From: Michael Tremer <michael.tremer@ipfire.org>
Date: Fri, 16 Apr 2010 14:58:42 +0000 (+0200)
Subject: Speedup the arp packet parsing function.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c39c644181083b102f70f397bb6c6df0aa8f9daa;p=oddments%2Fcappie.git

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 28f9060..036d70c 100644
--- 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])