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[bug] Calling `wasi_snapshot_preview1` `path_open` without "extra steps" returns BADF (error 8)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
typescript, wasm
Domain
operating-systems

Research direction

Start with the wasi_snapshot_preview1 path_open implementation used by @vscode/wasm-wasi and compare its handling of the repro.wat call with node:wasi and Wasmtime. Reproduce the fd=3 call through createProcess and verify that direct path_open succeeds without breaking the existing C fopen("test.txt", "r") case.

Written by the indexing model from the issue text.

Description

bug

When the following is compiled with WASI SDK to test.wasm:

#include <stdio.h>

int main(int argc, const char **argv)
{
    FILE *file = fopen("test.txt", "r");
    if (file == NULL)
    {
        return 1;
    }

    char buffer[1024];
    while (fgets(buffer, sizeof(buffer), file) != NULL)
    {
        fputs(buffer, stdout);
    }
    fclose(file);

    return 0;
}

and executed using this setup:

import { Wasm } from "@vscode/wasm-wasi";

// ...
const wasm: Wasm = await Wasm.api();
const pty = wasm.createPseudoterminal();
const terminal = vscode.window.createTerminal({
    name: "test",
    pty,
    isTransient: true,
});
terminal.show(true);

try {
    const process = await wasm.createProcess(
        "test.wasm",
        currentCompilerModule,
        {
            stdio: pty.stdio,
            mountPoints: [
                {
                    kind: "vscodeFileSystem",
                    uri: workspaceUri,
                    mountPoint: "/",
                },
            ],
        }
    );

    const exitCode = await process.run();
    if (exitCode !== 0) {
        vscode.window.showErrorMessage(
            `Process exited with code: ${exitCode}`
        );
    }
} catch (error) {
    vscode.window.showErrorMessage((error as Error).message);
    terminal.dispose();
}

VSCode properly reads test.txt file from the current workspace and print it to created terminal.

However:

Trying to call wasi_snapshot_preview1 path_open function with fd=3, path="test.txt" directly always returns EBADF (code 8).

Minimal reproduction:

(; repro.wat ;)
(module
  (type (;0;) (func (param i32 i32 i32 i32 i32 i64 i64 i32 i32) (result i32)))
  (type (;1;) (func (param i32)))
  (type (;2;) (func))
  (import "wasi_snapshot_preview1" "path_open" (func (;0;) (type 0)))
  (import "wasi_snapshot_preview1" "proc_exit" (func (;1;) (type 1)))
  (func $_start (type 2)
    (local i32)
    i32.const 3
    i32.const 1
    i32.const 68314
    i32.const 8
    i32.const 0
    i64.const 264240830
    i64.const 268435455
    i32.const 0
    i32.const 67188
    call 0
    local.set 0
    local.get 0
    call 1)
  (memory (;0;) 40)
  (export "memory" (memory 0))
  (export "_start" (func $_start))
  (data (;0;) (i32.const 68314) "test.txt"))

P.S: Arguments to the function were extracted by using node:wasi and logging calls of all import functions.

Running repro.wat works fine in both node:wasi and wasmtime.

Dominant language
TypeScript
Stars
456
Forks
42
Avg merge
3d 19h
Merged PRs (30d)
7

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