Remove Option from InvoiceRequest::amount_msats

If an InvoiceRequest::amount_msats is None, the expected amount can be
determined by the offer. Remove Option from the its return type and use
the value from the offer instead, taking into account the quantity.
Note, InvoiceRequest::amount_msats must be set if the offer uses an
Amount::Currency.

Author: jkczyz

lightning/src/offers/invoice_request.rs

@@ -60,7 +60,7 @@ use crate::io;
 use crate::ln::features::InvoiceRequestFeatures;
 use crate::ln::msgs::DecodeError;
 use crate::offers::merkle::{SignError, SignatureTlvStream, SignatureTlvStreamRef, self};
-use crate::offers::offer::{Offer, OfferContents, OfferTlvStream, OfferTlvStreamRef};
+use crate::offers::offer::{Amount, Offer, OfferContents, OfferTlvStream, OfferTlvStreamRef};
 use crate::offers::parse::{ParseError, ParsedMessage, SemanticError};
 use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
 use crate::util::ser::{HighZeroBytesDroppedBigSize, SeekReadable, WithoutLength, Writeable, Writer};
@@ -283,8 +283,17 @@ impl InvoiceRequest {
 	/// must be greater than or equal to [`Offer::amount`], converted if necessary.
 	///
 	/// [`chain`]: Self::chain
-	pub fn amount_msats(&self) -> Option<u64> {
+	pub fn amount_msats(&self) -> u64 {
 		self.contents.amount_msats
+			.unwrap_or_else(|| {
+				let offer_amount_msats = match self.contents.offer.amount() {
+					None => 0,
+					Some(&Amount::Bitcoin { amount_msats }) => amount_msats,
+					Some(&Amount::Currency { .. }) => unreachable!(),
+				};
+
+				offer_amount_msats * self.quantity().unwrap_or(1)
+			})
 	}
 
 	/// Features pertaining to requesting an invoice.
@@ -533,7 +542,7 @@ mod tests {
 		assert_eq!(invoice_request.bytes, buffer.as_slice());
 		assert_eq!(invoice_request.metadata(), &[1; 32]);
 		assert_eq!(invoice_request.chain(), ChainHash::using_genesis_block(Network::Bitcoin));
-		assert_eq!(invoice_request.amount_msats(), None);
+		assert_eq!(invoice_request.amount_msats(), 1000);
 		assert_eq!(invoice_request.features(), &InvoiceRequestFeatures::empty());
 		assert_eq!(invoice_request.quantity(), None);
 		assert_eq!(invoice_request.payer_id(), payer_pubkey());
@@ -694,7 +703,7 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
-		assert_eq!(invoice_request.amount_msats(), Some(1000));
+		assert_eq!(invoice_request.amount_msats(), 1000);
 		assert_eq!(tlv_stream.amount, Some(1000));
 
 		let invoice_request = OfferBuilder::new("foo".into(), recipient_pubkey())
@@ -706,7 +715,7 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
-		assert_eq!(invoice_request.amount_msats(), Some(1000));
+		assert_eq!(invoice_request.amount_msats(), 1000);
 		assert_eq!(tlv_stream.amount, Some(1000));
 
 		let invoice_request = OfferBuilder::new("foo".into(), recipient_pubkey())
@@ -717,7 +726,7 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
-		assert_eq!(invoice_request.amount_msats(), Some(1001));
+		assert_eq!(invoice_request.amount_msats(), 1001);
 		assert_eq!(tlv_stream.amount, Some(1001));
 
 		match OfferBuilder::new("foo".into(), recipient_pubkey())
@@ -838,9 +847,21 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
-		assert_eq!(invoice_request.amount_msats(), Some(10_000));
+		assert_eq!(invoice_request.amount_msats(), 10_000);
 		assert_eq!(tlv_stream.amount, Some(10_000));
 
+		let invoice_request = OfferBuilder::new("foo".into(), recipient_pubkey())
+			.amount_msats(1000)
+			.supported_quantity(Quantity::Bounded(ten))
+			.build().unwrap()
+			.request_invoice(vec![1; 32], payer_pubkey()).unwrap()
+			.quantity(10).unwrap()
+			.build().unwrap()
+			.sign(payer_sign).unwrap();
+		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
+		assert_eq!(invoice_request.amount_msats(), 10_000);
+		assert_eq!(tlv_stream.amount, None);
+
 		match OfferBuilder::new("foo".into(), recipient_pubkey())
 			.amount_msats(1000)
 			.supported_quantity(Quantity::Bounded(ten))
@@ -863,7 +884,7 @@ mod tests {
 			.build().unwrap()
 			.sign(payer_sign).unwrap();
 		let (_, _, tlv_stream, _) = invoice_request.as_tlv_stream();
-		assert_eq!(invoice_request.amount_msats(), Some(2_000));
+		assert_eq!(invoice_request.amount_msats(), 2_000);
 		assert_eq!(tlv_stream.amount, Some(2_000));
 
 		match OfferBuilder::new("foo".into(), recipient_pubkey())