//! Witness
//!
//! This module contains the [`Witness`] struct and related methods to operate on it
//!
use consensus::encode::{Error, MAX_VEC_SIZE};
use consensus::{Decodable, Encodable, WriteExt};
use io::{self, Read, Write};
use prelude::*;
use VarInt;
#[cfg(feature = "serde")]
use serde;
/// The Witness is the data used to unlock bitcoins since the [segwit upgrade](https://github.com/bitcoin/bips/blob/master/bip-0143.mediawiki)
///
/// Can be logically seen as an array of byte-arrays `Vec<Vec<u8>>` and indeed you can convert from
/// it [`Witness::from_vec`] and convert into it [`Witness::to_vec`].
///
/// For serialization and deserialization performance it is stored internally as a single `Vec`,
/// saving some allocations.
///
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
pub struct Witness {
/// contains the witness Vec<Vec<u8>> serialization without the initial varint indicating the
/// number of elements (which is stored in `witness_elements`)
content: Vec<u8>,
/// Number of elements in the witness.
/// It is stored separately (instead of as VarInt in the initial part of content) so that method
/// like [`Witness::push`] doesn't have case requiring to shift the entire array
witness_elements: usize,
/// If `witness_elements > 0` it's a valid index pointing to the last witness element in `content`
/// (Including the varint specifying the length of the element)
last: usize,
/// If `witness_elements > 1` it's a valid index pointing to the second-to-last witness element in `content`
/// (Including the varint specifying the length of the element)
second_to_last: usize,
}
/// Support structure to allow efficient and convenient iteration over the Witness elements
pub struct Iter<'a>(::core::slice::Iter<'a, u8>);
impl Decodable for Witness {
fn consensus_decode<D: Read>(mut d: D) -> Result<Self, Error> {
let witness_elements = VarInt::consensus_decode(&mut d)?.0 as usize;
if witness_elements == 0 {
Ok(Witness::default())
} else {
let mut cursor = 0usize;
let mut last = 0usize;
let mut second_to_last = 0usize;
// this number should be determined as high enough to cover most witness, and low enough
// to avoid wasting space without reallocating
let mut content = vec![0u8; 128];
for _ in 0..witness_elements {
second_to_last = last;
last = cursor;
let element_size_varint = VarInt::consensus_decode(&mut d)?;
let element_size_varint_len = element_size_varint.len();
let element_size = element_size_varint.0 as usize;
let required_len = cursor
.checked_add(element_size)
.ok_or_else(|| self::Error::OversizedVectorAllocation {
requested: usize::max_value(),
max: MAX_VEC_SIZE,
})?
.checked_add(element_size_varint_len)
.ok_or_else(|| self::Error::OversizedVectorAllocation {
requested: usize::max_value(),
max: MAX_VEC_SIZE,
})?;
if required_len > MAX_VEC_SIZE {
return Err(self::Error::OversizedVectorAllocation {
requested: required_len,
max: MAX_VEC_SIZE,
});
}
resize_if_needed(&mut content, required_len);
element_size_varint
.consensus_encode(&mut content[cursor..cursor + element_size_varint_len])?;
cursor += element_size_varint_len;
d.read_exact(&mut content[cursor..cursor + element_size])?;
cursor += element_size;
}
content.truncate(cursor);
Ok(Witness {
content,
witness_elements,
last,
second_to_last,
})
}
}
}
fn resize_if_needed(vec: &mut Vec<u8>, required_len: usize) {
if required_len >= vec.len() {
let mut new_len = vec.len().max(1);
while new_len <= required_len {
new_len *= 2;
}
vec.resize(new_len, 0);
}
}
impl Encodable for Witness {
fn consensus_encode<W: Write>(&self, mut writer: W) -> Result<usize, io::Error> {
let len = VarInt(self.witness_elements as u64);
len.consensus_encode(&mut writer)?;
writer.emit_slice(&self.content[..])?;
Ok(self.content.len() + len.len())
}
}
impl Witness {
/// Create a new empty [`Witness`]
pub fn new() -> Self {
Witness::default()
}
/// Creates [`Witness`] object from an array of byte-arrays
pub fn from_vec(vec: Vec<Vec<u8>>) -> Self {
let witness_elements = vec.len();
let content_size: usize = vec
.iter()
.map(|el| el.len() + VarInt(el.len() as u64).len())
.sum();
let mut content = vec![0u8; content_size];
let mut cursor = 0usize;
let mut last = 0;
let mut second_to_last = 0;
for el in vec {
second_to_last = last;
last = cursor;
let el_len_varint = VarInt(el.len() as u64);
el_len_varint
.consensus_encode(&mut content[cursor..cursor + el_len_varint.len()])
.expect("writers on vec don't errors, space granted by content_size");
cursor += el_len_varint.len();
content[cursor..cursor + el.len()].copy_from_slice(&el);
cursor += el.len();
}
Witness {
witness_elements,
content,
last,
second_to_last,
}
}
/// Convenience method to create an array of byte-arrays from this witness
pub fn to_vec(&self) -> Vec<Vec<u8>> {
self.iter().map(|s| s.to_vec()).collect()
}
/// Returns `true` if the witness contains no element
pub fn is_empty(&self) -> bool {
self.witness_elements == 0
}
/// Returns a struct implementing [`Iterator`]
pub fn iter(&self) -> Iter {
Iter(self.content.iter())
}
/// Returns the number of elements this witness holds
pub fn len(&self) -> usize {
self.witness_elements as usize
}
/// Returns the bytes required when this Witness is consensus encoded
pub fn serialized_len(&self) -> usize {
self.iter()
.map(|el| VarInt(el.len() as u64).len() + el.len())
.sum::<usize>()
+ VarInt(self.witness_elements as u64).len()
}
/// Clear the witness
pub fn clear(&mut self) {
self.content.clear();
self.witness_elements = 0;
self.last = 0;
self.second_to_last = 0;
}
/// Push a new element on the witness, requires an allocation
pub fn push<T: AsRef<[u8]>>(&mut self, new_element: T) {
let new_element = new_element.as_ref();
self.witness_elements += 1;
self.second_to_last = self.last;
self.last = self.content.len();
let element_len_varint = VarInt(new_element.len() as u64);
let current_content_len = self.content.len();
self.content
.resize(current_content_len + element_len_varint.len() + new_element.len(), 0);
let end_varint = current_content_len + element_len_varint.len();
element_len_varint
.consensus_encode(&mut self.content[current_content_len..end_varint])
.expect("writers on vec don't error, space granted through previous resize");
self.content[end_varint..].copy_from_slice(new_element);
}
fn element_at(&self, index: usize) -> Option<&[u8]> {
let varint = VarInt::consensus_decode(&self.content[index..]).ok()?;
let start = index + varint.len();
Some(&self.content[start..start + varint.0 as usize])
}
/// Return the last element in the witness, if any
pub fn last(&self) -> Option<&[u8]> {
if self.witness_elements == 0 {
None
} else {
self.element_at(self.last)
}
}
/// Return the second-to-last element in the witness, if any
pub fn second_to_last(&self) -> Option<&[u8]> {
if self.witness_elements <= 1 {
None
} else {
self.element_at(self.second_to_last)
}
}
}
impl Default for Witness {
fn default() -> Self {
// from https://doc.rust-lang.org/std/vec/struct.Vec.html#method.new
// The vector will not allocate until elements are pushed onto it.
Witness {
content: Vec::new(),
witness_elements: 0,
last: 0,
second_to_last: 0,
}
}
}
impl<'a> Iterator for Iter<'a> {
type Item = &'a [u8];
fn next(&mut self) -> Option<Self::Item> {
let varint = VarInt::consensus_decode(self.0.as_slice()).ok()?;
self.0.nth(varint.len() - 1)?; // VarInt::len returns at least 1
let len = varint.0 as usize;
let slice = &self.0.as_slice()[..len];
if len > 0 {
// we don't need to advance if the element is empty
self.0.nth(len - 1)?;
}
Some(slice)
}
}
// Serde keep backward compatibility with old Vec<Vec<u8>> format
#[cfg(feature = "serde")]
impl serde::Serialize for Witness {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
let vec: Vec<_> = self.to_vec();
serde::Serialize::serialize(&vec, serializer)
}
}
#[cfg(feature = "serde")]
impl<'de> serde::Deserialize<'de> for Witness {
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where
D: serde::Deserializer<'de>,
{
let vec: Vec<Vec<u8>> = serde::Deserialize::deserialize(deserializer)?;
Ok(Witness::from_vec(vec))
}
}
#[cfg(test)]
mod test {
use blockdata::witness::Witness;
use consensus::{deserialize, serialize};
use hashes::hex::{FromHex, ToHex};
use Transaction;
#[test]
fn test_push() {
let mut witness = Witness::default();
assert_eq!(witness.last(), None);
assert_eq!(witness.second_to_last(), None);
witness.push(&vec![0u8]);
let expected = Witness {
witness_elements: 1,
content: vec![1u8, 0],
last: 0,
second_to_last: 0,
};
assert_eq!(witness, expected);
assert_eq!(witness.last(), Some(&[0u8][..]));
assert_eq!(witness.second_to_last(), None);
witness.push(&vec![2u8, 3u8]);
let expected = Witness {
witness_elements: 2,
content: vec![1u8, 0, 2, 2, 3],
last: 2,
second_to_last: 0,
};
assert_eq!(witness, expected);
assert_eq!(witness.last(), Some(&[2u8, 3u8][..]));
assert_eq!(witness.second_to_last(), Some(&[0u8][..]));
}
#[test]
fn test_witness() {
let w0 =
Vec::from_hex("03d2e15674941bad4a996372cb87e1856d3652606d98562fe39c5e9e7e413f2105")
.unwrap();
let w1 = Vec::from_hex("000000").unwrap();
let witness_vec = vec![w0.clone(), w1.clone()];
let witness_serialized: Vec<u8> = serialize(&witness_vec);
let witness = Witness {
content: witness_serialized[1..].to_vec(),
witness_elements: 2,
last: 34,
second_to_last: 0,
};
for (i, el) in witness.iter().enumerate() {
assert_eq!(witness_vec[i], el);
}
assert_eq!(witness.last(), Some(&w1[..]));
assert_eq!(witness.second_to_last(), Some(&w0[..]));
let w_into = Witness::from_vec(witness_vec);
assert_eq!(w_into, witness);
assert_eq!(witness_serialized, serialize(&witness));
}
#[test]
fn test_tx() {
let s = "02000000000102b44f26b275b8ad7b81146ba3dbecd081f9c1ea0dc05b97516f56045cfcd3df030100000000ffffffff1cb4749ae827c0b75f3d0a31e63efc8c71b47b5e3634a4c698cd53661cab09170100000000ffffffff020b3a0500000000001976a9143ea74de92762212c96f4dd66c4d72a4deb20b75788ac630500000000000016001493a8dfd1f0b6a600ab01df52b138cda0b82bb7080248304502210084622878c94f4c356ce49c8e33a063ec90f6ee9c0208540888cfab056cd1fca9022014e8dbfdfa46d318c6887afd92dcfa54510e057565e091d64d2ee3a66488f82c0121026e181ffb98ebfe5a64c983073398ea4bcd1548e7b971b4c175346a25a1c12e950247304402203ef00489a0d549114977df2820fab02df75bebb374f5eee9e615107121658cfa02204751f2d1784f8e841bff6d3bcf2396af2f1a5537c0e4397224873fbd3bfbe9cf012102ae6aa498ce2dd204e9180e71b4fb1260fe3d1a95c8025b34e56a9adf5f278af200000000";
let tx_bytes = Vec::from_hex(s).unwrap();
let tx: Transaction = deserialize(&tx_bytes).unwrap();
let expected_wit = ["304502210084622878c94f4c356ce49c8e33a063ec90f6ee9c0208540888cfab056cd1fca9022014e8dbfdfa46d318c6887afd92dcfa54510e057565e091d64d2ee3a66488f82c01", "026e181ffb98ebfe5a64c983073398ea4bcd1548e7b971b4c175346a25a1c12e95"];
for (i, wit_el) in tx.input[0].witness.iter().enumerate() {
assert_eq!(expected_wit[i], wit_el.to_hex());
}
assert_eq!(expected_wit[1], tx.input[0].witness.last().unwrap().to_hex());
assert_eq!(expected_wit[0], tx.input[0].witness.second_to_last().unwrap().to_hex());
let tx_bytes_back = serialize(&tx);
assert_eq!(tx_bytes_back, tx_bytes);
}
#[test]
fn fuzz_cases() {
let s = "26ff0000000000c94ce592cf7a4cbb68eb00ce374300000057cd0000000000000026";
let bytes = Vec::from_hex(s).unwrap();
assert!(deserialize::<Witness>(&bytes).is_err()); // OversizedVectorAllocation
let s = "24000000ffffffffffffffffffffffff";
let bytes = Vec::from_hex(s).unwrap();
assert!(deserialize::<Witness>(&bytes).is_err()); // OversizedVectorAllocation
}
#[cfg(feature = "serde")]
#[test]
fn test_serde() {
use serde_json;
let old_witness_format = vec![vec![0u8], vec![2]];
let new_witness_format = Witness::from_vec(old_witness_format.clone());
let old = serde_json::to_string(&old_witness_format).unwrap();
let new = serde_json::to_string(&new_witness_format).unwrap();
assert_eq!(old, new);
let back = serde_json::from_str(&new).unwrap();
assert_eq!(new_witness_format, back);
}
}