Expose shortid method for SessionContext (payjoin#698)

By exposing the shortid method for SessionContext it allows us to be
able to track the id across all psbt intermediate steps and allows us to
not need this method duplicated in every step of the process.

Closes payjoin#697

Author: arminsabouri

payjoin/src/receive/multiparty/mod.rs

@@ -44,8 +44,8 @@ impl UncheckedProposalBuilder {
         {
             return Err(InternalMultipartyError::IdenticalProposals(
                 IdenticalProposalError::IdenticalContexts(
-                    Box::new(duplicate_context.id()),
-                    Box::new(proposal.id()),
+                    Box::new(duplicate_context.context.id()),
+                    Box::new(proposal.context.id()),
                 ),
             )
             .into());
@@ -249,8 +249,8 @@ impl FinalizedProposal {
         {
             return Err(InternalMultipartyError::IdenticalProposals(
                 IdenticalProposalError::IdenticalContexts(
-                    Box::new(duplicate_context.id()),
-                    Box::new(proposal.id()),
+                    Box::new(duplicate_context.context.id()),
+                    Box::new(proposal.context.id()),
                 ),
             )
             .into());
@@ -366,8 +366,8 @@ mod test {
                 e.to_string(),
                 MultipartyError::from(InternalMultipartyError::IdenticalProposals(
                     IdenticalProposalError::IdenticalContexts(
-                        Box::new(proposal_one.id()),
-                        Box::new(proposal_two.id())
+                        Box::new(proposal_one.context.id()),
+                        Box::new(proposal_two.context.id())
                     )
                 ))
                 .to_string()

payjoin/src/receive/v2/mod.rs

@@ -56,6 +56,11 @@ impl SessionContext {
             .join(&format!("/{directory_base}"))
             .map_err(|e| InternalSessionError::ParseUrl(e.into()))
     }
+
+    /// The per-session identifier
+    pub fn id(&self) -> ShortId {
+        sha256::Hash::hash(&self.s.public_key().to_compressed_bytes()).into()
+    }
 }
 
 fn deserialize_address_assume_checked<'de, D>(deserializer: D) -> Result<Address, D::Error>
@@ -182,7 +187,7 @@ impl Receiver {
         ([u8; crate::directory::ENCAPSULATED_MESSAGE_BYTES], ohttp::ClientResponse),
         OhttpEncapsulationError,
     > {
-        let fallback_target = subdir(&self.context.directory, &self.id());
+        let fallback_target = subdir(&self.context.directory, &self.context.id());
         ohttp_encapsulate(&mut self.context.ohttp_keys, "GET", fallback_target.as_str(), None)
     }
 
@@ -236,17 +241,14 @@ impl Receiver {
     /// Build a V2 Payjoin URI from the receiver's context
     pub fn pj_uri<'a>(&self) -> crate::PjUri<'a> {
         use crate::uri::{PayjoinExtras, UrlExt};
-        let mut pj = subdir(&self.context.directory, &self.id()).clone();
+        let mut pj = subdir(&self.context.directory, &self.context.id()).clone();
         pj.set_receiver_pubkey(self.context.s.public_key().clone());
         pj.set_ohttp(self.context.ohttp_keys.clone());
         pj.set_exp(self.context.expiry);
         let extras =
             PayjoinExtras { endpoint: pj, output_substitution: OutputSubstitution::Enabled };
         bitcoin_uri::Uri::with_extras(self.context.address.clone(), extras)
     }
-
-    /// The per-session identifier
-    pub fn id(&self) -> ShortId { id(&self.context.s) }
 }
 
 /// The sender's original PSBT and optional parameters
@@ -308,7 +310,7 @@ impl UncheckedProposal {
         err: &JsonReply,
         ohttp_relay: impl IntoUrl,
     ) -> Result<(Request, ohttp::ClientResponse), SessionError> {
-        let subdir = subdir(&self.context.directory, &id(&self.context.s));
+        let subdir = subdir(&self.context.directory, &self.context.id());
         let (body, ohttp_ctx) = ohttp_encapsulate(
             &mut self.context.ohttp_keys,
             "POST",
@@ -338,9 +340,6 @@ impl UncheckedProposal {
             _ => Err(InternalSessionError::UnexpectedStatusCode(response.status()).into()),
         }
     }
-
-    /// The per-session identifier
-    pub fn id(&self) -> ShortId { id(&self.context.s) }
 }
 
 /// Typestate to validate that the Original PSBT has no receiver-owned inputs.
@@ -630,11 +629,6 @@ fn subdir(directory: &Url, id: &ShortId) -> Url {
     url
 }
 
-/// The per-session identifier
-fn id(s: &HpkeKeyPair) -> ShortId {
-    sha256::Hash::hash(&s.public_key().to_compressed_bytes()).into()
-}
-
 #[cfg(test)]
 pub mod test {
     use std::str::FromStr;
@@ -724,7 +718,7 @@ pub mod test {
     #[test]
     fn receiver_ser_de_roundtrip() -> Result<(), serde_json::Error> {
         let session = Receiver { context: SHARED_CONTEXT.clone() };
-        let short_id = id(&session.context.s);
+        let short_id = &session.context.id();
         assert_eq!(session.key().as_ref(), short_id.as_bytes());
         let serialized = serde_json::to_string(&session)?;
         let deserialized: Receiver = serde_json::from_str(&serialized)?;

payjoin/src/receive/v2/persist.rs

@@ -1,6 +1,6 @@
 use std::fmt::{self, Display};
 
-use super::{id, Receiver};
+use super::Receiver;
 use crate::persist::{self};
 use crate::uri::ShortId;
 
@@ -13,7 +13,7 @@ impl Display for ReceiverToken {
 }
 
 impl From<Receiver> for ReceiverToken {
-    fn from(receiver: Receiver) -> Self { ReceiverToken(id(&receiver.context.s)) }
+    fn from(receiver: Receiver) -> Self { ReceiverToken(receiver.context.id()) }
 }
 
 impl AsRef<[u8]> for ReceiverToken {
@@ -23,5 +23,5 @@ impl AsRef<[u8]> for ReceiverToken {
 impl persist::Value for Receiver {
     type Key = ReceiverToken;
 
-    fn key(&self) -> Self::Key { ReceiverToken(id(&self.context.s)) }
+    fn key(&self) -> Self::Key { ReceiverToken(self.context.id()) }
 }