fix(consul): one invalid node should not discard the remaining nodes of the service

[nic-6443]

Description

A single malformed entry in the consul health API response (an entry without the Service field, e.g. from an agent on a reclaimed cloud instance) currently wipes out the whole service. The per-node check in fetch_services_from_server() does goto CONTINUE, but the ::CONTINUE:: label sits outside the node loop, so one bad entry skips all the remaining nodes, the sort, and the up_services[key] = nodes assignment. If the malformed entry comes first, the service ends up with no nodes, update_all_services() deletes it from the shared dict, and requests start failing with "no valid upstream node".

The fix makes the skip local to the node loop (goto CONTINUE_NODE with the label at the end of the loop body) and logs a warning for the skipped entry. After the change, a malformed entry only drops that one node and the remaining healthy nodes keep serving traffic.

Added a regression test (t/discovery/consul-malformed-node.t) with a mock consul server returning one malformed entry followed by two valid ones; it fails without the fix and passes with it.

Which issue(s) this PR fixes:

Fixes #12937

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[Copilot]

Pull request overview

This PR fixes a reliability bug in the Consul service discovery client where a single malformed entry (missing the Service field) could incorrectly skip the rest of the nodes for that service, potentially causing the service to disappear from discovery and break traffic routing.

Changes:

• Make the “skip malformed node” logic local to the per-node loop (so one bad entry doesn’t discard the entire service’s node list) and emit a warning log for the skipped entry.
• Add a regression test that mocks a Consul health response containing one malformed entry followed by valid nodes.

Reviewed changes

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

File	Description
apisix/discovery/consul/client.lua	Adjusts node-iteration control flow to skip only malformed nodes and logs a warning for the skipped entry.
t/discovery/consul-malformed-node.t	Adds a regression test covering malformed health entries to ensure remaining valid nodes are still used.

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[membphis]

Reviewed. No blocking issues found.