Add additional RoCE extended transport headers (such as DETH and ImmDt)

[haggaie]

Allow parsing unreliable datagram headers. The code adds guess_payload_class
functions to find the correct sub-header according to BTH.opcode, and also
automatic selection of the opcode when possible.

[codecov]

Codecov Report

❌ Patch coverage is 96.29630% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.02%. Comparing base (ded1d73) to head (491a485).

Files with missing lines	Patch %	Lines
scapy/contrib/roce.py	96.29%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3408      +/-   ##
==========================================
- Coverage   80.10%   80.02%   -0.09%     
==========================================
  Files         370      370              
  Lines       91727    91767      +40     
==========================================
- Hits        73477    73433      -44     
- Misses      18250    18334      +84     

Files with missing lines	Coverage Δ
scapy/contrib/roce.py	95.12% <96.29%> (-0.06%)	⬇️

... and 13 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[gpotter2]

Very sorry about the delay regarding this PR !

[haggaie]

Very sorry about the delay regarding this PR !

Don't worry about it 😄

[albydnc]

is this PR going to be merged?

[gpotter2]

Not as-is, no. A lot feedback has not been addressed.

[haggaie]

Hi @gpotter2, I would be happy to fix this pull request (and continue with other parts of the RoCE spec), but I wanted to consult with you on how to best represent the RoCE protocol stack within scapy. I believe the main issue with the pull request was how the code examines upper layers in order to determine the next layer. With RoCE, a single opcode field within the BTH header can decide several subsequent layers. For example, an opcode of UD_SEND_ONLY_WITH_IMMEDIATE should tell the parser that the next header after BTH is the DETH header, and the one after that is the ImmDt. I'm not sure what's the best way to represent this in scapy. I can see three alternatives:

1. Using logic in guess_payload and post_build to describe the layers that are expected (as this patch tried to do).
2. Using conditional fields and storing the full set of alternative headers as one big layer. E.g., we could have all the DETH fields and ImmDt fields moved into BTH under conditions that test the opcode for UD_SEND_ONLY or UD_SEND_ONLY_WITH_IMMEDIATE.
3. Creating a separate layer for every combination under BTH and use bind_layers to link each opcode with the appropriate layer. For example, we could have a DETHImmDt layer for the combination of DETH and ImmDt and bind it to BTH when the opcode is UD_SEND_ONLY_WITH_IMMEDIATE.

I can see there are pros and cons to each method, so I wonder if the scapy project has a preferred approach, or if you have any other alternative I haven't considered.

Thanks,
Haggai