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data-id="wasi" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.20.1 documentation</h1> 93 <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 94 <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 95 <path fill="none" d="M0 0h24v24H0z" /> 96 <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 97 <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 98 </svg> 99 <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 100 <path d="M0 0h24v24H0z" fill="none" /> 101 <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 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123<li><a href="https://nodejs.org/docs/latest-v14.x/api/wasi.html">14.x <b>LTS</b></a></li> 124<li><a href="https://nodejs.org/docs/latest-v13.x/api/wasi.html">13.x</a></li> 125<li><a href="https://nodejs.org/docs/latest-v12.x/api/wasi.html">12.x <b>LTS</b></a></li></ol> 126 </li> 127 128 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/wasi.md">Edit on GitHub</a></li> 129 </ul> 130 </div> 131 <hr> 132 </header> 133 134 <details id="toc" open><summary>Table of contents</summary><ul> 135<li><span class="stability_1"><a href="#wasi_webassembly_system_interface_wasi">WebAssembly System Interface (WASI)</a></span> 136<ul> 137<li><a href="#wasi_class_wasi">Class: <code>WASI</code></a> 138<ul> 139<li><a href="#wasi_new_wasi_options"><code>new WASI([options])</code></a></li> 140<li><a href="#wasi_wasi_start_instance"><code>wasi.start(instance)</code></a></li> 141<li><a href="#wasi_wasi_initialize_instance"><code>wasi.initialize(instance)</code></a></li> 142<li><a href="#wasi_wasi_wasiimport"><code>wasi.wasiImport</code></a></li> 143</ul> 144</li> 145</ul> 146</li> 147</ul></details> 148 149 <div id="apicontent"> 150 <h2>WebAssembly System Interface (WASI)<span><a class="mark" href="#wasi_webassembly_system_interface_wasi" id="wasi_webassembly_system_interface_wasi">#</a></span></h2> 151 152<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 153<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.20.1/lib/wasi.js">lib/wasi.js</a></p> 154<p>The WASI API provides an implementation of the <a href="https://wasi.dev/">WebAssembly System Interface</a> 155specification. WASI gives sandboxed WebAssembly applications access to the 156underlying operating system via a collection of POSIX-like functions.</p> 157 158<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'fs'</span>; 159<span class="hljs-keyword">import</span> { <span class="hljs-variable constant_">WASI</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'wasi'</span>; 160 161<span class="hljs-keyword">const</span> wasi = <span class="hljs-keyword">new</span> <span class="hljs-title function_">WASI</span>({ 162 <span class="hljs-attr">args</span>: process.<span class="hljs-property">argv</span>, 163 <span class="hljs-attr">env</span>: process.<span class="hljs-property">env</span>, 164 <span class="hljs-attr">preopens</span>: { 165 <span class="hljs-string">'/sandbox'</span>: <span class="hljs-string">'/some/real/path/that/wasm/can/access'</span> 166 } 167}); 168<span class="hljs-keyword">const</span> importObject = { <span class="hljs-attr">wasi_snapshot_preview1</span>: wasi.<span class="hljs-property">wasiImport</span> }; 169 170<span class="hljs-keyword">const</span> wasm = <span class="hljs-keyword">await</span> <span class="hljs-title class_">WebAssembly</span>.<span class="hljs-title function_">compile</span>(fs.<span class="hljs-title function_">readFileSync</span>(<span class="hljs-string">'./demo.wasm'</span>)); 171<span class="hljs-keyword">const</span> instance = <span class="hljs-keyword">await</span> <span class="hljs-title class_">WebAssembly</span>.<span class="hljs-title function_">instantiate</span>(wasm, importObject); 172 173wasi.<span class="hljs-title function_">start</span>(instance);</code><code class="language-js cjs"><span class="hljs-meta">'use strict'</span>; 174<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'fs'</span>); 175<span class="hljs-keyword">const</span> { <span class="hljs-variable constant_">WASI</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'wasi'</span>); 176<span class="hljs-keyword">const</span> wasi = <span class="hljs-keyword">new</span> <span class="hljs-title function_">WASI</span>({ 177 <span class="hljs-attr">args</span>: process.<span class="hljs-property">argv</span>, 178 <span class="hljs-attr">env</span>: process.<span class="hljs-property">env</span>, 179 <span class="hljs-attr">preopens</span>: { 180 <span class="hljs-string">'/sandbox'</span>: <span class="hljs-string">'/some/real/path/that/wasm/can/access'</span> 181 } 182}); 183<span class="hljs-keyword">const</span> importObject = { <span class="hljs-attr">wasi_snapshot_preview1</span>: wasi.<span class="hljs-property">wasiImport</span> }; 184 185(<span class="hljs-keyword">async</span> () => { 186 <span class="hljs-keyword">const</span> wasm = <span class="hljs-keyword">await</span> <span class="hljs-title class_">WebAssembly</span>.<span class="hljs-title function_">compile</span>(fs.<span class="hljs-title function_">readFileSync</span>(<span class="hljs-string">'./demo.wasm'</span>)); 187 <span class="hljs-keyword">const</span> instance = <span class="hljs-keyword">await</span> <span class="hljs-title class_">WebAssembly</span>.<span class="hljs-title function_">instantiate</span>(wasm, importObject); 188 189 wasi.<span class="hljs-title function_">start</span>(instance); 190})();</code></pre> 191<p>To run the above example, create a new WebAssembly text format file named 192<code>demo.wat</code>:</p> 193<pre><code class="language-text">(module 194 ;; Import the required fd_write WASI function which will write the given io vectors to stdout 195 ;; The function signature for fd_write is: 196 ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written 197 (import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32))) 198 199 (memory 1) 200 (export "memory" (memory 0)) 201 202 ;; Write 'hello world\n' to memory at an offset of 8 bytes 203 ;; Note the trailing newline which is required for the text to appear 204 (data (i32.const 8) "hello world\n") 205 206 (func $main (export "_start") 207 ;; Creating a new io vector within linear memory 208 (i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string 209 (i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string 210 211 (call $fd_write 212 (i32.const 1) ;; file_descriptor - 1 for stdout 213 (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0 214 (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one. 215 (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written 216 ) 217 drop ;; Discard the number of bytes written from the top of the stack 218 ) 219)</code></pre> 220<p>Use <a href="https://github.com/WebAssembly/wabt">wabt</a> to compile <code>.wat</code> to <code>.wasm</code></p> 221<pre><code class="language-console"><span class="hljs-meta">$ </span><span class="language-bash">wat2wasm demo.wat</span></code></pre> 222<p>The <code>--experimental-wasi-unstable-preview1</code> and <code>--experimental-wasm-bigint</code> 223CLI arguments are needed for this example to run.</p> 224<section><h3>Class: <code>WASI</code><span><a class="mark" href="#wasi_class_wasi" id="wasi_class_wasi">#</a></span></h3> 225<div class="api_metadata"> 226<span>Added in: v13.3.0, v12.16.0</span> 227</div> 228<p>The <code>WASI</code> class provides the WASI system call API and additional convenience 229methods for working with WASI-based applications. Each <code>WASI</code> instance 230represents a distinct sandbox environment. For security purposes, each <code>WASI</code> 231instance must have its command-line arguments, environment variables, and 232sandbox directory structure configured explicitly.</p> 233<h4><code>new WASI([options])</code><span><a class="mark" href="#wasi_new_wasi_options" id="wasi_new_wasi_options">#</a></span></h4> 234<div class="api_metadata"> 235<span>Added in: v13.3.0, v12.16.0</span> 236</div> 237<ul> 238<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 239<ul> 240<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> An array of strings that the WebAssembly application will 241see as command-line arguments. The first argument is the virtual path to the 242WASI command itself. <strong>Default:</strong> <code>[]</code>.</li> 243<li><code>env</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> An object similar to <code>process.env</code> that the WebAssembly 244application will see as its environment. <strong>Default:</strong> <code>{}</code>.</li> 245<li><code>preopens</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> This object represents the WebAssembly application's 246sandbox directory structure. The string keys of <code>preopens</code> are treated as 247directories within the sandbox. The corresponding values in <code>preopens</code> are 248the real paths to those directories on the host machine.</li> 249<li><code>returnOnExit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> By default, WASI applications terminate the Node.js 250process via the <code>__wasi_proc_exit()</code> function. Setting this option to <code>true</code> 251causes <code>wasi.start()</code> to return the exit code rather than terminate the 252process. <strong>Default:</strong> <code>false</code>.</li> 253<li><code>stdin</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The file descriptor used as standard input in the 254WebAssembly application. <strong>Default:</strong> <code>0</code>.</li> 255<li><code>stdout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The file descriptor used as standard output in the 256WebAssembly application. <strong>Default:</strong> <code>1</code>.</li> 257<li><code>stderr</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The file descriptor used as standard error in the 258WebAssembly application. <strong>Default:</strong> <code>2</code>.</li> 259</ul> 260</li> 261</ul> 262<h4><code>wasi.start(instance)</code><span><a class="mark" href="#wasi_wasi_start_instance" id="wasi_wasi_start_instance">#</a></span></h4> 263<div class="api_metadata"> 264<span>Added in: v13.3.0, v12.16.0</span> 265</div> 266<ul> 267<li><code>instance</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance" class="type"><WebAssembly.Instance></a></li> 268</ul> 269<p>Attempt to begin execution of <code>instance</code> as a WASI command by invoking its 270<code>_start()</code> export. If <code>instance</code> does not contain a <code>_start()</code> export, or if 271<code>instance</code> contains an <code>_initialize()</code> export, then an exception is thrown.</p> 272<p><code>start()</code> requires that <code>instance</code> exports a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory"><code>WebAssembly.Memory</code></a> named 273<code>memory</code>. If <code>instance</code> does not have a <code>memory</code> export an exception is thrown.</p> 274<p>If <code>start()</code> is called more than once, an exception is thrown.</p> 275<h4><code>wasi.initialize(instance)</code><span><a class="mark" href="#wasi_wasi_initialize_instance" id="wasi_wasi_initialize_instance">#</a></span></h4> 276<div class="api_metadata"> 277<span>Added in: v14.6.0</span> 278</div> 279<ul> 280<li><code>instance</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance" class="type"><WebAssembly.Instance></a></li> 281</ul> 282<p>Attempt to initialize <code>instance</code> as a WASI reactor by invoking its 283<code>_initialize()</code> export, if it is present. If <code>instance</code> contains a <code>_start()</code> 284export, then an exception is thrown.</p> 285<p><code>initialize()</code> requires that <code>instance</code> exports a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Memory"><code>WebAssembly.Memory</code></a> named 286<code>memory</code>. If <code>instance</code> does not have a <code>memory</code> export an exception is thrown.</p> 287<p>If <code>initialize()</code> is called more than once, an exception is thrown.</p> 288<h4><code>wasi.wasiImport</code><span><a class="mark" href="#wasi_wasi_wasiimport" id="wasi_wasi_wasiimport">#</a></span></h4> 289<div class="api_metadata"> 290<span>Added in: v13.3.0, v12.16.0</span> 291</div> 292<ul> 293<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 294</ul> 295<p><code>wasiImport</code> is an object that implements the WASI system call API. This object 296should be passed as the <code>wasi_snapshot_preview1</code> import during the instantiation 297of a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance"><code>WebAssembly.Instance</code></a>.</p></section> 298 <!-- API END --> 299 </div> 300 </div> 301 </div> 302 <script> 303 'use strict'; 304 { 305 const kCustomPreference = 'customDarkTheme'; 306 const userSettings = sessionStorage.getItem(kCustomPreference); 307 const themeToggleButton = document.getElementById('theme-toggle-btn'); 308 if (userSettings === null && window.matchMedia) { 309 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 310 if ('onchange' in mq) { 311 function mqChangeListener(e) { 312 document.body.classList.toggle('dark-mode', e.matches); 313 } 314 mq.addEventListener('change', mqChangeListener); 315 if (themeToggleButton) { 316 themeToggleButton.addEventListener('click', function() { 317 mq.removeEventListener('change', mqChangeListener); 318 }, { once: true }); 319 } 320 } 321 if (mq.matches) { 322 document.body.classList.add('dark-mode'); 323 } 324 } else if (userSettings === 'true') { 325 document.body.classList.add('dark-mode'); 326 } 327 if (themeToggleButton) { 328 themeToggleButton.hidden = false; 329 themeToggleButton.addEventListener('click', function() { 330 sessionStorage.setItem( 331 kCustomPreference, 332 document.body.classList.toggle('dark-mode') 333 ); 334 }); 335 } 336 } 337 </script> 338</body> 339</html> 340