Import #0 "wasi_snapshot_preview1": module is not an object or function

[inhahe]

I have a WASI C++ program that when I compile it and try to import it in my html, I get Uncaught (in promise) TypeError: WebAssembly.instantiate(): Import #0 "wasi_snapshot_preview1": module is not an object or function

What could be causing this?

I added -Oz to the clang command line and that fixed it temporarily, but then when I tried to -Wl,--export=mainloop, I got the error back again. Then I narrowed down one specific part of my C++ code that causes the error, but nothing in that section seemed special or out of the ordinary. It did use some variables that were defined with uint32_t and uint8_t, so I tried redefining them as ints, but I still got the error. Then I kept getting the error even when commenting out the stuff that commenting out made the error go away to begin with!

[sbc100]

The WASI APIs that are part of wasi_snapshot_preview1 are not part of the web platform, so if you want to run a WASI program on the web you would need to use something like https://github.com/bytecodealliance/jco or emscripten.

[inhahe]

The WASI APIs that are part of wasi_snapshot_preview1 are not part of the web platform, so if you want to run a WASI program on the web you would need to use something like https://github.com/bytecodealliance/jco or emscripten.

Hmm, I'm not sure what you mean by WASI APIs - WASI functions that you can call in your program? Because I only use normal C++ library functions as far as I can tell. Is there a way to find out what function is trying to load wasi_snapshot_preview1 so that I can eliminate it? Thanks

I have another WASI program that somebody else wrote that's a lot simpler and doesn't give me this error on the web, so I know it's not absolutely necessary to use something like jco or Emscripten.

[sbc100]

Pretty much any WASI program (i.e. any program build with wasi-sdk) will depend on one or more WASI APIs. In theory could could try to build a pure compute module that doesn't call any inports, but there are not very many useful programs in that category and wasi-sdk doesn't have any mechanism to enforce such a thing.. Most WASI program depends on WASI imports, by design.

If you want to find out why a given import is needed you can disassembly the module using wasm-dis (from binaryen) or wasm2wat (from wabt) and then look for wasi_snapshot_preview1 to see which functions are being imported.. you can then search for those function by name to see where there are using in your program.

[guest271314]

Here's a minimal WASI snapshot preview version 1 that is tested and works using node, deno, and bun https://gitlab.com/-/snippets/4782260/raw/main/wasi-minimal.js.

E.g.,

import { readFile } from "node:fs/promises";
import process from "node:process";
import { WASI } from "./wasi-minimal-min.js"; // https://gitlab.com/-/snippets/4782260/raw/main/wasi-minimal.js
import * as fs from "node:fs";
try {
  const [embeddedModule, pluginModule] = await Promise.all([
    compileModule("./nm_javy_permutations.wasm"),
    compileModule("./plugin.wasm"),
  ]);
  const result = await runJavy(embeddedModule, pluginModule);
} catch (e) {
  process.stdout.write(e.message, "utf8");
} finally {
  process.exit();
}
async function compileModule(wasmPath) {
  const bytes = await readFile(new URL(wasmPath, import.meta.url));
  return WebAssembly.compile(bytes);
}
async function runJavy(embeddedModule, pluginModule) {
  try {
    let wasi = new WASI({
      env: {},
      args: [],
      fds: [
        {
          type: 2,
          handle: fs,
        },
        {
          type: 2,
          handle: fs,
        },
        {
          type: 2,
          handle: fs,
        },
      ],
    });

    const pluginInstance = await WebAssembly.instantiate(
      pluginModule,
      { "wasi_snapshot_preview1": wasi.exports },
    );
    const instance = await WebAssembly.instantiate(embeddedModule, {
      "javy_quickjs_provider_v3": pluginInstance.exports,
    });

    wasi.memory = pluginInstance.exports.memory;
    instance.exports._start();
    return;
  } catch (e) {
    if (e instanceof WebAssembly.RuntimeError) {
      if (e) {
        throw new Error(e);
      }
    }
    throw e;
  }
}

$ printf '4 5' | deno -A run-wasi.js 
5 of 23 (0-indexed, factorial 24) => [0,3,2,1]
$ printf '4 5' | node run-wasi.js 
5 of 23 (0-indexed, factorial 24) => [0,3,2,1]
$ printf '4 5' | bun run run-wasi.js 
5 of 23 (0-indexed, factorial 24) => [0,3,2,1]