Re: Iteration in dissectors?

[Tyson Key <tyson.key () gmail com>]

I eventually managed to get thing working by using a combination of a
modified version of Chris's second approach, and use of
tvb_new_subset_remaining() to capture data after the Number of Blocks
byte.

Since I've also managed to get Polling Request/Response, and Read
Without Encryption Response packets mostly dissected (apart from a few
context-dependent data tables related to Status Flags), I might submit
the dissector for review.

Of course, there are other commands - although some are undocumented
and aren't present in the FeliCa Lite protocol "profile"/subset (e.g.
the authentication-related ones - which only get a brief mention in
the FeliCa Standard datasheets, and in the relevant Japanese
Industrial Standard (JIS X 6319-4)); and Write Without Encryption
Request/Response doesn't appear in my traces, so I can't easily test
an implementation of it.

Thanks once again,

Tyson.

On 22 January 2012 21:41, Tyson Key <tyson.key () gmail com> wrote:
> Thanks Chris,
>
> If I remember correctly, apart from an annoying, misleading "malformed
> packet" error, I eventually managed to dump all of the block IDs (1-4)
> using either :
>
> /* Start counting from 13 */
>             for (rwe_pos = 13; rwe_pos < tvb_get_guint8(tvb, 13); rwe_pos+=2) {
>               proto_tree_add_item(felica_tree, hf_felica_block_nbr, tvb,
> rwe_pos+1, 1, ENC_BIG_ENDIAN);
>             }
>
> or
>
> /* Start counting from 13 */
>             for (rwe_pos = 13; rwe_pos < tvb_get_guint8(tvb, 12); rwe_pos+=2) {
>               proto_tree_add_item(felica_tree, hf_felica_block_nbr, tvb,
> rwe_pos+1, 1, ENC_BIG_ENDIAN);
>             }
>
> I've found that removing the extraneous "+1" from that code will cause
> all of the IDs to be "128" (which is incorrect) - so it's probably
> just a case of trying to break the loop at the right time.
>
> For what it's worth, this also seems to work (with caveats):
>
>            /* Start counting from 13 */
>             for (rwe_pos = 13; tvb_get_guint8(tvb, 12) < rwe_pos; rwe_pos+=2) {
>               printf (rwe_pos);
>
>               proto_tree_add_item(felica_tree, hf_felica_block_nbr,
> tvb, rwe_pos+1, 1, ENC_BIG_ENDIAN);
>             }
>
> In that case, I see the following error messages on stdout:
>
> 21:01:04          Warn Dissector bug, protocol FeliCa, in packet 5:
> More than 1000000 items in the tree -- possible infinite loop
> 21:01:04          Warn Dissector bug, protocol FeliCa, in packet 8:
> More than 1000000 items in the tree -- possible infinite loop
>
> After trying your initial examples, and doing some of my own
> experimentation, I've came to the conclusion that I can either
> "successfully fail" and obtain all of the block IDs along with an
> error message; or "fail successfully" and obtain nothing - since the
> conditions being tested are contradictory (e.g. the number of blocks
> is less than the position - therefore, we don't move the cursor).
>
> Tyson.
>
> On 22 January 2012 18:16, Chris Maynard <Chris.Maynard () gtech com> wrote:
> > Tyson Key <tyson.key@...> writes:
> >
> > > My (partially working) iteration code looks like:
> > >
> > >            /* Start counting from 13 */
> > >            for (rwe_pos = 13; rwe_pos < tvb_get_guint8(tvb, 13); rwe_pos++) {
> > >              proto_tree_add_item(felica_tree, hf_felica_block_nbr, tvb,
> > > rwe_pos + 1, 1, ENC_BIG_ENDIAN);
> > >            }
> >
> > How about something like this:
> >
> >    /* Start counting from 14 */
> >    for (rwe_pos = 14; rwe_pos < tvb_get_guint8(tvb, 12); rwe_pos+=2) {
> >        proto_tree_add_item(felica_tree, hf_felica_block_nbr, tvb, rwe_pos, 1,
> > ENC_BIG_ENDIAN);
> >    }
> >
> > ... or if you want the 0x80 byte highlighted as part of the block number
> > (instead of skipping it), then do something like:
> >
> >    /* Start counting from 13 */
> >    for (rwe_pos = 13; rwe_pos < tvb_get_guint8(tvb, 12); rwe_pos+=2) {
> >        proto_tree_add_uint(felica_tree, hf_felica_block_nbr, tvb, rwe_pos, 2,
> > tvb_get_guint8(tvb, rwe_pos + 1));
> >    }
> >
> > - Chris
> >
> >
> > ___________________________________________________________________________
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>
>
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