Test IPv6 and dual-stack entrypoints

[dkropachev]

Jira task: https://scylladb.atlassian.net/browse/DRIVER-913
Jira epic: https://scylladb.atlassian.net/browse/DRIVER-823

Summary

• exercise direct IPv6 literal /localnodes discovery
• deterministically verify DNS fallback from broken IPv6 to IPv4 and from broken IPv4 to IPv6
• verify all unavailable DNS records return clearly and active refresh recovers through the original IPv6 seed

The existing IPv6 URL and operation-routing tests continue to cover bracketed authorities.

Tests

• make test-unit
• make lint

[Copilot]

Pull request overview

Adds IPv6 and dual-stack discovery coverage for the synchronous client.

Changes:

• Tests IPv6 literal /localnodes requests and refresh behavior.
• Tests IPv4/IPv6 DNS fallback and unavailable records.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
tests/unit/test_sync_manager.py	Covers refreshes through an IPv6 seed.
tests/unit/test_http.py	Adds IPv6 server and dual-stack HTTP tests.

Suppressed comments (2)

tests/unit/test_http.py:321

• The process proxy configuration can intercept this URL. Because the unconditional getaddrinfo mock then resolves the proxy hostname to these records, the test can pass without resolving or directly connecting to entrypoint.test; force proxy bypass so it deterministically exercises the intended dual-stack endpoint resolution.

        with patch("socket.getaddrinfo", return_value=records):
            nodes = create_sync_http_fetcher(timeout_seconds=1.0)(
                f"http://entrypoint.test:{server.server_port}/localnodes"
            )

tests/unit/test_http.py:337

• With an ambient HTTP proxy, this patches resolution of the proxy rather than entrypoint.test, so returning [] does not prove that the entrypoint's IPv4 and IPv6 records were exhausted. Explicitly bypass proxies while applying the DNS mock.

        with patch("socket.getaddrinfo", return_value=records):
            nodes = create_sync_http_fetcher(timeout_seconds=0.5)(
                "http://entrypoint.test:9/localnodes"
            )

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

Suppressed comments (2)

tests/unit/test_http.py:265

• If IPv6-to-IPv4 fallback stops working, no request reaches this server and handle_request() can remain blocked indefinitely. Since join(timeout=2) does not terminate a non-daemon thread, this regression can hang the test process instead of producing a normal assertion failure; daemonize the one-shot thread (or configure a server timeout).

        thread = Thread(target=server.handle_request)

tests/unit/test_http.py:304

• If IPv4-to-IPv6 fallback stops working, this non-daemon handle_request() thread receives no request and may wait forever. The timed join() only stops waiting for it, so a failed test can hang the process; daemonize the one-shot thread (or configure a server timeout).

        thread = Thread(target=server.handle_request)

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.