feat: with actual executor

Signed-off-by: kjuulh <contact@kjuulh.io>

crates/churn-agent/src/main.rs

@@ -14,7 +14,7 @@ use axum::{
 use churn_domain::AgentEnrollReq;
 use clap::{Parser, Subcommand};
 use serde_json::json;
-use wasmtime::{Caller, Engine, Linker, Module, Store};
+use wasmtime::{Caller, Engine, Extern, Func, Linker, Module, Store};
 
 #[derive(Parser)]
 #[command(author, version, about, long_about = None, subcommand_required = true)]
@@ -102,20 +102,42 @@ async fn handle_command(cmd: Command) -> anyhow::Result<()> {
                 let engine = Engine::default();
                 let module = Module::from_file(&engine, exe)?;
 
-                // Create a `Linker` which will be later used to instantiate this module.
-                // Host functionality is defined by name within the `Linker`.
                 let mut linker = Linker::new(&engine);
-                linker.func_wrap("print", "print", |caller: Caller<'_, u32>, param: i32| {
-                    println!("Got {} from WebAssembly", param);
-                    println!("my host state is: {}", caller.data());
-                })?;
+                linker.func_wrap(
+                    "$root",
+                    "print",
+                    |mut caller: Caller<'_, ()>, ptr: i32, len: i32| {
+                        // Use our `caller` context to learn about the memory export of the
+                        // module which called this host function.
+                        let mem = match caller.get_export("memory") {
+                            Some(Extern::Memory(mem)) => mem,
+                            _ => panic!("failed to find host memory"),
+                        };
+
+                        // Use the `ptr` and `len` values to get a subslice of the wasm-memory
+                        // which we'll attempt to interpret as utf-8.
+                        let data = mem
+                            .data(&caller)
+                            .get(ptr as u32 as usize..)
+                            .and_then(|arr| arr.get(..len as u32 as usize));
+                        let string = match data {
+                            Some(data) => match std::str::from_utf8(data) {
+                                Ok(s) => s,
+                                Err(_) => panic!("invalid utf-8"),
+                            },
+                            None => panic!("pointer/length out of bounds"),
+                        };
+
+                        println!("Got {} from WebAssembly", string);
+                    },
+                )?;
 
                 // All wasm objects operate within the context of a "store". Each
                 // `Store` has a type parameter to store host-specific data, which in
                 // this case we're using `4` for.
-                let mut store = Store::new(&engine, 4);
+                let mut store = Store::new(&engine, ());
                 let instance = linker.instantiate(&mut store, &module)?;
-                let hello = instance.get_typed_func::<(), ()>(&mut store, "hello")?;
+                let hello = instance.get_typed_func::<(), ()>(&mut store, "run")?;
 
                 // And finally we can call the wasm!
                 hello.call(&mut store, ())?;