rewrite: fix wrong index check in trimPathPrefix (#7812)

Author: alhudz

modules/caddyhttp/rewrite/rewrite.go

@@ -432,7 +432,7 @@ func trimPathPrefix(escapedPath, prefix string) string {
 	}
 
 	// if we iterated through the entire prefix, we found it, so trim it
-	if iPath >= len(prefix) {
+	if iPrefix >= len(prefix) {
 		return escapedPath[iPath:]
 	}
 

modules/caddyhttp/rewrite/rewrite_test.go

@@ -267,6 +267,12 @@ func TestRewrite(t *testing.T) {
 			input:  newRequest(t, "GET", "/foo/prefix/bar"),
 			expect: newRequest(t, "GET", "/foo/prefix/bar"),
 		},
+		{
+			// shorter (percent-encoded) path that is not the prefix must be left alone
+			rule:   Rewrite{StripPathPrefix: "/aaaaaa"},
+			input:  newRequest(t, "GET", "/%61%61"),
+			expect: newRequest(t, "GET", "/%61%61"),
+		},
 		{
 			rule: Rewrite{StripPathPrefix: "//prefix"},
 			// scheme and host needed for URL parser to succeed in setting up test