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> Can the variable be anything *other* than a packet of some sort?
There are only the mentioned 5 representations planned for pcap files since
this is what our capture device may capture into a pcap file. The
representation gives at least the ability to extend in the future. Do you have
anything specific in mind?
> only packets of various types, but I was reading "variable" in the
> programming language sense, rather than in the sense that the total content
> has a "fixed part", that being the trailer, and a "variable part", that being
> the packet preceding the trailer. Is the latter the sense in which the word
> "variable" should be understood?
Yes it is the latter sense! I see there is a potential for misunderstanding so
I renamed the "variable"-fields that actually refer to the payload and also
adjusted the description accordingly.
https://kb.hilscher.com/x/brDJBw
> It also appears that the boundary between the payload and the trailer would
> be determined by fetching the VarSize field at the end of the trailer. The
> first VarSize bytes of the data would be the payload, and the remaining
> sizeof(footer) bytes would be the trailer. Is that the case?
This is also correct. The remaining bytes of incl_len - VarSize is the footer
size.
Some fields of the footer (like the ID) may seem to be redundant and not of
much purpose in the wireshark or tcpdump context but we use the footer
structure everywhere in our software stack. This way we eliminated converting
structures between different parts of our software when dealing with captured
data.
> This also means that NETANALYZER_NG data must *not* be cut off at the end by
> any "slicing" process, such as capturing with a "slice length"/"snapshot
> length". Is it possible that the frame in the payload is "sliced" in that
> fashion?
Slicing a captured packet is not supported by our capturing device.
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