contrib/gorilla/mux: add a router monitoring wrapper (#1175)

contrib/gorilla/mux/mux.go

@@ -7,13 +7,11 @@
 package mux // import "gopkg.in/DataDog/dd-trace-go.v1/contrib/gorilla/mux"
 
 import (
-	"math"
 	"net/http"
 	"strings"
 
 	httptrace "gopkg.in/DataDog/dd-trace-go.v1/contrib/net/http"
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
-	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
 	"gopkg.in/DataDog/dd-trace-go.v1/internal/log"
 
@@ -76,20 +74,7 @@ func (r *Router) UseEncodedPath() *Router {
 
 // NewRouter returns a new router instance traced with the global tracer.
 func NewRouter(opts ...RouterOption) *Router {
-	cfg := new(routerConfig)
-	defaults(cfg)
-	for _, fn := range opts {
-		fn(cfg)
-	}
-	if !math.IsNaN(cfg.analyticsRate) {
-		cfg.spanOpts = append(cfg.spanOpts, tracer.Tag(ext.EventSampleRate, cfg.analyticsRate))
-	}
-	cfg.spanOpts = append(cfg.spanOpts, tracer.Measured())
-	log.Debug("contrib/gorilla/mux: Configuring Router: %#v", cfg)
-	return &Router{
-		Router: mux.NewRouter(),
-		config: cfg,
-	}
+	return WrapRouter(mux.NewRouter(), opts...)
 }
 
 // ServeHTTP dispatches the request to the handler
@@ -126,6 +111,17 @@ func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	})
 }
 
+// WrapRouter returns the given router wrapped with the tracing of the HTTP
+// requests and responses served by the router.
+func WrapRouter(router *mux.Router, opts ...RouterOption) *Router {
+	cfg := newConfig(opts)
+	log.Debug("contrib/gorilla/mux: Configuring Router: %#v", cfg)
+	return &Router{
+		Router: router,
+		config: cfg,
+	}
+}
+
 // defaultResourceNamer attempts to quantize the resource for an HTTP request by
 // retrieving the path template associated with the route from the request.
 func defaultResourceNamer(router *Router, req *http.Request) string {

contrib/gorilla/mux/option.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
+	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/ext"
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer"
 	"gopkg.in/DataDog/dd-trace-go.v1/internal"
 	"gopkg.in/DataDog/dd-trace-go.v1/internal/globalconfig"
@@ -29,6 +30,19 @@ type routerConfig struct {
 // RouterOption represents an option that can be passed to NewRouter.
 type RouterOption func(*routerConfig)
 
+func newConfig(opts []RouterOption) *routerConfig {
+	cfg := new(routerConfig)
+	defaults(cfg)
+	for _, fn := range opts {
+		fn(cfg)
+	}
+	if !math.IsNaN(cfg.analyticsRate) {
+		cfg.spanOpts = append(cfg.spanOpts, tracer.Tag(ext.EventSampleRate, cfg.analyticsRate))
+	}
+	cfg.spanOpts = append(cfg.spanOpts, tracer.Measured())
+	return cfg
+}
+
 func defaults(cfg *routerConfig) {
 	if internal.BoolEnv("DD_TRACE_MUX_ANALYTICS_ENABLED", false) {
 		cfg.analyticsRate = 1.0