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108 lines
2.2 KiB
108 lines
2.2 KiB
/**
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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*
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* @format
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*/
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"use strict";
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const encode = require("./encode");
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const MAX_SEGMENT_LENGTH = 7;
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const ONE_MEG = 1024 * 1024;
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const COMMA = 0x2c;
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const SEMICOLON = 0x3b;
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/**
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* Efficient builder for base64 VLQ mappings strings.
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*
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* This class uses a buffer that is preallocated with one megabyte and is
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* reallocated dynamically as needed, doubling its size.
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*
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* Encoding never creates any complex value types (strings, objects), and only
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* writes character values to the buffer.
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*
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* For details about source map terminology and specification, check
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* https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
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*/
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class B64Builder {
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constructor() {
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this.buffer = Buffer.alloc(ONE_MEG);
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this.pos = 0;
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this.hasSegment = false;
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}
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/**
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* Adds `n` markers for generated lines to the mappings.
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*/
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markLines(n) {
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if (n < 1) {
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return this;
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}
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this.hasSegment = false;
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if (this.pos + n >= this.buffer.length) {
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this._realloc();
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}
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while (n--) {
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this.buffer[this.pos++] = SEMICOLON;
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}
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return this;
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}
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/**
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* Starts a segment at the specified column offset in the current line.
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*/
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startSegment(column) {
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if (this.hasSegment) {
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this._writeByte(COMMA);
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} else {
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this.hasSegment = true;
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}
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this.append(column);
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return this;
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}
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/**
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* Appends a single number to the mappings.
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*/
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append(value) {
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if (this.pos + MAX_SEGMENT_LENGTH >= this.buffer.length) {
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this._realloc();
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}
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this.pos = encode(value, this.buffer, this.pos);
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return this;
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}
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/**
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* Returns the string representation of the mappings.
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*/
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toString() {
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return this.buffer.toString("ascii", 0, this.pos);
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}
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_writeByte(byte) {
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if (this.pos === this.buffer.length) {
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this._realloc();
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}
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this.buffer[this.pos++] = byte;
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}
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_realloc() {
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const { buffer } = this;
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this.buffer = Buffer.alloc(buffer.length * 2);
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buffer.copy(this.buffer);
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}
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}
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module.exports = B64Builder;
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