Refactor amount checks and fix currency check

Modified check_amount_msats_for_quantity to trust the
user-provided msats amount and moved/fixed the currency
check to the InvoiceRequest parsing code. We check if
the user attempts to use an Amount:Currency and return
an error if so.

Author: slanesuke

lightning/src/ln/offers_tests.rs

@@ -55,6 +55,7 @@ use crate::offers::invoice_error::InvoiceError;
 use crate::offers::invoice_request::{InvoiceRequest, InvoiceRequestFields};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::onion_message::messenger::{Destination, PeeledOnion};
+use crate::offers::offer::Amount;
 use crate::onion_message::offers::OffersMessage;
 use crate::onion_message::packet::ParsedOnionMessageContents;
 use crate::routing::gossip::{NodeAlias, NodeId};
@@ -1607,9 +1608,9 @@ fn fails_creating_or_paying_for_offer_without_connected_peers() {
 	reconnect_nodes(args);
 
 	let offer = alice.node
-		.create_offer_builder(Some(absolute_expiry)).unwrap()
-		.amount_msats(10_000_000)
-		.build().unwrap();
+		.create_offer_builder(None).unwrap()
+		.amount(Amount::Currency {iso4217_code: *b"USD", amount: 6_000})
+		.build_unchecked();
 
 	let payment_id = PaymentId([1; 32]);
 
@@ -1771,8 +1772,9 @@ fn fails_creating_invoice_request_without_blinded_reply_path() {
 
 	let offer = alice.node
 		.create_offer_builder(None).unwrap()
-		.amount_msats(10_000_000)
-		.build().unwrap();
+		.amount(Amount::Currency {iso4217_code: *b"USD", amount: 6_000})
+		.build_unchecked();
+
 
 	let payment_id = PaymentId([1; 32]);
 

lightning/src/offers/invoice_request.rs

@@ -71,7 +71,7 @@ use crate::ln::msgs::DecodeError;
 use crate::offers::invoice::BlindedPayInfo;
 use crate::offers::merkle::{SignError, SignFn, SignatureTlvStream, SignatureTlvStreamRef, TaggedHash, self};
 use crate::offers::nonce::Nonce;
-use crate::offers::offer::{Offer, OfferContents, OfferId, OfferTlvStream, OfferTlvStreamRef};
+use crate::offers::offer::{Amount, Offer, OfferContents, OfferId, OfferTlvStream, OfferTlvStreamRef};
 use crate::offers::parse::{Bolt12ParseError, ParsedMessage, Bolt12SemanticError};
 use crate::offers::payer::{PayerContents, PayerTlvStream, PayerTlvStreamRef};
 use crate::offers::signer::{Metadata, MetadataMaterial};
@@ -1158,8 +1158,12 @@ impl TryFrom<PartialInvoiceRequestTlvStream> for InvoiceRequestContents {
 			return Err(Bolt12SemanticError::MissingAmount);
 		}
 
-		offer.check_quantity(quantity)?;
+		match offer.amount() {
+			Some(Amount::Currency {..}) => return Err(Bolt12SemanticError::UnsupportedCurrency),
+			_ => { },
+		};
 		offer.check_amount_msats_for_quantity(amount, quantity)?;
+		offer.check_quantity(quantity)?;
 
 		let features = features.unwrap_or_else(InvoiceRequestFeatures::empty);
 

lightning/src/offers/offer.rs

@@ -310,7 +310,7 @@ macro_rules! offer_builder_methods { (
 	/// Sets the [`Offer::amount`].
 	///
 	/// Successive calls to this method will override the previous setting.
-	pub(super) fn amount($($self_mut)* $self: $self_type, amount: Amount) -> $return_type {
+	pub(crate) fn amount($($self_mut)* $self: $self_type, amount: Amount) -> $return_type {
 		$self.offer.amount = Some(amount);
 		$return_value
 	}
@@ -460,7 +460,7 @@ macro_rules! offer_builder_test_methods { (
 	}
 
 	#[cfg_attr(c_bindings, allow(dead_code))]
-	pub(super) fn build_unchecked($self: $self_type) -> Offer {
+	pub(crate) fn build_unchecked($self: $self_type) -> Offer {
 		$self.build_without_checks()
 	}
 } }
@@ -857,9 +857,8 @@ impl OfferContents {
 		&self, amount_msats: Option<u64>, quantity: Option<u64>
 	) -> Result<(), Bolt12SemanticError> {
 		let offer_amount_msats = match self.amount {
-			None => 0,
-			Some(Amount::Bitcoin { amount_msats }) => amount_msats,
-			Some(Amount::Currency { .. }) => return Err(Bolt12SemanticError::UnsupportedCurrency),
+			Some(Amount::Bitcoin {amount_msats}) => amount_msats,
+			_ => 0,
 		};
 
 		if !self.expects_quantity() || quantity.is_some() {