Allow starting from SSZ genesis state

beacon_node/beacon_chain/src/beacon_chain_builder.rs

@@ -4,9 +4,10 @@ use lighthouse_bootstrap::Bootstrapper;
 use merkle_proof::MerkleTree;
 use rayon::prelude::*;
 use slog::Logger;
-use ssz::Encode;
+use ssz::{Decode, Encode};
 use state_processing::initialize_beacon_state_from_eth1;
 use std::fs::File;
+use std::io::prelude::*;
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::SystemTime;
@@ -61,6 +62,20 @@ impl<T: BeaconChainTypes> BeaconChainBuilder<T> {
         Ok(Self::from_genesis_state(genesis_state, spec, log))
     }
 
+    pub fn ssz_state(file: &PathBuf, spec: ChainSpec, log: Logger) -> Result<Self, String> {
+        let mut file = File::open(file.clone())
+            .map_err(|e| format!("Unable to open SSZ genesis state file {:?}: {:?}", file, e))?;
+
+        let mut bytes = vec![];
+        file.read_to_end(&mut bytes)
+            .map_err(|e| format!("Failed to read SSZ file: {:?}", e))?;
+
+        let genesis_state = BeaconState::from_ssz_bytes(&bytes)
+            .map_err(|e| format!("Unable to parse SSZ genesis state file: {:?}", e))?;
+
+        Ok(Self::from_genesis_state(genesis_state, spec, log))
+    }
+
     pub fn http_bootstrap(server: &str, spec: ChainSpec, log: Logger) -> Result<Self, String> {
         let bootstrapper = Bootstrapper::from_server_string(server.to_string())
             .map_err(|e| format!("Failed to initialize bootstrap client: {}", e))?;

beacon_node/client/src/config.rs

@@ -54,6 +54,8 @@ pub enum BeaconChainStartMethod {
     },
     /// Create a new beacon chain by loading a YAML-encoded genesis state from a file.
     Yaml { file: PathBuf },
+    /// Create a new beacon chain by loading a SSZ-encoded genesis state from a file.
+    Ssz { file: PathBuf },
     /// Create a new beacon chain by using a HTTP server (running our REST-API) to load genesis and
     /// finalized states and blocks.
     HttpBootstrap { server: String, port: Option<u16> },

beacon_node/client/src/lib.rs

@@ -138,6 +138,15 @@ where
                 );
                 BeaconChainBuilder::yaml_state(file, spec.clone(), log.clone())?
             }
+            BeaconChainStartMethod::Ssz { file } => {
+                info!(
+                    log,
+                    "Starting beacon chain";
+                    "file" => format!("{:?}", file),
+                    "method" => "ssz"
+                );
+                BeaconChainBuilder::ssz_state(file, spec.clone(), log.clone())?
+            }
             BeaconChainStartMethod::HttpBootstrap { server, port } => {
                 info!(
                     log,