wafrift_encoding/url_mutate.rs
1//! URL / query-string payload mutation — opt-in attack surface for
2//! the proxy `--mutate-url` flag and the strategy engine's URL-aware
3//! evade variants.
4//!
5//! Most production attacks live in the URL, not the request body:
6//! `?id=1' OR 1=1--`, `?q=<script>alert(1)</script>`,
7//! `?file=../../etc/passwd`. The default proxy pipeline only mutates
8//! HTTP-layer artefacts (headers, body) which leaves this surface
9//! uncovered. This module fills that gap when the operator opts in.
10//!
11//! Scope:
12//! - mutates query parameter VALUES (not names — those drive routing)
13//! - optionally mutates the path's last segment (rest is routing)
14//! - never touches the host / scheme / port — those are pre-routing
15//! - returns the URL unchanged when no `?` is present and path
16//! mutation is disabled
17//!
18//! Mutation strategies are intentionally a small fixed set chosen to
19//! be effective against signature WAFs without requiring the heavier
20//! grammar/encoding pipeline. Callers that want full pipeline
21//! mutation should round-trip through `wafrift_strategy::evade` with
22//! the parameter value lifted into the request body.
23
24use std::borrow::Cow;
25
26/// Knobs for [`mutate_url`].
27#[derive(Debug, Clone, Copy, PartialEq, Eq)]
28pub struct UrlMutateConfig {
29 /// Mutate the query string. Default true.
30 pub mutate_query_values: bool,
31 /// Mutate the path's last segment (everything after the last `/`).
32 /// Default false — disabled because changing path semantics is
33 /// likely to break routing on most targets.
34 pub mutate_last_path_segment: bool,
35 /// Strategy to apply per value.
36 pub strategy: UrlStrategy,
37}
38
39impl Default for UrlMutateConfig {
40 fn default() -> Self {
41 Self {
42 mutate_query_values: true,
43 mutate_last_path_segment: false,
44 strategy: UrlStrategy::PercentEncodeAggressive,
45 }
46 }
47}
48
49/// Hard cap on the input size accepted by [`UrlStrategy::DoublePercentEncode`].
50/// Two passes of aggressive percent-encoding can produce up to ~9×
51/// the input length, so an unbounded input is a `DoS` vector. Real WAF
52/// values are kilobytes at most; 1 MB is generous.
53pub const MAX_DOUBLE_ENCODE_INPUT: usize = 1024 * 1024;
54
55/// Per-value mutation choice.
56#[derive(Debug, Clone, Copy, PartialEq, Eq)]
57pub enum UrlStrategy {
58 /// Percent-encode every byte that isn't alphanumeric. Most signatures
59 /// match decoded payloads but verify by raw-byte regex — this
60 /// breaks both checks at once.
61 PercentEncodeAggressive,
62 /// Double-percent-encode (`%` → `%25`, then percent-encode again).
63 /// Bypasses URL-decode-then-match WAFs that decode exactly once.
64 DoublePercentEncode,
65 /// Mix in `+` for spaces, `0x2F` for `/`, etc. — non-canonical
66 /// encodings that some upstream parsers normalise but signatures
67 /// don't.
68 NonCanonicalSpaces,
69 /// Insert empty PHP-style array brackets `[]` after the param name
70 /// to force HTTP Parameter Pollution path.
71 ///
72 /// **Audit (2026-05-10): NOT YET IMPLEMENTED.** `apply_bytes` only
73 /// receives the value — the (name, value) pair lives one layer up
74 /// in `mutate_query_string`. The current behaviour is a value
75 /// pass-through, which is a stub. Selecting this strategy will
76 /// log a `tracing::warn` but otherwise return the value unchanged
77 /// so existing callers don't break. Real HPP needs a query-level
78 /// mutator that operates on the pair list — track via a dedicated
79 /// `query_pollute_pairs()` function rather than as a `UrlStrategy`
80 /// variant.
81 Hpp,
82}
83
84impl UrlStrategy {
85 /// Apply the strategy to a single decoded value, returning the
86 /// mutated raw form (already URL-safe — caller does not re-encode).
87 #[must_use]
88 pub fn apply(self, value: &str) -> String {
89 self.apply_bytes(value.as_bytes())
90 }
91
92 /// Byte-clean variant of [`Self::apply`] for percent-encoding
93 /// strategies. Lets callers run a non-UTF-8 byte sequence (e.g.
94 /// the raw bytes from a percent-decode on `%FF%FE`) through the
95 /// pipeline without it being silently rewritten to U+FFFD by
96 /// `String::from_utf8_lossy`. Each strategy that only operates
97 /// on bytes (`PercentEncodeAggressive`, `DoublePercentEncode`) is
98 /// byte-pure here. Strategies that need character semantics
99 /// (`NonCanonicalSpaces`) lossy-convert internally.
100 #[must_use]
101 pub fn apply_bytes(self, value: &[u8]) -> String {
102 self.apply_bytes_with_label(value).0
103 }
104
105 /// Apply the strategy and return BOTH the encoded output AND the
106 /// label that honestly describes what was done. For most strategies
107 /// this is just `Self::label()`, but `DoublePercentEncode` silently
108 /// downgrades to single-percent encoding above `MAX_DOUBLE_ENCODE_INPUT`
109 /// (to avoid 9× output blowup) — pre-fix the technique log still
110 /// reported `url:double_percent` even though only one pass ran,
111 /// poisoning every WAF-decay statistic. Now the downgrade is
112 /// surfaced via `url:double_percent_downgraded` so callers (and
113 /// the gene-bank) see what actually shipped.
114 ///
115 /// Audit (2026-05-10).
116 #[must_use]
117 pub fn apply_bytes_with_label(self, value: &[u8]) -> (String, &'static str) {
118 match self {
119 Self::PercentEncodeAggressive => (
120 percent_encode_aggressive_bytes(value),
121 "url:percent_encode",
122 ),
123 Self::DoublePercentEncode => {
124 // Two passes of aggressive percent-encoding can blow
125 // up to roughly 9× the input size on worst-case
126 // inputs (every byte → %XX → %25%XX). Cap the input
127 // so a malicious caller can't OOM via a 100 MB
128 // string asking for 900 MB of output.
129 if value.len() > MAX_DOUBLE_ENCODE_INPUT {
130 return (
131 percent_encode_aggressive_bytes(value),
132 "url:double_percent_downgraded",
133 );
134 }
135 let first = percent_encode_aggressive_bytes(value);
136 (
137 percent_encode_aggressive_bytes(first.as_bytes()),
138 "url:double_percent",
139 )
140 }
141 Self::NonCanonicalSpaces => {
142 let s = String::from_utf8_lossy(value);
143 (non_canonical_spaces(&s), "url:noncanon_spaces")
144 }
145 Self::Hpp => {
146 // Honest no-op label so the technique log doesn't claim
147 // HPP was applied. See the Hpp variant docstring for
148 // the architectural fix path.
149 if std::str::from_utf8(value).is_err() {
150 // Lossy convert with a warn — a non-UTF-8 value
151 // would have been silently U+FFFD'd before.
152 tracing::warn!(
153 bytes = value.len(),
154 "UrlStrategy::Hpp dropped non-UTF-8 bytes; HPP transform NOT YET IMPLEMENTED"
155 );
156 }
157 (
158 String::from_utf8_lossy(value).into_owned(),
159 "url:hpp_unimplemented",
160 )
161 }
162 }
163 }
164
165 /// Stable name used for technique logging.
166 #[must_use]
167 pub fn label(self) -> &'static str {
168 match self {
169 Self::PercentEncodeAggressive => "url:percent_encode",
170 Self::DoublePercentEncode => "url:double_percent",
171 Self::NonCanonicalSpaces => "url:noncanon_spaces",
172 Self::Hpp => "url:hpp",
173 }
174 }
175}
176
177/// Mutate `path_and_query` (no scheme/host) per `cfg`. Returns the
178/// mutated string and a list of technique labels actually applied.
179///
180/// Inputs are accepted in either form:
181/// `/path/segment?a=1&b=2`
182/// `/path/segment` (no query — query mutation is a no-op)
183/// `?a=1` (no path — path mutation is a no-op)
184/// `/path?a=1#frag` (fragment preserved verbatim)
185///
186/// Never panics, never returns empty for non-empty input.
187#[must_use]
188pub fn mutate_url(path_and_query: &str, cfg: &UrlMutateConfig) -> (String, Vec<&'static str>) {
189 // Reject full URLs (with scheme://host/...) at the boundary —
190 // mutate_url's contract is "path-and-query only". Pre-fix a full
191 // URL got split on '?' such that the scheme + host leaked into
192 // the "path" and got mutated, e.g. `https://example.com/p?q=1`
193 // had `https://example.com/p` percent-encoded as the last path
194 // segment. The caller almost certainly meant to pass the
195 // path-and-query directly; pass-through is the safe behaviour.
196 if path_and_query.starts_with("http://")
197 || path_and_query.starts_with("https://")
198 || path_and_query.starts_with("//")
199 {
200 return (path_and_query.to_string(), Vec::new());
201 }
202
203 // Split off any #fragment FIRST so query mutation can't encode the
204 // '#' delimiter and destroy fragment routing. Pre-fix the
205 // mutator turned `/p?q=1#frag` into `/p?q=1%23frag`, which the
206 // upstream then treated as a single (broken) query value.
207 let (without_frag, fragment) = match path_and_query.split_once('#') {
208 Some((rest, frag)) => (rest, Some(frag)),
209 None => (path_and_query, None),
210 };
211
212 let (path, query) = match without_frag.split_once('?') {
213 Some((p, q)) => (p.to_string(), Some(q.to_string())),
214 None => (without_frag.to_string(), None),
215 };
216 let mut techniques: Vec<&'static str> = Vec::new();
217
218 let new_path = if cfg.mutate_last_path_segment {
219 match mutate_last_segment(&path, cfg.strategy) {
220 Some(p) => {
221 techniques.push("url:path_segment");
222 techniques.push(cfg.strategy.label());
223 p
224 }
225 None => path,
226 }
227 } else {
228 path
229 };
230
231 let new_query = if cfg.mutate_query_values {
232 if let Some(q) = query.as_ref() {
233 let (mq, label) = mutate_query_string(q, cfg.strategy);
234 if let Some(honest_label) = label {
235 techniques.push("url:query_values");
236 // Use the honest label returned by apply_bytes_with_label
237 // (may be a "_downgraded" variant) instead of the
238 // nominal cfg.strategy.label(). Audit (2026-05-10).
239 techniques.push(honest_label);
240 }
241 Some(mq)
242 } else {
243 query
244 }
245 } else {
246 query
247 };
248
249 let mut result = match new_query {
250 Some(q) => format!("{new_path}?{q}"),
251 None => new_path,
252 };
253 if let Some(frag) = fragment {
254 result.push('#');
255 result.push_str(frag);
256 }
257 (result, techniques)
258}
259
260fn mutate_last_segment(path: &str, strategy: UrlStrategy) -> Option<String> {
261 // Treat both literal '/' and percent-encoded slash (%2F or %2f)
262 // as segment boundaries — otherwise an attacker who pre-encodes
263 // a slash inside what looks like the last segment (e.g.
264 // /a/b%2Fc) would have the WHOLE tail (b%2Fc) mutated, when the
265 // logical last segment is `c`.
266 let normalized_last_slash = {
267 let lit = path.rfind('/');
268 let pct_upper = path.rfind("%2F").map(|i| i + 2);
269 let pct_lower = path.rfind("%2f").map(|i| i + 2);
270 [lit, pct_upper, pct_lower].into_iter().flatten().max()?
271 };
272 let (head, tail) = path.split_at(normalized_last_slash + 1);
273 if tail.is_empty() {
274 return None;
275 }
276 // Decode pre-existing percent escapes BEFORE re-applying the
277 // mutation strategy, into raw bytes (NOT through from_utf8_lossy)
278 // so that `%FF%FE` and other non-UTF-8 byte sequences survive
279 // the round-trip instead of being silently mangled into U+FFFD
280 // sequences (`%EF%BF%BD`).
281 let decoded = percent_decode_bytes(tail);
282 let mutated = strategy.apply_bytes(&decoded);
283 Some(format!("{head}{mutated}"))
284}
285
286/// Mutate every `name=value` pair, leaving `name` alone and mutating
287/// `value`. Pairs without `=` (bare flags) are passed through.
288///
289/// Empty pairs (consecutive `&&` separators) are PRESERVED rather
290/// than collapsed — some upstream frameworks (e.g. PHP, Rails 5+)
291/// treat them as distinct empty parameters, so collapsing changes
292/// the parsed parameter count.
293///
294/// `+` in a query value is interpreted as space per RFC 1866 form
295/// encoding before the strategy is applied — otherwise `q=1+1`
296/// would be mutated as if `+` were a literal plus sign.
297/// Returns `(mutated_query, Some(honest_label))` if any pair was
298/// mutated, or `(unchanged_query, None)` if not. The label tracks
299/// per-input downgrades — e.g. `DoublePercentEncode` on an oversize
300/// input returns `"url:double_percent_downgraded"` instead of the
301/// nominal `"url:double_percent"`. Audit (2026-05-10).
302fn mutate_query_string(query: &str, strategy: UrlStrategy) -> (String, Option<&'static str>) {
303 let mut out = Vec::with_capacity(8);
304 let mut last_label: Option<&'static str> = None;
305 for pair in query.split('&') {
306 if pair.is_empty() {
307 out.push(String::new());
308 continue;
309 }
310 if let Some((name, value)) = pair.split_once('=') {
311 if value.is_empty() {
312 out.push(format!("{name}="));
313 continue;
314 }
315 let form_decoded = value.replace('+', " ");
316 let decoded = percent_decode_bytes(&form_decoded);
317 let (mutated, label) = strategy.apply_bytes_with_label(&decoded);
318 if mutated.as_bytes() != value.as_bytes() {
319 // If different inputs in the same query produce
320 // different labels (one downgraded, others not),
321 // PREFER the downgraded one — operators care most
322 // about the worst case.
323 if last_label
324 .is_none_or(|l| !l.contains("downgraded"))
325 {
326 last_label = Some(label);
327 }
328 }
329 out.push(format!("{name}={mutated}"));
330 } else {
331 out.push(pair.to_string());
332 }
333 }
334 (out.join("&"), last_label)
335}
336
337/// Aggressive percent-encoding: every byte that is not `[A-Za-z0-9]`
338/// is encoded. Drops the URL safe-list (`-._~`) intentionally — those
339/// are the bytes signatures most often fail to canonicalise.
340#[allow(dead_code)]
341fn percent_encode_aggressive(s: &str) -> String {
342 percent_encode_aggressive_bytes(s.as_bytes())
343}
344
345/// Byte-clean variant of [`percent_encode_aggressive`]. Used by the
346/// byte-pipeline paths so non-UTF-8 input bytes (which a real
347/// `%FF%FE`-style WAF-bypass payload contains) survive end-to-end
348/// instead of being silently rewritten to U+FFFD.
349fn percent_encode_aggressive_bytes(bytes: &[u8]) -> String {
350 let mut out = String::with_capacity(bytes.len().saturating_mul(3));
351 for &b in bytes {
352 if b.is_ascii_alphanumeric() {
353 out.push(b as char);
354 } else {
355 use std::fmt::Write;
356 let _ = write!(&mut out, "%{b:02X}");
357 }
358 }
359 out
360}
361
362fn non_canonical_spaces(s: &str) -> String {
363 // saturating_mul to avoid usize overflow on 32-bit targets when
364 // someone hands us a ~2 GB string.
365 let mut out = String::with_capacity(s.len().saturating_mul(3));
366 // Pre-fix the `_ => out.push(other)` arm passed through `&`, `=`,
367 // `%`, `#`, `+`, `?`, `\0`, control chars, etc. After percent-decode
368 // had already turned `%26c%3Devil` into the literal bytes `&c=evil`,
369 // this re-emitted them verbatim and the server then split the value
370 // on `&` and `=` into THREE pairs — HTTP parameter injection. The
371 // audit caught this as CRITICAL.
372 //
373 // Fix: percent-encode every byte that would be parsed as URL/form
374 // structure or as an ASCII control. The cosmetic substitutions above
375 // (` `→`+`, `/`→`%2F`, etc.) are kept for the WAF-bypass shape; the
376 // dangerous bytes get the standard `%XX` form.
377 for ch in s.chars() {
378 match ch {
379 ' ' => out.push('+'),
380 '/' => out.push_str("%2F"),
381 '\\' => out.push_str("%5C"),
382 '<' => out.push_str("%3C"),
383 '>' => out.push_str("%3E"),
384 '\'' => out.push_str("%27"),
385 '"' => out.push_str("%22"),
386 '(' => out.push_str("%28"),
387 ')' => out.push_str("%29"),
388 // Structural URL / form delimiters — must always be encoded
389 // so they cannot escape the value into a sibling pair.
390 '&' => out.push_str("%26"),
391 '=' => out.push_str("%3D"),
392 '%' => out.push_str("%25"),
393 '#' => out.push_str("%23"),
394 '?' => out.push_str("%3F"),
395 '+' => out.push_str("%2B"),
396 ';' => out.push_str("%3B"),
397 // Control chars (incl. NUL): %XX-encode exactly.
398 other if (other as u32) < 0x20 || other as u32 == 0x7F => {
399 use std::fmt::Write;
400 let _ = write!(&mut out, "%{:02X}", other as u32);
401 }
402 other => out.push(other),
403 }
404 }
405 out
406}
407
408/// Decode `%xx` escapes into raw bytes, treating invalid sequences
409/// (lone `%`, `%G1`) as literal. Unlike [`percent_decode_lossy`],
410/// this never round-trips through `from_utf8_lossy` so non-UTF-8
411/// byte sequences (e.g. `%FF%FE`, overlong UTF-8 `%C0%AF`) survive
412/// intact. The downstream encoders re-emit them as exact `%XX`
413/// pairs instead of mangling them into `%EF%BF%BD` (U+FFFD), which
414/// is what removes WAF-bypass vectors.
415fn percent_decode_bytes(s: &str) -> Vec<u8> {
416 let bytes = s.as_bytes();
417 let mut out = Vec::with_capacity(bytes.len());
418 let mut i = 0;
419 while i < bytes.len() {
420 if bytes[i] == b'%'
421 && i + 2 < bytes.len()
422 && let (Some(h), Some(l)) = (hex_digit(bytes[i + 1]), hex_digit(bytes[i + 2]))
423 {
424 out.push(h * 16 + l);
425 i += 3;
426 continue;
427 }
428 out.push(bytes[i]);
429 i += 1;
430 }
431 out
432}
433
434/// Decode `%xx` escapes lossily, treating invalid sequences as
435/// literal. Returns `Cow::Borrowed` when nothing needed decoding.
436#[allow(dead_code)]
437fn percent_decode_lossy(s: &str) -> Cow<'_, str> {
438 if !s.contains('%') {
439 return Cow::Borrowed(s);
440 }
441 let bytes = s.as_bytes();
442 let mut out = Vec::with_capacity(bytes.len());
443 let mut i = 0;
444 while i < bytes.len() {
445 if bytes[i] == b'%'
446 && i + 2 < bytes.len()
447 && let (Some(h), Some(l)) = (hex_digit(bytes[i + 1]), hex_digit(bytes[i + 2]))
448 {
449 out.push(h * 16 + l);
450 i += 3;
451 continue;
452 }
453 out.push(bytes[i]);
454 i += 1;
455 }
456 Cow::Owned(String::from_utf8_lossy(&out).into_owned())
457}
458
459fn hex_digit(b: u8) -> Option<u8> {
460 match b {
461 b'0'..=b'9' => Some(b - b'0'),
462 b'a'..=b'f' => Some(b - b'a' + 10),
463 b'A'..=b'F' => Some(b - b'A' + 10),
464 _ => None,
465 }
466}
467
468#[cfg(test)]
469mod tests {
470 use super::*;
471
472 fn cfg(strategy: UrlStrategy, mutate_path: bool) -> UrlMutateConfig {
473 UrlMutateConfig {
474 mutate_query_values: true,
475 mutate_last_path_segment: mutate_path,
476 strategy,
477 }
478 }
479
480 // ── default-OFF semantics ──────────────────────────────────
481
482 #[test]
483 fn default_config_does_not_touch_path() {
484 let c = UrlMutateConfig::default();
485 assert!(!c.mutate_last_path_segment);
486 let (out, _) = mutate_url("/admin/login?id=1", &c);
487 assert!(
488 out.starts_with("/admin/login?"),
489 "path must stay verbatim, got {out}"
490 );
491 }
492
493 #[test]
494 fn no_query_no_path_mutation_returns_input_unchanged() {
495 let c = UrlMutateConfig::default();
496 let (out, techniques) = mutate_url("/just/a/path", &c);
497 assert_eq!(out, "/just/a/path");
498 assert!(
499 techniques.is_empty(),
500 "no mutation must report no technique"
501 );
502 }
503
504 #[test]
505 fn empty_value_pair_passes_through_unmutated() {
506 let c = UrlMutateConfig::default();
507 let (out, _) = mutate_url("/p?a=&b=2", &c);
508 assert!(out.contains("a=&"), "empty value must stay empty");
509 }
510
511 #[test]
512 fn bare_flag_param_passes_through() {
513 let c = UrlMutateConfig::default();
514 let (out, _) = mutate_url("/p?flag&other=1", &c);
515 assert!(out.contains("flag&"));
516 }
517
518 // ── per-strategy correctness ───────────────────────────────
519
520 #[test]
521 fn percent_encode_aggressive_encodes_quotes_and_spaces() {
522 let c = cfg(UrlStrategy::PercentEncodeAggressive, false);
523 let (out, t) = mutate_url("/p?id=1' OR '1'='1", &c);
524 // Every non-alphanumeric must be encoded.
525 assert!(out.contains("id=1%27%20OR%20%271%27%3D%271"), "got {out}");
526 assert!(t.contains(&"url:percent_encode"));
527 assert!(t.contains(&"url:query_values"));
528 }
529
530 #[test]
531 fn percent_encode_aggressive_skips_alphanumerics() {
532 let c = cfg(UrlStrategy::PercentEncodeAggressive, false);
533 let (out, _) = mutate_url("/p?q=ABCxyz123", &c);
534 assert!(
535 out.ends_with("q=ABCxyz123"),
536 "alnum must not be encoded; got {out}"
537 );
538 }
539
540 #[test]
541 fn double_percent_encode_doubles_each_byte() {
542 let c = cfg(UrlStrategy::DoublePercentEncode, false);
543 let (out, _) = mutate_url("/p?id='", &c);
544 // "'" → %27 → %2527
545 assert!(out.contains("id=%2527"), "got {out}");
546 }
547
548 #[test]
549 fn non_canonical_spaces_swaps_known_chars() {
550 let c = cfg(UrlStrategy::NonCanonicalSpaces, false);
551 let (out, _) = mutate_url("/p?q=hello world<", &c);
552 assert!(out.contains("q=hello+world%3C"), "got {out}");
553 }
554
555 // ── path-segment mutation ──────────────────────────────────
556
557 #[test]
558 fn path_segment_mutation_changes_last_segment_only_when_enabled() {
559 let c = cfg(UrlStrategy::PercentEncodeAggressive, true);
560 // Tail contains `.` (non-alphanumeric) so the strategy bites.
561 let (out, t) = mutate_url("/api/v1/admin.php", &c);
562 assert!(out.starts_with("/api/v1/"), "head must stay; got {out}");
563 assert_ne!(out, "/api/v1/admin.php", "tail must change; got {out}");
564 assert!(
565 out.contains("admin%2Ephp"),
566 "dot must be percent-encoded; got {out}"
567 );
568 assert!(t.contains(&"url:path_segment"));
569 }
570
571 #[test]
572 fn path_with_trailing_slash_is_not_mutated() {
573 let c = cfg(UrlStrategy::PercentEncodeAggressive, true);
574 let (out, t) = mutate_url("/api/v1/admin/", &c);
575 // Empty tail after the trailing `/` → no mutation
576 assert_eq!(out, "/api/v1/admin/");
577 assert!(t.is_empty());
578 }
579
580 // ── round-tripping pre-encoded input ──────────────────────
581
582 #[test]
583 fn pre_encoded_query_value_is_decoded_then_re_mutated() {
584 // Operator's input is `%27` (encoded `'`); we should decode
585 // first and then apply the strategy so we don't end up
586 // double-encoding accidentally on PercentEncodeAggressive.
587 let c = cfg(UrlStrategy::PercentEncodeAggressive, false);
588 let (out, _) = mutate_url("/p?q=%27OR%27", &c);
589 // Decoded: `'OR'` → re-aggressive-encoded: `%27OR%27`
590 assert!(out.contains("q=%27OR%27"));
591 }
592
593 // ── adversarial / robustness ──────────────────────────────
594
595 #[test]
596 fn does_not_panic_on_invalid_percent_escape() {
597 let c = UrlMutateConfig::default();
598 // %ZZ is invalid — must be treated as literal `%ZZ`
599 let _ = mutate_url("/p?q=%ZZbad", &c);
600 }
601
602 #[test]
603 fn does_not_panic_on_empty_input() {
604 let c = UrlMutateConfig::default();
605 let (out, _) = mutate_url("", &c);
606 assert_eq!(out, "");
607 }
608
609 #[test]
610 fn does_not_panic_on_trailing_question_mark() {
611 let c = UrlMutateConfig::default();
612 let (out, _) = mutate_url("/p?", &c);
613 assert_eq!(out, "/p?");
614 }
615
616 #[test]
617 fn handles_extremely_long_value() {
618 let c = UrlMutateConfig::default();
619 let long = "A".repeat(50_000);
620 let (out, _) = mutate_url(&format!("/p?q={long}"), &c);
621 // Alphanumeric → unchanged (50K A's)
622 assert!(out.ends_with(&long), "alnum long string must pass through");
623 }
624
625 #[test]
626 fn multiple_pairs_each_get_mutated_independently() {
627 let c = cfg(UrlStrategy::PercentEncodeAggressive, false);
628 let (out, _) = mutate_url("/p?a=1'&b=2\"&c=3", &c);
629 assert!(out.contains("a=1%27"));
630 assert!(out.contains("b=2%22"));
631 assert!(out.contains("c=3"));
632 }
633
634 #[test]
635 fn query_value_containing_equals_preserves_extra_equals() {
636 let c = UrlMutateConfig::default();
637 // `?key=base64==` is common (b64 padding)
638 let (out, _) = mutate_url("/p?key=b64==", &c);
639 // First `=` is the separator; "b64==" is the value
640 assert!(out.starts_with("/p?key="));
641 }
642}