f - split set_custom_bit

Author: jkczyz

lightning/src/ln/features.rs

@@ -747,11 +747,29 @@ impl<T: sealed::Context> Features<T> {
 		true
 	}
 
-	/// Sets a custom feature bit. Errors if `bit` is outside the custom range as defined by
-	/// [bLIP 2] or if it is a known `T` feature.
+	/// Sets a required custom feature bit. Errors if `bit` is outside the custom range as defined
+	/// by [bLIP 2] or if it is a known `T` feature.
+	///
+	/// Note: Required bits are even. If an odd bit is given, then the corresponding even bit will
+	/// be set instead (i.e., `bit - 1`).
 	///
 	/// [bLIP 2]: https://github.com/lightning/blips/blob/master/blip-0002.md#feature-bits
-	pub fn set_custom_bit(&mut self, bit: usize) -> Result<(), ()> {
+	pub fn set_required_custom_bit(&mut self, bit: usize) -> Result<(), ()> {
+		self.set_custom_bit(bit - (bit % 2))
+	}
+
+	/// Sets an optional custom feature bit. Errors if `bit` is outside the custom range as defined
+	/// by [bLIP 2] or if it is a known `T` feature.
+	///
+	/// Note: Optional bits are odd. If an even bit is given, then the corresponding odd bit will be
+	/// set instead (i.e., `bit + 1`).
+	///
+	/// [bLIP 2]: https://github.com/lightning/blips/blob/master/blip-0002.md#feature-bits
+	pub fn set_optional_custom_bit(&mut self, bit: usize) -> Result<(), ()> {
+		self.set_custom_bit(bit + (1 - (bit % 2)))
+	}
+
+	fn set_custom_bit(&mut self, bit: usize) -> Result<(), ()> {
 		if bit < 256 {
 			return Err(());
 		}
@@ -1016,18 +1034,28 @@ mod tests {
 		features.set_variable_length_onion_optional();
 		assert_eq!(features.flags[1], 0b00000010);
 
-		assert!(features.set_custom_bit(255).is_err());
-		assert!(features.set_custom_bit(256).is_ok());
-		assert!(features.set_custom_bit(258).is_ok());
+		assert!(features.set_optional_custom_bit(255).is_err());
+		assert!(features.set_required_custom_bit(256).is_ok());
+		assert!(features.set_required_custom_bit(258).is_ok());
 		assert_eq!(features.flags[31], 0b00000000);
 		assert_eq!(features.flags[32], 0b00000101);
 
 		let known_bit = <sealed::InvoiceContext as sealed::PaymentSecret>::EVEN_BIT;
 		let byte_offset = <sealed::InvoiceContext as sealed::PaymentSecret>::BYTE_OFFSET;
 		assert_eq!(byte_offset, 1);
 		assert_eq!(features.flags[byte_offset], 0b00000010);
-		assert!(features.set_custom_bit(known_bit).is_err());
+		assert!(features.set_required_custom_bit(known_bit).is_err());
 		assert_eq!(features.flags[byte_offset], 0b00000010);
+
+		let mut features = InvoiceFeatures::empty();
+		assert!(features.set_optional_custom_bit(256).is_ok());
+		assert!(features.set_optional_custom_bit(259).is_ok());
+		assert_eq!(features.flags[32], 0b00001010);
+
+		let mut features = InvoiceFeatures::empty();
+		assert!(features.set_required_custom_bit(257).is_ok());
+		assert!(features.set_required_custom_bit(258).is_ok());
+		assert_eq!(features.flags[32], 0b00000101);
 	}
 
 	#[test]