Wireshark-dev: Re: [Wireshark-dev] When to use tree != NULL check?
From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Mon, 10 Sep 2012 20:57:36 -0700
On Sep 10, 2012, at 7:37 PM, mmann78@xxxxxxxxxxxx wrote:
 
> I guess I've always used the rule that simple [1] dissectors (no matter how large) should all have the tree != NULL check before any dissection really takes place.

"Simple" would also have to include "no subdissectors" so that you don't end up skipping subdissector calls if you're not building a protocol tree.

> Most of the "expert info" I've seen is attached to "tree items" along the lines of "field validation" (command/value not supported/recognized, length incorrect, etc).  Without the tree, they don't seem very useful.

The "expert info" shows up not only in the protocol tree but also in the Analyze -> Expert Info window, and the highest "expert info" level shows up in a colored light on the status bar (hopefully it's still of use to colorblind users...), so it needs to be added when the capture is first read in.

> I've also seen dissectors that appear to be more geared towards tshark (lots of data in COL_INFO) than Wireshark,

Data in COL_INFO is useful to Wireshark users as well, if they're scanning the packet list pane.