contrib/net/http: add dynamic resource naming

contrib/net/http/http.go

@@ -53,6 +53,7 @@ func (mux *ServeMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 // WrapHandler wraps an http.Handler with tracing using the given service and resource.
+// If the WithResourceNamer option is provided as part of opts, it will take precedence over the resource argument.
 func WrapHandler(h http.Handler, service, resource string, opts ...Option) http.Handler {
 	cfg := new(config)
 	defaults(cfg)
@@ -65,6 +66,9 @@ func WrapHandler(h http.Handler, service, resource string, opts ...Option) http.
 			h.ServeHTTP(w, req)
 			return
 		}
+		if dynamicResource := cfg.resourceNamer(req); dynamicResource != "" {
+			resource = dynamicResource
+		}
 		TraceAndServe(h, w, req, &ServeConfig{
 			Service:    service,
 			Resource:   resource,

contrib/net/http/option.go

@@ -22,6 +22,7 @@ type config struct {
 	spanOpts      []ddtrace.StartSpanOption
 	finishOpts    []ddtrace.FinishOption
 	ignoreRequest func(*http.Request) bool
+	resourceNamer func(*http.Request) string
 }
 
 // MuxOption has been deprecated in favor of Option.
@@ -45,6 +46,7 @@ func defaults(cfg *config) {
 		cfg.spanOpts = append(cfg.spanOpts, tracer.Tag(ext.EventSampleRate, cfg.analyticsRate))
 	}
 	cfg.ignoreRequest = func(_ *http.Request) bool { return false }
+	cfg.resourceNamer = func(_ *http.Request) string { return "" }
 }
 
 // WithIgnoreRequest holds the function to use for determining if the
@@ -95,6 +97,13 @@ func WithSpanOptions(opts ...ddtrace.StartSpanOption) Option {
 	}
 }
 
+// WithResourceNamer populates the name of a resource based on a custom function.
+func WithResourceNamer(namer func(req *http.Request) string) Option {
+	return func(cfg *config) {
+		cfg.resourceNamer = namer
+	}
+}
+
 // NoDebugStack prevents stack traces from being attached to spans finishing
 // with an error. This is useful in situations where errors are frequent and
 // performance is critical.