Fix unresumable Sender (payjoin#443)

The Sender was generating new hpke keys on resume since keygen was being
done in `extract_v2`. This caused a problem where when the Sender was
persisted, stopped, and resumed, the receiver would have already pushed
a response to a different ShortId than the one the Sender would look for
it in the resumed state.

By generating a key on Sender creation and persisting that the Sender
can produce a consistent HpkeContext every single run.

The e2e test did not catch this because it was not propagating errors.
The e2e test has been fixed.

Cargo-minimal.lock

@@ -1577,7 +1577,7 @@ checksum = "8835116a5c179084a830efb3adc117ab007512b535bc1a21c991d3b32a6b44dd"
 
 [[package]]
 name = "payjoin"
-version = "0.21.0"
+version = "0.22.0"
 dependencies = [
  "bhttp",
  "bitcoin",

Cargo-recent.lock

@@ -1577,7 +1577,7 @@ checksum = "8835116a5c179084a830efb3adc117ab007512b535bc1a21c991d3b32a6b44dd"
 
 [[package]]
 name = "payjoin"
-version = "0.21.0"
+version = "0.22.0"
 dependencies = [
  "bhttp",
  "bitcoin",

payjoin-cli/Cargo.toml

@@ -37,7 +37,7 @@ hyper = { version = "1", features = ["http1", "server"], optional = true }
 hyper-rustls = { version = "0.26", optional = true }
 hyper-util = { version = "0.1", optional = true }
 log = "0.4.7"
-payjoin = { version = "0.21.0", features = ["send", "receive", "base64"] }
+payjoin = { version = "0.22.0", features = ["send", "receive", "base64"] }
 rcgen = { version = "0.11.1", optional = true }
 reqwest = { version = "0.12", default-features = false }
 rustls = { version = "0.22.4", optional = true }

payjoin-cli/tests/e2e.rs

@@ -293,7 +293,7 @@ mod e2e {
                 .stderr(Stdio::inherit())
                 .spawn()
                 .expect("Failed to execute payjoin-cli");
-            let _ = send_until_request_timeout(cli_send_initiator).await;
+            send_until_request_timeout(cli_send_initiator).await?;
 
             let cli_receive_resumer = Command::new(payjoin_cli)
                 .arg("--rpchost")
@@ -309,7 +309,7 @@ mod e2e {
                 .stderr(Stdio::inherit())
                 .spawn()
                 .expect("Failed to execute payjoin-cli");
-            let _ = respond_with_payjoin(cli_receive_resumer).await;
+            respond_with_payjoin(cli_receive_resumer).await?;
 
             let cli_send_resumer = Command::new(payjoin_cli)
                 .arg("--rpchost")
@@ -328,7 +328,7 @@ mod e2e {
                 .stderr(Stdio::inherit())
                 .spawn()
                 .expect("Failed to execute payjoin-cli");
-            let _ = check_payjoin_sent(cli_send_resumer).await;
+            check_payjoin_sent(cli_send_resumer).await?;
             Ok(())
         }
 

payjoin/CHANGELOG.md

@@ -1,5 +1,10 @@
 # Payjoin Changelog
 
+## 0.22.0
+
+- Propagate Uri Fragment parameter errors to the caller
+- Have `Sender` to persist reply key so resumption listens where a previous sender left off
+
 ## 0.21.0
 
 - Upgrade rustls v0.22.4

payjoin/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "payjoin"
-version = "0.21.0"
+version = "0.22.0"
 authors = ["Dan Gould <d@ngould.dev>"]
 description = "Payjoin Library for the BIP78 Pay to Endpoint protocol."
 repository = "https://github.com/payjoin/rust-payjoin"

payjoin/src/hpke.rs

@@ -31,6 +31,11 @@ impl From<HpkeKeyPair> for (HpkeSecretKey, HpkePublicKey) {
 }
 
 impl HpkeKeyPair {
+    pub fn from_secret_key(secret_key: &HpkeSecretKey) -> Self {
+        let public_key = <SecpK256HkdfSha256 as hpke::Kem>::sk_to_pk(&secret_key.0);
+        Self(secret_key.clone(), HpkePublicKey(public_key))
+    }
+
     pub fn gen_keypair() -> Self {
         let (sk, pk) = <SecpK256HkdfSha256 as hpke::Kem>::gen_keypair(&mut OsRng);
         Self(HpkeSecretKey(sk), HpkePublicKey(pk))

payjoin/src/send/mod.rs

@@ -34,7 +34,9 @@ use serde::{Deserialize, Serialize};
 use url::Url;
 
 #[cfg(feature = "v2")]
-use crate::hpke::{decrypt_message_b, encrypt_message_a, HpkeKeyPair, HpkePublicKey};
+use crate::hpke::{
+    decrypt_message_b, encrypt_message_a, HpkeKeyPair, HpkePublicKey, HpkeSecretKey,
+};
 #[cfg(feature = "v2")]
 use crate::ohttp::{ohttp_decapsulate, ohttp_encapsulate};
 use crate::psbt::PsbtExt;
@@ -228,6 +230,8 @@ impl<'a> SenderBuilder<'a> {
             fee_contribution,
             payee,
             min_fee_rate: self.min_fee_rate,
+            #[cfg(feature = "v2")]
+            reply_key: HpkeKeyPair::gen_keypair().0,
         })
     }
 }
@@ -246,6 +250,8 @@ pub struct Sender {
     min_fee_rate: FeeRate,
     /// Script of the person being paid
     payee: ScriptBuf,
+    #[cfg(feature = "v2")]
+    reply_key: HpkeSecretKey,
 }
 
 impl Sender {
@@ -298,7 +304,7 @@ impl Sender {
             self.fee_contribution,
             self.min_fee_rate,
         )?;
-        let hpke_ctx = HpkeContext::new(rs);
+        let hpke_ctx = HpkeContext::new(rs, &self.reply_key);
         let body = encrypt_message_a(
             body,
             &hpke_ctx.reply_pair.public_key().clone(),
@@ -475,8 +481,8 @@ struct HpkeContext {
 
 #[cfg(feature = "v2")]
 impl HpkeContext {
-    pub fn new(receiver: HpkePublicKey) -> Self {
-        Self { receiver, reply_pair: HpkeKeyPair::gen_keypair() }
+    pub fn new(receiver: HpkePublicKey, reply_key: &HpkeSecretKey) -> Self {
+        Self { receiver, reply_pair: HpkeKeyPair::from_secret_key(reply_key) }
     }
 }
 
@@ -975,6 +981,7 @@ mod test {
             fee_contribution: None,
             min_fee_rate: FeeRate::ZERO,
             payee: ScriptBuf::from(vec![0x00]),
+            reply_key: HpkeKeyPair::gen_keypair().0,
         };
         let serialized = serde_json::to_string(&req_ctx).unwrap();
         let deserialized = serde_json::from_str(&serialized).unwrap();