D7788: rust-node: binary Node ID and conversion utilities
gracinet (Georges Racinet)
phabricator at mercurial-scm.org
Wed Jan 22 15:53:02 EST 2020
Closed by commit rHG7f86426fdd2c: rust-node: binary Node ID and conversion utilities (authored by gracinet).
gracinet marked 3 inline comments as done.
This revision was automatically updated to reflect the committed changes.
This revision was not accepted when it landed; it landed in state "Needs Review".
REPOSITORY
rHG Mercurial
CHANGES SINCE LAST UPDATE
https://phab.mercurial-scm.org/D7788?vs=19521&id=19523
CHANGES SINCE LAST ACTION
https://phab.mercurial-scm.org/D7788/new/
REVISION DETAIL
https://phab.mercurial-scm.org/D7788
AFFECTED FILES
rust/Cargo.lock
rust/hg-core/Cargo.toml
rust/hg-core/src/revlog.rs
rust/hg-core/src/revlog/node.rs
CHANGE DETAILS
diff --git a/rust/hg-core/src/revlog/node.rs b/rust/hg-core/src/revlog/node.rs
new file mode 100644
--- /dev/null
+++ b/rust/hg-core/src/revlog/node.rs
@@ -0,0 +1,191 @@
+// Copyright 2019-2020 Georges Racinet <georges.racinet at 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 hex::{self, FromHex, FromHexError};
+
+/// 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.
+const NODE_BYTES_LENGTH: usize = 20;
+
+/// 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;
+
+/// 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 fail immediately at runtime with [`ExactLengthRequired`].
+///
+/// [`nybbles_len`]: #method.nybbles_len
+/// [`ExactLengthRequired`]: struct.NodeError#variant.ExactLengthRequired
+#[derive(Clone, Debug, PartialEq)]
+pub struct Node {
+ data: NodeData,
+}
+
+/// The node value for NULL_REVISION
+pub const NULL_NODE: Node = Node {
+ data: [0; NODE_BYTES_LENGTH],
+};
+
+impl From<NodeData> for Node {
+ fn from(data: NodeData) -> Node {
+ Node { data }
+ }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum NodeError {
+ ExactLengthRequired(usize, String),
+ HexError(FromHexError, String),
+}
+
+/// 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: &str) -> Result<Node, NodeError> {
+ Ok(NodeData::from_hex(hex)
+ .map_err(|e| NodeError::from((e, hex)))?
+ .into())
+ }
+
+ /// Convert to hexadecimal string representation
+ ///
+ /// To be used in FFI and I/O only, in order to facilitate future
+ /// changes of hash format.
+ pub fn encode_hex(&self) -> String {
+ hex::encode(self.data)
+ }
+
+ /// 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
+ }
+}
+
+impl From<(FromHexError, &str)> for NodeError {
+ fn from(err_offender: (FromHexError, &str)) -> Self {
+ let (err, offender) = err_offender;
+ match err {
+ FromHexError::InvalidStringLength => {
+ NodeError::ExactLengthRequired(
+ NODE_NYBBLES_LENGTH,
+ offender.to_string(),
+ )
+ }
+ _ => NodeError::HexError(err, offender.to_string()),
+ }
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ fn sample_node() -> Node {
+ let mut data = [0; NODE_BYTES_LENGTH];
+ data.copy_from_slice(&[
+ 0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef, 0xfe, 0xdc, 0xba,
+ 0x98, 0x76, 0x54, 0x32, 0x10, 0xde, 0xad, 0xbe, 0xef,
+ ]);
+ data.into()
+ }
+
+ /// Pad an hexadecimal string to reach `NODE_NYBBLES_LENGTH`
+ ///
+ /// The padding is made with zeros
+ fn hex_pad_right(hex: &str) -> String {
+ let mut res = hex.to_string();
+ while res.len() < NODE_NYBBLES_LENGTH {
+ res.push('0');
+ }
+ res
+ }
+
+ fn sample_node_hex() -> String {
+ hex_pad_right("0123456789abcdeffedcba9876543210deadbeef")
+ }
+
+ #[test]
+ fn test_node_from_hex() {
+ assert_eq!(Node::from_hex(&sample_node_hex()), Ok(sample_node()));
+
+ let mut short = hex_pad_right("0123");
+ short.pop();
+ short.pop();
+ assert_eq!(
+ Node::from_hex(&short),
+ Err(NodeError::ExactLengthRequired(NODE_NYBBLES_LENGTH, short)),
+ );
+
+ let not_hex = hex_pad_right("012... oops");
+ assert_eq!(
+ Node::from_hex(¬_hex),
+ Err(NodeError::HexError(
+ FromHexError::InvalidHexCharacter { c: '.', index: 3 },
+ not_hex,
+ )),
+ );
+ }
+
+ #[test]
+ fn test_node_encode_hex() {
+ assert_eq!(sample_node().encode_hex(), sample_node_hex());
+ }
+}
diff --git a/rust/hg-core/src/revlog.rs b/rust/hg-core/src/revlog.rs
--- a/rust/hg-core/src/revlog.rs
+++ b/rust/hg-core/src/revlog.rs
@@ -5,7 +5,9 @@
// GNU General Public License version 2 or any later version.
//! Mercurial concepts for handling revision history
+pub mod node;
pub mod nodemap;
+pub use node::{Node, NodeError};
/// Mercurial revision numbers
///
diff --git a/rust/hg-core/Cargo.toml b/rust/hg-core/Cargo.toml
--- a/rust/hg-core/Cargo.toml
+++ b/rust/hg-core/Cargo.toml
@@ -10,6 +10,7 @@
[dependencies]
byteorder = "1.3.1"
+hex = "0.4.0"
lazy_static = "1.3.0"
memchr = "2.2.0"
rand = "0.6.5"
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -124,10 +124,16 @@
]
[[package]]
+name = "hex"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
name = "hg-core"
version = "0.1.0"
dependencies = [
"byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
"lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
"memchr 2.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
"rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -483,6 +489,7 @@
"checksum either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "bb1f6b1ce1c140482ea30ddd3335fc0024ac7ee112895426e0a629a6c20adfe3"
"checksum fuchsia-cprng 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
"checksum getrandom 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "473a1265acc8ff1e808cd0a1af8cee3c2ee5200916058a2ca113c29f2d903571"
+"checksum hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "023b39be39e3a2da62a94feb433e91e8bcd37676fbc8bea371daf52b7a769a3e"
"checksum lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
"checksum libc 0.2.64 (registry+https://github.com/rust-lang/crates.io-index)" = "74dfca3d9957906e8d1e6a0b641dc9a59848e793f1da2165889fd4f62d10d79c"
"checksum memchr 2.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88579771288728879b57485cc7d6b07d648c9f0141eb955f8ab7f9d45394468e"
To: gracinet, #hg-reviewers, kevincox, martinvonz
Cc: martinvonz, durin42, kevincox, mercurial-devel
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