Headers response modifier is directly applied by headers middleware

Co-authored-by: Ludovic Fernandez <ldez@users.noreply.github.com>

pkg/server/service/internalhandler.go

@@ -8,11 +8,10 @@ import (
 	"strings"
 
 	"github.com/containous/traefik/v2/pkg/config/runtime"
-	"github.com/containous/traefik/v2/pkg/log"
 )
 
 type serviceManager interface {
-	BuildHTTP(rootCtx context.Context, serviceName string, responseModifier func(*http.Response) error) (http.Handler, error)
+	BuildHTTP(rootCtx context.Context, serviceName string) (http.Handler, error)
 	LaunchHealthCheck()
 }
 
@@ -43,87 +42,18 @@ func NewInternalHandlers(api func(configuration *runtime.Configuration) http.Han
 	}
 }
 
-type responseModifier struct {
-	r *http.Request
-	w http.ResponseWriter
-
-	headersSent bool // whether headers have already been sent
-	code        int  // status code, must default to 200
-
-	modifier    func(*http.Response) error // can be nil
-	modified    bool                       // whether modifier has already been called for the current request
-	modifierErr error                      // returned by modifier call
-}
-
-// modifier can be nil.
-func newResponseModifier(w http.ResponseWriter, r *http.Request, modifier func(*http.Response) error) *responseModifier {
-	return &responseModifier{
-		r:        r,
-		w:        w,
-		modifier: modifier,
-		code:     http.StatusOK,
-	}
-}
-
-func (w *responseModifier) WriteHeader(code int) {
-	if w.headersSent {
-		return
-	}
-	defer func() {
-		w.code = code
-		w.headersSent = true
-	}()
-
-	if w.modifier == nil || w.modified {
-		w.w.WriteHeader(code)
-		return
-	}
-
-	resp := http.Response{
-		Header:  w.w.Header(),
-		Request: w.r,
-	}
-
-	if err := w.modifier(&resp); err != nil {
-		w.modifierErr = err
-		// we are propagating when we are called in Write, but we're logging anyway,
-		// because we could be called from another place which does not take care of
-		// checking w.modifierErr.
-		log.Errorf("Error when applying response modifier: %v", err)
-		w.w.WriteHeader(http.StatusInternalServerError)
-		return
-	}
-
-	w.modified = true
-	w.w.WriteHeader(code)
-}
-
-func (w *responseModifier) Header() http.Header {
-	return w.w.Header()
-}
-
-func (w *responseModifier) Write(b []byte) (int, error) {
-	w.WriteHeader(w.code)
-	if w.modifierErr != nil {
-		return 0, w.modifierErr
-	}
-
-	return w.w.Write(b)
-}
-
 // BuildHTTP builds an HTTP handler.
-func (m *InternalHandlers) BuildHTTP(rootCtx context.Context, serviceName string, respModifier func(*http.Response) error) (http.Handler, error) {
+func (m *InternalHandlers) BuildHTTP(rootCtx context.Context, serviceName string) (http.Handler, error) {
 	if !strings.HasSuffix(serviceName, "@internal") {
-		return m.serviceManager.BuildHTTP(rootCtx, serviceName, respModifier)
+		return m.serviceManager.BuildHTTP(rootCtx, serviceName)
 	}
 
 	internalHandler, err := m.get(serviceName)
 	if err != nil {
 		return nil, err
 	}
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		internalHandler.ServeHTTP(newResponseModifier(w, r, respModifier), r)
-	}), nil
+
+	return internalHandler, nil
 }
 
 func (m *InternalHandlers) get(serviceName string) (http.Handler, error) {