1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
# WebAssembly System Interface (WASI)
<!--introduced_in=v12.16.0-->
> Stability: 1 - Experimental
<!-- source_link=lib/wasi.js -->
The WASI API provides an implementation of the [WebAssembly System Interface][]
specification. WASI gives sandboxed WebAssembly applications access to the
underlying operating system via a collection of POSIX-like functions.
```js
import fs from 'fs';
import { WASI } from 'wasi';
const wasi = new WASI({
args: process.argv,
env: process.env,
preopens: {
'/sandbox': '/some/real/path/that/wasm/can/access'
}
});
const importObject = { wasi_snapshot_preview1: wasi.wasiImport };
const wasm = await WebAssembly.compile(fs.readFileSync('./demo.wasm'));
const instance = await WebAssembly.instantiate(wasm, importObject);
wasi.start(instance);
```
To run the above example, create a new WebAssembly text format file named
`demo.wat`:
```text
(module
;; Import the required fd_write WASI function which will write the given io vectors to stdout
;; The function signature for fd_write is:
;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
(import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))
(memory 1)
(export "memory" (memory 0))
;; Write 'hello world\n' to memory at an offset of 8 bytes
;; Note the trailing newline which is required for the text to appear
(data (i32.const 8) "hello world\n")
(func $main (export "_start")
;; Creating a new io vector within linear memory
(i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
(i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string
(call $fd_write
(i32.const 1) ;; file_descriptor - 1 for stdout
(i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
(i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
(i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
)
drop ;; Discard the number of bytes written from the top of the stack
)
)
```
Use [wabt](https://github.com/WebAssembly/wabt) to compile `.wat` to `.wasm`
```console
$ wat2wasm demo.wat
```
The `--experimental-wasi-unstable-preview1` CLI argument is needed for this
example to run.
## Class: `WASI`
<!-- YAML
added:
- v13.3.0
- v12.16.0
-->
The `WASI` class provides the WASI system call API and additional convenience
methods for working with WASI-based applications. Each `WASI` instance
represents a distinct sandbox environment. For security purposes, each `WASI`
instance must have its command-line arguments, environment variables, and
sandbox directory structure configured explicitly.
### `new WASI([options])`
<!-- YAML
added:
- v13.3.0
- v12.16.0
-->
* `options` {Object}
* `args` {Array} An array of strings that the WebAssembly application will
see as command-line arguments. The first argument is the virtual path to the
WASI command itself. **Default:** `[]`.
* `env` {Object} An object similar to `process.env` that the WebAssembly
application will see as its environment. **Default:** `{}`.
* `preopens` {Object} This object represents the WebAssembly application's
sandbox directory structure. The string keys of `preopens` are treated as
directories within the sandbox. The corresponding values in `preopens` are
the real paths to those directories on the host machine.
* `returnOnExit` {boolean} By default, WASI applications terminate the Node.js
process via the `__wasi_proc_exit()` function. Setting this option to `true`
causes `wasi.start()` to return the exit code rather than terminate the
process. **Default:** `false`.
* `stdin` {integer} The file descriptor used as standard input in the
WebAssembly application. **Default:** `0`.
* `stdout` {integer} The file descriptor used as standard output in the
WebAssembly application. **Default:** `1`.
* `stderr` {integer} The file descriptor used as standard error in the
WebAssembly application. **Default:** `2`.
### `wasi.start(instance)`
<!-- YAML
added:
- v13.3.0
- v12.16.0
-->
* `instance` {WebAssembly.Instance}
Attempt to begin execution of `instance` as a WASI command by invoking its
`_start()` export. If `instance` does not contain a `_start()` export, or if
`instance` contains an `_initialize()` export, then an exception is thrown.
`start()` requires that `instance` exports a [`WebAssembly.Memory`][] named
`memory`. If `instance` does not have a `memory` export an exception is thrown.
If `start()` is called more than once, an exception is thrown.
### `wasi.initialize(instance)`
<!-- YAML
added:
- v14.6.0
- v12.19.0
-->
* `instance` {WebAssembly.Instance}
Attempt to initialize `instance` as a WASI reactor by invoking its
`_initialize()` export, if it is present. If `instance` contains a `_start()`
export, then an exception is thrown.
`initialize()` requires that `instance` exports a [`WebAssembly.Memory`][] named
`memory`. If `instance` does not have a `memory` export an exception is thrown.
If `initialize()` is called more than once, an exception is thrown.
### `wasi.wasiImport`
<!-- YAML
added:
- v13.3.0
- v12.16.0
-->
* {Object}
`wasiImport` is an object that implements the WASI system call API. This object
should be passed as the `wasi_snapshot_preview1` import during the instantiation
of a [`WebAssembly.Instance`][].
[WebAssembly System Interface]: https://wasi.dev/
[`WebAssembly.Instance`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance
[`WebAssembly.Memory`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory
|