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https://github.com/extism/rust-pdk
Extism Plug-in Development Kit (PDK) for Rust
https://github.com/extism/rust-pdk
Last synced: 20 days ago
JSON representation
Extism Plug-in Development Kit (PDK) for Rust
- Host: GitHub
- URL: https://github.com/extism/rust-pdk
- Owner: extism
- License: bsd-3-clause
- Created: 2022-08-26T15:48:04.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2024-11-20T06:49:04.000Z (23 days ago)
- Last Synced: 2024-11-20T11:41:01.533Z (23 days ago)
- Language: Rust
- Homepage: https://docs.rs/extism-pdk
- Size: 6.55 MB
- Stars: 48
- Watchers: 3
- Forks: 8
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
- Codeowners: .github/CODEOWNERS
Awesome Lists containing this project
- awesome-wasm-runtimes - `Rust`
README
# Extism Rust PDK
[](https://crates.io/crates/extism-pdk)
This library can be used to write
[Extism Plug-ins](https://extism.org/docs/concepts/plug-in) in Rust.
## Install
Generate a `lib` project with Cargo:
```bash
cargo new --lib my-plugin
```
Add the library from [crates.io](https://crates.io/crates/extism-pdk).
```bash
cargo add extism-pdk
```
Change your `Cargo.toml` to set the crate-type to `cdylib` (this instructs the
compiler to produce a dynamic library, which for our target will be a Wasm
binary):
```toml
[lib]
crate_type = ["cdylib"]
```
### Rustup and wasm32-unknown-unknown installation
Our example below will use the `wasm32-unknown-unknown` target. If this is not
installed you will need to do so before this example will build. The easiest way
to do this is use [`rustup`](https://rustup.rs/).
```bash
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
```
Once `rustup` is installed, add the `wasm32-unknown-unknown` target:
```bash
rustup target add wasm32-unknown-unknown
```
## Getting Started
The goal of writing an
[Extism plug-in](https://extism.org/docs/concepts/plug-in) is to compile your
Rust code to a Wasm module with exported functions that the host application can
invoke. The first thing you should understand is creating an export. Let's write
a simple program that exports a `greet` function which will take a name as a
string and return a greeting string. For this, we use the `#[plugin_fn]` macro
on our exported function:
```rust
use extism_pdk::*;
#[plugin_fn]
pub fn greet(name: String) -> FnResult {
Ok(format!("Hello, {}!", name))
}
```
Since we don't need any system access for this, we can compile this to the
lightweight `wasm32-unknown-unknown` target instead of using the `wasm32-wasi`
target:
```bash
cargo build --target wasm32-unknown-unknown
```
> **Note**: You can also put a default target in `.cargo/config.toml`:
```toml
[build]
target = "wasm32-unknown-unknown"
```
This will put your compiled wasm in `target/wasm32-unknown-unknown/debug`. We
can now test it using the [Extism CLI](https://github.com/extism/cli)'s `run`
command:
```bash
extism call target/wasm32-unknown-unknown/debug/my_plugin.wasm greet --input "Benjamin"
# => Hello, Benjamin!
```
> **Note**: We also have a web-based, plug-in tester called the
> [Extism Playground](https://playground.extism.org/)
### More About Exports
Adding the
[plugin_fn](https://docs.rs/extism-pdk/latest/extism_pdk/attr.plugin_fn.html)
macro to your function does a couple things. It exposes your function as an
export and it handles some of the lower level ABI details that allow you to
declare your Wasm function as if it were a normal Rust function. Here are a few
examples of exports you can define.
### Primitive Types
A common thing you may want to do is pass some primitive Rust data back and
forth. The
[plugin_fn](https://docs.rs/extism-pdk/latest/extism_pdk/attr.plugin_fn.html)
macro can map these types for you:
> **Note**: The
> [plugin_fn](https://docs.rs/extism-pdk/latest/extism_pdk/attr.plugin_fn.html)
> macro uses the
> [convert crate](https://github.com/extism/extism/tree/main/convert) to
> automatically convert and pass types across the guest / host boundary.
```rust
// f32 and f64
#[plugin_fn]
pub fn add_pi(input: f32) -> FnResult {
Ok(input as f64 + 3.14f64)
}
// i32, i64, u32, u64
#[plugin_fn]
pub fn sum_42(input: i32) -> FnResult {
Ok(input as i64 + 42i64)
}
// u8 vec
#[plugin_fn]
pub fn process_bytes(input: Vec) -> FnResult> {
// process bytes here
Ok(input)
}
// Strings
#[plugin_fn]
pub fn process_string(input: String) -> FnResult {
// process string here
Ok(input)
}
```
### Json
We provide a
[Json](https://docs.rs/extism-pdk/latest/extism_pdk/struct.Json.html) type that
allows you to pass structs that implement serde::Deserialize as parameters and
serde::Serialize as returns:
```rust
#[derive(serde::Deserialize)]
struct Add {
a: u32,
b: u32,
}
#[derive(serde::Serialize)]
struct Sum {
sum: u32,
}
#[plugin_fn]
pub fn add(Json(add): Json) -> FnResult> {
let sum = Sum { sum: add.a + add.b };
Ok(Json(sum))
}
```
The same thing can be accomplished using the `extism-convert` derive macros:
```rust
#[derive(serde::Deserialize, FromBytes)]
#[encoding(Json)]
struct Add {
a: u32,
b: u32,
}
#[derive(serde::Serialize, ToBytes)]
#[encoding(Json)]
struct Sum {
sum: u32,
}
#[plugin_fn]
pub fn add(add: Add) -> FnResult {
let sum = Sum { sum: add.a + add.b };
Ok(sum)
}
```
### Raw Export Interface
[plugin_fn](https://docs.rs/extism-pdk/latest/extism_pdk/attr.plugin_fn.html) is
a nice macro abstraction but there may be times where you want more control. You
can code directly to the raw ABI interface of export functions.
```rust
#[no_mangle]
pub unsafe extern "C" fn greet() -> i32 {
let name = unwrap!(input::());
let result = format!("Hello, {}!", name);
unwrap!(output(result));
0i32
}
```
## Configs
Configs are key-value pairs that can be passed in by the host when creating a
plug-in. These can be useful to statically configure the plug-in with some data
that exists across every function call. Here is a trivial example:
```rust
#[plugin_fn]
pub fn greet() -> FnResult {
let user = config::get("user").expect("'user' key set in config");
Ok(format!("Hello, {}!", user))
}
```
To test it, the [Extism CLI](https://github.com/extism/cli) has a `--config`
option that lets you pass in `key=value` pairs:
```bash
extism call my_plugin.wasm greet --config user=Benjamin
# => Hello, Benjamin!
```
## Variables
Variables are another key-value mechanism but it's a mutable data store that
will persist across function calls. These variables will persist as long as the
host has loaded and not freed the plug-in. You can use
[var::get](https://docs.rs/extism-pdk/latest/extism_pdk/var/fn.get.html) and
[var::set](https://docs.rs/extism-pdk/latest/extism_pdk/var/fn.set.html) to
manipulate them.
```rust
#[plugin_fn]
pub fn count() -> FnResult {
let mut c = var::get("count")?.unwrap_or(0);
c = c + 1;
var::set("count", c)?;
Ok(c)
}
```
## Logging
Because Wasm modules by default do not have access to the system, printing to
stdout won't work (unless you use WASI). Extism provides some simple logging
macros that allow you to use the host application to log without having to give
the plug-in permission to make syscalls. The primary one is
[log!](https://docs.rs/extism-pdk/latest/extism_pdk/macro.log.html) but we also
have some convenience macros named by log level:
```rust
#[plugin_fn]
pub fn log_stuff() -> FnResult<()> {
log!(LogLevel::Info, "Some info!");
log!(LogLevel::Warn, "A warning!");
log!(LogLevel::Error, "An error!");
// optionally you can use the leveled macros:
info!("Some info!");
warn!("A warning!");
error!("An error!");
Ok(())
}
```
From [Extism CLI](https://github.com/extism/cli):
```bash
extism call my_plugin.wasm log_stuff --log-level=info
2023/09/30 11:52:17 Some info!
2023/09/30 11:52:17 A warning!
2023/09/30 11:52:17 An error!
```
> _Note_: From the CLI you need to pass a level with `--log-level`. If you are
> running the plug-in in your own host using one of our SDKs, you need to make
> sure that you call `set_log_file` to `"stdout"` or some file location.
## HTTP
Sometimes it is useful to let a plug-in make HTTP calls.
> **Note**: See
> [HttpRequest](https://docs.rs/extism-pdk/latest/extism_pdk/struct.HttpRequest.html)
> docs for more info on the request and response types:
```rust
#[plugin_fn]
pub fn http_get(Json(req): Json) -> FnResult> {
let res = http::request::<()>(&req, None)?;
Ok(res.body())
}
```
## Imports (Host Functions)
Like any other code module, Wasm not only let's you export functions to the
outside world, you can import them too. Host Functions allow a plug-in to import
functions defined in the host. For example, if you host application is written
in Python, it can pass a Python function down to your Rust plug-in where you can
invoke it.
This topic can get fairly complicated and we have not yet fully abstracted the
Wasm knowledge you need to do this correctly. So we recommend reading out
[concept doc on Host Functions](https://extism.org/docs/concepts/host-functions)
before you get started.
### A Simple Example
Host functions have a similar interface as exports. You just need to declare
them as `extern` on the top of your `lib.rs`. You only declare the interface as
it is the host's responsibility to provide the implementation:
```rust
#[host_fn]
extern "ExtismHost" {
fn a_python_func(input: String) -> String;
}
```
> **Note**: Under the hood this macro turns this into an interface that passes a
> pointer as an argument and a pointer as a return. If you want to pass raw,
> dereferenced wasm values see the raw interface documentation below.
To declare a host function in a specific namespace, pass the module name to the
`host_fn` macro:
```rust
#[host_fn("extism:host/user")]
```
> **Note**: The types we accept here are the same as the exports as the
> interface also uses the
> [convert crate](https://docs.rs/extism-convert/latest/extism_convert/).
To call this function, we must use the `unsafe` keyword. Also note that it
automatically wraps the function return with a Result in case the call fails.
```rust
#[plugin_fn]
pub fn hello_from_python() -> FnResult {
let output = unsafe { a_python_func("An argument to send to Python".into())? };
Ok(output)
}
```
### Testing it out
We can't really test this from the Extism CLI as something must provide the
implementation. So let's write out the Python side here. Check out the
[docs for Host SDKs](https://extism.org/docs/concepts/host-sdk) to implement a
host function in a language of your choice.
```python
from extism import host_fn, Plugin
@host_fn()
def a_python_func(input: str) -> str:
# just printing this out to prove we're in Python land
print("Hello from Python!")
# let's just add "!" to the input string
# but you could imagine here we could add some
# applicaiton code like query or manipulate the database
# or our application APIs
return input + "!"
```
Now when we load the plug-in we pass the host function:
```python
manifest = {"wasm": [{"path": "/path/to/plugin.wasm"}]}
plugin = Plugin(manifest, functions=[a_python_func], wasi=True)
result = plugin.call('hello_from_python', b'').decode('utf-8')
print(result)
```
```bash
python3 app.py
# => Hello from Python!
# => An argument to send to Python!
```
## Raw Import Interface
Like exports, with imports we do some magic to turn the parameters and returns
into pointers for you. In some rare situations, you might wish to pass raw wasm
values to the host (not pointers). If you do, you need to drop down into a raw
interface. E.g, imagine an interface that sums two i64s
```rust
extern "C" {
fn sum(a: i64, b: i64) -> i64;
}
```
## Generating Bindings
It's often very useful to define a schema to describe the function signatures
and types you want to use between Extism SDK and PDK languages.
[XTP Bindgen](https://github.com/dylibso/xtp-bindgen) is an open source
framework to generate PDK bindings for Extism plug-ins. It's used by the
[XTP Platform](https://www.getxtp.com/), but can be used outside of the platform
to define any Extism compatible plug-in system.
### 1. Install the `xtp` CLI.
See installation instructions
[here](https://docs.xtp.dylibso.com/docs/cli#installation).
### 2. Create a schema using our OpenAPI-inspired IDL:
```yaml
version: v1-draft
exports:
CountVowels:
input:
type: string
contentType: text/plain; charset=utf-8
output:
$ref: "#/components/schemas/VowelReport"
contentType: application/json
# components.schemas defined in example-schema.yaml...
```
> See an example in [example-schema.yaml](./example-schema.yaml), or a full
> "kitchen sink" example on
> [the docs page](https://docs.xtp.dylibso.com/docs/concepts/xtp-schema/).
### 3. Generate bindings to use from your plugins:
```
xtp plugin init --schema-file ./example-schema.yaml
1. TypeScript
2. Go
> 3. Rust
4. Python
5. C#
6. Zig
7. C++
8. GitHub Template
9. Local Template
```
This will create an entire boilerplate plugin project for you to get started
with:
```rust
// returns VowelReport (The result of counting vowels on the Vowels input.)
pub(crate) fn count_vowels(input: String ) -> Result {
todo!("Implement count_vowels")
}
```
Implement the empty function(s), and run `xtp plugin build` to compile your
plugin.
> For more information about XTP Bindgen, see the
> [dylibso/xtp-bindgen](https://github.com/dylibso/xtp-bindgen) repository and
> the official
> [XTP Schema documentation](https://docs.xtp.dylibso.com/docs/concepts/xtp-schema).
## Reach Out!
Have a question or just want to drop in and say hi?
[Hop on the Discord](https://extism.org/discord)!