lighthouse/beacon_chain/utils/ssz/src/encode.rs

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use super::{
LENGTH_BYTES,
MAX_LIST_SIZE,
};
#[derive(Debug)]
pub enum EncodeError {
ListTooLong,
}
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pub trait Encodable {
fn ssz_append(&self, s: &mut SszStream);
}
/// Provides a buffer for appending ssz-encodable values.
///
/// 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.
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pub struct SszStream {
buffer: Vec<u8>
}
impl SszStream {
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/// Create a new, empty stream for writing ssz values.
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pub fn new() -> Self {
SszStream {
buffer: Vec::new()
}
}
/// 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
}
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/// Append some ssz encoded bytes to the stream.
///
/// The length of the supplied bytes will be concatenated
/// to the stream before the supplied bytes.
pub fn append_encoded_val(&mut self, vec: &Vec<u8>) {
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self.buffer.extend_from_slice(
&encode_length(vec.len(),
LENGTH_BYTES));
self.buffer.extend_from_slice(&vec);
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}
/// 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: &Vec<u8>) {
self.buffer.extend_from_slice(&vec);
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}
/// 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.
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pub fn append_vec<E>(&mut self, vec: &Vec<E>)
where E: Encodable
{
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let mut list_stream = SszStream::new();
for item in vec {
item.ssz_append(&mut list_stream);
}
self.append_encoded_val(&list_stream.drain());
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}
/// Consume the stream and return the underlying bytes.
pub fn drain(self) -> Vec<u8> {
self.buffer
}
}
/// Encode some length into a ssz size prefix.
///
/// The ssz size prefix is 4 bytes, which is treated as a continuious
/// 32bit big-endian integer.
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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 in 0..length_bytes {
let offset = (length_bytes - i - 1) * 8;
header[i] = ((len >> offset) & 0xff) as u8;
};
header
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[should_panic]
fn test_encode_length_0_bytes_panic() {
encode_length(0, 0);
}
#[test]
fn test_encode_length_4_bytes() {
assert_eq!(
encode_length(0, LENGTH_BYTES),
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vec![0; 4]
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);
assert_eq!(
encode_length(1, LENGTH_BYTES),
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vec![0, 0, 0, 1]
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);
assert_eq!(
encode_length(255, LENGTH_BYTES),
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vec![0, 0, 0, 255]
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);
assert_eq!(
encode_length(256, LENGTH_BYTES),
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vec![0, 0, 1, 0]
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);
assert_eq!(
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encode_length(4294967295, LENGTH_BYTES), // 2^(3*8) - 1
vec![255, 255, 255, 255]
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);
}
#[test]
#[should_panic]
fn test_encode_length_4_bytes_panic() {
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encode_length(4294967296, LENGTH_BYTES); // 2^(3*8)
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}
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#[test]
fn test_encode_list() {
let test_vec: Vec<u16> = vec![256; 12];
let mut stream = SszStream::new();
stream.append_vec(&test_vec);
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let ssz = stream.drain();
assert_eq!(ssz.len(), 4 + (12 * 2));
assert_eq!(ssz[0..4], *vec![0, 0, 0, 24]);
assert_eq!(ssz[4..6], *vec![1, 0]);
}
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}