[Guy Harris <guy@xxxxxxxxxx>]

On Tue, Apr 29, 2003 at 01:46:11PM +0200, Ana Rodr�guez wrote:
> I'm programming a DSR dissector

Is that DSR as in the Dynamic Source Routing protocol, i.e.:

	http://www.ietf.org/internet-drafts/draft-ietf-manet-dsr-09.txt

If so, then:

> and I have problems calling next 
> dissector. The question is that I want to call ICMP protocol, because I 
> have ICMP in the packet. The order I want it apears in the Ethereal tree 
> is:  Ethernet, IP, DSR and ICMP.
> This is the code I made, and it doesn't work:
> 
> static dissector_handle_t icmp_handle;
> 
> next_tvb=tvb_new_subset(tvb,offset,-1,-1);
> call_dissector(icmp_handle,next_tvb,pinfo,dsr_tree);
> 
> void proto_reg_handoff_dsr(void)
> {
>     dissector_handle_t dsr_handle;
> 
>     icmp_handle=find_dissector("icmp");
> 
>     dsr_handle = create_dissector_handle(dissect_dsr,proto_dsr);
>     dissector_add("ip.proto", IP_PROTO_DSR, dsr_handle);
> }

I'm not sure you want to do that; the I-D in question says

  6. DSR Options Header Format

     The Dynamic Source Routing protocol makes use of a special header
     carrying control information that can be included in any existing
     IP packet.  This DSR Options header in a packet contains a small
     fixed-sized, 4-octet portion, followed by a sequence of zero or more
     DSR options carrying optional information.  The end of the sequence
     of DSR options in the DSR Options header is implied by total length
     of the DSR Options header.

     For IPv4, the DSR Options header MUST immediately follow the IP
     header in the packet.  (If a Hop-by-Hop Options extension header, as
     defined in IPv6 [7], becomes defined for IPv4, the DSR Options header
     MUST immediately follow the Hop-by-Hop Options extension header, if
     one is present in the packet, and MUST otherwise immediately follow
     the IP header.)

     To add a DSR Options header to a packet, the DSR Options header is
     inserted following the packet's IP header, before any following
     header such as a traditional (e.g., TCP or UDP) transport layer
     header.  Specifically, the Protocol field in the IP header is used
     to indicate that a DSR Options header follows the IP header, and the
     Next Header field in the DSR Options header is used to indicate the
     type of protocol header (such as a transport layer header) following
     the DSR Options header.

so you don't want to check the Next Header field for specific values,
you want to use the same handoff table that IP uses (because there's
more than just ICMP following the DSR header).  If you do that, it'll
automatically call the appropriate dissector, whether it be the TCP
dissector, the UDP dissector, the SCTP dissector, the ICMP dissector,
etc..

You can get that handoff table by calling

	find_dissector_table("ip.proto")

and using the return value in a call to "dissector_try_port()", using
the protocol number from the Next Header field.