Wireshark-dev: Re: [Wireshark-dev] Plugin dissector registration order problem
From: Ulf Lamping <[email protected]>
Date: Fri, 05 Oct 2007 09:00:34 +0200
Sebastien Dubois schrieb:
Hi,

I'm currently having problems trying to implement a new plugin as a sub-dissector to another plugin. The first plugin (let's call it foo_proto) registers itself and adds itself as a dissector that uses a given udp port as follows:
-------------------------------------------------------
*void** proto_register_foo_proto*(*void*)
{
    module_t* foo_proto_module;
   * if* (proto_foo_proto == -1)
    {
proto_foo_proto =* proto_register_protocol*("Foo Protocol ", "foo_proto", "foo_proto"); * register_dissector*("foo_proto", dissect_foo_proto, proto_foo_proto); * proto_register_field_array*(proto_foo_proto, hf, array_length(hf));
       * proto_register_subtree_array*(ett, array_length(ett));
    }
foo_proto_module =* prefs_register_protocol*(proto_foo_proto, proto_reg_handoff_foo_proto);
}

*void** proto_reg_handoff_foo_proto*(*void*)
{
   * static** int* Initialized = FALSE;
   * if* (!Initialized)
    {
foo_proto_handle =* create_dissector_handle*(dissect_foo_proto, proto_foo_proto);
       * dissector_add*("udp.port", foo_proto_port, foo_proto_handle);
        Initialized = TRUE;
    }
} -------------------------------------------------------
The second plugin (let's call it foo2_proto) also registers itself and 
adds itself as a dissector that uses a registered field in the 
previous dissector foo_proto as follows:
-------------------------------------------------------
*void** proto_register_foo2_proto*(*void*)
{
    module_t* foo2_proto_module;
   * if* (proto_foo2_proto == -1)
    {
proto_foo2_proto =* proto_register_protocol*("Foo2 Protocol ", "foo2_proto", "foo2_proto"); * register_dissector*("foo2_proto", dissect_foo2_proto, proto_foo2_proto); * proto_register_field_array*(proto_foo2_proto, hf, array_length(hf));
       * proto_register_subtree_array*(ett, array_length(ett));
    }
foo2_proto_module =* prefs_register_protocol*(proto_foo2_proto, proto_reg_handoff_foo2_proto);
}

*void** proto_reg_handoff_foo2_proto*(*void*)
{
   * static** int* Initialized = FALSE;
   * if* (!Initialized)
    {
foo2_proto_handle =* create_dissector_handle*(dissect_foo2_proto, proto_foo2_proto); * dissector_add*("foo_proto.hf_some_field", foo2_proto_port, foo2_proto_handle);
        Initialized = TRUE;
    }
} -------------------------------------------------------
  This compiles fine, but I get the following assertion failure in 
function dissector_add(...) at startup:
Err  file packet.c: line 671: assertion failed: (sub_dissectors)

It seems that the first plugin (foo) is not registered when the second one (foo2) calls dissector_add on it.
So, how does this work?  How can you add a plugin dissector to another 
plugin dissector?  Is it at all possible?
Wireshark will call all register functions (it knows of) before calling any of the handoff functions. So this sequence should not be your problem.
The line 671 of the assert might get a hint, but it's a bit worthless 
together with your code snippet ...
Regards, ULFL