1 //! Feature flag definitions for the Lightning protocol according to [BOLT #9].
3 //! Lightning nodes advertise a supported set of operation through feature flags. Features are
4 //! applicable for a specific context as indicated in some [messages]. [`Features`] encapsulates
5 //! behavior for specifying and checking feature flags for a particular context. Each feature is
6 //! defined internally by a trait specifying the corresponding flags (i.e., even and odd bits). A
7 //! [`Context`] is used to parameterize [`Features`] and defines which features it can support.
9 //! Whether a feature is considered "known" or "unknown" is relative to the implementation, whereas
10 //! the term "supports" is used in reference to a particular set of [`Features`]. That is, a node
11 //! supports a feature if it advertises the feature (as either required or optional) to its peers.
12 //! And the implementation can interpret a feature if the feature is known to it.
14 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
15 //! [messages]: ../msgs/index.html
16 //! [`Features`]: struct.Features.html
17 //! [`Context`]: sealed/trait.Context.html
20 use std::result::Result;
21 use std::marker::PhantomData;
23 use ln::msgs::DecodeError;
24 use util::ser::{Readable, Writeable, Writer};
27 /// The context in which [`Features`] are applicable. Defines which features are required and
28 /// which are optional for the context.
30 /// [`Features`]: ../struct.Features.html
32 /// Features that are known to the implementation, where a required feature is indicated by
33 /// its even bit and an optional feature is indicated by its odd bit.
34 const KNOWN_FEATURE_FLAGS: &'static [u8];
36 /// Bitmask for selecting features that are known to the implementation, regardless of
37 /// whether each feature is required or optional.
38 const KNOWN_FEATURE_MASK: &'static [u8];
41 /// Defines a [`Context`] by stating which features it requires and which are optional. Features
42 /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
43 /// feature identifiers.
45 /// [`Context`]: trait.Context.html
46 macro_rules! define_context {
48 required_features: [$( $( $required_feature: ident )|*, )*],
49 optional_features: [$( $( $optional_feature: ident )|*, )*],
51 pub struct $context {}
53 impl Context for $context {
54 const KNOWN_FEATURE_FLAGS: &'static [u8] = &[
55 // For each byte, use bitwise-OR to compute the applicable flags for known
56 // required features `r_i` and optional features `o_j` for all `i` and `j` such
57 // that the following slice is formed:
60 // `r_0` | `r_1` | ... | `o_0` | `o_1` | ...,
65 <Self as $required_feature>::REQUIRED_MASK)*
67 <Self as $optional_feature>::OPTIONAL_MASK)*,
71 const KNOWN_FEATURE_MASK: &'static [u8] = &[
72 // Similar as above, but set both flags for each feature regardless of whether
73 // the feature is required or optional.
76 <Self as $required_feature>::REQUIRED_MASK |
77 <Self as $required_feature>::OPTIONAL_MASK)*
79 <Self as $optional_feature>::REQUIRED_MASK |
80 <Self as $optional_feature>::OPTIONAL_MASK)*,
87 define_context!(InitContext {
98 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript,
100 VariableLengthOnion | PaymentSecret,
105 define_context!(NodeContext {
116 DataLossProtect | UpfrontShutdownScript,
118 VariableLengthOnion | PaymentSecret,
123 define_context!(ChannelContext {
124 required_features: [],
125 optional_features: [],
128 /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
129 /// useful for manipulating feature flags.
131 /// [`Context`]: trait.Context.html
132 macro_rules! define_feature {
133 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr) => {
136 /// See [BOLT #9] for details.
138 /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
139 pub trait $feature: Context {
140 /// The bit used to signify that the feature is required.
141 const EVEN_BIT: usize = $odd_bit - 1;
143 /// The bit used to signify that the feature is optional.
144 const ODD_BIT: usize = $odd_bit;
146 /// Assertion that [`EVEN_BIT`] is actually even.
148 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
149 const ASSERT_EVEN_BIT_PARITY: usize;
151 /// Assertion that [`ODD_BIT`] is actually odd.
153 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
154 const ASSERT_ODD_BIT_PARITY: usize;
156 /// The byte where the feature is set.
157 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
159 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
161 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
162 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
164 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
166 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
167 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
169 /// Returns whether the feature is supported by the given flags.
171 fn supports_feature(flags: &Vec<u8>) -> bool {
172 flags.len() > Self::BYTE_OFFSET &&
173 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
176 /// Sets the feature's optional (odd) bit in the given flags.
178 fn set_optional_bit(flags: &mut Vec<u8>) {
179 if flags.len() <= Self::BYTE_OFFSET {
180 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
183 flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
186 /// Clears the feature's required (even) and optional (odd) bits from the given
189 fn clear_bits(flags: &mut Vec<u8>) {
190 if flags.len() > Self::BYTE_OFFSET {
191 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
192 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
198 impl $feature for $context {
200 const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
203 const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
209 define_feature!(1, DataLossProtect, [InitContext, NodeContext],
210 "Feature flags for `option_data_loss_protect`.");
211 // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
212 define_feature!(3, InitialRoutingSync, [InitContext],
213 "Feature flags for `initial_routing_sync`.");
214 define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
215 "Feature flags for `option_upfront_shutdown_script`.");
216 define_feature!(9, VariableLengthOnion, [InitContext, NodeContext],
217 "Feature flags for `var_onion_optin`.");
218 define_feature!(15, PaymentSecret, [InitContext, NodeContext],
219 "Feature flags for `payment_secret`.");
220 define_feature!(17, BasicMPP, [InitContext, NodeContext],
221 "Feature flags for `basic_mpp`.");
224 /// Tracks the set of features which a node implements, templated by the context in which it
226 pub struct Features<T: sealed::Context> {
227 /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
229 mark: PhantomData<T>,
232 impl<T: sealed::Context> Clone for Features<T> {
233 fn clone(&self) -> Self {
235 flags: self.flags.clone(),
240 impl<T: sealed::Context> PartialEq for Features<T> {
241 fn eq(&self, o: &Self) -> bool {
242 self.flags.eq(&o.flags)
245 impl<T: sealed::Context> fmt::Debug for Features<T> {
246 fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
251 /// Features used within an `init` message.
252 pub type InitFeatures = Features<sealed::InitContext>;
253 /// Features used within a `node_announcement` message.
254 pub type NodeFeatures = Features<sealed::NodeContext>;
255 /// Features used within a `channel_announcement` message.
256 pub type ChannelFeatures = Features<sealed::ChannelContext>;
259 /// Writes all features present up to, and including, 13.
260 pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
261 let len = cmp::min(2, self.flags.len());
262 w.size_hint(len + 2);
263 (len as u16).write(w)?;
264 for i in (0..len).rev() {
266 self.flags[i].write(w)?;
268 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
269 // up-to-and-including-bit-5, 0-indexed, on this byte:
270 (self.flags[i] & 0b00_11_11_11).write(w)?;
276 /// or's another InitFeatures into this one.
277 pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
278 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
279 self.flags.resize(total_feature_len, 0u8);
280 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
287 impl ChannelFeatures {
288 /// Takes the flags that we know how to interpret in an init-context features that are also
289 /// relevant in a channel-context features and creates a channel-context features from them.
290 pub(crate) fn with_known_relevant_init_flags(_init_ctx: &InitFeatures) -> Self {
291 // There are currently no channel flags defined that we understand.
292 Self { flags: Vec::new(), mark: PhantomData, }
297 /// Takes the flags that we know how to interpret in an init-context features that are also
298 /// relevant in a node-context features and creates a node-context features from them.
299 /// Be sure to blank out features that are unknown to us.
300 pub(crate) fn with_known_relevant_init_flags(init_ctx: &InitFeatures) -> Self {
301 use ln::features::sealed::Context;
302 let byte_count = sealed::NodeContext::KNOWN_FEATURE_MASK.len();
304 let mut flags = Vec::new();
305 for (i, feature_byte) in init_ctx.flags.iter().enumerate() {
307 flags.push(feature_byte & sealed::NodeContext::KNOWN_FEATURE_MASK[i]);
310 Self { flags, mark: PhantomData, }
314 impl<T: sealed::Context> Features<T> {
315 /// Create a blank Features with no features set
316 pub fn empty() -> Features<T> {
323 /// Creates features known by the implementation as defined by [`T::KNOWN_FEATURE_FLAGS`].
325 /// [`T::KNOWN_FEATURE_FLAGS`]: sealed/trait.Context.html#associatedconstant.KNOWN_FEATURE_FLAGS
326 pub fn known() -> Features<T> {
328 flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
334 /// Create a Features given a set of flags, in LE.
335 pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
343 /// Gets the underlying flags set, in LE.
344 pub fn le_flags(&self) -> &Vec<u8> {
348 pub(crate) fn requires_unknown_bits(&self) -> bool {
349 use ln::features::sealed::Context;
350 let byte_count = sealed::InitContext::KNOWN_FEATURE_MASK.len();
352 // Bitwise AND-ing with all even bits set except for known features will select unknown
353 // required features.
354 self.flags.iter().enumerate().any(|(i, &byte)| {
355 let required_features = 0b01_01_01_01;
356 let unknown_features = if i < byte_count {
357 !sealed::InitContext::KNOWN_FEATURE_MASK[i]
361 (byte & (required_features & unknown_features)) != 0
365 pub(crate) fn supports_unknown_bits(&self) -> bool {
366 use ln::features::sealed::Context;
367 let byte_count = sealed::InitContext::KNOWN_FEATURE_MASK.len();
369 // Bitwise AND-ing with all even and odd bits set except for known features will select
371 self.flags.iter().enumerate().any(|(i, &byte)| {
372 let unknown_features = if i < byte_count {
373 !sealed::InitContext::KNOWN_FEATURE_MASK[i]
377 (byte & unknown_features) != 0
381 /// The number of bytes required to represent the feature flags present. This does not include
382 /// the length bytes which are included in the serialized form.
383 pub(crate) fn byte_count(&self) -> usize {
388 pub(crate) fn set_require_unknown_bits(&mut self) {
389 let newlen = cmp::max(3, self.flags.len());
390 self.flags.resize(newlen, 0u8);
391 self.flags[2] |= 0x40;
395 pub(crate) fn clear_require_unknown_bits(&mut self) {
396 let newlen = cmp::max(3, self.flags.len());
397 self.flags.resize(newlen, 0u8);
398 self.flags[2] &= !0x40;
399 if self.flags.len() == 3 && self.flags[2] == 0 {
400 self.flags.resize(2, 0u8);
402 if self.flags.len() == 2 && self.flags[1] == 0 {
403 self.flags.resize(1, 0u8);
408 impl<T: sealed::DataLossProtect> Features<T> {
409 pub(crate) fn supports_data_loss_protect(&self) -> bool {
410 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
414 impl<T: sealed::UpfrontShutdownScript> Features<T> {
415 pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
416 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
419 pub(crate) fn unset_upfront_shutdown_script(&mut self) {
420 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags)
424 impl<T: sealed::VariableLengthOnion> Features<T> {
425 pub(crate) fn supports_variable_length_onion(&self) -> bool {
426 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
430 impl<T: sealed::InitialRoutingSync> Features<T> {
431 pub(crate) fn initial_routing_sync(&self) -> bool {
432 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
434 pub(crate) fn clear_initial_routing_sync(&mut self) {
435 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
439 impl<T: sealed::PaymentSecret> Features<T> {
441 // Note that we never need to test this since what really matters is the invoice - iff the
442 // invoice provides a payment_secret, we assume that we can use it (ie that the recipient
443 // supports payment_secret).
444 pub(crate) fn supports_payment_secret(&self) -> bool {
445 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
449 impl<T: sealed::BasicMPP> Features<T> {
450 // We currently never test for this since we don't actually *generate* multipath routes.
452 pub(crate) fn supports_basic_mpp(&self) -> bool {
453 <T as sealed::BasicMPP>::supports_feature(&self.flags)
457 impl<T: sealed::Context> Writeable for Features<T> {
458 fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
459 w.size_hint(self.flags.len() + 2);
460 (self.flags.len() as u16).write(w)?;
461 for f in self.flags.iter().rev() { // Swap back to big-endian
468 impl<T: sealed::Context> Readable for Features<T> {
469 fn read<R: ::std::io::Read>(r: &mut R) -> Result<Self, DecodeError> {
470 let mut flags: Vec<u8> = Readable::read(r)?;
471 flags.reverse(); // Swap to little-endian
481 use super::{ChannelFeatures, InitFeatures, NodeFeatures, Features};
484 fn sanity_test_our_features() {
485 assert!(!ChannelFeatures::known().requires_unknown_bits());
486 assert!(!ChannelFeatures::known().supports_unknown_bits());
487 assert!(!InitFeatures::known().requires_unknown_bits());
488 assert!(!InitFeatures::known().supports_unknown_bits());
489 assert!(!NodeFeatures::known().requires_unknown_bits());
490 assert!(!NodeFeatures::known().supports_unknown_bits());
492 assert!(InitFeatures::known().supports_upfront_shutdown_script());
493 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
495 assert!(InitFeatures::known().supports_data_loss_protect());
496 assert!(NodeFeatures::known().supports_data_loss_protect());
498 assert!(InitFeatures::known().supports_variable_length_onion());
499 assert!(NodeFeatures::known().supports_variable_length_onion());
501 assert!(InitFeatures::known().supports_payment_secret());
502 assert!(NodeFeatures::known().supports_payment_secret());
504 assert!(InitFeatures::known().supports_basic_mpp());
505 assert!(NodeFeatures::known().supports_basic_mpp());
507 let mut init_features = InitFeatures::known();
508 assert!(init_features.initial_routing_sync());
509 init_features.clear_initial_routing_sync();
510 assert!(!init_features.initial_routing_sync());
514 fn sanity_test_unkown_bits_testing() {
515 let mut features = ChannelFeatures::known();
516 features.set_require_unknown_bits();
517 assert!(features.requires_unknown_bits());
518 features.clear_require_unknown_bits();
519 assert!(!features.requires_unknown_bits());
523 fn test_node_with_known_relevant_init_flags() {
524 // Create an InitFeatures with initial_routing_sync supported.
525 let init_features = InitFeatures::known();
526 assert!(init_features.initial_routing_sync());
528 // Attempt to pull out non-node-context feature flags from these InitFeatures.
529 let res = NodeFeatures::with_known_relevant_init_flags(&init_features);
532 // Check that the flags are as expected: optional_data_loss_protect,
533 // option_upfront_shutdown_script, var_onion_optin, payment_secret, and
535 assert_eq!(res.flags.len(), 3);
536 assert_eq!(res.flags[0], 0b00100010);
537 assert_eq!(res.flags[1], 0b10000010);
538 assert_eq!(res.flags[2], 0b00000010);
541 // Check that the initial_routing_sync feature was correctly blanked out.
542 let new_features: InitFeatures = Features::from_le_bytes(res.flags);
543 assert!(!new_features.initial_routing_sync());