Add new invoice CreationError::InvalidAmount for use in checking create_inbound_payment

in an invoice creation utility. Note that if the error type of `create_inbound_payment` ever
changed, we'd be forced to update the invoice utility's callsite to handle the new error

Author: valentinewallace

lightning-invoice/src/lib.rs

@@ -1413,6 +1413,9 @@ pub enum CreationError {
 
 	/// The supplied expiry time could cause an overflow if added to a `PositiveTimestamp`
 	ExpiryTimeOutOfBounds,
+
+	/// The supplied millisatoshi amount was greater than the total bitcoin supply.
+	InvalidAmount,
 }
 
 impl Display for CreationError {
@@ -1422,6 +1425,7 @@ impl Display for CreationError {
 			CreationError::RouteTooLong => f.write_str("The specified route has too many hops and can't be encoded"),
 			CreationError::TimestampOutOfBounds => f.write_str("The unix timestamp of the supplied date is <0 or can't be represented as `SystemTime`"),
 			CreationError::ExpiryTimeOutOfBounds => f.write_str("The supplied expiry time could cause an overflow if added to a `PositiveTimestamp`"),
+			CreationError::InvalidAmount => f.write_str("The supplied millisatoshi amount was greater than the total bitcoin supply"),
 		}
 	}
 }

lightning-invoice/src/utils.rs

@@ -1,6 +1,6 @@
 //! Convenient utilities to create an invoice.
 
-use {Currency, DEFAULT_EXPIRY_TIME, Invoice, InvoiceBuilder, SignOrCreationError, RawInvoice};
+use {CreationError, Currency, DEFAULT_EXPIRY_TIME, Invoice, InvoiceBuilder, SignOrCreationError, RawInvoice};
 use payment::{Payer, Router};
 
 use bech32::ToBase32;
@@ -60,10 +60,11 @@ where
 		}]));
 	}
 
+	// `create_inbound_payment` only returns an error if the amount is greater than the total bitcoin
+	// supply.
 	let (payment_hash, payment_secret) = channelmanager.create_inbound_payment(
-		amt_msat,
-		DEFAULT_EXPIRY_TIME.try_into().unwrap(),
-	).unwrap();
+		amt_msat, DEFAULT_EXPIRY_TIME.try_into().unwrap())
+		.map_err(|()| SignOrCreationError::CreationError(CreationError::InvalidAmount))?;
 	let our_node_pubkey = channelmanager.get_our_node_id();
 	let mut invoice = InvoiceBuilder::new(network)
 		.description(description)