Update SszEncoder

eth2/utils/ssz/src/encode.rs

@@ -32,10 +32,14 @@ pub struct SszEncoder {
 }
 
 impl SszEncoder {
+    pub fn list(num_fixed_bytes: usize) -> Self {
+        Self::container(num_fixed_bytes)
+    }
+
     pub fn container(num_fixed_bytes: usize) -> Self {
         Self {
             offset: num_fixed_bytes,
-            fixed_bytes: vec![],
+            fixed_bytes: Vec::with_capacity(num_fixed_bytes),
             variable_bytes: vec![],
         }
     }
@@ -51,10 +55,9 @@ impl SszEncoder {
         }
     }
 
-    pub fn drain(mut self) -> Vec<u8> {
-        self.fixed_bytes.append(&mut self.variable_bytes);
-
-        self.fixed_bytes
+    pub fn drain_onto(mut self, buf: &mut Vec<u8>) {
+        buf.append(&mut self.fixed_bytes);
+        buf.append(&mut self.variable_bytes);
     }
 }
 
@@ -63,6 +66,7 @@ pub struct VariableLengths {
     pub variable_bytes_length: usize,
 }
 
+/*
 /// Provides a buffer for appending SSZ values.
 #[derive(Default)]
 pub struct SszStream {
@@ -152,6 +156,7 @@ impl SszStream {
         self.fixed_bytes
     }
 }
+*/
 
 /// Encode `len` as a little-endian byte vec of `BYTES_PER_LENGTH_OFFSET` length.
 ///

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

@@ -31,7 +31,6 @@ impl<T: Encodable> Encodable for Vec<T> {
     }
 
     fn ssz_append(&self, buf: &mut Vec<u8>) {
-
         if T::is_ssz_fixed_len() {
             buf.reserve(T::ssz_fixed_len() * self.len());
 
@@ -39,28 +38,13 @@ impl<T: Encodable> Encodable for Vec<T> {
                 item.ssz_append(buf);
             }
         } 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![];
+            let mut encoder = SszEncoder::list(self.len() * BYTES_PER_LENGTH_OFFSET);
 
             for item in self {
-                fixed.append(&mut encode_length(offset));
-                let mut bytes = item.as_ssz_bytes();
-                offset += bytes.len();
-                variable.append(&mut bytes);
+                encoder.append(item);
             }
 
-            buf.append(&mut fixed);
-            buf.append(&mut variable);
+            encoder.drain_onto(buf);
         }
     }
 }

eth2/utils/ssz/src/lib.rs

@@ -17,21 +17,19 @@ mod decode;
 mod encode;
 
 pub use decode::{Decodable, DecodeError, SszDecoderBuilder};
-pub use encode::{Encodable, SszEncoder, SszStream};
+pub use encode::{Encodable, SszEncoder};
 
 pub const BYTES_PER_LENGTH_OFFSET: usize = 4;
 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,
 {
-    let mut buf = vec![];
-
-    val.ssz_append(&mut buf);
-
-    buf
+    val.as_ssz_bytes()
 }
 
 /*