Allow bigger snapshot lengths for D-Bus captures.

Use WTAP_MAX_PACKET_SIZE_STANDARD, set to 256KB, for everything except
for D-Bus captures.  Use WTAP_MAX_PACKET_SIZE_DBUS, set to 128MB, for
them, because that's the largest possible D-Bus message size.  See

	https://bugs.freedesktop.org/show_bug.cgi?id=100220

for an example of the problems caused by limiting the snapshot length to
256KB for D-Bus.

Have a snapshot length of 0 in a capture_file structure mean "there is
no snapshot length for the file"; we don't need the has_snap field in
that case, a value of 0 mean "no, we don't have a snapshot length".

In dumpcap, start out with a pipe buffer size of 2KB, and grow it as
necessary.  When checking for a too-big packet from a pipe, check
against the appropriate maximum - 128MB for DLT_DBUS, 256KB for
everything else.

Change-Id: Ib2ce7a0cf37b971fbc0318024fd011e18add8b20
Reviewed-on: https://code.wireshark.org/review/21952
Petri-Dish: Guy Harris <guy@alum.mit.edu>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Guy Harris <guy@alum.mit.edu>
(cherry picked from commit d0865fd619454a9ac06b1c7d287dc438aff50bb0)
Reviewed-on: https://code.wireshark.org/review/21955

1 files changed, 9 insertions, 5 deletions

diff --git a/wiretap/wtap.h b/wiretap/wtap.h
index ee68a8eabe..ca58afb9c9 100644
--- a/wiretap/wtap.h
+++ b/wiretap/wtap.h
@@ -375,11 +375,15 @@ extern "C" {
 /* if you add to the above, update wtap_tsprec_string() */
 
 /*
- * Maximum packet size we'll support.
- * 262144 is the largest snapshot length that libpcap supports, so we
- * use that.
- */
-#define WTAP_MAX_PACKET_SIZE    262144
+ * We support one maximum packet size for most link-layer header types
+ * and another for D-Bus, because the maximum packet size for D-Bus
+ * is 128MB, and that's a lot bigger than the 256KB that we use elsewhere.
+ * We don't want to write out files that specify a maximum packet size of
+ * 128MB if we don't have to, as software reading those files might
+ * allocate a buffer much larger than necessary, wasting memory.
+ */
+#define WTAP_MAX_PACKET_SIZE_STANDARD    262144
+#define WTAP_MAX_PACKET_SIZE_DBUS        (128*1024*1024)
 
 /*
  * "Pseudo-headers" are used to supply to the clients of wiretap