Wireshark is a network sniffer which can show and save HTTP transactions. Because it works on packet level rather than on HTTP level, the client does not need to be configured in order to capture the request.

  1. Start Wireshark. You may have to start it as root so that you have enough permissions to sniff some packets.
  2. If the computer on which you are sniffing is the same computer that initiates the HTTP transaction, disable promiscuous mode on the interface. This means that it does not listen to all packets, but just the packets meant for this network interface.
    How to disable promiscuous mode in Wireshark
  3. You may want to enter a filter like tcp.port == 80 in the filter bar.
  4. Do your request.
  5. Find a packet with the request in it. It will usually start with GET or POST.
  6. Right click and select "Follow TCP stream". How to follow a TCP stream in Wireshark
  7. A window appears with the HTTP conversation. You can save it using the Save As button. The window showing the HTTP transaction in Wireshark

Read a book about Wireshark: