Localhost packet analyzer for Mac

Question

Packet sniffers generally do not capture localhost traffic. I need to inspect some post data in a localhost environment (being generated from a Ruby on Rails development). Do you know of any programs that expose localhost packets?

Answer 1

I use fiddler on my Windows box for http sniffing. Since its only looking at http traffic you don't get nearly the amount of noise you get with something like WireShark.

The trick to getting it to work with data sent and received locally is to use a different endpoint for your urls. Using http://127.0.0.1./YourServiceName instead of http://localhost/YourServiceName has always worked for me. Its important to include the trailing 'dot' in the IP address. Don't ask me why though.

Answer 2

If you use Firefox, you could use the HTTP Logging feature:

https://developer.mozilla.org/en/HTTP_Logging

Answer 3

If you just change your address from localhost to an assigned IP address (like 192.168.12.34 or whatever you may have), your packet sniffer should be able to see the packets.

Answer 4

These packets probably do not exist. There is no reason to packetize data when it is not leaving the host. The data should just go from socket to socket.

You might use something like Instruments or Dtrace to monitor the send system call.

Answer 5

I'm a satisfied user of HTTPScoop: http://www.tuffcode.com/

It's similar to the HTTP traffic analyzer addons you'll see for firefox etc. but works systemwide which is convenient and can be switched to observe any of your available network interfaces.

It is not free, nor does it observe HTTPS traffic, but other than that it's a worthwhile addition to your toolbox.