rust/hg-core/src/logging.rs

rust: bump to memmap2 0.5.3, micro-timer 0.4.0, and crossbeam-channel 0.5.0

The merge in 12adf8c695ed had conflicts in rust/Cargo.lock and
rust/hg-core/Cargo.toml . Let's ignore rust/Cargo.lock - it is regenerated.

For rust/hg-core/Cargo.toml, stable had dd6b67d5c256 "rust: fix unsound
`OwningDirstateMap`" which introduced ouroboros (and dropped
stable_deref_trait).

Default had ec8d9b5a5e7c "rust-hg-core: upgrade dependencies" which had a lot
of churn bumping minimum versions - also patch versions. It is indeed a good
idea to bump to *allow* use of latest package. That means that major versions
should be bumped for packages after 1.0, and for packages below 1.0 minor
versions should be bumped too. But it doesn't work to try enforce a policy of
using latest patch by bumping versions at arbitrary times.

For good or bad, the merge doesn't seem to have resolved the conflicts
correctly, and many of the minor "upgrade dependencies" were lost again.

Unfortunately, it also lost the bump of memmap2 to 0.5.3, which is needed for
Fedora packaging where 0.4 isn't available. Same with micro-timer bump to 0.4
(which already is used in rhg). crossbeam-channel bump was also lost.

This change fixes that regression by redoing these "important" lines of the
merge "correctly".

I propose this for stable, even though dependency changes on stable branches
are annoying.

use crate::errors::{HgError, HgResultExt, IoErrorContext, IoResultExt};
use crate::vfs::Vfs;
use std::io::Write;

/// An utility to append to a log file with the given name, and optionally
/// rotate it after it reaches a certain maximum size.
///
/// Rotation works by renaming "example.log" to "example.log.1", after renaming
/// "example.log.1" to "example.log.2" etc up to the given maximum number of
/// files.
pub struct LogFile<'a> {
    vfs: Vfs<'a>,
    name: &'a str,
    max_size: Option<u64>,
    max_files: u32,
}

impl<'a> LogFile<'a> {
    pub fn new(vfs: Vfs<'a>, name: &'a str) -> Self {
        Self {
            vfs,
            name,
            max_size: None,
            max_files: 0,
        }
    }

    /// Rotate before writing to a log file that was already larger than the
    /// given size, in bytes. `None` disables rotation.
    pub fn max_size(mut self, value: Option<u64>) -> Self {
        self.max_size = value;
        self
    }

    /// Keep this many rotated files `{name}.1` up to `{name}.{max}`, in
    /// addition to the original `{name}` file.
    pub fn max_files(mut self, value: u32) -> Self {
        self.max_files = value;
        self
    }

    /// Append the given `bytes` as-is to the log file, after rotating if
    /// needed.
    ///
    /// No trailing newline is added. Make sure to include one in `bytes` if
    /// desired.
    pub fn write(&self, bytes: &[u8]) -> Result<(), HgError> {
        let path = self.vfs.join(self.name);
        let context = || IoErrorContext::WritingFile(path.clone());
        let open = || {
            std::fs::OpenOptions::new()
                .create(true)
                .append(true)
                .open(&path)
                .with_context(context)
        };
        let mut file = open()?;
        if let Some(max_size) = self.max_size {
            if file.metadata().with_context(context)?.len() >= max_size {
                // For example with `max_files == 5`, the first iteration of
                // this loop has `i == 4` and renames `{name}.4` to `{name}.5`.
                // The last iteration renames `{name}.1` to
                // `{name}.2`
                for i in (1..self.max_files).rev() {
                    self.vfs
                        .rename(
                            format!("{}.{}", self.name, i),
                            format!("{}.{}", self.name, i + 1),
                        )
                        .io_not_found_as_none()?;
                }
                // Then rename `{name}` to `{name}.1`. This is the
                // previously-opened `file`.
                self.vfs
                    .rename(self.name, format!("{}.1", self.name))
                    .io_not_found_as_none()?;
                // Finally, create a new `{name}` file and replace our `file`
                // handle.
                file = open()?;
            }
        }
        file.write_all(bytes).with_context(context)?;
        file.sync_all().with_context(context)
    }
}

#[test]
fn test_rotation() {
    let temp = tempfile::tempdir().unwrap();
    let vfs = Vfs { base: temp.path() };
    let logger = LogFile::new(vfs, "log").max_size(Some(3)).max_files(2);
    logger.write(b"one\n").unwrap();
    logger.write(b"two\n").unwrap();
    logger.write(b"3\n").unwrap();
    logger.write(b"four\n").unwrap();
    logger.write(b"five\n").unwrap();
    assert_eq!(vfs.read("log").unwrap(), b"five\n");
    assert_eq!(vfs.read("log.1").unwrap(), b"3\nfour\n");
    assert_eq!(vfs.read("log.2").unwrap(), b"two\n");
    assert!(vfs.read("log.3").io_not_found_as_none().unwrap().is_none());
}