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 $optional_feature>::OPTIONAL_MASK)*,
95 define_context!(InitContext {
108 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
110 VariableLengthOnion | PaymentSecret,
117 define_context!(NodeContext {
130 DataLossProtect | UpfrontShutdownScript | GossipQueries,
132 VariableLengthOnion | PaymentSecret,
139 define_context!(ChannelContext {
140 required_features: [],
141 optional_features: [],
143 define_context!(InvoiceContext {
144 required_features: [,,,],
149 VariableLengthOnion | PaymentSecret,
155 /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
156 /// useful for manipulating feature flags.
158 /// [`Context`]: trait.Context.html
159 macro_rules! define_feature {
160 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr) => {
163 /// See [BOLT #9] for details.
165 /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
166 pub trait $feature: Context {
167 /// The bit used to signify that the feature is required.
168 const EVEN_BIT: usize = $odd_bit - 1;
170 /// The bit used to signify that the feature is optional.
171 const ODD_BIT: usize = $odd_bit;
173 /// Assertion that [`EVEN_BIT`] is actually even.
175 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
176 const ASSERT_EVEN_BIT_PARITY: usize;
178 /// Assertion that [`ODD_BIT`] is actually odd.
180 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
181 const ASSERT_ODD_BIT_PARITY: usize;
183 /// The byte where the feature is set.
184 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
186 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
188 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
189 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
191 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
193 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
194 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
196 /// Returns whether the feature is required by the given flags.
198 fn requires_feature(flags: &Vec<u8>) -> bool {
199 flags.len() > Self::BYTE_OFFSET &&
200 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
203 /// Returns whether the feature is supported by the given flags.
205 fn supports_feature(flags: &Vec<u8>) -> bool {
206 flags.len() > Self::BYTE_OFFSET &&
207 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
210 /// Sets the feature's required (even) bit in the given flags.
212 fn set_required_bit(flags: &mut Vec<u8>) {
213 if flags.len() <= Self::BYTE_OFFSET {
214 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
217 flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
220 /// Sets the feature's optional (odd) bit in the given flags.
222 fn set_optional_bit(flags: &mut Vec<u8>) {
223 if flags.len() <= Self::BYTE_OFFSET {
224 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
227 flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
230 /// Clears the feature's required (even) and optional (odd) bits from the given
233 fn clear_bits(flags: &mut Vec<u8>) {
234 if flags.len() > Self::BYTE_OFFSET {
235 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
236 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
239 let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
240 let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
241 flags.resize(size, 0u8);
246 impl $feature for $context {
248 const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
251 const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
257 define_feature!(1, DataLossProtect, [InitContext, NodeContext],
258 "Feature flags for `option_data_loss_protect`.");
259 // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
260 define_feature!(3, InitialRoutingSync, [InitContext],
261 "Feature flags for `initial_routing_sync`.");
262 define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
263 "Feature flags for `option_upfront_shutdown_script`.");
264 define_feature!(7, GossipQueries, [InitContext, NodeContext],
265 "Feature flags for `gossip_queries`.");
266 define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
267 "Feature flags for `var_onion_optin`.");
268 define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
269 "Feature flags for `option_static_remotekey`.");
270 define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
271 "Feature flags for `payment_secret`.");
272 define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext],
273 "Feature flags for `basic_mpp`.");
274 define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
275 "Feature flags for `opt_shutdown_anysegwit`.");
278 define_context!(TestingContext {
298 define_feature!(23, UnknownFeature, [TestingContext],
299 "Feature flags for an unknown feature used in testing.");
302 /// Tracks the set of features which a node implements, templated by the context in which it
305 /// (C-not exported) as we map the concrete feature types below directly instead
306 pub struct Features<T: sealed::Context> {
307 /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
309 mark: PhantomData<T>,
312 impl<T: sealed::Context> Clone for Features<T> {
313 fn clone(&self) -> Self {
315 flags: self.flags.clone(),
320 impl<T: sealed::Context> PartialEq for Features<T> {
321 fn eq(&self, o: &Self) -> bool {
322 self.flags.eq(&o.flags)
325 impl<T: sealed::Context> fmt::Debug for Features<T> {
326 fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
331 /// Features used within an `init` message.
332 pub type InitFeatures = Features<sealed::InitContext>;
333 /// Features used within a `node_announcement` message.
334 pub type NodeFeatures = Features<sealed::NodeContext>;
335 /// Features used within a `channel_announcement` message.
336 pub type ChannelFeatures = Features<sealed::ChannelContext>;
337 /// Features used within an invoice.
338 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
341 /// Writes all features present up to, and including, 13.
342 pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
343 let len = cmp::min(2, self.flags.len());
344 w.size_hint(len + 2);
345 (len as u16).write(w)?;
346 for i in (0..len).rev() {
348 self.flags[i].write(w)?;
350 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
351 // up-to-and-including-bit-5, 0-indexed, on this byte:
352 (self.flags[i] & 0b00_11_11_11).write(w)?;
358 /// or's another InitFeatures into this one.
359 pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
360 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
361 self.flags.resize(total_feature_len, 0u8);
362 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
368 /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
369 /// are included in the result.
370 pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
371 self.to_context_internal()
375 impl InvoiceFeatures {
376 /// Converts `InvoiceFeatures` to `Features<C>`. Only known `InvoiceFeatures` relevant to
377 /// context `C` are included in the result.
378 pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
379 self.to_context_internal()
383 impl<T: sealed::Context> Features<T> {
384 /// Create a blank Features with no features set
385 pub fn empty() -> Self {
392 /// Creates features known by the implementation as defined by [`T::KNOWN_FEATURE_FLAGS`].
394 /// [`T::KNOWN_FEATURE_FLAGS`]: sealed/trait.Context.html#associatedconstant.KNOWN_FEATURE_FLAGS
395 pub fn known() -> Self {
397 flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
402 /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
403 /// included in the result.
404 fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
405 let byte_count = C::KNOWN_FEATURE_MASK.len();
406 let mut flags = Vec::new();
407 for (i, byte) in self.flags.iter().enumerate() {
409 let known_source_features = T::KNOWN_FEATURE_MASK[i];
410 let known_target_features = C::KNOWN_FEATURE_MASK[i];
411 flags.push(byte & known_source_features & known_target_features);
414 Features::<C> { flags, mark: PhantomData, }
418 /// Create a Features given a set of flags, in LE.
419 pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
427 /// Gets the underlying flags set, in LE.
428 pub fn le_flags(&self) -> &Vec<u8> {
432 pub(crate) fn requires_unknown_bits(&self) -> bool {
433 // Bitwise AND-ing with all even bits set except for known features will select required
435 let byte_count = T::KNOWN_FEATURE_MASK.len();
436 self.flags.iter().enumerate().any(|(i, &byte)| {
437 let required_features = 0b01_01_01_01;
438 let unknown_features = if i < byte_count {
439 !T::KNOWN_FEATURE_MASK[i]
443 (byte & (required_features & unknown_features)) != 0
447 pub(crate) fn supports_unknown_bits(&self) -> bool {
448 // Bitwise AND-ing with all even and odd bits set except for known features will select
449 // both required and optional unknown features.
450 let byte_count = T::KNOWN_FEATURE_MASK.len();
451 self.flags.iter().enumerate().any(|(i, &byte)| {
452 let unknown_features = if i < byte_count {
453 !T::KNOWN_FEATURE_MASK[i]
457 (byte & unknown_features) != 0
461 /// The number of bytes required to represent the feature flags present. This does not include
462 /// the length bytes which are included in the serialized form.
463 pub(crate) fn byte_count(&self) -> usize {
468 pub(crate) fn set_required_unknown_bits(&mut self) {
469 <sealed::TestingContext as sealed::UnknownFeature>::set_required_bit(&mut self.flags);
473 pub(crate) fn set_optional_unknown_bits(&mut self) {
474 <sealed::TestingContext as sealed::UnknownFeature>::set_optional_bit(&mut self.flags);
478 pub(crate) fn clear_unknown_bits(&mut self) {
479 <sealed::TestingContext as sealed::UnknownFeature>::clear_bits(&mut self.flags);
483 impl<T: sealed::DataLossProtect> Features<T> {
485 pub(crate) fn requires_data_loss_protect(&self) -> bool {
486 <T as sealed::DataLossProtect>::requires_feature(&self.flags)
488 pub(crate) fn supports_data_loss_protect(&self) -> bool {
489 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
493 impl<T: sealed::UpfrontShutdownScript> Features<T> {
495 pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
496 <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
498 pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
499 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
502 pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
503 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
509 impl<T: sealed::GossipQueries> Features<T> {
511 pub(crate) fn requires_gossip_queries(&self) -> bool {
512 <T as sealed::GossipQueries>::requires_feature(&self.flags)
514 pub(crate) fn supports_gossip_queries(&self) -> bool {
515 <T as sealed::GossipQueries>::supports_feature(&self.flags)
518 pub(crate) fn clear_gossip_queries(mut self) -> Self {
519 <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
524 impl<T: sealed::VariableLengthOnion> Features<T> {
526 pub(crate) fn requires_variable_length_onion(&self) -> bool {
527 <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
529 pub(crate) fn supports_variable_length_onion(&self) -> bool {
530 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
534 impl<T: sealed::StaticRemoteKey> Features<T> {
535 pub(crate) fn supports_static_remote_key(&self) -> bool {
536 <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
539 pub(crate) fn requires_static_remote_key(&self) -> bool {
540 <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
544 impl<T: sealed::InitialRoutingSync> Features<T> {
545 pub(crate) fn initial_routing_sync(&self) -> bool {
546 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
548 // We are no longer setting initial_routing_sync now that gossip_queries
549 // is enabled. This feature is ignored by a peer when gossip_queries has
552 pub(crate) fn clear_initial_routing_sync(&mut self) {
553 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
557 impl<T: sealed::PaymentSecret> Features<T> {
559 pub(crate) fn requires_payment_secret(&self) -> bool {
560 <T as sealed::PaymentSecret>::requires_feature(&self.flags)
562 // Note that we never need to test this since what really matters is the invoice - iff the
563 // invoice provides a payment_secret, we assume that we can use it (ie that the recipient
564 // supports payment_secret).
566 pub(crate) fn supports_payment_secret(&self) -> bool {
567 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
571 impl<T: sealed::BasicMPP> Features<T> {
573 pub(crate) fn requires_basic_mpp(&self) -> bool {
574 <T as sealed::BasicMPP>::requires_feature(&self.flags)
576 // We currently never test for this since we don't actually *generate* multipath routes.
578 pub(crate) fn supports_basic_mpp(&self) -> bool {
579 <T as sealed::BasicMPP>::supports_feature(&self.flags)
583 impl<T: sealed::ShutdownAnySegwit> Features<T> {
584 pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
585 <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
588 pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
589 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
594 impl<T: sealed::Context> Writeable for Features<T> {
595 fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
596 w.size_hint(self.flags.len() + 2);
597 (self.flags.len() as u16).write(w)?;
598 for f in self.flags.iter().rev() { // Swap back to big-endian
605 impl<T: sealed::Context> Readable for Features<T> {
606 fn read<R: ::std::io::Read>(r: &mut R) -> Result<Self, DecodeError> {
607 let mut flags: Vec<u8> = Readable::read(r)?;
608 flags.reverse(); // Swap to little-endian
618 use super::{ChannelFeatures, InitFeatures, NodeFeatures};
621 fn sanity_test_known_features() {
622 assert!(!ChannelFeatures::known().requires_unknown_bits());
623 assert!(!ChannelFeatures::known().supports_unknown_bits());
624 assert!(!InitFeatures::known().requires_unknown_bits());
625 assert!(!InitFeatures::known().supports_unknown_bits());
626 assert!(!NodeFeatures::known().requires_unknown_bits());
627 assert!(!NodeFeatures::known().supports_unknown_bits());
629 assert!(InitFeatures::known().supports_upfront_shutdown_script());
630 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
631 assert!(!InitFeatures::known().requires_upfront_shutdown_script());
632 assert!(!NodeFeatures::known().requires_upfront_shutdown_script());
634 assert!(InitFeatures::known().supports_gossip_queries());
635 assert!(NodeFeatures::known().supports_gossip_queries());
636 assert!(!InitFeatures::known().requires_gossip_queries());
637 assert!(!NodeFeatures::known().requires_gossip_queries());
639 assert!(InitFeatures::known().supports_data_loss_protect());
640 assert!(NodeFeatures::known().supports_data_loss_protect());
641 assert!(!InitFeatures::known().requires_data_loss_protect());
642 assert!(!NodeFeatures::known().requires_data_loss_protect());
644 assert!(InitFeatures::known().supports_variable_length_onion());
645 assert!(NodeFeatures::known().supports_variable_length_onion());
646 assert!(!InitFeatures::known().requires_variable_length_onion());
647 assert!(!NodeFeatures::known().requires_variable_length_onion());
649 assert!(InitFeatures::known().supports_static_remote_key());
650 assert!(NodeFeatures::known().supports_static_remote_key());
651 assert!(InitFeatures::known().requires_static_remote_key());
652 assert!(NodeFeatures::known().requires_static_remote_key());
654 assert!(InitFeatures::known().supports_payment_secret());
655 assert!(NodeFeatures::known().supports_payment_secret());
656 assert!(!InitFeatures::known().requires_payment_secret());
657 assert!(!NodeFeatures::known().requires_payment_secret());
659 assert!(InitFeatures::known().supports_basic_mpp());
660 assert!(NodeFeatures::known().supports_basic_mpp());
661 assert!(!InitFeatures::known().requires_basic_mpp());
662 assert!(!NodeFeatures::known().requires_basic_mpp());
664 assert!(InitFeatures::known().supports_shutdown_anysegwit());
665 assert!(NodeFeatures::known().supports_shutdown_anysegwit());
667 let mut init_features = InitFeatures::known();
668 assert!(init_features.initial_routing_sync());
669 init_features.clear_initial_routing_sync();
670 assert!(!init_features.initial_routing_sync());
674 fn sanity_test_unknown_bits() {
675 let mut features = ChannelFeatures::empty();
676 assert!(!features.requires_unknown_bits());
677 assert!(!features.supports_unknown_bits());
679 features.set_required_unknown_bits();
680 assert!(features.requires_unknown_bits());
681 assert!(features.supports_unknown_bits());
683 features.clear_unknown_bits();
684 assert!(!features.requires_unknown_bits());
685 assert!(!features.supports_unknown_bits());
687 features.set_optional_unknown_bits();
688 assert!(!features.requires_unknown_bits());
689 assert!(features.supports_unknown_bits());
693 fn convert_to_context_with_relevant_flags() {
694 let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
695 assert!(init_features.initial_routing_sync());
696 assert!(!init_features.supports_upfront_shutdown_script());
697 assert!(!init_features.supports_gossip_queries());
699 let node_features: NodeFeatures = init_features.to_context();
701 // Check that the flags are as expected:
702 // - option_data_loss_protect
703 // - var_onion_optin | static_remote_key (req) | payment_secret
705 // - opt_shutdown_anysegwit
706 assert_eq!(node_features.flags.len(), 4);
707 assert_eq!(node_features.flags[0], 0b00000010);
708 assert_eq!(node_features.flags[1], 0b10010010);
709 assert_eq!(node_features.flags[2], 0b00000010);
710 assert_eq!(node_features.flags[3], 0b00001000);
713 // Check that cleared flags are kept blank when converting back:
714 // - initial_routing_sync was not applicable to NodeContext
715 // - upfront_shutdown_script was cleared before converting
716 // - gossip_queries was cleared before converting
717 let features: InitFeatures = node_features.to_context_internal();
718 assert!(!features.initial_routing_sync());
719 assert!(!features.supports_upfront_shutdown_script());
720 assert!(!init_features.supports_gossip_queries());