src/runtime_strings_extra.js

/**
 * @license
 * Copyright 2020 The Emscripten Authors
 * SPDX-License-Identifier: MIT
 */

// runtime_strings_extra.js: Strings related runtime functions that are available only in regular runtime.

// Given a pointer 'ptr' to a null-terminated ASCII-encoded string in the emscripten HEAP, returns
// a copy of that string as a Javascript String object.

function AsciiToString(ptr) {
#if CAN_ADDRESS_2GB
  ptr >>>= 0;
#endif
  var str = '';
  while (1) {
    var ch = {{{ makeGetValue('ptr++', 0, 'i8', null, true) }}};
    if (!ch) return str;
    str += String.fromCharCode(ch);
  }
}

// Copies the given Javascript String object 'str' to the emscripten HEAP at address 'outPtr',
// null-terminated and encoded in ASCII form. The copy will require at most str.length+1 bytes of space in the HEAP.

function stringToAscii(str, outPtr) {
  return writeAsciiToMemory(str, outPtr, false);
}

// Given a pointer 'ptr' to a null-terminated UTF16LE-encoded string in the emscripten HEAP, returns
// a copy of that string as a Javascript String object.

#if TEXTDECODER == 2
var UTF16Decoder = new TextDecoder{{{ USE_PTHREADS ? 'Wrapper' : ''}}}('utf-16le');
#else // TEXTDECODER == 2
#if TEXTDECODER
var UTF16Decoder = typeof TextDecoder !== 'undefined' ? new TextDecoder{{{ USE_PTHREADS ? 'Wrapper' : ''}}}('utf-16le') : undefined;
#endif // TEXTDECODER
#endif // TEXTDECODER == 2

function UTF16ToString(ptr, maxBytesToRead) {
#if ASSERTIONS
  assert(ptr % 2 == 0, 'Pointer passed to UTF16ToString must be aligned to two bytes!');
#endif
#if TEXTDECODER
  var endPtr = ptr;
  // TextDecoder needs to know the byte length in advance, it doesn't stop on null terminator by itself.
  // Also, use the length info to avoid running tiny strings through TextDecoder, since .subarray() allocates garbage.
  var idx = endPtr >> 1;
  var maxIdx = idx + maxBytesToRead / 2;
  // If maxBytesToRead is not passed explicitly, it will be undefined, and this
  // will always evaluate to true. This saves on code size.
  while (!(idx >= maxIdx) && HEAPU16[idx]) ++idx;
  endPtr = idx << 1;

#if TEXTDECODER != 2
  if (endPtr - ptr > 32 && UTF16Decoder) {
#endif // TEXTDECODER != 2
    return UTF16Decoder.decode(HEAPU8.subarray(ptr, endPtr));
#if TEXTDECODER != 2
  } else {
#endif // TEXTDECODER != 2
#endif // TEXTDECODER
    var str = '';

    // If maxBytesToRead is not passed explicitly, it will be undefined, and the for-loop's condition
    // will always evaluate to true. The loop is then terminated on the first null char.
    for (var i = 0; !(i >= maxBytesToRead / 2); ++i) {
      var codeUnit = {{{ makeGetValue('ptr', 'i*2', 'i16') }}};
      if (codeUnit == 0) break;
      // fromCharCode constructs a character from a UTF-16 code unit, so we can pass the UTF16 string right through.
      str += String.fromCharCode(codeUnit);
    }

    return str;
#if TEXTDECODER && TEXTDECODER != 2
  }
#endif // TEXTDECODER
}

// Copies the given Javascript String object 'str' to the emscripten HEAP at address 'outPtr',
// null-terminated and encoded in UTF16 form. The copy will require at most str.length*4+2 bytes of space in the HEAP.
// Use the function lengthBytesUTF16() to compute the exact number of bytes (excluding null terminator) that this function will write.
// Parameters:
//   str: the Javascript string to copy.
//   outPtr: Byte address in Emscripten HEAP where to write the string to.
//   maxBytesToWrite: The maximum number of bytes this function can write to the array. This count should include the null
//                    terminator, i.e. if maxBytesToWrite=2, only the null terminator will be written and nothing else.
//                    maxBytesToWrite<2 does not write any bytes to the output, not even the null terminator.
// Returns the number of bytes written, EXCLUDING the null terminator.

function stringToUTF16(str, outPtr, maxBytesToWrite) {
#if ASSERTIONS
  assert(outPtr % 2 == 0, 'Pointer passed to stringToUTF16 must be aligned to two bytes!');
#endif
#if ASSERTIONS
  assert(typeof maxBytesToWrite == 'number', 'stringToUTF16(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!');
#endif
  // Backwards compatibility: if max bytes is not specified, assume unsafe unbounded write is allowed.
  if (maxBytesToWrite === undefined) {
    maxBytesToWrite = 0x7FFFFFFF;
  }
  if (maxBytesToWrite < 2) return 0;
  maxBytesToWrite -= 2; // Null terminator.
  var startPtr = outPtr;
  var numCharsToWrite = (maxBytesToWrite < str.length*2) ? (maxBytesToWrite / 2) : str.length;
  for (var i = 0; i < numCharsToWrite; ++i) {
    // charCodeAt returns a UTF-16 encoded code unit, so it can be directly written to the HEAP.
    var codeUnit = str.charCodeAt(i); // possibly a lead surrogate
    {{{ makeSetValue('outPtr', 0, 'codeUnit', 'i16') }}};
    outPtr += 2;
  }
  // Null-terminate the pointer to the HEAP.
  {{{ makeSetValue('outPtr', 0, 0, 'i16') }}};
  return outPtr - startPtr;
}

// Returns the number of bytes the given Javascript string takes if encoded as a UTF16 byte array, EXCLUDING the null terminator byte.

function lengthBytesUTF16(str) {
  return str.length*2;
}

function UTF32ToString(ptr, maxBytesToRead) {
#if ASSERTIONS
  assert(ptr % 4 == 0, 'Pointer passed to UTF32ToString must be aligned to four bytes!');
#endif
  var i = 0;

  var str = '';
  // If maxBytesToRead is not passed explicitly, it will be undefined, and this
  // will always evaluate to true. This saves on code size.
  while (!(i >= maxBytesToRead / 4)) {
    var utf32 = {{{ makeGetValue('ptr', 'i*4', 'i32') }}};
    if (utf32 == 0) break;
    ++i;
    // Gotcha: fromCharCode constructs a character from a UTF-16 encoded code (pair), not from a Unicode code point! So encode the code point to UTF-16 for constructing.
    // See http://unicode.org/faq/utf_bom.html#utf16-3
    if (utf32 >= 0x10000) {
      var ch = utf32 - 0x10000;
      str += String.fromCharCode(0xD800 | (ch >> 10), 0xDC00 | (ch & 0x3FF));
    } else {
      str += String.fromCharCode(utf32);
    }
  }
  return str;
}

// Copies the given Javascript String object 'str' to the emscripten HEAP at address 'outPtr',
// null-terminated and encoded in UTF32 form. The copy will require at most str.length*4+4 bytes of space in the HEAP.
// Use the function lengthBytesUTF32() to compute the exact number of bytes (excluding null terminator) that this function will write.
// Parameters:
//   str: the Javascript string to copy.
//   outPtr: Byte address in Emscripten HEAP where to write the string to.
//   maxBytesToWrite: The maximum number of bytes this function can write to the array. This count should include the null
//                    terminator, i.e. if maxBytesToWrite=4, only the null terminator will be written and nothing else.
//                    maxBytesToWrite<4 does not write any bytes to the output, not even the null terminator.
// Returns the number of bytes written, EXCLUDING the null terminator.

function stringToUTF32(str, outPtr, maxBytesToWrite) {
#if CAN_ADDRESS_2GB
  outPtr >>>= 0;
#endif
#if ASSERTIONS
  assert(outPtr % 4 == 0, 'Pointer passed to stringToUTF32 must be aligned to four bytes!');
#endif
#if ASSERTIONS
  assert(typeof maxBytesToWrite == 'number', 'stringToUTF32(str, outPtr, maxBytesToWrite) is missing the third parameter that specifies the length of the output buffer!');
#endif
  // Backwards compatibility: if max bytes is not specified, assume unsafe unbounded write is allowed.
  if (maxBytesToWrite === undefined) {
    maxBytesToWrite = 0x7FFFFFFF;
  }
  if (maxBytesToWrite < 4) return 0;
  var startPtr = outPtr;
  var endPtr = startPtr + maxBytesToWrite - 4;
  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! We must decode the string to UTF-32 to the heap.
    // See http://unicode.org/faq/utf_bom.html#utf16-3
    var codeUnit = str.charCodeAt(i); // possibly a lead surrogate
    if (codeUnit >= 0xD800 && codeUnit <= 0xDFFF) {
      var trailSurrogate = str.charCodeAt(++i);
      codeUnit = 0x10000 + ((codeUnit & 0x3FF) << 10) | (trailSurrogate & 0x3FF);
    }
    {{{ makeSetValue('outPtr', 0, 'codeUnit', 'i32') }}};
    outPtr += 4;
    if (outPtr + 4 > endPtr) break;
  }
  // Null-terminate the pointer to the HEAP.
  {{{ makeSetValue('outPtr', 0, 0, 'i32') }}};
  return outPtr - startPtr;
}

// Returns the number of bytes the given Javascript string takes if encoded as a UTF16 byte array, EXCLUDING the null terminator byte.

function lengthBytesUTF32(str) {
  var len = 0;
  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! We must decode the string to UTF-32 to the heap.
    // See http://unicode.org/faq/utf_bom.html#utf16-3
    var codeUnit = str.charCodeAt(i);
    if (codeUnit >= 0xD800 && codeUnit <= 0xDFFF) ++i; // possibly a lead surrogate, so skip over the tail surrogate.
    len += 4;
  }

  return len;
}

// Allocate heap space for a JS string, and write it there.
// It is the responsibility of the caller to free() that memory.
function allocateUTF8(str) {
  var size = lengthBytesUTF8(str) + 1;
  var ret = {{{ makeMalloc('allocateUTF8', 'size') }}};
  if (ret) stringToUTF8Array(str, HEAP8, ret, size);
  return ret;
}

// Allocate stack space for a JS string, and write it there.
function allocateUTF8OnStack(str) {
  var size = lengthBytesUTF8(str) + 1;
  var ret = stackAlloc(size);
  stringToUTF8Array(str, HEAP8, ret, size);
  return ret;
}

// Deprecated: This function should not be called because it is unsafe and does not provide
// a maximum length limit of how many bytes it is allowed to write. Prefer calling the
// function stringToUTF8Array() instead, which takes in a maximum length that can be used
// to be secure from out of bounds writes.
/** @deprecated
    @param {boolean=} dontAddNull */
function writeStringToMemory(string, buffer, dontAddNull) {
  warnOnce('writeStringToMemory is deprecated and should not be called! Use stringToUTF8() instead!');

  var /** @type {number} */ lastChar, /** @type {number} */ end;
  if (dontAddNull) {
    // stringToUTF8Array always appends null. If we don't want to do that, remember the
    // character that existed at the location where the null will be placed, and restore
    // that after the write (below).
    end = buffer + lengthBytesUTF8(string);
    lastChar = HEAP8[end];
  }
  stringToUTF8(string, buffer, Infinity);
  if (dontAddNull) HEAP8[end] = lastChar; // Restore the value under the null character.
}

function writeArrayToMemory(array, buffer) {
#if ASSERTIONS
  assert(array.length >= 0, 'writeArrayToMemory array must have a length (should be an array or typed array)')
#endif
  HEAP8.set(array, buffer);
}

/** @param {boolean=} dontAddNull */
function writeAsciiToMemory(str, buffer, dontAddNull) {
  for (var i = 0; i < str.length; ++i) {
#if ASSERTIONS
    assert(str.charCodeAt(i) === str.charCodeAt(i)&0xff);
#endif
    {{{ makeSetValue('buffer++', 0, 'str.charCodeAt(i)', 'i8') }}};
  }
  // Null-terminate the pointer to the HEAP.
  if (!dontAddNull) {{{ makeSetValue('buffer', 0, 0, 'i8') }}};
}