Stream: git-wasmtime

Topic: wasmtime / issue #9653 wasi-http: can we call the `blocki...

Wasmtime GitHub notifications bot (Nov 22 2024 at 08:28):

iawia002 opened issue #9653:

My scenario is simple: I want to send a request with a large body, but the blocking_write_and_flush method can only write 4096 bytes at a time. Naturally, I decided to call this method multiple times to write the entire body:

let req = OutgoingRequest::new(...);

let outgoing_body = req.body().unwarp();
let request_body = outgoing_body.write().unwarp();

let chunks = buf.chunks(4096);
for chunk in chunks {
    request_body.blocking_write_and_flush(chunk).expect("writing response");
}

OutgoingBody::finish(outgoing_body, None).unwarp();

However, I found that the program gets stuck forever on the second call to blocking_write_and_flush. After debugging, I found that it actually gets stuck during the ready check in the second call:

https://github.com/bytecodealliance/wasmtime/blob/5af89308dc0229ca404cd7000eec694201022e2d/crates/wasi-http/src/body.rs#L662-L669

https://github.com/bytecodealliance/wasmtime/blob/5af89308dc0229ca404cd7000eec694201022e2d/crates/wasi-http/src/body.rs#L472

At this point, the writer has no capacity left, but my writing process hasn't finished, so the reader hasn't started consuming the data (?).

For my issue, I could stop using this method and instead combine check-write, subscribe, write, and flush manually to solve it. However, I'm curious whether we are inclined to allow or not allow this behavior. Because the current behavior is strange—the program doesn't report an error, it just hangs indefinitely.

Last updated: Nov 22 2024 at 16:03 UTC