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