Work on macro binding generation, some cleanup needed, rename runner to plugin

crates/plugin_runtime/src/wasm.rs

@@ -0,0 +1,182 @@
+use std::collections::HashMap;
+
+use anyhow::anyhow;
+
+use wasmtime::{Engine, Func, Instance, Memory, MemoryType, Module, Store, TypedFunc};
+
+use crate::*;
+
+pub struct Wasm<T> {
+    engine: Engine,
+    module: Module,
+    store: Store<T>,
+    instance: Instance,
+    alloc_buffer: TypedFunc<i32, i32>,
+    // free_buffer: TypedFunc<(i32, i32), ()>,
+}
+
+pub struct WasmPlugin<T> {
+    pub source_bytes: Vec<u8>,
+    pub store_data: T,
+}
+
+impl<T> Wasm<T> {
+    pub fn dump_memory(data: &[u8]) {
+        for (i, byte) in data.iter().enumerate() {
+            if i % 32 == 0 {
+                println!();
+            }
+            if i % 4 == 0 {
+                print!("|");
+            }
+            if *byte == 0 {
+                print!("__")
+            } else {
+                print!("{:02x}", byte);
+            }
+        }
+        println!();
+    }
+}
+
+impl<S> Runtime for Wasm<S> {
+    type Plugin = WasmPlugin<S>;
+    type Error = anyhow::Error;
+
+    fn init(plugin: WasmPlugin<S>) -> Result<Self, Self::Error> {
+        let engine = Engine::default();
+        let module = Module::new(&engine, plugin.source_bytes)?;
+        let mut store: Store<S> = Store::new(&engine, plugin.store_data);
+        let instance = Instance::new(&mut store, &module, &[])?;
+
+        let alloc_buffer = instance.get_typed_func(&mut store, "__alloc_buffer")?;
+        // let free_buffer = instance.get_typed_func(&mut store, "__free_buffer")?;
+
+        Ok(Wasm {
+            engine,
+            module,
+            store,
+            instance,
+            alloc_buffer,
+            // free_buffer,
+        })
+    }
+
+    fn constant<T: DeserializeOwned>(&mut self, handle: &Handle) -> Result<T, Self::Error> {
+        let export = self
+            .instance
+            .get_export(&mut self.store, handle.inner())
+            .ok_or_else(|| anyhow!("Could not get export"))?;
+
+        todo!()
+    }
+
+    // So this call function is kinda a dance, I figured it'd be a good idea to document it.
+    // the high level is we take a serde type, serialize it to a byte array,
+    // (we're doing this using bincode for now)
+    // then toss that byte array into webassembly.
+    // webassembly grabs that byte array, does some magic,
+    // and serializes the result into yet another byte array.
+    // we then grab *that* result byte array and deserialize it into a result.
+    //
+    // phew...
+    //
+    // now the problem is, webassambly doesn't support buffers.
+    // only really like i32s, that's it (yeah, it's sad. Not even unsigned!)
+    // (ok, I'm exaggerating a bit).
+    //
+    // the Wasm function that this calls must have a very specific signature:
+    //
+    // fn(pointer to byte array: i32, length of byte array: i32)
+    //     -> pointer to (
+    //            pointer to byte_array: i32,
+    //            length of byte array: i32,
+    //     ): i32
+    //
+    // This pair `(pointer to byte array, length of byte array)` is called a `Buffer`
+    // and can be found in the cargo_test plugin.
+    //
+    // so on the wasm side, we grab the two parameters to the function,
+    // stuff them into a `Buffer`,
+    // and then pray to the `unsafe` Rust gods above that a valid byte array pops out.
+    //
+    // On the flip side, when returning from a wasm function,
+    // we convert whatever serialized result we get into byte array,
+    // which we stuff into a Buffer and allocate on the heap,
+    // which pointer to we then return.
+    // Note the double indirection!
+    //
+    // So when returning from a function, we actually leak memory *twice*:
+    //
+    // 1) once when we leak the byte array
+    // 2) again when we leak the allocated `Buffer`
+    //
+    // This isn't a problem because Wasm stops executing after the function returns,
+    // so the heap is still valid for our inspection when we want to pull things out.
+
+    // TODO: dont' use as for conversions
+    fn call<A: Serialize, R: DeserializeOwned>(
+        &mut self,
+        handle: &Handle,
+        arg: A,
+    ) -> Result<R, Self::Error> {
+        // serialize the argument using bincode
+        let arg = bincode::serialize(&arg)?;
+        let arg_buffer_len = arg.len();
+
+        // allocate a buffer and write the argument to that buffer
+        let arg_buffer_ptr = self
+            .alloc_buffer
+            .call(&mut self.store, arg_buffer_len as i32)?;
+        let plugin_memory = self
+            .instance
+            .get_memory(&mut self.store, "memory")
+            .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
+        plugin_memory.write(&mut self.store, arg_buffer_ptr as usize, &arg)?;
+
+        // get the webassembly function we want to actually call
+        let fun = self
+            .instance
+            .get_typed_func::<(i32, i32), i32, _>(&mut self.store, handle.inner())?;
+
+        // call the function, passing in the buffer and its length
+        // this should return a pointer to a (ptr, lentgh) pair
+        let arg_buffer = (arg_buffer_ptr, arg_buffer_len as i32);
+        let result_buffer = fun.call(&mut self.store, arg_buffer)?;
+        dbg!(result_buffer);
+
+        // panic!();
+        // dbg!()
+
+        // create a buffer to read the (ptr, length) pair into
+        // this is a total of 4 + 4 = 8 bytes.
+        let buffer = &mut [0; 8];
+        plugin_memory.read(&mut self.store, result_buffer as usize, buffer)?;
+
+        // use these bytes (wasm stores things little-endian)
+        // to get a pointer to the buffer and its length
+        let b = buffer;
+        let result_buffer_ptr = u32::from_le_bytes([b[0], b[1], b[2], b[3]]) as usize;
+        let result_buffer_len = u32::from_le_bytes([b[4], b[5], b[6], b[7]]) as usize;
+        let result_buffer_end = result_buffer_ptr + result_buffer_len;
+
+        dbg!(result_buffer_ptr);
+        dbg!(result_buffer_len);
+
+        // read the buffer at this point into a byte array
+        // deserialize the byte array into the provided serde type
+        let result = &plugin_memory.data(&mut self.store)[result_buffer_ptr..result_buffer_end];
+        let result = bincode::deserialize(result)?;
+
+        // // deallocate the argument buffer
+        // self.free_buffer.call(&mut self.store, arg_buffer);
+
+        return Ok(result);
+    }
+
+    fn register_handle<T: AsRef<str>>(&mut self, name: T) -> bool {
+        self.instance
+            .get_export(&mut self.store, name.as_ref())
+            .is_some()
+    }
+}