Follow-up: Added CoAP socket #4334

[polybassa]

Description

This PR implements a CoAP socket, pretty similar on how ISOTPSoftSocket works.
I implemented the basic message exchange, mostly based on the RFC-7252.

• Congestion control
• Retransmission mechanism
• Separate responses
• Message duplication detection

Known-limitations

• No POST and DELETE methods
• No DTLS
• No discovery via multicast/broadcast, although you can still bind to one of these interfaces
• No observer
• The SR/SR1 functions cannot handle separate responses.

General comments

It has a dependency for from scapy.contrib.isotp.isotp_soft_socket import TimeoutScheduler, I found nice how this is implemented, so I just used it, I didn't want to copy/paste again.

Also I added some unit tests for the basic cases.

Quick usage

Client example:
    >>> with CoAPSocket("127.0.0.1", 1234) as coap_client:
    >>>     req = CoAPSocket.make_coap_req_packet(method=GET, uri="endpoint-uri", payload=b"")
    >>>     coap_client.send("127.0.0.1", 5683, req)
    >>>     res = coap_client.recv() # Careful, this will block until the coap_client receives something

Server without specifying resources:
    >>> with CoAPSocket("127.0.0.1", 5683) as coap_server:
    >>>     while True:
    >>>         pkg = coap_server.recv()
    >>>         handle_package(pkg)

Server with custom resources:
    >>> class DummyResource(CoAPResource):
    >>>     def get(self, payload, options, token, sa_ll):
    >>>         return {"type": ACK, "code": CONTENT_205, "options": [(CONTENT_FORMAT, CF_TEXT_PLAIN)], "payload": b'dummy response'}
    >>>
    >>> class DelayedResource(CoAPResource):
    >>>     def __init__(self, url):
    >>>         CoAPResource.__init__(self, url=url)
    >>>         self.delayed_tokens = []
    >>>
    >>>     def delayed_message(self):
    >>>         token, address = self.delayed_tokens.pop(0)
    >>>         pkt = CoAPSocket.make_delayed_resp_packet(token, [(CONTENT_FORMAT, CF_TEXT_PLAIN)], b"delayed payload")
    >>>         self._send_separate_response(pkt, address)
    >>>
    >>>     def get(self, payload, options, token, sa_ll):
    >>>         # We know that this can take a while, so we return an empty ACK now and wait for whatever resource to be available.
    >>>         TimeoutScheduler.schedule(1, self.delayed_message)
    >>>         self.delayed_tokens.append((token, sa_ll))
    >>>         return CoAPSocket.empty_ack_params()
    >>>
    >>> # Doesn't matter if it starts with "/dummy" or "dummy", but it is an error if it is in the end
    >>> lst_resources = [DummyResource("dummy"), DelayedResource("/delayed")].
    >>> with CoAPSocket("127.0.0.1", 5683, lst_resources=lst_resources) as coap_socket:
    >>>     while True:
    >>>         pkg = coap_socket.recv()
    >>>         # You can handle the packages inside your resources, here will only be the "unhandled" ones.

This follow-up reintegrates master and adds additional unit tests

[polybassa]

@gpotter2 How to add the "AI Trailer" the "old" commits which were created 2 years ago?

[gpotter2]

You can git rebase -i and use "edit" to change the commit. It's a bit annoying sorry :/

[polybassa]

Ok, that should work. I just disliked changing to much of the history.

What do you think about a start date? Like only commits from 2026 onward are filtered by the script?

[gpotter2]

Ok, that should work. I just disliked changing to much of the history.

What do you think about a start date? Like only commits from 2026 onward are filtered by the script?

Sure that's a good idea.

[Copilot]

Pull request overview

Adds a new CoAP socket implementation to Scapy’s contrib layer, expanding CoAP support beyond packet parsing to include client/server exchanges (retransmissions, separate responses, duplicate detection), and introduces regression + interop tests (libcoap) with CI support.

Changes:

• Introduce scapy.contrib.coap_socket implementing a CoAP-aware SuperSocket with resource handling and basic retransmission/separate-response behavior.
• Extend scapy.contrib.coap with exported CoAP constants plus hashret() / answers() to improve request/response matching in Scapy send/recv workflows.
• Add UTScapy regression + libcoap interoperability/stress tests and install libcoap binaries in CI.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
scapy/contrib/coap_socket.py	New CoAP socket implementation (client/server, resources, retransmission, separate responses).
scapy/contrib/coap.py	Adds exported constants and response-matching helpers (hashret, answers).
test/contrib/coap_socket.uts	New UTScapy regression + libcoap interoperability/stress tests for CoAPSocket.
.config/ci/install.sh	Installs libcoap binaries for CI to enable interop tests.

---

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[codecov]

Codecov Report

❌ Patch coverage is 89.74943% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.03%. Comparing base (30c07a1) to head (93ce604).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/contrib/coap_socket.py	89.05%	44 Missing ⚠️
scapy/contrib/coap.py	97.29%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5002      +/-   ##
==========================================
- Coverage   80.29%   80.03%   -0.27%     
==========================================
  Files         383      384       +1     
  Lines       95163    95601     +438     
==========================================
+ Hits        76407    76510     +103     
- Misses      18756    19091     +335     

Files with missing lines	Coverage Δ
scapy/contrib/coap.py	95.91% <97.29%> (+0.42%)	⬆️
scapy/contrib/coap_socket.py	89.05% <89.05%> (ø)

... and 24 files with indirect coverage changes

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