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js/dos/ext/string_decoder.js
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js/dos/ext/string_decoder.js
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// Copyright Joyent, Inc. and other Node contributors.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the
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// "Software"), to deal in the Software without restriction, including
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// without limitation the rights to use, copy, modify, merge, publish,
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// distribute, sublicense, and/or sell copies of the Software, and to permit
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// persons to whom the Software is furnished to do so, subject to the
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// following conditions:
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//
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// The above copyright notice and this permission notice shall be included
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// in all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
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// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
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// USE OR OTHER DEALINGS IN THE SOFTWARE.
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var Buffer = Require('buffer').Buffer;
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var isBufferEncoding = Buffer.isEncoding
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|| function(encoding) {
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switch (encoding && encoding.toLowerCase()) {
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case 'hex': case 'utf8': case 'utf-8': case 'ascii': case 'binary': case 'base64': case 'ucs2': case 'ucs-2': case 'utf16le': case 'utf-16le': case 'raw': return true;
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default: return false;
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}
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}
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function assertEncoding(encoding) {
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if (encoding && !isBufferEncoding(encoding)) {
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throw new Error('Unknown encoding: ' + encoding);
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}
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}
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var StringDecoder = exports.StringDecoder = function(encoding) {
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this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/, '');
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assertEncoding(encoding);
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switch (this.encoding) {
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case 'utf8':
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// CESU-8 represents each of Surrogate Pair by 3-bytes
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this.surrogateSize = 3;
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break;
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case 'ucs2':
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case 'utf16le':
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// UTF-16 represents each of Surrogate Pair by 2-bytes
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this.surrogateSize = 2;
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this.detectIncompleteChar = utf16DetectIncompleteChar;
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break;
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case 'base64':
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// Base-64 stores 3 bytes in 4 chars, and pads the remainder.
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this.surrogateSize = 3;
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this.detectIncompleteChar = base64DetectIncompleteChar;
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break;
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default:
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this.write = passThroughWrite;
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return;
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}
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this.charBuffer = new Buffer(6);
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this.charReceived = 0;
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this.charLength = 0;
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};
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StringDecoder.prototype.write = function(buffer) {
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var charStr = '';
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var offset = 0;
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// if our last write ended with an incomplete multibyte character
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while (this.charLength) {
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// determine how many remaining bytes this buffer has to offer for this char
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var i = (buffer.length >= this.charLength - this.charReceived) ?
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this.charLength - this.charReceived :
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buffer.length;
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// add the new bytes to the char buffer
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buffer.copy(this.charBuffer, this.charReceived, offset, i);
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this.charReceived += (i - offset);
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offset = i;
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if (this.charReceived < this.charLength) {
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// still not enough chars in this buffer? wait for more ...
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return '';
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}
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// get the character that was split
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charStr = this.charBuffer.slice(0, this.charLength).toString(this.encoding);
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// lead surrogate (D800-DBFF) is also the incomplete character
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var charCode = charStr.charCodeAt(charStr.length - 1);
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if (charCode >= 0xD800 && charCode <= 0xDBFF) {
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this.charLength += this.surrogateSize;
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charStr = '';
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continue;
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}
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this.charReceived = this.charLength = 0;
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// if there are no more bytes in this buffer, just emit our char
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if (i == buffer.length) return charStr;
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// otherwise cut off the characters end from the beginning of this buffer
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buffer = buffer.slice(i, buffer.length);
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break;
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}
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var lenIncomplete = this.detectIncompleteChar(buffer);
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var end = buffer.length;
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if (this.charLength) {
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// buffer the incomplete character bytes we got
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buffer.copy(this.charBuffer, 0, buffer.length - lenIncomplete, end);
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this.charReceived = lenIncomplete;
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end -= lenIncomplete;
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}
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charStr += buffer.toString(this.encoding, 0, end);
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var end = charStr.length - 1;
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var charCode = charStr.charCodeAt(end);
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// lead surrogate (D800-DBFF) is also the incomplete character
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if (charCode >= 0xD800 && charCode <= 0xDBFF) {
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var size = this.surrogateSize;
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this.charLength += size;
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this.charReceived += size;
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this.charBuffer.copy(this.charBuffer, size, 0, size);
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this.charBuffer.write(charStr.charAt(charStr.length - 1), this.encoding);
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return charStr.substring(0, end);
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}
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// or just emit the charStr
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return charStr;
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};
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StringDecoder.prototype.detectIncompleteChar = function(buffer) {
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// determine how many bytes we have to check at the end of this buffer
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var i = (buffer.length >= 3) ? 3 : buffer.length;
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// Figure out if one of the last i bytes of our buffer announces an
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// incomplete char.
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for (; i > 0; i--) {
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var c = buffer[buffer.length - i];
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// See http://en.wikipedia.org/wiki/UTF-8#Description
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// 110XXXXX
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if (i == 1 && c >> 5 == 0x06) {
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this.charLength = 2;
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break;
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}
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// 1110XXXX
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if (i <= 2 && c >> 4 == 0x0E) {
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this.charLength = 3;
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break;
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}
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// 11110XXX
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if (i <= 3 && c >> 3 == 0x1E) {
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this.charLength = 4;
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break;
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}
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}
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return i;
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};
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StringDecoder.prototype.end = function(buffer) {
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var res = '';
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if (buffer && buffer.length)
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res = this.write(buffer);
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if (this.charReceived) {
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var cr = this.charReceived;
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var buf = this.charBuffer;
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var enc = this.encoding;
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res += buf.slice(0, cr).toString(enc);
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}
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return res;
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};
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function passThroughWrite(buffer) {
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return buffer.toString(this.encoding);
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}
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function utf16DetectIncompleteChar(buffer) {
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var incomplete = this.charReceived = buffer.length % 2;
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this.charLength = incomplete ? 2 : 0;
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return incomplete;
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}
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function base64DetectIncompleteChar(buffer) {
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var incomplete = this.charReceived = buffer.length % 3;
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this.charLength = incomplete ? 3 : 0;
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return incomplete;
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}
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