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wireshark-dev: [Wireshark-dev] libtshark + scripting language su

[Wireshark-dev] libtshark + scripting language support

From: Mark Landriscina <mlandri1_at_nospam>
Date: Wed Aug 18 2010 - 17:34:55 GMT
To: wireshark-dev@wireshark.org


I'd like to contribute some work that I've done to the wireshark community and need some advice on the best way to do this, assuming there is interest. If not, that would be good to know as well. I suspect that it might be best to fork this off as a separate project vs. incorporating it directly into ongoing SVN builds.

My initial goal was to modify the tshark (command line wireshark) and wrap it as a Python module. I wanted to expose tshark dissections as Python objects during packet capture or capture file processing. In addition this, I found that it was quite easy to extend this idea a bit more, so that other scripting languages (in additional to Python) could leverage the same code base. See below for details.

My motivation was that I wanted to do some work with Scapy and needed to access application layer protocol dissections within Python without re-writing all the dissection code already available in tshark/wireshark.

This is what I have done to date (all Linux for now, but am porting to Windows):

a. Modified tshark code base and compiled it as a library, libtshark.a. This is the original tshark executable, more or less, with some notable additions. In particular, after packet dissection, the epan dissection tree data is copied off into another tree structure that I've defined. This t_dissect_node tree is then serialized and written out over a named-pipe. The name of the named-pipe is defined by the user at run-time. The code to unserialize the t_dissect_node tree is also part of libtshark.a. Also, I have incorporated some additional helper code that makes tree navigation easier. A function named 'run' is called to start tshark and accepts as parameters tshark command line args.

b. A compiled Python shared library, _tsharkPY.so. I used SWIG to generate the Python bindings. Hence one could take the SWIG interface file that I wrote for Python (tsharkPY.i) and modify for use with other SWIG supported languages: Ruby, Java, etc.

c. tsharkPY.py is the Python module file created by SWIG, leverages my tsharkPY.i SWIG interface file.

All the above is based off of the most recent SVN builds and generation of the two lib files above has been incorporated into the existing Wireshark build process. Hence, all you have to do is run 'make' and you get libtshark.a and _tsharkPY.so. 'make install' puts these files into your Python lib path as defined by libtool. I do need some help tweaking this, however. Right now, libtool wants to put these in /usr/local/lib/python2.6/site-packages/. However, they need to be placed in /usr/lib/python2.6/site-packages/. Any thoughts (other than hard coding the correct path)?

Some basic Python code to use the Python module is as follows.

import tsharkPY

#fork tshark. tshark will publish its dissections to 'tshark_pipe' FIFO. Will read and dissect 3 packets from mycapfile.
tsharkPY.run(["python","-W", "tshark_pipe","-c","3","-r","mycapfile"])

#subscribe to 'tshark_pipe'FIFO

packets = []

#grab packets one at a time from tshark and save them in 'packets' array
    #get packet from "tshark_pipe" FIFO
    p = tsharkPY.get_next_packet("tshark_pipe")
    #check for closed pipe/EOF. break out of loop when detected.
    if(p is None):
        #unsubscribe from tshark_pipe FIFO. cleans up FIFO file and does some other house keeping.
    #create protocol set, array, and dictionary objects and make them part of t_dissect_node object
    #create dictionary containing field names of all the nodes in the packet tree that has 'p' as its root.
    #append t_dissect_node object to 'packets' array

print "Protocol sets: unordered list of protocols found in packet."
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
    for proto in packet.protocol_set: #iterate over each protocol name (string) in t_dissect_tree's protocol set object.
        print proto, #print protocol name
    print #print extra line

print "\nProtocol array: ordered array of protocol-level t_dissect_node references."
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
    for node in packet.protocol_array: #iterate over t_dissect_node object references in packet's protocol array.
        if node.field_name is not None: #if node.field_name exists (is not NULL), print value
            print node.field_name,
print "\nProtocol dictionary: hash table indexed by protocol name. provides access to t_dissect_node references for protocol level nodes in dissection tree."
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
    d_keys = packet.protocol_dict.keys() #dump key list for packet's protocol_dict object
    for k in d_keys: #iterate over key valus
        node = packet.protocol_dict[k] #get reference to each protocol level node in series
        if node is not None and node.field_name is not None: #if successful in retrieving node using current key, print node's field_name
            print node.field_name,

print "\nPacket debug print"
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
    packet.print_tree() #print t_dissect_node tree info for current packet

print "\nPacket data as Python char list."
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
        p = packet.first_child.next.last_child #find a node in tree that probably has data
        data_list = p.binary_blob #get node data as a list of chars
        print data_list #print list

        pass #ignore any exceptions thrown from above code
print "\nNode dictionary: dictionary that hashes all nodes in node tree by their field names (if defined). If duplicate field_names exist, only the first one encountered is added."
for packet in packets: #iterate over array of t_dissect_node trees. Each tree is one packet's worth of data.
    d_keys = packet.node_dict.keys() #dump key list
    for k in d_keys: #iterate over key list
        print k, #print each key
    print "\n"
print "\nFind node by its field name. Looking for 'ip.dst_host' in second packet"
node = packets[1].node_dict['ip.dst_host'] #find node in second packet that has its field_name param set to 'ip.dst_host'.
if (node is not None):
    print node.field_name+" found! Showname is '"+node.showname+"'" #if found, print some stuff from t_dissect_node structure

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