view rust/hg-core/src/vfs.rs @ 48614:3efc8644dd00

test-http-bad-server: refactor the reading logic to avoid early return

Our ultimate goal is to add another way to define the connection needs to be
closed. To do so, we need the "read" code to be more unified.

Differential Revision: https://phab.mercurial-scm.org/D12045

use crate::errors::{HgError, IoErrorContext, IoResultExt};
use memmap2::{Mmap, MmapOptions};
use std::io::{ErrorKind, Write};
use std::path::{Path, PathBuf};

/// Filesystem access abstraction for the contents of a given "base" diretory
#[derive(Clone, Copy)]
pub struct Vfs<'a> {
    pub(crate) base: &'a Path,
}

struct FileNotFound(std::io::Error, PathBuf);

impl Vfs<'_> {
    pub fn join(&self, relative_path: impl AsRef<Path>) -> PathBuf {
        self.base.join(relative_path)
    }

    pub fn symlink_metadata(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<std::fs::Metadata, HgError> {
        let path = self.join(relative_path);
        std::fs::symlink_metadata(&path).when_reading_file(&path)
    }

    pub fn read_link(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<PathBuf, HgError> {
        let path = self.join(relative_path);
        std::fs::read_link(&path).when_reading_file(&path)
    }

    pub fn read(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Vec<u8>, HgError> {
        let path = self.join(relative_path);
        std::fs::read(&path).when_reading_file(&path)
    }

    fn mmap_open_gen(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Result<Mmap, FileNotFound>, HgError> {
        let path = self.join(relative_path);
        let file = match std::fs::File::open(&path) {
            Err(err) => {
                if let ErrorKind::NotFound = err.kind() {
                    return Ok(Err(FileNotFound(err, path)));
                };
                return (Err(err)).when_reading_file(&path);
            }
            Ok(file) => file,
        };
        // TODO: what are the safety requirements here?
        let mmap = unsafe { MmapOptions::new().map(&file) }
            .when_reading_file(&path)?;
        Ok(Ok(mmap))
    }

    pub fn mmap_open_opt(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Option<Mmap>, HgError> {
        self.mmap_open_gen(relative_path).map(|res| res.ok())
    }

    pub fn mmap_open(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Mmap, HgError> {
        match self.mmap_open_gen(relative_path)? {
            Err(FileNotFound(err, path)) => Err(err).when_reading_file(&path),
            Ok(res) => Ok(res),
        }
    }

    pub fn rename(
        &self,
        relative_from: impl AsRef<Path>,
        relative_to: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let from = self.join(relative_from);
        let to = self.join(relative_to);
        std::fs::rename(&from, &to)
            .with_context(|| IoErrorContext::RenamingFile { from, to })
    }

    pub fn remove_file(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let path = self.join(relative_path);
        std::fs::remove_file(&path)
            .with_context(|| IoErrorContext::RemovingFile(path))
    }

    #[cfg(unix)]
    pub fn create_symlink(
        &self,
        relative_link_path: impl AsRef<Path>,
        target_path: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let link_path = self.join(relative_link_path);
        std::os::unix::fs::symlink(target_path, &link_path)
            .when_writing_file(&link_path)
    }

    /// Write `contents` into a temporary file, then rename to `relative_path`.
    /// This makes writing to a file "atomic": a reader opening that path will
    /// see either the previous contents of the file or the complete new
    /// content, never a partial write.
    pub fn atomic_write(
        &self,
        relative_path: impl AsRef<Path>,
        contents: &[u8],
    ) -> Result<(), HgError> {
        let mut tmp = tempfile::NamedTempFile::new_in(self.base)
            .when_writing_file(self.base)?;
        tmp.write_all(contents)
            .and_then(|()| tmp.flush())
            .when_writing_file(tmp.path())?;
        let path = self.join(relative_path);
        tmp.persist(&path)
            .map_err(|e| e.error)
            .when_writing_file(&path)?;
        Ok(())
    }
}

fn fs_metadata(
    path: impl AsRef<Path>,
) -> Result<Option<std::fs::Metadata>, HgError> {
    let path = path.as_ref();
    match std::fs::metadata(path) {
        Ok(meta) => Ok(Some(meta)),
        Err(error) => match error.kind() {
            // TODO: when we require a Rust version where `NotADirectory` is
            // stable, invert this logic and return None for it and `NotFound`
            // and propagate any other error.
            ErrorKind::PermissionDenied => Err(error).with_context(|| {
                IoErrorContext::ReadingMetadata(path.to_owned())
            }),
            _ => Ok(None),
        },
    }
}

pub(crate) fn is_dir(path: impl AsRef<Path>) -> Result<bool, HgError> {
    Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_dir()))
}

pub(crate) fn is_file(path: impl AsRef<Path>) -> Result<bool, HgError> {
    Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_file()))
}