Using plugin support to handle pcap-ng block types

[Paul Offord <Paul.Offord () advance7 com>]

Hi,

I am writing a plugin that handles two new PCAP-NG block types - details here: 
https://wiki.wireshark.org/Adding%20Support%20for%20a%20New%20Block%20Type

I'm using Guy's code that adds support for plugins to handle pcap-ng block types, described in 
https://code.wireshark.org/review/#/c/1775/

I have written a read block handler and registered it with Wireshark using register_pcapng_block_type_handler() and the 
handler gets called correctly.  Once the block has been read by my handler, I want Wireshark to continue to process it, 
but currently the block is ignored and Wireshark just moves on to the next block.

The blocks are read via a while loop in the pcapng_read(...) function of pcapng.c.  After calling a function to read 
the block there is a "switch (wblock.type)" section of code that decides what next to do with the block.  My new block 
is not defined as a switch case (not surprising), but I believe the default case should take into account the fact that 
a block type may have been registered.  The code in this area currently looks like this:

        switch (wblock.type) {

            case(BLOCK_TYPE_SHB):
                pcapng_debug("pcapng_read: another section header block");
                g_array_append_val(wth->shb_hdrs, wblock.block);
                break;

            case(BLOCK_TYPE_PB):
            case(BLOCK_TYPE_SPB):
            case(BLOCK_TYPE_EPB):
            case(BLOCK_TYPE_SYSDIG_EVENT):
            case(BLOCK_TYPE_SYSDIG_EVF):
                /* packet block - we've found a packet */
                goto got_packet;

            case(BLOCK_TYPE_IDB):
                /* A new interface */
                pcapng_debug("pcapng_read: block type BLOCK_TYPE_IDB");
                pcapng_process_idb(wth, pcapng, &wblock);
                wtap_block_free(wblock.block);
                break;

            case(BLOCK_TYPE_NRB):
                /* More name resolution entries */
                pcapng_debug("pcapng_read: block type BLOCK_TYPE_NRB");
                if (wth->nrb_hdrs == NULL) {
                    wth->nrb_hdrs = g_array_new(FALSE, FALSE, sizeof(wtap_block_t));
                }
                g_array_append_val(wth->nrb_hdrs, wblock.block);
                break;

            case(BLOCK_TYPE_ISB):
                /* Another interface statistics report */
                pcapng_debug("pcapng_read: block type BLOCK_TYPE_ISB");
                if_stats_mand_block = (wtapng_if_stats_mandatory_t*)wtap_block_get_mandatory_data(wblock.block);

                ... lines deleted ...

                }
                wtap_block_free(wblock.block);
                break;

            default:
                /* XXX - improve handling of "unknown" blocks */
                pcapng_debug("pcapng_read: Unknown block type 0x%08x", wblock.type);
                break;
        }
    }

got_packet:

    /*pcapng_debug("Read length: %u Packet length: %u", bytes_read, wth->phdr.caplen);*/
    pcapng_debug("pcapng_read: data_offset is finally %" G_GINT64_MODIFIER "d", *data_offset);

    return TRUE;


I believe that the default condition should check for a plugin registered block type and then goto got_packet.  Also, 
as the code stands we never free wblock.block.

Is this a bug, or is my understanding of what's intended wrong?

Thanks and regards...Paul

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