Faye TCP/IP Traffic

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Up today, I would like to do a little exploration of faye channel communication. I would like to believe that, if my client has subscribed to channel "/foo" but not channel "/bar", then messages published to "/bar" are not seen (and ignored) by my client. I would like to cut down on traffic in high usage systems and am also interested in the ability to hold private conversations in faye.

To try this out, I establish a very simple faye server on my londo server. The code, taken directly off the faye site, is:

var Faye   = require('faye'),
    server = new Faye.NodeAdapter({mount: '/faye'});

server.listen(8000);

I run the server with:

cstrom@londo:~/tmp/faye-test$ node app.js

Next, on my laptop, whitefall, I setup a simple faye client on the node command line:

node> var faye = require('faye');
node> var client = new faye.Client('http://londo:8000/faye');
node> client.subscribe('/foo', function(message) {puts("[foo]: " + message)});

Lastly, I establish a second client, back on the server, to publish messages:

node> var faye = require('faye');
node> var client = new faye.Client('http://londo:8000/faye');
node> client.publish("/foo", "test");

Checking back on my laptop, I do see that message in the node repl:

node> [foo]: test
[foo]: test
...

When I publish a message on the "/bar" channel, I see nothing in the client node repl. This is all as expected. If I have not subscribed to a channel, I should not see messages on it. But, are the messages being sent out and ignored in the client or is the server smart enough not to send out the messages?

I suppose that I could read the documentation to figure this out, but I prefer to actually see it in action. For that, I trust tcpdump. Here, I ask to see the packet contents in ascii (-X) and all of the packets, not just the first 96 bytes (-s 0):

cstrom@whitefall:~/repos/my_fab_game$ sudo tcpdump -i eth1 -X -s 0 host londo and not port 22

Now, when I send a message on the "/foo" channel, the channel to which I am currently subscribed on this laptop, I see the data packets coming back:

22:19:56.459204 IP londo.8000 > whitefall.local.47662: Flags [P.], seq 1563677724:1563678119, ack 4040761713, win 54, options [nop,nop,TS val 348053887 ecr 151564770], length 395
...
        0x0030:  0908 b1e2 4854 5450 2f31 2e31 2032 3030  ....HTTP/1.1.200
        0x0040:  204f 4b0d 0a43 6f6e 7465 6e74 2d54 7970  .OK..Content-Typ
        0x0050:  653a 2061 7070 6c69 6361 7469 6f6e 2f6a  e:.application/j
        0x0060:  736f 6e0d 0a43 6f6e 6e65 6374 696f 6e3a  son..Connection:
...
        0x00f0:  3a22 2f6d 6574 612f 636f 6e6e 6563 7422  :"/meta/connect"
        0x0100:  2c22 7375 6363 6573 7366 756c 223a 7472  ,"successful":tr
        0x0110:  7565 2c22 6164 7669 6365 223a 7b22 7265  ue,"advice":{"re
        0x0120:  636f 6e6e 6563 7422 3a22 7265 7472 7922  connect":"retry"
        0x0130:  2c22 696e 7465 7276 616c 223a 302c 2274  ,"interval":0,"t
        0x0140:  696d 656f 7574 223a 3630 3030 307d 7d2c  imeout":60000}},
        0x0150:  7b22 6368 616e 6e65 6c22 3a22 2f66 6f6f  {"channel":"/foo
        0x0160:  222c 2264 6174 6122 3a22 7465 7374 2030  ","data":"test.0
        0x0170:  3122 2c22 636c 6965 6e74 4964 223a 2270  1","clientId":"p
        0x0180:  6e79 396d 3931 306f 3665 3268 326c 7832  ny9m910o6e2h2lx2
...

It is pretty cool to see this in action. Aside from that, it is pretty much as I expected—I am subscribed to the "/foo" channel, I already know that messages are getting back here, so I ought to see the TCP/IP data.

But what happens when I publish to the "/bar" channel to which I am not subscribed on this laptop? Nothing. No TCP/IP data is transmitted back. Perhaps I should have expected that (especially if I had read the documentation), but to actually see it... nice.

Before calling it a night, I do one last sanity check. I load a faye client in Firefox 3, which does not support websockets. I have no reason to expect the client and server to behave any differently, but I have to try it out in order to believe it. In the browser, I subscribe to the "/baz" channel:

>>> var client = new Faye.Client('http://londo:8000/faye');
>>> client.subscribe("/baz", function(message){console.debug(message)});

Again, when I publish to the "/bar" channel, there is no TCP/IP activity. When I publish to the "/baz" channel, I do see TCP/IP traffic. Nice.

About ready to call it a night, it occurs to me, what happens if I subscribe to a channel "/*"? In that case, I do see messages published to all channels:

node> client.subscribe('/*', function(message) {puts("[*]: " + message)});
...

node> [*]: bar test 01
[*]: foo test 01

So it seems that it is relatively easy to snoop on all faye messages. Tomorrow, I will investigate the extensions facility in faye to see if it is possible to limit that ability.


Day #188