Async recipient-side of static invoice server

fuzz/src/onion_message.rs

@@ -15,7 +15,8 @@ use lightning::ln::peer_handler::IgnoringMessageHandler;
 use lightning::ln::script::ShutdownScript;
 use lightning::offers::invoice::UnsignedBolt12Invoice;
 use lightning::onion_message::async_payments::{
-	AsyncPaymentsMessageHandler, HeldHtlcAvailable, ReleaseHeldHtlc,
+	AsyncPaymentsMessageHandler, HeldHtlcAvailable, OfferPaths, OfferPathsRequest, ReleaseHeldHtlc,
+	ServeStaticInvoice, StaticInvoicePersisted,
 };
 use lightning::onion_message::messenger::{
 	CustomOnionMessageHandler, Destination, MessageRouter, MessageSendInstructions,
@@ -124,6 +125,30 @@ impl OffersMessageHandler for TestOffersMessageHandler {
 struct TestAsyncPaymentsMessageHandler {}
 
 impl AsyncPaymentsMessageHandler for TestAsyncPaymentsMessageHandler {
+	fn handle_offer_paths_request(
+		&self, _message: OfferPathsRequest, _context: AsyncPaymentsContext,
+		responder: Option<Responder>,
+	) -> Option<(OfferPaths, ResponseInstruction)> {
+		let responder = match responder {
+			Some(resp) => resp,
+			None => return None,
+		};
+		Some((OfferPaths { paths: Vec::new(), paths_absolute_expiry: None }, responder.respond()))
+	}
+	fn handle_offer_paths(
+		&self, _message: OfferPaths, _context: AsyncPaymentsContext, _responder: Option<Responder>,
+	) -> Option<(ServeStaticInvoice, ResponseInstruction)> {
+		None
+	}
+	fn handle_serve_static_invoice(
+		&self, _message: ServeStaticInvoice, _context: AsyncPaymentsContext,
+		_responder: Option<Responder>,
+	) {
+	}
+	fn handle_static_invoice_persisted(
+		&self, _message: StaticInvoicePersisted, _context: AsyncPaymentsContext,
+	) {
+	}
 	fn handle_held_htlc_available(
 		&self, _message: HeldHtlcAvailable, _context: AsyncPaymentsContext,
 		responder: Option<Responder>,

lightning/src/blinded_path/message.rs

@@ -23,6 +23,7 @@ use crate::ln::channelmanager::PaymentId;
 use crate::ln::msgs::DecodeError;
 use crate::ln::onion_utils;
 use crate::offers::nonce::Nonce;
+use crate::offers::offer::OfferId;
 use crate::onion_message::packet::ControlTlvs;
 use crate::routing::gossip::{NodeId, ReadOnlyNetworkGraph};
 use crate::sign::{EntropySource, NodeSigner, Recipient};
@@ -404,6 +405,40 @@ pub enum OffersContext {
 /// [`AsyncPaymentsMessage`]: crate::onion_message::async_payments::AsyncPaymentsMessage
 #[derive(Clone, Debug)]
 pub enum AsyncPaymentsContext {
+	/// Context used by a reply path to an [`OfferPathsRequest`], provided back to us as an async
+	/// recipient in corresponding [`OfferPaths`] messages from the static invoice server.
+	///
+	/// [`OfferPathsRequest`]: crate::onion_message::async_payments::OfferPathsRequest
+	/// [`OfferPaths`]: crate::onion_message::async_payments::OfferPaths
+	OfferPaths {
+		/// The time as duration since the Unix epoch at which this path expires and messages sent over
+		/// it should be ignored.
+		///
+		/// This avoids the situation where the [`OfferPaths`] message is very delayed and thus
+		/// outdated.
+		///
+		/// [`OfferPaths`]: crate::onion_message::async_payments::OfferPaths
+		path_absolute_expiry: core::time::Duration,
+	},
+	/// Context used by a reply path to a [`ServeStaticInvoice`] message, provided back to us in
+	/// corresponding [`StaticInvoicePersisted`] messages.
+	///
+	/// [`ServeStaticInvoice`]: crate::onion_message::async_payments::ServeStaticInvoice
+	/// [`StaticInvoicePersisted`]: crate::onion_message::async_payments::StaticInvoicePersisted
+	StaticInvoicePersisted {
+		/// The id of the offer in the cache corresponding to the [`StaticInvoice`] that has been
+		/// persisted. This invoice is now ready to be provided by the static invoice server in response
+		/// to [`InvoiceRequest`]s, so the corresponding offer can be marked as ready to receive
+		/// payments.
+		///
+		/// [`StaticInvoice`]: crate::offers::static_invoice::StaticInvoice
+		/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
+		offer_id: OfferId,
+		/// The time as duration since the Unix epoch at which this path expires and messages sent over
+		/// it should be ignored. If we receive confirmation of an invoice over this path after its
+		/// expiry, it may be outdated and a new invoice update should be sent instead.
+		path_absolute_expiry: core::time::Duration,
+	},
 	/// Context contained within the reply [`BlindedMessagePath`] we put in outbound
 	/// [`HeldHtlcAvailable`] messages, provided back to us in corresponding [`ReleaseHeldHtlc`]
 	/// messages.
@@ -486,6 +521,13 @@ impl_writeable_tlv_based_enum!(AsyncPaymentsContext,
 		(2, hmac, required),
 		(4, path_absolute_expiry, required),
 	},
+	(2, OfferPaths) => {
+		(0, path_absolute_expiry, required),
+	},
+	(3, StaticInvoicePersisted) => {
+		(0, offer_id, required),
+		(2, path_absolute_expiry, required),
+	},
 );
 
 /// Contains a simple nonce for use in a blinded path's context.

lightning/src/ln/channelmanager.rs

@@ -86,6 +86,7 @@ use crate::ln::outbound_payment::{
 	StaleExpiration,
 };
 use crate::ln::types::ChannelId;
+use crate::offers::async_receive_offer_cache::AsyncReceiveOfferCache;
 use crate::offers::flow::OffersMessageFlow;
 use crate::offers::invoice::{
 	Bolt12Invoice, DerivedSigningPubkey, InvoiceBuilder, DEFAULT_RELATIVE_EXPIRY,
@@ -98,7 +99,8 @@ use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::Refund;
 use crate::offers::signer;
 use crate::onion_message::async_payments::{
-	AsyncPaymentsMessage, AsyncPaymentsMessageHandler, HeldHtlcAvailable, ReleaseHeldHtlc,
+	AsyncPaymentsMessage, AsyncPaymentsMessageHandler, HeldHtlcAvailable, OfferPaths,
+	OfferPathsRequest, ReleaseHeldHtlc, ServeStaticInvoice, StaticInvoicePersisted,
 };
 use crate::onion_message::dns_resolution::HumanReadableName;
 use crate::onion_message::messenger::{
@@ -5246,6 +5248,30 @@ where
 		)
 	}
 
+	#[cfg(async_payments)]
+	fn check_refresh_async_receive_offer_cache(&self, timer_tick_occurred: bool) {
+		let peers = self.get_peers_for_blinded_path();
+		let channels = self.list_usable_channels();
+		let entropy = &*self.entropy_source;
+		let router = &*self.router;
+		let refresh_res = self.flow.check_refresh_async_receive_offer_cache(
+			peers,
+			channels,
+			entropy,
+			router,
+			timer_tick_occurred,
+		);
+		match refresh_res {
+			Err(()) => {
+				log_error!(
+					self.logger,
+					"Failed to create blinded paths when requesting async receive offer paths"
+				);
+			},
+			Ok(()) => {},
+		}
+	}
+
 	#[cfg(async_payments)]
 	fn initiate_async_payment(
 		&self, invoice: &StaticInvoice, payment_id: PaymentId,
@@ -7240,6 +7266,9 @@ where
 				duration_since_epoch, &self.pending_events
 			);
 
+			#[cfg(async_payments)]
+			self.check_refresh_async_receive_offer_cache(true);
+
 			// Technically we don't need to do this here, but if we have holding cell entries in a
 			// channel that need freeing, it's better to do that here and block a background task
 			// than block the message queueing pipeline.
@@ -10999,9 +11028,29 @@ where
 	#[cfg(c_bindings)]
 	create_refund_builder!(self, RefundMaybeWithDerivedMetadataBuilder);
 
+	/// Retrieve an [`Offer`] for receiving async payments as an often-offline recipient. Will only
+	/// return an offer if [`Self::set_paths_to_static_invoice_server`] was called and we succeeded in
+	/// interactively building a [`StaticInvoice`] with the static invoice server.
+	///
+	/// Useful for posting offers to receive payments later, such as posting an offer on a website.
+	#[cfg(async_payments)]
+	pub fn get_async_receive_offer(&self) -> Result<Offer, ()> {
+		let (offer, needs_persist) = self.flow.get_async_receive_offer()?;
+		if needs_persist {
+			// We need to re-persist the cache if a fresh offer was just marked as used to ensure we
+			// continue to keep this offer's invoice updated and don't replace it with the server.
+			let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
+		}
+		Ok(offer)
+	}
+
 	/// Create an offer for receiving async payments as an often-offline recipient.
 	///
-	/// Because we may be offline when the payer attempts to request an invoice, you MUST:
+	/// Instead of using this method, it is preferable to call
+	/// [`Self::set_paths_to_static_invoice_server`] and retrieve the automatically built offer via
+	/// [`Self::get_async_receive_offer`].
+	///
+	/// If you want to build the [`StaticInvoice`] manually using this method instead, you MUST:
 	/// 1. Provide at least 1 [`BlindedMessagePath`] terminating at an always-online node that will
 	///    serve the [`StaticInvoice`] created from this offer on our behalf.
 	/// 2. Use [`Self::create_static_invoice_builder`] to create a [`StaticInvoice`] from this
@@ -11018,6 +11067,10 @@ where
 	/// Creates a [`StaticInvoiceBuilder`] from the corresponding [`Offer`] and [`Nonce`] that were
 	/// created via [`Self::create_async_receive_offer_builder`]. If `relative_expiry` is unset, the
 	/// invoice's expiry will default to [`STATIC_INVOICE_DEFAULT_RELATIVE_EXPIRY`].
+	///
+	/// Instead of using this method to manually build the invoice, it is preferable to set
+	/// [`Self::set_paths_to_static_invoice_server`] and retrieve the automatically built offer via
+	/// [`Self::get_async_receive_offer`].
 	#[cfg(async_payments)]
 	pub fn create_static_invoice_builder<'a>(
 		&self, offer: &'a Offer, offer_nonce: Nonce, relative_expiry: Option<Duration>,
@@ -11053,6 +11106,22 @@ where
 		)
 	}
 
+	/// Sets the [`BlindedMessagePath`]s that we will use as an async recipient to interactively build
+	/// [`Offer`]s with a static invoice server, so the server can serve [`StaticInvoice`]s to payers
+	/// on our behalf when we're offline.
+	///
+	/// This method only needs to be called once when the server first takes on the recipient as a
+	/// client, or when the paths change, e.g. if the paths are set to expire at a particular time.
+	#[cfg(async_payments)]
+	pub fn set_paths_to_static_invoice_server(
+		&self, paths_to_static_invoice_server: Vec<BlindedMessagePath>,
+	) -> Result<(), ()> {
+		self.flow.set_paths_to_static_invoice_server(paths_to_static_invoice_server)?;
+
+		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
+		Ok(())
+	}
+
 	/// Pays for an [`Offer`] using the given parameters by creating an [`InvoiceRequest`] and
 	/// enqueuing it to be sent via an onion message. [`ChannelManager`] will pay the actual
 	/// [`Bolt12Invoice`] once it is received.
@@ -11960,6 +12029,13 @@ where
 			return NotifyOption::SkipPersistHandleEvents;
 			//TODO: Also re-broadcast announcement_signatures
 		});
+
+		// While we usually refresh the AsyncReceiveOfferCache on a timer, we also want to start
+		// interactively building offers as soon as we can after startup. We can't start building offers
+		// until we have some peer connection(s) to send onion messages over, so as a minor optimization
+		// refresh the cache when a peer connects.
+		#[cfg(async_payments)]
+		self.check_refresh_async_receive_offer_cache(false);
 		res
 	}
 
@@ -13374,6 +13450,64 @@ where
 	MR::Target: MessageRouter,
 	L::Target: Logger,
 {
+	fn handle_offer_paths_request(
+		&self, _message: OfferPathsRequest, _context: AsyncPaymentsContext,
+		_responder: Option<Responder>,
+	) -> Option<(OfferPaths, ResponseInstruction)> {
+		None
+	}
+
+	fn handle_offer_paths(
+		&self, _message: OfferPaths, _context: AsyncPaymentsContext, _responder: Option<Responder>,
+	) -> Option<(ServeStaticInvoice, ResponseInstruction)> {
+		#[cfg(async_payments)]
+		{
+			let responder = match _responder {
+				Some(responder) => responder,
+				None => return None,
+			};
+			let (serve_static_invoice, reply_context) = match self.flow.handle_offer_paths(
+				_message,
+				_context,
+				responder.clone(),
+				self.get_peers_for_blinded_path(),
+				self.list_usable_channels(),
+				&*self.entropy_source,
+				&*self.router,
+			) {
+				Some((msg, ctx)) => (msg, ctx),
+				None => return None,
+			};
+
+			// We cached a new pending offer, so persist the cache.
+			let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
+
+			let response_instructions = responder.respond_with_reply_path(reply_context);
+			return Some((serve_static_invoice, response_instructions));
+		}
+
+		#[cfg(not(async_payments))]
+		return None;
+	}
+
+	fn handle_serve_static_invoice(
+		&self, _message: ServeStaticInvoice, _context: AsyncPaymentsContext,
+		_responder: Option<Responder>,
+	) {
+	}
+
+	fn handle_static_invoice_persisted(
+		&self, _message: StaticInvoicePersisted, _context: AsyncPaymentsContext,
+	) {
+		#[cfg(async_payments)]
+		{
+			let should_persist = self.flow.handle_static_invoice_persisted(_context);
+			if should_persist {
+				let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
+			}
+		}
+	}
+
 	fn handle_held_htlc_available(
 		&self, _message: HeldHtlcAvailable, _context: AsyncPaymentsContext,
 		_responder: Option<Responder>,
@@ -14239,6 +14373,7 @@ where
 			(15, self.inbound_payment_id_secret, required),
 			(17, in_flight_monitor_updates, option),
 			(19, peer_storage_dir, optional_vec),
+			(21, self.flow.writeable_async_receive_offer_cache(), required),
 		});
 
 		Ok(())
@@ -14818,6 +14953,7 @@ where
 		let mut decode_update_add_htlcs: Option<HashMap<u64, Vec<msgs::UpdateAddHTLC>>> = None;
 		let mut inbound_payment_id_secret = None;
 		let mut peer_storage_dir: Option<Vec<(PublicKey, Vec<u8>)>> = None;
+		let mut async_receive_offer_cache: AsyncReceiveOfferCache = AsyncReceiveOfferCache::new();
 		read_tlv_fields!(reader, {
 			(1, pending_outbound_payments_no_retry, option),
 			(2, pending_intercepted_htlcs, option),
@@ -14835,6 +14971,7 @@ where
 			(15, inbound_payment_id_secret, option),
 			(17, in_flight_monitor_updates, option),
 			(19, peer_storage_dir, optional_vec),
+			(21, async_receive_offer_cache, (default_value, async_receive_offer_cache)),
 		});
 		let mut decode_update_add_htlcs = decode_update_add_htlcs.unwrap_or_else(|| new_hash_map());
 		let peer_storage_dir: Vec<(PublicKey, Vec<u8>)> = peer_storage_dir.unwrap_or_else(Vec::new);
@@ -15521,7 +15658,7 @@ where
 			chain_hash, best_block, our_network_pubkey,
 			highest_seen_timestamp, expanded_inbound_key,
 			secp_ctx.clone(), args.message_router
-		);
+		).with_async_payments_offers_cache(async_receive_offer_cache);
 
 		let channel_manager = ChannelManager {
 			chain_hash,

lightning/src/ln/inbound_payment.rs

@@ -214,7 +214,7 @@ pub fn create_from_hash(
 }
 
 #[cfg(async_payments)]
-pub(super) fn create_for_spontaneous_payment(
+pub(crate) fn create_for_spontaneous_payment(
 	keys: &ExpandedKey, min_value_msat: Option<u64>, invoice_expiry_delta_secs: u32,
 	current_time: u64, min_final_cltv_expiry_delta: Option<u16>,
 ) -> Result<PaymentSecret, ()> {

lightning/src/ln/peer_handler.rs

@@ -31,7 +31,8 @@ use crate::ln::types::ChannelId;
 use crate::ln::wire;
 use crate::ln::wire::{Encode, Type};
 use crate::onion_message::async_payments::{
-	AsyncPaymentsMessageHandler, HeldHtlcAvailable, ReleaseHeldHtlc,
+	AsyncPaymentsMessageHandler, HeldHtlcAvailable, OfferPaths, OfferPathsRequest, ReleaseHeldHtlc,
+	ServeStaticInvoice, StaticInvoicePersisted,
 };
 use crate::onion_message::dns_resolution::{
 	DNSResolverMessage, DNSResolverMessageHandler, DNSSECProof, DNSSECQuery,
@@ -212,6 +213,26 @@ impl OffersMessageHandler for IgnoringMessageHandler {
 	}
 }
 impl AsyncPaymentsMessageHandler for IgnoringMessageHandler {
+	fn handle_offer_paths_request(
+		&self, _message: OfferPathsRequest, _context: AsyncPaymentsContext,
+		_responder: Option<Responder>,
+	) -> Option<(OfferPaths, ResponseInstruction)> {
+		None
+	}
+	fn handle_offer_paths(
+		&self, _message: OfferPaths, _context: AsyncPaymentsContext, _responder: Option<Responder>,
+	) -> Option<(ServeStaticInvoice, ResponseInstruction)> {
+		None
+	}
+	fn handle_serve_static_invoice(
+		&self, _message: ServeStaticInvoice, _context: AsyncPaymentsContext,
+		_responder: Option<Responder>,
+	) {
+	}
+	fn handle_static_invoice_persisted(
+		&self, _message: StaticInvoicePersisted, _context: AsyncPaymentsContext,
+	) {
+	}
 	fn handle_held_htlc_available(
 		&self, _message: HeldHtlcAvailable, _context: AsyncPaymentsContext,
 		_responder: Option<Responder>,