fix(kubernetes): include structured key/value context in client-go logs (#8490)

plugin/kubernetes/logger.go

@@ -1,16 +1,24 @@
 package kubernetes
 
 import (
+	"fmt"
+	"slices"
+	"strings"
+
 	clog "github.com/coredns/coredns/plugin/pkg/log"
 
 	"github.com/go-logr/logr"
 )
 
+// missingValue is what klog prints for a key without a value.
+const missingValue = "(MISSING)"
+
 // loggerAdapter is a simple wrapper around CoreDNS plugin logger made to implement logr.LogSink interface, which is used
 // as part of klog library for logging in Kubernetes client. By using this adapter CoreDNS is able to log messages/errors from
 // kubernetes client in a CoreDNS logging format
 type loggerAdapter struct {
 	clog.P
+	values []any // always even-length, see WithValues
 }
 
 func (l *loggerAdapter) Init(_ logr.RuntimeInfo) {
@@ -21,18 +29,71 @@ func (l *loggerAdapter) Enabled(_ int) bool {
 	return true
 }
 
-func (l *loggerAdapter) Info(_ int, msg string, _ ...any) {
-	l.P.Info(msg)
+func (l *loggerAdapter) Info(_ int, msg string, keysAndValues ...any) {
+	l.P.Info(l.sprint(msg, nil, keysAndValues))
 }
 
-func (l *loggerAdapter) Error(err error, msg string, _ ...any) {
-	l.Errorf("%s: %s", msg, err)
+func (l *loggerAdapter) Error(err error, msg string, keysAndValues ...any) {
+	l.P.Error(l.sprint(msg, err, keysAndValues))
 }
 
-func (l *loggerAdapter) WithValues(_ ...any) logr.LogSink {
-	return l
+func (l *loggerAdapter) WithValues(keysAndValues ...any) logr.LogSink {
+	if len(keysAndValues) == 0 {
+		return l
+	}
+	clone := *l
+	clone.values = append(slices.Clip(l.values), keysAndValues...)
+	if len(clone.values)%2 != 0 {
+		// pad like klog does, so later pairs don't shift
+		clone.values = append(clone.values, missingValue)
+	}
+	return &clone
 }
 
 func (l *loggerAdapter) WithName(_ string) logr.LogSink {
 	return l
 }
+
+// sprint renders the message followed by the error (if any) and key/value pairs,
+// since client-go puts most context (resource type, reflector name) in the latter.
+// Duplicate keys are collapsed with the last value winning, as in klog.
+func (l *loggerAdapter) sprint(msg string, err error, keysAndValues []any) string {
+	var b strings.Builder
+	b.WriteString(msg)
+	if err != nil {
+		b.WriteString(": ")
+		b.WriteString(err.Error())
+	}
+	kvs := keysAndValues
+	if len(l.values) > 0 {
+		kvs = append(slices.Clip(l.values), keysAndValues...)
+	}
+	for i := 0; i < len(kvs); i += 2 {
+		k := fmt.Sprint(kvs[i])
+		if hasLaterKey(kvs, i+2, k) {
+			continue
+		}
+		var v any = missingValue
+		if i+1 < len(kvs) {
+			v = kvs[i+1]
+		}
+		switch v := v.(type) {
+		case string:
+			fmt.Fprintf(&b, " %s=%q", k, v)
+		case error:
+			fmt.Fprintf(&b, " %s=%q", k, v.Error())
+		default:
+			fmt.Fprintf(&b, " %s=%v", k, v)
+		}
+	}
+	return b.String()
+}
+
+func hasLaterKey(kvs []any, from int, key string) bool {
+	for j := from; j < len(kvs); j += 2 {
+		if fmt.Sprint(kvs[j]) == key {
+			return true
+		}
+	}
+	return false
+}