cesium/Source/Core/getStringFromTypedArray.js

CesiumJS is a JavaScript library for creating 3D globes and 2D maps in a web browser without a plugin.

import defaultValue from "./defaultValue.js";
import defined from "./defined.js";
import DeveloperError from "./DeveloperError.js";
import RuntimeError from "./RuntimeError.js";

/**
 * Reads a string from a Uint8Array.
 *
 * @function
 *
 * @param {Uint8Array} uint8Array The Uint8Array to read from.
 * @param {Number} [byteOffset=0] The byte offset to start reading from.
 * @param {Number} [byteLength] The byte length to read. If byteLength is omitted the remainder of the buffer is read.
 * @returns {String} The string.
 *
 * @private
 */
function getStringFromTypedArray(uint8Array, byteOffset, byteLength) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(uint8Array)) {
    throw new DeveloperError("uint8Array is required.");
  }
  if (byteOffset < 0) {
    throw new DeveloperError("byteOffset cannot be negative.");
  }
  if (byteLength < 0) {
    throw new DeveloperError("byteLength cannot be negative.");
  }
  if (byteOffset + byteLength > uint8Array.byteLength) {
    throw new DeveloperError("sub-region exceeds array bounds.");
  }
  //>>includeEnd('debug');

  byteOffset = defaultValue(byteOffset, 0);
  byteLength = defaultValue(byteLength, uint8Array.byteLength - byteOffset);

  uint8Array = uint8Array.subarray(byteOffset, byteOffset + byteLength);

  return getStringFromTypedArray.decode(uint8Array);
}

// Exposed functions for testing
getStringFromTypedArray.decodeWithTextDecoder = function (view) {
  var decoder = new TextDecoder("utf-8");
  return decoder.decode(view);
};

getStringFromTypedArray.decodeWithFromCharCode = function (view) {
  var result = "";
  var codePoints = utf8Handler(view);
  var length = codePoints.length;
  for (var i = 0; i < length; ++i) {
    var cp = codePoints[i];
    if (cp <= 0xffff) {
      result += String.fromCharCode(cp);
    } else {
      cp -= 0x10000;
      result += String.fromCharCode((cp >> 10) + 0xd800, (cp & 0x3ff) + 0xdc00);
    }
  }
  return result;
};

function inRange(a, min, max) {
  return min <= a && a <= max;
}

// This code is inspired by public domain code found here: https://github.com/inexorabletash/text-encoding
function utf8Handler(utfBytes) {
  var codePoint = 0;
  var bytesSeen = 0;
  var bytesNeeded = 0;
  var lowerBoundary = 0x80;
  var upperBoundary = 0xbf;

  var codePoints = [];
  var length = utfBytes.length;
  for (var i = 0; i < length; ++i) {
    var currentByte = utfBytes[i];

    // If bytesNeeded = 0, then we are starting a new character
    if (bytesNeeded === 0) {
      // 1 Byte Ascii character
      if (inRange(currentByte, 0x00, 0x7f)) {
        // Return a code point whose value is byte.
        codePoints.push(currentByte);
        continue;
      }

      // 2 Byte character
      if (inRange(currentByte, 0xc2, 0xdf)) {
        bytesNeeded = 1;
        codePoint = currentByte & 0x1f;
        continue;
      }

      // 3 Byte character
      if (inRange(currentByte, 0xe0, 0xef)) {
        // If byte is 0xE0, set utf-8 lower boundary to 0xA0.
        if (currentByte === 0xe0) {
          lowerBoundary = 0xa0;
        }
        // If byte is 0xED, set utf-8 upper boundary to 0x9F.
        if (currentByte === 0xed) {
          upperBoundary = 0x9f;
        }

        bytesNeeded = 2;
        codePoint = currentByte & 0xf;
        continue;
      }

      // 4 Byte character
      if (inRange(currentByte, 0xf0, 0xf4)) {
        // If byte is 0xF0, set utf-8 lower boundary to 0x90.
        if (currentByte === 0xf0) {
          lowerBoundary = 0x90;
        }
        // If byte is 0xF4, set utf-8 upper boundary to 0x8F.
        if (currentByte === 0xf4) {
          upperBoundary = 0x8f;
        }

        bytesNeeded = 3;
        codePoint = currentByte & 0x7;
        continue;
      }

      throw new RuntimeError("String decoding failed.");
    }

    // Out of range, so ignore the first part(s) of the character and continue with this byte on its own
    if (!inRange(currentByte, lowerBoundary, upperBoundary)) {
      codePoint = bytesNeeded = bytesSeen = 0;
      lowerBoundary = 0x80;
      upperBoundary = 0xbf;
      --i;
      continue;
    }

    // Set appropriate boundaries, since we've now checked byte 2 of a potential longer character
    lowerBoundary = 0x80;
    upperBoundary = 0xbf;

    // Add byte to code point
    codePoint = (codePoint << 6) | (currentByte & 0x3f);

    // We have the correct number of bytes, so push and reset for next character
    ++bytesSeen;
    if (bytesSeen === bytesNeeded) {
      codePoints.push(codePoint);
      codePoint = bytesNeeded = bytesSeen = 0;
    }
  }

  return codePoints;
}

if (typeof TextDecoder !== "undefined") {
  getStringFromTypedArray.decode =
    getStringFromTypedArray.decodeWithTextDecoder;
} else {
  getStringFromTypedArray.decode =
    getStringFromTypedArray.decodeWithFromCharCode;
}
export default getStringFromTypedArray;