text.js

/*
 * Copyright 2017 Sam Thorogood. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

/**
 * @fileoverview Polyfill for TextEncoder and TextDecoder.
 *
 * You probably want `text.min.js`, and not this file directly.
 */

(function(scope) {
'use strict';

// fail early
if (scope['TextEncoder'] && scope['TextDecoder']) {
  return false;
}

/**
 * @constructor
 * @param {string=} utfLabel
 */
function FastTextEncoder(utfLabel='utf-8') {
  if (utfLabel !== 'utf-8') {
    throw new RangeError(
      `Failed to construct 'TextEncoder': The encoding label provided ('${utfLabel}') is invalid.`);
  }
}

Object.defineProperty(FastTextEncoder.prototype, 'encoding', {value: 'utf-8'});

/**
 * @param {string} string
 * @param {{stream: boolean}=} options
 * @return {!Uint8Array}
 */
FastTextEncoder.prototype.encode = function(string, options={stream: false}) {
  if (options.stream) {
    throw new Error(`Failed to encode: the 'stream' option is unsupported.`);
  }

  let pos = 0;
  const len = string.length;
  const out = [];

  let at = 0;  // output position
  let tlen = Math.max(32, len + (len >> 1) + 7);  // 1.5x size
  let target = new Uint8Array((tlen >> 3) << 3);  // ... but at 8 byte offset

  while (pos < len) {
    let value = string.charCodeAt(pos++);
    if (value >= 0xd800 && value <= 0xdbff) {
      // high surrogate
      if (pos < len) {
        const extra = string.charCodeAt(pos);
        if ((extra & 0xfc00) === 0xdc00) {
          ++pos;
          value = ((value & 0x3ff) << 10) + (extra & 0x3ff) + 0x10000;
        }
      }
      if (value >= 0xd800 && value <= 0xdbff) {
        continue;  // drop lone surrogate
      }
    }

    // expand the buffer if we couldn't write 4 bytes
    if (at + 4 > target.length) {
      tlen += 8;  // minimum extra
      tlen *= (1.0 + (pos / string.length) * 2);  // take 2x the remaining
      tlen = (tlen >> 3) << 3;  // 8 byte offset

      const update = new Uint8Array(tlen);
      update.set(target);
      target = update;
    }

    if ((value & 0xffffff80) === 0) {  // 1-byte
      target[at++] = value;  // ASCII
      continue;
    } else if ((value & 0xfffff800) === 0) {  // 2-byte
      target[at++] = ((value >>  6) & 0x1f) | 0xc0;
    } else if ((value & 0xffff0000) === 0) {  // 3-byte
      target[at++] = ((value >> 12) & 0x0f) | 0xe0;
      target[at++] = ((value >>  6) & 0x3f) | 0x80;
    } else if ((value & 0xffe00000) === 0) {  // 4-byte
      target[at++] = ((value >> 18) & 0x07) | 0xf0;
      target[at++] = ((value >> 12) & 0x3f) | 0x80;
      target[at++] = ((value >>  6) & 0x3f) | 0x80;
    } else {
      // FIXME: do we care
      continue;
    }

    target[at++] = (value & 0x3f) | 0x80;
  }

  return target.slice(0, at);
}

/**
 * @constructor
 * @param {string=} utfLabel
 * @param {{fatal: boolean}=} options
 */
function FastTextDecoder(utfLabel='utf-8', options={fatal: false}) {
  if (utfLabel !== 'utf-8') {
    throw new RangeError(
      `Failed to construct 'TextDecoder': The encoding label provided ('${utfLabel}') is invalid.`);
  }
  if (options.fatal) {
    throw new Error(`Failed to construct 'TextDecoder': the 'fatal' option is unsupported.`);
  }
}

Object.defineProperty(FastTextDecoder.prototype, 'encoding', {value: 'utf-8'});

Object.defineProperty(FastTextDecoder.prototype, 'fatal', {value: false});

Object.defineProperty(FastTextDecoder.prototype, 'ignoreBOM', {value: false});

/**
 * @param {(!ArrayBuffer|!ArrayBufferView)} buffer
 * @param {{stream: boolean}=} options
 */
FastTextDecoder.prototype.decode = function(buffer, options={stream: false}) {
  if (options['stream']) {
    throw new Error(`Failed to decode: the 'stream' option is unsupported.`);
  }

  const bytes = new Uint8Array(buffer);
  let pos = 0;
  const len = bytes.length;
  const out = [];

  while (pos < len) {
    const byte1 = bytes[pos++];
    if (byte1 === 0) {
      break;  // NULL
    }
  
    if ((byte1 & 0x80) === 0) {  // 1-byte
      out.push(byte1);
    } else if ((byte1 & 0xe0) === 0xc0) {  // 2-byte
      const byte2 = bytes[pos++] & 0x3f;
      out.push(((byte1 & 0x1f) << 6) | byte2);
    } else if ((byte1 & 0xf0) === 0xe0) {
      const byte2 = bytes[pos++] & 0x3f;
      const byte3 = bytes[pos++] & 0x3f;
      out.push(((byte1 & 0x1f) << 12) | (byte2 << 6) | byte3);
    } else if ((byte1 & 0xf8) === 0xf0) {
      const byte2 = bytes[pos++] & 0x3f;
      const byte3 = bytes[pos++] & 0x3f;
      const byte4 = bytes[pos++] & 0x3f;

      // this can be > 0xffff, so possibly generate surrogates
      let codepoint = ((byte1 & 0x07) << 0x12) | (byte2 << 0x0c) | (byte3 << 0x06) | byte4;
      if (codepoint > 0xffff) {
        // codepoint &= ~0x10000;
        codepoint -= 0x10000;
        out.push((codepoint >>> 10) & 0x3ff | 0xd800)
        codepoint = 0xdc00 | codepoint & 0x3ff;
      }
      out.push(codepoint);
    } else {
      // FIXME: we're ignoring this
    }
  }

  return String.fromCharCode.apply(null, out);
}

scope['TextEncoder'] = FastTextEncoder;
scope['TextDecoder'] = FastTextDecoder;

}(typeof window !== 'undefined' ? window : (typeof global !== 'undefined' ? global : this)));