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::IntoFunc;
10use wasmtime::{Caller, Config, Engine, Instance, Linker, Module, Store, TypedFunc};
11use wasmtime_wasi::{Dir, WasiCtx, WasiCtxBuilder};
12
13pub struct WasiResource(u32);
14
15pub struct WasiFn<A: Serialize, R: DeserializeOwned> {
16 function: TypedFunc<(u32, u32), u32>,
17 _function_type: PhantomData<fn(A) -> R>,
18}
19
20impl<A: Serialize, R: DeserializeOwned> Copy for WasiFn<A, R> {}
21
22impl<A: Serialize, R: DeserializeOwned> Clone for WasiFn<A, R> {
23 fn clone(&self) -> Self {
24 Self {
25 function: self.function,
26 _function_type: PhantomData,
27 }
28 }
29}
30
31// impl<A: Serialize, R: DeserializeOwned> WasiFn<A, R> {
32// #[inline(always)]
33// pub async fn call(&self, runtime: &mut Wasi, arg: A) -> Result<R, Error> {
34// runtime.call(self, arg).await
35// }
36// }
37
38pub struct Wasi {
39 engine: Engine,
40 module: Module,
41 store: Store<WasiCtx>,
42 instance: Instance,
43 alloc_buffer: TypedFunc<u32, u32>,
44 // free_buffer: TypedFunc<(u32, u32), ()>,
45}
46
47// type signature derived from:
48// https://docs.rs/wasmtime/latest/wasmtime/struct.Linker.html#method.func_wrap2_async
49// macro_rules! dynHostFunction {
50// () => {
51// Box<
52// dyn for<'a> Fn(Caller<'a, WasiCtx>, u32, u32)
53// -> Box<dyn Future<Output = u32> + Send + 'a>
54// + Send
55// + Sync
56// + 'static
57// >
58// };
59// }
60
61// macro_rules! implHostFunction {
62// () => {
63// impl for<'a> Fn(Caller<'a, WasiCtx>, u32, u32)
64// -> Box<dyn Future<Output = u32> + Send + 'a>
65// + Send
66// + Sync
67// + 'static
68// };
69// }
70
71// This type signature goodness gracious
72pub type HostFunction = Box<dyn IntoFunc<WasiCtx, (u32, u32), u32>>;
73
74pub struct WasiPluginBuilder {
75 host_functions: HashMap<String, HostFunction>,
76 wasi_ctx_builder: WasiCtxBuilder,
77}
78
79impl WasiPluginBuilder {
80 pub fn new() -> Self {
81 WasiPluginBuilder {
82 host_functions: HashMap::new(),
83 wasi_ctx_builder: WasiCtxBuilder::new(),
84 }
85 }
86
87 pub fn new_with_default_ctx() -> WasiPluginBuilder {
88 let mut this = Self::new();
89 this.wasi_ctx_builder = this.wasi_ctx_builder.inherit_stdin().inherit_stderr();
90 this
91 }
92
93 fn wrap_host_function<A: Serialize, R: DeserializeOwned>(
94 function: impl Fn(A) -> R + Send + Sync + 'static,
95 ) -> HostFunction {
96 Box::new(move |ptr, len| {
97 function(todo!());
98 todo!()
99 })
100 }
101
102 pub fn host_function<A: Serialize, R: DeserializeOwned>(
103 mut self,
104 name: &str,
105 function: impl Fn(A) -> R + Send + Sync + 'static,
106 ) -> Self {
107 self.host_functions
108 .insert(name.to_string(), Self::wrap_host_function(function));
109 self
110 }
111
112 pub fn wasi_ctx(mut self, config: impl FnOnce(WasiCtxBuilder) -> WasiCtxBuilder) -> Self {
113 self.wasi_ctx_builder = config(self.wasi_ctx_builder);
114 self
115 }
116
117 pub async fn init<T: AsRef<[u8]>>(self, module: T) -> Result<Wasi, Error> {
118 let plugin = WasiPlugin {
119 module: module.as_ref().to_vec(),
120 wasi_ctx: self.wasi_ctx_builder.build(),
121 host_functions: self.host_functions,
122 };
123
124 Wasi::init(plugin).await
125 }
126}
127
128/// Represents a to-be-initialized plugin.
129/// Please use [`WasiPluginBuilder`], don't use this directly.
130pub struct WasiPlugin {
131 pub module: Vec<u8>,
132 pub wasi_ctx: WasiCtx,
133 pub host_functions: HashMap<String, HostFunction>,
134}
135
136impl Wasi {
137 pub fn dump_memory(data: &[u8]) {
138 for (i, byte) in data.iter().enumerate() {
139 if i % 32 == 0 {
140 println!();
141 }
142 if i % 4 == 0 {
143 print!("|");
144 }
145 if *byte == 0 {
146 print!("__")
147 } else {
148 print!("{:02x}", byte);
149 }
150 }
151 println!();
152 }
153}
154
155impl Wasi {
156 async fn init(plugin: WasiPlugin) -> Result<Self, Error> {
157 let mut config = Config::default();
158 config.async_support(true);
159 let engine = Engine::new(&config)?;
160 let mut linker = Linker::new(&engine);
161
162 linker
163 .func_wrap("env", "__command", |x: u32, y: u32| x + y)
164 .unwrap();
165 linker.func_wrap("env", "__hello", |x: u32| x * 2).unwrap();
166 linker.func_wrap("env", "__bye", |x: u32| x / 2).unwrap();
167
168 wasmtime_wasi::add_to_linker(&mut linker, |s| s)?;
169
170 let mut store: Store<_> = Store::new(&engine, plugin.wasi_ctx);
171 let module = Module::new(&engine, plugin.module)?;
172
173 linker.module_async(&mut store, "", &module).await?;
174 let instance = linker.instantiate_async(&mut store, &module).await?;
175
176 let alloc_buffer = instance.get_typed_func(&mut store, "__alloc_buffer")?;
177 // let free_buffer = instance.get_typed_func(&mut store, "__free_buffer")?;
178
179 Ok(Wasi {
180 engine,
181 module,
182 store,
183 instance,
184 alloc_buffer,
185 // free_buffer,
186 })
187 }
188
189 /// Attaches a file or directory the the given system path to the runtime.
190 /// Note that the resource must be freed by calling `remove_resource` afterwards.
191 pub fn attach_path<T: AsRef<Path>>(&mut self, path: T) -> Result<WasiResource, Error> {
192 // grab the WASI context
193 let ctx = self.store.data_mut();
194
195 // open the file we want, and convert it into the right type
196 // this is a footgun and a half
197 let file = File::open(&path).unwrap();
198 let dir = Dir::from_std_file(file);
199 let dir = Box::new(wasmtime_wasi::dir::Dir::from_cap_std(dir));
200
201 // grab an empty file descriptor, specify capabilities
202 let fd = ctx.table().push(Box::new(()))?;
203 let caps = dir::DirCaps::all();
204 let file_caps = file::FileCaps::all();
205
206 // insert the directory at the given fd,
207 // return a handle to the resource
208 ctx.insert_dir(fd, dir, caps, file_caps, path.as_ref().to_path_buf());
209 Ok(WasiResource(fd))
210 }
211
212 /// Returns `true` if the resource existed and was removed.
213 pub fn remove_resource(&mut self, resource: WasiResource) -> Result<(), Error> {
214 self.store
215 .data_mut()
216 .table()
217 .delete(resource.0)
218 .ok_or_else(|| anyhow!("Resource did not exist, but a valid handle was passed in"))?;
219 Ok(())
220 }
221
222 // pub fn with_resource<T>(
223 // &mut self,
224 // resource: WasiResource,
225 // callback: fn(&mut Self) -> Result<T, Error>,
226 // ) -> Result<T, Error> {
227 // let result = callback(self);
228 // self.remove_resource(resource)?;
229 // return result;
230 // }
231
232 // So this call function is kinda a dance, I figured it'd be a good idea to document it.
233 // the high level is we take a serde type, serialize it to a byte array,
234 // (we're doing this using bincode for now)
235 // then toss that byte array into webassembly.
236 // webassembly grabs that byte array, does some magic,
237 // and serializes the result into yet another byte array.
238 // we then grab *that* result byte array and deserialize it into a result.
239 //
240 // phew...
241 //
242 // now the problem is, webassambly doesn't support buffers.
243 // only really like i32s, that's it (yeah, it's sad. Not even unsigned!)
244 // (ok, I'm exaggerating a bit).
245 //
246 // the Wasm function that this calls must have a very specific signature:
247 //
248 // fn(pointer to byte array: i32, length of byte array: i32)
249 // -> pointer to (
250 // pointer to byte_array: i32,
251 // length of byte array: i32,
252 // ): i32
253 //
254 // This pair `(pointer to byte array, length of byte array)` is called a `Buffer`
255 // and can be found in the cargo_test plugin.
256 //
257 // so on the wasm side, we grab the two parameters to the function,
258 // stuff them into a `Buffer`,
259 // and then pray to the `unsafe` Rust gods above that a valid byte array pops out.
260 //
261 // On the flip side, when returning from a wasm function,
262 // we convert whatever serialized result we get into byte array,
263 // which we stuff into a Buffer and allocate on the heap,
264 // which pointer to we then return.
265 // Note the double indirection!
266 //
267 // So when returning from a function, we actually leak memory *twice*:
268 //
269 // 1) once when we leak the byte array
270 // 2) again when we leak the allocated `Buffer`
271 //
272 // This isn't a problem because Wasm stops executing after the function returns,
273 // so the heap is still valid for our inspection when we want to pull things out.
274
275 /// Takes an item, allocates a buffer, serializes the argument to that buffer,
276 /// and returns a (ptr, len) pair to that buffer.
277 async fn serialize_to_buffer<T: Serialize>(&mut self, item: T) -> Result<(u32, u32), Error> {
278 // serialize the argument using bincode
279 let item = bincode::serialize(&item)?;
280 let buffer_len = item.len() as u32;
281
282 // allocate a buffer and write the argument to that buffer
283 let buffer_ptr = self
284 .alloc_buffer
285 .call_async(&mut self.store, buffer_len)
286 .await?;
287 let plugin_memory = self
288 .instance
289 .get_memory(&mut self.store, "memory")
290 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
291 plugin_memory.write(&mut self.store, buffer_ptr as usize, &item)?;
292 Ok((buffer_ptr, buffer_len))
293 }
294
295 /// Takes a ptr to a (ptr, len) pair and returns the corresponding deserialized buffer
296 fn deserialize_from_buffer<R: DeserializeOwned>(&mut self, buffer: u32) -> Result<R, Error> {
297 // create a buffer to read the (ptr, length) pair into
298 // this is a total of 4 + 4 = 8 bytes.
299 let raw_buffer = &mut [0; 8];
300 let plugin_memory = self
301 .instance
302 .get_memory(&mut self.store, "memory")
303 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
304 plugin_memory.read(&mut self.store, buffer as usize, raw_buffer)?;
305
306 // use these bytes (wasm stores things little-endian)
307 // to get a pointer to the buffer and its length
308 let b = raw_buffer;
309 let buffer_ptr = u32::from_le_bytes([b[0], b[1], b[2], b[3]]) as usize;
310 let buffer_len = u32::from_le_bytes([b[4], b[5], b[6], b[7]]) as usize;
311 let buffer_end = buffer_ptr + buffer_len;
312
313 // read the buffer at this point into a byte array
314 // deserialize the byte array into the provided serde type
315 let result = &plugin_memory.data(&mut self.store)[buffer_ptr..buffer_end];
316 let result = bincode::deserialize(result)?;
317
318 // TODO: this is handled wasm-side, but I'd like to double-check
319 // // deallocate the argument buffer
320 // self.free_buffer.call(&mut self.store, arg_buffer);
321
322 Ok(result)
323 }
324
325 pub fn function<A: Serialize, R: DeserializeOwned, T: AsRef<str>>(
326 &mut self,
327 name: T,
328 ) -> Result<WasiFn<A, R>, Error> {
329 let fun_name = format!("__{}", name.as_ref());
330 let fun = self
331 .instance
332 .get_typed_func::<(u32, u32), u32, _>(&mut self.store, &fun_name)?;
333 Ok(WasiFn {
334 function: fun,
335 _function_type: PhantomData,
336 })
337 }
338
339 // TODO: dont' use as for conversions
340 pub async fn call<A: Serialize, R: DeserializeOwned>(
341 &mut self,
342 handle: &WasiFn<A, R>,
343 arg: A,
344 ) -> Result<R, Error> {
345 // dbg!(&handle.name);
346 // dbg!(serde_json::to_string(&arg)).unwrap();
347
348 // write the argument to linear memory
349 // this returns a (ptr, lentgh) pair
350 let arg_buffer = self.serialize_to_buffer(arg).await?;
351
352 // get the webassembly function we want to actually call
353 // TODO: precompute handle
354 // let fun_name = format!("__{}", handle);
355 // let fun = self
356 // .instance
357 // .get_typed_func::<(u32, u32), u32, _>(&mut self.store, &fun_name)?;
358 let fun = handle.function;
359
360 // call the function, passing in the buffer and its length
361 // this returns a ptr to a (ptr, lentgh) pair
362 let result_buffer = fun.call_async(&mut self.store, arg_buffer).await?;
363
364 self.deserialize_from_buffer(result_buffer)
365 }
366}