1use std::{
2 collections::HashMap, fs::File, future::Future, marker::PhantomData, path::Path, pin::Pin,
3};
4
5use anyhow::{anyhow, Error};
6use serde::{de::DeserializeOwned, Serialize};
7
8use wasi_common::{dir, file};
9use wasmtime::{
10 AsContext, AsContextMut, Caller, Config, Engine, Extern, Instance, Linker, Module, Store,
11 StoreContext, StoreContextMut, Trap, TypedFunc, WasmParams,
12};
13use wasmtime::{IntoFunc, Memory};
14use wasmtime_wasi::{Dir, WasiCtx, WasiCtxBuilder};
15
16pub struct WasiResource(u32);
17
18#[repr(C)]
19struct WasiBuffer {
20 ptr: u32,
21 len: u32,
22}
23
24impl WasiBuffer {
25 pub fn into_u64(self) -> u64 {
26 ((self.ptr as u64) << 32) | (self.len as u64)
27 }
28
29 pub fn from_u64(packed: u64) -> Self {
30 WasiBuffer {
31 ptr: (packed >> 32) as u32,
32 len: packed as u32,
33 }
34 }
35}
36
37pub struct WasiFn<A: Serialize, R: DeserializeOwned> {
38 function: TypedFunc<u64, u64>,
39 _function_type: PhantomData<fn(A) -> R>,
40}
41
42impl<A: Serialize, R: DeserializeOwned> Copy for WasiFn<A, R> {}
43
44impl<A: Serialize, R: DeserializeOwned> Clone for WasiFn<A, R> {
45 fn clone(&self) -> Self {
46 Self {
47 function: self.function,
48 _function_type: PhantomData,
49 }
50 }
51}
52
53pub struct WasiPluginBuilder {
54 wasi_ctx: WasiCtx,
55 engine: Engine,
56 linker: Linker<WasiCtxAlloc>,
57}
58
59impl WasiPluginBuilder {
60 pub fn new(wasi_ctx: WasiCtx) -> Result<Self, Error> {
61 let mut config = Config::default();
62 config.async_support(true);
63 let engine = Engine::new(&config)?;
64 let linker = Linker::new(&engine);
65
66 Ok(WasiPluginBuilder {
67 // host_functions: HashMap::new(),
68 wasi_ctx,
69 engine,
70 linker,
71 })
72 }
73
74 pub fn new_with_default_ctx() -> Result<Self, Error> {
75 let wasi_ctx = WasiCtxBuilder::new()
76 .inherit_stdin()
77 .inherit_stderr()
78 .build();
79 Self::new(wasi_ctx)
80 }
81
82 pub fn host_function<A: DeserializeOwned + Send, R: Serialize + Send + Sync + Clone>(
83 mut self,
84 name: &str,
85 function: impl Fn(A) -> R + Send + Sync + 'static,
86 ) -> Result<Self, Error> {
87 self.linker.func_wrap1_async(
88 "env",
89 &format!("__{}", name),
90 move |mut caller: Caller<'_, WasiCtxAlloc>, packed_buffer: u64| {
91 // TODO: use try block once avaliable
92 let result: Result<(Memory, Vec<u8>), Trap> = (|| {
93 // grab a handle to the memory
94 let mut plugin_memory = match caller.get_export("memory") {
95 Some(Extern::Memory(mem)) => mem,
96 _ => return Err(Trap::new("Could not grab slice of plugin memory"))?,
97 };
98
99 // get the args passed from Guest
100 let args = Wasi::deserialize_from_buffer(
101 &mut plugin_memory,
102 &caller,
103 WasiBuffer::from_u64(packed_buffer),
104 )?;
105
106 // Call the Host-side function
107 let result: R = function(args);
108
109 // Serialize the result back to guest
110 let result = Wasi::serialize(result).map_err(|_| {
111 Trap::new("Could not serialize value returned from function")
112 })?;
113 Ok((plugin_memory, result))
114 })();
115
116 Box::new(async move {
117 let (mut plugin_memory, result) = result?;
118
119 let buffer = Wasi::serialize_to_buffer(
120 caller.data().alloc_buffer(),
121 &mut plugin_memory,
122 &mut caller,
123 result,
124 )
125 .await?;
126
127 Ok(buffer.into_u64())
128 })
129 },
130 )?;
131 Ok(self)
132 }
133
134 pub async fn init<T: AsRef<[u8]>>(self, module: T) -> Result<Wasi, Error> {
135 Wasi::init(module.as_ref().to_vec(), self).await
136 }
137}
138
139// // TODO: remove
140// /// Represents a to-be-initialized plugin.
141// /// Please use [`WasiPluginBuilder`], don't use this directly.
142// pub struct WasiPlugin {
143// pub module: Vec<u8>,
144// pub wasi_ctx: WasiCtx,
145// pub host_functions:
146// HashMap<String, Box<dyn Fn(&str, &mut Linker<WasiCtx>) -> Result<(), Error>>>,
147// }
148
149#[derive(Copy, Clone)]
150struct WasiAlloc {
151 alloc_buffer: TypedFunc<u32, u32>,
152 free_buffer: TypedFunc<u64, ()>,
153}
154
155struct WasiCtxAlloc {
156 wasi_ctx: WasiCtx,
157 alloc: Option<WasiAlloc>,
158}
159
160impl WasiCtxAlloc {
161 fn alloc_buffer(&self) -> TypedFunc<u32, u32> {
162 self.alloc
163 .expect("allocator has been not initialized, cannot allocate buffer!")
164 .alloc_buffer
165 }
166
167 fn free_buffer(&self) -> TypedFunc<u64, ()> {
168 self.alloc
169 .expect("allocator has been not initialized, cannot free buffer!")
170 .free_buffer
171 }
172
173 fn init_alloc(&mut self, alloc: WasiAlloc) {
174 self.alloc = Some(alloc)
175 }
176}
177
178pub struct Wasi {
179 engine: Engine,
180 module: Module,
181 store: Store<WasiCtxAlloc>,
182 instance: Instance,
183}
184
185impl Wasi {
186 pub fn dump_memory(data: &[u8]) {
187 for (i, byte) in data.iter().enumerate() {
188 if i % 32 == 0 {
189 println!();
190 }
191 if i % 4 == 0 {
192 print!("|");
193 }
194 if *byte == 0 {
195 print!("__")
196 } else {
197 print!("{:02x}", byte);
198 }
199 }
200 println!();
201 }
202}
203
204impl Wasi {
205 async fn init(module: Vec<u8>, plugin: WasiPluginBuilder) -> Result<Self, Error> {
206 // initialize the WebAssembly System Interface context
207 let engine = plugin.engine;
208 let mut linker = plugin.linker;
209 wasmtime_wasi::add_to_linker(&mut linker, |s| &mut s.wasi_ctx)?;
210
211 // create a store, note that we can't initialize the allocator,
212 // because we can't grab the functions until initialized.
213 let mut store: Store<WasiCtxAlloc> = Store::new(
214 &engine,
215 WasiCtxAlloc {
216 wasi_ctx: plugin.wasi_ctx,
217 alloc: None,
218 },
219 );
220 let module = Module::new(&engine, module)?;
221
222 // load the provided module into the asynchronous runtime
223 linker.module_async(&mut store, "", &module).await?;
224 let instance = linker.instantiate_async(&mut store, &module).await?;
225
226 // now that the module is initialized,
227 // we can initialize the store's allocator
228 let alloc_buffer = instance.get_typed_func(&mut store, "__alloc_buffer")?;
229 let free_buffer = instance.get_typed_func(&mut store, "__free_buffer")?;
230 store.data_mut().init_alloc(WasiAlloc {
231 alloc_buffer,
232 free_buffer,
233 });
234
235 Ok(Wasi {
236 engine,
237 module,
238 store,
239 instance,
240 })
241 }
242
243 /// Attaches a file or directory the the given system path to the runtime.
244 /// Note that the resource must be freed by calling `remove_resource` afterwards.
245 pub fn attach_path<T: AsRef<Path>>(&mut self, path: T) -> Result<WasiResource, Error> {
246 // grab the WASI context
247 let ctx = self.store.data_mut();
248
249 // open the file we want, and convert it into the right type
250 // this is a footgun and a half
251 let file = File::open(&path).unwrap();
252 let dir = Dir::from_std_file(file);
253 let dir = Box::new(wasmtime_wasi::dir::Dir::from_cap_std(dir));
254
255 // grab an empty file descriptor, specify capabilities
256 let fd = ctx.wasi_ctx.table().push(Box::new(()))?;
257 let caps = dir::DirCaps::all();
258 let file_caps = file::FileCaps::all();
259
260 // insert the directory at the given fd,
261 // return a handle to the resource
262 ctx.wasi_ctx
263 .insert_dir(fd, dir, caps, file_caps, path.as_ref().to_path_buf());
264 Ok(WasiResource(fd))
265 }
266
267 /// Returns `true` if the resource existed and was removed.
268 pub fn remove_resource(&mut self, resource: WasiResource) -> Result<(), Error> {
269 self.store
270 .data_mut()
271 .wasi_ctx
272 .table()
273 .delete(resource.0)
274 .ok_or_else(|| anyhow!("Resource did not exist, but a valid handle was passed in"))?;
275 Ok(())
276 }
277
278 // pub fn with_resource<T>(
279 // &mut self,
280 // resource: WasiResource,
281 // callback: fn(&mut Self) -> Result<T, Error>,
282 // ) -> Result<T, Error> {
283 // let result = callback(self);
284 // self.remove_resource(resource)?;
285 // return result;
286 // }
287
288 // So this call function is kinda a dance, I figured it'd be a good idea to document it.
289 // the high level is we take a serde type, serialize it to a byte array,
290 // (we're doing this using bincode for now)
291 // then toss that byte array into webassembly.
292 // webassembly grabs that byte array, does some magic,
293 // and serializes the result into yet another byte array.
294 // we then grab *that* result byte array and deserialize it into a result.
295 //
296 // phew...
297 //
298 // now the problem is, webassambly doesn't support buffers.
299 // only really like i32s, that's it (yeah, it's sad. Not even unsigned!)
300 // (ok, I'm exaggerating a bit).
301 //
302 // the Wasm function that this calls must have a very specific signature:
303 //
304 // fn(pointer to byte array: i32, length of byte array: i32)
305 // -> pointer to (
306 // pointer to byte_array: i32,
307 // length of byte array: i32,
308 // ): i32
309 //
310 // This pair `(pointer to byte array, length of byte array)` is called a `Buffer`
311 // and can be found in the cargo_test plugin.
312 //
313 // so on the wasm side, we grab the two parameters to the function,
314 // stuff them into a `Buffer`,
315 // and then pray to the `unsafe` Rust gods above that a valid byte array pops out.
316 //
317 // On the flip side, when returning from a wasm function,
318 // we convert whatever serialized result we get into byte array,
319 // which we stuff into a Buffer and allocate on the heap,
320 // which pointer to we then return.
321 // Note the double indirection!
322 //
323 // So when returning from a function, we actually leak memory *twice*:
324 //
325 // 1) once when we leak the byte array
326 // 2) again when we leak the allocated `Buffer`
327 //
328 // This isn't a problem because Wasm stops executing after the function returns,
329 // so the heap is still valid for our inspection when we want to pull things out.
330
331 fn serialize<A: Serialize>(item: A) -> Result<Vec<u8>, Error> {
332 // serialize the argument using bincode
333 let item = bincode::serialize(&item)?;
334 Ok(item)
335 }
336
337 /// Takes an item, allocates a buffer, serializes the argument to that buffer,
338 /// and returns a (ptr, len) pair to that buffer.
339 async fn serialize_to_buffer(
340 alloc_buffer: TypedFunc<u32, u32>,
341 plugin_memory: &mut Memory,
342 mut store: impl AsContextMut<Data = WasiCtxAlloc>,
343 item: Vec<u8>,
344 ) -> Result<WasiBuffer, Error> {
345 // allocate a buffer and write the argument to that buffer
346 let len = item.len() as u32;
347 let ptr = alloc_buffer.call_async(&mut store, len).await?;
348 plugin_memory.write(&mut store, ptr as usize, &item)?;
349 Ok(WasiBuffer { ptr, len })
350 }
351
352 // /// Takes `ptr to a `(ptr, len)` pair, and returns `(ptr, len)`.
353 // fn deref_buffer(
354 // plugin_memory: &mut Memory,
355 // store: impl AsContext<Data = WasiCtxAlloc>,
356 // buffer: u32,
357 // ) -> Result<(u32, u32), Error> {
358 // // create a buffer to read the (ptr, length) pair into
359 // // this is a total of 4 + 4 = 8 bytes.
360 // let raw_buffer = &mut [0; 8];
361 // plugin_memory.read(store, buffer as usize, raw_buffer)?;
362
363 // // use these bytes (wasm stores things little-endian)
364 // // to get a pointer to the buffer and its length
365 // let b = raw_buffer;
366 // let buffer_ptr = u32::from_le_bytes([b[0], b[1], b[2], b[3]]);
367 // let buffer_len = u32::from_le_bytes([b[4], b[5], b[6], b[7]]);
368
369 // return Ok((buffer_ptr, buffer_len));
370 // }
371
372 /// Takes a `(ptr, len)` pair and returns the corresponding deserialized buffer.
373 fn deserialize_from_buffer<R: DeserializeOwned>(
374 plugin_memory: &mut Memory,
375 store: impl AsContext<Data = WasiCtxAlloc>,
376 buffer: WasiBuffer,
377 ) -> Result<R, Error> {
378 let buffer_start = buffer.ptr as usize;
379 let buffer_end = buffer_start + buffer.len as usize;
380
381 // read the buffer at this point into a byte array
382 // deserialize the byte array into the provided serde type
383 let result = &plugin_memory.data(store.as_context())[buffer_start..buffer_end];
384 let result = bincode::deserialize(result)?;
385
386 // TODO: this is handled wasm-side
387 // // deallocate the argument buffer
388 // self.free_buffer.call(&mut self.store, arg_buffer);
389
390 Ok(result)
391 }
392
393 /// Retrieves the handle to a function of a given type.
394 pub fn function<A: Serialize, R: DeserializeOwned, T: AsRef<str>>(
395 &mut self,
396 name: T,
397 ) -> Result<WasiFn<A, R>, Error> {
398 let fun_name = format!("__{}", name.as_ref());
399 let fun = self
400 .instance
401 .get_typed_func::<u64, u64, _>(&mut self.store, &fun_name)?;
402 Ok(WasiFn {
403 function: fun,
404 _function_type: PhantomData,
405 })
406 }
407
408 // TODO: dont' use as for conversions
409 /// Asynchronously calls a function defined Guest-side.
410 pub async fn call<A: Serialize, R: DeserializeOwned>(
411 &mut self,
412 handle: &WasiFn<A, R>,
413 arg: A,
414 ) -> Result<R, Error> {
415 // dbg!(&handle.name);
416 // dbg!(serde_json::to_string(&arg)).unwrap();
417
418 let mut plugin_memory = self
419 .instance
420 .get_memory(&mut self.store, "memory")
421 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
422
423 // write the argument to linear memory
424 // this returns a (ptr, lentgh) pair
425 let arg_buffer = Self::serialize_to_buffer(
426 self.store.data().alloc_buffer(),
427 &mut plugin_memory,
428 &mut self.store,
429 Self::serialize(arg)?,
430 )
431 .await?;
432
433 // call the function, passing in the buffer and its length
434 // this returns a ptr to a (ptr, lentgh) pair
435 let result_buffer = handle
436 .function
437 .call_async(&mut self.store, arg_buffer.into_u64())
438 .await?;
439
440 Self::deserialize_from_buffer(
441 &mut plugin_memory,
442 &mut self.store,
443 WasiBuffer::from_u64(result_buffer),
444 )
445 }
446}