WIP: instrument net/http.ServeHTTP implementations

TODO - description

Fixes #173

_integration-tests/tests/net_http/net_http.go

@@ -26,6 +26,22 @@ type TestCase struct {
  *http.Server
 }
 
+type handler struct{}
+
+func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+ defer r.Body.Close()
+
+ b, err := io.ReadAll(r.Body)
+ if err != nil {
+ w.WriteHeader(http.StatusBadRequest)
+ w.Write([]byte(err.Error()))
+ return
+ }
+
+ w.WriteHeader(http.StatusOK)
+ w.Write(b)
+}
+
 func (tc *TestCase) Setup(t *testing.T) {
  mux := http.NewServeMux()
  tc.Server = &http.Server{
@@ -35,6 +51,21 @@ func (tc *TestCase) Setup(t *testing.T) {
 
  mux.HandleFunc("/hit", tc.handleHit)
  mux.HandleFunc("/", tc.handleRoot)
+ // TODO: hit these endpoints, check for spans
+ mux.Handle("/handler", handler{})
+ mux.HandleFunc("/literal", func(w http.ResponseWriter, r *http.Request) {
+ defer r.Body.Close()
+
+ b, err := io.ReadAll(r.Body)
+ if err != nil {
+ w.WriteHeader(http.StatusBadRequest)
+ w.Write([]byte(err.Error()))
+ return
+ }
+
+ w.WriteHeader(http.StatusOK)
+ w.Write(b)
+ })
 
  go func() { assert.ErrorIs(t, tc.Server.ListenAndServe(), http.ErrServerClosed) }()
 }

instrument/http.go

@@ -21,6 +21,24 @@ func resourceNamer(r *http.Request) string {
  return fmt.Sprintf("%s %s", r.Method, r.URL.Path)
 }
 
+// MaybeWrapHandler instruments an http.Handler if it is nil or an *http.ServeMux,
+// and otherwise returns the same handler.
+// This is intended for instrumenting http.ListenAndServe, etc,
+// where we may already be passed an instrumented handler.
+// We assume it is already instrumented unless it's a net/http handler.
+func MaybeWrapHandler(handler http.Handler) http.Handler {
+ if handler == nil {
+ handler = http.DefaultServeMux
+ }
+ switch handler.(type) {
+ case *http.ServeMux, *http.HandlerFunc:
+ return WrapHandler(handler)
+ default:
+ // Don't change it, it may have already been instrumented
+ return handler
+ }
+}
+
 func WrapHandler(handler http.Handler) http.Handler {
  return httptrace.WrapHandler(handler, "", "", httptrace.WithResourceNamer(resourceNamer))
  // TODO: We'll reintroduce this later when we stop hard-coding dd-trace-go as above.