Add GetSpanDetails option

tracing/opencensus/endpoint.go

@@ -31,14 +31,25 @@ func TraceEndpoint(name string, options ...EndpointOption) endpoint.Middleware {
 
 	return func(next endpoint.Endpoint) endpoint.Endpoint {
 		return func(ctx context.Context, request interface{}) (response interface{}, err error) {
-			if name == TraceEndpointDefaultName && cfg.GetSpanName != nil {
-				name = cfg.GetSpanName(ctx)
+			var attributes []trace.Attribute
+
+			if cfg.GetSpanDetails != nil {
+				var newName string
+
+				newName, attributes = cfg.GetSpanDetails(ctx, name)
+
+				if newName != "" {
+					name = newName
+				}
 			}
 
 			ctx, span := trace.StartSpan(ctx, name)
 			if len(cfg.Attributes) > 0 {
 				span.AddAttributes(cfg.Attributes...)
 			}
+			if len(attributes) > 0 {
+				span.AddAttributes(attributes...)
+			}
 			defer span.End()
 
 			defer func() {

tracing/opencensus/endpoint_options.go

@@ -16,10 +16,12 @@ type EndpointOptions struct {
 	// creation by our Endpoint middleware.
 	Attributes []trace.Attribute
 
-	// GetSpanName holds the function to use for generating the span name
-	// from the information found in the incoming Request.
-	// Defaults to the name that the middleware was initialized with.
-	GetSpanName func(ctx context.Context) string
+	// GetSpanDetails holds the function to use for generating the span name
+	// based on the current name and from the information found in the incoming Request.
+	// It can also return additional attributes for the span.
+	//
+	// A returned empty name defaults to the name that the middleware was initialized with.
+	GetSpanDetails func(ctx context.Context, name string) (string, []trace.Attribute)
 }
 
 // EndpointOption allows for functional options to our OpenCensus endpoint
@@ -49,3 +51,10 @@ func WithIgnoreBusinessError(val bool) EndpointOption {
 		o.IgnoreBusinessError = val
 	}
 }
+
+// WithSpanDetails extracts details from the request context (like span name and additional attributes).
+func WithSpanDetails(fn func(ctx context.Context, name string) (string, []trace.Attribute)) EndpointOption {
+	return func(o *EndpointOptions) {
+		o.GetSpanDetails = fn
+	}
+}

tracing/opencensus/endpoint_test.go

@@ -82,10 +82,16 @@ func TestTraceEndpoint(t *testing.T) {
 	mw(passEndpoint)(ctx, failedResponse{err: err4})
 
 	// span6
-	opts = opencensus.EndpointOptions{GetSpanName: func(ctx context.Context) string {
-		return span6
-	}}
-	mw = opencensus.TraceEndpoint("", opencensus.WithEndpointConfig(opts))
+	span6Attrs := []trace.Attribute{
+		trace.StringAttribute("string", "value"),
+		trace.Int64Attribute("int64", 42),
+	}
+	mw = opencensus.TraceEndpoint(
+		"",
+		opencensus.WithSpanDetails(func(ctx context.Context, name string) (string, []trace.Attribute) {
+			return span6, span6Attrs
+		}),
+	)
 	mw(endpoint.Nop)(ctx, nil)
 
 	// check span count
@@ -169,4 +175,8 @@ func TestTraceEndpoint(t *testing.T) {
 	if want, have := span6, span.Name; want != have {
 		t.Errorf("incorrect span name, wanted %q, got %q", want, have)
 	}
+
+	if want, have := 2, len(span.Attributes); want != have {
+		t.Fatalf("incorrect attribute count, wanted %d, got %d", want, have)
+	}
 }