Track invoice_slot in ServeStaticInvoice context

In the initially-merged version of the static invoice server protocol, the
static invoice server would sometimes have to find a specific static invoice
based on (recipient_id, invoice_slot) and sometime based on (recipient_id,
invoice_id). This made the API harder to use in terms of how the server would
index into the KVStore.

We'd like to transition to the server always finding a specific invoice based on
(recipient_id, invoice_slot) and get rid of the invoice_id concept.

As part of this series of commits, include the invoice_slot in the
ServeStaticInvoice blinded path context that the server creates when sending an
offer_paths message. This is possible due to a previous commit including the
invoice_slot in the initial offer_paths_request from the recipient, and lays
the groundwork for removing the invoice_id field from this blinded path
context.

Author: valentinewallace

lightning/src/blinded_path/message.rs

@@ -494,6 +494,13 @@ pub enum AsyncPaymentsContext {
 		/// [`StaticInvoice`]: crate::offers::static_invoice::StaticInvoice
 		/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 		invoice_id: u128,
+		/// The slot number for the specific [`StaticInvoice`] that the recipient is requesting be
+		/// served on their behalf. Useful when surfaced alongside the above `recipient_id` when payers
+		/// send an [`InvoiceRequest`], to pull the specific static invoice from the database.
+		///
+		/// [`StaticInvoice`]: crate::offers::static_invoice::StaticInvoice
+		/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
+		invoice_slot: u16,
 		/// The time as duration since the Unix epoch at which this path expires and messages sent over
 		/// it should be ignored.
 		///
@@ -595,6 +602,7 @@ impl_writeable_tlv_based_enum!(AsyncPaymentsContext,
 		(0, recipient_id, required),
 		(2, invoice_id, required),
 		(4, path_absolute_expiry, required),
+		(6, invoice_slot, required),
 	},
 );
 

lightning/src/ln/channelmanager.rs

@@ -14441,13 +14441,13 @@ where
 	L::Target: Logger,
 {
 	fn handle_offer_paths_request(
-		&self, _message: OfferPathsRequest, context: AsyncPaymentsContext,
+		&self, message: OfferPathsRequest, context: AsyncPaymentsContext,
 		responder: Option<Responder>,
 	) -> Option<(OfferPaths, ResponseInstruction)> {
 		let peers = self.get_peers_for_blinded_path();
 		let entropy = &*self.entropy_source;
 		let (message, reply_path_context) =
-			match self.flow.handle_offer_paths_request(context, peers, entropy) {
+			match self.flow.handle_offer_paths_request(&message, context, peers, entropy) {
 				Some(msg) => msg,
 				None => return None,
 			};
@@ -14490,17 +14490,17 @@ where
 			None => return,
 		};
 
-		let (recipient_id, invoice_id) =
+		let (recipient_id, invoice_slot, invoice_id) =
 			match self.flow.verify_serve_static_invoice_message(&message, context) {
-				Ok((recipient_id, inv_id)) => (recipient_id, inv_id),
+				Ok((recipient_id, inv_slot, inv_id)) => (recipient_id, inv_slot, inv_id),
 				Err(()) => return,
 			};
 
 		let mut pending_events = self.pending_events.lock().unwrap();
 		pending_events.push_back((
 			Event::PersistStaticInvoice {
 				invoice: message.invoice,
-				invoice_slot: message.invoice_slot,
+				invoice_slot,
 				recipient_id,
 				invoice_id,
 				invoice_persisted_path: responder,

lightning/src/offers/flow.rs

@@ -1374,7 +1374,8 @@ where
 	/// wants us (the static invoice server) to serve [`StaticInvoice`]s to payers on their behalf.
 	/// Sends out [`OfferPaths`] onion messages in response.
 	pub fn handle_offer_paths_request<ES: Deref>(
-		&self, context: AsyncPaymentsContext, peers: Vec<MessageForwardNode>, entropy_source: ES,
+		&self, request: &OfferPathsRequest, context: AsyncPaymentsContext,
+		peers: Vec<MessageForwardNode>, entropy_source: ES,
 	) -> Option<(OfferPaths, MessageContext)>
 	where
 		ES::Target: EntropySource,
@@ -1420,6 +1421,7 @@ where
 			MessageContext::AsyncPayments(AsyncPaymentsContext::ServeStaticInvoice {
 				recipient_id,
 				invoice_id,
+				invoice_slot: request.invoice_slot,
 				path_absolute_expiry,
 			})
 		};
@@ -1588,7 +1590,7 @@ where
 	/// [`ServeStaticInvoice::invoice`]: crate::onion_message::async_payments::ServeStaticInvoice::invoice
 	pub fn verify_serve_static_invoice_message(
 		&self, message: &ServeStaticInvoice, context: AsyncPaymentsContext,
-	) -> Result<(Vec<u8>, u128), ()> {
+	) -> Result<(Vec<u8>, u16, u128), ()> {
 		if message.invoice.is_expired_no_std(self.duration_since_epoch()) {
 			return Err(());
 		}
@@ -1599,13 +1601,14 @@ where
 			AsyncPaymentsContext::ServeStaticInvoice {
 				recipient_id,
 				invoice_id,
+				invoice_slot,
 				path_absolute_expiry,
 			} => {
 				if self.duration_since_epoch() > path_absolute_expiry {
 					return Err(());
 				}
 
-				return Ok((recipient_id, invoice_id));
+				return Ok((recipient_id, invoice_slot, invoice_id));
 			},
 			_ => return Err(()),
 		};