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 $optional_feature>::OPTIONAL_MASK)*,
95 define_context!(InitContext {
108 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
110 VariableLengthOnion | PaymentSecret,
117 define_context!(NodeContext {
130 DataLossProtect | UpfrontShutdownScript | GossipQueries,
132 VariableLengthOnion | PaymentSecret,
139 define_context!(ChannelContext {
140 required_features: [],
141 optional_features: [],
144 /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
145 /// useful for manipulating feature flags.
147 /// [`Context`]: trait.Context.html
148 macro_rules! define_feature {
149 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr) => {
152 /// See [BOLT #9] for details.
154 /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
155 pub trait $feature: Context {
156 /// The bit used to signify that the feature is required.
157 const EVEN_BIT: usize = $odd_bit - 1;
159 /// The bit used to signify that the feature is optional.
160 const ODD_BIT: usize = $odd_bit;
162 /// Assertion that [`EVEN_BIT`] is actually even.
164 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
165 const ASSERT_EVEN_BIT_PARITY: usize;
167 /// Assertion that [`ODD_BIT`] is actually odd.
169 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
170 const ASSERT_ODD_BIT_PARITY: usize;
172 /// The byte where the feature is set.
173 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
175 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
177 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
178 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
180 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
182 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
183 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
185 /// Returns whether the feature is required by the given flags.
187 fn requires_feature(flags: &Vec<u8>) -> bool {
188 flags.len() > Self::BYTE_OFFSET &&
189 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
192 /// Returns whether the feature is supported by the given flags.
194 fn supports_feature(flags: &Vec<u8>) -> bool {
195 flags.len() > Self::BYTE_OFFSET &&
196 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
199 /// Sets the feature's required (even) bit in the given flags.
201 fn set_required_bit(flags: &mut Vec<u8>) {
202 if flags.len() <= Self::BYTE_OFFSET {
203 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
206 flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
209 /// Sets the feature's optional (odd) bit in the given flags.
211 fn set_optional_bit(flags: &mut Vec<u8>) {
212 if flags.len() <= Self::BYTE_OFFSET {
213 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
216 flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
219 /// Clears the feature's required (even) and optional (odd) bits from the given
222 fn clear_bits(flags: &mut Vec<u8>) {
223 if flags.len() > Self::BYTE_OFFSET {
224 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
225 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
228 let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
229 let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
230 flags.resize(size, 0u8);
235 impl $feature for $context {
237 const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
240 const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
246 define_feature!(1, DataLossProtect, [InitContext, NodeContext],
247 "Feature flags for `option_data_loss_protect`.");
248 // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
249 define_feature!(3, InitialRoutingSync, [InitContext],
250 "Feature flags for `initial_routing_sync`.");
251 define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
252 "Feature flags for `option_upfront_shutdown_script`.");
253 define_feature!(7, GossipQueries, [InitContext, NodeContext],
254 "Feature flags for `gossip_queries`.");
255 define_feature!(9, VariableLengthOnion, [InitContext, NodeContext],
256 "Feature flags for `var_onion_optin`.");
257 define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
258 "Feature flags for `option_static_remotekey`.");
259 define_feature!(15, PaymentSecret, [InitContext, NodeContext],
260 "Feature flags for `payment_secret`.");
261 define_feature!(17, BasicMPP, [InitContext, NodeContext],
262 "Feature flags for `basic_mpp`.");
263 define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
264 "Feature flags for `opt_shutdown_anysegwit`.");
267 define_context!(TestingContext {
287 define_feature!(23, UnknownFeature, [TestingContext],
288 "Feature flags for an unknown feature used in testing.");
291 /// Tracks the set of features which a node implements, templated by the context in which it
294 /// (C-not exported) as we map the concrete feature types below directly instead
295 pub struct Features<T: sealed::Context> {
296 /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
298 mark: PhantomData<T>,
301 impl<T: sealed::Context> Clone for Features<T> {
302 fn clone(&self) -> Self {
304 flags: self.flags.clone(),
309 impl<T: sealed::Context> PartialEq for Features<T> {
310 fn eq(&self, o: &Self) -> bool {
311 self.flags.eq(&o.flags)
314 impl<T: sealed::Context> fmt::Debug for Features<T> {
315 fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
320 /// Features used within an `init` message.
321 pub type InitFeatures = Features<sealed::InitContext>;
322 /// Features used within a `node_announcement` message.
323 pub type NodeFeatures = Features<sealed::NodeContext>;
324 /// Features used within a `channel_announcement` message.
325 pub type ChannelFeatures = Features<sealed::ChannelContext>;
328 /// Writes all features present up to, and including, 13.
329 pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
330 let len = cmp::min(2, self.flags.len());
331 w.size_hint(len + 2);
332 (len as u16).write(w)?;
333 for i in (0..len).rev() {
335 self.flags[i].write(w)?;
337 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
338 // up-to-and-including-bit-5, 0-indexed, on this byte:
339 (self.flags[i] & 0b00_11_11_11).write(w)?;
345 /// or's another InitFeatures into this one.
346 pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
347 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
348 self.flags.resize(total_feature_len, 0u8);
349 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
355 /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
356 /// are included in the result.
357 pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
358 self.to_context_internal()
362 impl<T: sealed::Context> Features<T> {
363 /// Create a blank Features with no features set
364 pub fn empty() -> Self {
371 /// Creates features known by the implementation as defined by [`T::KNOWN_FEATURE_FLAGS`].
373 /// [`T::KNOWN_FEATURE_FLAGS`]: sealed/trait.Context.html#associatedconstant.KNOWN_FEATURE_FLAGS
374 pub fn known() -> Self {
376 flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
381 /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
382 /// included in the result.
383 fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
384 let byte_count = C::KNOWN_FEATURE_MASK.len();
385 let mut flags = Vec::new();
386 for (i, byte) in self.flags.iter().enumerate() {
388 let known_source_features = T::KNOWN_FEATURE_MASK[i];
389 let known_target_features = C::KNOWN_FEATURE_MASK[i];
390 flags.push(byte & known_source_features & known_target_features);
393 Features::<C> { flags, mark: PhantomData, }
397 /// Create a Features given a set of flags, in LE.
398 pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
406 /// Gets the underlying flags set, in LE.
407 pub fn le_flags(&self) -> &Vec<u8> {
411 pub(crate) fn requires_unknown_bits(&self) -> bool {
412 // Bitwise AND-ing with all even bits set except for known features will select required
414 let byte_count = T::KNOWN_FEATURE_MASK.len();
415 self.flags.iter().enumerate().any(|(i, &byte)| {
416 let required_features = 0b01_01_01_01;
417 let unknown_features = if i < byte_count {
418 !T::KNOWN_FEATURE_MASK[i]
422 (byte & (required_features & unknown_features)) != 0
426 pub(crate) fn supports_unknown_bits(&self) -> bool {
427 // Bitwise AND-ing with all even and odd bits set except for known features will select
428 // both required and optional unknown features.
429 let byte_count = T::KNOWN_FEATURE_MASK.len();
430 self.flags.iter().enumerate().any(|(i, &byte)| {
431 let unknown_features = if i < byte_count {
432 !T::KNOWN_FEATURE_MASK[i]
436 (byte & unknown_features) != 0
440 /// The number of bytes required to represent the feature flags present. This does not include
441 /// the length bytes which are included in the serialized form.
442 pub(crate) fn byte_count(&self) -> usize {
447 pub(crate) fn set_required_unknown_bits(&mut self) {
448 <sealed::TestingContext as sealed::UnknownFeature>::set_required_bit(&mut self.flags);
452 pub(crate) fn set_optional_unknown_bits(&mut self) {
453 <sealed::TestingContext as sealed::UnknownFeature>::set_optional_bit(&mut self.flags);
457 pub(crate) fn clear_unknown_bits(&mut self) {
458 <sealed::TestingContext as sealed::UnknownFeature>::clear_bits(&mut self.flags);
462 impl<T: sealed::DataLossProtect> Features<T> {
464 pub(crate) fn requires_data_loss_protect(&self) -> bool {
465 <T as sealed::DataLossProtect>::requires_feature(&self.flags)
467 pub(crate) fn supports_data_loss_protect(&self) -> bool {
468 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
472 impl<T: sealed::UpfrontShutdownScript> Features<T> {
474 pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
475 <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
477 pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
478 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
481 pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
482 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
488 impl<T: sealed::GossipQueries> Features<T> {
490 pub(crate) fn requires_gossip_queries(&self) -> bool {
491 <T as sealed::GossipQueries>::requires_feature(&self.flags)
493 pub(crate) fn supports_gossip_queries(&self) -> bool {
494 <T as sealed::GossipQueries>::supports_feature(&self.flags)
497 pub(crate) fn clear_gossip_queries(mut self) -> Self {
498 <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
503 impl<T: sealed::VariableLengthOnion> Features<T> {
505 pub(crate) fn requires_variable_length_onion(&self) -> bool {
506 <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
508 pub(crate) fn supports_variable_length_onion(&self) -> bool {
509 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
513 impl<T: sealed::StaticRemoteKey> Features<T> {
514 pub(crate) fn supports_static_remote_key(&self) -> bool {
515 <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
518 pub(crate) fn requires_static_remote_key(&self) -> bool {
519 <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
523 impl<T: sealed::InitialRoutingSync> Features<T> {
524 pub(crate) fn initial_routing_sync(&self) -> bool {
525 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
527 // We are no longer setting initial_routing_sync now that gossip_queries
528 // is enabled. This feature is ignored by a peer when gossip_queries has
531 pub(crate) fn clear_initial_routing_sync(&mut self) {
532 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
536 impl<T: sealed::PaymentSecret> Features<T> {
538 pub(crate) fn requires_payment_secret(&self) -> bool {
539 <T as sealed::PaymentSecret>::requires_feature(&self.flags)
541 // Note that we never need to test this since what really matters is the invoice - iff the
542 // invoice provides a payment_secret, we assume that we can use it (ie that the recipient
543 // supports payment_secret).
545 pub(crate) fn supports_payment_secret(&self) -> bool {
546 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
550 impl<T: sealed::BasicMPP> Features<T> {
552 pub(crate) fn requires_basic_mpp(&self) -> bool {
553 <T as sealed::BasicMPP>::requires_feature(&self.flags)
555 // We currently never test for this since we don't actually *generate* multipath routes.
557 pub(crate) fn supports_basic_mpp(&self) -> bool {
558 <T as sealed::BasicMPP>::supports_feature(&self.flags)
562 impl<T: sealed::ShutdownAnySegwit> Features<T> {
563 pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
564 <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
567 pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
568 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
573 impl<T: sealed::Context> Writeable for Features<T> {
574 fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
575 w.size_hint(self.flags.len() + 2);
576 (self.flags.len() as u16).write(w)?;
577 for f in self.flags.iter().rev() { // Swap back to big-endian
584 impl<T: sealed::Context> Readable for Features<T> {
585 fn read<R: ::std::io::Read>(r: &mut R) -> Result<Self, DecodeError> {
586 let mut flags: Vec<u8> = Readable::read(r)?;
587 flags.reverse(); // Swap to little-endian
597 use super::{ChannelFeatures, InitFeatures, NodeFeatures};
600 fn sanity_test_known_features() {
601 assert!(!ChannelFeatures::known().requires_unknown_bits());
602 assert!(!ChannelFeatures::known().supports_unknown_bits());
603 assert!(!InitFeatures::known().requires_unknown_bits());
604 assert!(!InitFeatures::known().supports_unknown_bits());
605 assert!(!NodeFeatures::known().requires_unknown_bits());
606 assert!(!NodeFeatures::known().supports_unknown_bits());
608 assert!(InitFeatures::known().supports_upfront_shutdown_script());
609 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
610 assert!(!InitFeatures::known().requires_upfront_shutdown_script());
611 assert!(!NodeFeatures::known().requires_upfront_shutdown_script());
613 assert!(InitFeatures::known().supports_gossip_queries());
614 assert!(NodeFeatures::known().supports_gossip_queries());
615 assert!(!InitFeatures::known().requires_gossip_queries());
616 assert!(!NodeFeatures::known().requires_gossip_queries());
618 assert!(InitFeatures::known().supports_data_loss_protect());
619 assert!(NodeFeatures::known().supports_data_loss_protect());
620 assert!(!InitFeatures::known().requires_data_loss_protect());
621 assert!(!NodeFeatures::known().requires_data_loss_protect());
623 assert!(InitFeatures::known().supports_variable_length_onion());
624 assert!(NodeFeatures::known().supports_variable_length_onion());
625 assert!(!InitFeatures::known().requires_variable_length_onion());
626 assert!(!NodeFeatures::known().requires_variable_length_onion());
628 assert!(InitFeatures::known().supports_static_remote_key());
629 assert!(NodeFeatures::known().supports_static_remote_key());
630 assert!(InitFeatures::known().requires_static_remote_key());
631 assert!(NodeFeatures::known().requires_static_remote_key());
633 assert!(InitFeatures::known().supports_payment_secret());
634 assert!(NodeFeatures::known().supports_payment_secret());
635 assert!(!InitFeatures::known().requires_payment_secret());
636 assert!(!NodeFeatures::known().requires_payment_secret());
638 assert!(InitFeatures::known().supports_basic_mpp());
639 assert!(NodeFeatures::known().supports_basic_mpp());
640 assert!(!InitFeatures::known().requires_basic_mpp());
641 assert!(!NodeFeatures::known().requires_basic_mpp());
643 assert!(InitFeatures::known().supports_shutdown_anysegwit());
644 assert!(NodeFeatures::known().supports_shutdown_anysegwit());
646 let mut init_features = InitFeatures::known();
647 assert!(init_features.initial_routing_sync());
648 init_features.clear_initial_routing_sync();
649 assert!(!init_features.initial_routing_sync());
653 fn sanity_test_unknown_bits() {
654 let mut features = ChannelFeatures::empty();
655 assert!(!features.requires_unknown_bits());
656 assert!(!features.supports_unknown_bits());
658 features.set_required_unknown_bits();
659 assert!(features.requires_unknown_bits());
660 assert!(features.supports_unknown_bits());
662 features.clear_unknown_bits();
663 assert!(!features.requires_unknown_bits());
664 assert!(!features.supports_unknown_bits());
666 features.set_optional_unknown_bits();
667 assert!(!features.requires_unknown_bits());
668 assert!(features.supports_unknown_bits());
672 fn convert_to_context_with_relevant_flags() {
673 let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
674 assert!(init_features.initial_routing_sync());
675 assert!(!init_features.supports_upfront_shutdown_script());
676 assert!(!init_features.supports_gossip_queries());
678 let node_features: NodeFeatures = init_features.to_context();
680 // Check that the flags are as expected:
681 // - option_data_loss_protect
682 // - var_onion_optin | static_remote_key (req) | payment_secret
684 // - opt_shutdown_anysegwit
685 assert_eq!(node_features.flags.len(), 4);
686 assert_eq!(node_features.flags[0], 0b00000010);
687 assert_eq!(node_features.flags[1], 0b10010010);
688 assert_eq!(node_features.flags[2], 0b00000010);
689 assert_eq!(node_features.flags[3], 0b00001000);
692 // Check that cleared flags are kept blank when converting back:
693 // - initial_routing_sync was not applicable to NodeContext
694 // - upfront_shutdown_script was cleared before converting
695 // - gossip_queries was cleared before converting
696 let features: InitFeatures = node_features.to_context_internal();
697 assert!(!features.initial_routing_sync());
698 assert!(!features.supports_upfront_shutdown_script());
699 assert!(!init_features.supports_gossip_queries());