Re: Re: -e vs. -x, revisited

[Guy Harris <guy () netapp com>]

On Wed, Dec 18, 2002 at 09:45:41AM -0500, Andrew Brown wrote:
> > (BTW, as per another recent discussioin, that means multi-line output
> > even if "-v" isn't specified....)
>
> we're already pretty much in that boat if the dissector calls
> default_print(), right?

Yes, which argues that it should do so only if "-x" was specified or
"-v" was specified.

> if (1) default_print_packet() were allowed to ignore its arguments so
> that it could behave "properly" as per the given flags, (2) it set a
> flag once called, that we could clear somewhere else, (3) a shim layer
> was added in between pcap and the xxx_if_print() routines, then (4)
> you could remove all xflag processing from all the xxx_if_print()
> routines.

If by "xflag processing" you mean checking "xflag", that could be done
*now*, without *any* of that stuff, by removing it and adding the "if
(xflag)" test to "default_print_packet()".

However, if you centralize the *calls* to "default_print_packet()" in
the shim layer, it won't know how long the link-layer header is, so they
won't know how to skip it.

To handle that, one could have the "xxx_if_print()" routines return the
link-layer header length.  Once one's done that, however, one doesn't
need any global variables - the shim routine would look something like

        void
        print_packet(u_char *user, const struct pcap_pkthdr *h, const u_char *p)
        {
                void (*if_print)(const struct pcap_pkthdr *h, const
                    u_char *p) = user;
                u_int hdrlen;

                hdrlen = (*user)(h, p);
                if (xflag)
                        default_print(p, h->caplen, hdrlen);
        }

("main()" would set "pcap_userdata()" to the results of
"lookup_printer()", and set "printer" to "print_packet").

Of course, once we've done *that*, we should probably then do

        void
        print_packet(u_char *user, const struct pcap_pkthdr *h, const u_char *p)
        {
                void (*if_print)(const struct pcap_pkthdr *h, const
                    u_char *p) = user;
                u_int hdrlen;

                ++infodelay;
                ts_print(&h->ts);

                hdrlen = (*user)(h, p);
                if (xflag)
                        default_print_packet(p, h->caplen, hdrlen);

                putchar('\n');

                --infodelay;
                if (infoprint)
                        info(0);
        }

and remove all that stuff from the if_print routines, centralizing that
in "print_packet()" as well.
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