--- a/rust/hg-core/src/dirstate_tree/on_disk.rs Wed May 19 13:15:00 2021 +0200
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs Wed May 19 13:15:00 2021 +0200
@@ -1,4 +1,335 @@
+//! The "version 2" disk representation of the dirstate
+//!
+//! # File format
+//!
+//! The file starts with a fixed-sized header, whose layout is defined by the
+//! `Header` struct. Its `root` field contains the slice (offset and length) to
+//! the nodes representing the files and directories at the root of the
+//! repository. Each node is also fixed-size, defined by the `Node` struct.
+//! Nodes in turn contain slices to variable-size paths, and to their own child
+//! nodes (if any) for nested files and directories.
+
+use crate::dirstate::parsers::clear_ambiguous_mtime;
+use crate::dirstate::parsers::Timestamp;
+use crate::dirstate_tree::dirstate_map::{self, DirstateMap};
+use crate::dirstate_tree::path_with_basename::WithBasename;
+use crate::errors::HgError;
+use crate::utils::hg_path::HgPath;
+use crate::DirstateEntry;
+use crate::DirstateError;
+use crate::DirstateParents;
+use bytes_cast::unaligned::{I32Be, U32Be, U64Be};
+use bytes_cast::BytesCast;
+use std::borrow::Cow;
+use std::convert::{TryFrom, TryInto};
+
/// Added at the start of `.hg/dirstate` when the "v2" format is used.
-/// Acts like a "magic number". This is a sanity check, not strictly necessary
-/// since `.hg/requires` already governs which format should be used.
+/// This a redundant sanity check more than an actual "magic number" since
+/// `.hg/requires` already governs which format should be used.
pub const V2_FORMAT_MARKER: &[u8; 12] = b"dirstate-v2\n";
+
+#[derive(BytesCast)]
+#[repr(C)]
+struct Header {
+ marker: [u8; V2_FORMAT_MARKER.len()],
+
+ /// `dirstatemap.parents()` in `mercurial/dirstate.py` relies on this
+ /// `parents` field being at this offset, immediately after `marker`.
+ parents: DirstateParents,
+
+ root: ChildNodes,
+ nodes_with_entry_count: Size,
+ nodes_with_copy_source_count: Size,
+}
+
+#[derive(BytesCast)]
+#[repr(C)]
+struct Node {
+ full_path: PathSlice,
+
+ /// In bytes from `self.full_path.start`
+ base_name_start: Size,
+
+ copy_source: OptPathSlice,
+ entry: OptEntry,
+ children: ChildNodes,
+ tracked_descendants_count: Size,
+}
+
+/// Either nothing if `state == b'\0'`, or a dirstate entry like in the v1
+/// format
+#[derive(BytesCast)]
+#[repr(C)]
+struct OptEntry {
+ state: u8,
+ mode: I32Be,
+ mtime: I32Be,
+ size: I32Be,
+}
+
+/// Counted in bytes from the start of the file
+///
+/// NOTE: If we decide to never support `.hg/dirstate` files larger than 4 GiB
+/// we could save space by using `U32Be` instead.
+type Offset = U64Be;
+
+/// Counted in number of items
+///
+/// NOTE: not supporting directories with more than 4 billion direct children,
+/// or filenames more than 4 GiB.
+type Size = U32Be;
+
+/// Location of consecutive, fixed-size items.
+///
+/// An item can be a single byte for paths, or a struct with
+/// `derive(BytesCast)`.
+#[derive(BytesCast, Copy, Clone)]
+#[repr(C)]
+struct Slice {
+ start: Offset,
+ len: Size,
+}
+
+/// A contiguous sequence of `len` times `Node`, representing the child nodes
+/// of either some other node or of the repository root.
+///
+/// Always sorted by ascending `full_path`, to allow binary search.
+/// Since nodes with the same parent nodes also have the same parent path,
+/// only the `base_name`s need to be compared during binary search.
+type ChildNodes = Slice;
+
+/// A `HgPath` of `len` bytes
+type PathSlice = Slice;
+
+/// Either nothing if `start == 0`, or a `HgPath` of `len` bytes
+type OptPathSlice = Slice;
+
+/// Make sure that size-affecting changes are made knowingly
+fn _static_assert_size_of() {
+ let _ = std::mem::transmute::<Header, [u8; 72]>;
+ let _ = std::mem::transmute::<Node, [u8; 57]>;
+}
+
+pub(super) fn read<'on_disk>(
+ on_disk: &'on_disk [u8],
+) -> Result<(DirstateMap<'on_disk>, Option<DirstateParents>), DirstateError> {
+ if on_disk.is_empty() {
+ return Ok((DirstateMap::empty(on_disk), None));
+ }
+ let (header, _) = Header::from_bytes(on_disk)
+ .map_err(|_| HgError::corrupted("truncated dirstate-v2"))?;
+ let Header {
+ marker,
+ parents,
+ root,
+ nodes_with_entry_count,
+ nodes_with_copy_source_count,
+ } = header;
+ if marker != V2_FORMAT_MARKER {
+ return Err(HgError::corrupted("missing dirstated-v2 marker").into());
+ }
+ let dirstate_map = DirstateMap {
+ on_disk,
+ root: read_nodes(on_disk, *root)?,
+ nodes_with_entry_count: nodes_with_entry_count.get(),
+ nodes_with_copy_source_count: nodes_with_copy_source_count.get(),
+ };
+ let parents = Some(parents.clone());
+ Ok((dirstate_map, parents))
+}
+
+impl Node {
+ pub(super) fn path<'on_disk>(
+ &self,
+ on_disk: &'on_disk [u8],
+ ) -> Result<dirstate_map::NodeKey<'on_disk>, HgError> {
+ let full_path = read_hg_path(on_disk, self.full_path)?;
+ let base_name_start = usize::try_from(self.base_name_start.get())
+ // u32 -> usize, could only panic on a 16-bit CPU
+ .expect("dirstate-v2 base_name_start out of bounds");
+ if base_name_start < full_path.len() {
+ Ok(WithBasename::from_raw_parts(full_path, base_name_start))
+ } else {
+ Err(HgError::corrupted(
+ "dirstate-v2 base_name_start out of bounds",
+ ))
+ }
+ }
+
+ pub(super) fn copy_source<'on_disk>(
+ &self,
+ on_disk: &'on_disk [u8],
+ ) -> Result<Option<Cow<'on_disk, HgPath>>, HgError> {
+ Ok(if self.copy_source.start.get() != 0 {
+ Some(read_hg_path(on_disk, self.copy_source)?)
+ } else {
+ None
+ })
+ }
+
+ pub(super) fn entry(&self) -> Result<Option<DirstateEntry>, HgError> {
+ Ok(if self.entry.state != b'\0' {
+ Some(DirstateEntry {
+ state: self.entry.state.try_into()?,
+ mode: self.entry.mode.get(),
+ mtime: self.entry.mtime.get(),
+ size: self.entry.size.get(),
+ })
+ } else {
+ None
+ })
+ }
+
+ pub(super) fn to_in_memory_node<'on_disk>(
+ &self,
+ on_disk: &'on_disk [u8],
+ ) -> Result<dirstate_map::Node<'on_disk>, HgError> {
+ Ok(dirstate_map::Node {
+ children: read_nodes(on_disk, self.children)?,
+ copy_source: self.copy_source(on_disk)?,
+ entry: self.entry()?,
+ tracked_descendants_count: self.tracked_descendants_count.get(),
+ })
+ }
+}
+
+fn read_nodes(
+ on_disk: &[u8],
+ slice: ChildNodes,
+) -> Result<dirstate_map::ChildNodes, HgError> {
+ read_slice::<Node>(on_disk, slice)?
+ .iter()
+ .map(|node| {
+ Ok((node.path(on_disk)?, node.to_in_memory_node(on_disk)?))
+ })
+ .collect()
+}
+
+fn read_hg_path(on_disk: &[u8], slice: Slice) -> Result<Cow<HgPath>, HgError> {
+ let bytes = read_slice::<u8>(on_disk, slice)?;
+ Ok(Cow::Borrowed(HgPath::new(bytes)))
+}
+
+fn read_slice<T>(on_disk: &[u8], slice: Slice) -> Result<&[T], HgError>
+where
+ T: BytesCast,
+{
+ // Either `usize::MAX` would result in "out of bounds" error since a single
+ // `&[u8]` cannot occupy the entire addess space.
+ let start = usize::try_from(slice.start.get()).unwrap_or(std::usize::MAX);
+ let len = usize::try_from(slice.len.get()).unwrap_or(std::usize::MAX);
+ on_disk
+ .get(start..)
+ .and_then(|bytes| T::slice_from_bytes(bytes, len).ok())
+ .map(|(slice, _rest)| slice)
+ .ok_or_else(|| {
+ HgError::corrupted("dirstate v2 slice is out of bounds")
+ })
+}
+
+pub(super) fn write(
+ dirstate_map: &mut DirstateMap,
+ parents: DirstateParents,
+ now: Timestamp,
+) -> Result<Vec<u8>, DirstateError> {
+ // TODO: how do we want to handle this in 2038?
+ let now: i32 = now.0.try_into().expect("time overflow");
+
+ let header_len = std::mem::size_of::<Header>();
+
+ // This ignores the space for paths, and for nodes without an entry.
+ // TODO: better estimate? Skip the `Vec` and write to a file directly?
+ let size_guess = header_len
+ + std::mem::size_of::<Node>()
+ * dirstate_map.nodes_with_entry_count as usize;
+ let mut out = Vec::with_capacity(size_guess);
+
+ // Keep space for the header. We’ll fill it out at the end when we know the
+ // actual offset for the root nodes.
+ out.resize(header_len, 0_u8);
+
+ let root = write_nodes(&mut dirstate_map.root, now, &mut out)?;
+
+ let header = Header {
+ marker: *V2_FORMAT_MARKER,
+ parents: parents,
+ root,
+ nodes_with_entry_count: dirstate_map.nodes_with_entry_count.into(),
+ nodes_with_copy_source_count: dirstate_map
+ .nodes_with_copy_source_count
+ .into(),
+ };
+ out[..header_len].copy_from_slice(header.as_bytes());
+ Ok(out)
+}
+
+/// Serialize the dirstate to the `v2` format after clearing ambigous `mtime`s.
+fn write_nodes(
+ nodes: &mut dirstate_map::ChildNodes,
+ now: i32,
+ out: &mut Vec<u8>,
+) -> Result<ChildNodes, DirstateError> {
+ // `dirstate_map::ChildNodes` is a `HashMap` with undefined iteration
+ // order. Sort to enable binary search in the written file.
+ let nodes = dirstate_map::Node::sorted(nodes);
+
+ // First accumulate serialized nodes in a `Vec`
+ let mut on_disk_nodes = Vec::with_capacity(nodes.len());
+ for (full_path, node) in nodes {
+ on_disk_nodes.push(Node {
+ children: write_nodes(&mut node.children, now, out)?,
+ tracked_descendants_count: node.tracked_descendants_count.into(),
+ full_path: write_slice::<u8>(
+ full_path.full_path().as_bytes(),
+ out,
+ ),
+ base_name_start: u32::try_from(full_path.base_name_start())
+ // Could only panic for paths over 4 GiB
+ .expect("dirstate-v2 offset overflow")
+ .into(),
+ copy_source: if let Some(source) = &node.copy_source {
+ write_slice::<u8>(source.as_bytes(), out)
+ } else {
+ Slice {
+ start: 0.into(),
+ len: 0.into(),
+ }
+ },
+ entry: if let Some(entry) = &mut node.entry {
+ clear_ambiguous_mtime(entry, now);
+ OptEntry {
+ state: entry.state.into(),
+ mode: entry.mode.into(),
+ mtime: entry.mtime.into(),
+ size: entry.size.into(),
+ }
+ } else {
+ OptEntry {
+ state: b'\0',
+ mode: 0.into(),
+ mtime: 0.into(),
+ size: 0.into(),
+ }
+ },
+ })
+ }
+ // … so we can write them contiguously
+ Ok(write_slice::<Node>(&on_disk_nodes, out))
+}
+
+fn write_slice<T>(slice: &[T], out: &mut Vec<u8>) -> Slice
+where
+ T: BytesCast,
+{
+ let start = u64::try_from(out.len())
+ // Could only panic on a 128-bit CPU with a dirstate over 16 EiB
+ .expect("dirstate-v2 offset overflow")
+ .into();
+ let len = u32::try_from(slice.len())
+ // Could only panic for paths over 4 GiB or nodes with over 4 billions
+ // child nodes
+ .expect("dirstate-v2 offset overflow")
+ .into();
+ out.extend(slice.as_bytes());
+ Slice { start, len }
+}