flow-info.py: Do not print any information if a flow is "empty" meaning no L4 payload seen so far.

* added JsonDecodeError to provide more information if builtin JSON decoder fails

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

dependencies/nDPIsrvd.py

@@ -295,6 +295,7 @@ class nDPIsrvdException(Exception):
     INVALID_LINE_RECEIVED    = 4
     CALLBACK_RETURNED_FALSE  = 5
     SOCKET_TIMEOUT           = 6
+    JSON_DECODE_ERROR        = 7
 
     def __init__(self, etype):
         self.etype = etype
@@ -341,6 +342,14 @@ class SocketTimeout(nDPIsrvdException):
     def __str__(self):
         return 'Socket timeout.'
 
+class JsonDecodeError(nDPIsrvdException):
+    def __init__(self, json_exception, failed_line):
+        super().__init__(nDPIsrvdException.JSON_DECODE_ERROR)
+        self.json_exception = json_exception
+        self.failed_line = failed_line
+    def __str__(self):
+        return '{}: {}'.format(self.json_exception, self.failed_line)
+
 class JsonFilter():
     def __init__(self, filter_string):
         self.filter_string = filter_string
@@ -456,7 +465,7 @@ class nDPIsrvdSocket:
                 json_dict = dict()
                 self.failed_lines += [received_line]
                 self.lines = self.lines[1:]
-                raise(e)
+                raise JsonDecodeError(e, received_line)
 
             instance = self.flow_mgr.getInstance(json_dict)
             if instance is None:

examples/py-flow-info/flow-info.py

@@ -498,6 +498,11 @@ def onJsonLineRecvd(json_dict, instance, current_flow, global_user_data):
         if args.print_hostname is True:
             line_suffix += '[{}]'.format(json_dict['ndpi']['hostname'])
 
+    if args.skip_empty is True:
+        if json_dict['flow_src_tot_l4_payload_len'] == 0 or json_dict['flow_dst_tot_l4_payload_len'] == 0:
+            stats.printStatus()
+            return True
+
     if args.print_bytes is True:
         src_color = ''
         dst_color = ''
@@ -566,6 +571,8 @@ if __name__ == '__main__':
                            help='Print received/transmitted source/dest bytes for every flow.')
     argparser.add_argument('--print-packets', action='store_true', default=False,
                            help='Print received/transmitted source/dest packets for every flow.')
+    argparser.add_argument('--skip-empty', action='store_true', default=False,
+                           help='Do not print flows that did not carry any layer7 payload.')
     argparser.add_argument('--guessed',    action='store_true', default=False, help='Print only guessed flow events.')
     argparser.add_argument('--not-detected', action='store_true', default=False, help='Print only undetected flow events.')
     argparser.add_argument('--detected',   action='store_true', default=False, help='Print only detected flow events.')