mozilla-central/third_party/rust/wasi/README.md

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<h1><code>wasi</code></h1>
<strong>A <a href="https://bytecodealliance.org/">Bytecode Alliance</a> project</strong>
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<strong>WASI API Bindings for Rust</strong>
</p>
<p>
</p>
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This crate contains API bindings for [WASI](https://github.com/WebAssembly/WASI)
system calls in Rust, and currently reflects the `wasi_snapshot_preview1`
module. This crate is quite low-level and provides conceptually a "system call"
interface. In most settings, it's better to use the Rust standard library, which
has WASI support.
The `wasi` crate is also entirely procedurally generated from the `*.witx` files
describing the WASI apis. While some conveniences are provided the bindings here
are intentionally low-level!
# Usage
First you can depend on this crate via `Cargo.toml`:
```toml
[dependencies]
wasi = "0.8.0"
```
Next you can use the APIs in the root of the module like so:
```rust
fn main() {
let stdout = 1;
let message = "Hello, World!\n";
let data = [wasi::Ciovec {
buf: message.as_ptr(),
buf_len: message.len(),
}];
wasi::fd_write(stdout, &data).unwrap();
}
```
Next you can use a tool like [`cargo
wasi`](https://github.com/bytecodealliance/cargo-wasi) to compile and run your
project:
To compile Rust projects to wasm using WASI, use the `wasm32-wasi` target,
like this:
```
$ cargo wasi run
Compiling wasi v0.8.0+wasi-snapshot-preview1
Compiling wut v0.1.0 (/code)
Finished dev [unoptimized + debuginfo] target(s) in 0.34s
Running `/.cargo/bin/cargo-wasi target/wasm32-wasi/debug/wut.wasm`
Running `target/wasm32-wasi/debug/wut.wasm`
Hello, World!
```
# Development
The bulk of the `wasi` crate is generated by the `witx-bindgen` tool, which lives at
`crates/witx-bindgen` and is part of the cargo workspace.
The `src/lib_generated.rs` file can be re-generated with the following
command:
```
cargo run -p witx-bindgen -- crates/witx-bindgen/WASI/phases/snapshot/witx/wasi_snapshot_preview1.witx > src/lib_generated.rs
```
Note that this uses the WASI standard repository as a submodule. If you do not
have this submodule present in your source tree, run:
```
git submodule update --init
```
# License
This project is licensed under the Apache 2.0 license with the LLVM exception.
See [LICENSE](LICENSE) for more details.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this project by you, as defined in the Apache-2.0 license,
shall be licensed as above, without any additional terms or conditions.