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var StringDecoder = exports.StringDecoder = function(encoding) {
this.encoding = (encoding || 'utf8').toLowerCase().replace(/[-_]/, '');
if (this.encoding === 'utf8') {
this.charBuffer = new Buffer(4);
this.charReceived = 0;
this.charLength = 0;
}
};
StringDecoder.prototype.write = function(buffer) {
// If not utf8...
if (this.encoding !== 'utf8') {
return buffer.toString(this.encoding);
}
var charStr = '';
// if our last write ended with an incomplete multibyte character
if (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, 0, i);
this.charReceived += 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.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);
}
// 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;
}
}
if (!this.charLength) {
// no incomplete char at the end of this buffer, emit the whole thing
return charStr + buffer.toString();
}
// buffer the incomplete character bytes we got
buffer.copy(this.charBuffer, 0, buffer.length - i, buffer.length);
this.charReceived = i;
if (buffer.length - i > 0) {
// buffer had more bytes before the incomplete char, emit them
return charStr + buffer.toString('utf8', 0, buffer.length - i);
}
// or just emit the charStr
return charStr;
};
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