Make the capture file's interface description filterable

This patch introduces the frame.interface_description field.

While testing this new functionality it became obvious that we have
a non-optimal interaction between the existing cfile.c's
cap_file_get_interface_name(), the recently added frame.interface_name
field and this new frame.interface_description field.

The string returned from cap_file_get_interface_name() may in fact
come from one of three different sources: the idb's interface name
(if it exists) or the idb's interface description (if that exists)
or a default text of "unknown".  The string ultimately becomes the
rame.interface_name whether or not the idb had an interface name
option to begin with.  This behavior does not allow one to test for
the simple presence of frame.interface_name.  The new peer function
cap_file_get_interface_description() added by this patch returns
NULL instead of "unknown" if the idb does not have an interface
description.  Should cap_file_get_interface_name() be similarly
modified to return NULL if the idb does not have an interface name?

Bug: 9781
Change-Id: Ie479f373c5080c004dd22bd88919838feca71e95
Reviewed-on: https://code.wireshark.org/review/19861
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/file.c b/file.c
index c8c9c13449..ff39a9dffe 100644
--- a/file.c
+++ b/file.c
@@ -283,6 +283,7 @@ ws_epan_new(capture_file *cf)
   epan->data = cf;
   epan->get_frame_ts = ws_get_frame_ts;
   epan->get_interface_name = cap_file_get_interface_name;
+  epan->get_interface_description = cap_file_get_interface_description;
   epan->get_user_comment = ws_get_user_comment;
 
   return epan;