contrib/gin-gonic: add option to ignore request (#1061)

This commit adds an option allowing users to configure a function which
decides whether a request should be traced or not.

Fixes #1060

contrib/gin-gonic/gin/gintrace.go

@@ -29,6 +29,9 @@ func Middleware(service string, opts ...Option) gin.HandlerFunc {
 	}
 	log.Debug("contrib/gin-gonic/gin: Configuring Middleware: Service: %s, %#v", service, cfg)
 	return func(c *gin.Context) {
+		if cfg.ignoreRequest(c) {
+			return
+		}
 		resource := cfg.resourceNamer(c)
 		opts := []ddtrace.StartSpanOption{
 			tracer.ServiceName(cfg.serviceName),

contrib/gin-gonic/gin/gintrace_test.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"html/template"
 	"net/http/httptest"
+	"strings"
 	"testing"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
@@ -340,6 +341,34 @@ func TestResourceNamerSettings(t *testing.T) {
 	})
 }
 
+func TestIgnoreRequestSettings(t *testing.T) {
+	router := gin.New()
+	router.Use(Middleware("foobar", WithIgnoreRequest(func(c *gin.Context) bool {
+		return strings.HasPrefix(c.Request.URL.Path, "/skip")
+	})))
+
+	router.GET("/OK", func(c *gin.Context) {
+		c.Writer.Write([]byte("OK"))
+	})
+
+	router.GET("/skip", func(c *gin.Context) {
+		c.Writer.Write([]byte("Skip"))
+	})
+
+	for path, shouldSkip := range map[string]bool{
+		"/OK":      false,
+		"/skip":    true,
+		"/skipfoo": true,
+	} {
+		mt := mocktracer.Start()
+		defer mt.Reset()
+
+		r := httptest.NewRequest("GET", "http://localhost"+path, nil)
+		router.ServeHTTP(httptest.NewRecorder(), r)
+		assert.Equal(t, shouldSkip, len(mt.FinishedSpans()) == 0)
+	}
+}
+
 func TestServiceName(t *testing.T) {
 	t.Run("default", func(t *testing.T) {
 		assert := assert.New(t)

contrib/gin-gonic/gin/option.go

@@ -19,6 +19,7 @@ type config struct {
 	analyticsRate float64
 	resourceNamer func(c *gin.Context) string
 	serviceName   string
+	ignoreRequest func(c *gin.Context) bool
 }
 
 func newConfig(service string) *config {
@@ -36,6 +37,7 @@ func newConfig(service string) *config {
 		analyticsRate: rate,
 		resourceNamer: defaultResourceNamer,
 		serviceName:   service,
+		ignoreRequest: func(_ *gin.Context) bool { return false },
 	}
 }
 
@@ -73,6 +75,14 @@ func WithResourceNamer(namer func(c *gin.Context) string) Option {
 	}
 }
 
+// WithIgnoreRequest specifies a function to use for determining if the
+// incoming HTTP request tracing should be skipped.
+func WithIgnoreRequest(f func(c *gin.Context) bool) Option {
+	return func(cfg *config) {
+		cfg.ignoreRequest = f
+	}
+}
+
 func defaultResourceNamer(c *gin.Context) string {
 	// getName is a hacky way to check whether *gin.Context implements the FullPath()
 	// method introduced in v1.4.0, falling back to the previous implementation otherwise.