Wireshark-dev: Re: [Wireshark-dev] Using tcp_dissect pdus and fragment, segment reassembly
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Graham Bloice wrote:
> I've been attempting to add tcp fragment reassembly using
> tcp_dissect_pdus() to an existing dissector that already used the epan
> reassembly code for an internal part of the protocol.
>
> However it seems that when I add the tcp_dissect_pdus() call then the
> other reassembly stops working. The call to fragment_add_seq_check()
> never returns a non-null fragment_data pointer.
>
> I grep'd all the other dissectors and didn't find any using a
> combination of both methods.
>
> Is there a problem with using both, or have I just gone wrong somewhere?
>
I've now resolved my issues with the combination of the two reassembly
options, and the problem was down to errors in my dissector.
In doing so, I ran across a couple of documentation issues:
In the Developers Guide, Section 9.3, Example 9.17. Decompressing data
packets for dissection
The code calls tvb_set_free_cb() for the newly created next_tvb. This
is unnecessary as the call to tvb_set_child_real_data() adds next_tvb to
the chained list of tvb, thus ensuring that next_tvb is correctly
deleted. In fact when I had the call in, Visual Studio kept breaking
deep down in ntdll.dll, probably because of a double free every time the
main tvb was deleted.
In README.developer, para 2..2.7 The example conversation code doesn't
assign the result of conversation_new() back into the conversation variable.
I've attached patches for these two items.
- --
Regards,
Graham Bloice
Software Developer
Trihedral UK Limited
Tel: +44 (0)7002 874433
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Attachment:
README.developer.patch.sig
Description: Binary data
Attachment:
WSDG_chapter_dissection.xml.patch.sig
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Index: doc/README.developer
===================================================================
--- doc/README.developer (revision 20501)
+++ doc/README.developer (working copy)
@@ -2809,7 +2809,7 @@
/* create the conversation with your data pointer */
- conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
+ conversation = conversation_new(pinfo->fd->num, &pinfo->src, &pinfo->dst, pinfo->ptype,
pinfo->srcport, pinfo->destport, 0);
conversation_add_proto_data(conversation, my_proto, (void *)data_ptr);
}
Index: docbook/wsdg_src/WSDG_chapter_dissection.xml
===================================================================
--- docbook/wsdg_src/WSDG_chapter_dissection.xml (revision 20501)
+++ docbook/wsdg_src/WSDG_chapter_dissection.xml (working copy)
@@ -682,7 +682,6 @@
next_tvb = tvb_new_real_data(decompressed_buffer, orig_size, orig_size);
tvb_set_child_real_data_tvbuff(tvb, next_tvb);
add_new_data_source(pinfo, next_tvb, "Decompressed Data");
- tvb_set_free_cb(next_tvb, g_free);
} else {
next_tvb = tvb_new_subset(tvb, offset, -1, -1);
}
