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/Cargo.toml

@@ -36,6 +36,7 @@ reqwest = { version = "0.12", default-features = false, optional = true }
 rustls = { version = "0.22.4", optional = true }
 url = "2.2.2"
 serde_json = "1.0.108"
+percent-encoding-rfc3986 = "0.1.3"
 
 [dev-dependencies]
 bitcoind = { version = "0.36.0", features = ["0_21_2"] }

payjoin/src/uri/mod.rs

@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use bitcoin::address::NetworkChecked;
 use bitcoin::{Address, Amount};
 pub use error::PjParseError;
+use percent_encoding_rfc3986::{utf8_percent_encode, AsciiSet, CONTROLS};
 use url::Url;
 
 use crate::uri::error::InternalPjParseError;
@@ -192,14 +193,16 @@ impl<'a> bip21::SerializeParams for &'a MaybePayjoinExtras {
     }
 }
 
+const FRAGMENT_SEPARATOR: &AsciiSet = &CONTROLS.add(b'#');
+
 impl<'a> bip21::SerializeParams for &'a PayjoinExtras {
     type Key = &'static str;
     type Value = String;
     type Iterator = std::vec::IntoIter<(Self::Key, Self::Value)>;
 
     fn serialize_params(self) -> Self::Iterator {
         vec![
-            ("pj", self.endpoint.as_str().to_string()),
+            ("pj", utf8_percent_encode(self.endpoint.as_str(), FRAGMENT_SEPARATOR).to_string()), // FIXME remove work around bip21::Uri not escaping '#' in query parameter values once fixed upstream
             ("pjos", if self.disable_output_substitution { "1" } else { "0" }.to_string()),
         ]
         .into_iter()

payjoin/src/uri/url_ext.rs

@@ -128,9 +128,16 @@ mod tests {
 
     #[test]
     fn test_valid_v2_url_fragment_on_bip21() {
+        let uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=0.01\
+                   &pjos=0&pj=https://example.com\
+                   %23ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw";
+        let uri = Uri::try_from(uri).unwrap().assume_checked().check_pj_supported().unwrap();
+        assert!(uri.extras.endpoint().ohttp().is_some());
+
         let uri = "bitcoin:12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX?amount=0.01\
                    &pj=https://example.com\
-                   #ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw";
+                   %23ohttp%3DAQO6SMScPUqSo60A7MY6Ak2hDO0CGAxz7BLYp60syRu0gw\
+                   &pjos=0";
         let uri = Uri::try_from(uri).unwrap().assume_checked().check_pj_supported().unwrap();
         assert!(uri.extras.endpoint().ohttp().is_some());
     }