Replace ncat.exe with a dedicated TCP broker supporting zero-delimited framing

[emrainey]

This was flagged by a corporate security audit when I downloaded pycyphal. While I'm on a Mac and I can't directly run this, it does beg the question, why is this needed here?

[pavel-kirienko]

It is necessary for testing Cyphal/serial on Windows. On GNU/Linux, it is installed as a package during CI workflow execution, but there is no clean way of doing so for Windows that I could find. Here is how it's used:

pycyphal/noxfile.py

Lines 18 to 20 in de11875

	DEPS_DIR = ROOT_DIR / ".test_deps"
	assert DEPS_DIR.is_dir(), "Invalid configuration"
	os.environ["PATH"] += os.pathsep + str(DEPS_DIR)

pycyphal/noxfile.py

Line 78 in de11875

broker_process = subprocess.Popen(["ncat", "--broker", "--listen", "-p", "50905"], env=session.env)

If you have a better solution in mind, please send a pull request; for now I am closing this. Also, keep in mind that the default Windows security policies tend to misidentify ncat.exe as a "hacking tool"...

[thirtytwobits]

There's got to be a python solution available here?

[pavel-kirienko]

A contribution changing ncat.exe to something else would be accepted.

[thirtytwobits]

@emrainey , do you think we could replace this function with a Python library?

[emrainey]

Likely we could with a raw socket over UDP? Looks like there are some minor implementation on stack overflow. https://stackoverflow.com/questions/1908878/netcat-implementation-in-python.

ChatGPT could probably pound out an implementation in no time. :)

[pavel-kirienko]

This is just a TCP broker that bridges all connections accepted through some specified port; it can be implemented easily. Note that it has to be TCP, not UDP.

[pavel-kirienko]

While we're at it, we should also use zero-byte frame delimiters on each connection to prevent output-queue mangling. This is an issue with ncat.exe that complicates the testing of larger networks.