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// Copyright Joyent, Inc. and other Node contributors.

//

// Permission is hereby granted, free of charge, to any person obtaining a

// copy of this software and associated documentation files (the

// "Software"), to deal in the Software without restriction, including

// without limitation the rights to use, copy, modify, merge, publish,

// distribute, sublicense, and/or sell copies of the Software, and to permit

// persons to whom the Software is furnished to do so, subject to the

// following conditions:

//

// The above copyright notice and this permission notice shall be included

// in all copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS

// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN

// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,

// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR

// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE

// USE OR OTHER DEALINGS IN THE SOFTWARE.

var StringDecoder = exports.StringDecoder = function(encoding) {

this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/, '');

switch (this.encoding) {

case 'utf8':

// CESU-8 represents each of Surrogate Pair by 3-bytes

this.surrogateSize = 3;

break;

case 'ucs2':

case 'utf16le':

// UTF-16 represents each of Surrogate Pair by 2-bytes

this.surrogateSize = 2;

this.detectIncompleteChar = utf16DetectIncompleteChar;

break;

default:

this.write = passThroughWrite;

return;

}

this.charBuffer = new Buffer(6);

this.charReceived = 0;

this.charLength = 0;

};

StringDecoder.prototype.write = function(buffer) {

var charStr = '';

var offset = 0;

// if our last write ended with an incomplete multibyte character

while (this.charLength) {

// determine how many remaining bytes this buffer has to offer for this char

var i = (buffer.length >= this.charLength - this.charReceived) ?

this.charLength - this.charReceived :

buffer.length;

// add the new bytes to the char buffer

buffer.copy(this.charBuffer, this.charReceived, offset, i);

this.charReceived += (i - offset);

offset = i;

if (this.charReceived < this.charLength) {

// still not enough chars in this buffer? wait for more ...

return '';

}

// get the character that was split

charStr = this.charBuffer.slice(0, this.charLength).toString(this.encoding);

// lead surrogate (D800-DBFF) is also the incomplete character

var charCode = charStr.charCodeAt(charStr.length - 1);

if (charCode >= 0xD800 && charCode <= 0xDBFF) {

this.charLength += this.surrogateSize;

charStr = '';

continue;

}

this.charReceived = this.charLength = 0;

// if there are no more bytes in this buffer, just emit our char

if (i == buffer.length) return charStr;

// otherwise cut off the characters end from the beginning of this buffer

buffer = buffer.slice(i, buffer.length);

break;

}

var lenIncomplete = this.detectIncompleteChar(buffer);

var end = buffer.length;

if (this.charLength) {

// buffer the incomplete character bytes we got

buffer.copy(this.charBuffer, 0, buffer.length - lenIncomplete, end);

this.charReceived = lenIncomplete;

end -= lenIncomplete;

}

charStr += buffer.toString(this.encoding, 0, end);

var end = charStr.length - 1;

var charCode = charStr.charCodeAt(end);

// lead surrogate (D800-DBFF) is also the incomplete character

if (charCode >= 0xD800 && charCode <= 0xDBFF) {

var size = this.surrogateSize;

this.charLength += size;

this.charReceived += size;

this.charBuffer.copy(this.charBuffer, size, 0, size);

this.charBuffer.write(charStr.charAt(charStr.length - 1), this.encoding);

return charStr.substring(0, end);

}

// or just emit the charStr

return charStr;

};

StringDecoder.prototype.detectIncompleteChar = function(buffer) {

// determine how many bytes we have to check at the end of this buffer

var i = (buffer.length >= 3) ? 3 : buffer.length;

// Figure out if one of the last i bytes of our buffer announces an

// incomplete char.

for (; i > 0; i--) {

var c = buffer[buffer.length - i];

// See http://en.wikipedia.org/wiki/UTF-8#Description

// 110XXXXX

if (i == 1 && c >> 5 == 0x06) {

this.charLength = 2;

break;

}

// 1110XXXX

if (i <= 2 && c >> 4 == 0x0E) {

this.charLength = 3;

break;

}

// 11110XXX

if (i <= 3 && c >> 3 == 0x1E) {

this.charLength = 4;

break;

}

}

return i;

};

function passThroughWrite(buffer) {

return buffer.toString(this.encoding);

}

function utf16DetectIncompleteChar(buffer) {

var incomplete = this.charReceived = buffer.length % 2;

this.charLength = incomplete ? 2 : 0;

return incomplete;

}