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</div> 112 <div id="gtoc"> 113 <ul> 114 <li class="pinned-header">Node.js v18.20.1</li> 115 116 <li class="picker-header"> 117 <a href="#"> 118 <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 119 Table of contents 120 </a> 121 122 <div class="picker"><div class="toc"><ul> 123<li><span class="stability_1"><a href="#webassembly-system-interface-wasi">WebAssembly System Interface (WASI)</a></span> 124<ul> 125<li><a href="#class-wasi">Class: <code>WASI</code></a> 126<ul> 127<li><a href="#new-wasioptions"><code>new WASI([options])</code></a></li> 128<li><a href="#wasistartinstance"><code>wasi.start(instance)</code></a></li> 129<li><a href="#wasiinitializeinstance"><code>wasi.initialize(instance)</code></a></li> 130<li><a href="#wasiwasiimport"><code>wasi.wasiImport</code></a></li> 131</ul> 132</li> 133</ul> 134</li> 135</ul></div></div> 136 </li> 137 138 139 <li class="picker-header"> 140 <a href="#"> 141 <span class="collapsed-arrow">►</span><span 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228 </a> 229 <div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v21.x/api/wasi.html">21.x</a></li> 230<li><a href="https://nodejs.org/docs/latest-v20.x/api/wasi.html">20.x <b>LTS</b></a></li> 231<li><a href="https://nodejs.org/docs/latest-v19.x/api/wasi.html">19.x</a></li> 232<li><a href="https://nodejs.org/docs/latest-v18.x/api/wasi.html">18.x <b>LTS</b></a></li> 233<li><a href="https://nodejs.org/docs/latest-v17.x/api/wasi.html">17.x</a></li> 234<li><a href="https://nodejs.org/docs/latest-v16.x/api/wasi.html">16.x</a></li> 235<li><a href="https://nodejs.org/docs/latest-v15.x/api/wasi.html">15.x</a></li> 236<li><a href="https://nodejs.org/docs/latest-v14.x/api/wasi.html">14.x</a></li> 237<li><a href="https://nodejs.org/docs/latest-v13.x/api/wasi.html">13.x</a></li> 238<li><a href="https://nodejs.org/docs/latest-v12.x/api/wasi.html">12.x</a></li></ol></div> 239 </li> 240 241 <li class="picker-header"> 242 <a href="#"> 243 <span class="collapsed-arrow">►</span><span class="expanded-arrow">▼</span> 244 Options 245 </a> 246 247 <div class="picker"> 248 <ul> 249 <li> 250 <a href="all.html">View on single page</a> 251 </li> 252 <li> 253 <a href="wasi.json">View as JSON</a> 254 </li> 255 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/wasi.md">Edit on GitHub</a></li> 256 </ul> 257 </div> 258 </li> 259 </ul> 260 </div> 261 <hr> 262 </header> 263 264 <details id="toc" open><summary>Table of contents</summary><ul> 265<li><span class="stability_1"><a href="#webassembly-system-interface-wasi">WebAssembly System Interface (WASI)</a></span> 266<ul> 267<li><a href="#class-wasi">Class: <code>WASI</code></a> 268<ul> 269<li><a href="#new-wasioptions"><code>new WASI([options])</code></a></li> 270<li><a href="#wasistartinstance"><code>wasi.start(instance)</code></a></li> 271<li><a href="#wasiinitializeinstance"><code>wasi.initialize(instance)</code></a></li> 272<li><a href="#wasiwasiimport"><code>wasi.wasiImport</code></a></li> 273</ul> 274</li> 275</ul> 276</li> 277</ul></details> 278 279 <div id="apicontent"> 280 <h2>WebAssembly System Interface (WASI)<span><a class="mark" href="#webassembly-system-interface-wasi" id="webassembly-system-interface-wasi">#</a></span><a aria-hidden="true" class="legacy" id="wasi_webassembly_system_interface_wasi"></a></h2> 281 282<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> 283<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v18.20.1/lib/wasi.js">lib/wasi.js</a></p> 284<p>The WASI API provides an implementation of the <a href="https://wasi.dev/">WebAssembly System Interface</a> 285specification. WASI gives sandboxed WebAssembly applications access to the 286underlying operating system via a collection of POSIX-like functions.</p> 287 288<pre class="with-49-chars"><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> { readFile } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>; 289<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>; 290<span class="hljs-keyword">import</span> { argv, env } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; 291 292<span class="hljs-keyword">const</span> wasi = <span class="hljs-keyword">new</span> <span class="hljs-title function_">WASI</span>({ 293 <span class="hljs-attr">args</span>: argv, 294 env, 295 <span class="hljs-attr">preopens</span>: { 296 <span class="hljs-string">'/sandbox'</span>: <span class="hljs-string">'/some/real/path/that/wasm/can/access'</span>, 297 }, 298}); 299 300<span class="hljs-comment">// Some WASI binaries require:</span> 301<span class="hljs-comment">// const importObject = { wasi_unstable: wasi.wasiImport };</span> 302<span class="hljs-keyword">const</span> importObject = { <span class="hljs-attr">wasi_snapshot_preview1</span>: wasi.<span class="hljs-property">wasiImport</span> }; 303 304<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>( 305 <span class="hljs-keyword">await</span> <span class="hljs-title function_">readFile</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(<span class="hljs-string">'./demo.wasm'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>)), 306); 307<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); 308 309wasi.<span class="hljs-title function_">start</span>(instance);</code><code class="language-js cjs"><span class="hljs-meta">'use strict'</span>; 310<span class="hljs-keyword">const</span> { readFile } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs/promises'</span>); 311<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>); 312<span class="hljs-keyword">const</span> { argv, env } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>); 313<span class="hljs-keyword">const</span> { join } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:path'</span>); 314 315<span class="hljs-keyword">const</span> wasi = <span class="hljs-keyword">new</span> <span class="hljs-title function_">WASI</span>({ 316 <span class="hljs-attr">args</span>: argv, 317 env, 318 <span class="hljs-attr">preopens</span>: { 319 <span class="hljs-string">'/sandbox'</span>: <span class="hljs-string">'/some/real/path/that/wasm/can/access'</span>, 320 }, 321}); 322 323<span class="hljs-comment">// Some WASI binaries require:</span> 324<span class="hljs-comment">// const importObject = { wasi_unstable: wasi.wasiImport };</span> 325<span class="hljs-keyword">const</span> importObject = { <span class="hljs-attr">wasi_snapshot_preview1</span>: wasi.<span class="hljs-property">wasiImport</span> }; 326 327(<span class="hljs-keyword">async</span> () => { 328 <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>( 329 <span class="hljs-keyword">await</span> <span class="hljs-title function_">readFile</span>(<span class="hljs-title function_">join</span>(__dirname, <span class="hljs-string">'demo.wasm'</span>)), 330 ); 331 <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); 332 333 wasi.<span class="hljs-title function_">start</span>(instance); 334})();</code><button class="copy-button">copy</button></pre> 335<p>To run the above example, create a new WebAssembly text format file named 336<code>demo.wat</code>:</p> 337<pre><code class="language-text">(module 338 ;; Import the required fd_write WASI function which will write the given io vectors to stdout 339 ;; The function signature for fd_write is: 340 ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written 341 (import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32))) 342 343 (memory 1) 344 (export "memory" (memory 0)) 345 346 ;; Write 'hello world\n' to memory at an offset of 8 bytes 347 ;; Note the trailing newline which is required for the text to appear 348 (data (i32.const 8) "hello world\n") 349 350 (func $main (export "_start") 351 ;; Creating a new io vector within linear memory 352 (i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string 353 (i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\n' string 354 355 (call $fd_write 356 (i32.const 1) ;; file_descriptor - 1 for stdout 357 (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0 358 (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one. 359 (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written 360 ) 361 drop ;; Discard the number of bytes written from the top of the stack 362 ) 363)</code> <button class="copy-button">copy</button></pre> 364<p>Use <a href="https://github.com/WebAssembly/wabt">wabt</a> to compile <code>.wat</code> to <code>.wasm</code></p> 365<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">wat2wasm demo.wat</span></code> <button class="copy-button">copy</button></pre> 366<section><h3>Class: <code>WASI</code><span><a class="mark" href="#class-wasi" id="class-wasi">#</a></span><a aria-hidden="true" class="legacy" id="wasi_class_wasi"></a></h3> 367<div class="api_metadata"> 368<span>Added in: v13.3.0, v12.16.0</span> 369</div> 370<p>The <code>WASI</code> class provides the WASI system call API and additional convenience 371methods for working with WASI-based applications. Each <code>WASI</code> instance 372represents a distinct sandbox environment. For security purposes, each <code>WASI</code> 373instance must have its command-line arguments, environment variables, and 374sandbox directory structure configured explicitly.</p> 375<h4><code>new WASI([options])</code><span><a class="mark" href="#new-wasioptions" id="new-wasioptions">#</a></span><a aria-hidden="true" class="legacy" id="wasi_new_wasi_options"></a></h4> 376<div class="api_metadata"> 377<span>Added in: v13.3.0, v12.16.0</span> 378</div> 379<ul> 380<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 381<ul> 382<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 383see as command-line arguments. The first argument is the virtual path to the 384WASI command itself. <strong>Default:</strong> <code>[]</code>.</li> 385<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 386application will see as its environment. <strong>Default:</strong> <code>{}</code>.</li> 387<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 388sandbox directory structure. The string keys of <code>preopens</code> are treated as 389directories within the sandbox. The corresponding values in <code>preopens</code> are 390the real paths to those directories on the host machine.</li> 391<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 392process via the <code>__wasi_proc_exit()</code> function. Setting this option to <code>true</code> 393causes <code>wasi.start()</code> to return the exit code rather than terminate the 394process. <strong>Default:</strong> <code>false</code>.</li> 395<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 396WebAssembly application. <strong>Default:</strong> <code>0</code>.</li> 397<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 398WebAssembly application. <strong>Default:</strong> <code>1</code>.</li> 399<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 400WebAssembly application. <strong>Default:</strong> <code>2</code>.</li> 401</ul> 402</li> 403</ul> 404<h4><code>wasi.start(instance)</code><span><a class="mark" href="#wasistartinstance" id="wasistartinstance">#</a></span><a aria-hidden="true" class="legacy" id="wasi_wasi_start_instance"></a></h4> 405<div class="api_metadata"> 406<span>Added in: v13.3.0, v12.16.0</span> 407</div> 408<ul> 409<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> 410</ul> 411<p>Attempt to begin execution of <code>instance</code> as a WASI command by invoking its 412<code>_start()</code> export. If <code>instance</code> does not contain a <code>_start()</code> export, or if 413<code>instance</code> contains an <code>_initialize()</code> export, then an exception is thrown.</p> 414<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 415<code>memory</code>. If <code>instance</code> does not have a <code>memory</code> export an exception is thrown.</p> 416<p>If <code>start()</code> is called more than once, an exception is thrown.</p> 417<h4><code>wasi.initialize(instance)</code><span><a class="mark" href="#wasiinitializeinstance" id="wasiinitializeinstance">#</a></span><a aria-hidden="true" class="legacy" id="wasi_wasi_initialize_instance"></a></h4> 418<div class="api_metadata"> 419<span>Added in: v14.6.0, v12.19.0</span> 420</div> 421<ul> 422<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> 423</ul> 424<p>Attempt to initialize <code>instance</code> as a WASI reactor by invoking its 425<code>_initialize()</code> export, if it is present. If <code>instance</code> contains a <code>_start()</code> 426export, then an exception is thrown.</p> 427<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 428<code>memory</code>. If <code>instance</code> does not have a <code>memory</code> export an exception is thrown.</p> 429<p>If <code>initialize()</code> is called more than once, an exception is thrown.</p> 430<h4><code>wasi.wasiImport</code><span><a class="mark" href="#wasiwasiimport" id="wasiwasiimport">#</a></span><a aria-hidden="true" class="legacy" id="wasi_wasi_wasiimport"></a></h4> 431<div class="api_metadata"> 432<span>Added in: v13.3.0, v12.16.0</span> 433</div> 434<ul> 435<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 436</ul> 437<p><code>wasiImport</code> is an object that implements the WASI system call API. This object 438should be passed as the <code>wasi_snapshot_preview1</code> import during the instantiation 439of a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/Instance"><code>WebAssembly.Instance</code></a>.</p></section> 440 <!-- API END --> 441 </div> 442 </div> 443 </div> 444</body> 445</html> 446