deterministic-wasi-ctx

About this repo

A Rust crate for creating a wasmtime-wasi WASI context implementation that is fully deterministic.

Determinism refers to the property that a provided WASI function will always return the same series of results for the same series of invocations. For example, invoking clock_time_get against the system clock will always return the same timestamp. Or invoking random_get will always return 155 on the first invocation followed by always returning 111 on the second invocation.

This can be useful in a variety of contexts. For example, caching the results of invoking a function in a Wasm module.

Features

• wasi-common - Enabling this feature exposes APIs that use the wasi-common crate instead of wasmtime-wasi.

Usage

let engine = Engine::default();
let mut wasi_builder = WasiCtxBuilder::new();
let mut linker = Linker::new(&engine);

deterministic_wasi_ctx::add_determinism_to_wasi_ctx_builder(&mut wasi_builder);
let wasi = wasi_builder.build_p1();
wasmtime_wasi::preview1::add_to_linker_sync(&mut linker, |s| s)?;
deterministic_wasi_ctx::replace_scheduling_functions(&mut linker)?;

let mut store = Store::new(&engine, wasi);
let module_path = ...; // path to a Wasm module
let module = Module::from_file(&engine, module_path).unwrap();
let instance = linker.instantiate(&mut store, &module).unwrap();
... // invoke functions on `instance`

Contributing

We welcome feedback, bug reports and bug fixes. We're also happy to discuss feature development but please discuss the features in an issue before contributing.

Build dependencies

• rustup
• The latest release of Rust on the stable channel
• wasm32-wasip1 target, can be installed by running rustup target add wasm32-wasip1

Building

After all the dependencies are installed, run make build-deterministic-wasi-ctx to build the crate.

Testing

Run make test to run integration tests.

Structure

The deterministic-wasi-ctx-test-programs crate is used to build a collection of Wasm files invoking WASI functions that the integration tests in the deterministic-wasi-ctx crate use to verify the output from those Wasm files is deterministic.

Releasing

1. Create and merge a PR incrementing the crates' versions in accordance with SemVer based on changes from the previous release
2. Create a new release in Github with a name like v0.1.0 where the version matches the crates' versions
3. Publish the new version of the crate by running make publish