* plugin/k8s_external: Fixes a nil pointer dereference panic when upstream lookup returns no response
When a CNAME-hosted service is resolved, k8s_external performs internal
upstream lookups for the target name. Upstream.Lookup can return a nil
message with a nil error when the internal self-query's plugin chain
returns a ClientWrite rcode without writing a response (for example
acl's drop action), and the a/aaaa/srv handlers then dereference
resp.Answer on a nil resp and panic.
Guard all four lookups with err == nil && resp != nil, matching the nil
checks already used in plugin/backend_lookup.go and the guard recently
added to plugin/dns64 (#8511).
Signed-off-by: zjncs <18910855655@163.com>
* plugin/k8s_external: silence unused-parameter lint in nil upstream test
The CI lint flagged the test handler's unused 'w' parameter. Rename it
to '_' so golangci-lint (revive unused-parameter) passes. No behavior
change.
Signed-off-by: zjncs <18910855655@163.com>
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Signed-off-by: zjncs <18910855655@163.com>
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