Update to enable offline sniff() to use a PacketList

[piersoh]

This minor patch allows for providing a PacketList tosniff(offline=my_packet_list). The existing behaviour is to fail ("AttributeError: 'list' object has no attribute 'read'") when provided with a PacketList.

The test suit runs against it ok.

[codecov]

Codecov Report

Merging #3026 (85acb7d) into master (2a8733a) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3026      +/-   ##
==========================================
- Coverage   85.37%   85.35%   -0.02%     
==========================================
  Files         255      256       +1     
  Lines       53968    54135     +167     
==========================================
+ Hits        46075    46209     +134     
- Misses       7893     7926      +33     

Impacted Files	Coverage Δ
scapy/sendrecv.py	84.46% <100.00%> (ø)
scapy/contrib/automotive/bmw/hsfz.py	53.22% <0.00%> (-1.78%)	⬇️
scapy/layers/can.py	94.63% <0.00%> (-1.45%)	⬇️
scapy/arch/windows/__init__.py	67.73% <0.00%> (-1.09%)	⬇️
scapy/data.py	87.85% <0.00%> (-0.52%)	⬇️
scapy/contrib/automotive/gm/gmlanutils.py	88.26% <0.00%> (-0.50%)	⬇️
scapy/arch/linux.py	0.73% <0.00%> (-0.50%)	⬇️
scapy/contrib/automotive/gm/gmlan.py	92.33% <0.00%> (-0.36%)	⬇️
scapy/fields.py	91.20% <0.00%> (-0.29%)	⬇️
scapy/utils.py	78.70% <0.00%> (-0.20%)	⬇️
... and 15 more

[guedou]

could you add a unit test in this section https://github.com/secdev/scapy/blob/master/test/regression.uts#L2018 ?

[gpotter2]

We need to find something more efficient than this. We can probably just check the first element and assume the type list is consistent..

[piersoh]

Howabout: isinstance(offline, (list, PacketList)) ?

%timeit isinstance(pktlist, (list, PacketList))
191 ns ± 1.59 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

%timeit isinstance(pktlist, list)
150 ns ± 3.02 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

%timeit isinstance(pktlist, list) or isinstance(pktlist, PacketList)
220 ns ± 5.1 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

[p-l-]

I think @gpotter2 was actually talking about the next check (all(...))

[p-l-]

I agree with you @gpotter2 but that's not related to this PR. The proposed patch looks good to me.

[piersoh]

Ah ok thanks. Agree all() check can be a bit of a delay - Looking at where the call graph goes it ends in calling PcapWriter() whilst it checks for None type one could just add a Packet type check there...