util: Move packet trace file read to protolib

This patch moves the code for opening an input protobuf packet trace into
a function defined in the protobuf library. This is because the code is
commonly used in decode scripts and is independent of the src protobuf
message.

util/decode_packet_trace.py

@@ -48,7 +48,6 @@
 # r,128,64,4000,0
 # w,232123,64,500000,0
 
-import gzip
 import protolib
 import sys
 
@@ -81,22 +80,8 @@ def main():
         print "Usage: ", sys.argv[0], " <protobuf input> <ASCII output>"
         exit(-1)
 
-    try:
+    # Open the file in read mode
-        # First see if this file is gzipped
+    proto_in = protolib.openFileRd(sys.argv[1])
-        try:
-            # Opening the file works even if it is not a gzip file
-            proto_in = gzip.open(sys.argv[1], 'rb')
-
-            # Force a check of the magic number by seeking in the
-            # file. If we do not do it here the error will occur when
-            # reading the first message.
-            proto_in.seek(1)
-            proto_in.seek(0)
-        except IOError:
-            proto_in = open(sys.argv[1], 'rb')
-    except IOError:
-        print "Failed to open ", sys.argv[1], " for reading"
-        exit(-1)
 
     try:
         ascii_out = open(sys.argv[2], 'w')

util/protolib.py

@@ -71,8 +71,33 @@
 # with protobuf python messages. For eg, the decode scripts for different
 # types of proto objects can use the same function to decode a single message
 
+import gzip
 import struct
 
+def openFileRd(in_file):
+    """
+    This opens the file passed as argument for reading using an appropriate
+    function depending on if it is gzipped or not. It returns the file
+    handle.
+    """
+    try:
+        # First see if this file is gzipped
+        try:
+            # Opening the file works even if it is not a gzip file
+            proto_in = gzip.open(in_file, 'rb')
+
+            # Force a check of the magic number by seeking in the
+            # file. If we do not do it here the error will occur when
+            # reading the first message.
+            proto_in.seek(1)
+            proto_in.seek(0)
+        except IOError:
+            proto_in = open(in_file, 'rb')
+    except IOError:
+        print "Failed to open ", in_file, " for reading"
+        exit(-1)
+    return proto_in
+
 def DecodeVarint(in_file):
     """
     The decoding of the Varint32 is copied from