Dropping future returned from creating an HTTP request immediately cancels the operation

[alexcrichton]

This input:

use anyhow::Context as _;
use futures::join;
use std::io::{self, Read};
use test_programs::p3::wasi::http::client;
use test_programs::p3::wasi::http::types::{
    Headers, Method, Request, RequestOptions, Response, Scheme,
};
use test_programs::p3::{wit_future, wit_stream};

struct Component;

test_programs::p3::export!(Component);

impl test_programs::p3::exports::wasi::cli::run::Guest for Component {
    async fn run() -> Result<(), ()> {
        const LEN: usize = 1 << 20;
        let body = vec![1; LEN];

        let addr = test_programs::p3::wasi::cli::environment::get_environment()
            .into_iter()
            .find_map(|(k, v)| k.eq("HTTP_SERVER").then_some(v))
            .unwrap();

        let headers = Headers::from_list(&[]).unwrap();
        let (mut contents_tx, contents_rx) = wit_stream::new();
        let (trailers_tx, trailers_rx) = wit_future::new(|| Ok(None));
        drop(trailers_tx);
        let options = RequestOptions::new();
        let (request, transmit) =
            Request::new(headers, Some(contents_rx), trailers_rx, Some(options));
        request.set_method(&Method::Post).unwrap();
        request.set_scheme(Some(&Scheme::Http)).unwrap();
        request.set_authority(Some(&addr)).unwrap();
        request.set_path_with_query(Some("/post")).unwrap();

        drop(transmit);

        let ((), echoed) = join!(
            async {
                let remaining = contents_tx.write_all((&body[..]).into()).await;
                assert!(remaining.is_empty());
                drop(contents_tx);
            },
            async {
                let response = client::send(request).await.context("send failed").unwrap();
                let status = response.get_status_code();
                assert_eq!(status, 200);
                let (_, result_rx) = wit_future::new(|| Ok(()));
                let (body_rx, _trailers_rx) = Response::consume_body(response, result_rx);
                body_rx.collect().await
            },
        );

        assert_eq!(
            echoed.len(),
            LEN,
            "response body was truncated after dropping the transmit future"
        );
        Ok(())
    }
}

fn main() {}

tested with:

diff --git a/crates/wasi-http/tests/all/p3/mod.rs b/crates/wasi-http/tests/all/p3/mod.rs
index 1fc17440f9..3b30567446 100644
--- a/crates/wasi-http/tests/all/p3/mod.rs
+++ b/crates/wasi-http/tests/all/p3/mod.rs
@@ -946,3 +946,9 @@ async fn p3_http_outbound_request_chunk_size() -> Result<()> {
     let server = Server::http1(1)?;
     run_cli(P3_HTTP_OUTBOUND_REQUEST_CHUNK_SIZE_COMPONENT, &server).await
 }
+
+#[test_log::test(tokio::test(flavor = "multi_thread"))]
+async fn p3_http_drop_transmit() -> Result<()> {
+    let server = Server::http1(1)?;
+    run_cli(P3_HTTP_DROP_TRANSMIT_COMPONENT, &server).await
+}

yields:

Details

   Compiling test-programs-artifacts v0.0.0 (/home/alex/code/wasmtime2/crates/test-programs/artifacts)
   Compiling wasmtime-wasi-http v49.0.0-dev (/home/alex/code/wasmtime2/crates/wasi-http)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 9.08s
     Running unittests src/lib.rs (target/debug/deps/wasmtime_wasi_http-65e7d209d05ca930)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 10 filtered out; finished in 0.00s

     Running tests/all/main.rs (target/debug/deps/all-ccf405becb83689e)

running 1 test

thread '<unnamed>' (1) panicked at crates/test-programs/src/bin/p3_http_drop_transmit.rs:56:9:
assertion `left == right` failed: response body was truncated after dropping the transmit future
  left: 8025
 right: 1048576
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
test p3::p3_http_drop_transmit ... FAILED

failures:

---- p3::p3_http_drop_transmit stdout ----
2026-08-28T19:38:21.167664Z  WARN all::http_server: failed to serve connection i=0 err=error writing a body to connection
Error: failed to call `wasi:cli/run#run`

Caused by:
    0: error while executing at wasm backtrace:
    0:  0x4fdc2 - abort
                    at wasisdk://v33.0+m/build/sysroot/wasi-libc-wasm32-wasip1-build-prefix/src/wasi-libc-wasm32-wasip1-build-build/wasisdk://v33.0+m/src/wasi-libc/libc-bottom-half/sources/abort.c:5:3
    1:  0x4729a - std[bc29ef7725180ca4]::sys::pal::wasi::abort_internal
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/sys/pal/wasi/mod.rs:27:14
    2:  0x44ee0 - std[bc29ef7725180ca4]::process::abort
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/process.rs:2638:5
    3:  0x455d7 - __rustc[4b1ee1ef74718a7b]::__rust_abort
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/rt.rs:33:5
    4:  0x43bff - __rustc[4b1ee1ef74718a7b]::__rust_start_panic
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/panic_abort/src/lib.rs:50:5
    5:  0x4546e - __rustc[4b1ee1ef74718a7b]::rust_panic
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/panicking.rs:887:25
    6:  0x44928 - std[bc29ef7725180ca4]::panicking::panic_with_hook
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/panicking.rs:840:5
    7:  0x4458f - std[bc29ef7725180ca4]::panicking::panic_handler::{closure#0}
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/panicking.rs:688:13
    8:  0x444f7 - std[bc29ef7725180ca4]::sys::backtrace::__rust_end_short_backtrace::<std[bc29ef7725180ca4]::panicking::panic_handler::{closure#0}, !>
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/sys/backtrace.rs:182:18
    9:  0x456ba - __rustc[4b1ee1ef74718a7b]::rust_begin_unwind
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/std/src/panicking.rs:679:5
   10:  0x53c89 - core[207ea530fe29b66a]::panicking::panic_fmt
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/core/src/panicking.rs:80:14
   11:  0x537c3 - core[207ea530fe29b66a]::panicking::assert_failed_inner
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/core/src/panicking.rs:434:23
   12:  0x5385a - core[207ea530fe29b66a]::panicking::assert_failed::<usize, usize>
                    at /rustc/88d9e12ae178fab0fb5cc050a94da85685d449ea/library/core/src/panicking.rs:394:5
   13:   0x3953 - <p3_http_drop_transmit[dd4cfef12b085f04]::Component as test_programs[6528a46e635fc4bb]::p3::exports::wasi::cli::run::Guest>::run::{closure#0}
                    at /home/alex/code/wasmtime2/crates/test-programs/src/bin/p3_http_drop_transmit.rs:56:9
   14:   0x3b32 - test_programs[6528a46e635fc4bb]::p3::exports::wasi::cli::run::_export_run_cabi::<p3_http_drop_transmit[dd4cfef12b085f04]::Component>::{closure#0}
                    at /home/alex/code/wasmtime2/crates/test-programs/src/p3/mod.rs:4:1
   15:  0x34378 - <core[207ea530fe29b66a]::pin::Pin<alloc[abfb239ceb7de59d]::boxed::Box<dyn core[207ea530fe29b66a]::future::future::Future<Output = ()>>> as core[207ea530fe29b66a]::future::future::Future>::poll
                    at /home/alex/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/future/future.rs:133:9
                - <futures_util[1c5cead8f231934d]::stream::futures_unordered::FuturesUnordered<core[207ea530fe29b66a]::pin::Pin<alloc[abfb239ceb7de59d]::boxed::Box<dyn core[207ea530fe29b66a]::future::future::Future<Output = ()>>>> as futures_core[929563e02d1dc578]::stream::Stream>::poll_next
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/futures-util-0.3.31/src/stream/futures_unordered/mod.rs:528:24
   16:  0x36dba - <futures_util[1c5cead8f231934d]::stream::futures_unordered::FuturesUnordered<core[207ea530fe29b66a]::pin::Pin<alloc[abfb239ceb7de59d]::boxed::Box<dyn core[207ea530fe29b66a]::future::future::Future<Output = ()>>>> as futures_util[1c5cead8f231934d]::stream::stream::StreamExt>::poll_next_unpin
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/futures-util-0.3.31/src/stream/stream/mod.rs:1638:24
                - <wit_bindgen[bc7f8915fbd6868b]::rt::async_support::spawn::Tasks>::poll_next
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.61.1/src/rt/async_support/spawn.rs:34:35
                - <wit_bindgen[bc7f8915fbd6868b]::rt::async_support::TaskState>::callback::{closure#0}
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.61.1/src/rt/async_support.rs:237:37
                - <wit_bindgen[bc7f8915fbd6868b]::rt::async_support::TaskState>::with_p3_task_set::<wit_bindgen[bc7f8915fbd6868b]::rt::async_support::CallbackCode, <wit_bindgen[bc7f8915fbd6868b]::rt::async_support::TaskState>::callback::{closure#0}>
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.61.1/src/rt/async_support.rs:346:9
                - <wit_bindgen[bc7f8915fbd6868b]::rt::async_support::TaskState>::callback
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.61.1/src/rt/async_support.rs:202:14
   17:  0x3741f - wit_bindgen[bc7f8915fbd6868b]::rt::async_support::callback
                    at /home/alex/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/wit-bindgen-0.61.1/src/rt/async_support.rs:642:27
   18:   0x784c - test_programs[6528a46e635fc4bb]::p3::exports::wasi::cli::run::__callback_run
                    at /home/alex/code/wasmtime2/crates/test-programs/src/p3/mod.rs:4:1
   19:   0x39eb - [callback][async-lift]wasi:cli/run@0.3.0#run
                    at /home/alex/code/wasmtime2/crates/test-programs/src/bin/p3_http_drop_transmit.rs:12:1
    1: wasm trap: wasm `unreachable` instruction executed



failures:
    p3::p3_http_drop_transmit

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 65 filtered out; finished in 1.17s

error: test failed, to rerun pass `-p wasmtime-wasi-http --test all`

This is a regression from #14148 (cc @adamrk) and if it's helpful there's an LLM summary here