1 // This file is Copyright its original authors, visible in version control
4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
7 // You may not use this file except in accordance with one or both of these
10 //! Feature flag definitions for the Lightning protocol according to [BOLT #9].
12 //! Lightning nodes advertise a supported set of operation through feature flags. Features are
13 //! applicable for a specific context as indicated in some [messages]. [`Features`] encapsulates
14 //! behavior for specifying and checking feature flags for a particular context. Each feature is
15 //! defined internally by a trait specifying the corresponding flags (i.e., even and odd bits). A
16 //! [`Context`] is used to parameterize [`Features`] and defines which features it can support.
18 //! Whether a feature is considered "known" or "unknown" is relative to the implementation, whereas
19 //! the term "supports" is used in reference to a particular set of [`Features`]. That is, a node
20 //! supports a feature if it advertises the feature (as either required or optional) to its peers.
21 //! And the implementation can interpret a feature if the feature is known to it.
23 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
24 //! [messages]: ../msgs/index.html
25 //! [`Features`]: struct.Features.html
26 //! [`Context`]: sealed/trait.Context.html
29 use std::marker::PhantomData;
31 use ln::msgs::DecodeError;
32 use util::ser::{Readable, Writeable, Writer};
35 /// The context in which [`Features`] are applicable. Defines which features are required and
36 /// which are optional for the context.
38 /// [`Features`]: ../struct.Features.html
40 /// Features that are known to the implementation, where a required feature is indicated by
41 /// its even bit and an optional feature is indicated by its odd bit.
42 const KNOWN_FEATURE_FLAGS: &'static [u8];
44 /// Bitmask for selecting features that are known to the implementation, regardless of
45 /// whether each feature is required or optional.
46 const KNOWN_FEATURE_MASK: &'static [u8];
49 /// Defines a [`Context`] by stating which features it requires and which are optional. Features
50 /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
51 /// feature identifiers.
53 /// [`Context`]: trait.Context.html
54 macro_rules! define_context {
56 required_features: [$( $( $required_feature: ident )|*, )*],
57 optional_features: [$( $( $optional_feature: ident )|*, )*],
59 pub struct $context {}
61 impl Context for $context {
62 const KNOWN_FEATURE_FLAGS: &'static [u8] = &[
63 // For each byte, use bitwise-OR to compute the applicable flags for known
64 // required features `r_i` and optional features `o_j` for all `i` and `j` such
65 // that the following slice is formed:
68 // `r_0` | `r_1` | ... | `o_0` | `o_1` | ...,
73 <Self as $required_feature>::REQUIRED_MASK)*
75 <Self as $optional_feature>::OPTIONAL_MASK)*,
79 const KNOWN_FEATURE_MASK: &'static [u8] = &[
80 // Similar as above, but set both flags for each feature regardless of whether
81 // the feature is required or optional.
84 <Self as $required_feature>::REQUIRED_MASK |
85 <Self as $required_feature>::OPTIONAL_MASK)*
87 <Self as $optional_feature>::REQUIRED_MASK |
88 <Self as $optional_feature>::OPTIONAL_MASK)*,
95 define_context!(InitContext {
106 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
108 VariableLengthOnion | PaymentSecret,
113 define_context!(NodeContext {
124 DataLossProtect | UpfrontShutdownScript | GossipQueries,
126 VariableLengthOnion | PaymentSecret,
131 define_context!(ChannelContext {
132 required_features: [],
133 optional_features: [],
136 /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
137 /// useful for manipulating feature flags.
139 /// [`Context`]: trait.Context.html
140 macro_rules! define_feature {
141 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr) => {
144 /// See [BOLT #9] for details.
146 /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
147 pub trait $feature: Context {
148 /// The bit used to signify that the feature is required.
149 const EVEN_BIT: usize = $odd_bit - 1;
151 /// The bit used to signify that the feature is optional.
152 const ODD_BIT: usize = $odd_bit;
154 /// Assertion that [`EVEN_BIT`] is actually even.
156 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
157 const ASSERT_EVEN_BIT_PARITY: usize;
159 /// Assertion that [`ODD_BIT`] is actually odd.
161 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
162 const ASSERT_ODD_BIT_PARITY: usize;
164 /// The byte where the feature is set.
165 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
167 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
169 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
170 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
172 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
174 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
175 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
177 /// Returns whether the feature is required by the given flags.
179 fn requires_feature(flags: &Vec<u8>) -> bool {
180 flags.len() > Self::BYTE_OFFSET &&
181 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
184 /// Returns whether the feature is supported by the given flags.
186 fn supports_feature(flags: &Vec<u8>) -> bool {
187 flags.len() > Self::BYTE_OFFSET &&
188 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
191 /// Sets the feature's required (even) bit in the given flags.
193 fn set_required_bit(flags: &mut Vec<u8>) {
194 if flags.len() <= Self::BYTE_OFFSET {
195 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
198 flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
201 /// Sets the feature's optional (odd) bit in the given flags.
203 fn set_optional_bit(flags: &mut Vec<u8>) {
204 if flags.len() <= Self::BYTE_OFFSET {
205 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
208 flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
211 /// Clears the feature's required (even) and optional (odd) bits from the given
214 fn clear_bits(flags: &mut Vec<u8>) {
215 if flags.len() > Self::BYTE_OFFSET {
216 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
217 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
220 let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
221 let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
222 flags.resize(size, 0u8);
227 impl $feature for $context {
229 const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
232 const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
238 define_feature!(1, DataLossProtect, [InitContext, NodeContext],
239 "Feature flags for `option_data_loss_protect`.");
240 // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
241 define_feature!(3, InitialRoutingSync, [InitContext],
242 "Feature flags for `initial_routing_sync`.");
243 define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
244 "Feature flags for `option_upfront_shutdown_script`.");
245 define_feature!(7, GossipQueries, [InitContext, NodeContext],
246 "Feature flags for `gossip_queries`.");
247 define_feature!(9, VariableLengthOnion, [InitContext, NodeContext],
248 "Feature flags for `var_onion_optin`.");
249 define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
250 "Feature flags for `option_static_remotekey`.");
251 define_feature!(15, PaymentSecret, [InitContext, NodeContext],
252 "Feature flags for `payment_secret`.");
253 define_feature!(17, BasicMPP, [InitContext, NodeContext],
254 "Feature flags for `basic_mpp`.");
257 define_context!(TestingContext {
277 define_feature!(23, UnknownFeature, [TestingContext],
278 "Feature flags for an unknown feature used in testing.");
281 /// Tracks the set of features which a node implements, templated by the context in which it
284 /// (C-not exported) as we map the concrete feature types below directly instead
285 pub struct Features<T: sealed::Context> {
286 /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
288 mark: PhantomData<T>,
291 impl<T: sealed::Context> Clone for Features<T> {
292 fn clone(&self) -> Self {
294 flags: self.flags.clone(),
299 impl<T: sealed::Context> PartialEq for Features<T> {
300 fn eq(&self, o: &Self) -> bool {
301 self.flags.eq(&o.flags)
304 impl<T: sealed::Context> fmt::Debug for Features<T> {
305 fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
310 /// Features used within an `init` message.
311 pub type InitFeatures = Features<sealed::InitContext>;
312 /// Features used within a `node_announcement` message.
313 pub type NodeFeatures = Features<sealed::NodeContext>;
314 /// Features used within a `channel_announcement` message.
315 pub type ChannelFeatures = Features<sealed::ChannelContext>;
318 /// Writes all features present up to, and including, 13.
319 pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
320 let len = cmp::min(2, self.flags.len());
321 w.size_hint(len + 2);
322 (len as u16).write(w)?;
323 for i in (0..len).rev() {
325 self.flags[i].write(w)?;
327 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
328 // up-to-and-including-bit-5, 0-indexed, on this byte:
329 (self.flags[i] & 0b00_11_11_11).write(w)?;
335 /// or's another InitFeatures into this one.
336 pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
337 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
338 self.flags.resize(total_feature_len, 0u8);
339 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
345 /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
346 /// are included in the result.
347 pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
348 self.to_context_internal()
352 impl<T: sealed::Context> Features<T> {
353 /// Create a blank Features with no features set
354 pub fn empty() -> Self {
361 /// Creates features known by the implementation as defined by [`T::KNOWN_FEATURE_FLAGS`].
363 /// [`T::KNOWN_FEATURE_FLAGS`]: sealed/trait.Context.html#associatedconstant.KNOWN_FEATURE_FLAGS
364 pub fn known() -> Self {
366 flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
371 /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
372 /// included in the result.
373 fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
374 let byte_count = C::KNOWN_FEATURE_MASK.len();
375 let mut flags = Vec::new();
376 for (i, byte) in self.flags.iter().enumerate() {
378 let known_source_features = T::KNOWN_FEATURE_MASK[i];
379 let known_target_features = C::KNOWN_FEATURE_MASK[i];
380 flags.push(byte & known_source_features & known_target_features);
383 Features::<C> { flags, mark: PhantomData, }
387 /// Create a Features given a set of flags, in LE.
388 pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
396 /// Gets the underlying flags set, in LE.
397 pub fn le_flags(&self) -> &Vec<u8> {
401 pub(crate) fn requires_unknown_bits(&self) -> bool {
402 // Bitwise AND-ing with all even bits set except for known features will select required
404 let byte_count = T::KNOWN_FEATURE_MASK.len();
405 self.flags.iter().enumerate().any(|(i, &byte)| {
406 let required_features = 0b01_01_01_01;
407 let unknown_features = if i < byte_count {
408 !T::KNOWN_FEATURE_MASK[i]
412 (byte & (required_features & unknown_features)) != 0
416 pub(crate) fn supports_unknown_bits(&self) -> bool {
417 // Bitwise AND-ing with all even and odd bits set except for known features will select
418 // both required and optional unknown features.
419 let byte_count = T::KNOWN_FEATURE_MASK.len();
420 self.flags.iter().enumerate().any(|(i, &byte)| {
421 let unknown_features = if i < byte_count {
422 !T::KNOWN_FEATURE_MASK[i]
426 (byte & unknown_features) != 0
430 /// The number of bytes required to represent the feature flags present. This does not include
431 /// the length bytes which are included in the serialized form.
432 pub(crate) fn byte_count(&self) -> usize {
437 pub(crate) fn set_required_unknown_bits(&mut self) {
438 <sealed::TestingContext as sealed::UnknownFeature>::set_required_bit(&mut self.flags);
442 pub(crate) fn set_optional_unknown_bits(&mut self) {
443 <sealed::TestingContext as sealed::UnknownFeature>::set_optional_bit(&mut self.flags);
447 pub(crate) fn clear_unknown_bits(&mut self) {
448 <sealed::TestingContext as sealed::UnknownFeature>::clear_bits(&mut self.flags);
452 impl<T: sealed::DataLossProtect> Features<T> {
454 pub(crate) fn requires_data_loss_protect(&self) -> bool {
455 <T as sealed::DataLossProtect>::requires_feature(&self.flags)
457 pub(crate) fn supports_data_loss_protect(&self) -> bool {
458 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
462 impl<T: sealed::UpfrontShutdownScript> Features<T> {
464 pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
465 <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
467 pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
468 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
471 pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
472 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
478 impl<T: sealed::GossipQueries> Features<T> {
480 pub(crate) fn requires_gossip_queries(&self) -> bool {
481 <T as sealed::GossipQueries>::requires_feature(&self.flags)
483 pub(crate) fn supports_gossip_queries(&self) -> bool {
484 <T as sealed::GossipQueries>::supports_feature(&self.flags)
487 pub(crate) fn clear_gossip_queries(mut self) -> Self {
488 <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
493 impl<T: sealed::VariableLengthOnion> Features<T> {
495 pub(crate) fn requires_variable_length_onion(&self) -> bool {
496 <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
498 pub(crate) fn supports_variable_length_onion(&self) -> bool {
499 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
503 impl<T: sealed::StaticRemoteKey> Features<T> {
504 pub(crate) fn supports_static_remote_key(&self) -> bool {
505 <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
508 pub(crate) fn requires_static_remote_key(&self) -> bool {
509 <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
513 impl<T: sealed::InitialRoutingSync> Features<T> {
514 pub(crate) fn initial_routing_sync(&self) -> bool {
515 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
517 // We are no longer setting initial_routing_sync now that gossip_queries
518 // is enabled. This feature is ignored by a peer when gossip_queries has
521 pub(crate) fn clear_initial_routing_sync(&mut self) {
522 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
526 impl<T: sealed::PaymentSecret> Features<T> {
528 pub(crate) fn requires_payment_secret(&self) -> bool {
529 <T as sealed::PaymentSecret>::requires_feature(&self.flags)
531 // Note that we never need to test this since what really matters is the invoice - iff the
532 // invoice provides a payment_secret, we assume that we can use it (ie that the recipient
533 // supports payment_secret).
535 pub(crate) fn supports_payment_secret(&self) -> bool {
536 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
540 impl<T: sealed::BasicMPP> Features<T> {
542 pub(crate) fn requires_basic_mpp(&self) -> bool {
543 <T as sealed::BasicMPP>::requires_feature(&self.flags)
545 // We currently never test for this since we don't actually *generate* multipath routes.
547 pub(crate) fn supports_basic_mpp(&self) -> bool {
548 <T as sealed::BasicMPP>::supports_feature(&self.flags)
552 impl<T: sealed::Context> Writeable for Features<T> {
553 fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
554 w.size_hint(self.flags.len() + 2);
555 (self.flags.len() as u16).write(w)?;
556 for f in self.flags.iter().rev() { // Swap back to big-endian
563 impl<T: sealed::Context> Readable for Features<T> {
564 fn read<R: ::std::io::Read>(r: &mut R) -> Result<Self, DecodeError> {
565 let mut flags: Vec<u8> = Readable::read(r)?;
566 flags.reverse(); // Swap to little-endian
576 use super::{ChannelFeatures, InitFeatures, NodeFeatures};
579 fn sanity_test_known_features() {
580 assert!(!ChannelFeatures::known().requires_unknown_bits());
581 assert!(!ChannelFeatures::known().supports_unknown_bits());
582 assert!(!InitFeatures::known().requires_unknown_bits());
583 assert!(!InitFeatures::known().supports_unknown_bits());
584 assert!(!NodeFeatures::known().requires_unknown_bits());
585 assert!(!NodeFeatures::known().supports_unknown_bits());
587 assert!(InitFeatures::known().supports_upfront_shutdown_script());
588 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
589 assert!(!InitFeatures::known().requires_upfront_shutdown_script());
590 assert!(!NodeFeatures::known().requires_upfront_shutdown_script());
592 assert!(InitFeatures::known().supports_gossip_queries());
593 assert!(NodeFeatures::known().supports_gossip_queries());
594 assert!(!InitFeatures::known().requires_gossip_queries());
595 assert!(!NodeFeatures::known().requires_gossip_queries());
597 assert!(InitFeatures::known().supports_data_loss_protect());
598 assert!(NodeFeatures::known().supports_data_loss_protect());
599 assert!(!InitFeatures::known().requires_data_loss_protect());
600 assert!(!NodeFeatures::known().requires_data_loss_protect());
602 assert!(InitFeatures::known().supports_variable_length_onion());
603 assert!(NodeFeatures::known().supports_variable_length_onion());
604 assert!(!InitFeatures::known().requires_variable_length_onion());
605 assert!(!NodeFeatures::known().requires_variable_length_onion());
607 assert!(InitFeatures::known().supports_static_remote_key());
608 assert!(NodeFeatures::known().supports_static_remote_key());
609 assert!(InitFeatures::known().requires_static_remote_key());
610 assert!(NodeFeatures::known().requires_static_remote_key());
612 assert!(InitFeatures::known().supports_payment_secret());
613 assert!(NodeFeatures::known().supports_payment_secret());
614 assert!(!InitFeatures::known().requires_payment_secret());
615 assert!(!NodeFeatures::known().requires_payment_secret());
617 assert!(InitFeatures::known().supports_basic_mpp());
618 assert!(NodeFeatures::known().supports_basic_mpp());
619 assert!(!InitFeatures::known().requires_basic_mpp());
620 assert!(!NodeFeatures::known().requires_basic_mpp());
622 let mut init_features = InitFeatures::known();
623 assert!(init_features.initial_routing_sync());
624 init_features.clear_initial_routing_sync();
625 assert!(!init_features.initial_routing_sync());
629 fn sanity_test_unknown_bits() {
630 let mut features = ChannelFeatures::empty();
631 assert!(!features.requires_unknown_bits());
632 assert!(!features.supports_unknown_bits());
634 features.set_required_unknown_bits();
635 assert!(features.requires_unknown_bits());
636 assert!(features.supports_unknown_bits());
638 features.clear_unknown_bits();
639 assert!(!features.requires_unknown_bits());
640 assert!(!features.supports_unknown_bits());
642 features.set_optional_unknown_bits();
643 assert!(!features.requires_unknown_bits());
644 assert!(features.supports_unknown_bits());
648 fn convert_to_context_with_relevant_flags() {
649 let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
650 assert!(init_features.initial_routing_sync());
651 assert!(!init_features.supports_upfront_shutdown_script());
652 assert!(!init_features.supports_gossip_queries());
654 let node_features: NodeFeatures = init_features.to_context();
656 // Check that the flags are as expected:
657 // - option_data_loss_protect
658 // - var_onion_optin | static_remote_key (req) | payment_secret
660 assert_eq!(node_features.flags.len(), 3);
661 assert_eq!(node_features.flags[0], 0b00000010);
662 assert_eq!(node_features.flags[1], 0b10010010);
663 assert_eq!(node_features.flags[2], 0b00000010);
666 // Check that cleared flags are kept blank when converting back:
667 // - initial_routing_sync was not applicable to NodeContext
668 // - upfront_shutdown_script was cleared before converting
669 // - gossip_queries was cleared before converting
670 let features: InitFeatures = node_features.to_context_internal();
671 assert!(!features.initial_routing_sync());
672 assert!(!features.supports_upfront_shutdown_script());
673 assert!(!init_features.supports_gossip_queries());