var Buffer = require('buffer').Buffer; var Utf8Decoder = exports.Utf8Decoder = function() { this.charBuffer = new Buffer(4); this.charReceived = 0; this.charLength = 0; }; Utf8Decoder.prototype.write = function(buffer) { 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 (i == buffer.length) { // if there are no more bytes in this buffer, just emit our char this.onString(charStr) return; } // otherwise cut of 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--) { 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 this.onString(charStr+buffer.toString()); return; } // 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 this.onString(charStr+buffer.slice(0, buffer.length - i).toString()); } else if (charStr) { // or just emit the charStr if any this.onString(charStr); } };