Stream: git-wasmtime

Topic: wasmtime / issue #14769 wasi-http p3: reused instance lea...

Wasmtime GitHub notifications bot (Oct 15 2026 at 04:30):

avkonst opened issue #14769:

A wasi:http/handler@0.3 instance that is reused for many requests leaks handles until it traps, if all three of these are true:

1. the guest's response sets content-length;
2. the host reads exactly content-length bytes of the response body and then drops the body without polling it to the end. hyper does this when it serves a response with content-length, so wasmtime serve-style embeddings will hit it;
3. at least 2 requests are in flight on the instance at once.

If any one of these is false, 300,000 requests run fine on one instance.

The trap is raised while the guest creates the next response, so it looks like resources from earlier responses are never released:

wasmtime	Fails after	Error
50.0.0-rc.1	~100,000 requests	resource table has no free keys, in the guest's Response::new
49.0.3	~25,400 requests	cannot allocate another handle: store handle limit exceeded, in the guest's BodyWriter::new

Test Case

Repro: https://github.com/avkonst/wasi-repro (./run.sh runs the failing case and the three passing ones). In summary:

• guest: a wasip3::http_compat component with two routes that differ only in whether the response sets content-length.
• host: one instance in one Store, with up to N calls in flight, each started with handler::Prepared inside Store::run_concurrent. Each response body is either read to the end (full) or read until content-length bytes have arrived and then dropped (until-length, like hyper).

Steps to Reproduce

git clone https://github.com/avkonst/wasi-repro && cd wasi-repro
./run.sh   # rust-toolchain.toml pins rustc 1.99.0 + wasm32-wasip2

# or by hand:
W=guest/target/wasm32-wasip2/release/guest.wasm
H=host/target/release/host

# fails
$H $W /with-content-length    300000 until-length 2 direct
# pass
$H $W /with-content-length    300000 until-length 1 direct
$H $W /with-content-length    300000 full         2 direct
$H $W /without-content-length 300000 until-length 2 direct

Expected Results

All 300,000 requests succeed on one instance, as they do when any one of the three conditions is removed.

Actual Results

instance failed after 99998 requests: error while executing at wasm backtrace:
    0:  0x3ee1d - <unknown>!<wasm function 9>
    1:   0x8ead - guest.wasm!wasip3::service::wasi::http::types::Response::new
    2:   0x53db - guest.wasm!wasip3::http_compat::conversions::http_into_wasi_response
    3:   0x5924 - guest.wasm!wasip3::service::exports::wasi::http::handler::_export_handle_cabi::{{closure}}
    4:  0x112ca - guest.wasm!<futures_util::stream::futures_unordered::FuturesUnordered<Fut> as futures_core::stream::Stream>::poll_next
    5:  0x14a0c - guest.wasm!wit_bindgen::rt::async_support::spawn::Tasks::poll_next
    6:  0x11876 - guest.wasm!wit_bindgen::rt::async_support::TaskState::callback
    7:  0x116a2 - guest.wasm!wit_bindgen::rt::async_support::callback
    8:   0x55bf - guest.wasm!wit_bindgen::rt::async_support::start_task
    9:   0x7e65 - guest.wasm![async-lift]wasi:http/handler@0.3.0#handle

Caused by:
    resource table has no free keys

<details><summary>On 49.0.3</summary>

instance failed after 25394 requests: error while executing at wasm backtrace:
    0:  0x10262 - guest.wasm!wasip3::http_compat::body_writer::BodyWriter::new
    1:   0x538a - guest.wasm!wasip3::http_compat::conversions::http_into_wasi_response
    ...
Caused by:
    cannot allocate another handle: store handle limit exceeded

To build the host against 49.0.3, change =50.0.0-rc.1 to =49.0.3 in host/Cargo.toml, and TaskGroupId to GuestTaskId in host/src/main.rs.
</details>

Results (/with-content-length unless noted):

Driver	Body	In flight	50.0.0-rc.1	49.0.3
direct	until-length	1	300,000 ok	300,000 ok
direct	until-length	2	traps after 99,998	traps after 25,394
direct	until-length	64	traps after 99,968	traps after 25,344
direct	full	64	300,000 ok	300,000 ok
direct, /without-content-length	until-length	64	300,000 ok	300,000 ok
ProxyHandler (reuse, never expire)	until-length	64	6,000,000 ok over 25 instances	worker trapped or panicked after 2,263,112 over 27 instances
ProxyHandler (reuse, never expire)	full	64	3,000,000 ok over 27 instances	3,000,000 ok over 26 instances

The ProxyHandler only starts a concurrent request on an instance whose tasks are blocked on I/O, so each instance sees less overlap. On 49.0.3 that only delays the failure.

Versions and Environment

• Wasmtime version or commit: wasmtime, wasmtime-wasi, wasmtime-wasi-http 50.0.0-rc.1 (component-model-async); also 49.0.3
• Guest: wasip3 0.9.0+wasi-0.3.0 (http-compat), wit-bindgen 0.62.0
• rustc 1.99.0, target wasm32-wasip2
• Operating system: Linux
• Architecture: x86_64

Extra Info

• With content-length, wasmtime-wasi-http consumes the guest body with LimitedGuestBodyConsumer (src/p3/body.rs), not UnlimitedGuestBodyConsumer. GuestBody::size_hint is then exact, which is what lets hyper stop after the declared length and drop the body.
• The guest writes the body and then the trailers from a task that http_into_wasi_response spawns (spawn_local, then BodyWriter::send_http_body). That task, or the stream and future ends it holds, may be what never completes once the host drops the body. If so, it may be partly or wholly a wasip3/wit-bindgen issue and not only a host-side one.
• Workaround attempt on 49.0.3: polling the dropped body to the end on a spawned host task made the trap less frequent but did not stop it.

Guest

The whole guest, for reference (the host is in the repo):

//! A `wasi:http/handler@0.3` component with two routes that differ only in
//! whether the response carries a `content-length` header:
//!
//! - `GET /with-content-length`
//! - `GET /without-content-length`

use bytes::Bytes;
use http::header;
use http_body_util::Full;
use wasip3::http::types::{self, ErrorCode};
use wasip3::http_compat::{http_from_wasi_request, http_into_wasi_response};

wasip3::http::service::export!(Guest);

struct Guest;

impl wasip3::exports::http::handler::Guest for Guest {
    async fn handle(request: types::Request) -> Result<types::Response, ErrorCode> {
        let request = http_from_wasi_request(request)?;
        let body = "hello\n";
        let mut response = http::Response::new(Full::new(Bytes::from_static(body.as_bytes())));
        if request.uri().path() == "/with-content-length" {
            response
                .headers_mut()
                .insert(header::CONTENT_LENGTH, body.len().into());
        }
        http_into_wasi_response(response)
    }
}

Wasmtime GitHub notifications bot (Oct 15 2026 at 04:30):

avkonst added the bug label to Issue #14769.

Last updated: Oct 31 2026 at 23:03 UTC