fix: use EscapedPath as header value when RawPath is empty

pkg/middlewares/replacepathregex/replace_path_regex.go

@@ -16,9 +16,7 @@ import (
 	"github.com/traefik/traefik/v2/pkg/tracing"
 )
 
-const (
-	typeName = "ReplacePathRegex"
-)
+const typeName = "ReplacePathRegex"
 
 // ReplacePathRegex is a middleware used to replace the path of a URL request with a regular expression.
 type replacePathRegex struct {
@@ -50,16 +48,13 @@ func (rp *replacePathRegex) GetTracingInformation() (string, ext.SpanKindEnum) {
 }
 
 func (rp *replacePathRegex) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
-	var currentPath string
-	if req.URL.RawPath == "" {
-		currentPath = req.URL.Path
-	} else {
-		currentPath = req.URL.RawPath
+	currentPath := req.URL.RawPath
+	if currentPath == "" {
+		currentPath = req.URL.EscapedPath()
 	}
 
 	if rp.regexp != nil && len(rp.replacement) > 0 && rp.regexp.MatchString(currentPath) {
 		req.Header.Add(replacepath.ReplacedPathHeader, currentPath)
-
 		req.URL.RawPath = rp.regexp.ReplaceAllString(currentPath, rp.replacement)
 
 		// as replacement can introduce escaped characters

pkg/middlewares/replacepathregex/replace_path_regex_test.go

@@ -106,6 +106,16 @@ func TestReplacePathRegex(t *testing.T) {
 			expectedPath:    "/aaa/bbb",
 			expectedRawPath: "/aaa%2Fbbb",
 		},
+		{
+			desc: "path with percent encoded backspace char",
+			path: "/foo/%08bar",
+			config: dynamic.ReplacePathRegex{
+				Replacement: "/$1",
+				Regex:       `^/foo/(.*)`,
+			},
+			expectedPath:    "/\bbar",
+			expectedRawPath: "/%08bar",
+		},
 	}
 
 	for _, test := range testCases {