test: BIP324: add check for detection of missing garbage terminator

[theStack]

This PR adds test coverage for the "missing garbage terminator" detection on incoming v2 transport (BIP324) connections:

bitcoin/src/net.cpp

Lines 1205 to 1209 in 04265ba

	} else if (m_recv_buffer.size() == MAX_GARBAGE_LEN + BIP324Cipher::GARBAGE_TERMINATOR_LEN) {
	// We've reached the maximum length for garbage + garbage terminator, and the
	// terminator still does not match. Abort.
	LogPrint(BCLog::NET, "V2 transport error: missing garbage terminator, peer=%d\n", m_nodeid);
	return false;

Note that this always happens at the same exact amount of bytes sent in (after 64 + 4095 + 16 = 4175 bytes), if at no point, the last 16 bytes of potential authentication data match the garbage, i.e. all the previous bytes after the ellswift pubkey. To keep it simple, we just send in zero-value bytes here and verify that the detection hits exactly after the last bytes is sent.

AFAICT, with this PR all the v2 transport errors that can be triggered in this simple way of "just open a socket and send in a fixed byte-string" are covered. For more advanced test, we need BIP324 cryptography in the test framework in order to perform a v2 handshake etc. (PRs #28374, #24748).

[DrahtBot]

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Code Coverage

For detailed information about the code coverage, see the test coverage report.

Reviews

See the guideline for information on the review process.

Type	Reviewers
ACK	laanwj, sipa

If your review is incorrectly listed, please react with 👎 to this comment and the bot will ignore it on the next update.

[laanwj]

ACK 3bb51c2
Test code looks correct, and similar to other test cases in this unit

[sipa]

utACK 3bb51c2