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;
}

// used for FastTextDecoder
const validUtfLabels = ['utf-8', 'utf8', 'unicode-1-1-utf-8'];

/**
 * @constructor
 */
function FastTextEncoder() {
  // This does not accept an encoding, and always uses UTF-8:
  //   https://www.w3.org/TR/encoding/#dom-textencoder
}

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;

  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 {
      continue;  // out of range
    }

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

  // Use subarray if slice isn't supported (IE11). This will use more memory
  // because the original array still exists.
  return target.slice ? target.slice(0, at) : target.subarray(0, at);
}

/**
 * @constructor
 * @param {string=} utfLabel
 * @param {{fatal: boolean}=} options
 */
function FastTextDecoder(utfLabel='utf-8', options={fatal: false}) {
  if (validUtfLabels.indexOf(utfLabel.toLowerCase()) === -1) {
    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 {!Uint8Array} bytes
 * @return {string}
 */
function decodeBuffer(bytes) {
  return Buffer.from(bytes.buffer, bytes.byteOffset, bytes.byteLength).toString('utf-8');
}

/**
 * @param {!Uint8Array} bytes
 * @return {string}
 */
function decodeSyncXHR(bytes) {
  const b = new Blob([bytes], {type: 'text/plain;charset=UTF-8'});
  const u = URL.createObjectURL(b);

  // This hack will fail in non-Edgium Edge because sync XHRs are disabled (and
  // possibly in other places), so ensure there's a fallback call.
  try {
    const x = new XMLHttpRequest();
    x.open('GET', u, false);
    x.send();
    return x.responseText;
  } catch (e) {
    return decodeFallback(bytes);
  } finally {
    URL.revokeObjectURL(u);
  }
}

/**
 * @param {!Uint8Array} bytes
 * @return {string}
 */
function decodeFallback(bytes) {
  let inputIndex = 0;

  // Create a working buffer for UTF-16 code points, but don't generate one
  // which is too large for small input sizes. UTF-8 to UCS-16 conversion is
  // going to be at most 1:1, if all code points are ASCII. The other extreme
  // is 4-byte UTF-8, which results in two UCS-16 points, but this is still 50%
  // fewer entries in the output.
  const pendingSize = Math.min(256 * 256, bytes.length + 1);
  const pending = new Uint16Array(pendingSize);
  const chunks = [];
  let pendingIndex = 0;

  for (;;) {
    const more = inputIndex < bytes.length;

    // If there's no more data or there'd be no room for two UTF-16 values,
    // create a chunk. This isn't done at the end by simply slicing the data
    // into equal sized chunks as we might hit a surrogate pair.
    if (!more || (pendingIndex >= pendingSize - 1)) {
      // nb. .apply and friends are *really slow*. Low-hanging fruit is to
      // expand this to literally pass pending[0], pending[1], ... etc, but
      // the output code expands pretty fast in this case.
      chunks.push(String.fromCharCode.apply(null, pending.subarray(0, pendingIndex)));

      if (!more) {
        return chunks.join('');
      }

      // Move the buffer forward and create another chunk.
      bytes = bytes.subarray(inputIndex);
      inputIndex = 0;
      pendingIndex = 0;
    }

    // The native TextDecoder will generate "REPLACEMENT CHARACTER" where the
    // input data is invalid. Here, we blindly parse the data even if it's
    // wrong: e.g., if a 3-byte sequence doesn't have two valid continuations.

    const byte1 = bytes[inputIndex++];
    if ((byte1 & 0x80) === 0) {  // 1-byte or null
      pending[pendingIndex++] = byte1;
    } else if ((byte1 & 0xe0) === 0xc0) {  // 2-byte
      const byte2 = bytes[inputIndex++] & 0x3f;
      pending[pendingIndex++] = ((byte1 & 0x1f) << 6) | byte2;
    } else if ((byte1 & 0xf0) === 0xe0) {  // 3-byte
      const byte2 = bytes[inputIndex++] & 0x3f;
      const byte3 = bytes[inputIndex++] & 0x3f;
      pending[pendingIndex++] = ((byte1 & 0x1f) << 12) | (byte2 << 6) | byte3;
    } else if ((byte1 & 0xf8) === 0xf0) {  // 4-byte
      const byte2 = bytes[inputIndex++] & 0x3f;
      const byte3 = bytes[inputIndex++] & 0x3f;
      const byte4 = bytes[inputIndex++] & 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;
        pending[pendingIndex++] = (codepoint >>> 10) & 0x3ff | 0xd800;
        codepoint = 0xdc00 | codepoint & 0x3ff;
      }
      pending[pendingIndex++] = codepoint;
    } else {
      // invalid initial byte
    }
  }
}

// Decoding a string is pretty slow, but use alternative options where possible.
let decodeImpl = decodeFallback;
if (typeof Buffer === 'function' && Buffer.from) {
  // Buffer.from was added in Node v5.10.0 (2015-11-17).
  decodeImpl = decodeBuffer;
} else if (typeof Blob === 'function' && typeof URL === 'function' && typeof URL.createObjectURL === 'function') {
  // Blob and URL.createObjectURL are available from IE10, Safari 6, Chrome 19
  // (all released in 2012), Firefox 19 (2013), ...
  decodeImpl = decodeSyncXHR;
}

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

  // Accept Uint8Array instances as-is.
  let bytes = buffer;

  // Look for ArrayBufferView, which isn't a real type, but basically represents
  // all the valid TypedArray types plus DataView. They all have ".buffer" as
  // an instance of ArrayBuffer.
  if (!(bytes instanceof Uint8Array) && bytes.buffer instanceof ArrayBuffer) {
    bytes = new Uint8Array(buffer.buffer);
  }

  return decodeImpl(/** @type {!Uint8Array} */ (bytes));
}

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

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