#wasi #deterministic #context #system #invoking #return


A wasi-common WasiCtx implementation that is fully deterministic

20 releases

0.1.20 Mar 21, 2024
0.1.18 Jan 29, 2024
0.1.16 Oct 30, 2023
0.1.14 Jul 18, 2023
0.1.5 Jul 21, 2022

#70 in WebAssembly

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Apache-2.0 WITH LLVM-exception

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About this repo

A Rust crate for creating a wasi-common 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.


let wasi = deterministic_wasi_ctx::build_wasi_ctx();
let engine = Engine::default();
let mut linker = Linker::new(&engine);
wasmtime_wasi::add_to_linker(&mut linker, |s| s).unwrap();
let module_path = ...; // path to a Wasm module
let module = Module::from_file(&engine, module_path).unwrap();
let mut store = Store::new(&engine, wasi);
linker.module(&mut store, "", &module).unwrap();
let instance = linker.instantiate(&mut store, &module).unwrap();
... // invoke functions on `instance`


deterministic-wasi-ctx is a beta project and will be under major development. 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-wasi target, can be installed by running rustup target add wasm32-wasi


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


Run make test to run integration tests.


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.


  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


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