Workers WASI

Work in progress

An experimental implementation of the WebAssembly System Interface designed to run on Cloudflare Workers

Usage

import { WASI } from 'workers-wasi';
import mywasm from './mywasm.wasm';

const wasi = new WASI();
const instance = new WebAssembly.Instance(mywasm, {
   wasi_snapshot_preview1: wasi.wasiImport
});

await wasi.start(instance);

Development

Install Rust and nvm then run

nvm use --lts

Build and test

git clone --recursive [email protected]:cloudflare/workers-wasi.git
cd ./workers-wasi
make -j test

Build with Docker

git clone --recursive [email protected]:cloudflare/workers-wasi.git
cd ./workers-wasi
cat ./Dockerfile | docker build -t workers-wasi-build -
docker run --rm -it -v $(pwd):/workers-wasi workers-wasi-build

Testing

We aim to be interchangeable with other WASI implementations. Integration tests are run locally using Miniflare against the following test suites:

• (52/52) https://github.com/caspervonb/wasi-test-suite
• (27/42) https://github.com/bytecodealliance/wasmtime/tree/main/crates/test-programs/wasi-tests

Notes

An ephemeral filesystem implementation built on littlefs is included. Both soft and hard links are not yet supported.

The following syscalls are not yet supported and return ENOSYS

• fd_readdir
• path_link
• path_readlink
• path_symlink
• poll_oneoff
• sock_recv
• sock_send
• sock_shutdown

Timestamps are captured using Date.now() which has unique behavior on the Workers platform for security reasons. This affects the implementation of

• clock_res_get
• clock_time_get
• fd_filestat_set_times
• path_filestat_set_times

TODO (remove)

Misc TODO:

• path_rename (update old path for existing open fds)
• clean up tmp_alloc() - wrap all exports
• fix preopens interface (use object), and update options docs
• document difference between nodejs options and ours (streams/fs)
• complete memfs.cc todos
• fd_close (stdio)
• fd_renumber (stdio)
• fd_read/fd_write does not work with renumbering stdio
• update file timestamps appropriately