Sniffer::HTTP - multi-connection sniffer driver


  use Sniffer::HTTP;
  my $VERBOSE = 0;

  my $sniffer = Sniffer::HTTP->new(
    callbacks => {
      request  => sub { my ($req,$conn) = @_; print $req->uri,"\n" if $req },
      response => sub { my ($res,$req,$conn) = @_; print $res->code,"\n" },
      log      => sub { print $_[0] if $VERBOSE },
      tcp_log  => sub { print $_[0] if $VERBOSE > 1 },
    timeout => 5*60, # seconds after which a connection is considered stale
      => sub { my ($s,$conn,$key);
               $s->log->("Connection $key is stale.");

  $sniffer->run(); # uses the "best" default device

  # Or, if you want to feed it the packets yourself:

  while (1) {

    # retrieve ethernet packet into $eth,
    # for example via Net::Pcap
    my $eth = sniff_ethernet_packet;

    # And handle the packet. Callbacks will be invoked as soon
    # as complete data is available

This driver gives you callbacks with the completely accumulated HTTP::Requests or HTTP::Responses as sniffed from the TCP traffic. You need to feed it the Ethernet, IP or TCP packets either from a dump file or from Net::Pcap by unpacking them via NetPacket.

As the whole response data is accumulated in memory you should be aware of memory issues. If you want to write stuff directly to disk, you will need to submit patches to Sniffer::Connection::HTTP.

A good example to start from is the script that comes with the distribution.


new %ARGS

Creates a new object for handling many HTTP requests. You can pass in the following arguments:

  • connections - preexisting connections (optional)

  • callbacks - callbacks for the new connections (hash reference)

  • timeout - timeout in seconds after which a connection is considered stale

  • stale_connection - callback for stale connections

  • snaplen - maximum size of data to capture per packet. The default is 16384, which should be plenty for all cases.

Usually, you will want to create a new object like this:

  my $sniffer = Sniffer::HTTP->new( callbacks => {
    request  => sub { my ($req, $conn) = @_; print $req->uri,"\n"; },
    response => sub { my ($res,$req,$conn) = @_; print $res->code,"\n"; },

except that you will likely do more work than this example.

$sniffer->remove_connection KEY

Removes a connection (or a key) from the list of connections. This will not have the intended effect if the connection is still alive, as it will be recreated as soon as the next packet for it is received.

$sniffer->find_or_create_connection TCP, %ARGS

This parses a TCP packet and creates the TCP connection to keep track of the packet order and resent packets.

$sniffer->stale_connections( TIMEOUT, TIMESTAMP, HANDLER )

Will call the handler HANDLER for all connections that have a last_activity before TIMESTAMP - TIMEOUT.

All parameters are optional and default to:

  TIMEOUT   - $sniffer->timeout
  TIMESTAMP - time()
  HANDLER   - $sniffer->stale_connection

It returns all stale connections.

$sniffer->live_connections TIMEOUT, TIMESTAMP

Returns all live connections. No callback mechanism is provided here.

The defaults are TIMEOUT - $sniffer->timeout TIMESTAMP - time()

$sniffer->handle_eth_packet ETH [, TIMESTAMP]

Processes a raw ethernet packet. Net::PCap will return this kind of packet for most Ethernet network cards.

You need to call this method (or one of the other protocol methods) for every packet you wish to handle.

The optional TIMESTAMP corresponds to the epoch time the packet was captured at. It defaults to the value of time().

$sniffer->handle_ip_packet IP [, TIMESTAMP]

Processes a raw ip packet.

The optional TIMESTAMP corresponds to the epoch time the packet was captured at. It defaults to the value of time().

$sniffer->handle_tcp_packet TCP [, TIMESTAMP]

Processes a raw tcp packet. This processes the packet by handing it off to the Sniffer::Connection which handles the reordering of TCP packets.

It returns the Sniffer::Connection::HTTP object that handled the packet.

The optional TIMESTAMP corresponds to the epoch time the packet was captured at. It defaults to the value of time().


Listens on the given device for all TCP traffic from and to port 80 and invokes the callbacks as necessary. If you want finer control over what Net::Pcap does, you need to set up Net::Pcap yourself.

The DEVICE_NAME parameter is used to determine the device via find_device from Net::Pcap::FindDevice.

The %OPTIONS can be the following options:

  • capture_file - filename to which the whole capture stream is written, in Net::Pcap format.

    This is mostly useful for remote debugging of a problematic sequence of connections.

  • device - a preconfigured Net::Pcap device.

    This skips the detection of the device by name. If you have special configuration options, configure the device to your needs in your code and then pass it in.

  • netmask - the netmask to capture on.

    If you want to skip netmask detection, for example because your capture device has no IP address, you can pass in the netmask through this option.

  • snaplen - size of the Net::Pcap capture buffer

    The size of this buffer can determine whether you lose packets while processing. A large value led to lost packets in at least one case. The default value is 16384.

  • timeout - the read timeout in ms while waiting for packets. The default is 500 ms.


"Listens" to the packets dumped into a file. This is convenient to use if you have packet captures from a remote machine or want to test new protocol sniffers.

The file is presumed to contain an ethernet stream of packets.


request REQ, CONN

The request callback is called with the parsed request and the connection object. The request will be an instance of HTTP::Request and will have an absolute URI if possible. Currently, the hostname for the absolute URI is constructed from the Host: header.

response RES, REQ, CONN

The response callback is called with the parsed response, the request and the connection object.


The log callback is called whenever the connection makes progress and in other various situations.

tcp_log MESSAGE

The tcp_log callback is passed on to the underlying Sniffer::Connection object and can be used to monitor the TCP connection.

stale_connection SNIFFER, CONN

Is called whenever a connection goes over the timeout limit without any activity. The default handler weeds out stale connections with the following code:

  sub {
    my ($self,$conn,$key);
    $self->log->("Connection $key is stale.");
    delete $self->connections->{ $key }


Here are some example Net::Pcap filters for common things:

Capture all HTTP traffic between your machine and

     (dest && (tcp port 80))
  || (src && (tcp port 80))

Capture all HTTP traffic between your machine and or

    (dest && (tcp port 80))
  ||(src  && (tcp port 80))
  ||(dest && (tcp port 80))
  ||(src  && (tcp port 80))

Note that Net::Pcap resolves the IP addresses before using them, so you might actually get more data than you asked for.


Closing Connections Properly

Currently, it is not well-detected when a connection is closed by the starting side and no FIN ACK packet is received from the remote side. This can even happen is you close the browser window instead of waiting for the connections to auto-close.

I'm not sure how to fix this besides employing better guesswork and "closing" connections as soon as the FIN packet gets sent.

Small Testsuite

The whole module suite has almost no tests.

If you experience problems, please supply me with a complete, relevant packet dump as the included creates. Even better, supply me with (failing) tests.


Max Maischein (


Copyright (C) 2005-2021 Max Maischein. All Rights Reserved.

This code is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


HTTP::Proxy,|Wireshark, Sniffer::Connnection