extcap: Use stderr to print error message

This patch reads out the stderr messages from an extcap
utility and displays it to an user. It was tested on Qt
but not on GTK, but should work their as well.

On Mac OS/X and Windows the child_watch does not behave
as it was intended. Therefore in extcap_cleanup, the callbacks
are called manually, if and only if, they have not been
called already.

The reason why it displays two error messages is, that
by the time the first one is being displayed, glib has not
returned from the spawned process on Linux yet. So there
is no way to add the stderr correctly, and putting a handler
to stderr into interface_opts will lead to memory errors,
cause then the code tries to access memory outside of its
protection.

Bug: 11892
Change-Id: I2db60dd480fed3e01428b91a705057e4f088bd15
Reviewed-on: https://code.wireshark.org/review/12954
Reviewed-by: Roland Knall <rknall@gmail.com>
Petri-Dish: Roland Knall <rknall@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Dario Lombardo <lomato@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 70 insertions, 4 deletions

diff --git a/doc/extcap_example.py b/doc/extcap_example.py
index ab9967c489..9007e26bba 100755
--- a/doc/extcap_example.py
+++ b/doc/extcap_example.py
@@ -40,6 +40,7 @@ other script-based formates beside VBScript
 
 """
 
+from __future__ import print_function
 import os
 import sys
 import signal
@@ -52,12 +53,40 @@ from threading import Thread
 
 ERROR_USAGE		= 0
 ERROR_ARG 		= 1
-ERROR_INTERFACE = 2
+ERROR_INTERFACE	= 2
 ERROR_FIFO 		= 3
+ERROR_DELAY		= 4
 
 doExit = False
 globalinterface = 0
 
+"""
+This code has been taken from http://stackoverflow.com/questions/5943249/python-argparse-and-controlling-overriding-the-exit-status-code - originally developed by Rob Cowie http://stackoverflow.com/users/46690/rob-cowie
+"""
+class ArgumentParser(argparse.ArgumentParser):
+	def _get_action_from_name(self, name):
+		"""Given a name, get the Action instance registered with this parser.
+		If only it were made available in the ArgumentError object. It is
+		passed as it's first arg...
+		"""
+		container = self._actions
+		if name is None:
+			return None
+		for action in container:
+			if '/'.join(action.option_strings) == name:
+				return action
+			elif action.metavar == name:
+				return action
+			elif action.dest == name:
+				return action
+
+	def error(self, message):
+		exc = sys.exc_info()[1]
+		if exc:
+			exc.argument = self._get_action_from_name(exc.argument_name)
+			raise exc
+		super(ArgumentParser, self).error(message)
+
 def signalHandler(signal, frame):
 	global doExit
 	doExit = True
@@ -214,6 +243,23 @@ def extcap_capture(interface, fifo, delay, verify, message, remote, fake_ip):
 
 	fh.close()
 
+def extcap_close_fifo(interface, fifo):
+	global doExit
+
+	signal.signal(signal.SIGINT, signalHandler)
+	signal.signal(signal.SIGTERM , signalHandler)
+
+	tdelay = delay if delay != 0 else 5
+
+	try:
+		os.stat(fifo)
+	except OSError:
+		doExit = True
+		print ( "Fifo does not exist!" )
+
+	fh = open(fifo, 'w+b', 0 )
+	fh.close()
+
 ####
 
 def usage():
@@ -227,7 +273,7 @@ if __name__ == '__main__':
 	message = ""
 	fake_ip = ""
 
-	parser = argparse.ArgumentParser(
+	parser = ArgumentParser(
 		prog="Extcap Example",
 		description="Extcap example program for python"
 		)
@@ -243,12 +289,26 @@ if __name__ == '__main__':
 
 	# Interface Arguments
 	parser.add_argument("--verify", help="Demonstrates a verification bool flag", action="store_true" )
-	parser.add_argument("--delay", help="Demonstrates an integer variable", type=int, default=0, choices=[0, 1, 2, 3, 4, 5] )
+	parser.add_argument("--delay", help="Demonstrates an integer variable", type=int, default=0, choices=[0, 1, 2, 3, 4, 5, 6] )
 	parser.add_argument("--remote", help="Demonstrates a selector choice", default="if1", choices=["if1", "if2"] )
 	parser.add_argument("--message", help="Demonstrates string variable", nargs='?', default="" )
 	parser.add_argument("--fake_ip", help="Add a fake sender IP adress", nargs='?', default="127.0.0.1" )
 
-	args, unknown = parser.parse_known_args()
+	try:
+		args, unknown = parser.parse_known_args()
+	except argparse.ArgumentError, exc:
+		print( "%s: %s" % ( exc.argument.dest, exc.message ), file=sys.stderr)
+		fifo_found = 0
+		fifo = ""
+		for arg in sys.argv:
+			if (arg == "--fifo" or arg == "--extcap-fifo") :
+				fifo_found = 1
+			elif ( fifo_found == 1 ):
+				fifo = arg
+				break
+		extcap_close_fifo("", fifo)
+		sys.exit(ERROR_ARG)
+
 	if ( len(sys.argv) <= 1 ):
 		parser.exit("No arguments given!")
 
@@ -282,6 +342,12 @@ if __name__ == '__main__':
 	elif args.capture:
 		if args.fifo is None:
 			sys.exit(ERROR_FIFO)
+		# The following code demonstrates error management with extcap
+		if args.delay > 5:
+			print("Value for delay [%d] too high" % args.delay, file=sys.stderr)
+			extcap_close_fifo(interface, args.fifo)
+			sys.exit(ERROR_DELAY)
+
 		extcap_capture(interface, args.fifo, args.delay, args.verify, message, args.remote, fake_ip)
 	else:
 		usage()