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