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>> That should also be noted in the specification.
I updated the specification with information about alignment, SrcID, and
PayloadType.
>>>> Slicing a captured packet is not supported by our capturing device.
>>>
>>> But some software can slice packets afterwards. Either that would have to
>>> be forbidden (meaning editcap and, I think, tcpdump
>>> would have to check for LINKTYPE_NETANALYZER_NG/DLT_NETANALYZR_NG and
>>> refuse to do slicing),
>>> or they would have to 1) ensure that the slice size is >= the footer size
>>> and 2) do the slicing specially, removing bytes *before* the
>>> footer, so that if incl_len < VarSize + footer_size, (VarSize +
>>> footer_size) - incl_len bytes have been sliced off.
>>
>> Both might be possible path to take for slicing. In any case the PayloadSize
>> should also be adjusted when the payload length is changed in my opinion. Is
>> this a Problem?
>
>So, with incl_len equal to {PayloadSize,VarSize} + 54, orig_len would be equal
>to {original PayloadSize} + 54, so the original payload size would be orig_len
>- 54.
>
>That would allow the original size and the sliced size of the payload to be
>calculated, so that should work.
Yes it should work.
I have the feeling this is more about the design then the implementation.
I will try to explain our design decision of the footer. We have observed that
customers using Wireshark don't think about the header when counting the bytes
in the hex dump and expect the frame to start at the first byte and as a result
read out wrong values. Therefore our idea was to put the additional info at the
end in form of a footer.
Maybe you can help me understand more of the general concept, how is this
slicing handled for a DLT with a header or footer in general?
If you take for example another DLT:
https://www.tcpdump.org/linktypes/LINKTYPE_LINUX_SLL.html it has 16 byte header
size, how does editcap or tcpdump take that into account? Is it possible to
slice without taking the header size into account?
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