Execute wasm file in NodeJS

[Gregoirevda]

I'd like to expand the tutorial on how to run the wasm file in NodeJS after running it with wasmtime.

Normally you can simply run WebAssembly.instantiate(buf), but here the demo.c contains arguments input.txt and output.txt.
The WebAssembly requires a wasi_unstable object and within that a fd_prestat_get function, but I don't know how it should look like...

index.js

const fs = require('fs');
const buf = fs.readFileSync('./demo.wasm');

(async () => {
  const res = await WebAssembly.instantiate(buf, {wasi_unstable: {fd_prestat_get: () => {}}});

  console.log(res.instance);
})();

[bjorn3]

https://github.com/devsnek/node-wasi may be what you want.

[Gregoirevda]

Thanks @bjorn3

I managed to run the wasm package, but get into the first error defined in the demo.c file
usage: (null) <from> <to>

You know how to pass params to wasm main function?

const WASI = require('wasi');
const fs = require('fs');

const buf = fs.readFileSync('./demo.wasm');

const wasi = new WASI({
  // preopenDirectories: { '.': '.' },
});

(async () => {
  let res = await WebAssembly.instantiate(buf, {
    wasi_unstable: wasi.exports
  });
  wasi.setMemory(res.instance.exports.memory);

  res.instance.exports._start("./input.txt", "output.txt");
})()

[bjorn3]

https://github.com/devsnek/node-wasi/blob/68902020ce28210ab1fc12dfaec090ef82c44263/index.js#L507

It seems like you can use new WASI({ args: ["arg1", "arg2"] }) to pass args.

[Gregoirevda]

It's overriding the 1st arg, so I tried passing the wasm executable path and the 2 other args
args: ["fullpath/demo.wasm", "input.txt", "output.txt"]

but getting

TypeError: wasm function signature contains illegal type
    at openat (wasm-function[24]:318)
    at open (wasm-function[26]:114)
    at main (wasm-function[15]:209)
    at _start (wasm-function[14]:405)
    at /wasi/index.js:19:24

Line 19 res.instance.exports._start()

[devsnek]

@Gregoirevda you'll need to run it with node --experimental-wasm-bigint

[Gregoirevda]

I managed to make it work with path.resolve

js
const WASI = require('wasi');
const fs = require('fs');
const path = require('path');

const buf = fs.readFileSync('./demo.wasm');

const wasi = new WASI({
  preopenDirectories: { '.': '.' },
  args: [path.resolve(__dirname, "test.wasm"), path.resolve(__dirname, 'test.txt'), path.resolve(__dirname, 'output.txt')]
});

(async () => {
  let res = await WebAssembly.instantiate(buf, {
    wasi_unstable: wasi.exports
  });

  wasi.setMemory(res.instance.exports.memory);
  res.instance.exports._start();
})()

I'm getting the next error error opening input /Users/gvanderauw001/dev/workshop/wasi/test.txt: Capabilities insufficient

Is there a way to give capability with WASI like
wasmtime --dir=. --dir=/tmp demo.wasm test.txt /tmp/somewhere.txt?

[bjorn3]

Is there a way to give capability with WASI like
wasmtime --dir=. --dir=/tmp demo.wasm test.txt /tmp/somewhere.txt?

That's what preopenDirectories does: preopenDirectories: { '.': '.', '/tmp': '/tmp' },

[Gregoirevda]

@bjorn3 both input.txt and output.txt are in the same folder. I tried passing ., ./, {__dirname} without success...

[Gregoirevda]

What are key:value used for?

[devsnek]

pathForWasi: realPath

e.g. if you wanted to expose ./project/sandbox as / to wasi you would do '/': './project/sandbox'

[Gregoirevda]

Thanks @devsnek
I went back to

const wasi = new WASI({
  preopenDirectories: { '.': '.' },
  args: [__dirname, 'test.txt', 'output.txt']
});

instead of path.resolve(__dirname, 'file.txt'), which fixed the permission error.

I also went from node 11.x to node 12.3.0 and there only I could have access to the --experimental-wasm-bigint flag, which deleted the typeError.

Arguments are now red correctly, files are opened, but the C code fails at writing.
I'm getting: write error: Bad file descriptor

From this file. But it ofcourse works with wasmtime.

I tried changing the out file to int out = open(argv[2], O_CREAT | O_RDWR, 0660); or other flags with no luck.

[Gregoirevda]

Same error with stdio

[bjorn3]

I think this can be closed. It isn't related to Cranelift or Wasmtime.