Simplify the logic in the opencensus interceptor. (#58)

interceptor/opencensus/opencensus.go

@@ -62,17 +62,6 @@ var errTraceExportProtocolViolation = errors.New("protocol violation: Export's f
 // Export is the gRPC method that receives streamed traces from
 // OpenCensus-traceproto compatible libraries/applications.
 func (oci *OCInterceptor) Export(tes agenttracepb.TraceService_ExportServer) error {
-	// The first message MUST have a non-nil Node.
-	firstMessage, err := tes.Recv()
-	if err != nil {
-		return err
-	}
-
-	if firstMessage.Node == nil {
-		return errTraceExportProtocolViolation
-	}
-
-	// Now that we've got the node, we can start to receive streamed up spans.
 	// The bundler will receive batches of spans i.e. []*tracepb.Span
 	traceBundler := bundler.NewBundler((*spansAndNode)(nil), oci.batchSpanExporting)
 	spanBufferPeriod := oci.spanBufferPeriod
@@ -88,30 +77,36 @@ func (oci *OCInterceptor) Export(tes agenttracepb.TraceService_ExportServer) err
 	traceBundler.DelayThreshold = spanBufferPeriod
 	traceBundler.BundleCountThreshold = spanBufferCount
 
-	var lastNonNilNode *commonpb.Node = firstMessage.Node
+	// The first message MUST have a non-nil Node.
+	recv, err := tes.Recv()
+	if err != nil {
+		return err
+	}
 
-	// If the firstMessage has spans, we MUST add them
-	// See https://github.com/census-instrumentation/opencensus-service/issues/51
-	if len(firstMessage.Spans) > 0 {
-		firstPayload := &spansAndNode{node: lastNonNilNode, spans: firstMessage.Spans}
-		traceBundler.Add(firstPayload, len(firstPayload.spans))
+	// Check the condition that the first message has a non-nil Node.
+	if recv.Node == nil {
+		return errTraceExportProtocolViolation
 	}
 
-	for {
-		recv, err := tes.Recv()
-		if err != nil {
-			return err
-		}
+	var lastNonNilNode *commonpb.Node
 
+	// Now that we've got the first message with a Node, we can start to receive streamed up spans.
+	for {
 		// If a Node has been sent from downstream, save and use it.
-		node := recv.Node
-		if node != nil {
-			lastNonNilNode = node
+		if recv.Node != nil {
+			lastNonNilNode = recv.Node
 		}
 
 		// Otherwise add them to the bundler.
-		bundlerPayload := &spansAndNode{node: lastNonNilNode, spans: recv.Spans}
-		traceBundler.Add(bundlerPayload, len(bundlerPayload.spans))
+		if len(recv.Spans) > 0 {
+			bundlerPayload := &spansAndNode{node: lastNonNilNode, spans: recv.Spans}
+			traceBundler.Add(bundlerPayload, len(bundlerPayload.spans))
+		}
+
+		recv, err = tes.Recv()
+		if err != nil {
+			return err
+		}
 	}
 }