Node.JS - How to stop a piped stream conditionally

I'm a newbee to java-script & nodejs...

I have a file processing-stream which is composed of multiple streams pipped together. Works great...I'd like to enhance this by conditionally stopping the stream from processing and reading when a threshold has been reached.

    inputStream.
    pipe(unzip()).
    pipe(latin1Decoder).
    pipe(
         combine(
                 through(function(obj){
                      //part-1 -
                      this.push(obj);
                      }),
                 through(function(obj){
                      //part-2-
                      this.push(obj);
                      })
         ));

In part-1 if I do this.push(null) then the combiner will ignore incoming input.

However, I can't stop reading the file. That's annoying because the file is pretty huge.

What is the best way for me to access the input stream from inside the pipe-line to close it?