Source Code: lib/wasi.js
\nThe WASI API provides an implementation of the WebAssembly System Interface\nspecification. WASI gives sandboxed WebAssembly applications access to the\nunderlying operating system via a collection of POSIX-like functions.
\n'use strict';\nconst fs = require('fs');\nconst { WASI } = require('wasi');\nconst wasi = new WASI({\n args: process.argv,\n env: process.env,\n preopens: {\n '/sandbox': '/some/real/path/that/wasm/can/access'\n }\n});\nconst importObject = { wasi_snapshot_preview1: wasi.wasiImport };\n\n(async () => {\n const wasm = await WebAssembly.compile(fs.readFileSync('./demo.wasm'));\n const instance = await WebAssembly.instantiate(wasm, importObject);\n\n wasi.start(instance);\n})();\nTo run the above example, create a new WebAssembly text format file named\ndemo.wat:
(module\n ;; Import the required fd_write WASI function which will write the given io vectors to stdout\n ;; The function signature for fd_write is:\n ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written\n (import \"wasi_snapshot_preview1\" \"fd_write\" (func $fd_write (param i32 i32 i32 i32) (result i32)))\n\n (memory 1)\n (export \"memory\" (memory 0))\n\n ;; Write 'hello world\\n' to memory at an offset of 8 bytes\n ;; Note the trailing newline which is required for the text to appear\n (data (i32.const 8) \"hello world\\n\")\n\n (func $main (export \"_start\")\n ;; Creating a new io vector within linear memory\n (i32.store (i32.const 0) (i32.const 8)) ;; iov.iov_base - This is a pointer to the start of the 'hello world\\n' string\n (i32.store (i32.const 4) (i32.const 12)) ;; iov.iov_len - The length of the 'hello world\\n' string\n\n (call $fd_write\n (i32.const 1) ;; file_descriptor - 1 for stdout\n (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0\n (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.\n (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written\n )\n drop ;; Discard the number of bytes written from the top of the stack\n )\n)\nUse wabt to compile .wat to .wasm
$ wat2wasm demo.wat\nThe --experimental-wasi-unstable-preview1 and --experimental-wasm-bigint\nCLI arguments are needed for this example to run.
The WASI class provides the WASI system call API and additional convenience\nmethods for working with WASI-based applications. Each WASI instance\nrepresents a distinct sandbox environment. For security purposes, each WASI\ninstance must have its command line arguments, environment variables, and\nsandbox directory structure configured explicitly.
Attempt to begin execution of instance as a WASI command by invoking its\n_start() export. If instance does not contain a _start() export, or if\ninstance contains an _initialize() export, then an exception is thrown.
start() requires that instance exports a WebAssembly.Memory named\nmemory. If instance does not have a memory export an exception is thrown.
If start() is called more than once, an exception is thrown.
Attempt to initialize instance as a WASI reactor by invoking its\n_initialize() export, if it is present. If instance contains a _start()\nexport, then an exception is thrown.
initialize() requires that instance exports a WebAssembly.Memory named\nmemory. If instance does not have a memory export an exception is thrown.
If initialize() is called more than once, an exception is thrown.
wasiImport is an object that implements the WASI system call API. This object\nshould be passed as the wasi_snapshot_preview1 import during the instantiation\nof a WebAssembly.Instance.