Work around '#' escaping bug in bip21 crate

The `pj` parameter of the BIP 21 URL is itself a URL which contains a
fragment.

This is not escaped by bip21 during serialization, which according to
RFC 3986 truncates the `pj` parameter, making everything that follows
part of the fragment.

Deserialization likewise ignores #, parsing it as part of the value
which round trips with the incorrect serialization behavior.

payjoin/src/uri/mod.rs

@@ -41,7 +41,26 @@ impl PayjoinExtras {
 }
 
 pub type Uri<'a, NetworkValidation> = bip21::Uri<'a, NetworkValidation, MaybePayjoinExtras>;
-pub type PjUri<'a> = bip21::Uri<'a, NetworkChecked, PayjoinExtras>;
+#[derive(Clone)]
+pub struct PjUri<'a>(bip21::Uri<'a, NetworkChecked, PayjoinExtras>);
+
+impl<'a> std::fmt::Display for PjUri<'a> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        // FIXME bip21 does not escape # in pj parameter
+        // work around this by overriding
+        let malformed_uri = format!("{}", self.0);
+        let escaped = malformed_uri.replacen("#", "%23", 1);
+        write!(f, "{}", escaped)
+    }
+}
+
+impl<'a> std::ops::Deref for PjUri<'a> {
+    type Target = bip21::Uri<'a, NetworkChecked, PayjoinExtras>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
 
 mod sealed {
     use bitcoin::address::NetworkChecked;
@@ -65,7 +84,7 @@ impl<'a> UriExt<'a> for Uri<'a, NetworkChecked> {
                 uri.label = self.label;
                 uri.message = self.message;
 
-                Ok(uri)
+                Ok(PjUri(uri))
             }
             MaybePayjoinExtras::Unsupported => {
                 let mut uri = bip21::Uri::new(self.address);
@@ -157,7 +176,7 @@ impl PjUriBuilder {
         pj_uri.amount = self.amount;
         pj_uri.label = self.label.map(Into::into);
         pj_uri.message = self.message.map(Into::into);
-        pj_uri
+        PjUri(pj_uri)
     }
 }
 

payjoin/src/uri/url_ext.rs

@@ -129,9 +129,20 @@ mod tests {
     #[test]
     fn test_valid_v2_url_fragment_on_bip21() {
         let uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=0.01\
-                   &pj=https://example.com\
-                   #ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw";
-        let uri = Uri::try_from(uri).unwrap().assume_checked().check_pj_supported().unwrap();
-        assert!(uri.extras.endpoint().ohttp().is_some());
+                   &pj=https://example.com/\
+                   %23ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw\
+                   &pjos=0";
+        let pjuri = Uri::try_from(uri).unwrap().assume_checked().check_pj_supported().unwrap();
+
+        assert!(pjuri.extras.endpoint().ohttp().is_some());
+        assert_eq!(format!("{}", pjuri), uri);
+
+        let reordered = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=0.01\
+                   &pjos=0&pj=https://example.com/\
+                   %23ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw";
+        let pjuri =
+            Uri::try_from(reordered).unwrap().assume_checked().check_pj_supported().unwrap();
+        assert!(pjuri.extras.endpoint().ohttp().is_some());
+        assert_eq!(format!("{}", pjuri), uri);
     }
 }