Save max fee rate in receiver session context (#1033)

Author: arminsabouri

payjoin-cli/src/app/v2/mod.rs

@@ -162,6 +162,7 @@ impl AppTrait for App {
         let session =
             ReceiverBuilder::new(address, self.config.v2()?.pj_directory.clone(), ohttp_keys)?
                 .with_amount(amount)
+                .with_max_fee_rate(self.config.max_fee_rate.unwrap_or(FeeRate::BROADCAST_MIN))
                 .build()
                 .save(&persister)?;
 

payjoin-ffi/src/receive/mod.rs

@@ -15,7 +15,7 @@ use crate::error::ForeignError;
 pub use crate::error::{ImplementationError, SerdeJsonError};
 use crate::ohttp::OhttpKeys;
 use crate::receive::error::{ReceiverPersistedError, ReceiverReplayError};
-use crate::uri::error::IntoUrlError;
+use crate::uri::error::{FeeRateError, IntoUrlError};
 use crate::{ClientResponse, OutputSubstitution, Request};
 
 pub mod error;
@@ -274,6 +274,16 @@ impl ReceiverBuilder {
         Self(self.0.clone().with_expiry(Duration::from_secs(expiry)))
     }
 
+    /// Set the maximum effective fee rate the receiver is willing to pay for their own input/output contributions
+    pub fn with_max_fee_rate(
+        &self,
+        max_effective_fee_rate_sat_per_vb: u64,
+    ) -> Result<Self, FeeRateError> {
+        let fee_rate = bitcoin_ffi::FeeRate::from_sat_per_vb(max_effective_fee_rate_sat_per_vb)
+            .map_err(FeeRateError::from)?;
+        Ok(Self(self.0.clone().with_max_fee_rate(fee_rate.into())))
+    }
+
     pub fn build(&self) -> InitialReceiveTransition {
         InitialReceiveTransition(Arc::new(RwLock::new(Some(self.0.clone().build()))))
     }

payjoin-ffi/src/uri/error.rs

@@ -25,3 +25,7 @@ pub struct UrlParseError(#[from] payjoin::ParseError);
 #[derive(Debug, thiserror::Error, uniffi::Object)]
 #[error(transparent)]
 pub struct IntoUrlError(#[from] payjoin::IntoUrlError);
+
+#[derive(Debug, thiserror::Error, uniffi::Object)]
+#[error(transparent)]
+pub struct FeeRateError(#[from] bitcoin_ffi::error::FeeRateError);

payjoin/src/core/receive/v2/mod.rs

@@ -73,6 +73,7 @@ pub struct SessionContext {
     amount: Option<Amount>,
     receiver_key: HpkeKeyPair,
     reply_key: Option<HpkePublicKey>,
+    max_fee_rate: FeeRate,
 }
 
 impl SessionContext {
@@ -299,6 +300,7 @@ impl ReceiverBuilder {
             amount: None,
             mailbox: None,
             reply_key: None,
+            max_fee_rate: FeeRate::BROADCAST_MIN,
         };
         Ok(Self(session_context))
     }
@@ -315,6 +317,11 @@ impl ReceiverBuilder {
         Ok(Self(SessionContext { mailbox: Some(mailbox.into_url()?), ..self.0 }))
     }
 
+    /// Set the maximum effective fee rate the receiver is willing to pay for their own input/output contributions
+    pub fn with_max_fee_rate(self, max_fee_rate: FeeRate) -> Self {
+        Self(SessionContext { max_fee_rate, ..self.0 })
+    }
+
     pub fn build(self) -> NextStateTransition<SessionEvent, Receiver<Initialized>> {
         NextStateTransition::success(
             SessionEvent::Created(self.0.clone()),
@@ -908,6 +915,8 @@ impl Receiver<WantsFeeRange> {
         min_fee_rate: Option<FeeRate>,
         max_effective_fee_rate: Option<FeeRate>,
     ) -> MaybeFatalTransition<SessionEvent, Receiver<ProvisionalProposal>, ProtocolError> {
+        let max_effective_fee_rate =
+            max_effective_fee_rate.or(Some(self.state.session_context.max_fee_rate));
         let psbt_context = match self
             .state
             .inner
@@ -1132,6 +1141,7 @@ pub mod test {
         receiver_key: HpkeKeyPair::gen_keypair(),
         reply_key: None,
         amount: None,
+        max_fee_rate: FeeRate::BROADCAST_MIN,
     });
 
     pub(crate) fn unchecked_proposal_v2_from_test_vector() -> UncheckedOriginalPayload {
@@ -1396,6 +1406,36 @@ pub mod test {
         }
     }
 
+    #[test]
+    fn default_max_fee_rate() {
+        let noop_persister = NoopSessionPersister::default();
+        let receiver = ReceiverBuilder::new(
+            SHARED_CONTEXT.address.clone(),
+            SHARED_CONTEXT.directory.clone(),
+            SHARED_CONTEXT.ohttp_keys.clone(),
+        )
+        .expect("constructor on test vector should not fail")
+        .build()
+        .save(&noop_persister)
+        .expect("Noop persister shouldn't fail");
+
+        assert_eq!(receiver.context.max_fee_rate, FeeRate::BROADCAST_MIN);
+
+        let non_default_max_fee_rate =
+            FeeRate::from_sat_per_vb(1000).expect("Fee rate should be valid");
+        let receiver = ReceiverBuilder::new(
+            SHARED_CONTEXT.address.clone(),
+            SHARED_CONTEXT.directory.clone(),
+            SHARED_CONTEXT.ohttp_keys.clone(),
+        )
+        .expect("constructor on test vector should not fail")
+        .with_max_fee_rate(non_default_max_fee_rate)
+        .build()
+        .save(&noop_persister)
+        .expect("Noop persister shouldn't fail");
+        assert_eq!(receiver.context.max_fee_rate, non_default_max_fee_rate);
+    }
+
     #[test]
     fn build_receiver_with_non_default_expiry() {
         let now = SystemTime::now();