Expose send_payment_for_bolt12_invoice

UserConfig::manually_handle_bolt12_invoices allows deferring payment of
BOLT12 invoices by generating Event::InvoiceReceived. Expose
ChannelManager::send_payment_for_bolt12_invoice to allow users to pay
the Bolt12Invoice included in the event. While the event contains the
PaymentId for reference, that parameter is now removed from the method
in favor of extracting the PaymentId from the invoice's payer_metadata.

WIP: send_payment_for_bolt12_invoice

Author: jkczyz

lightning/src/events/mod.rs

@@ -720,8 +720,15 @@ pub enum Event {
 	/// Indicates a [`Bolt12Invoice`] in response to an [`InvoiceRequest`] or a [`Refund`] was
 	/// received.
 	///
+	/// This event will only be generated if [`UserConfig::manually_handle_bolt12_invoices`] is set.
+	/// Use [`ChannelManager::send_payment_for_bolt12_invoice`] to pay the invoice or
+	/// [`ChannelManager::abandon_payment`] to abandon the associated payment.
+	///
 	/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 	/// [`Refund`]: crate::offers::refund::Refund
+	/// [`UserConfig::manually_handle_bolt12_invoices`]: crate::util::config::UserConfig::manually_handle_bolt12_invoices
+	/// [`ChannelManager::send_payment_for_bolt12_invoice`]: crate::ln::channelmanager::ChannelManager::send_payment_for_bolt12_invoice
+	/// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
 	InvoiceReceived {
 		/// The `payment_id` associated with payment for the invoice.
 		payment_id: PaymentId,

lightning/src/ln/channelmanager.rs

@@ -58,7 +58,7 @@ use crate::ln::onion_utils::{HTLCFailReason, INVALID_ONION_BLINDING};
 use crate::ln::msgs::{ChannelMessageHandler, DecodeError, LightningError};
 #[cfg(test)]
 use crate::ln::outbound_payment;
-use crate::ln::outbound_payment::{Bolt12PaymentError, OutboundPayments, PaymentAttempts, PendingOutboundPayment, SendAlongPathArgs, StaleExpiration};
+use crate::ln::outbound_payment::{OutboundPayments, PaymentAttempts, PendingOutboundPayment, SendAlongPathArgs, StaleExpiration};
 use crate::ln::wire::Encode;
 use crate::offers::invoice::{BlindedPayInfo, Bolt12Invoice, DEFAULT_RELATIVE_EXPIRY, DerivedSigningPubkey, ExplicitSigningPubkey, InvoiceBuilder, UnsignedBolt12Invoice};
 use crate::offers::invoice_error::InvoiceError;
@@ -105,7 +105,7 @@ use core::time::Duration;
 use core::ops::Deref;
 
 // Re-export this for use in the public API.
-pub use crate::ln::outbound_payment::{PaymentSendFailure, ProbeSendFailure, Retry, RetryableSendFailure, RecipientOnionFields};
+pub use crate::ln::outbound_payment::{Bolt12PaymentError, PaymentSendFailure, ProbeSendFailure, Retry, RetryableSendFailure, RecipientOnionFields};
 use crate::ln::script::ShutdownScript;
 
 // We hold various information about HTLC relay in the HTLC objects in Channel itself:
@@ -3996,7 +3996,28 @@ where
 		self.pending_outbound_payments.test_set_payment_metadata(payment_id, new_payment_metadata);
 	}
 
-	pub(super) fn send_payment_for_bolt12_invoice(&self, invoice: &Bolt12Invoice, payment_id: PaymentId) -> Result<(), Bolt12PaymentError> {
+	/// Pays the [`Bolt12Invoice`] associated with the `payment_id` encoded in its `payer_metadata`.
+	///
+	/// The invoice's `payer_metadata` is used to authenticate that the invoice was indeed requested
+	/// before attempting a payment. [`Bolt12PaymentError::UnexpectedInvoice`] is returned if this
+	/// fails or if the encoded `payment_id` is not recognized. The latter may happen once the
+	/// invoice is paid and the payment no longer tracked.
+	///
+	/// Attempting to pay the same invoice twice while the first payment is still pending will
+	/// result in a [`Bolt12PaymentError::DuplicateInvoice`].
+	///
+	/// Otherwise, either [`Event::PaymentSent`] or [`Event::PaymentFailed`] are used to indicate
+	/// whether or not the payment was successful.
+	pub fn send_payment_for_bolt12_invoice(&self, invoice: &Bolt12Invoice) -> Result<(), Bolt12PaymentError> {
+		let secp_ctx = &self.secp_ctx;
+		let expanded_key = &self.inbound_payment_key;
+		match invoice.verify(expanded_key, secp_ctx) {
+			Ok(payment_id) => self.send_payment_for_verified_bolt12_invoice(invoice, payment_id),
+			Err(()) => Err(Bolt12PaymentError::UnexpectedInvoice),
+		}
+	}
+
+	fn send_payment_for_verified_bolt12_invoice(&self, invoice: &Bolt12Invoice, payment_id: PaymentId) -> Result<(), Bolt12PaymentError> {
 		let best_block_height = self.best_block.read().unwrap().height;
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
 		self.pending_outbound_payments
@@ -10287,7 +10308,7 @@ where
 							self.pending_events.lock().unwrap().push_back((event, None));
 							return ResponseInstruction::NoResponse;
 						} else {
-							self.send_payment_for_bolt12_invoice(&invoice, payment_id)
+							self.send_payment_for_verified_bolt12_invoice(&invoice, payment_id)
 								.map_err(|e| {
 									log_trace!(self.logger, "Failed paying invoice: {:?}", e);
 									InvoiceError::from_string(format!("{:?}", e))

lightning/src/ln/outbound_payment.rs

@@ -501,9 +501,9 @@ pub enum PaymentSendFailure {
 	},
 }
 
-/// An error when attempting to pay a BOLT 12 invoice.
+/// An error when attempting to pay a [`Bolt12Invoice`].
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub(super) enum Bolt12PaymentError {
+pub enum Bolt12PaymentError {
 	/// The invoice was not requested.
 	UnexpectedInvoice,
 	/// Payment for an invoice with the corresponding [`PaymentId`] was already initiated.

lightning/src/util/config.rs

@@ -850,12 +850,16 @@ pub struct UserConfig {
 	/// If this is set to true, the user needs to manually pay [`Bolt12Invoice`]s when received.
 	///
 	/// When set to true, [`Event::InvoiceReceived`] will be generated for each received
-	/// [`Bolt12Invoice`] instead of being automatically paid after verification.
+	/// [`Bolt12Invoice`] instead of being automatically paid after verification. Use
+	/// [`ChannelManager::send_payment_for_bolt12_invoice`] to pay the invoice or
+	/// [`ChannelManager::abandon_payment`] to abandon the associated payment.
 	///
 	/// Default value: false.
 	///
 	/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
 	/// [`Event::InvoiceReceived`]: crate::events::Event::InvoiceReceived
+	/// [`ChannelManager::send_payment_for_bolt12_invoice`]: crate::ln::channelmanager::ChannelManager::send_payment_for_bolt12_invoice
+	/// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
 	pub manually_handle_bolt12_invoices: bool,
 }