6.1. Hellopacket

6.1.1. Introduction

Every language needs a “helloworld”. Haka, being as much a language as a network tool, needs its own helloworld, called “hellopacket”.

This “hellopacket” reads a pcap file and prints a couple of tcp/ip fields of each packet in the file.

6.1.2. How-to

Launch hakapcap with a pcap file and a lua script file as arguments.

$ cd <haka_install_path>/share/haka/sample/hellopacket
$ hakapcap hellopacket.lua hellopacket.pcap

Hakapcap will first dump infos about registered dissectors and rules and then process the pcap file, outputing information on each packet (packet source and destination, connection establishment, etc.):

    info  core: load module 'packet/pcap.ho', Pcap Module
    info  core: setting packet mode to pass-through

    info  core: loading rule file 'hellopacket.lua'
    info  core: initializing thread 0
    info  dissector: register new dissector 'raw'
    info  pcap:      opening file 'hellopacket.pcap'
    info  dissector: register new dissector 'ipv4'
    info  dissector: register new dissector 'tcp'
    info  dissector: register new dissector 'tcp-connection'
    info  core:      1 rule(s) on event 'ipv4:receive_packet'
    info  core:      1 rule(s) on event 'tcp-connection:new_connection'
    info  core:      2 rule(s) registered

    info  core:      starting single threaded processing

    info  pcap:      progress 10,23 %
    info  Hello:     packet from 192.168.10.1 to 192.168.10.99
    info  Hello:     TCP connection from 192.168.10.1:47161 to 192.168.10.99:3000
    info  alert:     id = 1
            time = Wed Apr 23 15:13:40 2014
            severity = low
            description = A simple alert  !!!!
    info  Hello:     packet from 192.168.10.99 to 192.168.10.1
    info  Hello:     packet from 192.168.10.1 to 192.168.10.99
    info  Hello:     packet from 192.168.10.1 to 192.168.10.99
    info  Hello:     packet from 192.168.10.99 to 192.168.10.1
    info  Hello:     packet from 192.168.10.1 to 192.168.10.99
    info  Hello:     packet from 192.168.10.99 to 192.168.10.1
    info  Hello:     packet from 192.168.10.1 to 192.168.10.99
    info  core:      unload module 'Pcap Module'
    

Each new connection and each packet is properly logged. The pcap file is a standard format that can be opened by various network tools, including wireshark.

Below is the content of the hellopacket.lua file:

------------------------------------
-- Loading dissectors
------------------------------------

-- Each dissector provides hooks to intercept and modify packets.
-- We need ipv4 to intercept incoming packets
-- We need tcp to intercept new connections
local ipv4 = require('protocol/ipv4')
local tcp_connection = require('protocol/tcp_connection')

-- Log info about incoming ipv4 packets
haka.rule{
    -- Rule evaluated whenever a new ipv4 packet is received
    hook = ipv4.events.receive_packet,
    -- Evauation function taking ipv4 packet structure
    -- as argument
    eval = function (pkt)
        -- All fields are accessible through pkt variable.
        -- See the Haka documentation for a complete list.
        haka.log("Hello", "packet from %s to %s", pkt.src, pkt.dst)
    end
}

-- Log info about connection establsihments
haka.rule{
    -- Rule evaluated at connection establishment attempt
    hook = tcp_connection.events.new_connection,
    -- Rule evaluated at connection establishment attempt
    eval = function (flow, tcp)
        -- Fields from previous layer are accessible too
        haka.log("Hello", "TCP connection from %s:%d to %s:%d", tcp.ip.src,
            tcp.srcport, tcp.ip.dst, tcp.dstport)
        -- Raise a simple alert for testing purpose
        haka.alert{
            description = "A simple alert",
            severity = "low"
        }
    end
}

6.1.3. Going further

All fields are available in read/write mode. For example, you can get the IP version, ttl or proto simply by using pkt.version, pkt.ttl or pkt.proto.

See also

ipv4 for a list of all ipv4 accessors.

See also

tcp for a list of all tcp accessors.