Impl of `Buf` with default `copy_to_bytes` impl could stack overflow

[discord9]

i.e if one impl Buf trait for a struct and not impl copy_to_bytes code like this can stack over flow:

#[test]
fn test_buffer_overflow() {
    let parts: Vec<Bytes> = vec![];
    let buf = Buffer::from(parts);

    let mut ret = BytesMut::with_capacity(buf.len());
    ret.put(buf.clone());
}

in which Buffer impl Buf but not copy_to_bytes, so calling put(while ret.cap==0) will call src's copy_to_bytes which in turn (in default impl) will call BytesMut's put (also ret.cap==0), and so on, and so on.
Maybe provide a default impl for Buf's copy_to_bytes that not cause stack overflow? Although this is a small problem and easy to debug, but providing a more explictly notify could be better

[paolobarbolini]

Could you post the full reproducer that leads to the stackoverflow?

[discord9]

Could you post the full reproducer that leads to the stackoverflow?

reproduce/test/fix in #803

[paolobarbolini]

I've tested it both locally and with the playground and the test passes even without your patch. You patch changes Buf::copy_to_bytes, but it tests BufMut::put.

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=ca38118c9921a86133c79a6f45938691

[discord9]

I've tested it both locally and with the playground and the test passes even without your patch. You patch changes Buf::copy_to_bytes, but it tests BufMut::put.

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=ca38118c9921a86133c79a6f45938691

wired, I encounter it while using this Buffer in that test case https://github.com/apache/opendal/blob/main/core/src/types/buffer.rs will provide reproduce several hours later if needed, yeah it's a combination of byte mut trying to reuse allocation and default impl of Buf caused that, the reuse itself seems fine so had to patch copy_to_bytes anyway

[discord9]

I've tested it both locally and with the playground and the test passes even without your patch. You patch changes Buf::copy_to_bytes, but it tests BufMut::put.

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=ca38118c9921a86133c79a6f45938691

oh I see you need the main branch, the 0.10.1 on crates.io doesn't contain that allocation reuse optimization

[paolobarbolini]

That explains it. I think, as your reproducer demonstrates, that the issue is with <BytesMut as BufMut>::put, not Buf::copy_to_bytes. Here's a smaller reproducer that still fails on master and succeeds in 1.10.1:

use bytes::{BufMut, BytesMut};

#[test]
fn reproducer() {
    let mut buf = BytesMut::new();
    buf.put(&[] as &[u8]);
}