Add arbitrary_url fuzz target

I moved some of the logic from the existing `decode_url` target into
this one to utilize the fuzzer to test different inputs

Author: shinghim

fuzz/Cargo.toml

@@ -37,3 +37,9 @@ name = "url_decode_url"
 path = "fuzz_targets/url/decode_url.rs"
 doc = false
 bench = false
+
+[[bin]]
+name = "arbitrary_url"
+path = "fuzz_targets/url/arbitrary_url.rs"
+doc = false
+bench = false

fuzz/fuzz_targets/url/arbitrary_url.rs

@@ -0,0 +1,42 @@
+#![no_main]
+
+use arbitrary::{Arbitrary, Unstructured};
+use libfuzzer_sys::fuzz_target;
+use payjoin::Url;
+
+fn do_test(data: &[u8]) {
+    let mut u = Unstructured::new(data);
+    if let Ok(mut url) = Url::arbitrary(&mut u) {
+        if let Ok(port) = u.arbitrary::<Option<u16>>() {
+            url.set_port(port);
+        }
+        if let Ok(fragment) = u.arbitrary::<Option<&str>>() {
+            url.set_fragment(fragment);
+        }
+        if let Ok((key, value)) = u.arbitrary::<(&str, &str)>() {
+            url.query_pairs_mut().append_pair(key, value);
+            url.clear_query();
+        }
+        if let Some(mut segs) = url.path_segments_mut() {
+            if let Ok(segment) = u.arbitrary::<&str>() {
+                segs.push(segment);
+            }
+        }
+        if let Ok(segment) = String::arbitrary(&mut u) {
+            let _ = url.join(&segment);
+        }
+    }
+}
+
+fuzz_target!(|data| {
+    do_test(data);
+});
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn duplicate_crash() {
+        let data = b"\x00";
+        super::do_test(&data[..]);
+    }
+}

fuzz/fuzz_targets/url/decode_url.rs

@@ -9,7 +9,7 @@ use payjoin::Url;
 fn do_test(data: &[u8]) {
     let Ok(s) = str::from_utf8(data) else { return };
 
-    let Ok(mut url) = Url::parse(s) else { return };
+    let Ok(url) = Url::parse(s) else { return };
 
     let _ = url.scheme();
     let _ = url.domain();
@@ -44,23 +44,6 @@ fn do_test(data: &[u8]) {
             reparsed.as_str()
         );
     }
-
-    url.set_port(Some(8080));
-    url.set_port(None);
-    url.set_fragment(Some("fuzz"));
-    url.set_fragment(None);
-    url.query_pairs_mut().append_pair("k", "v");
-    url.clear_query();
-    url.query_pairs_mut().append_pair("fuzz_key", "fuzz_val");
-
-    if let Some(mut segs) = url.path_segments_mut() {
-        segs.push("fuzz_segment");
-    }
-
-    let _ = url.join("relative/path");
-    let _ = url.join("/absolute/path");
-    let _ = url.join("../dotdot");
-    let _ = url.join("https://other.example.com/new");
 }
 
 fuzz_target!(|data| {