plugin/trace: make zipkin and datadog reporters log errors using CoreDNS logger (#5452)

plugin/trace/logger.go

+package trace
+
+import (
+	clog "github.com/coredns/coredns/plugin/pkg/log"
+)
+
+// loggerAdapter is a simple adapter around plugin logger made to implement io.Writer and ddtrace.Logger interface
+// in order to log errors from span reporters as warnings
+type loggerAdapter struct {
+	clog.P
+}
+
+func (l *loggerAdapter) Write(p []byte) (n int, err error) {
+	l.P.Warning(string(p))
+	return len(p), nil
+}
+
+func (l *loggerAdapter) Log(msg string) {
+	l.P.Warning(msg)
+}

plugin/trace/trace.go

@@ -4,6 +4,7 @@ package trace
 import (
 	"context"
 	"fmt"
+	stdlog "log"
 	"net/http"
 	"sync"
 	"sync/atomic"
@@ -12,7 +13,7 @@ import (
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/metadata"
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
-	"github.com/coredns/coredns/plugin/pkg/log"
+	clog "github.com/coredns/coredns/plugin/pkg/log"
 	"github.com/coredns/coredns/plugin/pkg/rcode"
 	_ "github.com/coredns/coredns/plugin/pkg/trace" // Plugin the trace package.
 	"github.com/coredns/coredns/request"
@@ -35,6 +36,8 @@ const (
 	metaTraceIdKey          = "trace/traceid"
 )
 
+var log = clog.NewWithPlugin("trace")
+
 type traceTags struct {
 	Name   string
 	Type   string
@@ -90,10 +93,11 @@ func (t *trace) OnStartup() error {
 		case "datadog":
 			tracer := opentracer.New(
 				tracer.WithAgentAddr(t.Endpoint),
-				tracer.WithDebugMode(log.D.Value()),
+				tracer.WithDebugMode(clog.D.Value()),
 				tracer.WithGlobalTag(ext.SpanTypeDNS, true),
 				tracer.WithServiceName(t.serviceName),
 				tracer.WithAnalyticsRate(t.datadogAnalyticsRate),
+				tracer.WithLogger(&loggerAdapter{log}),
 			)
 			t.tracer = tracer
 			t.tagSet = tagByProvider["datadog"]
@@ -105,7 +109,8 @@ func (t *trace) OnStartup() error {
 }
 
 func (t *trace) setupZipkin() error {
-	reporter := zipkinhttp.NewReporter(t.Endpoint)
+	logOpt := zipkinhttp.Logger(stdlog.New(&loggerAdapter{log}, "", 0))
+	reporter := zipkinhttp.NewReporter(t.Endpoint, logOpt)
 	recorder, err := zipkin.NewEndpoint(t.serviceName, t.serviceEndpoint)
 	if err != nil {
 		log.Warningf("build Zipkin endpoint found err: %v", err)