handler.rs

use crate::FieldMap;
use crate::p3::bindings::http::client::{Host, HostWithStore};
use crate::p3::bindings::http::types::{Request, Response};
use crate::p3::body::{Body, BodyExt as _};
use crate::p3::{HttpError, HttpResult};
use crate::{Error, WasiHttp, WasiHttpCtxView};
use core::task::{Context, Poll, Waker};
use http_body_util::BodyExt as _;
use std::sync::Arc;
use tokio::sync::oneshot;
use tokio::task::{self, JoinHandle};
use tracing::debug;
use wasmtime::component::{Accessor, Resource};
use wasmtime::error::Context as _;

/// A wrapper around [`JoinHandle`], which will [`JoinHandle::abort`] the task
/// when dropped
struct AbortOnDropJoinHandle(JoinHandle<()>);

impl Drop for AbortOnDropJoinHandle {
    fn drop(&mut self) {
        self.0.abort();
    }
}

const DROPPED_FUTURE_ERROR: &str =
    "Future indicating transmission result dropped without being resolved.";

async fn io_task_result(
    rx: oneshot::Receiver<(
        Option<Arc<AbortOnDropJoinHandle>>,
        oneshot::Receiver<Result<(), Error>>,
    )>,
) -> Result<(), Error> {
    let Ok((_io, io_result_rx)) = rx.await else {
        return Err(Error::InternalError(Some(DROPPED_FUTURE_ERROR.to_string())));
    };
    io_result_rx
        .await
        .unwrap_or_else(|_| Err(Error::InternalError(Some(DROPPED_FUTURE_ERROR.to_string()))))
}

fn send_dummy_io(
    result: Result<(), Error>,
    io_result_tx: oneshot::Sender<(
        Option<Arc<AbortOnDropJoinHandle>>,
        oneshot::Receiver<Result<(), Error>>,
    )>,
) {
    let (tx, rx) = oneshot::channel();
    let _ = tx.send(result);
    let _ = io_result_tx.send((None, rx));
}

fn send_dummy_io_err<T>(
    store: &Accessor<T, WasiHttp>,
    e: Error,
    io_result_tx: oneshot::Sender<(
        Option<Arc<AbortOnDropJoinHandle>>,
        oneshot::Receiver<Result<(), Error>>,
    )>,
) -> HttpError {
    let err_code = store.with(|mut store| store.get().error_to_p3(&e));
    send_dummy_io(Err(e), io_result_tx);
    err_code.into()
}

impl<T> HostWithStore<T> for WasiHttp {
    async fn send(
        store: &Accessor<T, Self>,
        req: Resource<Request>,
    ) -> HttpResult<Resource<Response>> {
        // A handle to the I/O task, if spawned, will be sent on this channel
        // and kept as part of request body state
        let (io_task_tx, io_task_rx) = oneshot::channel();

        // A handle to the I/O task, if spawned, will be sent on this channel
        // along with the result receiver
        let (io_result_tx, io_result_rx) = oneshot::channel();

        // Response processing result will be sent on this channel
        let (res_result_tx, res_result_rx) = oneshot::channel();

        let getter = store.getter();
        let fut = store.with(|mut store| {
            let WasiHttpCtxView { table, .. } = store.get();
            let req = table
                .delete(req)
                .context("failed to delete request from table")
                .map_err(HttpError::trap)?;
            let (req, options) =
                req.into_http_with_getter(&mut store, io_task_result(io_result_rx), getter)?;
            HttpResult::Ok(store.get().hooks.send_request(
                // Attach a reference to the io task to the body so that it
                // isn't cancelled if the body is dropped.
                req.map(|body| body.with_state(io_task_rx).boxed_unsync()),
                options.as_deref().copied(),
                Box::new(async {
                    // Forward the response processing result to `WasiHttpCtx` implementation
                    let Ok(fut) = res_result_rx.await else {
                        return Ok(());
                    };
                    Box::into_pin(fut).await
                }),
            ))
        });
        let fut = match fut {
            Ok(fut) => fut,
            Err(e) => match e.downcast() {
                Ok(err_code) => {
                    send_dummy_io(Err(err_code.clone().into()), io_result_tx);
                    return Err(err_code.into());
                }
                Err(e) => {
                    let e = Error::InternalError(Some(format!("{e}")));
                    return Err(send_dummy_io_err(store, e, io_result_tx));
                }
            },
        };
        let (res, io) = match Box::into_pin(fut).await {
            Ok(r) => r,
            Err(e) => {
                return Err(send_dummy_io_err(store, e, io_result_tx));
            }
        };
        let (
            http::response::Parts {
                status, headers, ..
            },
            body,
        ) = res.into_parts();

        let mut io = Box::into_pin(io);
        let body = match io.as_mut().poll(&mut Context::from_waker(Waker::noop())) {
            Poll::Ready(Ok(())) => {
                send_dummy_io(Ok(()), io_result_tx);
                body
            }
            Poll::Ready(Err(e)) => {
                return Err(send_dummy_io_err(store, e, io_result_tx));
            }
            Poll::Pending => {
                // I/O driver still needs to be polled, spawn a task and send handles to it
                let (tx, rx) = oneshot::channel();
                let io = Arc::new(AbortOnDropJoinHandle(task::spawn(async move {
                    let res = io.await;
                    debug!(?res, "`send_request` I/O future finished");
                    _ = tx.send(res);
                })));
                _ = io_result_tx.send((Some(Arc::clone(&io)), rx));
                _ = io_task_tx.send(Arc::clone(&io));
                // Attach a reference to the io task to the body so that it
                // isn't cancelled if the body is dropped.
                body.with_state(io).boxed_unsync()
            }
        };
        store.with(|mut store| {
            let res = Response {
                status,
                headers: FieldMap::new_immutable(store.get().hooks, headers),
                body: Body::Host {
                    body,
                    result_tx: res_result_tx,
                },
            };
            store
                .get()
                .table
                .push(res)
                .context("failed to push response to table")
                .map_err(HttpError::trap)
        })
    }
}

impl Host for WasiHttpCtxView<'_> {}