On Jul 27, 2018, at 10:40 AM, Guy Harris <guy@xxxxxxxxxxxx> wrote:
> Oh, and another thing not to do:
>
> Don't repurpose a command-line flag intended for one purpose for another unrelated purpose.
>
> For example, don't repurpose a command-line flag (for concreteness, let's pick the hypothetical example of a flag called "--extcap-version"), intended for one purpose (in this hypothetical example, used to ask a program to report its version number), for a separate purpose (in this hypothetical example, used to tell a program the version number of the program running that other program), with the two unrelated meanings distinguished based on whether the flag has an argument or not.
>
> I.e., for Wireshark 3.0, let's do the latter function with --extcap-wireshark-version X.Y or --extcap-wireshark-version=X.Y, with --extcap-version *never* taking an argument and *always* meaning "report your version number" and with --extcap-wireshark-version *always* taking an argument and *always* meaning "here's the version of Wireshark that's running you".
Unfortunately, *that* means that Wireshark 3.0 running an older extcap program that doesn't know about --extcap-wireshark-version may fail when run with that flag; at least with --extcap-version used for that purpose, the argument parser, *if* it doesn't fail if the option has a value, will just cause it to print the version of the program.
Now, that might *also* cause an issue, with the extra output.
How about we pass the Wireshark version as an *environment variable* - EXTCAP_WIRESHARK_VERSION - so that:
programs that don't know about it won't care, and will work with pre-3.0 and 3.0-and-later Wiresharks;
programs that do know about it *AND* that don't bogusly assume it's always set will somehow do the right thing if run by a pre-3.0 Wireshark.
