Sender Session Events (payjoin#777)

This PR adds session events generated by processing the sender state
machine. To enable serialization and deserialization of session events,
we implement `serde::Serialize` and `serde::Deserialize` on the
underlying v1 & v2 types that are captured in session events.

To enable comparisons between `SessionEvents` during tests, all event
types must also implement `PartialEq` and `Eq`.

Tests cover roundtrip ser/deserialization of each session event.

Author: arminsabouri

payjoin-ffi/src/receive/uni.rs

@@ -11,7 +11,7 @@ use crate::uri::error::IntoUrlError;
 use crate::{ClientResponse, OhttpKeys, OutputSubstitution, Request};
 
 #[derive(Clone, uniffi::Object, serde::Serialize, serde::Deserialize)]
-pub struct SessionEvent(super::SessionEvent);
+pub struct ReceiverSessionEvent(super::SessionEvent);
 
 #[derive(Debug, uniffi::Object)]
 pub struct NewReceiver(pub super::NewReceiver);

payjoin-ffi/src/send/mod.rs

@@ -14,6 +14,17 @@ pub mod error;
 #[cfg(feature = "uniffi")]
 pub mod uni;
 
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct SessionEvent(payjoin::send::v2::SessionEvent);
+
+impl From<SessionEvent> for payjoin::send::v2::SessionEvent {
+    fn from(value: SessionEvent) -> Self { value.0 }
+}
+
+impl From<payjoin::send::v2::SessionEvent> for SessionEvent {
+    fn from(value: payjoin::send::v2::SessionEvent) -> Self { SessionEvent(value) }
+}
+
 ///Builder for sender-side payjoin parameters
 ///
 ///These parameters define how client wants to handle Payjoin.

payjoin-ffi/src/send/uni.rs

@@ -6,6 +6,30 @@ pub use crate::send::{
 };
 use crate::{ClientResponse, ImplementationError, PjUri, Request};
 
+#[derive(uniffi::Object, Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct SenderSessionEvent(super::SessionEvent);
+
+impl From<SenderSessionEvent> for super::SessionEvent {
+    fn from(value: SenderSessionEvent) -> Self { value.0 }
+}
+
+impl From<super::SessionEvent> for SenderSessionEvent {
+    fn from(value: super::SessionEvent) -> Self { SenderSessionEvent(value) }
+}
+
+#[uniffi::export]
+impl SenderSessionEvent {
+    pub fn to_json(&self) -> Result<String, SerdeJsonError> {
+        serde_json::to_string(&self.0).map_err(Into::into)
+    }
+
+    #[uniffi::constructor]
+    pub fn from_json(json: String) -> Result<Self, SerdeJsonError> {
+        let event: payjoin::send::v2::SessionEvent = serde_json::from_str(&json)?;
+        Ok(SenderSessionEvent(event.into()))
+    }
+}
+
 #[derive(uniffi::Object)]
 pub struct SenderBuilder(super::SenderBuilder);
 

payjoin/src/send/mod.rs

@@ -52,6 +52,7 @@ pub(crate) struct AdditionalFeeContribution {
 
 /// Data required to validate the response against the original PSBT.
 #[derive(Debug, Clone)]
+#[cfg_attr(feature = "v2", derive(serde::Serialize, serde::Deserialize, PartialEq, Eq))]
 pub struct PsbtContext {
     original_psbt: Psbt,
     output_substitution: OutputSubstitution,

payjoin/src/send/v2/mod.rs

@@ -25,7 +25,7 @@ use bitcoin::hashes::{sha256, Hash};
 pub use error::{CreateRequestError, EncapsulationError};
 use error::{InternalCreateRequestError, InternalEncapsulationError};
 use ohttp::ClientResponse;
-pub use persist::SenderToken;
+pub use persist::{SenderToken, SessionEvent};
 use serde::{Deserialize, Serialize};
 use url::Url;
 
@@ -163,7 +163,7 @@ impl NewSender {
 
 /// A payjoin V2 sender, allowing the construction of a payjoin V2 request
 /// and the resulting [`V2PostContext`].
-#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct WithReplyKey {
     /// The v1 Sender.
     pub(crate) v1: v1::Sender,
@@ -341,7 +341,7 @@ impl Sender<V2PostContext> {
 ///
 /// This type is used to make a BIP77 GET request and process the response.
 /// Call [`Sender<V2GetContext>::process_response`] on it to continue the BIP77 flow.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 pub struct V2GetContext {
     /// The endpoint in the Payjoin URI
     pub(crate) endpoint: Url,
@@ -415,7 +415,7 @@ impl Sender<V2GetContext> {
 }
 
 #[cfg(feature = "v2")]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 pub(crate) struct HpkeContext {
     pub(crate) receiver: HpkePublicKey,
     pub(crate) reply_pair: HpkeKeyPair,

payjoin/src/send/v2/persist.rs

@@ -4,6 +4,7 @@ use url::Url;
 
 use super::{Sender, WithReplyKey};
 use crate::persist::Value;
+use crate::send::v2::V2GetContext;
 
 /// Opaque key type for the sender
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -26,3 +27,69 @@ impl Value for Sender<WithReplyKey> {
 
     fn key(&self) -> Self::Key { SenderToken(self.endpoint().clone()) }
 }
+
+#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub enum SessionEvent {
+    /// Sender was created with a HPKE key pair
+    CreatedReplyKey(WithReplyKey),
+    /// Sender POST'd the original PSBT, and waiting to receive a Proposal PSBT using GET context
+    V2GetContext(V2GetContext),
+    /// Sender received a Proposal PSBT
+    ProposalReceived(bitcoin::Psbt),
+    /// Invalid session
+    SessionInvalid(String),
+}
+
+#[cfg(test)]
+mod tests {
+    use bitcoin::{FeeRate, ScriptBuf};
+    use payjoin_test_utils::PARSED_ORIGINAL_PSBT;
+
+    use super::*;
+    use crate::send::v2::HpkeContext;
+    use crate::send::{v1, PsbtContext};
+    use crate::{HpkeKeyPair, OutputSubstitution};
+
+    #[test]
+    fn test_sender_session_event_serialization_roundtrip() {
+        let endpoint = Url::parse("http://localhost:1234").expect("Valid URL");
+        let keypair = HpkeKeyPair::gen_keypair();
+        let sender_with_reply_key = WithReplyKey {
+            v1: v1::Sender {
+                psbt: PARSED_ORIGINAL_PSBT.clone(),
+                endpoint: endpoint.clone(),
+                output_substitution: OutputSubstitution::Enabled,
+                fee_contribution: None,
+                min_fee_rate: FeeRate::ZERO,
+                payee: ScriptBuf::from(vec![0x00]),
+            },
+            reply_key: keypair.0.clone(),
+        };
+
+        let v2_get_context = V2GetContext {
+            endpoint,
+            psbt_ctx: PsbtContext {
+                original_psbt: PARSED_ORIGINAL_PSBT.clone(),
+                output_substitution: OutputSubstitution::Enabled,
+                fee_contribution: None,
+                min_fee_rate: FeeRate::ZERO,
+                payee: ScriptBuf::from(vec![0x00]),
+            },
+            hpke_ctx: HpkeContext { receiver: keypair.clone().1, reply_pair: keypair },
+        };
+
+        let test_cases = vec![
+            SessionEvent::CreatedReplyKey(sender_with_reply_key.clone()),
+            SessionEvent::V2GetContext(v2_get_context.clone()),
+            SessionEvent::ProposalReceived(PARSED_ORIGINAL_PSBT.clone()),
+            SessionEvent::SessionInvalid("error message".to_string()),
+        ];
+
+        for event in test_cases {
+            let serialized = serde_json::to_string(&event).expect("Should serialize");
+            let deserialized: SessionEvent =
+                serde_json::from_str(&serialized).expect("Should deserialize");
+            assert_eq!(event, deserialized);
+        }
+    }
+}