Support reading the new payment_metadata field in invoices

This adds support for reading the new `PaymentMetadata` BOLT11
invoice field, giving us access to the `Vec<u8>` storing arbitrary
bytes we have to send to the recipient.

Author: TheBlueMatt

lightning-invoice/src/de.rs

@@ -457,6 +457,8 @@ impl FromBase32 for TaggedField {
 				Ok(TaggedField::PrivateRoute(PrivateRoute::from_base32(field_data)?)),
 			constants::TAG_PAYMENT_SECRET =>
 				Ok(TaggedField::PaymentSecret(PaymentSecret::from_base32(field_data)?)),
+			constants::TAG_PAYMENT_METADATA =>
+				Ok(TaggedField::PaymentMetadata(Vec::<u8>::from_base32(field_data)?)),
 			constants::TAG_FEATURES =>
 				Ok(TaggedField::Features(InvoiceFeatures::from_base32(field_data)?)),
 			_ => {

lightning-invoice/src/lib.rs

@@ -414,6 +414,7 @@ pub enum TaggedField {
 	Fallback(Fallback),
 	PrivateRoute(PrivateRoute),
 	PaymentSecret(PaymentSecret),
+	PaymentMetadata(Vec<u8>),
 	Features(InvoiceFeatures),
 }
 
@@ -479,6 +480,7 @@ pub mod constants {
 	pub const TAG_FALLBACK: u8 = 9;
 	pub const TAG_PRIVATE_ROUTE: u8 = 3;
 	pub const TAG_PAYMENT_SECRET: u8 = 16;
+	pub const TAG_PAYMENT_METADATA: u8 = 27;
 	pub const TAG_FEATURES: u8 = 5;
 }
 
@@ -937,6 +939,10 @@ impl RawInvoice {
 		find_extract!(self.known_tagged_fields(), TaggedField::PaymentSecret(ref x), x)
 	}
 
+	pub fn payment_metadata(&self) -> Option<&Vec<u8>> {
+		find_extract!(self.known_tagged_fields(), TaggedField::PaymentMetadata(ref x), x)
+	}
+
 	pub fn features(&self) -> Option<&InvoiceFeatures> {
 		find_extract!(self.known_tagged_fields(), TaggedField::Features(ref x), x)
 	}
@@ -1203,6 +1209,11 @@ impl Invoice {
 		self.signed_invoice.payment_secret().expect("was checked by constructor")
 	}
 
+	/// Get the payment metadata blob if one was included in the invoice
+	pub fn payment_metadata(&self) -> Option<&Vec<u8>> {
+		self.signed_invoice.payment_metadata()
+	}
+
 	/// Get the invoice features if they were included in the invoice
 	pub fn features(&self) -> Option<&InvoiceFeatures> {
 		self.signed_invoice.features()
@@ -1305,6 +1316,7 @@ impl TaggedField {
 			TaggedField::Fallback(_) => constants::TAG_FALLBACK,
 			TaggedField::PrivateRoute(_) => constants::TAG_PRIVATE_ROUTE,
 			TaggedField::PaymentSecret(_) => constants::TAG_PAYMENT_SECRET,
+			TaggedField::PaymentMetadata(_) => constants::TAG_PAYMENT_METADATA,
 			TaggedField::Features(_) => constants::TAG_FEATURES,
 		};
 

lightning-invoice/src/ser.rs

@@ -446,6 +446,9 @@ impl ToBase32 for TaggedField {
 			TaggedField::PaymentSecret(ref payment_secret) => {
 				  write_tagged_field(writer, constants::TAG_PAYMENT_SECRET, payment_secret)
 			},
+			TaggedField::PaymentMetadata(ref payment_metadata) => {
+				  write_tagged_field(writer, constants::TAG_PAYMENT_METADATA, payment_metadata)
+			},
 			TaggedField::Features(ref features) => {
 				write_tagged_field(writer, constants::TAG_FEATURES, features)
 			},