base64 streamer

var EventEmitter = require('events').EventEmitter,
    sys = require('sys');

this.Base64Stream = function(){
    EventEmitter.call(this);
    this.current = "";
}
sys.inherits(this.Base64Stream, EventEmitter);

this.Base64Stream.prototype.push = function(data){
    var remainder = 0;
    this.current += data.replace(/[^\w+\/=]/g,'');
    this.emit("stream", new Buffer(this.current.substr(0, this.current.length - this.current.length % 4),"base64"));
    this.current = (remainder=this.current.length % 4)?this.current.substr(- remainder):"";
}

this.Base64Stream.prototype.end = function(){
    this.emit("end");
}

// TEST:

var b64streamer = new this.Base64Stream();

// client, listens for the stream
b64streamer.on("stream",function(buffer){
    // buffer: buffer containing the bytestream
    console.log(buffer.toString("utf-8"))
});

b64streamer.on("end",function(){
    console.log("stream completed")
}); 

// server, sends some test data
var test_data = "U2FpbiB0w6RuYSBUVMOcIGtpcmphc3R1c2VzdCBrw6R0dGUgYWpha2lyamEgQSZBIHV1ZSBudW1i\r\n"+
        "cmkgKDIvMjAxMCksIGt1cyBvbiBzZWVzIG1pbnUgYXJ0aWtrZWwgR29vZ2xlIEFwcCBFbmdpbmUg\r\n"+
        "a2FzdXRhbWlzZXN0IChrYWhqdWtzIHBvbGUgc2VkYSBvbmxpbmUga3Vza2lsdCB2aWlkYXRhKS4g\r\n"+
        "S2lpcmVsdCBvdHNpZGVzIGxlaWRzaW4gdGVydmUgcml2aSBiYWthbGF1cmV1c2V0w7ZpZCBqYSB2\r\n"+
        "w6RoZW1hbHQgw7xoZSBtYWdpc3RyaXTDtsO2LCBtaXMgYWxsaWthbmEgdmlpdGF2YWQgbcO1bmVs\r\n"+
        "ZSBBJkEgYXJ0aWtsaWxlLCBzZWVnYSBvbiB0ZWd1IHTDpGllc3RpIHJlc3Bla3RhYWJsaSBhdmFs\r\n"+
        "ZGFtaXNrb2hhZ2EgOikNCg0KQWludXMgcHJvbGJlZW0gYW50dWQgYWpha2lyamEganV1cmVzIG9u\r\n"+
        "LCBldCBzZWRhIG9uIHByYWt0aWxpc2VsdCB2w7VpbWF0dSBrdXNraWx0IG9zdGEuIE1pbmEgbsOk\r\n"+
        "aXRla3MgcG9sZSBzZWRhIGt1c2tpbCBtw7zDvGdpbCBuw6RpbnVkLiBBdXNhbHQgw7ZlbGRlcywg\r\n"+
        "bWEgZWkgdGVhZG51ZGtpIHNlbGxlc3QgYWpha2lyamFzdCBzdXVydCBtaWRhZ2kgZW5uZSBrdWkg\r\n"+
        "bXVsbGUgcGFrdXRpIHbDtWltYWx1c3Qgc2lubmEgb21hIGFydGlra2VsIGtpcmp1dGFkYS4gS3V1\r\n"+
        "bG51ZCBvbGluLCBhZ2EgbsOkaW51ZCBtaXR0ZS4=\r\n",
        
        cur_pos = 0, step = 27;
        
while(cur_pos < test_data.length){
    b64streamer.push(test_data.substr(cur_pos, step))
    cur_pos+=step;
}
b64streamer.end();

Base64Stream makes it possible to parse asynchronously base64 encoded data in large quantities - for example binary e-mail attachments in MIME formatted messages. Instead of reading the whole data into memory, it can be processed in smaller chunks.