f - check offer amount in invoice builder

Author: jkczyz

lightning/src/offers/invoice.rs

@@ -25,7 +25,7 @@ use crate::ln::features::{BlindedHopFeatures, Bolt12InvoiceFeatures};
 use crate::ln::msgs::DecodeError;
 use crate::offers::invoice_request::{InvoiceRequest, InvoiceRequestContents, InvoiceRequestTlvStream, InvoiceRequestTlvStreamRef};
 use crate::offers::merkle::{SignError, SignatureTlvStream, SignatureTlvStreamRef, WithoutSignatures, self};
-use crate::offers::offer::{OfferTlvStream, OfferTlvStreamRef};
+use crate::offers::offer::{Amount, OfferTlvStream, OfferTlvStreamRef};
 use crate::offers::parse::{ParseError, ParsedMessage, SemanticError};
 use crate::offers::payer::{PayerTlvStream, PayerTlvStreamRef};
 use crate::offers::refund::RefundContents;
@@ -68,14 +68,24 @@ impl<'a> InvoiceBuilder<'a> {
 			return Err(SemanticError::InvalidPayInfo);
 		}
 
+		let amount_msats = match invoice_request.amount_msats() {
+			Some(amount_msats) => amount_msats,
+			None => match invoice_request.contents.offer.amount() {
+				Some(Amount::Bitcoin { amount_msats }) => {
+					amount_msats * invoice_request.quantity().unwrap_or(1)
+				},
+				Some(Amount::Currency { .. }) => return Err(SemanticError::UnsupportedCurrency),
+				None => return Err(SemanticError::MissingAmount),
+			},
+		};
+
 		Ok(Self {
 			bytes: &invoice_request.bytes,
 			invoice: InvoiceContents::ForOffer {
 				invoice_request: invoice_request.contents.clone(),
 				fields: InvoiceFields {
-					paths, payinfo, created_at, relative_expiry: None, payment_hash,
-					amount_msats: invoice_request.amount_msats(), fallbacks: None,
-					features: Bolt12InvoiceFeatures::empty(), code: None,
+					paths, payinfo, created_at, relative_expiry: None, payment_hash, amount_msats,
+					fallbacks: None, features: Bolt12InvoiceFeatures::empty(), code: None,
 				},
 			},
 		})