Wireshark · Wireshark-dev: Re: [Wireshark-dev] How can I register a link layer protocol?

[Armando Vázquez <avr989@xxxxxxxxx>]

Hi  Alex,

The plugin you attached is meant to open filetypes different than pcap, right? I don't understand how to use this knowledge with my problem. I'm using a pcap file, thing is I want wireshark to dissect a protocol in the link layer which is not included in wireshark.
Armando Vázquez Ramírez

On Mon, Mar 5, 2012 at 9:11 AM, Alex Lindberg <alindber@xxxxxxxxx> wrote:

I needed to read a unsupported file structure and protocol into Wireshark.  I did this by creating a plugin that registered the necessary routines to read a file and determine if the file was the one I needed. 

1st - register with wtap:

/* register with wtap */
void wtap_register_mst(void) {
    static struct file_type_info fi = {
        "My PROTOCOL File",        /* name */
        "mst_file",            /* short name */
        "*.*",                 /* file extensions */
        NULL,                 /* file extension default */
        FALSE,                 /* writing seek must */
        FALSE,                /* has name resolution */
        NULL,                /* can write this type of file encap? */
        NULL                /* function to open for writing */
    };
    wtap_register_open_routine(myproto_open, TRUE);
    encap_mst_file = wtap_register_encap_type("My PROTOCOL FILE", "myproto_file");
    wf_myproto_file = wtap_register_file_type(&fi);
}

As you see, you need a open routine (myproto_open).  The open routine determines of the file is of the flavor you are looking for, if so it created a file structure used by Wireshark.

int myproto_open(wtap *wth, int *err, gchar **err_info _U_) {
    /* open routine.  First determine if it is a myproto file. */
    /* The open_file_* routines should return:
        -1 on an I/O error;
        1 if the file they're reading is one of the types it handles;
        0 if the file they're reading isn't the type they're checking for.
    If the routine handles this type of file, it should set the "file_type"
    field in the "struct wtap" to the type of the file. */
    if (!(myproto_check_file(wth, err))) {
        if (*err == 0) {
            return 0;
        }
        else {
            return -1;
        }
    }

    /* point to 1st line */
    if(file_seek(wth->fh,0, SEEK_SET, err) == -1) {
        return -1;
    }
   
    wth->data_offset = 0;
    wth->file_encap = WTAP_ENCAP_USER15; /* encap type to use if save as pcap file */
    wth->file_type = WTAP_ENCAP_USER15;
    wth->subtype_read = myproto_read;    /* routines to go for reading and seeking */
    wth->subtype_seek_read = myproto_seek_read;
    wth->snapshot_length = 0;    /* not known */
    wth->tsprecision = WTAP_FILE_TSPREC_CSEC;

    return 1;
}

As an FYI, to get the plungin's wtap routines to register, I had to modify the local Makefile.am for plugin.c to look for the wtap register routine (only for the Python build which I am using)

plugin.c: $(DISSECTOR_SRC) $(top_srcdir)/tools/make-dissector-reg \
    $(top_srcdir)/tools/make-dissector-reg.py
    @if test -n "$(PYTHON)"; then \
        echo Making plugin.c with python ; \
        $(PYTHON) $(top_srcdir)/tools/make-dissector-reg.py $(srcdir) \
            plugin_wtap $(DISSECTOR_SRC) ; \
    else \
        echo Making plugin.c with shell script ; \
        $(top_srcdir)/tools/make-dissector-reg $(srcdir) \
            $(plugin_src) plugin_wtap $(DISSECTOR_SRC) ; \
    fi

Examples of these functions can be found in the wiretap directory.  Best of luck

Alex Lindberg

--- On Sat, 3/3/12, ashish goel <ashish.kumar.goel1@xxxxxxxxx> wrote:

From: ashish goel <ashish.kumar.goel1@xxxxxxxxx>
Subject: Re: [Wireshark-dev] How can I register a link layer protocol?
To: "Developer support list for Wireshark" <wireshark-dev@xxxxxxxxxxxxx>
Date: Saturday, March 3, 2012, 12:30 PM

Hi Armando,

Have you checked if your protocol is registered or not. One way to check this is to type your protocol's name in Wireshark's Display Filter textbox, the textbox's background should turn green.
If your protocol is registered and it is not showing as valid protocol while adding to DLT_User encapsulation table then DLT_user file might have been corrupted.
Try creating a new workspace and implement your changes into that. It should work.

2012/3/3 Armando Vázquez <avr989@xxxxxxxxx>

Thanks ashis!

When I tried this my protocol does not show up as a valid protocol, why is that? I tried using my dissector for the header protocol, but it should also disscet 2 trailer bytes, does that represent a problem ? What should I put in the header size field?

Besides, I've read that using the GUI and editing the DLT_User is the same as using the function dissector_add_uint(), am I right? If so, why isn't working? should I change something else in pcap-common.c or wtap.c or wtap.h?

Armando Vázquez Ramírez

On Sat, Mar 3, 2012 at 6:27 AM, ashish goel <ashish.kumar.goel1@xxxxxxxxx> wrote:

Hi Armando,

The is a way you can do it through wireshark GUI. Go to preferences -> protocols -> DLT_User. Here click on edit and add your protocol on any of the User DLTs(147 - 162). But make sure that that the pcap file you are using must have defined the same DLT value in its global header.

Hope this helps.

Thanks,

Ashish

2012/3/2 Armando Vázquez <avr989@xxxxxxxxx>

Hi guys,

I've read the developers guide, README.developer, wiretap plugin wiki and found no answer. Here is my problem. I'm trying to use Wireshark for dissecting a pcap capture of a protocol that it's not currently defined in wireshark. So I started writing a plugin, but I haven't been able to declare or register this dissector so it is enabled as a link layer dissector. I need to achieve this because this is not a internet protocol, so I need to identify it in this layer.

I've already read this dev-topic (http://www.mail-archive.com/wireshark-dev@xxxxxxxxxxxxx/msg05931.html) but I didn't understand it well.

The dissection part works fine, I've tested it using a pcap and nesting it on top of TCP. I would really appreciate your help. 

Also I've added in wtap.h

#define WTAP_ENCAP_MYPROTOCOL 147

and in wtap.c

static struct encap_type_info encap_table_base[] = {

...

{ "RESERVED 138", "res0" },

{ "RESERVED 139", "res1" },

{ "RESERVED 140", "res2" },

{ "RESERVED 141", "res3" },

{ "RESERVED 142", "res4" },

{ "RESERVED 143", "res5" },

{ "RESERVED 144", "res6" },

{ "RESERVED 145", "res7" },

{ "RESERVED 146", "res8" },

/* WTAP_ENCAP_MYPROTOCOL*/

{ "MY PROTOCOL, "myprotocol" }

};

Here are the register and handoff sections of my code

----------------------------------------------------------------------------------

void proto_register_myprotocol (void)

{

...

myprotocol_dissector_table = register_dissector_table("myprotocol.proto","ACN protocol number", FT_UINT8, BASE_HEX);

proto_register_field_array (proto_myprotocol, hf, array_length (hf));

proto_register_subtree_array (ett, array_length (ett));

register_dissector("myprotocol", dissect_myprotocol, proto_myprotocol);

}

void proto_reg_handoff_myprotocol(void)

{

data_handle = find_dissector("data");

myprotocol_handle = create_dissector_handle(dissect_myprotocol, proto_myprotocol);

dissector_add_uint("wtap_encap", WTAP_ENCAP_MYPROTOCOL, myprotocol_handle);

dissector_add_uint("tcp.port", global_myprotocol_port, myprotocol_handle); // Registering this on top of TCP was only to develop the dissection part, this won't be present in the release version

}

----------------------------------------------------------------------------------

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--
Thanks,
Ashish

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--
Thanks,
Ashish

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