Function stringToUTF8Array

test/tests/emscripten/readdir_empty.js:760–810

(str, outU8Array, outIdx, maxBytesToWrite)

// Returns the number of bytes written, EXCLUDING the null terminator.

function stringToUTF8Array(str, outU8Array, outIdx, maxBytesToWrite) {
  if (!(maxBytesToWrite > 0)) // Parameter maxBytesToWrite is not optional. Negative values, 0, null, undefined and false each don't write out any bytes.
    return 0;

  var startIdx = outIdx;
  var endIdx = outIdx + maxBytesToWrite - 1; // -1 for string null terminator.
  for (var i = 0; i < str.length; ++i) {
    // Gotcha: charCodeAt returns a 16-bit word that is a UTF-16 encoded code unit, not a Unicode code point of the character! So decode UTF16->UTF32->UTF8.
    // See http://unicode.org/faq/utf_bom.html#utf16-3
    // For UTF8 byte structure, see http://en.wikipedia.org/wiki/UTF-8#Description and https://www.ietf.org/rfc/rfc2279.txt and https://tools.ietf.org/html/rfc3629
    var u = str.charCodeAt(i); // possibly a lead surrogate
    if (u >= 0xD800 && u <= 0xDFFF) u = 0x10000 + ((u & 0x3FF) << 10) | (str.charCodeAt(++i) & 0x3FF);
    if (u <= 0x7F) {
      if (outIdx >= endIdx) break;
      outU8Array[outIdx++] = u;
    } else if (u <= 0x7FF) {
      if (outIdx + 1 >= endIdx) break;
      outU8Array[outIdx++] = 0xC0 | (u >> 6);
      outU8Array[outIdx++] = 0x80 | (u & 63);
    } else if (u <= 0xFFFF) {
      if (outIdx + 2 >= endIdx) break;
      outU8Array[outIdx++] = 0xE0 | (u >> 12);
      outU8Array[outIdx++] = 0x80 | ((u >> 6) & 63);
      outU8Array[outIdx++] = 0x80 | (u & 63);
    } else if (u <= 0x1FFFFF) {
      if (outIdx + 3 >= endIdx) break;
      outU8Array[outIdx++] = 0xF0 | (u >> 18);
      outU8Array[outIdx++] = 0x80 | ((u >> 12) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 6) & 63);
      outU8Array[outIdx++] = 0x80 | (u & 63);
    } else if (u <= 0x3FFFFFF) {
      if (outIdx + 4 >= endIdx) break;
      outU8Array[outIdx++] = 0xF8 | (u >> 24);
      outU8Array[outIdx++] = 0x80 | ((u >> 18) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 12) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 6) & 63);
      outU8Array[outIdx++] = 0x80 | (u & 63);
    } else {
      if (outIdx + 5 >= endIdx) break;
      outU8Array[outIdx++] = 0xFC | (u >> 30);
      outU8Array[outIdx++] = 0x80 | ((u >> 24) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 18) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 12) & 63);
      outU8Array[outIdx++] = 0x80 | ((u >> 6) & 63);
      outU8Array[outIdx++] = 0x80 | (u & 63);
    }
  }
  // Null-terminate the pointer to the buffer.
  outU8Array[outIdx] = 0;
  return outIdx - startIdx;
}
Module["stringToUTF8Array"] = stringToUTF8Array;

// Copies the given Javascript String object 'str' to the emscripten HEAP at address 'outPtr',