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