1use std::future::Future;
2use std::pin::Pin;
3use std::{fs::File, marker::PhantomData, path::Path};
4
5use anyhow::{anyhow, Error};
6use serde::{de::DeserializeOwned, Serialize};
7
8use wasi_common::{dir, file};
9use wasmtime::Memory;
10use wasmtime::{
11 AsContext, AsContextMut, Caller, Config, Engine, Extern, Instance, Linker, Module, Store, Trap,
12 TypedFunc,
13};
14use wasmtime_wasi::{Dir, WasiCtx, WasiCtxBuilder};
15
16/// Represents a resource currently managed by the plugin, like a file descriptor.
17pub struct PluginResource(u32);
18
19#[repr(C)]
20struct WasiBuffer {
21 ptr: u32,
22 len: u32,
23}
24
25impl WasiBuffer {
26 pub fn into_u64(self) -> u64 {
27 ((self.ptr as u64) << 32) | (self.len as u64)
28 }
29
30 pub fn from_u64(packed: u64) -> Self {
31 WasiBuffer {
32 ptr: (packed >> 32) as u32,
33 len: packed as u32,
34 }
35 }
36}
37
38/// Represents a typed WebAssembly function.
39pub struct WasiFn<A: Serialize, R: DeserializeOwned> {
40 function: TypedFunc<u64, u64>,
41 _function_type: PhantomData<fn(A) -> R>,
42}
43
44impl<A: Serialize, R: DeserializeOwned> Copy for WasiFn<A, R> {}
45
46impl<A: Serialize, R: DeserializeOwned> Clone for WasiFn<A, R> {
47 fn clone(&self) -> Self {
48 Self {
49 function: self.function,
50 _function_type: PhantomData,
51 }
52 }
53}
54
55/// This struct is used to build a new [`Plugin`], using the builder pattern.
56/// Create a new default plugin with `PluginBuilder::new_with_default_ctx`,
57/// and add host-side exported functions using `host_function` and `host_function_async`.
58/// Finalize the plugin by calling [`init`].
59pub struct PluginBuilder {
60 wasi_ctx: WasiCtx,
61 engine: Engine,
62 linker: Linker<WasiCtxAlloc>,
63}
64
65impl PluginBuilder {
66 /// Create a new [`PluginBuilder`] with the given WASI context.
67 /// Using the default context is a safe bet, see [`new_with_default_context`].
68 pub fn new(wasi_ctx: WasiCtx) -> Result<Self, Error> {
69 dbg!("new plugin");
70 let mut config = Config::default();
71 config.async_support(true);
72 let engine = Engine::new(&config)?;
73 let linker = Linker::new(&engine);
74
75 Ok(PluginBuilder {
76 // host_functions: HashMap::new(),
77 wasi_ctx,
78 engine,
79 linker,
80 })
81 }
82
83 /// Create a new `PluginBuilder` that inherits the
84 /// host processes' access to `stdout` and `stderr`.
85 pub fn new_with_default_ctx() -> Result<Self, Error> {
86 let wasi_ctx = WasiCtxBuilder::new()
87 .inherit_stdout()
88 .inherit_stderr()
89 .build();
90 Self::new(wasi_ctx)
91 }
92
93 /// Add an `async` host function. See [`host_function`] for details.
94 pub fn host_function_async<F, A, R, Fut>(
95 mut self,
96 name: &str,
97 function: F,
98 ) -> Result<Self, Error>
99 where
100 F: Fn(A) -> Fut + Send + Sync + 'static,
101 Fut: Future<Output = R> + Send + 'static,
102 A: DeserializeOwned + Send + 'static,
103 R: Serialize + Send + Sync + 'static,
104 {
105 self.linker.func_wrap1_async(
106 "env",
107 &format!("__{}", name),
108 move |mut caller: Caller<'_, WasiCtxAlloc>, packed_buffer: u64| {
109 // TODO: use try block once avaliable
110 let result: Result<(WasiBuffer, Memory, _), Trap> = (|| {
111 // grab a handle to the memory
112 let mut plugin_memory = match caller.get_export("memory") {
113 Some(Extern::Memory(mem)) => mem,
114 _ => return Err(Trap::new("Could not grab slice of plugin memory"))?,
115 };
116
117 let buffer = WasiBuffer::from_u64(packed_buffer);
118
119 // get the args passed from Guest
120 let args = Plugin::buffer_to_bytes(&mut plugin_memory, &mut caller, &buffer)?;
121
122 let args: A = Plugin::deserialize_to_type(&args)?;
123
124 // Call the Host-side function
125 let result = function(args);
126
127 Ok((buffer, plugin_memory, result))
128 })();
129
130 Box::new(async move {
131 let (buffer, mut plugin_memory, future) = result?;
132
133 let result: R = future.await;
134 let result: Result<Vec<u8>, Error> = Plugin::serialize_to_bytes(result)
135 .map_err(|_| {
136 Trap::new("Could not serialize value returned from function").into()
137 });
138 let result = result?;
139
140 Plugin::buffer_to_free(caller.data().free_buffer(), &mut caller, buffer)
141 .await?;
142
143 let buffer = Plugin::bytes_to_buffer(
144 caller.data().alloc_buffer(),
145 &mut plugin_memory,
146 &mut caller,
147 result,
148 )
149 .await?;
150
151 Ok(buffer.into_u64())
152 })
153 },
154 )?;
155 Ok(self)
156 }
157
158 /// Add a new host function to the given `PluginBuilder`.
159 /// A host function is a function defined host-side, in Rust,
160 /// that is accessible guest-side, in WebAssembly.
161 /// You can specify host-side functions to import using
162 /// the `#[input]` macro attribute:
163 /// ```ignore
164 /// #[input]
165 /// fn total(counts: Vec<f64>) -> f64;
166 /// ```
167 /// When loading a plugin, you need to provide all host functions the plugin imports:
168 /// ```ignore
169 /// let plugin = PluginBuilder::new_with_default_context()
170 /// .host_function("total", |counts| counts.iter().fold(0.0, |tot, n| tot + n))
171 /// // and so on...
172 /// ```
173 /// And that's a wrap!
174 pub fn host_function<A, R>(
175 mut self,
176 name: &str,
177 function: impl Fn(A) -> R + Send + Sync + 'static,
178 ) -> Result<Self, Error>
179 where
180 A: DeserializeOwned + Send,
181 R: Serialize + Send + Sync,
182 {
183 self.linker.func_wrap1_async(
184 "env",
185 &format!("__{}", name),
186 move |mut caller: Caller<'_, WasiCtxAlloc>, packed_buffer: u64| {
187 // TODO: use try block once avaliable
188 let result: Result<(WasiBuffer, Memory, Vec<u8>), Trap> = (|| {
189 // grab a handle to the memory
190 let mut plugin_memory = match caller.get_export("memory") {
191 Some(Extern::Memory(mem)) => mem,
192 _ => return Err(Trap::new("Could not grab slice of plugin memory"))?,
193 };
194
195 let buffer = WasiBuffer::from_u64(packed_buffer);
196
197 // get the args passed from Guest
198 let args = Plugin::buffer_to_type(&mut plugin_memory, &mut caller, &buffer)?;
199
200 // Call the Host-side function
201 let result: R = function(args);
202
203 // Serialize the result back to guest
204 let result = Plugin::serialize_to_bytes(result).map_err(|_| {
205 Trap::new("Could not serialize value returned from function")
206 })?;
207
208 Ok((buffer, plugin_memory, result))
209 })();
210
211 Box::new(async move {
212 let (buffer, mut plugin_memory, result) = result?;
213
214 Plugin::buffer_to_free(caller.data().free_buffer(), &mut caller, buffer)
215 .await?;
216
217 let buffer = Plugin::bytes_to_buffer(
218 caller.data().alloc_buffer(),
219 &mut plugin_memory,
220 &mut caller,
221 result,
222 )
223 .await?;
224
225 Ok(buffer.into_u64())
226 })
227 },
228 )?;
229 Ok(self)
230 }
231
232 /// Initializes a [`Plugin`] from a given compiled Wasm module.
233 /// Both binary (`.wasm`) and text (`.wat`) module formats are supported.
234 pub async fn init<T: AsRef<[u8]>>(self, module: T) -> Result<Plugin, Error> {
235 dbg!("initializing plugin");
236 Plugin::init(module.as_ref().to_vec(), self).await
237 }
238}
239
240#[derive(Copy, Clone)]
241struct WasiAlloc {
242 alloc_buffer: TypedFunc<u32, u32>,
243 free_buffer: TypedFunc<u64, ()>,
244}
245
246struct WasiCtxAlloc {
247 wasi_ctx: WasiCtx,
248 alloc: Option<WasiAlloc>,
249}
250
251impl WasiCtxAlloc {
252 fn alloc_buffer(&self) -> TypedFunc<u32, u32> {
253 self.alloc
254 .expect("allocator has been not initialized, cannot allocate buffer!")
255 .alloc_buffer
256 }
257
258 fn free_buffer(&self) -> TypedFunc<u64, ()> {
259 self.alloc
260 .expect("allocator has been not initialized, cannot free buffer!")
261 .free_buffer
262 }
263
264 fn init_alloc(&mut self, alloc: WasiAlloc) {
265 self.alloc = Some(alloc)
266 }
267}
268
269/// Represents a WebAssembly plugin, with access to the WebAssembly System Inferface.
270/// Build a new plugin using [`PluginBuilder`].
271pub struct Plugin {
272 engine: Engine,
273 module: Module,
274 store: Store<WasiCtxAlloc>,
275 instance: Instance,
276}
277
278impl Plugin {
279 /// Dumps the *entirety* of Wasm linear memory to `stdout`.
280 /// Don't call this unless you're debugging a memory issue!
281 pub fn dump_memory(data: &[u8]) {
282 for (i, byte) in data.iter().enumerate() {
283 if i % 32 == 0 {
284 println!();
285 }
286 if i % 4 == 0 {
287 print!("|");
288 }
289 if *byte == 0 {
290 print!("__")
291 } else {
292 print!("{:02x}", byte);
293 }
294 }
295 println!();
296 }
297}
298
299impl Plugin {
300 async fn init(module: Vec<u8>, plugin: PluginBuilder) -> Result<Self, Error> {
301 dbg!("started initialization");
302 // initialize the WebAssembly System Interface context
303 let engine = plugin.engine;
304 let mut linker = plugin.linker;
305 wasmtime_wasi::add_to_linker(&mut linker, |s| &mut s.wasi_ctx)?;
306
307 // create a store, note that we can't initialize the allocator,
308 // because we can't grab the functions until initialized.
309 let mut store: Store<WasiCtxAlloc> = Store::new(
310 &engine,
311 WasiCtxAlloc {
312 wasi_ctx: plugin.wasi_ctx,
313 alloc: None,
314 },
315 );
316 let module = Module::new(&engine, module)?;
317 dbg!("created store");
318
319 // load the provided module into the asynchronous runtime
320 linker.module_async(&mut store, "", &module).await?;
321 let instance = linker.instantiate_async(&mut store, &module).await?;
322
323 // now that the module is initialized,
324 // we can initialize the store's allocator
325 let alloc_buffer = instance.get_typed_func(&mut store, "__alloc_buffer")?;
326 let free_buffer = instance.get_typed_func(&mut store, "__free_buffer")?;
327 store.data_mut().init_alloc(WasiAlloc {
328 alloc_buffer,
329 free_buffer,
330 });
331
332 dbg!("bound funcitons");
333
334 Ok(Plugin {
335 engine,
336 module,
337 store,
338 instance,
339 })
340 }
341
342 /// Attaches a file or directory the the given system path to the runtime.
343 /// Note that the resource must be freed by calling `remove_resource` afterwards.
344 pub fn attach_path<T: AsRef<Path>>(&mut self, path: T) -> Result<PluginResource, Error> {
345 // grab the WASI context
346 let ctx = self.store.data_mut();
347
348 // open the file we want, and convert it into the right type
349 // this is a footgun and a half
350 let file = File::open(&path).unwrap();
351 let dir = Dir::from_std_file(file);
352 let dir = Box::new(wasmtime_wasi::dir::Dir::from_cap_std(dir));
353
354 // grab an empty file descriptor, specify capabilities
355 let fd = ctx.wasi_ctx.table().push(Box::new(()))?;
356 let caps = dir::DirCaps::all();
357 let file_caps = file::FileCaps::all();
358
359 // insert the directory at the given fd,
360 // return a handle to the resource
361 ctx.wasi_ctx
362 .insert_dir(fd, dir, caps, file_caps, path.as_ref().to_path_buf());
363 Ok(PluginResource(fd))
364 }
365
366 /// Returns `true` if the resource existed and was removed.
367 /// Currently the only resource we support is adding scoped paths (e.g. folders and files)
368 /// to plugins using [`attach_path`].
369 pub fn remove_resource(&mut self, resource: PluginResource) -> Result<(), Error> {
370 self.store
371 .data_mut()
372 .wasi_ctx
373 .table()
374 .delete(resource.0)
375 .ok_or_else(|| anyhow!("Resource did not exist, but a valid handle was passed in"))?;
376 Ok(())
377 }
378
379 // So this call function is kinda a dance, I figured it'd be a good idea to document it.
380 // the high level is we take a serde type, serialize it to a byte array,
381 // (we're doing this using bincode for now)
382 // then toss that byte array into webassembly.
383 // webassembly grabs that byte array, does some magic,
384 // and serializes the result into yet another byte array.
385 // we then grab *that* result byte array and deserialize it into a result.
386 //
387 // phew...
388 //
389 // now the problem is, webassambly doesn't support buffers.
390 // only really like i32s, that's it (yeah, it's sad. Not even unsigned!)
391 // (ok, I'm exaggerating a bit).
392 //
393 // the Wasm function that this calls must have a very specific signature:
394 //
395 // fn(pointer to byte array: i32, length of byte array: i32)
396 // -> pointer to (
397 // pointer to byte_array: i32,
398 // length of byte array: i32,
399 // ): i32
400 //
401 // This pair `(pointer to byte array, length of byte array)` is called a `Buffer`
402 // and can be found in the cargo_test plugin.
403 //
404 // so on the wasm side, we grab the two parameters to the function,
405 // stuff them into a `Buffer`,
406 // and then pray to the `unsafe` Rust gods above that a valid byte array pops out.
407 //
408 // On the flip side, when returning from a wasm function,
409 // we convert whatever serialized result we get into byte array,
410 // which we stuff into a Buffer and allocate on the heap,
411 // which pointer to we then return.
412 // Note the double indirection!
413 //
414 // So when returning from a function, we actually leak memory *twice*:
415 //
416 // 1) once when we leak the byte array
417 // 2) again when we leak the allocated `Buffer`
418 //
419 // This isn't a problem because Wasm stops executing after the function returns,
420 // so the heap is still valid for our inspection when we want to pull things out.
421
422 /// Serializes a given type to bytes.
423 fn serialize_to_bytes<A: Serialize>(item: A) -> Result<Vec<u8>, Error> {
424 // serialize the argument using bincode
425 let bytes = bincode::serialize(&item)?;
426 Ok(bytes)
427 }
428
429 /// Deserializes a given type from bytes.
430 fn deserialize_to_type<R: DeserializeOwned>(bytes: &[u8]) -> Result<R, Error> {
431 // serialize the argument using bincode
432 let bytes = bincode::deserialize(bytes)?;
433 Ok(bytes)
434 }
435
436 // fn deserialize<R: DeserializeOwned>(
437 // plugin_memory: &mut Memory,
438 // mut store: impl AsContextMut<Data = WasiCtxAlloc>,
439 // buffer: WasiBuffer,
440 // ) -> Result<R, Error> {
441 // let buffer_start = buffer.ptr as usize;
442 // let buffer_end = buffer_start + buffer.len as usize;
443
444 // // read the buffer at this point into a byte array
445 // // deserialize the byte array into the provided serde type
446 // let item = &plugin_memory.data(store.as_context())[buffer_start..buffer_end];
447 // let item = bincode::deserialize(bytes)?;
448 // Ok(item)
449 // }
450
451 /// Takes an item, allocates a buffer, serializes the argument to that buffer,
452 /// and returns a (ptr, len) pair to that buffer.
453 async fn bytes_to_buffer(
454 alloc_buffer: TypedFunc<u32, u32>,
455 plugin_memory: &mut Memory,
456 mut store: impl AsContextMut<Data = WasiCtxAlloc>,
457 item: Vec<u8>,
458 ) -> Result<WasiBuffer, Error> {
459 // allocate a buffer and write the argument to that buffer
460 let len = item.len() as u32;
461 let ptr = alloc_buffer.call_async(&mut store, len).await?;
462 plugin_memory.write(&mut store, ptr as usize, &item)?;
463 Ok(WasiBuffer { ptr, len })
464 }
465
466 /// Takes a `(ptr, len)` pair and returns the corresponding deserialized buffer.
467 fn buffer_to_type<R: DeserializeOwned>(
468 plugin_memory: &Memory,
469 store: impl AsContext<Data = WasiCtxAlloc>,
470 buffer: &WasiBuffer,
471 ) -> Result<R, Error> {
472 let buffer_start = buffer.ptr as usize;
473 let buffer_end = buffer_start + buffer.len as usize;
474
475 // read the buffer at this point into a byte array
476 // deserialize the byte array into the provided serde type
477 let result = &plugin_memory.data(store.as_context())[buffer_start..buffer_end];
478 let result = bincode::deserialize(result)?;
479
480 Ok(result)
481 }
482
483 // TODO: don't allocate a new `Vec`!
484 /// Takes a `(ptr, len)` pair and returns the corresponding deserialized buffer.
485 fn buffer_to_bytes<'a>(
486 plugin_memory: &'a Memory,
487 store: impl AsContext<Data = WasiCtxAlloc> + 'a,
488 buffer: &WasiBuffer,
489 ) -> Result<Vec<u8>, Error> {
490 let buffer_start = buffer.ptr as usize;
491 let buffer_end = buffer_start + buffer.len as usize;
492
493 // read the buffer at this point into a byte array
494 // deserialize the byte array into the provided serde type
495 let result = plugin_memory.data(store.as_context())[buffer_start..buffer_end].to_vec();
496 Ok(result)
497 }
498
499 async fn buffer_to_free(
500 free_buffer: TypedFunc<u64, ()>,
501 mut store: impl AsContextMut<Data = WasiCtxAlloc>,
502 buffer: WasiBuffer,
503 ) -> Result<(), Error> {
504 // deallocate the argument buffer
505 Ok(free_buffer
506 .call_async(&mut store, buffer.into_u64())
507 .await?)
508 }
509
510 /// Retrieves the handle to a function of a given type.
511 pub fn function<A: Serialize, R: DeserializeOwned, T: AsRef<str>>(
512 &mut self,
513 name: T,
514 ) -> Result<WasiFn<A, R>, Error> {
515 let fun_name = format!("__{}", name.as_ref());
516 let fun = self
517 .instance
518 .get_typed_func::<u64, u64, _>(&mut self.store, &fun_name)?;
519 Ok(WasiFn {
520 function: fun,
521 _function_type: PhantomData,
522 })
523 }
524
525 // TODO: dont' use as for conversions
526 /// Asynchronously calls a function defined Guest-side.
527 pub async fn call<A: Serialize, R: DeserializeOwned>(
528 &mut self,
529 handle: &WasiFn<A, R>,
530 arg: A,
531 ) -> Result<R, Error> {
532 let mut plugin_memory = self
533 .instance
534 .get_memory(&mut self.store, "memory")
535 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
536
537 // write the argument to linear memory
538 // this returns a (ptr, lentgh) pair
539 let arg_buffer = Self::bytes_to_buffer(
540 self.store.data().alloc_buffer(),
541 &mut plugin_memory,
542 &mut self.store,
543 Self::serialize_to_bytes(arg)?,
544 )
545 .await?;
546
547 // call the function, passing in the buffer and its length
548 // this returns a ptr to a (ptr, lentgh) pair
549 let result_buffer = handle
550 .function
551 .call_async(&mut self.store, arg_buffer.into_u64())
552 .await?;
553
554 Self::buffer_to_type(
555 &mut plugin_memory,
556 &mut self.store,
557 &WasiBuffer::from_u64(result_buffer),
558 )
559 }
560}