 0, 9, 0, 0, 0]),
+            Err(DecodeError::OutOfBoundsByte { i: 9 })
+        );
+    }
+
+    #[test]
+    fn vec_of_vec_of_u16() {
+        assert_eq!(
+            <Vec<Vec<u16>>>::from_ssz_bytes(&[4, 0, 0, 0]),
+            Ok(vec![vec![]])
+        );
+
+        assert_eq!(
+            <Vec<u16>>::from_ssz_bytes(&[0, 0, 1, 0, 2, 0, 3, 0]),
+            Ok(vec![0, 1, 2, 3])
+        );
+        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
+        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
+        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[255]),
+            Err(DecodeError::InvalidByteLength {
+                len: 1,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[]),
+            Err(DecodeError::InvalidByteLength {
+                len: 0,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[0, 1, 2]),
+            Err(DecodeError::InvalidByteLength {
+                len: 3,
+                expected: 2
+            })
+        );
+    }
+
+    #[test]
+    fn vec_of_u16() {
+        assert_eq!(<Vec<u16>>::from_ssz_bytes(&[0, 0, 0, 0]), Ok(vec![0, 0]));
+        assert_eq!(
+            <Vec<u16>>::from_ssz_bytes(&[0, 0, 1, 0, 2, 0, 3, 0]),
+            Ok(vec![0, 1, 2, 3])
+        );
+        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
+        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
+        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[255]),
+            Err(DecodeError::InvalidByteLength {
+                len: 1,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[]),
+            Err(DecodeError::InvalidByteLength {
+                len: 0,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[0, 1, 2]),
+            Err(DecodeError::InvalidByteLength {
+                len: 3,
+                expected: 2
+            })
+        );
+    }
+
+    #[test]
+    fn u16() {
+        assert_eq!(<u16>::from_ssz_bytes(&[0, 0]), Ok(0));
+        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
+        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
+        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[255]),
+            Err(DecodeError::InvalidByteLength {
+                len: 1,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[]),
+            Err(DecodeError::InvalidByteLength {
+                len: 0,
+                expected: 2
+            })
+        );
+
+        assert_eq!(
+            <u16>::from_ssz_bytes(&[0, 1, 2]),
+            Err(DecodeError::InvalidByteLength {
+                len: 3,
+                expected: 2
+            })
+        );
+    }
+}

eth2/utils/ssz/src/encode.rs

@@ -1,85 +1,159 @@
-use super::LENGTH_BYTES;
+use super::*;
 
-pub trait Encodable {
-    fn ssz_append(&self, s: &mut SszStream);
-}
+mod impls;
 
-/// Provides a buffer for appending ssz-encodable values.
+/// Provides SSZ encoding (serialization) via the `as_ssz_bytes(&self)` method.
 ///
-/// Use the `append()` fn to add a value to a list, then use
-/// the `drain()` method to consume the struct and return the
-/// ssz encoded bytes.
-#[derive(Default)]
-pub struct SszStream {
-    buffer: Vec<u8>,
+/// See `examples/` for manual implementations or the crate root for implementations using
+/// `#[derive(Encode)]`.
+pub trait Encode {
+    /// Returns `true` if this object has a fixed-length.
+    ///
+    /// I.e., there are no variable length items in this object or any of it's contained objects.
+    fn is_ssz_fixed_len() -> bool;
+
+    /// Append the encoding `self` to `buf`.
+    ///
+    /// Note, variable length objects need only to append their "variable length" portion, they do
+    /// not need to provide their offset.
+    fn ssz_append(&self, buf: &mut Vec<u8>);
+
+    /// The number of bytes this object occupies in the fixed-length portion of the SSZ bytes.
+    ///
+    /// By default, this is set to `BYTES_PER_LENGTH_OFFSET` which is suitable for variable length
+    /// objects, but not fixed-length objects. Fixed-length objects _must_ return a value which
+    /// represents their length.
+    fn ssz_fixed_len() -> usize {
+        BYTES_PER_LENGTH_OFFSET
+    }
+
+    /// Returns the full-form encoding of this object.
+    ///
+    /// The default implementation of this method should suffice for most cases.
+    fn as_ssz_bytes(&self) -> Vec<u8> {
+        let mut buf = vec![];
+
+        self.ssz_append(&mut buf);
+
+        buf
+    }
 }
 
-impl SszStream {
-    /// Create a new, empty stream for writing ssz values.
-    pub fn new() -> Self {
-        SszStream { buffer: Vec::new() }
-    }
+/// Allow for encoding an ordered series of distinct or indistinct objects as SSZ bytes.
+///
+/// **You must call `finalize(..)` after the final `append(..)` call** to ensure the bytes are
+/// written to `buf`.
+///
+/// ## Example
+///
+/// Use `SszEncoder` to produce identical output to `foo.as_ssz_bytes()`:
+///
+/// ```rust
+/// use ssz_derive::{Encode, Decode};
+/// use ssz::{Decode, Encode, SszEncoder};
+///
+/// #[derive(PartialEq, Debug, Encode, Decode)]
+/// struct Foo {
+///     a: u64,
+///     b: Vec<u16>,
+/// }
+///
+/// fn main() {
+///     let foo = Foo {
+///         a: 42,
+///         b: vec![1, 3, 3, 7]
+///     };
+///
+///     let mut buf: Vec<u8> = vec![];
+///     let offset = <u64 as Encode>::ssz_fixed_len() + <Vec<u16> as Encode>::ssz_fixed_len();
+///
+///     let mut encoder = SszEncoder::container(&mut buf, offset);
+///
+///     encoder.append(&foo.a);
+///     encoder.append(&foo.b);
+///
+///     encoder.finalize();
+///
+///     assert_eq!(foo.as_ssz_bytes(), buf);
+/// }
+///
+/// ```
+pub struct SszEncoder<'a> {
+    offset: usize,
+    buf: &'a mut Vec<u8>,
+    variable_bytes: Vec<u8>,
+}
 
-    /// Append some ssz encodable value to the stream.
-    pub fn append<E>(&mut self, value: &E) -> &mut Self
-    where
-        E: Encodable,
-    {
-        value.ssz_append(self);
-        self
-    }
-
-    /// Append some ssz encoded bytes to the stream.
+impl<'a> SszEncoder<'a> {
+    /// Instantiate a new encoder for encoding a SSZ list.
     ///
-    /// The length of the supplied bytes will be concatenated
-    /// to the stream before the supplied bytes.
-    pub fn append_encoded_val(&mut self, vec: &[u8]) {
-        self.buffer
-            .extend_from_slice(&encode_length(vec.len(), LENGTH_BYTES));
-        self.buffer.extend_from_slice(&vec);
+    /// Identical to `Self::container`.
+    pub fn list(buf: &'a mut Vec<u8>, num_fixed_bytes: usize) -> Self {
+        Self::container(buf, num_fixed_bytes)
     }
 
-    /// Append some ssz encoded bytes to the stream without calculating length
-    ///
-    /// The raw bytes will be concatenated to the stream.
-    pub fn append_encoded_raw(&mut self, vec: &[u8]) {
-        self.buffer.extend_from_slice(&vec);
-    }
+    /// Instantiate a new encoder for encoding a SSZ container.
+    pub fn container(buf: &'a mut Vec<u8>, num_fixed_bytes: usize) -> Self {
+        buf.reserve(num_fixed_bytes);
 
-    /// Append some vector (list) of encodable values to the stream.
-    ///
-    /// The length of the list will be concatenated to the stream, then
-    /// each item in the vector will be encoded and concatenated.
-    pub fn append_vec<E>(&mut self, vec: &[E])
-    where
-        E: Encodable,
-    {
-        let mut list_stream = SszStream::new();
-        for item in vec {
-            item.ssz_append(&mut list_stream);
+        Self {
+            offset: num_fixed_bytes,
+            buf,
+            variable_bytes: vec![],
         }
-        self.append_encoded_val(&list_stream.drain());
     }
 
-    /// Consume the stream and return the underlying bytes.
-    pub fn drain(self) -> Vec<u8> {
-        self.buffer
+    /// Append some `item` to the SSZ bytes.
+    pub fn append<T: Encode>(&mut self, item: &T) {
+        if T::is_ssz_fixed_len() {
+            item.ssz_append(&mut self.buf);
+        } else {
+            self.buf
+                .append(&mut encode_length(self.offset + self.variable_bytes.len()));
+
+            item.ssz_append(&mut self.variable_bytes);
+        }
+    }
+
+    /// Write the variable bytes to `self.bytes`.
+    ///
+    /// This method must be called after the final `append(..)` call when serializing
+    /// variable-length items.
+    pub fn finalize(&mut self) -> &mut Vec<u8> {
+        self.buf.append(&mut self.variable_bytes);
+
+        &mut self.buf
     }
 }
 
-/// Encode some length into a ssz size prefix.
+/// Encode `len` as a little-endian byte vec of `BYTES_PER_LENGTH_OFFSET` length.
 ///
-/// The ssz size prefix is 4 bytes, which is treated as a continuious
-/// 32bit little-endian integer.
-pub fn encode_length(len: usize, length_bytes: usize) -> Vec<u8> {
-    assert!(length_bytes > 0); // For sanity
-    assert!((len as usize) < 2usize.pow(length_bytes as u32 * 8));
-    let mut header: Vec<u8> = vec![0; length_bytes];
-    for (i, header_byte) in header.iter_mut().enumerate() {
-        let offset = i * 8;
-        *header_byte = ((len >> offset) & 0xff) as u8;
-    }
-    header
+/// If `len` is larger than `2 ^ BYTES_PER_LENGTH_OFFSET`, a `debug_assert` is raised.
+pub fn encode_length(len: usize) -> Vec<u8> {
+    // Note: it is possible for `len` to be larger than what can be encoded in
+    // `BYTES_PER_LENGTH_OFFSET` bytes, triggering this debug assertion.
+    //
+    // These are the alternatives to using a `debug_assert` here:
+    //
+    // 1. Use `assert`.
+    // 2. Push an error to the caller (e.g., `Option` or `Result`).
+    // 3. Ignore it completely.
+    //
+    // I have avoided (1) because it's basically a choice between "produce invalid SSZ" or "kill
+    // the entire program". I figure it may be possible for an attacker to trigger this assert and
+    // take the program down -- I think producing invalid SSZ is a better option than this.
+    //
+    // I have avoided (2) because this error will need to be propagated upstream, making encoding a
+    // function which may fail. I don't think this is ergonomic and the upsides don't outweigh the
+    // downsides.
+    //
+    // I figure a `debug_assertion` is better than (3) as it will give us a change to detect the
+    // error during testing.
+    //
+    // If you have a different opinion, feel free to start an issue and tag @paulhauner.
+    debug_assert!(len <= MAX_LENGTH_VALUE);
+
+    len.to_le_bytes()[0..BYTES_PER_LENGTH_OFFSET].to_vec()
 }
 
 #[cfg(test)]
@@ -87,84 +161,27 @@ mod tests {
     use super::*;
 
     #[test]
-    #[should_panic]
-    fn test_encode_length_0_bytes_panic() {
-        encode_length(0, 0);
-    }
+    fn test_encode_length() {
+        assert_eq!(encode_length(0), vec![0; 4]);
+
+        assert_eq!(encode_length(1), vec![1, 0, 0, 0]);
 
-    #[test]
-    fn test_encode_length_4_bytes() {
-        assert_eq!(encode_length(0, LENGTH_BYTES), vec![0; 4]);
-        assert_eq!(encode_length(1, LENGTH_BYTES), vec![1, 0, 0, 0]);
-        assert_eq!(encode_length(255, LENGTH_BYTES), vec![255, 0, 0, 0]);
-        assert_eq!(encode_length(256, LENGTH_BYTES), vec![0, 1, 0, 0]);
         assert_eq!(
-            encode_length(4294967295, LENGTH_BYTES), // 2^(3*8) - 1
-            vec![255, 255, 255, 255]
+            encode_length(MAX_LENGTH_VALUE),
+            vec![255; BYTES_PER_LENGTH_OFFSET]
         );
     }
 
-    #[test]
-    fn test_encode_lower_length() {
-        assert_eq!(encode_length(0, LENGTH_BYTES - 2), vec![0; 2]);
-        assert_eq!(encode_length(1, LENGTH_BYTES - 2), vec![1, 0]);
-    }
-
-    #[test]
-    fn test_encode_higher_length() {
-        assert_eq!(encode_length(0, LENGTH_BYTES + 2), vec![0; 6]);
-        assert_eq!(encode_length(1, LENGTH_BYTES + 2), vec![1, 0, 0, 0, 0, 0]);
-    }
-
     #[test]
     #[should_panic]
-    fn test_encode_length_4_bytes_panic() {
-        encode_length(4294967296, LENGTH_BYTES); // 2^(3*8)
+    #[cfg(debug_assertions)]
+    fn test_encode_length_above_max_debug_panics() {
+        encode_length(MAX_LENGTH_VALUE + 1);
     }
 
     #[test]
-    fn test_encode_list() {
-        let test_vec: Vec<u16> = vec![256; 12];
-        let mut stream = SszStream::new();
-        stream.append_vec(&test_vec);
-        let ssz = stream.drain();
-
-        assert_eq!(ssz.len(), LENGTH_BYTES + (12 * 2));
-        assert_eq!(ssz[0..4], *vec![24, 0, 0, 0]);
-        assert_eq!(ssz[4..6], *vec![0, 1]);
-    }
-
-    #[test]
-    fn test_encode_mixed_prefixed() {
-        let test_vec: Vec<u16> = vec![100, 200];
-        let test_value: u8 = 5;
-
-        let mut stream = SszStream::new();
-        stream.append_vec(&test_vec);
-        stream.append(&test_value);
-        let ssz = stream.drain();
-
-        assert_eq!(ssz.len(), LENGTH_BYTES + (2 * 2) + 1);
-        assert_eq!(ssz[0..4], *vec![4, 0, 0, 0]);
-        assert_eq!(ssz[4..6], *vec![100, 0]);
-        assert_eq!(ssz[6..8], *vec![200, 0]);
-        assert_eq!(ssz[8], 5);
-    }
-
-    #[test]
-    fn test_encode_mixed_postfixed() {
-        let test_value: u8 = 5;
-        let test_vec: Vec<u16> = vec![100, 200];
-
-        let mut stream = SszStream::new();
-        stream.append(&test_value);
-        stream.append_vec(&test_vec);
-        let ssz = stream.drain();
-
-        assert_eq!(ssz.len(), 1 + LENGTH_BYTES + (2 * 2));
-        assert_eq!(ssz[0], 5);
-        assert_eq!(ssz[1..5], *vec![4, 0, 0, 0]);
-        assert_eq!(ssz[5..7], *vec![100, 0]);
-        assert_eq!(ssz[7..9], *vec![200, 0]);
+    #[cfg(not(debug_assertions))]
+    fn test_encode_length_above_max_not_debug_does_not_panic() {
+        assert_eq!(encode_length(MAX_LENGTH_VALUE + 1), vec![0; 4]);
     }
 }

eth2/utils/ssz/src/encode/impls.rs

@@ -0,0 +1,202 @@
+use super::*;
+use ethereum_types::H256;
+
+macro_rules! impl_encodable_for_uint {
+    ($type: ident, $bit_size: expr) => {
+        impl Encode for $type {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $bit_size / 8
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                buf.extend_from_slice(&self.to_le_bytes());
+            }
+        }
+    };
+}
+
+impl_encodable_for_uint!(u8, 8);
+impl_encodable_for_uint!(u16, 16);
+impl_encodable_for_uint!(u32, 32);
+impl_encodable_for_uint!(u64, 64);
+impl_encodable_for_uint!(usize, 64);
+
+impl<T: Encode> Encode for Vec<T> {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        if T::is_ssz_fixed_len() {
+            buf.reserve(T::ssz_fixed_len() * self.len());
+
+            for item in self {
+                item.ssz_append(buf);
+            }
+        } else {
+            let mut encoder = SszEncoder::list(buf, self.len() * BYTES_PER_LENGTH_OFFSET);
+
+            for item in self {
+                encoder.append(item);
+            }
+
+            encoder.finalize();
+        }
+    }
+}
+
+impl Encode for bool {
+    fn is_ssz_fixed_len() -> bool {
+        true
+    }
+
+    fn ssz_fixed_len() -> usize {
+        1
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        buf.extend_from_slice(&(*self as u8).to_le_bytes());
+    }
+}
+
+impl Encode for H256 {
+    fn is_ssz_fixed_len() -> bool {
+        true
+    }
+
+    fn ssz_fixed_len() -> usize {
+        32
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        buf.extend_from_slice(self.as_bytes());
+    }
+}
+
+macro_rules! impl_encodable_for_u8_array {
+    ($len: expr) => {
+        impl Encode for [u8; $len] {
+            fn is_ssz_fixed_len() -> bool {
+                true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                $len
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                buf.extend_from_slice(&self[..]);
+            }
+        }
+    };
+}
+
+impl_encodable_for_u8_array!(4);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn vec_of_u8() {
+        let vec: Vec<u8> = vec![];
+        assert_eq!(vec.as_ssz_bytes(), vec![]);
+
+        let vec: Vec<u8> = vec![1];
+        assert_eq!(vec.as_ssz_bytes(), vec![1]);
+
+        let vec: Vec<u8> = vec![0, 1, 2, 3];
+        assert_eq!(vec.as_ssz_bytes(), vec![0, 1, 2, 3]);
+    }
+
+    #[test]
+    fn vec_of_vec_of_u8() {
+        let vec: Vec<Vec<u8>> = vec![];
+        assert_eq!(vec.as_ssz_bytes(), vec![]);
+
+        let vec: Vec<Vec<u8>> = vec![vec![]];
+        assert_eq!(vec.as_ssz_bytes(), vec![4, 0, 0, 0]);
+
+        let vec: Vec<Vec<u8>> = vec![vec![], vec![]];
+        assert_eq!(vec.as_ssz_bytes(), vec![8, 0, 0, 0, 8, 0, 0, 0]);
+
+        let vec: Vec<Vec<u8>> = vec![vec![0, 1, 2], vec![11, 22, 33]];
+        assert_eq!(
+            vec.as_ssz_bytes(),
+            vec![8, 0, 0, 0, 11, 0, 0, 0, 0, 1, 2, 11, 22, 33]
+        );
+    }
+
+    #[test]
+    fn ssz_encode_u8() {
+        assert_eq!(0_u8.as_ssz_bytes(), vec![0]);
+        assert_eq!(1_u8.as_ssz_bytes(), vec![1]);
+        assert_eq!(100_u8.as_ssz_bytes(), vec![100]);
+        assert_eq!(255_u8.as_ssz_bytes(), vec![255]);
+    }
+
+    #[test]
+    fn ssz_encode_u16() {
+        assert_eq!(1_u16.as_ssz_bytes(), vec![1, 0]);
+        assert_eq!(100_u16.as_ssz_bytes(), vec![100, 0]);
+        assert_eq!((1_u16 << 8).as_ssz_bytes(), vec![0, 1]);
+        assert_eq!(65535_u16.as_ssz_bytes(), vec![255, 255]);
+    }
+
+    #[test]
+    fn ssz_encode_u32() {
+        assert_eq!(1_u32.as_ssz_bytes(), vec![1, 0, 0, 0]);
+        assert_eq!(100_u32.as_ssz_bytes(), vec![100, 0, 0, 0]);
+        assert_eq!((1_u32 << 16).as_ssz_bytes(), vec![0, 0, 1, 0]);
+        assert_eq!((1_u32 << 24).as_ssz_bytes(), vec![0, 0, 0, 1]);
+        assert_eq!((!0_u32).as_ssz_bytes(), vec![255, 255, 255, 255]);
+    }
+
+    #[test]
+    fn ssz_encode_u64() {
+        assert_eq!(1_u64.as_ssz_bytes(), vec![1, 0, 0, 0, 0, 0, 0, 0]);
+        assert_eq!(
+            (!0_u64).as_ssz_bytes(),
+            vec![255, 255, 255, 255, 255, 255, 255, 255]
+        );
+    }
+
+    #[test]
+    fn ssz_encode_usize() {
+        assert_eq!(1_usize.as_ssz_bytes(), vec![1, 0, 0, 0, 0, 0, 0, 0]);
+        assert_eq!(
+            (!0_usize).as_ssz_bytes(),
+            vec![255, 255, 255, 255, 255, 255, 255, 255]
+        );
+    }
+
+    #[test]
+    fn ssz_encode_bool() {
+        assert_eq!(true.as_ssz_bytes(), vec![1]);
+        assert_eq!(false.as_ssz_bytes(), vec![0]);
+    }
+
+    #[test]
+    fn ssz_encode_h256() {
+        assert_eq!(H256::from(&[0; 32]).as_ssz_bytes(), vec![0; 32]);
+        assert_eq!(H256::from(&[1; 32]).as_ssz_bytes(), vec![1; 32]);
+
+        let bytes = vec![
+            1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0,
+        ];
+
+        assert_eq!(H256::from_slice(&bytes).as_ssz_bytes(), bytes);
+    }
+
+    #[test]
+    fn ssz_encode_u8_array_4() {
+        assert_eq!([0, 0, 0, 0].as_ssz_bytes(), vec![0; 4]);
+        assert_eq!([1, 0, 0, 0].as_ssz_bytes(), vec![1, 0, 0, 0]);
+        assert_eq!([1, 2, 3, 4].as_ssz_bytes(), vec![1, 2, 3, 4]);
+    }
+}

eth2/utils/ssz/src/impl_decode.rs

@@ -1,306 +0,0 @@
-use super::decode::decode_ssz_list;
-use super::ethereum_types::{Address, H256};
-use super::{Decodable, DecodeError};
-
-macro_rules! impl_decodable_for_uint {
-    ($type: ident, $bit_size: expr) => {
-        impl Decodable for $type {
-            fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-                assert!((0 < $bit_size) & ($bit_size <= 64) & ($bit_size % 8 == 0));
-                let max_bytes = $bit_size / 8;
-                if bytes.len() >= (index + max_bytes) {
-                    let end_bytes = index + max_bytes;
-                    let mut result: $type = 0;
-                    for (i, byte) in bytes.iter().enumerate().take(end_bytes).skip(index) {
-                        let offset = (i - index) * 8;
-                        result |= ($type::from(*byte)) << offset;
-                    }
-                    Ok((result, end_bytes))
-                } else {
-                    Err(DecodeError::TooShort)
-                }
-            }
-        }
-    };
-}
-
-macro_rules! impl_decodable_for_u8_array {
-    ($len: expr) => {
-        impl Decodable for [u8; $len] {
-            fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-                if index + $len > bytes.len() {
-                    Err(DecodeError::TooShort)
-                } else {
-                    let mut array: [u8; $len] = [0; $len];
-                    array.copy_from_slice(&bytes[index..index + $len]);
-
-                    Ok((array, index + $len))
-                }
-            }
-        }
-    };
-}
-
-impl_decodable_for_uint!(u16, 16);
-impl_decodable_for_uint!(u32, 32);
-impl_decodable_for_uint!(u64, 64);
-impl_decodable_for_uint!(usize, 64);
-
-impl_decodable_for_u8_array!(4);
-
-impl Decodable for u8 {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        if index >= bytes.len() {
-            Err(DecodeError::TooShort)
-        } else {
-            Ok((bytes[index], index + 1))
-        }
-    }
-}
-
-impl Decodable for bool {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        if index >= bytes.len() {
-            Err(DecodeError::TooShort)
-        } else {
-            let result = match bytes[index] {
-                0b0000_0000 => false,
-                0b0000_0001 => true,
-                _ => return Err(DecodeError::Invalid),
-            };
-            Ok((result, index + 1))
-        }
-    }
-}
-
-impl Decodable for H256 {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() < 32 || bytes.len() - 32 < index {
-            Err(DecodeError::TooShort)
-        } else {
-            Ok((H256::from_slice(&bytes[index..(index + 32)]), index + 32))
-        }
-    }
-}
-
-impl Decodable for Address {
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        if bytes.len() < 20 || bytes.len() - 20 < index {
-            Err(DecodeError::TooShort)
-        } else {
-            Ok((Address::from_slice(&bytes[index..(index + 20)]), index + 20))
-        }
-    }
-}
-
-impl<T> Decodable for Vec<T>
-where
-    T: Decodable,
-{
-    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
-        decode_ssz_list(bytes, index)
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::super::{decode, DecodeError};
-    use super::*;
-
-    #[test]
-    fn test_ssz_decode_h256() {
-        /*
-         * Input is exact length
-         */
-        let input = vec![42_u8; 32];
-        let (decoded, i) = H256::ssz_decode(&input, 0).unwrap();
-        assert_eq!(decoded.as_bytes(), &input[..]);
-        assert_eq!(i, 32);
-
-        /*
-         * Input is too long
-         */
-        let mut input = vec![42_u8; 32];
-        input.push(12);
-        let (decoded, i) = H256::ssz_decode(&input, 0).unwrap();
-        assert_eq!(decoded.as_bytes(), &input[0..32]);
-        assert_eq!(i, 32);
-
-        /*
-         * Input is too short
-         */
-        let input = vec![42_u8; 31];
-        let res = H256::ssz_decode(&input, 0);
-        assert_eq!(res, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    fn test_ssz_decode_u16() {
-        let ssz = vec![0, 0];
-
-        let (result, index): (u16, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(result, 0);
-        assert_eq!(index, 2);
-
-        let ssz = vec![16, 0];
-        let (result, index): (u16, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(result, 16);
-        assert_eq!(index, 2);
-
-        let ssz = vec![0, 1];
-        let (result, index): (u16, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(result, 256);
-        assert_eq!(index, 2);
-
-        let ssz = vec![255, 255];
-        let (result, index): (u16, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 2);
-        assert_eq!(result, 65535);
-
-        let ssz = vec![1];
-        let result: Result<(u16, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    fn test_ssz_decode_u32() {
-        let ssz = vec![0, 0, 0, 0];
-        let (result, index): (u32, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(result, 0);
-        assert_eq!(index, 4);
-
-        let ssz = vec![0, 1, 0, 0];
-        let (result, index): (u32, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 4);
-        assert_eq!(result, 256);
-
-        let ssz = vec![255, 255, 255, 0, 1, 0, 0];
-        let (result, index): (u32, usize) = <_>::ssz_decode(&ssz, 3).unwrap();
-        assert_eq!(index, 7);
-        assert_eq!(result, 256);
-
-        let ssz = vec![0, 1, 200, 0];
-        let (result, index): (u32, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 4);
-        assert_eq!(result, 13107456);
-
-        let ssz = vec![255, 255, 255, 255];
-        let (result, index): (u32, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 4);
-        assert_eq!(result, 4294967295);
-
-        let ssz = vec![1, 0, 0];
-        let result: Result<(u32, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    fn test_ssz_decode_u64() {
-        let ssz = vec![0, 0, 0, 0, 0, 0, 0, 0];
-        let (result, index): (u64, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 8);
-        assert_eq!(result, 0);
-
-        let ssz = vec![255, 255, 255, 255, 255, 255, 255, 255];
-        let (result, index): (u64, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 8);
-        assert_eq!(result, 18446744073709551615);
-
-        let ssz = vec![0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 255];
-        let (result, index): (u64, usize) = <_>::ssz_decode(&ssz, 3).unwrap();
-        assert_eq!(index, 11);
-        assert_eq!(result, 18374686479671623680);
-
-        let ssz = vec![0, 0, 0, 0, 0, 0, 0];
-        let result: Result<(u64, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    fn test_ssz_decode_usize() {
-        let ssz = vec![0, 0, 0, 0, 0, 0, 0, 0];
-        let (result, index): (usize, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 8);
-        assert_eq!(result, 0);
-
-        let ssz = vec![0, 0, 8, 255, 255, 255, 255, 255, 255, 255, 255];
-        let (result, index): (usize, usize) = <_>::ssz_decode(&ssz, 3).unwrap();
-        assert_eq!(index, 11);
-        assert_eq!(result, 18446744073709551615);
-
-        let ssz = vec![255, 255, 255, 255, 255, 255, 255, 255, 255];
-        let (result, index): (usize, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 8);
-        assert_eq!(result, 18446744073709551615);
-
-        let ssz = vec![0, 0, 0, 0, 0, 0, 1];
-        let result: Result<(usize, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    fn test_decode_ssz_bounds() {
-        let err: Result<(u16, usize), DecodeError> = <_>::ssz_decode(&vec![1], 2);
-        assert_eq!(err, Err(DecodeError::TooShort));
-
-        let err: Result<(u16, usize), DecodeError> = <_>::ssz_decode(&vec![0, 0, 0, 0], 3);
-        assert_eq!(err, Err(DecodeError::TooShort));
-
-        let result: u16 = <_>::ssz_decode(&vec![0, 0, 0, 1, 0], 3).unwrap().0;
-        assert_eq!(result, 1);
-    }
-
-    #[test]
-    fn test_decode_ssz_bool() {
-        let ssz = vec![0b0000_0000, 0b0000_0001];
-        let (result, index): (bool, usize) = <_>::ssz_decode(&ssz, 0).unwrap();
-        assert_eq!(index, 1);
-        assert_eq!(result, false);
-
-        let (result, index): (bool, usize) = <_>::ssz_decode(&ssz, 1).unwrap();
-        assert_eq!(index, 2);
-        assert_eq!(result, true);
-
-        let ssz = vec![0b0100_0000];
-        let result: Result<(bool, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::Invalid));
-
-        let ssz = vec![];
-        let result: Result<(bool, usize), DecodeError> = <_>::ssz_decode(&ssz, 0);
-        assert_eq!(result, Err(DecodeError::TooShort));
-    }
-
-    #[test]
-    #[should_panic]
-    fn test_decode_ssz_list_underflow() {
-        // SSZ encoded (u16::[1, 1, 1], u16::2)
-        let mut encoded = vec![6, 0, 0, 0, 1, 0, 1, 0, 1, 0, 2, 0];
-        let (decoded_array, i): (Vec<u16>, usize) = <_>::ssz_decode(&encoded, 0).unwrap();
-        let (decoded_u16, i): (u16, usize) = <_>::ssz_decode(&encoded, i).unwrap();
-        assert_eq!(decoded_array, vec![1, 1, 1]);
-        assert_eq!(decoded_u16, 2);
-        assert_eq!(i, 12);
-
-        // Underflow
-        encoded[0] = 4; // change length to 4 from 6
-        let (decoded_array, i): (Vec<u16>, usize) = <_>::ssz_decode(&encoded, 0).unwrap();
-        let (decoded_u16, _): (u16, usize) = <_>::ssz_decode(&encoded, i).unwrap();
-        assert_eq!(decoded_array, vec![1, 1]);
-        assert_eq!(decoded_u16, 2);
-    }
-
-    #[test]
-    fn test_decode_too_long() {
-        let encoded = vec![6, 0, 0, 0, 1, 0, 1, 0, 1, 0, 2];
-        let decoded_array: Result<Vec<u16>, DecodeError> = decode(&encoded);
-        assert_eq!(decoded_array, Err(DecodeError::TooLong));
-    }
-
-    #[test]
-    fn test_decode_u8_array() {
-        let ssz = vec![0, 1, 2, 3];
-        let result: [u8; 4] = decode(&ssz).unwrap();
-        assert_eq!(result.len(), 4);
-        assert_eq!(result, [0, 1, 2, 3]);
-    }
-}

eth2/utils/ssz/src/impl_encode.rs

@@ -1,275 +0,0 @@
-extern crate bytes;
-
-use self::bytes::{BufMut, BytesMut};
-use super::ethereum_types::{Address, H256};
-use super::{Encodable, SszStream};
-
-/*
- * Note: there is a "to_bytes" function for integers
- * in Rust nightly. When it is in stable, we should
- * use it instead.
- */
-macro_rules! impl_encodable_for_uint {
-    ($type: ident, $bit_size: expr) => {
-        impl Encodable for $type {
-            #[allow(clippy::cast_lossless)]
-            fn ssz_append(&self, s: &mut SszStream) {
-                // Ensure bit size is valid
-                assert!(
-                    (0 < $bit_size)
-                        && ($bit_size % 8 == 0)
-                        && (2_u128.pow($bit_size) > *self as u128)
-                );
-
-                // Serialize to bytes
-                let mut buf = BytesMut::with_capacity($bit_size / 8);
-
-                // Match bit size with encoding
-                match $bit_size {
-                    8 => buf.put_u8(*self as u8),
-                    16 => buf.put_u16_le(*self as u16),
-                    32 => buf.put_u32_le(*self as u32),
-                    64 => buf.put_u64_le(*self as u64),
-                    _ => {}
-                }
-
-                // Append bytes to the SszStream
-                s.append_encoded_raw(&buf.to_vec());
-            }
-        }
-    };
-}
-
-macro_rules! impl_encodable_for_u8_array {
-    ($len: expr) => {
-        impl Encodable for [u8; $len] {
-            fn ssz_append(&self, s: &mut SszStream) {
-                let bytes: Vec<u8> = self.iter().cloned().collect();
-                s.append_encoded_raw(&bytes);
-            }
-        }
-    };
-}
-
-impl_encodable_for_uint!(u8, 8);
-impl_encodable_for_uint!(u16, 16);
-impl_encodable_for_uint!(u32, 32);
-impl_encodable_for_uint!(u64, 64);
-impl_encodable_for_uint!(usize, 64);
-
-impl_encodable_for_u8_array!(4);
-
-impl Encodable for bool {
-    fn ssz_append(&self, s: &mut SszStream) {
-        let byte = if *self { 0b0000_0001 } else { 0b0000_0000 };
-        s.append_encoded_raw(&[byte]);
-    }
-}
-
-impl Encodable for H256 {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(self.as_bytes());
-    }
-}
-
-impl Encodable for Address {
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_encoded_raw(self.as_bytes());
-    }
-}
-
-impl<T> Encodable for Vec<T>
-where
-    T: Encodable,
-{
-    fn ssz_append(&self, s: &mut SszStream) {
-        s.append_vec(&self);
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::ssz_encode;
-
-    #[test]
-    fn test_ssz_encode_h256() {
-        let h = H256::zero();
-        let mut ssz = SszStream::new();
-        ssz.append(&h);
-        assert_eq!(ssz.drain(), vec![0; 32]);
-    }
-
-    #[test]
-    fn test_ssz_encode_address() {
-        let h = Address::zero();
-        let mut ssz = SszStream::new();
-        ssz.append(&h);
-        assert_eq!(ssz.drain(), vec![0; 20]);
-    }
-
-    #[test]
-    fn test_ssz_encode_u8() {
-        let x: u8 = 0;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0]);
-
-        let x: u8 = 1;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![1]);
-
-        let x: u8 = 100;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![100]);
-
-        let x: u8 = 255;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![255]);
-    }
-
-    #[test]
-    fn test_ssz_encode_u16() {
-        let x: u16 = 1;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![1, 0]);
-
-        let x: u16 = 100;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![100, 0]);
-
-        let x: u16 = 1 << 8;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0, 1]);
-
-        let x: u16 = 65535;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![255, 255]);
-    }
-
-    #[test]
-    fn test_ssz_encode_u32() {
-        let x: u32 = 1;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![1, 0, 0, 0]);
-
-        let x: u32 = 100;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![100, 0, 0, 0]);
-
-        let x: u32 = 1 << 16;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0, 0, 1, 0]);
-
-        let x: u32 = 1 << 24;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0, 0, 0, 1]);
-
-        let x: u32 = !0;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![255, 255, 255, 255]);
-    }
-
-    #[test]
-    fn test_ssz_encode_u64() {
-        let x: u64 = 1;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![1, 0, 0, 0, 0, 0, 0, 0]);
-
-        let x: u64 = 100;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![100, 0, 0, 0, 0, 0, 0, 0]);
-
-        let x: u64 = 1 << 32;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0, 0, 0, 0, 1, 0, 0, 0]);
-
-        let x: u64 = !0;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![255, 255, 255, 255, 255, 255, 255, 255]);
-    }
-
-    #[test]
-    fn test_ssz_encode_usize() {
-        let x: usize = 1;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![1, 0, 0, 0, 0, 0, 0, 0]);
-
-        let x: usize = 100;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![100, 0, 0, 0, 0, 0, 0, 0]);
-
-        let x: usize = 1 << 32;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0, 0, 0, 0, 1, 0, 0, 0]);
-
-        let x: usize = !0;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![255, 255, 255, 255, 255, 255, 255, 255]);
-    }
-
-    #[test]
-    fn test_ssz_mixed() {
-        let mut stream = SszStream::new();
-
-        let h = Address::zero();
-        let a: u8 = 100;
-        let b: u16 = 65535;
-        let c: u32 = 1 << 24;
-
-        stream.append(&h);
-        stream.append(&a);
-        stream.append(&b);
-        stream.append(&c);
-
-        let ssz = stream.drain();
-        assert_eq!(ssz[0..20], *vec![0; 20]);
-        assert_eq!(ssz[20], 100);
-        assert_eq!(ssz[21..23], *vec![255, 255]);
-        assert_eq!(ssz[23..27], *vec![0, 0, 0, 1]);
-    }
-
-    #[test]
-    fn test_ssz_encode_bool() {
-        let x: bool = false;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0b0000_0000]);
-
-        let x: bool = true;
-        let mut ssz = SszStream::new();
-        ssz.append(&x);
-        assert_eq!(ssz.drain(), vec![0b0000_0001]);
-    }
-
-    #[test]
-    fn test_ssz_encode_u8_array() {
-        let x: [u8; 4] = [0, 1, 7, 8];
-        let ssz = ssz_encode(&x);
-        assert_eq!(ssz, vec![0, 1, 7, 8]);
-
-        let x: [u8; 4] = [255, 255, 255, 255];
-        let ssz = ssz_encode(&x);
-        assert_eq!(ssz, vec![255, 255, 255, 255]);
-    }
-}

eth2/utils/ssz/src/lib.rs

@@ -1,225 +1,59 @@
-/*
- * This is a WIP of implementing an alternative
- * serialization strategy. It attempts to follow Vitalik's
- * "simpleserialize" format here:
- * https://github.com/ethereum/beacon_chain/blob/master/beacon_chain/utils/simpleserialize.py
- *
- * This implementation is not final and would almost certainly
- * have issues.
- */
-extern crate bytes;
-extern crate ethereum_types;
+//! Provides encoding (serialization) and decoding (deserialization) in the SimpleSerialize (SSZ)
+//! format designed for use in Ethereum 2.0.
+//!
+//! Conforms to
+//! [v0.6.1](https://github.com/ethereum/eth2.0-specs/blob/v0.6.1/specs/simple-serialize.md) of the
+//! Ethereum 2.0 specification.
+//!
+//! ## Example
+//!
+//! ```rust
+//! use ssz_derive::{Encode, Decode};
+//! use ssz::{Decode, Encode};
+//!
+//! #[derive(PartialEq, Debug, Encode, Decode)]
+//! struct Foo {
+//!     a: u64,
+//!     b: Vec<u16>,
+//! }
+//!
+//! fn main() {
+//!     let foo = Foo {
+//!         a: 42,
+//!         b: vec![1, 3, 3, 7]
+//!     };
+//!
+//!     let ssz_bytes: Vec<u8> = foo.as_ssz_bytes();
+//!
+//!     let decoded_foo = Foo::from_ssz_bytes(&ssz_bytes).unwrap();
+//!
+//!     assert_eq!(foo, decoded_foo);
+//! }
+//!
+//! ```
+//!
+//! See `examples/` for manual implementations of the `Encode` and `Decode` traits.
 
-pub mod decode;
-pub mod encode;
+mod decode;
+mod encode;
+mod macros;
 
-mod impl_decode;
-mod impl_encode;
+pub use decode::{
+    impls::decode_list_of_variable_length_items, Decode, DecodeError, SszDecoder, SszDecoderBuilder,
+};
+pub use encode::{Encode, SszEncoder};
 
-pub use crate::decode::{decode, decode_ssz_list, Decodable, DecodeError};
-pub use crate::encode::{Encodable, SszStream};
-
-pub use hashing::hash;
-
-pub const LENGTH_BYTES: usize = 4;
-pub const MAX_LIST_SIZE: usize = 1 << (4 * 8);
+/// The number of bytes used to represent an offset.
+pub const BYTES_PER_LENGTH_OFFSET: usize = 4;
+/// The maximum value that can be represented using `BYTES_PER_LENGTH_OFFSET`.
+pub const MAX_LENGTH_VALUE: usize = (1 << (BYTES_PER_LENGTH_OFFSET * 8)) - 1;
 
 /// Convenience function to SSZ encode an object supporting ssz::Encode.
+///
+/// Equivalent to `val.as_ssz_bytes()`.
 pub fn ssz_encode<T>(val: &T) -> Vec<u8>
 where
-    T: Encodable,
+    T: Encode,
 {
-    let mut ssz_stream = SszStream::new();
-    ssz_stream.append(val);
-    ssz_stream.drain()
-}
-
-#[cfg(test)]
-mod tests {
-    extern crate hex;
-    extern crate yaml_rust;
-
-    use self::yaml_rust::yaml;
-    use super::*;
-    use std::{fs::File, io::prelude::*, path::PathBuf};
-
-    #[test]
-    pub fn test_vector_uint_bounds() {
-        let mut file = {
-            let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-            file_path_buf.push("src/test_vectors/uint_bounds.yaml");
-
-            File::open(file_path_buf).unwrap()
-        };
-        let mut yaml_str = String::new();
-        file.read_to_string(&mut yaml_str).unwrap();
-        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
-        let doc = &docs[0];
-
-        // Load test cases
-        let test_cases = doc["test_cases"].clone();
-
-        for test_case in test_cases {
-            // Only the valid cases are checked as parse::<uX>() will fail for all invalid cases
-            if test_case["valid"].as_bool().unwrap() {
-                // Convert test vector 'ssz' encoded yaml to Vec<u8>
-                let ssz = test_case["ssz"].as_str().unwrap().trim_start_matches("0x");
-                let test_vector_bytes = hex::decode(ssz).unwrap();
-
-                // Convert test vector 'value' to ssz encoded bytes
-                let mut bytes: Vec<u8>;
-                match test_case["type"].as_str().unwrap() {
-                    "uint8" => {
-                        let value: u8 = test_case["value"].as_str().unwrap().parse::<u8>().unwrap();
-                        bytes = ssz_encode::<u8>(&value); // check encoding
-
-                        // Check decoding
-                        let decoded = decode::<u8>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint16" => {
-                        let value: u16 =
-                            test_case["value"].as_str().unwrap().parse::<u16>().unwrap();
-                        bytes = ssz_encode::<u16>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u16>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint32" => {
-                        let value: u32 =
-                            test_case["value"].as_str().unwrap().parse::<u32>().unwrap();
-                        bytes = ssz_encode::<u32>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u32>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint64" => {
-                        let value: u64 =
-                            test_case["value"].as_str().unwrap().parse::<u64>().unwrap();
-                        bytes = ssz_encode::<u64>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u64>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    _ => continue,
-                };
-                assert_eq!(test_vector_bytes, bytes);
-            }
-        }
-    }
-
-    #[test]
-    pub fn test_vector_uint_random() {
-        let mut file = {
-            let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-            file_path_buf.push("src/test_vectors/uint_random.yaml");
-
-            File::open(file_path_buf).unwrap()
-        };
-        let mut yaml_str = String::new();
-        file.read_to_string(&mut yaml_str).unwrap();
-        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
-        let doc = &docs[0];
-
-        // Load test cases
-        let test_cases = doc["test_cases"].clone();
-
-        for test_case in test_cases {
-            // Only the valid cases are checked as parse::<uX>() will fail for all invalid cases
-            if test_case["valid"].as_bool().unwrap() {
-                // Convert test vector 'ssz' encoded yaml to Vec<u8>
-                let ssz = test_case["ssz"].as_str().unwrap().trim_start_matches("0x");
-                let test_vector_bytes = hex::decode(ssz).unwrap();
-
-                // Convert test vector 'value' to ssz encoded bytes
-                let mut bytes: Vec<u8>;
-                match test_case["type"].as_str().unwrap() {
-                    "uint8" => {
-                        let value: u8 = test_case["value"].as_str().unwrap().parse::<u8>().unwrap();
-                        bytes = ssz_encode::<u8>(&value); // check encoding
-
-                        // Check decoding
-                        let decoded = decode::<u8>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint16" => {
-                        let value: u16 =
-                            test_case["value"].as_str().unwrap().parse::<u16>().unwrap();
-                        bytes = ssz_encode::<u16>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u16>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint32" => {
-                        let value: u32 =
-                            test_case["value"].as_str().unwrap().parse::<u32>().unwrap();
-                        bytes = ssz_encode::<u32>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u32>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    "uint64" => {
-                        let value: u64 =
-                            test_case["value"].as_str().unwrap().parse::<u64>().unwrap();
-                        bytes = ssz_encode::<u64>(&value);
-
-                        // Check decoding
-                        let decoded = decode::<u64>(&test_vector_bytes).unwrap();
-                        assert_eq!(decoded, value);
-                    }
-                    _ => continue,
-                };
-                assert_eq!(test_vector_bytes, bytes);
-            }
-        }
-    }
-
-    #[test]
-    pub fn test_vector_uint_wrong_length() {
-        let mut file = {
-            let mut file_path_buf = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
-            file_path_buf.push("src/test_vectors/uint_wrong_length.yaml");
-
-            File::open(file_path_buf).unwrap()
-        };
-        let mut yaml_str = String::new();
-        file.read_to_string(&mut yaml_str).unwrap();
-        let docs = yaml::YamlLoader::load_from_str(&yaml_str).unwrap();
-        let doc = &docs[0];
-
-        // Load test cases
-        let test_cases = doc["test_cases"].clone();
-
-        for test_case in test_cases {
-            // Convert test vector 'ssz' encoded yaml to Vec<u8>
-            let ssz = test_case["ssz"].as_str().unwrap().trim_start_matches("0x");
-            let test_vector_bytes = hex::decode(ssz).unwrap();
-
-            // Attempt to decode invalid ssz bytes
-            match test_case["type"].as_str().unwrap() {
-                "uint8" => {
-                    let decoded = decode::<u8>(&test_vector_bytes);
-                    assert!(decoded.is_err());
-                }
-                "uint16" => {
-                    let decoded = decode::<u16>(&test_vector_bytes);
-                    assert!(decoded.is_err());
-                }
-                "uint32" => {
-                    let decoded = decode::<u32>(&test_vector_bytes);
-                    assert!(decoded.is_err());
-                }
-                "uint64" => {
-                    let decoded = decode::<u64>(&test_vector_bytes);
-                    assert!(decoded.is_err());
-                }
-                _ => continue,
-            };
-        }
-    }
+    val.as_ssz_bytes()
 }

eth2/utils/ssz/src/macros.rs

@@ -0,0 +1,96 @@
+/// Implements `Encode` for `$impl_type` using an implementation of `From<$impl_type> for
+/// $from_type`.
+///
+/// In effect, this allows for easy implementation of `Encode` for some type that implements a
+/// `From` conversion into another type that already has `Encode` implemented.
+#[macro_export]
+macro_rules! impl_encode_via_from {
+    ($impl_type: ty, $from_type: ty) => {
+        impl ssz::Encode for $impl_type {
+            fn is_ssz_fixed_len() -> bool {
+                <$from_type as ssz::Encode>::is_ssz_fixed_len()
+            }
+
+            fn ssz_fixed_len() -> usize {
+                <$from_type as ssz::Encode>::ssz_fixed_len()
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                let conv: $from_type = self.clone().into();
+
+                conv.ssz_append(buf)
+            }
+        }
+    };
+}
+
+/// Implements `Decode` for `$impl_type` using an implementation of `From<$impl_type> for
+/// $from_type`.
+///
+/// In effect, this allows for easy implementation of `Decode` for some type that implements a
+/// `From` conversion into another type that already has `Decode` implemented.
+#[macro_export]
+macro_rules! impl_decode_via_from {
+    ($impl_type: ty, $from_type: tt) => {
+        impl ssz::Decode for $impl_type {
+            fn is_ssz_fixed_len() -> bool {
+                <$from_type as ssz::Decode>::is_ssz_fixed_len()
+            }
+
+            fn ssz_fixed_len() -> usize {
+                <$from_type as ssz::Decode>::ssz_fixed_len()
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
+                $from_type::from_ssz_bytes(bytes).and_then(|dec| Ok(dec.into()))
+            }
+        }
+    };
+}
+
+#[cfg(test)]
+mod tests {
+    use crate as ssz;
+    use ssz::{Decode, Encode};
+
+    #[derive(PartialEq, Debug, Clone, Copy)]
+    struct Wrapper(u64);
+
+    impl From<u64> for Wrapper {
+        fn from(x: u64) -> Wrapper {
+            Wrapper(x)
+        }
+    }
+
+    impl From<Wrapper> for u64 {
+        fn from(x: Wrapper) -> u64 {
+            x.0
+        }
+    }
+
+    impl_encode_via_from!(Wrapper, u64);
+    impl_decode_via_from!(Wrapper, u64);
+
+    #[test]
+    fn impl_encode_via_from() {
+        let check_encode = |a: u64, b: Wrapper| assert_eq!(a.as_ssz_bytes(), b.as_ssz_bytes());
+
+        check_encode(0, Wrapper(0));
+        check_encode(1, Wrapper(1));
+        check_encode(42, Wrapper(42));
+    }
+
+    #[test]
+    fn impl_decode_via_from() {
+        let check_decode = |bytes: Vec<u8>| {
+            let a = u64::from_ssz_bytes(&bytes).unwrap();
+            let b = Wrapper::from_ssz_bytes(&bytes).unwrap();
+
+            assert_eq!(a, b.into())
+        };
+
+        check_decode(vec![0, 0, 0, 0, 0, 0, 0, 0]);
+        check_decode(vec![1, 0, 0, 0, 0, 0, 0, 0]);
+        check_decode(vec![1, 0, 0, 0, 2, 0, 0, 0]);
+    }
+}

eth2/utils/ssz/tests/tests.rs

@@ -0,0 +1,288 @@
+use ethereum_types::H256;
+use ssz::{Decode, DecodeError, Encode};
+use ssz_derive::{Decode, Encode};
+
+mod round_trip {
+    use super::*;
+
+    fn round_trip<T: Encode + Decode + std::fmt::Debug + PartialEq>(items: Vec<T>) {
+        for item in items {
+            let encoded = &item.as_ssz_bytes();
+            assert_eq!(T::from_ssz_bytes(&encoded), Ok(item));
+        }
+    }
+
+    #[test]
+    fn bool() {
+        let items: Vec<bool> = vec![true, false];
+
+        round_trip(items);
+    }
+
+    #[test]
+    fn u8_array_4() {
+        let items: Vec<[u8; 4]> = vec![[0, 0, 0, 0], [1, 0, 0, 0], [1, 2, 3, 4], [1, 2, 0, 4]];
+
+        round_trip(items);
+    }
+
+    #[test]
+    fn h256() {
+        let items: Vec<H256> = vec![H256::zero(), H256::from([1; 32]), H256::random()];
+
+        round_trip(items);
+    }
+
+    #[test]
+    fn vec_of_h256() {
+        let items: Vec<Vec<H256>> = vec![
+            vec![],
+            vec![H256::zero(), H256::from([1; 32]), H256::random()],
+        ];
+
+        round_trip(items);
+    }
+
+    #[test]
+    fn vec_u16() {
+        let items: Vec<Vec<u16>> = vec![
+            vec![],
+            vec![255],
+            vec![0, 1, 2],
+            vec![100; 64],
+            vec![255, 0, 255],
+        ];
+
+        round_trip(items);
+    }
+
+    #[test]
+    fn vec_of_vec_u16() {
+        let items: Vec<Vec<Vec<u16>>> = vec![
+            vec![],
+            vec![vec![]],
+            vec![vec![1, 2, 3]],
+            vec![vec![], vec![]],
+            vec![vec![], vec![1, 2, 3]],
+            vec![vec![1, 2, 3], vec![1, 2, 3]],
+            vec![vec![1, 2, 3], vec![], vec![1, 2, 3]],
+            vec![vec![], vec![], vec![1, 2, 3]],
+            vec![vec![], vec![1], vec![1, 2, 3]],
+            vec![vec![], vec![1], vec![1, 2, 3]],
+        ];
+
+        round_trip(items);
+    }
+
+    #[derive(Debug, PartialEq, Encode, Decode)]
+    struct FixedLen {
+        a: u16,
+        b: u64,
+        c: u32,
+    }
+
+    #[test]
+    fn fixed_len_struct_encoding() {
+        let items: Vec<FixedLen> = vec![
+            FixedLen { a: 0, b: 0, c: 0 },
+            FixedLen { a: 1, b: 1, c: 1 },
+            FixedLen { a: 1, b: 0, c: 1 },
+        ];
+
+        let expected_encodings = vec![
+            //  | u16--| u64----------------------------| u32----------|
+            vec![00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00],
+            vec![01, 00, 01, 00, 00, 00, 00, 00, 00, 00, 01, 00, 00, 00],
+            vec![01, 00, 00, 00, 00, 00, 00, 00, 00, 00, 01, 00, 00, 00],
+        ];
+
+        for i in 0..items.len() {
+            assert_eq!(
+                items[i].as_ssz_bytes(),
+                expected_encodings[i],
+                "Failed on {}",
+                i
+            );
+        }
+    }
+
+    #[test]
+    fn fixed_len_excess_bytes() {
+        let fixed = FixedLen { a: 1, b: 2, c: 3 };
+
+        let mut bytes = fixed.as_ssz_bytes();
+        bytes.append(&mut vec![0]);
+
+        assert_eq!(
+            FixedLen::from_ssz_bytes(&bytes),
+            Err(DecodeError::InvalidByteLength {
+                len: 15,
+                expected: 14,
+            })
+        );
+    }
+
+    #[test]
+    fn vec_of_fixed_len_struct() {
+        let items: Vec<FixedLen> = vec![
+            FixedLen { a: 0, b: 0, c: 0 },
+            FixedLen { a: 1, b: 1, c: 1 },
+            FixedLen { a: 1, b: 0, c: 1 },
+        ];
+
+        round_trip(items);
+    }
+
+    #[derive(Debug, PartialEq, Encode, Decode)]
+    struct VariableLen {
+        a: u16,
+        b: Vec<u16>,
+        c: u32,
+    }
+
+    #[test]
+    fn offset_into_fixed_bytes() {
+        let bytes = vec![
+            //  1   2   3   4   5   6   7   8   9   10  11  12  13  14  15
+            //      | offset        | u32           | variable
+            01, 00, 09, 00, 00, 00, 01, 00, 00, 00, 00, 00, 01, 00, 02, 00,
+        ];
+
+        assert_eq!(
+            VariableLen::from_ssz_bytes(&bytes),
+            Err(DecodeError::OutOfBoundsByte { i: 9 })
+        );
+    }
+
+    #[test]
+    fn variable_len_excess_bytes() {
+        let variable = VariableLen {
+            a: 1,
+            b: vec![2],
+            c: 3,
+        };
+
+        let mut bytes = variable.as_ssz_bytes();
+        bytes.append(&mut vec![0]);
+
+        // The error message triggered is not so helpful, it's caught by a side-effect. Just
+        // checking there is _some_ error is fine.
+        assert!(VariableLen::from_ssz_bytes(&bytes).is_err());
+    }
+
+    #[test]
+    fn first_offset_skips_byte() {
+        let bytes = vec![
+            //  1   2   3   4   5   6   7   8   9   10  11  12  13  14  15
+            //      | offset        | u32           | variable
+            01, 00, 11, 00, 00, 00, 01, 00, 00, 00, 00, 00, 01, 00, 02, 00,
+        ];
+
+        assert_eq!(
+            VariableLen::from_ssz_bytes(&bytes),
+            Err(DecodeError::OutOfBoundsByte { i: 11 })
+        );
+    }
+
+    #[test]
+    fn variable_len_struct_encoding() {
+        let items: Vec<VariableLen> = vec![
+            VariableLen {
+                a: 0,
+                b: vec![],
+                c: 0,
+            },
+            VariableLen {
+                a: 1,
+                b: vec![0],
+                c: 1,
+            },
+            VariableLen {
+                a: 1,
+                b: vec![0, 1, 2],
+                c: 1,
+            },
+        ];
+
+        let expected_encodings = vec![
+            //   00..................................09
+            //  | u16--| vec offset-----| u32------------| vec payload --------|
+            vec![00, 00, 10, 00, 00, 00, 00, 00, 00, 00],
+            vec![01, 00, 10, 00, 00, 00, 01, 00, 00, 00, 00, 00],
+            vec![
+                01, 00, 10, 00, 00, 00, 01, 00, 00, 00, 00, 00, 01, 00, 02, 00,
+            ],
+        ];
+
+        for i in 0..items.len() {
+            assert_eq!(
+                items[i].as_ssz_bytes(),
+                expected_encodings[i],
+                "Failed on {}",
+                i
+            );
+        }
+    }
+
+    #[test]
+    fn vec_of_variable_len_struct() {
+        let items: Vec<VariableLen> = vec![
+            VariableLen {
+                a: 0,
+                b: vec![],
+                c: 0,
+            },
+            VariableLen {
+                a: 255,
+                b: vec![0, 1, 2, 3],
+                c: 99,
+            },
+            VariableLen {
+                a: 255,
+                b: vec![0],
+                c: 99,
+            },
+            VariableLen {
+                a: 50,
+                b: vec![0],
+                c: 0,
+            },
+        ];
+
+        round_trip(items);
+    }
+
+    #[derive(Debug, PartialEq, Encode, Decode)]
+    struct ThreeVariableLen {
+        a: u16,
+        b: Vec<u16>,
+        c: Vec<u16>,
+        d: Vec<u16>,
+    }
+
+    #[test]
+    fn three_variable_len() {
+        let vec: Vec<ThreeVariableLen> = vec![ThreeVariableLen {
+            a: 42,
+            b: vec![0],
+            c: vec![1],
+            d: vec![2],
+        }];
+
+        round_trip(vec);
+    }
+
+    #[test]
+    fn offsets_decreasing() {
+        let bytes = vec![
+            //  1   2   3   4   5   6   7   8   9   10  11  12  13  14  15
+            //      | offset        | ofset         | offset        | variable
+            01, 00, 14, 00, 00, 00, 15, 00, 00, 00, 14, 00, 00, 00, 00, 00,
+        ];
+
+        assert_eq!(
+            ThreeVariableLen::from_ssz_bytes(&bytes),
+            Err(DecodeError::OutOfBoundsByte { i: 14 })
+        );
+    }
+}

eth2/utils/ssz_derive/src/lib.rs

@@ -1,39 +1,4 @@
-//! Provides the following procedural derive macros:
-//!
-//! - `#[derive(Encode)]`
-//! - `#[derive(Decode)]`
-//! - `#[derive(TreeHash)]`
-//!
-//! These macros provide SSZ encoding/decoding for a `struct`. Fields are encoded/decoded in the
-//! order they are defined.
-//!
-//! Presently, only `structs` with named fields are supported. `enum`s and tuple-structs are
-//! unsupported.
-//!
-//! Example:
-//! ```
-//! use ssz::{ssz_encode, Decodable};
-//! use ssz_derive::{Encode, Decode};
-//!
-//! #[derive(Encode, Decode)]
-//! struct Foo {
-//!     pub bar: bool,
-//!     pub baz: u64,
-//! }
-//!
-//! fn main() {
-//!     let foo = Foo {
-//!         bar: true,
-//!         baz: 42,
-//!     };
-//!
-//!     let bytes = ssz_encode(&foo);
-//!
-//!     let (decoded_foo, _i) = Foo::ssz_decode(&bytes, 0).unwrap();
-//!
-//!     assert_eq!(foo.baz, decoded_foo.baz);
-//! }
-//! ```
+#![recursion_limit = "128"]
 
 extern crate proc_macro;
 
@@ -41,21 +6,6 @@ use proc_macro::TokenStream;
 use quote::quote;
 use syn::{parse_macro_input, DeriveInput};
 
-/// Returns a Vec of `syn::Ident` for each named field in the struct.
-///
-/// # Panics
-/// Any unnamed struct field (like in a tuple struct) will raise a panic at compile time.
-fn get_named_field_idents<'a>(struct_data: &'a syn::DataStruct) -> Vec<&'a syn::Ident> {
-    struct_data
-        .fields
-        .iter()
-        .map(|f| match &f.ident {
-            Some(ref ident) => ident,
-            _ => panic!("ssz_derive only supports named struct fields."),
-        })
-        .collect()
-}
-
 /// Returns a Vec of `syn::Ident` for each named field in the struct, whilst filtering out fields
 /// that should not be serialized.
 ///
@@ -80,6 +30,22 @@ fn get_serializable_named_field_idents<'a>(
         .collect()
 }
 
+/// Returns a Vec of `syn::Type` for each named field in the struct, whilst filtering out fields
+/// that should not be serialized.
+fn get_serializable_field_types<'a>(struct_data: &'a syn::DataStruct) -> Vec<&'a syn::Type> {
+    struct_data
+        .fields
+        .iter()
+        .filter_map(|f| {
+            if should_skip_serializing(&f) {
+                None
+            } else {
+                Some(&f.ty)
+            }
+        })
+        .collect()
+}
+
 /// Returns true if some field has an attribute declaring it should not be serialized.
 ///
 /// The field attribute is: `#[ssz(skip_serializing)]`
@@ -92,7 +58,7 @@ fn should_skip_serializing(field: &syn::Field) -> bool {
     false
 }
 
-/// Implements `ssz::Encodable` for some `struct`.
+/// Implements `ssz::Encode` for some `struct`.
 ///
 /// Fields are encoded in the order they are defined.
 #[proc_macro_derive(Encode, attributes(ssz))]
@@ -108,13 +74,43 @@ pub fn ssz_encode_derive(input: TokenStream) -> TokenStream {
     };
 
     let field_idents = get_serializable_named_field_idents(&struct_data);
+    let field_types_a = get_serializable_field_types(&struct_data);
+    let field_types_b = field_types_a.clone();
+    let field_types_c = field_types_a.clone();
 
     let output = quote! {
-        impl #impl_generics ssz::Encodable for #name #ty_generics #where_clause {
-            fn ssz_append(&self, s: &mut ssz::SszStream) {
+        impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
+            fn is_ssz_fixed_len() -> bool {
                 #(
-                    s.append(&self.#field_idents);
+                    <#field_types_a as ssz::Encode>::is_ssz_fixed_len() &&
                 )*
+                    true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                if <Self as ssz::Encode>::is_ssz_fixed_len() {
+                    #(
+                        <#field_types_b as ssz::Encode>::ssz_fixed_len() +
+                    )*
+                        0
+                } else {
+                    ssz::BYTES_PER_LENGTH_OFFSET
+                }
+            }
+
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                let offset = #(
+                        <#field_types_c as ssz::Encode>::ssz_fixed_len() +
+                    )*
+                        0;
+
+                let mut encoder = ssz::SszEncoder::container(buf, offset);
+
+                #(
+                    encoder.append(&self.#field_idents);
+                )*
+
+                encoder.finalize();
             }
         }
     };
@@ -133,7 +129,7 @@ fn should_skip_deserializing(field: &syn::Field) -> bool {
     false
 }
 
-/// Implements `ssz::Decodable` for some `struct`.
+/// Implements `ssz::Decode` for some `struct`.
 ///
 /// Fields are decoded in the order they are defined.
 #[proc_macro_derive(Decode)]
@@ -148,21 +144,38 @@ pub fn ssz_decode_derive(input: TokenStream) -> TokenStream {
         _ => panic!("ssz_derive only supports structs."),
     };
 
-    let all_idents = get_named_field_idents(&struct_data);
+    let mut register_types = vec![];
+    let mut decodes = vec![];
+    let mut is_fixed_lens = vec![];
+    let mut fixed_lens = vec![];
 
     // Build quotes for fields that should be deserialized and those that should be built from
     // `Default`.
-    let mut quotes = vec![];
     for field in &struct_data.fields {
         match &field.ident {
             Some(ref ident) => {
                 if should_skip_deserializing(field) {
-                    quotes.push(quote! {
-                        let #ident = <_>::default();
+                    // Field should not be deserialized; use a `Default` impl to instantiate.
+                    decodes.push(quote! {
+                        #ident: <_>::default()
                     });
                 } else {
-                    quotes.push(quote! {
-                        let (#ident, i) = <_>::ssz_decode(bytes, i)?;
+                    let ty = &field.ty;
+
+                    register_types.push(quote! {
+                        builder.register_type::<#ty>()?;
+                    });
+
+                    decodes.push(quote! {
+                        #ident: decoder.decode_next()?
+                    });
+
+                    is_fixed_lens.push(quote! {
+                        <#ty as ssz::Decode>::is_ssz_fixed_len()
+                    });
+
+                    fixed_lens.push(quote! {
+                        <#ty as ssz::Decode>::ssz_fixed_len()
                     });
                 }
             }
@@ -171,20 +184,39 @@ pub fn ssz_decode_derive(input: TokenStream) -> TokenStream {
     }
 
     let output = quote! {
-        impl #impl_generics ssz::Decodable for #name #ty_generics #where_clause {
-            fn ssz_decode(bytes: &[u8], i: usize) -> Result<(Self, usize), ssz::DecodeError> {
+        impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
+            fn is_ssz_fixed_len() -> bool {
                 #(
-                    #quotes
+                    #is_fixed_lens &&
+                )*
+                    true
+            }
+
+            fn ssz_fixed_len() -> usize {
+                if <Self as ssz::Decode>::is_ssz_fixed_len() {
+                    #(
+                        #fixed_lens +
+                    )*
+                        0
+                } else {
+                    ssz::BYTES_PER_LENGTH_OFFSET
+                }
+            }
+
+            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
+                let mut builder = ssz::SszDecoderBuilder::new(bytes);
+
+                #(
+                    #register_types
                 )*
 
-                Ok((
-                    Self {
-                        #(
-                            #all_idents,
-                        )*
-                    },
-                    i
-                ))
+                let mut decoder = builder.build()?;
+
+                Ok(Self {
+                    #(
+                        #decodes,
+                    )*
+                })
             }
         }
     };

eth2/utils/ssz_derive/tests/tests.rs

@@ -0,0 +1,22 @@
+use ssz::Encode;
+use ssz_derive::Encode;
+
+#[derive(Debug, PartialEq, Encode)]
+pub struct Foo {
+    a: u16,
+    b: Vec<u8>,
+    c: u16,
+}
+
+#[test]
+fn encode() {
+    let foo = Foo {
+        a: 42,
+        b: vec![0, 1, 2, 3],
+        c: 11,
+    };
+
+    let bytes = vec![42, 0, 8, 0, 0, 0, 11, 0, 0, 1, 2, 3];
+
+    assert_eq!(foo.as_ssz_bytes(), bytes);
+}

validator_client/src/attestation_producer/grpc.rs

@@ -1,7 +1,7 @@
 use super::beacon_node_attestation::BeaconNodeAttestation;
 use crate::block_producer::{BeaconNodeError, PublishOutcome};
 use protos::services_grpc::AttestationServiceClient;
-use ssz::{ssz_encode, Decodable};
+use ssz::{Decode, Encode};
 
 use protos::services::{
     Attestation as GrpcAttestation, ProduceAttestationDataRequest, PublishAttestationRequest,
@@ -22,8 +22,8 @@ impl BeaconNodeAttestation for AttestationServiceClient {
             .produce_attestation_data(&req)
             .map_err(|err| BeaconNodeError::RemoteFailure(format!("{:?}", err)))?;
 
-        let (attestation_data, _index) =
-            AttestationData::ssz_decode(reply.get_attestation_data().get_ssz(), 0)
+        let attestation_data =
+            AttestationData::from_ssz_bytes(reply.get_attestation_data().get_ssz())
                 .map_err(|_| BeaconNodeError::DecodeFailure)?;
         Ok(attestation_data)
     }
@@ -34,7 +34,7 @@ impl BeaconNodeAttestation for AttestationServiceClient {
     ) -> Result<PublishOutcome, BeaconNodeError> {
         let mut req = PublishAttestationRequest::new();
 
-        let ssz = ssz_encode(&attestation);
+        let ssz = attestation.as_ssz_bytes();
 
         let mut grpc_attestation = GrpcAttestation::new();
         grpc_attestation.set_ssz(ssz);

validator_client/src/block_producer/grpc.rs

@@ -3,7 +3,7 @@ use protos::services::{
     BeaconBlock as GrpcBeaconBlock, ProduceBeaconBlockRequest, PublishBeaconBlockRequest,
 };
 use protos::services_grpc::BeaconBlockServiceClient;
-use ssz::{decode, ssz_encode};
+use ssz::{Decode, Encode};
 use std::sync::Arc;
 use types::{BeaconBlock, Signature, Slot};
 
@@ -33,7 +33,7 @@ impl BeaconNodeBlock for BeaconBlockGrpcClient {
         // request a beacon block from the node
         let mut req = ProduceBeaconBlockRequest::new();
         req.set_slot(slot.as_u64());
-        req.set_randao_reveal(ssz_encode(randao_reveal));
+        req.set_randao_reveal(randao_reveal.as_ssz_bytes());
 
         //TODO: Determine if we want an explicit timeout
         let reply = self
@@ -46,7 +46,8 @@ impl BeaconNodeBlock for BeaconBlockGrpcClient {
             let block = reply.get_block();
             let ssz = block.get_ssz();
 
-            let block = decode::<BeaconBlock>(&ssz).map_err(|_| BeaconNodeError::DecodeFailure)?;
+            let block =
+                BeaconBlock::from_ssz_bytes(&ssz).map_err(|_| BeaconNodeError::DecodeFailure)?;
 
             Ok(Some(block))
         } else {
@@ -61,7 +62,7 @@ impl BeaconNodeBlock for BeaconBlockGrpcClient {
     fn publish_beacon_block(&self, block: BeaconBlock) -> Result<PublishOutcome, BeaconNodeError> {
         let mut req = PublishBeaconBlockRequest::new();
 
-        let ssz = ssz_encode(&block);
+        let ssz = block.as_ssz_bytes();
 
         let mut grpc_block = GrpcBeaconBlock::new();
         grpc_block.set_ssz(ssz);