pdf-lib
Version:
Create and modify PDF files with JavaScript
370 lines • 15.1 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.hasUtf16BOM = exports.utf16Decode = exports.lowSurrogate = exports.highSurrogate = exports.hasSurrogates = exports.isWithinBMP = exports.utf16Encode = exports.utf8Encode = void 0;
var strings_1 = require("./strings");
/**
* Encodes a string to UTF-8.
*
* @param input The string to be encoded.
* @param byteOrderMark Whether or not a byte order marker (BOM) should be added
* to the start of the encoding. (default `true`)
* @returns A Uint8Array containing the UTF-8 encoding of the input string.
*
* -----------------------------------------------------------------------------
*
* JavaScript strings are composed of Unicode code points. Code points are
* integers in the range 0 to 1,114,111 (0x10FFFF). When serializing a string,
* it must be encoded as a sequence of words. A word is typically 8, 16, or 32
* bytes in size. As such, Unicode defines three encoding forms: UTF-8, UTF-16,
* and UTF-32. These encoding forms are described in the Unicode standard [1].
* This function implements the UTF-8 encoding form.
*
* -----------------------------------------------------------------------------
*
* In UTF-8, each code point is mapped to a sequence of 1, 2, 3, or 4 bytes.
* Note that the logic which defines this mapping is slightly convoluted, and
* not as straightforward as the mapping logic for UTF-16 or UTF-32. The UTF-8
* mapping logic is as follows [2]:
*
* • If a code point is in the range U+0000..U+007F, then view it as a 7-bit
* integer: 0bxxxxxxx. Map the code point to 1 byte with the first high order
* bit set to 0:
*
* b1=0b0xxxxxxx
*
* • If a code point is in the range U+0080..U+07FF, then view it as an 11-bit
* integer: 0byyyyyxxxxxx. Map the code point to 2 bytes with the first 5 bits
* of the code point stored in the first byte, and the last 6 bits stored in
* the second byte:
*
* b1=0b110yyyyy b2=0b10xxxxxx
*
* • If a code point is in the range U+0800..U+FFFF, then view it as a 16-bit
* integer, 0bzzzzyyyyyyxxxxxx. Map the code point to 3 bytes with the first
* 4 bits stored in the first byte, the next 6 bits stored in the second byte,
* and the last 6 bits in the third byte:
*
* b1=0b1110zzzz b2=0b10yyyyyy b3=0b10xxxxxx
*
* • If a code point is in the range U+10000...U+10FFFF, then view it as a
* 21-bit integer, 0bvvvzzzzzzyyyyyyxxxxxx. Map the code point to 4 bytes with
* the first 3 bits stored in the first byte, the next 6 bits stored in the
* second byte, the next 6 bits stored in the third byte, and the last 6 bits
* stored in the fourth byte:
*
* b1=0b11110xxx b2=0b10zzzzzz b3=0b10yyyyyy b4=0b10xxxxxx
*
* -----------------------------------------------------------------------------
*
* It is important to note, when iterating through the code points of a string
* in JavaScript, that if a character is encoded as a surrogate pair it will
* increase the string's length by 2 instead of 1 [4]. For example:
*
* ```
* > 'a'.length
* 1
* > '💩'.length
* 2
* > '語'.length
* 1
* > 'a💩語'.length
* 4
* ```
*
* The results of the above example are explained by the fact that the
* characters 'a' and '語' are not represented by surrogate pairs, but '💩' is.
*
* Because of this idiosyncrasy in JavaScript's string implementation and APIs,
* we must "jump" an extra index after encoding a character as a surrogate
* pair. In practice, this means we must increment the index of our for loop by
* 2 if we encode a surrogate pair, and 1 in all other cases.
*
* -----------------------------------------------------------------------------
*
* References:
* - [1] https://www.unicode.org/versions/Unicode12.0.0/UnicodeStandard-12.0.pdf
* 3.9 Unicode Encoding Forms - UTF-8
* - [2] http://www.herongyang.com/Unicode/UTF-8-UTF-8-Encoding.html
* - [3] http://www.herongyang.com/Unicode/UTF-8-UTF-8-Encoding-Algorithm.html
* - [4] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length#Description
*
*/
exports.utf8Encode = function (input, byteOrderMark) {
if (byteOrderMark === void 0) { byteOrderMark = true; }
var encoded = [];
if (byteOrderMark)
encoded.push(0xef, 0xbb, 0xbf);
for (var idx = 0, len = input.length; idx < len;) {
var codePoint = input.codePointAt(idx);
// One byte encoding
if (codePoint < 0x80) {
var byte1 = codePoint & 0x7f;
encoded.push(byte1);
idx += 1;
}
// Two byte encoding
else if (codePoint < 0x0800) {
var byte1 = ((codePoint >> 6) & 0x1f) | 0xc0;
var byte2 = (codePoint & 0x3f) | 0x80;
encoded.push(byte1, byte2);
idx += 1;
}
// Three byte encoding
else if (codePoint < 0x010000) {
var byte1 = ((codePoint >> 12) & 0x0f) | 0xe0;
var byte2 = ((codePoint >> 6) & 0x3f) | 0x80;
var byte3 = (codePoint & 0x3f) | 0x80;
encoded.push(byte1, byte2, byte3);
idx += 1;
}
// Four byte encoding (surrogate pair)
else if (codePoint < 0x110000) {
var byte1 = ((codePoint >> 18) & 0x07) | 0xf0;
var byte2 = ((codePoint >> 12) & 0x3f) | 0x80;
var byte3 = ((codePoint >> 6) & 0x3f) | 0x80;
var byte4 = ((codePoint >> 0) & 0x3f) | 0x80;
encoded.push(byte1, byte2, byte3, byte4);
idx += 2;
}
// Should never reach this case
else
throw new Error("Invalid code point: 0x" + strings_1.toHexString(codePoint));
}
return new Uint8Array(encoded);
};
/**
* Encodes a string to UTF-16.
*
* @param input The string to be encoded.
* @param byteOrderMark Whether or not a byte order marker (BOM) should be added
* to the start of the encoding. (default `true`)
* @returns A Uint16Array containing the UTF-16 encoding of the input string.
*
* -----------------------------------------------------------------------------
*
* JavaScript strings are composed of Unicode code points. Code points are
* integers in the range 0 to 1,114,111 (0x10FFFF). When serializing a string,
* it must be encoded as a sequence of words. A word is typically 8, 16, or 32
* bytes in size. As such, Unicode defines three encoding forms: UTF-8, UTF-16,
* and UTF-32. These encoding forms are described in the Unicode standard [1].
* This function implements the UTF-16 encoding form.
*
* -----------------------------------------------------------------------------
*
* In UTF-16, each code point is mapped to one or two 16-bit integers. The
* UTF-16 mapping logic is as follows [2]:
*
* • If a code point is in the range U+0000..U+FFFF, then map the code point to
* a 16-bit integer with the most significant byte first.
*
* • If a code point is in the range U+10000..U+10000, then map the code point
* to two 16-bit integers. The first integer should contain the high surrogate
* and the second integer should contain the low surrogate. Both surrogates
* should be written with the most significant byte first.
*
* -----------------------------------------------------------------------------
*
* It is important to note, when iterating through the code points of a string
* in JavaScript, that if a character is encoded as a surrogate pair it will
* increase the string's length by 2 instead of 1 [4]. For example:
*
* ```
* > 'a'.length
* 1
* > '💩'.length
* 2
* > '語'.length
* 1
* > 'a💩語'.length
* 4
* ```
*
* The results of the above example are explained by the fact that the
* characters 'a' and '語' are not represented by surrogate pairs, but '💩' is.
*
* Because of this idiosyncrasy in JavaScript's string implementation and APIs,
* we must "jump" an extra index after encoding a character as a surrogate
* pair. In practice, this means we must increment the index of our for loop by
* 2 if we encode a surrogate pair, and 1 in all other cases.
*
* -----------------------------------------------------------------------------
*
* References:
* - [1] https://www.unicode.org/versions/Unicode12.0.0/UnicodeStandard-12.0.pdf
* 3.9 Unicode Encoding Forms - UTF-8
* - [2] http://www.herongyang.com/Unicode/UTF-16-UTF-16-Encoding.html
* - [3] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length#Description
*
*/
exports.utf16Encode = function (input, byteOrderMark) {
if (byteOrderMark === void 0) { byteOrderMark = true; }
var encoded = [];
if (byteOrderMark)
encoded.push(0xfeff);
for (var idx = 0, len = input.length; idx < len;) {
var codePoint = input.codePointAt(idx);
// Two byte encoding
if (codePoint < 0x010000) {
encoded.push(codePoint);
idx += 1;
}
// Four byte encoding (surrogate pair)
else if (codePoint < 0x110000) {
encoded.push(exports.highSurrogate(codePoint), exports.lowSurrogate(codePoint));
idx += 2;
}
// Should never reach this case
else
throw new Error("Invalid code point: 0x" + strings_1.toHexString(codePoint));
}
return new Uint16Array(encoded);
};
/**
* Returns `true` if the `codePoint` is within the
* Basic Multilingual Plane (BMP). Code points inside the BMP are not encoded
* with surrogate pairs.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
exports.isWithinBMP = function (codePoint) {
return codePoint >= 0 && codePoint <= 0xffff;
};
/**
* Returns `true` if the given `codePoint` is valid and must be represented
* with a surrogate pair when encoded.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
exports.hasSurrogates = function (codePoint) {
return codePoint >= 0x010000 && codePoint <= 0x10ffff;
};
// From Unicode 3.0 spec, section 3.7:
// http://unicode.org/versions/Unicode3.0.0/ch03.pdf
exports.highSurrogate = function (codePoint) {
return Math.floor((codePoint - 0x10000) / 0x400) + 0xd800;
};
// From Unicode 3.0 spec, section 3.7:
// http://unicode.org/versions/Unicode3.0.0/ch03.pdf
exports.lowSurrogate = function (codePoint) {
return ((codePoint - 0x10000) % 0x400) + 0xdc00;
};
var ByteOrder;
(function (ByteOrder) {
ByteOrder["BigEndian"] = "BigEndian";
ByteOrder["LittleEndian"] = "LittleEndian";
})(ByteOrder || (ByteOrder = {}));
var REPLACEMENT = '�'.codePointAt(0);
/**
* Decodes a Uint8Array of data to a string using UTF-16.
*
* Note that this function attempts to recover from erronous input by
* inserting the replacement character (�) to mark invalid code points
* and surrogate pairs.
*
* @param input A Uint8Array containing UTF-16 encoded data
* @param byteOrderMark Whether or not a byte order marker (BOM) should be read
* at the start of the encoding. (default `true`)
* @returns The decoded string.
*/
exports.utf16Decode = function (input, byteOrderMark) {
if (byteOrderMark === void 0) { byteOrderMark = true; }
// Need at least 2 bytes of data in UTF-16 encodings
if (input.length <= 1)
return String.fromCodePoint(REPLACEMENT);
var byteOrder = byteOrderMark ? readBOM(input) : ByteOrder.BigEndian;
// Skip byte order mark if needed
var idx = byteOrderMark ? 2 : 0;
var codePoints = [];
while (input.length - idx >= 2) {
var first = decodeValues(input[idx++], input[idx++], byteOrder);
if (isHighSurrogate(first)) {
if (input.length - idx < 2) {
// Need at least 2 bytes left for the low surrogate that is required
codePoints.push(REPLACEMENT);
}
else {
var second = decodeValues(input[idx++], input[idx++], byteOrder);
if (isLowSurrogate(second)) {
codePoints.push(first, second);
}
else {
// Low surrogates should always follow high surrogates
codePoints.push(REPLACEMENT);
}
}
}
else if (isLowSurrogate(first)) {
// High surrogates should always come first since `decodeValues()`
// accounts for the byte ordering
idx += 2;
codePoints.push(REPLACEMENT);
}
else {
codePoints.push(first);
}
}
// There shouldn't be extra byte(s) left over
if (idx < input.length)
codePoints.push(REPLACEMENT);
return String.fromCodePoint.apply(String, codePoints);
};
/**
* Returns `true` if the given `codePoint` is a high surrogate.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
var isHighSurrogate = function (codePoint) {
return codePoint >= 0xd800 && codePoint <= 0xdbff;
};
/**
* Returns `true` if the given `codePoint` is a low surrogate.
* @param codePoint The code point to be evaluated.
*
* Reference: https://en.wikipedia.org/wiki/UTF-16#Description
*/
var isLowSurrogate = function (codePoint) {
return codePoint >= 0xdc00 && codePoint <= 0xdfff;
};
/**
* Decodes the given utf-16 values first and second using the specified
* byte order.
* @param first The first byte of the encoding.
* @param second The second byte of the encoding.
* @param byteOrder The byte order of the encoding.
* Reference: https://en.wikipedia.org/wiki/UTF-16#Examples
*/
var decodeValues = function (first, second, byteOrder) {
// Append the binary representation of the preceding byte by shifting the
// first one 8 to the left and than applying a bitwise or-operator to append
// the second one.
if (byteOrder === ByteOrder.LittleEndian)
return (second << 8) | first;
if (byteOrder === ByteOrder.BigEndian)
return (first << 8) | second;
throw new Error("Invalid byteOrder: " + byteOrder);
};
/**
* Returns whether the given array contains a byte order mark for the
* UTF-16BE or UTF-16LE encoding. If it has neither, BigEndian is assumed.
*
* Reference: https://en.wikipedia.org/wiki/Byte_order_mark#UTF-16
*
* @param bytes The byte array to be evaluated.
*/
// prettier-ignore
var readBOM = function (bytes) { return (hasUtf16BigEndianBOM(bytes) ? ByteOrder.BigEndian
: hasUtf16LittleEndianBOM(bytes) ? ByteOrder.LittleEndian
: ByteOrder.BigEndian); };
var hasUtf16BigEndianBOM = function (bytes) {
return bytes[0] === 0xfe && bytes[1] === 0xff;
};
var hasUtf16LittleEndianBOM = function (bytes) {
return bytes[0] === 0xff && bytes[1] === 0xfe;
};
exports.hasUtf16BOM = function (bytes) {
return hasUtf16BigEndianBOM(bytes) || hasUtf16LittleEndianBOM(bytes);
};
//# sourceMappingURL=unicode.js.map