# Wasmtime Engine Provider
This is a pluggable engine provider for the [waPC](https://wapc.io) RPC exchange protocol. This engine implements `WebAssemblyEngineProvider` for the the Bytecode Alliance's [wasmtime](https://github.com/bytecodealliance/wasmtime) WebAssembly runtime.
## Usage
```rust
use wasmtime_provider::WasmtimeEngineProviderBuilder;
use wapc::WapcHost;
use std::error::Error;
pub fn main() -> Result<(), Box<dyn Error>> {
// Sample host callback that prints the operation a WASM module requested.
let host_callback = |id: u64, bd: &str, ns: &str, op: &str, payload: &[u8]| {
println!("Guest {} invoked '{}->{}:{}' with a {} byte payload",
id, bd, ns, op, payload.len());
// Return success with zero-byte payload.
Ok(vec![])
};
let file = "../../wasm/crates/wasm-basic/build/wasm_basic.wasm";
let module_bytes = std::fs::read(file)?;
let engine = WasmtimeEngineProviderBuilder::new()
.module_bytes(&module_bytes)
.build()?;
let host = WapcHost::new(Box::new(engine), Some(Box::new(host_callback)))?;
let res = host.call("ping", b"payload bytes")?;
assert_eq!(res, b"payload bytes");
Ok(())
}
```
### `async` Support
The `async` feature enables the usage of this provider inside of an `async` context.
**Note:** this feature relies on the tokio runtime.
Check the [`WasmtimeEngineProviderAsync`] for more details.
### Creating a new instance
The [`WasmtimeEngineProviderBuilder`] is used to create new instances of [`WasmtimeEngineProvider`]
and [`WasmtimeEngineProviderAsync`].
Fresh instances of the engines can be created by using pre-initialized instances
like [`WasmtimeEngineProviderPre`] and [`WasmtimeEngineProviderAsyncPre`].
## Examples
### Running ping demo
```custom,{.language-bash}
cargo run -p wasmtime-provider \
--example wasmtime-demo \
./wasm/crates/wasm-basic/build/wasm_basic.wasm \
ping "hi"
```
### Running codec and module hotswapping demo
```custom,{.language-bash}
cargo run -p wasmtime-provider \
--example wasmtime-hash-mreplace \
AlexName
```
## See also
- [wasm3-provider](https://crates.io/crates/wasm3-provider)