Out of bounds memory access when using fetch

[mschuwalow]

Originally opened in the jco repository (bytecodealliance/jco#668). Also posting here for visibility. Feel free to close one of them.

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Here is a minimal reproduction:

Create the following files

wit/component.wit:

package pack:name;

world component {
  import wasi:http/outgoing-handler@0.2.0;
  export wasi:cli/run@0.2.0;
}

src/main.js:

const run = {
    async run() {
        try {
            var n = 0;
            let requests = [];
            while (n < 1000) {
                requests.push(fetch("https://jsonplaceholder.typicode.com/todos/1"));
                n += 1;
            }
            for (const request of requests) {
                const response = await request;
                const data = await response.json();
                console.log("HTTP Response:", data);
            }
        }
        catch (error) {
            console.error("HTTP Request Error:", error);
        }
    }
};

export { run };

Run the following commands:

• jco componentize -w wit -o dist/main.wasm src/main.js
• wasmtime run -S http=y dist/main.wasm

Output:

HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
HTTP Response: { userId: 1, id: 1, title: "delectus aut autem", completed: false }
Error: failed to run main module `dist/main.wasm`

Caused by:
    0: failed to invoke `run` function
    1: error while executing at wasm backtrace:
           0: 0x7fcce3 - <unknown>!<wasm function 13434>
           1: 0x242dac - <unknown>!<wasm function 5248>
           2: 0x80c526 - <unknown>!post_wasi:cli/run@0.2.0#run
    2: memory fault at wasm address 0x9ad94527 in linear memory of size 0xb10000
    3: wasm trap: out of bounds memory access

Exception: wasmtime exited with 134

Environment

System: Apple M4 Pro
OS: macOS 15.4.1 (24E263)

Tool Versions:

wasmtime 26.0.1
jco 1.10.2
componentize-js 0.18.0