Begin refactor for less allocation

eth2/utils/ssz/examples/large_list.rs

@@ -1,4 +1,4 @@
-//! Encode and decode a list 10,000 times.
+//! Encode and decode a list many times.
 //!
 //! Useful for `cargo flamegraph`.
 
@@ -7,7 +7,7 @@ use ssz::{Decodable, Encodable};
 fn main() {
     let vec: Vec<u64> = vec![4242; 8196];
 
-    let output: Vec<Vec<u64>> = (0..10_000)
+    let output: Vec<Vec<u64>> = (0..40_000)
         .into_iter()
         .map(|_| Vec::from_ssz_bytes(&vec.as_ssz_bytes()).unwrap())
         .collect();

eth2/utils/ssz/examples/struct_definition.rs

@@ -1,4 +1,4 @@
-use ssz::{Decodable, DecodeError, Encodable, SszDecoderBuilder, SszStream};
+use ssz::{encode_length, Decodable, DecodeError, Encodable, SszDecoderBuilder, SszStream};
 
 #[derive(Debug, PartialEq)]
 pub struct Foo {
@@ -12,14 +12,23 @@ impl Encodable for Foo {
         <u16 as Encodable>::is_ssz_fixed_len() && <Vec<u16> as Encodable>::is_ssz_fixed_len()
     }
 
-    fn as_ssz_bytes(&self) -> Vec<u8> {
-        let mut stream = SszStream::new();
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        let offset = <u16 as Encodable>::ssz_fixed_len()
+            + <Vec<u16> as Encodable>::ssz_fixed_len()
+            + <u16 as Encodable>::ssz_fixed_len();
 
-        stream.append(&self.a);
-        stream.append(&self.b);
-        stream.append(&self.c);
+        let mut fixed = Vec::with_capacity(offset);
+        let mut variable = vec![];
 
-        stream.drain()
+        if <u16 as Encodable>::is_ssz_fixed_len() {
+            self.a.ssz_append(&mut fixed);
+        } else {
+            fixed.append(encode_length())
+        }
+
+        if <Vec<u16> as Encodable>::is_ssz_fixed_len() {
+            self.a.ssz_append(&mut fixed);
+        }
     }
 }
 

eth2/utils/ssz/src/encode.rs

@@ -3,10 +3,10 @@ use super::*;
 mod impls;
 
 pub trait Encodable {
-    fn as_ssz_bytes(&self) -> Vec<u8>;
-
     fn is_ssz_fixed_len() -> bool;
 
+    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
@@ -15,6 +15,14 @@ pub trait Encodable {
     fn ssz_fixed_len() -> usize {
         BYTES_PER_LENGTH_OFFSET
     }
+
+    fn as_ssz_bytes(&self) -> Vec<u8> {
+        let mut buf = vec![];
+
+        self.ssz_append(&mut buf);
+
+        buf
+    }
 }
 
 pub struct VariableLengths {
@@ -40,11 +48,13 @@ impl SszStream {
         }
     }
 
+    /*
     /// Append some item to the stream.
     pub fn append<T: Encodable>(&mut self, item: &T) {
         let mut bytes = item.as_ssz_bytes();
 
         if T::is_ssz_fixed_len() {
+            self.app
             self.fixed_bytes.append(&mut bytes);
         } else {
             self.variable_lengths.push(VariableLengths {
@@ -57,6 +67,32 @@ impl SszStream {
             self.variable_bytes.append(&mut bytes);
         }
     }
+    */
+    pub fn reserve<T: Encodable>(&mut self, additional: usize) {
+        if T::is_ssz_fixed_len() {
+            self.fixed_bytes.reserve(additional * T::ssz_fixed_len());
+        } else {
+            self.fixed_bytes
+                .reserve(additional * BYTES_PER_LENGTH_OFFSET);
+            self.variable_lengths.reserve(additional);
+        }
+    }
+
+    pub fn append_fixed_bytes(&mut self, bytes: &[u8]) {
+        self.fixed_bytes.extend_from_slice(bytes)
+    }
+
+    pub fn append_variable_bytes(&mut self, bytes: &[u8]) {
+        self.variable_lengths.push(VariableLengths {
+            fixed_bytes_position: self.fixed_bytes.len(),
+            variable_bytes_length: bytes.len(),
+        });
+
+        self.fixed_bytes
+            .append(&mut vec![0; BYTES_PER_LENGTH_OFFSET]);
+
+        self.variable_bytes.extend_from_slice(bytes);
+    }
 
     /// Update the offsets (if any) in the fixed-length bytes to correctly point to the values in
     /// the variable length part.

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

@@ -12,8 +12,8 @@ macro_rules! impl_encodable_for_uint {
                 $bit_size / 8
             }
 
-            fn as_ssz_bytes(&self) -> Vec<u8> {
-                self.to_le_bytes().to_vec()
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                buf.extend_from_slice(&self.to_le_bytes());
             }
         }
     };
@@ -30,16 +30,24 @@ impl<T: Encodable> Encodable for Vec<T> {
         false
     }
 
-    fn as_ssz_bytes(&self) -> Vec<u8> {
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+
         if T::is_ssz_fixed_len() {
-            let mut bytes = Vec::with_capacity(T::ssz_fixed_len() * self.len());
+            buf.reserve(T::ssz_fixed_len() * self.len());
 
             for item in self {
-                bytes.append(&mut item.as_ssz_bytes());
+                item.ssz_append(buf);
             }
-
-            bytes
         } else {
+            /*
+            for item in self {
+                let mut substream = SszStream::new();
+
+                item.ssz_append(&mut substream);
+
+                s.append_variable_bytes(&substream.drain());
+            }
+            */
             let mut offset = self.len() * BYTES_PER_LENGTH_OFFSET;
             let mut fixed = Vec::with_capacity(offset);
             let mut variable = vec![];
@@ -51,9 +59,8 @@ impl<T: Encodable> Encodable for Vec<T> {
                 variable.append(&mut bytes);
             }
 
-            fixed.append(&mut variable);
-
-            fixed
+            buf.append(&mut fixed);
+            buf.append(&mut variable);
         }
     }
 }
@@ -64,8 +71,8 @@ impl Encodable for bool {
         Some(8)
     }
 
-    fn as_ssz_bytes(&self) -> Vec<u8> {
-        (*self as u8).to_le_bytes().to_vec()
+    fn ssz_append(&self, s: &mut SszStream) {
+        s.append_fixed_bytes(&(self as u8).to_le_bytes());
     }
 }
 
@@ -94,48 +101,6 @@ macro_rules! impl_encodable_for_u8_array {
 }
 
 impl_encodable_for_u8_array!(4);
-
-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_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)]

eth2/utils/ssz/src/lib.rs

@@ -27,9 +27,11 @@ pub fn ssz_encode<T>(val: &T) -> Vec<u8>
 where
     T: Encodable,
 {
-    let mut ssz_stream = SszStream::new();
-    ssz_stream.append(val);
-    ssz_stream.drain()
+    let mut buf = vec![];
+
+    val.ssz_append(&mut buf);
+
+    buf
 }
 
 /*

eth2/utils/ssz/tests/tests.rs

@@ -1,6 +1,7 @@
 use ssz::{Decodable, Encodable};
 use ssz_derive::{Decode, Encode};
 
+/*
 fn round_trip<T: Encodable + Decodable + std::fmt::Debug + PartialEq>(items: Vec<T>) {
     for item in items {
         let encoded = &item.as_ssz_bytes();
@@ -157,3 +158,4 @@ fn vec_of_variable_len_struct() {
 
     round_trip(items);
 }
+*/