5d9c8c5d05
Add `plugin.call_with_host_context` and `current_plugin.host_context` methods, enabling per-call context to be looped from the guest invocation to any host functions it calls. In an HTTP server environment, this enables re-using a plugin across multiple requests while switching out backing connections and user information in host functions. (Imagine a host function, `update_user` -- previously the plugin would have to have been aware of the user to pass to the host function. Now that information is ambient.) This is a backwards-compatible change and requires no changes to existing plugins. Implement by adding a global, mutable externref to the extism kernel. Since most programming languages, including Rust, don't let you define these natively, we accomplish this by using `wasm-merge` to combine the kernel Wasm with Wasm generated by a WAT file containing only the global. (This pattern might be useful for other Wasm constructs we can't use directly from Rust, like `v128` in argument parameters.) Wasmtime requires extern refs to be `Any + Send + Sync + 'static`; we additionally add `Clone`. I haven't tried this with an `Arc` directly, but it should work at least for container structs that hold `Arc`'s themselves.
Overview
Extism is a lightweight framework for building with WebAssembly (Wasm). It supports running Wasm code on servers, the edge, CLIs, IoT, browsers and everything in between. Extism is designed to be "universal" in that it supports a common interface, no matter where it runs.
Note: One of the primary use cases for Extism is building extensible software & plugins. You want to be able to execute arbitrary, untrusted code from your users? Extism makes this safe and practical to do.
Additionally, Extism adds some extra utilities on top of standard Wasm runtimes. For example, we support persistent memory/module-scope variables, secure & host-controlled HTTP without WASI, runtime limiters & timers, simpler host function linking, and more. Extism users build:
- plug-in systems
- FaaS platforms
- code generators
- web applications
- & much more...
Run WebAssembly In Your App
Pick a SDK to import into your program, and refer to the documentation to get started:
| Type | Language | Source Code | Package |
|---|---|---|---|
| Rust SDK |  |
https://github.com/extism/extism/tree/main/runtime | Crates.io |
| JS SDK |  |
https://github.com/extism/js-sdk (supports Web, Node, Deno & Bun!) |
NPM |
| Elixir SDK |  |
https://github.com/extism/elixir-sdk | Hex |
| Go SDK |  |
https://github.com/extism/go-sdk | Go mod |
| Haskell SDK |  |
https://github.com/extism/haskell-sdk | Hackage |
| Java SDK |  |
https://github.com/extism/java-sdk | Sonatype |
| .NET SDK |  |
https://github.com/extism/dotnet-sdk (supports C# & F#!) |
Nuget |
| OCaml SDK |  |
https://github.com/extism/ocaml-sdk | opam |
| Perl SDK |  |
https://github.com/extism/perl-sdk | N/A |
| PHP SDK |  |
https://github.com/extism/php-sdk | Packagist |
| Python SDK |  |
https://github.com/extism/python-sdk | PyPi |
| Ruby SDK |  |
https://github.com/extism/ruby-sdk | RubyGems |
| Zig SDK |  |
https://github.com/extism/zig-sdk | N/A |
| C SDK |  |
https://github.com/extism/extism/tree/main/libextism | N/A |
| C++ SDK |  |
https://github.com/extism/cpp-sdk | N/A |
Compile WebAssembly to run in Extism Hosts
Extism Hosts (running the SDK) must execute WebAssembly code that has a PDK
library compiled in to the .wasm binary. PDKs make it easy for plug-in /
extension code authors to read input from the host and return data back, read
provided configuration, set/get variables, make outbound HTTP calls if allowed,
and more.
Pick a PDK to import into your Wasm program, and refer to the documentation to get started:
| Type | Language | Source Code | Package |
|---|---|---|---|
| Rust PDK | |
https://github.com/extism/rust-pdk | Crates.io |
| JS PDK | |
https://github.com/extism/js-pdk | N/A |
| Go PDK | |
https://github.com/extism/go-pdk | Go mod |
| Haskell PDK | |
https://github.com/extism/haskell-pdk | Hackage |
| AssemblyScript PDK |  |
https://github.com/extism/assemblyscript-pdk | NPM |
| .NET PDK | |
https://github.com/extism/dotnet-pdk (supports C# & F#!) |
https://www.nuget.org/packages/Extism.Pdk |
| C PDK | |
https://github.com/extism/c-pdk | N/A |
| Zig PDK | |
https://github.com/extism/zig-pdk | N/A |
Support
Discord
If you experience any problems or have any questions, please join our Discord and let us know. Our community is very responsive and happy to help get you started.
Usage
Head to the project website for more information and docs. Also, consider reading an overview of Extism and its goals & approach.
Contribution
Thank you for considering a contribution to Extism, we are happy to help you make a PR or find something to work on!
The easiest way to start would be to join the
Discord or open an issue on the
extism/proposals issue tracker, which
can eventually become an Extism Improvement Proposal (EIP).
For more information, please read the Contributing guide.
Who's behind this?
Extism is an open-source product from the team at:
Reach out and tell us what you're building! We'd love to help: hello@dylibso.com