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Give more details on the "don't build the protocol tree if you don't 

have to", indicating that if it's too much work to explicitly test for a
null protocol tree, you might want to avoid those tests and rely on the
protocol tree routines not to do much work if passed a null protocol
tree pointer.

svn path=/trunk/; revision=11346
This commit is contained in:
Guy Harris 2004-07-08 21:16:04 +00:00
parent b50a28ec89
commit a354e21de5
1 changed files with 22 additions and 7 deletions
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29
doc/README.developer
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@ -1,4 +1,4 @@
$Id: README.developer,v 1.97 2004/06/25 07:04:03 jmayer Exp $
$Id: README.developer,v 1.98 2004/07/08 21:16:04 guy Exp $
This file is a HOWTO for Ethereal developers. It describes how to start coding
a Ethereal protocol dissector and the use some of the important functions and
@ -373,12 +373,12 @@ code inside
is needed only if you are using the "snprintf()" function.
The "$Id: README.developer,v 1.97 2004/06/25 07:04:03 jmayer Exp $"
The "$Id: README.developer,v 1.98 2004/07/08 21:16:04 guy Exp $"
in the comment will be updated by CVS when the file is
checked in; it will allow the RCS "ident" command to report which
version of the file is currently checked out.
When creating a new file, it is fine to just write "$Id: README.developer,v 1.97 2004/06/25 07:04:03 jmayer Exp $" as RCS will
When creating a new file, it is fine to just write "$Id: README.developer,v 1.98 2004/07/08 21:16:04 guy Exp $" as RCS will
automatically fill in the identifier at the time the file will be added to the
CVS repository (checked in).
@ -387,7 +387,7 @@ CVS repository (checked in).
* Routines for PROTONAME dissection
* Copyright 2000, YOUR_NAME <YOUR_EMAIL_ADDRESS>
*
* $Id: README.developer,v 1.97 2004/06/25 07:04:03 jmayer Exp $
* $Id: README.developer,v 1.98 2004/07/08 21:16:04 guy Exp $
*
* Ethereal - Network traffic analyzer
* By Gerald Combs <gerald@ethereal.com>
@ -503,9 +503,24 @@ dissect_PROTOABBREV(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
(b) <=> tree != NULL
In the interest of speed, if "tree" is NULL, avoid building a
protocol tree and adding stuff to it if possible. Note,
however, that you must call subdissectors regardless of whether
"tree" is NULL or not. */
protocol tree and adding stuff to it, or even looking at any packet
data needed only if you're building the protocol tree, if possible.
Note, however, that you must fill in column information, create
conversations, reassemble packets, build any other persistent state
needed for dissection, and call subdissectors regardless of whether
"tree" is NULL or not. This might be inconvenient to do without
doing most of the dissection work; the routines for adding items to
the protocol tree can be passed a null protocol tree pointer, in
which case they'll return a null item pointer, and
"proto_item_add_subtree()" returns a null tree pointer if passed a
null item pointer, so, if you're careful not to dereference any null
tree or item pointers, you can accomplish this by doing all the
dissection work. This might not be as efficient as skipping that
work if you're not building a protocol tree, but if the code would
have a lot of tests whether "tree" is null if you skipped that work,
you might still be better off just doing all that work regardless of
whether "tree" is null or not. */
if (tree) {
/* NOTE: The offset and length values in the call to