Stream: ComponentizeJS

Topic: ✔ Forcing resource drop

Chad Kimes (Feb 20 2024 at 22:15):

Hi! I'm poking at ComponentizeJS and trying to figure out how to explicitly drop a resource. I have this code targeting WASI preview 2 HTTP working in Rust:

    if let Some(body) = body {
        let req_body = req.body().expect("getting body");
        let stream = req_body.write().expect("getting body");
        stream.blocking_write_and_flush(body).expect("writing content");
        drop(stream);
        OutgoingBody::finish(req_body, None).expect("finishing body");
    }

As per the WIT definitions, dropping the writer is necessary before calling OutgoingBody::finish:

  resource outgoing-body {

    /// Returns a stream for writing the body contents.
    ///
    /// The returned `output-stream` is a child resource: it must be dropped
    /// before the parent `outgoing-body` resource is dropped (or finished),
    /// otherwise the `outgoing-body` drop or `finish` will trap.
    ///
    /// Returns success on the first call: the `output-stream` resource for
    /// this `outgoing-body` may be retrieved at most once. Subsequent calls
    /// will return error.
    write: func() -> result<output-stream>;

However I can't figure out how to cause the drop to execute in JS:

    if (body) {
        let reqBody = req.body();
        let stream = reqBody.write();
        stream.blockingWriteAndFlush(body);
        stream.drop(); // TypeError: stream.drop is not a function
        OutgoingBody.finish(reqBody);
    }

I know that I'm mostly on the right path, since GET methods work but my POSTs with a body are failing. Eliding the drop altogether results in the documented trap when calling OutgoingBody.finish. How can I force this stream to be dropped?

Guy Bedford (Feb 20 2024 at 22:25):

You can use stream[Symbol.for('dispose')](); to do the dispose from JS

Chad Kimes (Feb 20 2024 at 22:25):

And of course 5 minutes after posting that I find: https://github.com/bytecodealliance/ComponentizeJS/blob/89ac2c5730866ebe47afaf3a8ae231c59761796e/test/cases/resource-borrow-import/source.js#L3

I had tried with Symbol.dispose previously and that didn't work, so apparently the magic was Symbol.for('dispose')

Guy Bedford (Feb 20 2024 at 22:25):

When Spidermonkey supports Symbol.dispose we will switch to that

Guy Bedford (Feb 20 2024 at 22:25):

so then it will be the new using syntax eventually

Guy Bedford (Feb 20 2024 at 22:26):

we should better document this though certainly

Chad Kimes (Feb 20 2024 at 22:26):

Right, and I suppose if I had adopted typescript's using then I wouldn't have seen this at all

Chad Kimes (Feb 20 2024 at 22:32):

While you're active - is there a recommended bundler for joining multiple JS files together? I just want to unclutter my main file by putting some helpers somewhere else, but naive concat quickly runs into import collisions

Chad Kimes (Feb 20 2024 at 22:32):

preferably something invokeable from the mjs file

Guy Bedford (Feb 20 2024 at 22:46):

Note it's still Symbol.for('dispose') instead of Symbol.dispose. We could directly define Symbol.dispose = Symbol.for('dispose') to make this easier I suppose, posted https://github.com/bytecodealliance/ComponentizeJS/pull/81. For bundling modules, esbuild / swc / rollup are all good.

Chad Kimes (Feb 20 2024 at 22:53):

oh nice! that looks great

Notification Bot (Feb 20 2024 at 23:06):

Chad Kimes has marked this topic as resolved.

Last updated: Nov 22 2024 at 16:03 UTC