pump.js

exports.pump = function (readStream, writeStream, processChunk, callback) {
    if(!callback) {
        callback = processChunk;
        processChunk = undefined;
    }
    readStream.addListener("data", function (chunk) {
        var newChunk = processChunk ? processChunk(chunk) : chunk;
        if (newChunk != null && writeStream.write(newChunk) === false) {
            var l = function () {
                writeStream.removeListener("drain", l);
                readStream.resume();
            }
            writeStream.addListener("drain", l);
            readStream.pause();
        }
    });
    readStream.addListener("end", function () {
        writeStream.end();
    });
    if (callback) writeStream.addListener("close", callback);    
}