contrib/gin-gonic/gin: support globalconfig.ServiceName()

This change adds support for `globalconfig.ServiceName()` to the gin
trace middleware. Because this middleware does not follow the same pattern
as other http frameworks and requires a service parameter to be passed in
we use the empty string value as an indicator that the default service
name should be used.

Fixes DataDog#767

contrib/gin-gonic/gin/gintrace.go

@@ -19,16 +19,17 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// Middleware returns middleware that will trace incoming requests.
+// Middleware returns middleware that will trace incoming requests. If service is empty then the
+// default service name will be used.
 func Middleware(service string, opts ...Option) gin.HandlerFunc {
-	cfg := newConfig()
+	cfg := newConfig(service)
 	for _, opt := range opts {
 		opt(cfg)
 	}
 	return func(c *gin.Context) {
 		resource := cfg.resourceNamer(c)
 		opts := []ddtrace.StartSpanOption{
-			tracer.ServiceName(service),
+			tracer.ServiceName(cfg.serviceName),
 			tracer.ResourceName(resource),
 			tracer.SpanType(ext.SpanTypeWeb),
 			tracer.Tag(ext.HTTPMethod, c.Request.Method),

contrib/gin-gonic/gin/gintrace_test.go

@@ -339,3 +339,95 @@ func TestResourceNamerSettings(t *testing.T) {
 		router.ServeHTTP(w, r)
 	})
 }
+
+func TestServiceName(t *testing.T) {
+	t.Run("default", func(t *testing.T) {
+		assert := assert.New(t)
+		mt := mocktracer.Start()
+		defer mt.Stop()
+
+		router := gin.New()
+		router.Use(Middleware(""))
+		router.GET("/ping", func(c *gin.Context) {
+			span, ok := tracer.SpanFromContext(c.Request.Context())
+			assert.True(ok)
+			assert.Equal(span.(mocktracer.Span).Tag(ext.ServiceName), "gin.router")
+			c.Status(200)
+		})
+
+		r := httptest.NewRequest("GET", "/ping", nil)
+		w := httptest.NewRecorder()
+
+		// do and verify the request
+		router.ServeHTTP(w, r)
+		response := w.Result()
+		assert.Equal(response.StatusCode, 200)
+
+		// verify traces look good
+		spans := mt.FinishedSpans()
+		assert.Len(spans, 1)
+		span := spans[0]
+		assert.Equal("gin.router", span.Tag(ext.ServiceName))
+	})
+
+	t.Run("global", func(t *testing.T) {
+		globalconfig.SetServiceName("global-service")
+		defer globalconfig.SetServiceName("")
+
+		assert := assert.New(t)
+		mt := mocktracer.Start()
+		defer mt.Stop()
+
+		router := gin.New()
+		router.Use(Middleware(""))
+		router.GET("/ping", func(c *gin.Context) {
+			span, ok := tracer.SpanFromContext(c.Request.Context())
+			assert.True(ok)
+			assert.Equal(span.(mocktracer.Span).Tag(ext.ServiceName), "global-service")
+			c.Status(200)
+		})
+
+		r := httptest.NewRequest("GET", "/ping", nil)
+		w := httptest.NewRecorder()
+
+		// do and verify the request
+		router.ServeHTTP(w, r)
+		response := w.Result()
+		assert.Equal(response.StatusCode, 200)
+
+		// verify traces look good
+		spans := mt.FinishedSpans()
+		assert.Len(spans, 1)
+		span := spans[0]
+		assert.Equal("global-service", span.Tag(ext.ServiceName))
+	})
+
+	t.Run("custom", func(t *testing.T) {
+		assert := assert.New(t)
+		mt := mocktracer.Start()
+		defer mt.Stop()
+
+		router := gin.New()
+		router.Use(Middleware("my-service"))
+		router.GET("/ping", func(c *gin.Context) {
+			span, ok := tracer.SpanFromContext(c.Request.Context())
+			assert.True(ok)
+			assert.Equal(span.(mocktracer.Span).Tag(ext.ServiceName), "my-service")
+			c.Status(200)
+		})
+
+		r := httptest.NewRequest("GET", "/ping", nil)
+		w := httptest.NewRecorder()
+
+		// do and verify the request
+		router.ServeHTTP(w, r)
+		response := w.Result()
+		assert.Equal(response.StatusCode, 200)
+
+		// verify traces look good
+		spans := mt.FinishedSpans()
+		assert.Len(spans, 1)
+		span := spans[0]
+		assert.Equal("my-service", span.Tag(ext.ServiceName))
+	})
+}

contrib/gin-gonic/gin/option.go

@@ -17,16 +17,24 @@ import (
 type config struct {
 	analyticsRate float64
 	resourceNamer func(c *gin.Context) string
+	serviceName   string
 }
 
-func newConfig() *config {
+func newConfig(service string) *config {
+	if service == "" {
+		service = "gin.router"
+		if svc := globalconfig.ServiceName(); svc != "" {
+			service = svc
+		}
+	}
 	rate := globalconfig.AnalyticsRate()
 	if internal.BoolEnv("DD_TRACE_GIN_ANALYTICS_ENABLED", false) {
 		rate = 1.0
 	}
 	return &config{
 		analyticsRate: rate,
 		resourceNamer: defaultResourceNamer,
+		serviceName:   service,
 	}
 }