Stream: git-wasmtime

Topic: wasmtime / issue #12714 wasmtime serve fails to link wasi...

Wasmtime GitHub notifications bot (Mar 04 2026 at 01:38):

mizchi opened issue #12714:

Summary

wasmtime serve fails to link a wasi:http/service@0.3.0-rc-2026-01-06 component generated via wit-bindgen + wasm-tools component new.

The failure happens even without any compose step (wac / wasm-tools compose are not involved in this repro).

Versions

• wasmtime: 41.0.3 (db1c043b5 2026-02-04)
• wasm-tools: 1.245.1
• rustc: 1.92.0
• cargo: 1.92.0
• wit-bindgen crate: 0.51.0

Minimal Repro

src/lib.rs:

wit_bindgen::generate!({
    inline: r#"
      package vibe:http-adapter;

      world serviceonly {
        include wasi:http/service@0.3.0-rc-2026-01-06;
      }
    "#,
    // Uses wasmtime's bundled wasi-http p3 WIT package
    path: "<wasmtime repo>/crates/wasi-http/src/p3/wit",
    world: "vibe:http-adapter/serviceonly",
    pub_export_macro: true,
    generate_all,
});

use exports::wasi::http::handler::Guest;
use wasi::http::types::{ErrorCode, Request, Response};

struct Component;

impl Guest for Component {
    async fn handle(request: Request) -> Result<Response, ErrorCode> {
        let _ = request;
        Err(ErrorCode::InternalError(None))
    }
}

export!(Component);

Build & run:

cargo build --target wasm32-unknown-unknown --release
wasm-tools component new target/wasm32-unknown-unknown/release/<crate>.wasm -o service_only.component.wasm
wasmtime serve \
  -W component-model-async=y \
  -W component-model-async-builtins=y \
  --addr 127.0.0.1:0 \
  service_only.component.wasm

Actual

wasmtime serve fails immediately:

Error: component imports instance `wasi:http/types@0.3.0-rc-2026-01-06`, but a matching implementation was not found in the linker

Caused by:
    0: instance export `request` has the wrong type
    1: resource implementation is missing

Additional Notes

• This same error reproduces from a second path where we compose another component via wac plug, but the service-only repro above shows compose is not required.
• wasm-tools validate --features all service_only.component.wasm succeeds.

If this behavior is expected due to stricter type matching semantics in serve, guidance on the required shape for imported wasi:http/types in generated components would help.

Wasmtime GitHub notifications bot (Mar 04 2026 at 15:37):

alexcrichton commented on issue #12714:

WASIp3 is disabled by default, so if you pass -Sp3 does that resolve this error?

Last updated: Mar 23 2026 at 16:19 UTC