rewrite: preserve non-canonical path encoding after uri replace (#7907)

changePath cleared RawPath whenever it equalled url.Path, which
discarded a valid non-canonical percent-encoding produced by a
replacement. This compare `RawPath` against the default escaping of Path
instead.

modules/caddyhttp/rewrite/rewrite.go

@@ -513,12 +513,21 @@ func changePath(req *http.Request, newVal func(pathOrRawPath string) string) {
 	} else {
 		req.URL.Path = newVal(req.URL.Path)
 	}
-	// RawPath is only set if it's different from the normalized Path (std lib)
-	if req.URL.RawPath == req.URL.Path {
+	// RawPath is only needed if it is a valid, non-canonical encoding of Path;
+	// (see #6578). Mirror net/url.URL.setPath by comparing against the default
+	// escaping of Path instead.
+	if req.URL.RawPath == defaultEscapedPath(req.URL.Path) {
 		req.URL.RawPath = ""
 	}
 }
 
+// defaultEscapedPath returns the canonical percent-encoding of p, matching
+// what net/url.URL.EscapedPath() produces when RawPath is empty. It mirrors
+// the comparison net/url.URL.setPath uses to decide whether RawPath is needed.
+func defaultEscapedPath(p string) string {
+	return (&url.URL{Path: p}).EscapedPath()
+}
+
 // queryOps describes the operations to perform on query keys: add, set, rename and delete.
 type queryOps struct {
 	// Renames a query key from Key to Val, without affecting the value.

modules/caddyhttp/rewrite/rewrite_test.go

@@ -351,6 +351,19 @@ func TestRewrite(t *testing.T) {
 			input:  newRequest(t, "GET", "/foo/findme%2Fbar"),
 			expect: newRequest(t, "GET", "/foo/replaced%2Fbar"),
 		},
+		{
+			rule:   Rewrite{URISubstring: []substrReplacer{{Find: "%28", Replace: "("}}},
+			input:  newRequest(t, "GET", "/hello/%28%29"),
+			expect: newRequest(t, "GET", "/hello/(%29"),
+		},
+		{
+			rule: Rewrite{URISubstring: []substrReplacer{
+				{Find: "%28", Replace: "("},
+				{Find: "%29", Replace: ")"},
+			}},
+			input:  newRequest(t, "GET", "/hello/%28%29"),
+			expect: newRequest(t, "GET", "/hello/()"),
+		},
 
 		{
 			rule:   Rewrite{PathRegexp: []*regexReplacer{{Find: "/{2,}", Replace: "/"}}},