How to handle client disconnect?

[alanhe]

I'm trying bidirectional stream.

When a client crashes, by polling stream.next().await, I get an error:

Status {
    code: Unknown,
    message: "error reading a body from connection: broken pipe",
    source: Some(
        hyper::Error(
            Body,
            Error {
                kind: Io(
                    Kind(
                        BrokenPipe,
                    ),
                ),
            },
        ),
    ),
}

I want to have special treatment to the error kind, say, adding metrics to record the event.
How can I write code to match the error?

I try the code, but it does not work.

fn match_broken_pipe_error(err: &(dyn std::error::Error + 'static)) -> bool {
    if let Some(e) = err.downcast_ref::<hyper::Error>() {
        dbg!(&e);
        if let Some(e) = e.source() {
            if let Some(e) = e.downcast_ref::<std::io::Error>() {
                if e.kind() == std::io::ErrorKind::BrokenPipe {
                    return true;
                }
            }
        }
    }

    if let Some(source) = err.source() {
        match_broken_pipe_error(source)
    } else {
        false
    }
}

thx.

[davidpdrsn]

You need to recursively search the whole error chain. Not just the first one. Try using something like this

// attempt to downcast `err` into a `T` and if that fails recursively try and
// downcast `err`'s source
fn find_error_source<'a, T>(err: &'a (dyn Error + 'static)) -> Option<&'a T>
where
    T: Error + 'static,
{
    if let Some(err) = err.downcast_ref::<T>() {
        Some(err)
    } else if let Some(source) = err.source() {
        find_error_source(source)
    } else {
        None
    }
}

[alanhe]

I think I know why. It's wrapped in a h2::Error. It implements neither source nor cause, so the downcasting chain is broken.
https://github.com/hyperium/h2/blob/master/src/error.rs#L186

This is what I end up with:

fn match_broken_pipe_error(err: &(dyn std::error::Error + 'static)) -> bool {
    if let Some(e) = err.downcast_ref::<h2::Error>() {
        if let Some(e) = e.get_io() {
            if e.kind() == std::io::ErrorKind::BrokenPipe {
                return true;
            }
        }
    }

    if let Some(source) = err.source() {
        match_broken_pipe_error(source)
    } else {
        false
    }
}

Thanks for the help!