1use std::{fs::File, os::unix::prelude::AsRawFd, path::Path};
2
3use anyhow::{anyhow, Error};
4use serde::{de::DeserializeOwned, Serialize};
5
6use wasi_common::{dir, file};
7use wasmtime::{Engine, Instance, Linker, Module, Store, TypedFunc};
8use wasmtime_wasi::{Dir, WasiCtx, WasiCtxBuilder};
9
10pub struct WasiResource(u32);
11
12pub struct Wasi {
13 engine: Engine,
14 module: Module,
15 store: Store<WasiCtx>,
16 instance: Instance,
17 alloc_buffer: TypedFunc<u32, u32>,
18 // free_buffer: TypedFunc<(u32, u32), ()>,
19}
20
21pub struct WasiPlugin {
22 pub module: Vec<u8>,
23 pub wasi_ctx: WasiCtx,
24}
25
26impl Wasi {
27 pub fn dump_memory(data: &[u8]) {
28 for (i, byte) in data.iter().enumerate() {
29 if i % 32 == 0 {
30 println!();
31 }
32 if i % 4 == 0 {
33 print!("|");
34 }
35 if *byte == 0 {
36 print!("__")
37 } else {
38 print!("{:02x}", byte);
39 }
40 }
41 println!();
42 }
43}
44
45impl Wasi {
46 pub fn default_ctx() -> WasiCtx {
47 WasiCtxBuilder::new()
48 .inherit_stdout()
49 .inherit_stderr()
50 .build()
51 }
52
53 pub fn init(plugin: WasiPlugin) -> Result<Self, Error> {
54 let engine = Engine::default();
55 let mut linker = Linker::new(&engine);
56
57 linker.func_wrap("env", "__hello", |x: u32| x * 2).unwrap();
58 linker.func_wrap("env", "__bye", |x: u32| x / 2).unwrap();
59
60 wasmtime_wasi::add_to_linker(&mut linker, |s| s)?;
61
62 let mut store: Store<_> = Store::new(&engine, plugin.wasi_ctx);
63 let module = Module::new(&engine, plugin.module)?;
64
65 linker.module(&mut store, "", &module)?;
66 let instance = linker.instantiate(&mut store, &module)?;
67
68 let alloc_buffer = instance.get_typed_func(&mut store, "__alloc_buffer")?;
69 // let free_buffer = instance.get_typed_func(&mut store, "__free_buffer")?;
70
71 Ok(Wasi {
72 engine,
73 module,
74 store,
75 instance,
76 alloc_buffer,
77 // free_buffer,
78 })
79 }
80
81 /// Attaches a file or directory the the given system path to the runtime.
82 /// Note that the resource must be freed by calling `remove_resource` afterwards.
83 pub fn attach_path<T: AsRef<Path>>(&mut self, path: T) -> Result<WasiResource, Error> {
84 // grab the WASI context
85 let ctx = self.store.data_mut();
86
87 // open the file we want, and convert it into the right type
88 // this is a footgun and a half
89 let file = File::open(&path).unwrap();
90 let dir = Dir::from_std_file(file);
91 let dir = Box::new(wasmtime_wasi::dir::Dir::from_cap_std(dir));
92
93 // grab an empty file descriptor, specify capabilities
94 let fd = ctx.table().push(Box::new(()))?;
95 let caps = dir::DirCaps::all();
96 let file_caps = file::FileCaps::all();
97
98 // insert the directory at the given fd,
99 // return a handle to the resource
100 ctx.insert_dir(fd, dir, caps, file_caps, path.as_ref().to_path_buf());
101 Ok(WasiResource(fd))
102 }
103
104 /// Returns `true` if the resource existed and was removed.
105 pub fn remove_resource(&mut self, resource: WasiResource) -> Result<(), Error> {
106 self.store
107 .data_mut()
108 .table()
109 .delete(resource.0)
110 .ok_or_else(|| anyhow!("Resource did not exist, but a valid handle was passed in"))?;
111 Ok(())
112 }
113
114 // pub fn with_resource<T>(
115 // &mut self,
116 // resource: WasiResource,
117 // callback: fn(&mut Self) -> Result<T, Error>,
118 // ) -> Result<T, Error> {
119 // let result = callback(self);
120 // self.remove_resource(resource)?;
121 // return result;
122 // }
123
124 // So this call function is kinda a dance, I figured it'd be a good idea to document it.
125 // the high level is we take a serde type, serialize it to a byte array,
126 // (we're doing this using bincode for now)
127 // then toss that byte array into webassembly.
128 // webassembly grabs that byte array, does some magic,
129 // and serializes the result into yet another byte array.
130 // we then grab *that* result byte array and deserialize it into a result.
131 //
132 // phew...
133 //
134 // now the problem is, webassambly doesn't support buffers.
135 // only really like i32s, that's it (yeah, it's sad. Not even unsigned!)
136 // (ok, I'm exaggerating a bit).
137 //
138 // the Wasm function that this calls must have a very specific signature:
139 //
140 // fn(pointer to byte array: i32, length of byte array: i32)
141 // -> pointer to (
142 // pointer to byte_array: i32,
143 // length of byte array: i32,
144 // ): i32
145 //
146 // This pair `(pointer to byte array, length of byte array)` is called a `Buffer`
147 // and can be found in the cargo_test plugin.
148 //
149 // so on the wasm side, we grab the two parameters to the function,
150 // stuff them into a `Buffer`,
151 // and then pray to the `unsafe` Rust gods above that a valid byte array pops out.
152 //
153 // On the flip side, when returning from a wasm function,
154 // we convert whatever serialized result we get into byte array,
155 // which we stuff into a Buffer and allocate on the heap,
156 // which pointer to we then return.
157 // Note the double indirection!
158 //
159 // So when returning from a function, we actually leak memory *twice*:
160 //
161 // 1) once when we leak the byte array
162 // 2) again when we leak the allocated `Buffer`
163 //
164 // This isn't a problem because Wasm stops executing after the function returns,
165 // so the heap is still valid for our inspection when we want to pull things out.
166
167 /// Takes an item, allocates a buffer, serializes the argument to that buffer,
168 /// and returns a (ptr, len) pair to that buffer.
169 fn serialize_to_buffer<T: Serialize>(&mut self, item: T) -> Result<(u32, u32), Error> {
170 // serialize the argument using bincode
171 let item = bincode::serialize(&item)?;
172 let buffer_len = item.len() as u32;
173
174 // allocate a buffer and write the argument to that buffer
175 let buffer_ptr = self.alloc_buffer.call(&mut self.store, buffer_len)?;
176 let plugin_memory = self
177 .instance
178 .get_memory(&mut self.store, "memory")
179 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
180 plugin_memory.write(&mut self.store, buffer_ptr as usize, &item)?;
181 Ok((buffer_ptr, buffer_len))
182 }
183
184 /// Takes a ptr to a (ptr, len) pair and returns the corresponding deserialized buffer
185 fn deserialize_from_buffer<R: DeserializeOwned>(&mut self, buffer: u32) -> Result<R, Error> {
186 // create a buffer to read the (ptr, length) pair into
187 // this is a total of 4 + 4 = 8 bytes.
188 let raw_buffer = &mut [0; 8];
189 let plugin_memory = self
190 .instance
191 .get_memory(&mut self.store, "memory")
192 .ok_or_else(|| anyhow!("Could not grab slice of plugin memory"))?;
193 plugin_memory.read(&mut self.store, buffer as usize, raw_buffer)?;
194
195 // use these bytes (wasm stores things little-endian)
196 // to get a pointer to the buffer and its length
197 let b = raw_buffer;
198 let buffer_ptr = u32::from_le_bytes([b[0], b[1], b[2], b[3]]) as usize;
199 let buffer_len = u32::from_le_bytes([b[4], b[5], b[6], b[7]]) as usize;
200 let buffer_end = buffer_ptr + buffer_len;
201
202 // read the buffer at this point into a byte array
203 // deserialize the byte array into the provided serde type
204 let result = &plugin_memory.data(&mut self.store)[buffer_ptr..buffer_end];
205 let result = bincode::deserialize(result)?;
206
207 // TODO: this is handled wasm-side, but I'd like to double-check
208 // // deallocate the argument buffer
209 // self.free_buffer.call(&mut self.store, arg_buffer);
210
211 Ok(result)
212 }
213
214 // TODO: dont' use as for conversions
215 pub fn call<A: Serialize, R: DeserializeOwned>(
216 &mut self,
217 handle: &str,
218 arg: A,
219 ) -> Result<R, Error> {
220 let start = std::time::Instant::now();
221 dbg!(&handle);
222 // dbg!(serde_json::to_string(&arg)).unwrap();
223
224 // write the argument to linear memory
225 // this returns a (ptr, lentgh) pair
226 let arg_buffer = self.serialize_to_buffer(arg)?;
227
228 // get the webassembly function we want to actually call
229 // TODO: precompute handle
230 let fun_name = format!("__{}", handle);
231 let fun = self
232 .instance
233 .get_typed_func::<(u32, u32), u32, _>(&mut self.store, &fun_name)?;
234
235 // call the function, passing in the buffer and its length
236 // this returns a ptr to a (ptr, lentgh) pair
237 let result_buffer = fun.call(&mut self.store, arg_buffer)?;
238
239 self.deserialize_from_buffer(result_buffer)
240 }
241}