contrib/google.golang.org/grpc: add hostname tag (#2361)

contrib/google.golang.org/grpc/client.go

@@ -97,7 +97,7 @@ func StreamClientInterceptor(opts ...Option) grpc.StreamClientInterceptor {
 				span tracer.Span
 				err  error
 			)
-			span, ctx, err = doClientRequest(ctx, cfg, method, methodKind, opts,
+			span, ctx, err = doClientRequest(ctx, cfg, method, methodKind, cc, opts,
 				func(ctx context.Context, opts []grpc.CallOption) error {
 					var err error
 					stream, err = streamer(ctx, desc, cc, method, opts...)
@@ -154,7 +154,7 @@ func UnaryClientInterceptor(opts ...Option) grpc.UnaryClientInterceptor {
 		if _, ok := cfg.untracedMethods[method]; ok {
 			return invoker(ctx, method, req, reply, cc, opts...)
 		}
-		span, _, err := doClientRequest(ctx, cfg, method, methodKindUnary, opts,
+		span, _, err := doClientRequest(ctx, cfg, method, methodKindUnary, cc, opts,
 			func(ctx context.Context, opts []grpc.CallOption) error {
 				return invoker(ctx, method, req, reply, cc, opts...)
 			})
@@ -166,7 +166,7 @@ func UnaryClientInterceptor(opts ...Option) grpc.UnaryClientInterceptor {
 // doClientRequest starts a new span and invokes the handler with the new context
 // and options. The span should be finished by the caller.
 func doClientRequest(
-	ctx context.Context, cfg *config, method string, methodKind string, opts []grpc.CallOption,
+	ctx context.Context, cfg *config, method string, methodKind string, cc *grpc.ClientConn, opts []grpc.CallOption,
 	handler func(ctx context.Context, opts []grpc.CallOption) error,
 ) (ddtrace.Span, context.Context, error) {
 	// inject the trace id into the metadata
@@ -182,7 +182,11 @@ func doClientRequest(
 	if methodKind != "" {
 		span.SetTag(tagMethodKind, methodKind)
 	}
-
+	if cc != nil {
+		if host, _, err := net.SplitHostPort(cc.Target()); err == nil {
+			span.SetTag(ext.PeerHostname, host)
+		}
+	}
 	// fill in the peer so we can add it to the tags
 	var p peer.Peer
 	opts = append(opts, grpc.Peer(&p))
@@ -199,10 +203,10 @@ func doClientRequest(
 func setSpanTargetFromPeer(span ddtrace.Span, p peer.Peer) {
 	// if the peer was set, set the tags
 	if p.Addr != nil {
-		host, port, err := net.SplitHostPort(p.Addr.String())
+		ip, port, err := net.SplitHostPort(p.Addr.String())
 		if err == nil {
-			if host != "" {
-				span.SetTag(ext.TargetHost, host)
+			if ip != "" {
+				span.SetTag(ext.TargetHost, ip)
 			}
 			span.SetTag(ext.TargetPort, port)
 		}

contrib/google.golang.org/grpc/grpc_test.go

@@ -102,7 +102,9 @@ func TestUnary(t *testing.T) {
 			assert.NotNil(clientSpan)
 			assert.NotNil(rootSpan)
 
+			// this tag always contains the resolved address
 			assert.Equal(clientSpan.Tag(ext.TargetHost), "127.0.0.1")
+			assert.Equal(clientSpan.Tag(ext.PeerHostname), "localhost")
 			assert.Equal(clientSpan.Tag(ext.TargetPort), rig.port)
 			assert.Equal(clientSpan.Tag(tagCode), tt.wantCode.String())
 			assert.Equal(clientSpan.TraceID(), rootSpan.TraceID())
@@ -173,6 +175,7 @@ func TestStreaming(t *testing.T) {
 			case "grpc.client":
 				assert.Equal(t, "127.0.0.1", span.Tag(ext.TargetHost),
 					"expected target host tag to be set in span: %v", span)
+				assert.Equal(t, "localhost", span.Tag(ext.PeerHostname))
 				assert.Equal(t, rig.port, span.Tag(ext.TargetPort),
 					"expected target host port to be set in span: %v", span)
 				fallthrough
@@ -617,7 +620,7 @@ func newRigWithInterceptors(
 	// start our test fixtureServer.
 	go server.Serve(li)
 
-	conn, err := grpc.Dial(li.Addr().String(), clientInterceptors...)
+	conn, err := grpc.Dial("localhost:"+port, clientInterceptors...)
 	if err != nil {
 		return nil, fmt.Errorf("error dialing: %s", err)
 	}