/** * Copyright (c) Meta Platforms, Inc. and affiliates. * * This source code is licensed under the MIT license found in the * LICENSE file in the root directory of this source tree. * * @format * @flow strict */ 'use strict'; const MAGIC_NUMBER = require('../shared/output/RamBundle/magic-number'); const SIZEOF_UINT32 = 4; const HEADER_SIZE = 3; /** * Implementation of a RAM bundle parser in JS. * * It receives a Buffer as an input and implements two main methods, which are * able to run in constant time no matter the size of the bundle: * * getStartupCode(): returns the runtime and the startup code of the bundle. * getModule(): returns the code for the specified module. */ class RamBundleParser { _buffer: Buffer; _numModules: number; _startupCodeLength: number; _startOffset: number; constructor(buffer: Buffer) { this._buffer = buffer; if (this._readPosition(0) !== MAGIC_NUMBER) { throw new Error('File is not a RAM bundle file'); } this._numModules = this._readPosition(1); this._startupCodeLength = this._readPosition(2); // The startup code begins after the table of contents, which contains the // 3 fields on the header plus 2 entries per module. this._startOffset = (HEADER_SIZE + this._numModules * 2) * SIZEOF_UINT32; } _readPosition(pos: number): number { return this._buffer.readUInt32LE(pos * SIZEOF_UINT32); } getStartupCode(): string { const start = this._startOffset; const end = start + this._startupCodeLength - 1; return this._buffer.toString('utf8', start, end); } getModule(id: number): string { const moduleOffset = this._readPosition(HEADER_SIZE + id * 2); const moduleLength = this._readPosition(HEADER_SIZE + id * 2 + 1); const start = this._startOffset + moduleOffset; const end = start + moduleLength - 1; return this._buffer.toString('utf8', start, end); } } module.exports = RamBundleParser;