Update SszEncoder

eth2/utils/ssz/benches/benches.rs

@@ -4,6 +4,15 @@ extern crate criterion;
 use criterion::black_box;
 use criterion::{Benchmark, Criterion};
 use ssz::{Decodable, Encodable};
+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;
@@ -32,6 +41,39 @@ fn criterion_benchmark(c: &mut Criterion) {
         })
         .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);

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::{Decodable, Encodable};
+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

@@ -1,4 +1,4 @@
-use ssz::{Decodable, DecodeError, Encodable, SszDecoderBuilder, SszEncoder, SszStream};
+use ssz::{Decodable, DecodeError, Encodable, SszDecoderBuilder, SszEncoder};
 
 #[derive(Debug, PartialEq)]
 pub struct Foo {
@@ -23,7 +23,7 @@ impl Encodable for Foo {
         encoder.append(&self.b);
         encoder.append(&self.c);
 
-        buf.append(&mut encoder.drain());
+        encoder.drain_onto(buf);
     }
 }
 

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()
 }
 
 /*

eth2/utils/ssz_derive/src/lib.rs

@@ -81,6 +81,7 @@ 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 ssz::Encodable for #name {
@@ -102,14 +103,19 @@ pub fn ssz_encode_derive(input: TokenStream) -> TokenStream {
                 }
             }
 
-            fn as_ssz_bytes(&self) -> Vec<u8> {
-                let mut stream = ssz::SszStream::new();
+            fn ssz_append(&self, buf: &mut Vec<u8>) {
+                let offset = #(
+                        <#field_types_c as ssz::Encodable>::ssz_fixed_len() +
+                    )*
+                        0;
+
+                let mut encoder = ssz::SszEncoder::container(offset);
 
                 #(
-                    stream.append(&self.#field_idents);
+                    encoder.append(&self.#field_idents);
                 )*
 
-                stream.drain()
+                encoder.drain_onto(buf);
             }
         }
     };