+
+ // Returns true if the features within `self` are a subset of the features within `other`.
+ pub(crate) fn is_subset(&self, other: &Self) -> bool {
+ for (idx, byte) in self.flags.iter().enumerate() {
+ if let Some(other_byte) = other.flags.get(idx) {
+ if byte & other_byte != *byte {
+ // `self` has bits set that `other` doesn't.
+ return false;
+ }
+ } else {
+ if *byte > 0 {
+ // `self` has a non-zero byte that `other` doesn't.
+ return false;
+ }
+ }
+ }
+ true
+ }
+
+ /// 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_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(());
+ }
+
+ let byte_offset = bit / 8;
+ let mask = 1 << (bit - 8 * byte_offset);
+ if byte_offset < T::KNOWN_FEATURE_MASK.len() {
+ if (T::KNOWN_FEATURE_MASK[byte_offset] & mask) != 0 {
+ return Err(());
+ }
+ }
+
+ if self.flags.len() <= byte_offset {
+ self.flags.resize(byte_offset + 1, 0u8);
+ }
+
+ self.flags[byte_offset] |= mask;
+
+ Ok(())
+ }