Changing a node.js stream in the ondata event

Question

Changing a node.js stream in the ondata event

I am trying to edit a node.js http stream before sending it to the parser. I have implemented the following code

//catch any connection event to this server
server.on('secureConnection', function (stream) {
  //create a new buffer to hold what we are receiving in this stream
  var receiveBuffer = new Buffer(0);
  //store a link to the original ondata function so we can call it and restore it
  originalOnDataFunction = stream.ondata;
  //declare a new ondata function for this stream
  stream.ondata = function (d, start, end) {
    //record what we have received 
    receiveBuffer = Buffer.concat([receiveBuffer, d.slice(start, end)]);
    //if what we have received is greater than 4 (i.e. we have at least got a GET request)
    //then make changes
    if (receiveBuffer.length >= 4) {
      //reset the streams ondata function to the original
      //this is all we want to edit for this connection
      stream.ondata = originalOnDataFunction;
      //if the first 11 characters of the buffer are 'MKCALENDAR ' then make a change
      if (receiveBuffer.toString('ascii', 0, 11) === 'MKCALENDAR ') {
        //I change this to MKCOL /MKCALENDAR<rest of buffer> as this will work with the node.js http parser
        //and then I can check on the other side for a MKCOL method with /MKCALENDAR as the start of the url and 
        //know that it was a MKCALENDAR method
        var rewrittenBuffer = Buffer.concat([new Buffer('MKCOL /MKCALENDAR', 'ascii'), receiveBuffer.slice(11)]);
        //now call the original ondata function with this new buffer
        stream.ondata.apply(this, [rewrittenBuffer, 0, rewrittenBuffer.length]);
      } else {
        //no change needed just call the original ondata function with this buffer
        stream.ondata.apply(this, [receiveBuffer, 0, receiveBuffer.length]);
      }
    }
  }
});

which I got from an answer here Overriding Node.js HTTP parser

The above code seems to work about 95% of the time. However, it keeps dropping requests that then just timeout. I cannot see how or where it is dropping them. Can anyone help.

Thanks,

Mark

Note the on secureConnection is coming from a node.js https.createServer( call

node.js
https
stream

Answer 1

Are you sure you want

if (receiveBuffer.length >= 4)

If the first buffer is a partial MKCALENDAR with at least the first four bytes, the code above won't do the translation to MKCOL.

Answer 2

Jonathan the first packet in seems to be the all the headers so this line works fine. I did get it working and the problem seemed to be with the .apply statement not always working. The following works fine:

//catch any secure connection event to this server
server.on('secureConnection', function (stream) {
  //create a new buffer to hold what we are receiving in this stream
  var receiveBuffer = new Buffer(0);
  //store a link to the original ondata function so we can call it and restore it
  stream._ondataOld = stream.ondata;
  stream.ondata = function(d,start,end){
    receiveBuffer = Buffer.concat([receiveBuffer, d.slice(start, end)]);
    //if what we have received is greater than 4 (i.e. we have at least got a GET request)
    //then make changes
    if (receiveBuffer.length >= 4) {
      //reset the streams ondata function to the original
      //this is all we want to edit for this connection
      stream.ondata = stream._ondataOld;
      //if the first 11 characters of the buffer are 'MKCALENDAR ' then make a change
      if (receiveBuffer.toString('ascii', 0, 11) === 'MKCALENDAR ') {
        //I change this to MKCOL /MKCALENDAR<rest of buffer> as this will work with the node.js http parser
        //and then I can check on the other side for a MKCOL method with /MKCALENDAR as the start of the url and
        //know that it was a MKCALENDAR method
        //this facilitates MKCALENDAR calls on the CALDAV server
        var rewrittenBuffer = Buffer.concat([new Buffer('MKCOL /MKCALENDAR', 'ascii'), receiveBuffer.slice(11)]);
        //console.log(rewrittenBuffer.toString('ascii',0,rewrittenBuffer.length));
        //console.log(rewrittenBuffer.toString('ascii'));
        //now call the original ondata function with this new buffer
        stream.ondata(rewrittenBuffer,0,rewrittenBuffer.length);
      } else {
        //no change needed just call the original ondata function with this buffer
        stream.ondata(d,start,end);
      }
    } else {
      stream.ondata(d,start,end);
    }
  }
});