Speedup the arp packet parsing function.

Finally, do not provide information we do not use
later in the dict.

diff --git a/cappie.py b/cappie.py
index 28f9060d78b04e4de24ba009986953c2a91f6c38..036d70c914b919aaf099c762499dc136561052c2 100644 (file)
--- a/cappie.py
+++ b/cappie.py
@@ -10,6 +10,11 @@ import time
 from ConfigParser import ConfigParser
 from threading import Thread
 
+TYPE_ARP = 0
+
+OPERATION_REQUEST = 0
+OPERATION_RESPONSE = 1
+
 def getAllInterfaces():
        filters = ("lo", "any")
        ret = []
@@ -40,34 +45,36 @@ def decode_packet(data):
 
 def decode_arp_packet(data):
        operationmap = {
-               1 : "in",
-               2 : "out",
+               1 : OPERATION_REQUEST,
+               2 : OPERATION_RESPONSE,
        }
 
        if not len(data) == 42:
                raise DecodeError, "Data has wrong length"
 
        ret = {
-               #"hwtype" : data[:2],
-               "protocol" : val2int(struct.unpack("!2s", data[12:14])[0]),
-               "hw_addr_size" : val2int(struct.unpack("!1s", data[18:19])[0]),
-               "hw_prot_size" : val2int(struct.unpack("!1s", data[19:20])[0]),
-               "operation" : val2int(struct.unpack("!2s", data[20:22])[0]),
+               "type" : TYPE_ARP,
        }
 
+       #"hwtype" : data[:2],
+       protocol = val2int(struct.unpack("!2s", data[12:14])[0])
+       hw_addr_size = val2int(struct.unpack("!1s", data[18:19])[0])
+       hw_prot_size = val2int(struct.unpack("!1s", data[19:20])[0])
+       operation = val2int(struct.unpack("!2s", data[20:22])[0])
+
        # Sanity checks
-       if not ret["protocol"] == 0x0806:
+       if not protocol == 0x0806:
                raise PacketTypeError, "Not an ARP packet"
 
        # TODO Must check hwtype here...
 
        try:
-               ret["operation"] = operationmap[ret["operation"]]
+               ret["operation"] = operationmap[operation]
        except KeyError:
                raise DecodeError, "Unknown operation type"
 
-       address_length = ret["hw_addr_size"] + ret["hw_prot_size"]
-       unpack_str = "!%ss%ss" % (ret["hw_addr_size"], ret["hw_prot_size"])
+       address_length = hw_addr_size + hw_prot_size
+       unpack_str = "!%ss%ss" % (hw_addr_size, hw_prot_size)
 
        ret["source_address"], ret["source_ip_address"] = \
                struct.unpack(unpack_str, data[22:22 + address_length])