memmap2 write_all call panics on cacache 10

[chrisdickinson]

This appears to happen with any vec <= the memmap size.

thread 'main' panicked at 'source slice length (705) does not match destination slice length (0)', /Users/chris/.cargo/registry/src/github.com-1ecc6299db9ec823/cacache-10.0.0/src/content/write.rs:78:18

That backtrace points at:

impl Write for Writer {
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        self.builder.input(buf);
        if let Some(mmap) = &mut self.mmap {
            mmap.copy_from_slice(buf); // <-------------------------- this line
            Ok(buf.len())
        } else {
            self.tmpfile.write(buf)
        }
    }

    fn flush(&mut self) -> std::io::Result<()> {
        self.tmpfile.flush()
    }
}

I tested manually lowering the max memmap limit to 0 and it started working again; also pinning cacache at v9 seems to pass as well. I noticed this with both sync and async calls of cacache::write_hash.

My machine is:

• OS: macOS 12.2.1
• CPU: (10) arm64 Apple M1 Max
• Memory: 25.82 GB / 64.00 GB
• Shell: 3.2.57 - /bin/bash

If there's any other info I can post here to help please let me know, & thanks for cacache!

[zkat]

#31 there's a PR for this, but it seems to be a bug in memmap2 itself, so I've been hesitant to merge that PR. I thought the author had sent a bug report over to memmap2 but I guess that didn't happen. I'll go file that issue.

In the meantime, you can safely downgrade to cacache@9.0. The only thing that's changed since then is the bump to memmap2, which is what caused this crash.

[zkat]

^ and there's the memmap2 bug

[zkat]

Fixed in 10.0.1

[tgnottingham]

I'm still seeing this issue with inputs <= 1MiB.

That is, this works:

let _ = cacache::write_hash("./cache", &[b'a'; 1024 * 1024 + 1]).await;

But this results in a panic:

let _ = cacache::write_hash("./cache", &[b'a'; 1024 * 1024]).await;

thread 'blocking-1' panicked at 'source slice length (1048576) does not match destination slice length (0)', /home/tgnottingham/.cargo/registry/src/github.com-1ecc6299db9ec823/cacache-10.0.1/src/content/write.rs:260:38
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'async-std/runtime' panicked at 'task has failed', /home/tgnottingham/.cargo/registry/src/github.com-1ecc6299db9ec823/async-task-4.3.0/src/task.rs:426:45
thread 'main' panicked at 'task has failed', /home/tgnottingham/.cargo/registry/src/github.com-1ecc6299db9ec823/async-task-4.3.0/src/task.rs:426:45

The issue doesn't occur when using cacache::write.