modifier: pcap headers automatically generated to account to packet resizing (module option only). adds a new dependency, python-scapy. i don't know what this is in Fedora

Author: austineal

INSTALL

@@ -41,6 +41,10 @@ YMMV, depending on whether the minimum requirements are met.
             - Source: http://sourceforge.net/projects/pyusb/
             - Ubuntu 11.04: Not currently packaged
             - Fedora 14: Not currently packaged
+	* python-scapy
+	    - Needed only by usbmodify.py
+	    - Ubuntu 10.04 and later: python-scapy
+	    - Fedora 14: 
 
 In addition, for usbreplay, ensure that pyusb-1.0.0 is inserted into the 
 python tree.  For example, on some linux systems, a good location would be:

demos/tablet/modify_module.py

@@ -0,0 +1,18 @@
+from array import array
+from usbrevue import Packet
+
+def modify(packet_gen, commit_func):
+    packet_buf = []
+    for packet in packet_gen('-'):
+        for byte in packet.data:
+            if byte >= 0x80:
+                packet_template = Packet(packet.hdr, packet.datapack[:64] + array('c', ''.join(map(chr, packet_buf))))
+                
+                packet_template.length = len(packet_template.data)
+                packet_template.len_cap = len(packet_template.data)
+
+                commit_func(packet_template)
+                packet_buf = []
+                packet_buf.append(byte)
+            else:
+                packet_buf.append(byte)

demos/tablet/raw_dump.pcap

@@ -31,6 +31,9 @@
 import gflags
 import re
 import struct
+import tempfile
+import os
+from scapy.all import RawPcapWriter, RawPcapReader
 from usbrevue import Packet
 
 
@@ -56,7 +59,6 @@ def __init__(self, module_file, routine_file, cmdline_exps):
         self.routine_file = routine_file
         self.cmdline_exps = cmdline_exps
 
-
     def run(self):
         """If a user-supplied module file is present, simply run that
         module. Otherwise, Pass each packet from the packet stream
@@ -102,12 +104,13 @@ def packet_generator(self, input_stream='-'):
         self.pcap = pcapy.open_offline(input_stream)
 
         # create the Dumper object now that we have a Reader
-        self.out = self.pcap.dump_open('-')
+        if not sys.stdout.isatty():
+            self.out = self.pcap.dump_open('-')
 
         while True:
             (hdr, pack) = self.pcap.next()
             if hdr is None:
-                return # EOF
+               return # EOF
             # keep track of the most recent yielding packet, for diffing
             self.orig_packet = Packet(hdr, pack)
             yield Packet(hdr, pack)
@@ -135,8 +138,28 @@ def commit_packet(self, packet):
             sys.stderr.write('Attempted to dump packets without first reading them -- make sure to call packet_generator()')
             sys.exit(1)
         else:
+            # make a temp file, use scapy's RawPcapWriter to write the
+            # current packet to that file, then read that same packet
+            # in using a new instance of pcapy.open_offline, then
+            # write out to stdout the packet that we just read back
+            # in, then finally delete the temp file
+            # 
+            # we have to do it this way in case the size of the packet
+            # changed, in which case the packet's pcap header needs to
+            # be regenerated. RawPcapWriter does this for us
+            #
+            # on reflection, it would be pretty straightforward to
+            # copy RawPcapWriter's code for generating the pcap
+            # header(s) and do it ourselves, without the messy temp
+            # file stuff. this code should be re-worked to do that.
+            temp = tempfile.mkstemp()
+            rpw = RawPcapWriter(temp[1], linktype = 220, sync=True)
+            rpw.write(packet.repack())
+            mypcap = pcapy.open_offline(temp[1])
+            (myhdr, mypack) = mypcap.next()
             if not sys.stdout.isatty():
-                self.out.dump(packet.hdr, packet.datapack)
+                self.out.dump(myhdr, mypack)
+            os.remove(temp[1])
 
 
     def apply_routine_file(self, packet):