rust/hg-core/src/revlog/mod.rs

rust-index: drop offset_override

The inline `offsets` value diverge from the one on disk for added value, so the
offset_override tricks is not going to work well once we start having the full
revlog logic in Rust.

We remove it beforehand and align the Rust logic to the Python one (adjusting
the segment offset at read time for inline revlog).

// Copyright 2018-2023 Georges Racinet <[e-mail]>
//           and Mercurial contributors
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.
//! Mercurial concepts for handling revision history

pub mod node;
pub mod nodemap;
mod nodemap_docket;
pub mod path_encode;
pub use node::{FromHexError, Node, NodePrefix};
pub mod changelog;
pub mod filelog;
pub mod index;
pub mod manifest;
pub mod patch;

use std::borrow::Cow;
use std::io::Read;
use std::ops::Deref;
use std::path::Path;

use flate2::read::ZlibDecoder;
use sha1::{Digest, Sha1};
use std::cell::RefCell;
use zstd;

use self::node::{NODE_BYTES_LENGTH, NULL_NODE};
use self::nodemap_docket::NodeMapDocket;
use super::index::Index;
use super::index::INDEX_ENTRY_SIZE;
use super::nodemap::{NodeMap, NodeMapError};
use crate::errors::HgError;
use crate::vfs::Vfs;

/// As noted in revlog.c, revision numbers are actually encoded in
/// 4 bytes, and are liberally converted to ints, whence the i32
pub type BaseRevision = i32;

/// Mercurial revision numbers
/// In contrast to the more general [`UncheckedRevision`], these are "checked"
/// in the sense that they should only be used for revisions that are
/// valid for a given index (i.e. in bounds).
#[derive(
    Debug,
    derive_more::Display,
    Clone,
    Copy,
    Hash,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
)]
pub struct Revision(pub BaseRevision);

impl format_bytes::DisplayBytes for Revision {
    fn display_bytes(
        &self,
        output: &mut dyn std::io::Write,
    ) -> std::io::Result<()> {
        self.0.display_bytes(output)
    }
}

/// Unchecked Mercurial revision numbers.
///
/// Values of this type have no guarantee of being a valid revision number
/// in any context. Use method `check_revision` to get a valid revision within
/// the appropriate index object.
#[derive(
    Debug,
    derive_more::Display,
    Clone,
    Copy,
    Hash,
    PartialEq,
    Eq,
    PartialOrd,
    Ord,
)]
pub struct UncheckedRevision(pub BaseRevision);

impl format_bytes::DisplayBytes for UncheckedRevision {
    fn display_bytes(
        &self,
        output: &mut dyn std::io::Write,
    ) -> std::io::Result<()> {
        self.0.display_bytes(output)
    }
}

impl From<Revision> for UncheckedRevision {
    fn from(value: Revision) -> Self {
        Self(value.0)
    }
}

impl From<BaseRevision> for UncheckedRevision {
    fn from(value: BaseRevision) -> Self {
        Self(value)
    }
}

/// Marker expressing the absence of a parent
///
/// Independently of the actual representation, `NULL_REVISION` is guaranteed
/// to be smaller than all existing revisions.
pub const NULL_REVISION: Revision = Revision(-1);

/// Same as `mercurial.node.wdirrev`
///
/// This is also equal to `i32::max_value()`, but it's better to spell
/// it out explicitely, same as in `mercurial.node`
#[allow(clippy::unreadable_literal)]
pub const WORKING_DIRECTORY_REVISION: UncheckedRevision =
    UncheckedRevision(0x7fffffff);

pub const WORKING_DIRECTORY_HEX: &str =
    "ffffffffffffffffffffffffffffffffffffffff";

/// The simplest expression of what we need of Mercurial DAGs.
pub trait Graph {
    /// Return the two parents of the given `Revision`.
    ///
    /// Each of the parents can be independently `NULL_REVISION`
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError>;
}

#[derive(Clone, Debug, PartialEq)]
pub enum GraphError {
    ParentOutOfRange(Revision),
}

/// The Mercurial Revlog Index
///
/// This is currently limited to the minimal interface that is needed for
/// the [`nodemap`](nodemap/index.html) module
pub trait RevlogIndex {
    /// Total number of Revisions referenced in this index
    fn len(&self) -> usize;

    fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Return a reference to the Node or `None` for `NULL_REVISION`
    fn node(&self, rev: Revision) -> Option<&Node>;

    /// Return a [`Revision`] if `rev` is a valid revision number for this
    /// index.
    ///
    /// [`NULL_REVISION`] is considered to be valid.
    #[inline(always)]
    fn check_revision(&self, rev: UncheckedRevision) -> Option<Revision> {
        let rev = rev.0;

        if rev == NULL_REVISION.0 || (rev >= 0 && (rev as usize) < self.len())
        {
            Some(Revision(rev))
        } else {
            None
        }
    }
}

const REVISION_FLAG_CENSORED: u16 = 1 << 15;
const REVISION_FLAG_ELLIPSIS: u16 = 1 << 14;
const REVISION_FLAG_EXTSTORED: u16 = 1 << 13;
const REVISION_FLAG_HASCOPIESINFO: u16 = 1 << 12;

// Keep this in sync with REVIDX_KNOWN_FLAGS in
// mercurial/revlogutils/flagutil.py
const REVIDX_KNOWN_FLAGS: u16 = REVISION_FLAG_CENSORED
    | REVISION_FLAG_ELLIPSIS
    | REVISION_FLAG_EXTSTORED
    | REVISION_FLAG_HASCOPIESINFO;

const NULL_REVLOG_ENTRY_FLAGS: u16 = 0;

#[derive(Debug, derive_more::From, derive_more::Display)]
pub enum RevlogError {
    InvalidRevision,
    /// Working directory is not supported
    WDirUnsupported,
    /// Found more than one entry whose ID match the requested prefix
    AmbiguousPrefix,
    #[from]
    Other(HgError),
}

impl From<NodeMapError> for RevlogError {
    fn from(error: NodeMapError) -> Self {
        match error {
            NodeMapError::MultipleResults => RevlogError::AmbiguousPrefix,
            NodeMapError::RevisionNotInIndex(rev) => RevlogError::corrupted(
                format!("nodemap point to revision {} not in index", rev),
            ),
        }
    }
}

fn corrupted<S: AsRef<str>>(context: S) -> HgError {
    HgError::corrupted(format!("corrupted revlog, {}", context.as_ref()))
}

impl RevlogError {
    fn corrupted<S: AsRef<str>>(context: S) -> Self {
        RevlogError::Other(corrupted(context))
    }
}

/// Read only implementation of revlog.
pub struct Revlog {
    /// When index and data are not interleaved: bytes of the revlog index.
    /// When index and data are interleaved: bytes of the revlog index and
    /// data.
    index: Index,
    /// When index and data are not interleaved: bytes of the revlog data
    data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>>,
    /// When present on disk: the persistent nodemap for this revlog
    nodemap: Option<nodemap::NodeTree>,
}

impl Graph for Revlog {
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
        self.index.parents(rev)
    }
}

#[derive(Debug, Copy, Clone)]
pub enum RevlogVersionOptions {
    V0,
    V1 { generaldelta: bool },
    V2,
    ChangelogV2 { compute_rank: bool },
}

/// Options to govern how a revlog should be opened, usually from the
/// repository configuration or requirements.
#[derive(Debug, Copy, Clone)]
pub struct RevlogOpenOptions {
    /// The revlog version, along with any option specific to this version
    pub version: RevlogVersionOptions,
    /// Whether the revlog uses a persistent nodemap.
    pub use_nodemap: bool,
    // TODO other non-header/version options,
}

impl RevlogOpenOptions {
    pub fn new() -> Self {
        Self {
            version: RevlogVersionOptions::V1 { generaldelta: true },
            use_nodemap: false,
        }
    }

    fn default_index_header(&self) -> index::IndexHeader {
        index::IndexHeader {
            header_bytes: match self.version {
                RevlogVersionOptions::V0 => [0, 0, 0, 0],
                RevlogVersionOptions::V1 { generaldelta } => {
                    [0, if generaldelta { 3 } else { 1 }, 0, 1]
                }
                RevlogVersionOptions::V2 => 0xDEADu32.to_be_bytes(),
                RevlogVersionOptions::ChangelogV2 { compute_rank: _ } => {
                    0xD34Du32.to_be_bytes()
                }
            },
        }
    }
}

impl Default for RevlogOpenOptions {
    fn default() -> Self {
        Self::new()
    }
}

impl Revlog {
    /// Open a revlog index file.
    ///
    /// It will also open the associated data file if index and data are not
    /// interleaved.
    pub fn open(
        store_vfs: &Vfs,
        index_path: impl AsRef<Path>,
        data_path: Option<&Path>,
        options: RevlogOpenOptions,
    ) -> Result<Self, HgError> {
        Self::open_gen(store_vfs, index_path, data_path, options, None)
    }

    fn open_gen(
        store_vfs: &Vfs,
        index_path: impl AsRef<Path>,
        data_path: Option<&Path>,
        options: RevlogOpenOptions,
        nodemap_for_test: Option<nodemap::NodeTree>,
    ) -> Result<Self, HgError> {
        let index_path = index_path.as_ref();
        let index = {
            match store_vfs.mmap_open_opt(index_path)? {
                None => Index::new(
                    Box::<Vec<_>>::default(),
                    options.default_index_header(),
                ),
                Some(index_mmap) => {
                    let index = Index::new(
                        Box::new(index_mmap),
                        options.default_index_header(),
                    )?;
                    Ok(index)
                }
            }
        }?;

        let default_data_path = index_path.with_extension("d");

        // type annotation required
        // won't recognize Mmap as Deref<Target = [u8]>
        let data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>> =
            if index.is_inline() {
                None
            } else {
                let data_path = data_path.unwrap_or(&default_data_path);
                let data_mmap = store_vfs.mmap_open(data_path)?;
                Some(Box::new(data_mmap))
            };

        let nodemap = if index.is_inline() || !options.use_nodemap {
            None
        } else {
            NodeMapDocket::read_from_file(store_vfs, index_path)?.map(
                |(docket, data)| {
                    nodemap::NodeTree::load_bytes(
                        Box::new(data),
                        docket.data_length,
                    )
                },
            )
        };

        let nodemap = nodemap_for_test.or(nodemap);

        Ok(Revlog {
            index,
            data_bytes,
            nodemap,
        })
    }

    /// Return number of entries of the `Revlog`.
    pub fn len(&self) -> usize {
        self.index.len()
    }

    /// Returns `true` if the `Revlog` has zero `entries`.
    pub fn is_empty(&self) -> bool {
        self.index.is_empty()
    }

    /// Returns the node ID for the given revision number, if it exists in this
    /// revlog
    pub fn node_from_rev(&self, rev: UncheckedRevision) -> Option<&Node> {
        if rev == NULL_REVISION.into() {
            return Some(&NULL_NODE);
        }
        let rev = self.index.check_revision(rev)?;
        Some(self.index.get_entry(rev)?.hash())
    }

    /// Return the revision number for the given node ID, if it exists in this
    /// revlog
    pub fn rev_from_node(
        &self,
        node: NodePrefix,
    ) -> Result<Revision, RevlogError> {
        if let Some(nodemap) = &self.nodemap {
            nodemap
                .find_bin(&self.index, node)?
                .ok_or(RevlogError::InvalidRevision)
        } else {
            self.rev_from_node_no_persistent_nodemap(node)
        }
    }

    /// Same as `rev_from_node`, without using a persistent nodemap
    ///
    /// This is used as fallback when a persistent nodemap is not present.
    /// This happens when the persistent-nodemap experimental feature is not
    /// enabled, or for small revlogs.
    fn rev_from_node_no_persistent_nodemap(
        &self,
        node: NodePrefix,
    ) -> Result<Revision, RevlogError> {
        // Linear scan of the revlog
        // TODO: consider building a non-persistent nodemap in memory to
        // optimize these cases.
        let mut found_by_prefix = None;
        for rev in (-1..self.len() as BaseRevision).rev() {
            let rev = Revision(rev as BaseRevision);
            let candidate_node = if rev == Revision(-1) {
                NULL_NODE
            } else {
                let index_entry =
                    self.index.get_entry(rev).ok_or_else(|| {
                        HgError::corrupted(
                            "revlog references a revision not in the index",
                        )
                    })?;
                *index_entry.hash()
            };
            if node == candidate_node {
                return Ok(rev);
            }
            if node.is_prefix_of(&candidate_node) {
                if found_by_prefix.is_some() {
                    return Err(RevlogError::AmbiguousPrefix);
                }
                found_by_prefix = Some(rev)
            }
        }
        found_by_prefix.ok_or(RevlogError::InvalidRevision)
    }

    /// Returns whether the given revision exists in this revlog.
    pub fn has_rev(&self, rev: UncheckedRevision) -> bool {
        self.index.check_revision(rev).is_some()
    }

    /// Return the full data associated to a revision.
    ///
    /// All entries required to build the final data out of deltas will be
    /// retrieved as needed, and the deltas will be applied to the inital
    /// snapshot to rebuild the final data.
    pub fn get_rev_data(
        &self,
        rev: UncheckedRevision,
    ) -> Result<Cow<[u8]>, RevlogError> {
        if rev == NULL_REVISION.into() {
            return Ok(Cow::Borrowed(&[]));
        };
        self.get_entry(rev)?.data()
    }

    /// [`Self::get_rev_data`] for checked revisions.
    pub fn get_rev_data_for_checked_rev(
        &self,
        rev: Revision,
    ) -> Result<Cow<[u8]>, RevlogError> {
        if rev == NULL_REVISION {
            return Ok(Cow::Borrowed(&[]));
        };
        self.get_entry_for_checked_rev(rev)?.data()
    }

    /// Check the hash of some given data against the recorded hash.
    pub fn check_hash(
        &self,
        p1: Revision,
        p2: Revision,
        expected: &[u8],
        data: &[u8],
    ) -> bool {
        let e1 = self.index.get_entry(p1);
        let h1 = match e1 {
            Some(ref entry) => entry.hash(),
            None => &NULL_NODE,
        };
        let e2 = self.index.get_entry(p2);
        let h2 = match e2 {
            Some(ref entry) => entry.hash(),
            None => &NULL_NODE,
        };

        hash(data, h1.as_bytes(), h2.as_bytes()) == expected
    }

    /// Build the full data of a revision out its snapshot
    /// and its deltas.
    fn build_data_from_deltas(
        snapshot: RevlogEntry,
        deltas: &[RevlogEntry],
    ) -> Result<Vec<u8>, HgError> {
        let snapshot = snapshot.data_chunk()?;
        let deltas = deltas
            .iter()
            .rev()
            .map(RevlogEntry::data_chunk)
            .collect::<Result<Vec<_>, _>>()?;
        let patches: Vec<_> =
            deltas.iter().map(|d| patch::PatchList::new(d)).collect();
        let patch = patch::fold_patch_lists(&patches);
        Ok(patch.apply(&snapshot))
    }

    /// Return the revlog data.
    fn data(&self) -> &[u8] {
        match &self.data_bytes {
            Some(data_bytes) => data_bytes,
            None => panic!(
                "forgot to load the data or trying to access inline data"
            ),
        }
    }

    pub fn make_null_entry(&self) -> RevlogEntry {
        RevlogEntry {
            revlog: self,
            rev: NULL_REVISION,
            bytes: b"",
            compressed_len: 0,
            uncompressed_len: 0,
            base_rev_or_base_of_delta_chain: None,
            p1: NULL_REVISION,
            p2: NULL_REVISION,
            flags: NULL_REVLOG_ENTRY_FLAGS,
            hash: NULL_NODE,
        }
    }

    fn get_entry_for_checked_rev(
        &self,
        rev: Revision,
    ) -> Result<RevlogEntry, RevlogError> {
        if rev == NULL_REVISION {
            return Ok(self.make_null_entry());
        }
        let index_entry = self
            .index
            .get_entry(rev)
            .ok_or(RevlogError::InvalidRevision)?;
        let offset = index_entry.offset();
        let start = if self.index.is_inline() {
            offset + ((rev.0 as usize + 1) * INDEX_ENTRY_SIZE)
        } else {
            offset
        };
        let end = start + index_entry.compressed_len() as usize;
        let data = if self.index.is_inline() {
            self.index.data(start, end)
        } else {
            &self.data()[start..end]
        };
        let base_rev = self
            .index
            .check_revision(index_entry.base_revision_or_base_of_delta_chain())
            .ok_or_else(|| {
                RevlogError::corrupted(format!(
                    "base revision for rev {} is invalid",
                    rev
                ))
            })?;
        let p1 =
            self.index.check_revision(index_entry.p1()).ok_or_else(|| {
                RevlogError::corrupted(format!(
                    "p1 for rev {} is invalid",
                    rev
                ))
            })?;
        let p2 =
            self.index.check_revision(index_entry.p2()).ok_or_else(|| {
                RevlogError::corrupted(format!(
                    "p2 for rev {} is invalid",
                    rev
                ))
            })?;
        let entry = RevlogEntry {
            revlog: self,
            rev,
            bytes: data,
            compressed_len: index_entry.compressed_len(),
            uncompressed_len: index_entry.uncompressed_len(),
            base_rev_or_base_of_delta_chain: if base_rev == rev {
                None
            } else {
                Some(base_rev)
            },
            p1,
            p2,
            flags: index_entry.flags(),
            hash: *index_entry.hash(),
        };
        Ok(entry)
    }

    /// Get an entry of the revlog.
    pub fn get_entry(
        &self,
        rev: UncheckedRevision,
    ) -> Result<RevlogEntry, RevlogError> {
        if rev == NULL_REVISION.into() {
            return Ok(self.make_null_entry());
        }
        let rev = self.index.check_revision(rev).ok_or_else(|| {
            RevlogError::corrupted(format!("rev {} is invalid", rev))
        })?;
        self.get_entry_for_checked_rev(rev)
    }
}

/// The revlog entry's bytes and the necessary informations to extract
/// the entry's data.
#[derive(Clone)]
pub struct RevlogEntry<'revlog> {
    revlog: &'revlog Revlog,
    rev: Revision,
    bytes: &'revlog [u8],
    compressed_len: u32,
    uncompressed_len: i32,
    base_rev_or_base_of_delta_chain: Option<Revision>,
    p1: Revision,
    p2: Revision,
    flags: u16,
    hash: Node,
}

thread_local! {
  // seems fine to [unwrap] here: this can only fail due to memory allocation
  // failing, and it's normal for that to cause panic.
  static ZSTD_DECODER : RefCell<zstd::bulk::Decompressor<'static>> =
      RefCell::new(zstd::bulk::Decompressor::new().ok().unwrap());
}

fn zstd_decompress_to_buffer(
    bytes: &[u8],
    buf: &mut Vec<u8>,
) -> Result<usize, std::io::Error> {
    ZSTD_DECODER
        .with(|decoder| decoder.borrow_mut().decompress_to_buffer(bytes, buf))
}

impl<'revlog> RevlogEntry<'revlog> {
    pub fn revision(&self) -> Revision {
        self.rev
    }

    pub fn node(&self) -> &Node {
        &self.hash
    }

    pub fn uncompressed_len(&self) -> Option<u32> {
        u32::try_from(self.uncompressed_len).ok()
    }

    pub fn has_p1(&self) -> bool {
        self.p1 != NULL_REVISION
    }

    pub fn p1_entry(
        &self,
    ) -> Result<Option<RevlogEntry<'revlog>>, RevlogError> {
        if self.p1 == NULL_REVISION {
            Ok(None)
        } else {
            Ok(Some(self.revlog.get_entry_for_checked_rev(self.p1)?))
        }
    }

    pub fn p2_entry(
        &self,
    ) -> Result<Option<RevlogEntry<'revlog>>, RevlogError> {
        if self.p2 == NULL_REVISION {
            Ok(None)
        } else {
            Ok(Some(self.revlog.get_entry_for_checked_rev(self.p2)?))
        }
    }

    pub fn p1(&self) -> Option<Revision> {
        if self.p1 == NULL_REVISION {
            None
        } else {
            Some(self.p1)
        }
    }

    pub fn p2(&self) -> Option<Revision> {
        if self.p2 == NULL_REVISION {
            None
        } else {
            Some(self.p2)
        }
    }

    pub fn is_censored(&self) -> bool {
        (self.flags & REVISION_FLAG_CENSORED) != 0
    }

    pub fn has_length_affecting_flag_processor(&self) -> bool {
        // Relevant Python code: revlog.size()
        // note: ELLIPSIS is known to not change the content
        (self.flags & (REVIDX_KNOWN_FLAGS ^ REVISION_FLAG_ELLIPSIS)) != 0
    }

    /// The data for this entry, after resolving deltas if any.
    pub fn rawdata(&self) -> Result<Cow<'revlog, [u8]>, RevlogError> {
        let mut entry = self.clone();
        let mut delta_chain = vec![];

        // The meaning of `base_rev_or_base_of_delta_chain` depends on
        // generaldelta. See the doc on `ENTRY_DELTA_BASE` in
        // `mercurial/revlogutils/constants.py` and the code in
        // [_chaininfo] and in [index_deltachain].
        let uses_generaldelta = self.revlog.index.uses_generaldelta();
        while let Some(base_rev) = entry.base_rev_or_base_of_delta_chain {
            entry = if uses_generaldelta {
                delta_chain.push(entry);
                self.revlog.get_entry_for_checked_rev(base_rev)?
            } else {
                let base_rev = UncheckedRevision(entry.rev.0 - 1);
                delta_chain.push(entry);
                self.revlog.get_entry(base_rev)?
            };
        }

        let data = if delta_chain.is_empty() {
            entry.data_chunk()?
        } else {
            Revlog::build_data_from_deltas(entry, &delta_chain)?.into()
        };

        Ok(data)
    }

    fn check_data(
        &self,
        data: Cow<'revlog, [u8]>,
    ) -> Result<Cow<'revlog, [u8]>, RevlogError> {
        if self.revlog.check_hash(
            self.p1,
            self.p2,
            self.hash.as_bytes(),
            &data,
        ) {
            Ok(data)
        } else {
            if (self.flags & REVISION_FLAG_ELLIPSIS) != 0 {
                return Err(HgError::unsupported(
                    "ellipsis revisions are not supported by rhg",
                )
                .into());
            }
            Err(corrupted(format!(
                "hash check failed for revision {}",
                self.rev
            ))
            .into())
        }
    }

    pub fn data(&self) -> Result<Cow<'revlog, [u8]>, RevlogError> {
        let data = self.rawdata()?;
        if self.rev == NULL_REVISION {
            return Ok(data);
        }
        if self.is_censored() {
            return Err(HgError::CensoredNodeError.into());
        }
        self.check_data(data)
    }

    /// Extract the data contained in the entry.
    /// This may be a delta. (See `is_delta`.)
    fn data_chunk(&self) -> Result<Cow<'revlog, [u8]>, HgError> {
        if self.bytes.is_empty() {
            return Ok(Cow::Borrowed(&[]));
        }
        match self.bytes[0] {
            // Revision data is the entirety of the entry, including this
            // header.
            b'\0' => Ok(Cow::Borrowed(self.bytes)),
            // Raw revision data follows.
            b'u' => Ok(Cow::Borrowed(&self.bytes[1..])),
            // zlib (RFC 1950) data.
            b'x' => Ok(Cow::Owned(self.uncompressed_zlib_data()?)),
            // zstd data.
            b'\x28' => Ok(Cow::Owned(self.uncompressed_zstd_data()?)),
            // A proper new format should have had a repo/store requirement.
            format_type => Err(corrupted(format!(
                "unknown compression header '{}'",
                format_type
            ))),
        }
    }

    fn uncompressed_zlib_data(&self) -> Result<Vec<u8>, HgError> {
        let mut decoder = ZlibDecoder::new(self.bytes);
        if self.is_delta() {
            let mut buf = Vec::with_capacity(self.compressed_len as usize);
            decoder
                .read_to_end(&mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            Ok(buf)
        } else {
            let cap = self.uncompressed_len.max(0) as usize;
            let mut buf = vec![0; cap];
            decoder
                .read_exact(&mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            Ok(buf)
        }
    }

    fn uncompressed_zstd_data(&self) -> Result<Vec<u8>, HgError> {
        let cap = self.uncompressed_len.max(0) as usize;
        if self.is_delta() {
            // [cap] is usually an over-estimate of the space needed because
            // it's the length of delta-decoded data, but we're interested
            // in the size of the delta.
            // This means we have to [shrink_to_fit] to avoid holding on
            // to a large chunk of memory, but it also means we must have a
            // fallback branch, for the case when the delta is longer than
            // the original data (surprisingly, this does happen in practice)
            let mut buf = Vec::with_capacity(cap);
            match zstd_decompress_to_buffer(self.bytes, &mut buf) {
                Ok(_) => buf.shrink_to_fit(),
                Err(_) => {
                    buf.clear();
                    zstd::stream::copy_decode(self.bytes, &mut buf)
                        .map_err(|e| corrupted(e.to_string()))?;
                }
            };
            Ok(buf)
        } else {
            let mut buf = Vec::with_capacity(cap);
            let len = zstd_decompress_to_buffer(self.bytes, &mut buf)
                .map_err(|e| corrupted(e.to_string()))?;
            if len != self.uncompressed_len as usize {
                Err(corrupted("uncompressed length does not match"))
            } else {
                Ok(buf)
            }
        }
    }

    /// Tell if the entry is a snapshot or a delta
    /// (influences on decompression).
    fn is_delta(&self) -> bool {
        self.base_rev_or_base_of_delta_chain.is_some()
    }
}

/// Calculate the hash of a revision given its data and its parents.
fn hash(
    data: &[u8],
    p1_hash: &[u8],
    p2_hash: &[u8],
) -> [u8; NODE_BYTES_LENGTH] {
    let mut hasher = Sha1::new();
    let (a, b) = (p1_hash, p2_hash);
    if a > b {
        hasher.update(b);
        hasher.update(a);
    } else {
        hasher.update(a);
        hasher.update(b);
    }
    hasher.update(data);
    *hasher.finalize().as_ref()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::index::IndexEntryBuilder;
    use itertools::Itertools;

    #[test]
    fn test_empty() {
        let temp = tempfile::tempdir().unwrap();
        let vfs = Vfs { base: temp.path() };
        std::fs::write(temp.path().join("foo.i"), b"").unwrap();
        let revlog =
            Revlog::open(&vfs, "foo.i", None, RevlogOpenOptions::new())
                .unwrap();
        assert!(revlog.is_empty());
        assert_eq!(revlog.len(), 0);
        assert!(revlog.get_entry(0.into()).is_err());
        assert!(!revlog.has_rev(0.into()));
        assert_eq!(
            revlog.rev_from_node(NULL_NODE.into()).unwrap(),
            NULL_REVISION
        );
        let null_entry = revlog.get_entry(NULL_REVISION.into()).ok().unwrap();
        assert_eq!(null_entry.revision(), NULL_REVISION);
        assert!(null_entry.data().unwrap().is_empty());
    }

    #[test]
    fn test_inline() {
        let temp = tempfile::tempdir().unwrap();
        let vfs = Vfs { base: temp.path() };
        let node0 = Node::from_hex("2ed2a3912a0b24502043eae84ee4b279c18b90dd")
            .unwrap();
        let node1 = Node::from_hex("b004912a8510032a0350a74daa2803dadfb00e12")
            .unwrap();
        let node2 = Node::from_hex("dd6ad206e907be60927b5a3117b97dffb2590582")
            .unwrap();
        let entry0_bytes = IndexEntryBuilder::new()
            .is_first(true)
            .with_version(1)
            .with_inline(true)
            .with_node(node0)
            .build();
        let entry1_bytes = IndexEntryBuilder::new().with_node(node1).build();
        let entry2_bytes = IndexEntryBuilder::new()
            .with_p1(Revision(0))
            .with_p2(Revision(1))
            .with_node(node2)
            .build();
        let contents = vec![entry0_bytes, entry1_bytes, entry2_bytes]
            .into_iter()
            .flatten()
            .collect_vec();
        std::fs::write(temp.path().join("foo.i"), contents).unwrap();
        let revlog =
            Revlog::open(&vfs, "foo.i", None, RevlogOpenOptions::new())
                .unwrap();

        let entry0 = revlog.get_entry(0.into()).ok().unwrap();
        assert_eq!(entry0.revision(), Revision(0));
        assert_eq!(*entry0.node(), node0);
        assert!(!entry0.has_p1());
        assert_eq!(entry0.p1(), None);
        assert_eq!(entry0.p2(), None);
        let p1_entry = entry0.p1_entry().unwrap();
        assert!(p1_entry.is_none());
        let p2_entry = entry0.p2_entry().unwrap();
        assert!(p2_entry.is_none());

        let entry1 = revlog.get_entry(1.into()).ok().unwrap();
        assert_eq!(entry1.revision(), Revision(1));
        assert_eq!(*entry1.node(), node1);
        assert!(!entry1.has_p1());
        assert_eq!(entry1.p1(), None);
        assert_eq!(entry1.p2(), None);
        let p1_entry = entry1.p1_entry().unwrap();
        assert!(p1_entry.is_none());
        let p2_entry = entry1.p2_entry().unwrap();
        assert!(p2_entry.is_none());

        let entry2 = revlog.get_entry(2.into()).ok().unwrap();
        assert_eq!(entry2.revision(), Revision(2));
        assert_eq!(*entry2.node(), node2);
        assert!(entry2.has_p1());
        assert_eq!(entry2.p1(), Some(Revision(0)));
        assert_eq!(entry2.p2(), Some(Revision(1)));
        let p1_entry = entry2.p1_entry().unwrap();
        assert!(p1_entry.is_some());
        assert_eq!(p1_entry.unwrap().revision(), Revision(0));
        let p2_entry = entry2.p2_entry().unwrap();
        assert!(p2_entry.is_some());
        assert_eq!(p2_entry.unwrap().revision(), Revision(1));
    }

    #[test]
    fn test_nodemap() {
        let temp = tempfile::tempdir().unwrap();
        let vfs = Vfs { base: temp.path() };

        // building a revlog with a forced Node starting with zeros
        // This is a corruption, but it does not preclude using the nodemap
        // if we don't try and access the data
        let node0 = Node::from_hex("00d2a3912a0b24502043eae84ee4b279c18b90dd")
            .unwrap();
        let node1 = Node::from_hex("b004912a8510032a0350a74daa2803dadfb00e12")
            .unwrap();
        let entry0_bytes = IndexEntryBuilder::new()
            .is_first(true)
            .with_version(1)
            .with_inline(true)
            .with_node(node0)
            .build();
        let entry1_bytes = IndexEntryBuilder::new().with_node(node1).build();
        let contents = vec![entry0_bytes, entry1_bytes]
            .into_iter()
            .flatten()
            .collect_vec();
        std::fs::write(temp.path().join("foo.i"), contents).unwrap();

        let mut idx = nodemap::tests::TestNtIndex::new();
        idx.insert_node(Revision(0), node0).unwrap();
        idx.insert_node(Revision(1), node1).unwrap();

        let revlog = Revlog::open_gen(
            &vfs,
            "foo.i",
            None,
            RevlogOpenOptions::new(),
            Some(idx.nt),
        )
        .unwrap();

        // accessing the data shows the corruption
        revlog.get_entry(0.into()).unwrap().data().unwrap_err();

        assert_eq!(
            revlog.rev_from_node(NULL_NODE.into()).unwrap(),
            Revision(-1)
        );
        assert_eq!(revlog.rev_from_node(node0.into()).unwrap(), Revision(0));
        assert_eq!(revlog.rev_from_node(node1.into()).unwrap(), Revision(1));
        assert_eq!(
            revlog
                .rev_from_node(NodePrefix::from_hex("000").unwrap())
                .unwrap(),
            Revision(-1)
        );
        assert_eq!(
            revlog
                .rev_from_node(NodePrefix::from_hex("b00").unwrap())
                .unwrap(),
            Revision(1)
        );
        // RevlogError does not implement PartialEq
        // (ultimately because io::Error does not)
        match revlog
            .rev_from_node(NodePrefix::from_hex("00").unwrap())
            .expect_err("Expected to give AmbiguousPrefix error")
        {
            RevlogError::AmbiguousPrefix => (),
            e => {
                panic!("Got another error than AmbiguousPrefix: {:?}", e);
            }
        };
    }
}