README.md

wasi_snapshot_preview1.wasm

Note: This repository is a work in progress. This is intended to be an internal tool which not everyone has to look at but many might rely on. You may need to reach out via issues or Zulip to learn more about this repository.

This repository currently contains an implementation of a WebAssembly module: wasi_snapshot_preview1.wasm. This module bridges the wasi_snapshot_preview1 ABI to the preview2 ABI of the component model. At this time the preview2 APIs themselves are not done being specified so a local copy of wit/*.wit is used instead.

Building

This adapter can be built with:

cargo build -p wasi-preview1-component-adapter --target wasm32-unknown-unknown --release

And the artifact will be located at target/wasm32-unknown-unknown/release/wasi_snapshot_preview1.wasm.

This by default builds a "reactor" adapter which means that it only provides adaptation from preview1 to preview2. Alternatively you can also build a "command" adapter by passing --features command --no-default-features which will additionally export a run function entrypoint. This is suitable for use with preview1 binaries that export a _start function.

Alternatively the latest copy of the command and reactor adapters can be downloaded from the dev tag assets

Using

With a wasi_snapshot_preview1.wasm file on-hand you can create a component from a module that imports WASI functions using the wasm-tools CLI

$ cat foo.rs
fn main() {
    println!("Hello, world!");
}
$ rustc foo.rs --target wasm32-wasip1
$ wasm-tools print foo.wasm | grep '(import'
  (import "wasi_snapshot_preview1" "fd_write" (func ...
  (import "wasi_snapshot_preview1" "environ_get" (func ...
  (import "wasi_snapshot_preview1" "environ_sizes_get" ...
  (import "wasi_snapshot_preview1" "proc_exit" (func ...
$ wasm-tools component new foo.wasm --adapt wasi_snapshot_preview1.wasm -o component.wasm

# Inspect the generated `component.wasm`
$ wasm-tools validate component.wasm --features component-model
$ wasm-tools component wit component.wasm

Here the component.wasm that's generated is a ready-to-run component which imports wasi preview2 functions and is compatible with the wasi-preview1-using module internally.