Fix: TraceClient crashed in absense of a parentSpan in Context

Added TestTraceClientNoContextSpan to test for this situation

tracing/opentracing/endpoint.go

@@ -36,11 +36,15 @@ func TraceServer(tracer opentracing.Tracer, operationName string) endpoint.Middl
 func TraceClient(tracer opentracing.Tracer, operationName string) endpoint.Middleware {
 	return func(next endpoint.Endpoint) endpoint.Endpoint {
 		return func(ctx context.Context, request interface{}) (interface{}, error) {
-			parentSpan := opentracing.SpanFromContext(ctx)
-			clientSpan := tracer.StartSpan(
-				operationName,
-				opentracing.ChildOf(parentSpan.Context()),
-			)
+			var clientSpan opentracing.Span
+			if parentSpan := opentracing.SpanFromContext(ctx); parentSpan != nil {
+				clientSpan = tracer.StartSpan(
+					operationName,
+					opentracing.ChildOf(parentSpan.Context()),
+				)
+			} else {
+				clientSpan = tracer.StartSpan(operationName)
+			}
 			defer clientSpan.Finish()
 			otext.SpanKind.Set(clientSpan, otext.SpanKindRPCClient)
 			ctx = opentracing.ContextWithSpan(ctx, clientSpan)

tracing/opentracing/endpoint_test.go

@@ -94,3 +94,24 @@ func TestTraceClient(t *testing.T) {
 		t.Errorf("Want ParentID %q, have %q", want, have)
 	}
 }
+
+func TestTraceClientNoContextSpan(t *testing.T) {
+	tracer := mocktracer.New()
+
+	// Empty/background context.
+	tracedEndpoint := kitot.TraceClient(tracer, "testOp")(endpoint.Nop)
+	if _, err := tracedEndpoint(context.Background(), struct{}{}); err != nil {
+		t.Fatal(err)
+	}
+
+	// tracedEndpoint created a new Span.
+	finishedSpans := tracer.GetFinishedSpans()
+	if want, have := 1, len(finishedSpans); want != have {
+		t.Fatalf("Want %v span(s), found %v", want, have)
+	}
+
+	endpointSpan := finishedSpans[0]
+	if want, have := "testOp", endpointSpan.OperationName; want != have {
+		t.Fatalf("Want %q, have %q", want, have)
+	}
+}