Include InvoiceRequest fields to PaymentContext

When receiving a payment, it's useful to know information about the
InvoiceRequest. Include this data in PaymentContext::Bolt12Offer so
users can display information about an inbound payment (e.g., the payer
note).

Author: jkczyz

lightning/src/blinded_path/payment.rs

@@ -12,6 +12,7 @@ use crate::ln::channelmanager::CounterpartyForwardingInfo;
 use crate::ln::features::BlindedHopFeatures;
 use crate::ln::msgs::DecodeError;
 use crate::offers::invoice::BlindedPayInfo;
+use crate::offers::invoice_request::InvoiceRequestFields;
 use crate::offers::offer::OfferId;
 use crate::prelude::*;
 use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
@@ -115,6 +116,12 @@ pub enum PaymentContext {
 		///
 		/// [`Offer`]: crate::offers::offer::Offer
 		offer_id: OfferId,
+
+		/// Fields from an [`InvoiceRequest`] sent for a [`Bolt12Invoice`].
+		///
+		/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
+		/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
+		invoice_request: InvoiceRequestFields,
 	},
 	/// The payment was made for invoice sent for a BOLT 12 [`Refund`].
 	///
@@ -342,6 +349,7 @@ impl Readable for PaymentConstraints {
 impl_writeable_tlv_based_enum_upgradable!(PaymentContext,
 	(0, Bolt12Offer) => {
 		(0, offer_id, required),
+		(2, invoice_request, required),
 	},
 	(2, Bolt12Refund) => {},
 );

lightning/src/ln/channelmanager.rs

@@ -9499,6 +9499,7 @@ where
 
 				let payment_context = PaymentContext::Bolt12Offer {
 					offer_id: invoice_request.offer_id,
+					invoice_request: invoice_request.fields(),
 				};
 				let payment_paths = match self.create_blinded_payment_paths(
 					amount_msats, payment_secret, Some(payment_context)

lightning/src/offers/invoice_request.rs

@@ -77,8 +77,8 @@ use crate::offers::offer::{Offer, OfferContents, OfferId, OfferTlvStream, OfferT
 use crate::offers::parse::{Bolt12ParseError, ParsedMessage, Bolt12SemanticError};
 use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
 use crate::offers::signer::{Metadata, MetadataMaterial};
-use crate::util::ser::{HighZeroBytesDroppedBigSize, SeekReadable, WithoutLength, Writeable, Writer};
-use crate::util::string::PrintableString;
+use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, SeekReadable, WithoutLength, Writeable, Writer};
+use crate::util::string::{PrintableString, UntrustedString};
 
 #[cfg(not(c_bindings))]
 use {
@@ -872,6 +872,24 @@ impl VerifiedInvoiceRequest {
 	invoice_request_respond_with_derived_signing_pubkey_methods!(self, self.inner, InvoiceBuilder<DerivedSigningPubkey>);
 	#[cfg(c_bindings)]
 	invoice_request_respond_with_derived_signing_pubkey_methods!(self, self.inner, InvoiceWithDerivedSigningPubkeyBuilder);
+
+	pub(crate) fn fields(&self) -> InvoiceRequestFields {
+		let InvoiceRequestContents {
+			payer_id,
+			inner: InvoiceRequestContentsWithoutPayerId {
+				payer: _, offer: _, chain, amount_msats, features, quantity, payer_note
+			},
+		} = &self.inner.contents;
+
+		InvoiceRequestFields {
+			payer_id: *payer_id,
+			chain: *chain,
+			amount_msats: *amount_msats,
+			features: features.clone(),
+			quantity: *quantity,
+			payer_note: payer_note.clone().map(|mut s| { s.truncate(512); UntrustedString(s) }),
+		}
+	}
 }
 
 impl InvoiceRequestContents {
@@ -1100,6 +1118,66 @@ impl TryFrom<PartialInvoiceRequestTlvStream> for InvoiceRequestContents {
 	}
 }
 
+/// Fields sent in an [`InvoiceRequest`] message to include in [`PaymentContext::Bolt12Offer`].
+///
+/// [`PaymentContext::Bolt12Offer`]: crate::blinded_path::payment::PaymentContext::Bolt12Offer
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct InvoiceRequestFields {
+	/// A possibly transient pubkey used to sign the invoice request.
+	pub payer_id: PublicKey,
+
+	/// A chain from [`Offer::chains`] that the offer is valid for.
+	pub chain: Option<ChainHash>,
+
+	/// The amount to pay in msats (i.e., the minimum lightning-payable unit for [`chain`]), which
+	/// must be greater than or equal to [`Offer::amount`], converted if necessary.
+	///
+	/// [`chain`]: Self::chain
+	pub amount_msats: Option<u64>,
+
+	/// Features pertaining to requesting an invoice.
+	pub features: InvoiceRequestFeatures,
+
+	/// The quantity of the offer's item conforming to [`Offer::is_valid_quantity`].
+	pub quantity: Option<u64>,
+
+	/// A payer-provided note which will be seen by the recipient and reflected back in the invoice
+	/// response.
+	pub payer_note: Option<UntrustedString>,
+}
+
+impl Writeable for InvoiceRequestFields {
+	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
+		write_tlv_fields!(writer, {
+			(0, self.payer_id, required),
+			(2, self.chain, option),
+			(4, self.amount_msats, option),
+			(6, WithoutLength(&self.features), required),
+			(8, self.quantity, option),
+			(10, self.payer_note, option),
+		});
+		Ok(())
+	}
+}
+
+impl Readable for InvoiceRequestFields {
+	fn read<R: io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
+		_init_and_read_len_prefixed_tlv_fields!(reader, {
+			(0, payer_id, required),
+			(2, chain, option),
+			(4, amount_msats, option),
+			(6, features, (option, encoding: (InvoiceRequestFeatures, WithoutLength))),
+			(8, quantity, option),
+			(10, payer_note, option),
+		});
+		let features = features.unwrap_or(InvoiceRequestFeatures::empty());
+
+		Ok(InvoiceRequestFields {
+			payer_id: payer_id.0.unwrap(), chain, amount_msats, features, quantity, payer_note
+		})
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::{InvoiceRequest, InvoiceRequestTlvStreamRef, SIGNATURE_TAG, UnsignedInvoiceRequest};