rust: apply clippy lints
They are at most harmless and at best make the codebase more readable and
simpler.
// Copyright 2019-2020 Georges Racinet <georges.racinet@octobus.net>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.
//! Definitions and utilities for Revision nodes
//!
//! In Mercurial code base, it is customary to call "a node" the binary SHA
//! of a revision.
use crate::errors::HgError;
use bytes_cast::BytesCast;
use std::fmt;
/// The length in bytes of a `Node`
///
/// This constant is meant to ease refactors of this module, and
/// are private so that calling code does not expect all nodes have
/// the same size, should we support several formats concurrently in
/// the future.
pub const NODE_BYTES_LENGTH: usize = 20;
/// The length in bytes set aside on disk for a `Node`. Revlog up to v1 only
/// use 20 out of those 32.
pub const STORED_NODE_ID_BYTES: usize = 32;
/// Id of the null node.
///
/// Used to indicate the absence of node.
pub const NULL_NODE_ID: [u8; NODE_BYTES_LENGTH] = [0u8; NODE_BYTES_LENGTH];
/// The length in bytes of a `Node`
///
/// see also `NODES_BYTES_LENGTH` about it being private.
const NODE_NYBBLES_LENGTH: usize = 2 * NODE_BYTES_LENGTH;
/// Default for UI presentation
const SHORT_PREFIX_DEFAULT_NYBBLES_LENGTH: u8 = 12;
/// Private alias for readability and to ease future change
type NodeData = [u8; NODE_BYTES_LENGTH];
/// Binary revision SHA
///
/// ## Future changes of hash size
///
/// To accomodate future changes of hash size, Rust callers
/// should use the conversion methods at the boundaries (FFI, actual
/// computation of hashes and I/O) only, and only if required.
///
/// All other callers outside of unit tests should just handle `Node` values
/// and never make any assumption on the actual length, using [`nybbles_len`]
/// if they need a loop boundary.
///
/// All methods that create a `Node` either take a type that enforces
/// the size or return an error at runtime.
///
/// [`nybbles_len`]: #method.nybbles_len
#[derive(Copy, Clone, PartialEq, BytesCast, derive_more::From)]
#[repr(transparent)]
pub struct Node {
data: NodeData,
}
impl fmt::Debug for Node {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let n = format!("{:x?}", self.data);
// We're using debug_tuple because it makes the output a little
// more compact without losing data.
f.debug_tuple("Node").field(&n).finish()
}
}
/// The node value for NULL_REVISION
pub const NULL_NODE: Node = Node {
data: [0; NODE_BYTES_LENGTH],
};
/// Return an error if the slice has an unexpected length
impl<'a> TryFrom<&'a [u8]> for &'a Node {
type Error = ();
#[inline]
fn try_from(bytes: &'a [u8]) -> Result<Self, Self::Error> {
match Node::from_bytes(bytes) {
Ok((node, [])) => Ok(node),
_ => Err(()),
}
}
}
/// Return an error if the slice has an unexpected length
impl TryFrom<&'_ [u8]> for Node {
type Error = std::array::TryFromSliceError;
#[inline]
fn try_from(bytes: &'_ [u8]) -> Result<Self, Self::Error> {
let data = bytes.try_into()?;
Ok(Self { data })
}
}
impl From<&'_ NodeData> for Node {
#[inline]
fn from(data: &'_ NodeData) -> Self {
Self { data: *data }
}
}
impl fmt::LowerHex for Node {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
for &byte in &self.data {
write!(f, "{:02x}", byte)?
}
Ok(())
}
}
#[derive(Debug)]
pub struct FromHexError;
/// Low level utility function, also for prefixes
fn get_nybble(s: &[u8], i: usize) -> u8 {
if i % 2 == 0 {
s[i / 2] >> 4
} else {
s[i / 2] & 0x0f
}
}
impl Node {
/// Retrieve the `i`th half-byte of the binary data.
///
/// This is also the `i`th hexadecimal digit in numeric form,
/// also called a [nybble](https://en.wikipedia.org/wiki/Nibble).
pub fn get_nybble(&self, i: usize) -> u8 {
get_nybble(&self.data, i)
}
/// Length of the data, in nybbles
pub fn nybbles_len(&self) -> usize {
// public exposure as an instance method only, so that we can
// easily support several sizes of hashes if needed in the future.
NODE_NYBBLES_LENGTH
}
/// Convert from hexadecimal string representation
///
/// Exact length is required.
///
/// To be used in FFI and I/O only, in order to facilitate future
/// changes of hash format.
pub fn from_hex(hex: impl AsRef<[u8]>) -> Result<Node, FromHexError> {
let prefix = NodePrefix::from_hex(hex)?;
if prefix.nybbles_len() == NODE_NYBBLES_LENGTH {
Ok(Self { data: prefix.data })
} else {
Err(FromHexError)
}
}
/// `from_hex`, but for input from an internal file of the repository such
/// as a changelog or manifest entry.
///
/// An error is treated as repository corruption.
pub fn from_hex_for_repo(hex: impl AsRef<[u8]>) -> Result<Node, HgError> {
Self::from_hex(hex.as_ref()).map_err(|FromHexError| {
HgError::CorruptedRepository(format!(
"Expected a full hexadecimal node ID, found {}",
String::from_utf8_lossy(hex.as_ref())
))
})
}
/// Provide access to binary data
///
/// This is needed by FFI layers, for instance to return expected
/// binary values to Python.
pub fn as_bytes(&self) -> &[u8] {
&self.data
}
pub fn short(&self) -> NodePrefix {
NodePrefix {
nybbles_len: SHORT_PREFIX_DEFAULT_NYBBLES_LENGTH,
data: self.data,
}
}
pub fn pad_to_256_bits(&self) -> [u8; 32] {
let mut bits = [0; 32];
bits[..NODE_BYTES_LENGTH].copy_from_slice(&self.data);
bits
}
}
/// The beginning of a binary revision SHA.
///
/// Since it can potentially come from an hexadecimal representation with
/// odd length, it needs to carry around whether the last 4 bits are relevant
/// or not.
#[derive(Debug, PartialEq, Copy, Clone)]
pub struct NodePrefix {
/// In `1..=NODE_NYBBLES_LENGTH`
nybbles_len: u8,
/// The first `4 * length_in_nybbles` bits are used (considering bits
/// within a bytes in big-endian: most significant first), the rest
/// are zero.
data: NodeData,
}
impl NodePrefix {
/// Convert from hexadecimal string representation
///
/// Similarly to `hex::decode`, can be used with Unicode string types
/// (`String`, `&str`) as well as bytes.
///
/// To be used in FFI and I/O only, in order to facilitate future
/// changes of hash format.
pub fn from_hex(hex: impl AsRef<[u8]>) -> Result<Self, FromHexError> {
let hex = hex.as_ref();
let len = hex.len();
if len > NODE_NYBBLES_LENGTH || len == 0 {
return Err(FromHexError);
}
let mut data = [0; NODE_BYTES_LENGTH];
let mut nybbles_len = 0;
for &ascii_byte in hex {
let nybble = match char::from(ascii_byte).to_digit(16) {
Some(digit) => digit as u8,
None => return Err(FromHexError),
};
// Fill in the upper half of a byte first, then the lower half.
let shift = if nybbles_len % 2 == 0 { 4 } else { 0 };
data[nybbles_len as usize / 2] |= nybble << shift;
nybbles_len += 1;
}
Ok(Self { data, nybbles_len })
}
pub fn nybbles_len(&self) -> usize {
self.nybbles_len as _
}
pub fn is_prefix_of(&self, node: &Node) -> bool {
let full_bytes = self.nybbles_len() / 2;
if self.data[..full_bytes] != node.data[..full_bytes] {
return false;
}
if self.nybbles_len() % 2 == 0 {
return true;
}
let last = self.nybbles_len() - 1;
self.get_nybble(last) == node.get_nybble(last)
}
/// Retrieve the `i`th half-byte from the prefix.
///
/// This is also the `i`th hexadecimal digit in numeric form,
/// also called a [nybble](https://en.wikipedia.org/wiki/Nibble).
pub fn get_nybble(&self, i: usize) -> u8 {
assert!(i < self.nybbles_len());
get_nybble(&self.data, i)
}
fn iter_nybbles(&self) -> impl Iterator<Item = u8> + '_ {
(0..self.nybbles_len()).map(move |i| get_nybble(&self.data, i))
}
/// Return the index first nybble that's different from `node`
///
/// If the return value is `None` that means that `self` is
/// a prefix of `node`, but the current method is a bit slower
/// than `is_prefix_of`.
///
/// Returned index is as in `get_nybble`, i.e., starting at 0.
pub fn first_different_nybble(&self, node: &Node) -> Option<usize> {
self.iter_nybbles()
.zip(NodePrefix::from(*node).iter_nybbles())
.position(|(a, b)| a != b)
}
}
impl fmt::LowerHex for NodePrefix {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let full_bytes = self.nybbles_len() / 2;
for &byte in &self.data[..full_bytes] {
write!(f, "{:02x}", byte)?
}
if self.nybbles_len() % 2 == 1 {
let last = self.nybbles_len() - 1;
write!(f, "{:x}", self.get_nybble(last))?
}
Ok(())
}
}
/// A shortcut for full `Node` references
impl From<&'_ Node> for NodePrefix {
fn from(node: &'_ Node) -> Self {
NodePrefix {
nybbles_len: node.nybbles_len() as _,
data: node.data,
}
}
}
/// A shortcut for full `Node` references
impl From<Node> for NodePrefix {
fn from(node: Node) -> Self {
NodePrefix {
nybbles_len: node.nybbles_len() as _,
data: node.data,
}
}
}
impl PartialEq<Node> for NodePrefix {
fn eq(&self, other: &Node) -> bool {
self.data == other.data && self.nybbles_len() == other.nybbles_len()
}
}
#[cfg(test)]
pub use tests::hex_pad_right;
#[cfg(test)]
mod tests {
use super::*;
const SAMPLE_NODE_HEX: &str = "0123456789abcdeffedcba9876543210deadbeef";
const SAMPLE_NODE: Node = Node {
data: [
0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef, 0xfe, 0xdc, 0xba,
0x98, 0x76, 0x54, 0x32, 0x10, 0xde, 0xad, 0xbe, 0xef,
],
};
/// Pad an hexadecimal string to reach `NODE_NYBBLES_LENGTH`
/// The padding is made with zeros.
pub fn hex_pad_right(hex: &str) -> String {
let mut res = hex.to_string();
while res.len() < NODE_NYBBLES_LENGTH {
res.push('0');
}
res
}
#[test]
fn test_node_from_hex() {
let not_hex = "012... oops";
let too_short = "0123";
let too_long = format!("{}0", SAMPLE_NODE_HEX);
assert_eq!(Node::from_hex(SAMPLE_NODE_HEX).unwrap(), SAMPLE_NODE);
assert!(Node::from_hex(not_hex).is_err());
assert!(Node::from_hex(too_short).is_err());
assert!(Node::from_hex(too_long).is_err());
}
#[test]
fn test_node_encode_hex() {
assert_eq!(format!("{:x}", SAMPLE_NODE), SAMPLE_NODE_HEX);
}
#[test]
fn test_prefix_from_to_hex() -> Result<(), FromHexError> {
assert_eq!(format!("{:x}", NodePrefix::from_hex("0e1")?), "0e1");
assert_eq!(format!("{:x}", NodePrefix::from_hex("0e1a")?), "0e1a");
assert_eq!(
format!("{:x}", NodePrefix::from_hex(SAMPLE_NODE_HEX)?),
SAMPLE_NODE_HEX
);
Ok(())
}
#[test]
fn test_prefix_from_hex_errors() {
assert!(NodePrefix::from_hex("testgr").is_err());
let mut long = format!("{:x}", NULL_NODE);
long.push('c');
assert!(NodePrefix::from_hex(&long).is_err())
}
#[test]
fn test_is_prefix_of() -> Result<(), FromHexError> {
let mut node_data = [0; NODE_BYTES_LENGTH];
node_data[0] = 0x12;
node_data[1] = 0xca;
let node = Node::from(node_data);
assert!(NodePrefix::from_hex("12")?.is_prefix_of(&node));
assert!(!NodePrefix::from_hex("1a")?.is_prefix_of(&node));
assert!(NodePrefix::from_hex("12c")?.is_prefix_of(&node));
assert!(!NodePrefix::from_hex("12d")?.is_prefix_of(&node));
Ok(())
}
#[test]
fn test_get_nybble() -> Result<(), FromHexError> {
let prefix = NodePrefix::from_hex("dead6789cafe")?;
assert_eq!(prefix.get_nybble(0), 13);
assert_eq!(prefix.get_nybble(7), 9);
Ok(())
}
#[test]
fn test_first_different_nybble_even_prefix() {
let prefix = NodePrefix::from_hex("12ca").unwrap();
let mut node = Node::from([0; NODE_BYTES_LENGTH]);
assert_eq!(prefix.first_different_nybble(&node), Some(0));
node.data[0] = 0x13;
assert_eq!(prefix.first_different_nybble(&node), Some(1));
node.data[0] = 0x12;
assert_eq!(prefix.first_different_nybble(&node), Some(2));
node.data[1] = 0xca;
// now it is a prefix
assert_eq!(prefix.first_different_nybble(&node), None);
}
#[test]
fn test_first_different_nybble_odd_prefix() {
let prefix = NodePrefix::from_hex("12c").unwrap();
let mut node = Node::from([0; NODE_BYTES_LENGTH]);
assert_eq!(prefix.first_different_nybble(&node), Some(0));
node.data[0] = 0x13;
assert_eq!(prefix.first_different_nybble(&node), Some(1));
node.data[0] = 0x12;
assert_eq!(prefix.first_different_nybble(&node), Some(2));
node.data[1] = 0xca;
// now it is a prefix
assert_eq!(prefix.first_different_nybble(&node), None);
}
}