_ Git - rust-lightning/blob - lightning/src/ln/features.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   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
   8 // licenses.
   9
  10 //! Feature flag definitions for the Lightning protocol according to [BOLT #9].
  11 //!
  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).
  16 //!
  17 //! Whether a feature is considered "known" or "unknown" is relative to the implementation, whereas
  18 //! the term "supports" is used in reference to a particular set of [`Features`]. That is, a node
  19 //! supports a feature if it advertises the feature (as either required or optional) to its peers.
  20 //! And the implementation can interpret a feature if the feature is known to it.
  21 //!
  22 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
  23 //! [messages]: crate::ln::msgs
  24
  25 use io;
  26 use prelude::*;
  27 use core::{cmp, fmt};
  28 use core::marker::PhantomData;
  29
  30 use bitcoin::bech32;
  31 use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5, WriteBase32};
  32 use ln::msgs::DecodeError;
  33 use util::ser::{Readable, Writeable, Writer};
  34
  35 mod sealed {
  36         use prelude::*;
  37         use ln::features::Features;
  38
  39         /// The context in which [`Features`] are applicable. Defines which features are required and
  40         /// which are optional for the context.
  41         pub trait Context {
  42                 /// Features that are known to the implementation, where a required feature is indicated by
  43                 /// its even bit and an optional feature is indicated by its odd bit.
  44                 const KNOWN_FEATURE_FLAGS: &'static [u8];
  45
  46                 /// Bitmask for selecting features that are known to the implementation, regardless of
  47                 /// whether each feature is required or optional.
  48                 const KNOWN_FEATURE_MASK: &'static [u8];
  49         }
  50
  51         /// Defines a [`Context`] by stating which features it requires and which are optional. Features
  52         /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
  53         /// feature identifiers.
  54         macro_rules! define_context {
  55                 ($context: ident {
  56                         required_features: [$( $( $required_feature: ident )|*, )*],
  57                         optional_features: [$( $( $optional_feature: ident )|*, )*],
  58                 }) => {
  59                         #[derive(Eq, PartialEq)]
  60                         pub struct $context {}
  61
  62                         impl Context for $context {
  63                                 const KNOWN_FEATURE_FLAGS: &'static [u8] = &[
  64                                         // For each byte, use bitwise-OR to compute the applicable flags for known
  65                                         // required features `r_i` and optional features `o_j` for all `i` and `j` such
  66                                         // that the following slice is formed:
  67                                         //
  68                                         // [
  69                                         //  `r_0` | `r_1` | ... | `o_0` | `o_1` | ...,
  70                                         //  ...,
  71                                         // ]
  72                                         $(
  73                                                 0b00_00_00_00 $(|
  74                                                         <Self as $required_feature>::REQUIRED_MASK)*
  75                                                 $(|
  76                                                         <Self as $optional_feature>::OPTIONAL_MASK)*,
  77                                         )*
  78                                 ];
  79
  80                                 const KNOWN_FEATURE_MASK: &'static [u8] = &[
  81                                         // Similar as above, but set both flags for each feature regardless of whether
  82                                         // the feature is required or optional.
  83                                         $(
  84                                                 0b00_00_00_00 $(|
  85                                                         <Self as $required_feature>::REQUIRED_MASK |
  86                                                         <Self as $required_feature>::OPTIONAL_MASK)*
  87                                                 $(|
  88                                                         <Self as $optional_feature>::REQUIRED_MASK |
  89                                                         <Self as $optional_feature>::OPTIONAL_MASK)*,
  90                                         )*
  91                                 ];
  92                         }
  93
  94                         impl alloc::fmt::Display for Features<$context> {
  95                                 fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
  96                                         $(
  97                                                 $(
  98                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($required_feature),
  99                                                                 if <$context as $required_feature>::requires_feature(&self.flags) { "required" }
 100                                                                 else if <$context as $required_feature>::supports_feature(&self.flags) { "supported" }
 101                                                                 else { "not supported" }))?;
 102                                                 )*
 103                                                 $(
 104                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($optional_feature),
 105                                                                 if <$context as $optional_feature>::requires_feature(&self.flags) { "required" }
 106                                                                 else if <$context as $optional_feature>::supports_feature(&self.flags) { "supported" }
 107                                                                 else { "not supported" }))?;
 108                                                 )*
 109                                         )*
 110                                         fmt.write_fmt(format_args!("unknown flags: {}",
 111                                                 if self.requires_unknown_bits() { "required" }
 112                                                 else if self.supports_unknown_bits() { "supported" } else { "none" }))
 113                                 }
 114                         }
 115                 };
 116         }
 117
 118         define_context!(InitContext {
 119                 required_features: [
 120                         // Byte 0
 121                         ,
 122                         // Byte 1
 123                         VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 124                         // Byte 2
 125                         ,
 126                         // Byte 3
 127                         ,
 128                 ],
 129                 optional_features: [
 130                         // Byte 0
 131                         DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
 132                         // Byte 1
 133                         ,
 134                         // Byte 2
 135                         BasicMPP,
 136                         // Byte 3
 137                         ShutdownAnySegwit,
 138                 ],
 139         });
 140         define_context!(NodeContext {
 141                 required_features: [
 142                         // Byte 0
 143                         ,
 144                         // Byte 1
 145                         VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 146                         // Byte 2
 147                         ,
 148                         // Byte 3
 149                         ,
 150                         // Byte 4
 151                         ,
 152                         // Byte 5
 153                         ,
 154                         // Byte 6
 155                         ,
 156                 ],
 157                 optional_features: [
 158                         // Byte 0
 159                         DataLossProtect | UpfrontShutdownScript | GossipQueries,
 160                         // Byte 1
 161                         ,
 162                         // Byte 2
 163                         BasicMPP,
 164                         // Byte 3
 165                         ShutdownAnySegwit,
 166                         // Byte 4
 167                         ,
 168                         // Byte 5
 169                         ,
 170                         // Byte 6
 171                         Keysend,
 172                 ],
 173         });
 174         define_context!(ChannelContext {
 175                 required_features: [],
 176                 optional_features: [],
 177         });
 178         define_context!(InvoiceContext {
 179                 required_features: [
 180                         // Byte 0
 181                         ,
 182                         // Byte 1
 183                         VariableLengthOnion | PaymentSecret,
 184                         // Byte 2
 185                         ,
 186                 ],
 187                 optional_features: [
 188                         // Byte 0
 189                         ,
 190                         // Byte 1
 191                         ,
 192                         // Byte 2
 193                         BasicMPP,
 194                 ],
 195         });
 196
 197         /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
 198         /// useful for manipulating feature flags.
 199         macro_rules! define_feature {
 200                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 201                  $required_setter: ident) => {
 202                         #[doc = $doc]
 203                         ///
 204                         /// See [BOLT #9] for details.
 205                         ///
 206                         /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
 207                         pub trait $feature: Context {
 208                                 /// The bit used to signify that the feature is required.
 209                                 const EVEN_BIT: usize = $odd_bit - 1;
 210
 211                                 /// The bit used to signify that the feature is optional.
 212                                 const ODD_BIT: usize = $odd_bit;
 213
 214                                 /// Assertion that [`EVEN_BIT`] is actually even.
 215                                 ///
 216                                 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
 217                                 const ASSERT_EVEN_BIT_PARITY: usize;
 218
 219                                 /// Assertion that [`ODD_BIT`] is actually odd.
 220                                 ///
 221                                 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
 222                                 const ASSERT_ODD_BIT_PARITY: usize;
 223
 224                                 /// The byte where the feature is set.
 225                                 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
 226
 227                                 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
 228                                 ///
 229                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 230                                 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
 231
 232                                 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
 233                                 ///
 234                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 235                                 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
 236
 237                                 /// Returns whether the feature is required by the given flags.
 238                                 #[inline]
 239                                 fn requires_feature(flags: &Vec<u8>) -> bool {
 240                                         flags.len() > Self::BYTE_OFFSET &&
 241                                                 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
 242                                 }
 243
 244                                 /// Returns whether the feature is supported by the given flags.
 245                                 #[inline]
 246                                 fn supports_feature(flags: &Vec<u8>) -> bool {
 247                                         flags.len() > Self::BYTE_OFFSET &&
 248                                                 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
 249                                 }
 250
 251                                 /// Sets the feature's required (even) bit in the given flags.
 252                                 #[inline]
 253                                 fn set_required_bit(flags: &mut Vec<u8>) {
 254                                         if flags.len() <= Self::BYTE_OFFSET {
 255                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 256                                         }
 257
 258                                         flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
 259                                 }
 260
 261                                 /// Sets the feature's optional (odd) bit in the given flags.
 262                                 #[inline]
 263                                 fn set_optional_bit(flags: &mut Vec<u8>) {
 264                                         if flags.len() <= Self::BYTE_OFFSET {
 265                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 266                                         }
 267
 268                                         flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
 269                                 }
 270
 271                                 /// Clears the feature's required (even) and optional (odd) bits from the given
 272                                 /// flags.
 273                                 #[inline]
 274                                 fn clear_bits(flags: &mut Vec<u8>) {
 275                                         if flags.len() > Self::BYTE_OFFSET {
 276                                                 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
 277                                                 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
 278                                         }
 279
 280                                         let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
 281                                         let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
 282                                         flags.resize(size, 0u8);
 283                                 }
 284                         }
 285
 286                         impl <T: $feature> Features<T> {
 287                                 /// Set this feature as optional.
 288                                 pub fn $optional_setter(mut self) -> Self {
 289                                         <T as $feature>::set_optional_bit(&mut self.flags);
 290                                         self
 291                                 }
 292
 293                                 /// Set this feature as required.
 294                                 pub fn $required_setter(mut self) -> Self {
 295                                         <T as $feature>::set_required_bit(&mut self.flags);
 296                                         self
 297                                 }
 298                         }
 299
 300                         $(
 301                                 impl $feature for $context {
 302                                         // EVEN_BIT % 2 == 0
 303                                         const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
 304
 305                                         // ODD_BIT % 2 == 1
 306                                         const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
 307                                 }
 308                         )*
 309
 310                 }
 311         }
 312
 313         define_feature!(1, DataLossProtect, [InitContext, NodeContext],
 314                 "Feature flags for `option_data_loss_protect`.", set_data_loss_protect_optional,
 315                 set_data_loss_protect_required);
 316         // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
 317         define_feature!(3, InitialRoutingSync, [InitContext], "Feature flags for `initial_routing_sync`.",
 318                 set_initial_routing_sync_optional, set_initial_routing_sync_required);
 319         define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
 320                 "Feature flags for `option_upfront_shutdown_script`.", set_upfront_shutdown_script_optional,
 321                 set_upfront_shutdown_script_required);
 322         define_feature!(7, GossipQueries, [InitContext, NodeContext],
 323                 "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required);
 324         define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
 325                 "Feature flags for `var_onion_optin`.", set_variable_length_onion_optional,
 326                 set_variable_length_onion_required);
 327         define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
 328                 "Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
 329                 set_static_remote_key_required);
 330         define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
 331                 "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required);
 332         define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext],
 333                 "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required);
 334         define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
 335                 "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
 336                 set_shutdown_any_segwit_required);
 337         define_feature!(55, Keysend, [NodeContext],
 338                 "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required);
 339
 340         #[cfg(test)]
 341         define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext, InvoiceContext],
 342                 "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
 343                 set_unknown_feature_required);
 344 }
 345
 346 /// Tracks the set of features which a node implements, templated by the context in which it
 347 /// appears.
 348 ///
 349 /// (C-not exported) as we map the concrete feature types below directly instead
 350 #[derive(Eq)]
 351 pub struct Features<T: sealed::Context> {
 352         /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
 353         flags: Vec<u8>,
 354         mark: PhantomData<T>,
 355 }
 356
 357 impl<T: sealed::Context> Clone for Features<T> {
 358         fn clone(&self) -> Self {
 359                 Self {
 360                         flags: self.flags.clone(),
 361                         mark: PhantomData,
 362                 }
 363         }
 364 }
 365 impl<T: sealed::Context> PartialEq for Features<T> {
 366         fn eq(&self, o: &Self) -> bool {
 367                 self.flags.eq(&o.flags)
 368         }
 369 }
 370 impl<T: sealed::Context> fmt::Debug for Features<T> {
 371         fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 372                 self.flags.fmt(fmt)
 373         }
 374 }
 375
 376 /// Features used within an `init` message.
 377 pub type InitFeatures = Features<sealed::InitContext>;
 378 /// Features used within a `node_announcement` message.
 379 pub type NodeFeatures = Features<sealed::NodeContext>;
 380 /// Features used within a `channel_announcement` message.
 381 pub type ChannelFeatures = Features<sealed::ChannelContext>;
 382 /// Features used within an invoice.
 383 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
 384
 385 impl InitFeatures {
 386         /// Writes all features present up to, and including, 13.
 387         pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 388                 let len = cmp::min(2, self.flags.len());
 389                 w.size_hint(len + 2);
 390                 (len as u16).write(w)?;
 391                 for i in (0..len).rev() {
 392                         if i == 0 {
 393                                 self.flags[i].write(w)?;
 394                         } else {
 395                                 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
 396                                 // up-to-and-including-bit-5, 0-indexed, on this byte:
 397                                 (self.flags[i] & 0b00_11_11_11).write(w)?;
 398                         }
 399                 }
 400                 Ok(())
 401         }
 402
 403         /// or's another InitFeatures into this one.
 404         pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
 405                 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
 406                 self.flags.resize(total_feature_len, 0u8);
 407                 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
 408                         *byte |= *o_byte;
 409                 }
 410                 self
 411         }
 412
 413         /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
 414         /// are included in the result.
 415         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 416                 self.to_context_internal()
 417         }
 418 }
 419
 420 impl InvoiceFeatures {
 421         /// Converts `InvoiceFeatures` to `Features<C>`. Only known `InvoiceFeatures` relevant to
 422         /// context `C` are included in the result.
 423         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 424                 self.to_context_internal()
 425         }
 426
 427         /// Getting a route for a keysend payment to a private node requires providing the payee's
 428         /// features (since they were not announced in a node announcement). However, keysend payments
 429         /// don't have an invoice to pull the payee's features from, so this method is provided for use in
 430         /// [`get_keysend_route`], thus omitting the need for payers to manually construct an
 431         /// `InvoiceFeatures` for [`get_route`].
 432         ///
 433         /// [`get_keysend_route`]: crate::routing::router::get_keysend_route
 434         /// [`get_route`]: crate::routing::router::get_route
 435         pub(crate) fn for_keysend() -> InvoiceFeatures {
 436                 InvoiceFeatures::empty().set_variable_length_onion_optional()
 437         }
 438 }
 439
 440 impl ToBase32 for InvoiceFeatures {
 441         fn write_base32<W: WriteBase32>(&self, writer: &mut W) -> Result<(), <W as WriteBase32>::Err> {
 442                 // Explanation for the "4": the normal way to round up when dividing is to add the divisor
 443                 // minus one before dividing
 444                 let length_u5s = (self.flags.len() * 8 + 4) / 5 as usize;
 445                 let mut res_u5s: Vec<u5> = vec![u5::try_from_u8(0).unwrap(); length_u5s];
 446                 for (byte_idx, byte) in self.flags.iter().enumerate() {
 447                         let bit_pos_from_left_0_indexed = byte_idx * 8;
 448                         let new_u5_idx = length_u5s - (bit_pos_from_left_0_indexed / 5) as usize - 1;
 449                         let new_bit_pos = bit_pos_from_left_0_indexed % 5;
 450                         let shifted_chunk_u16 = (*byte as u16) << new_bit_pos;
 451                         let curr_u5_as_u8 = res_u5s[new_u5_idx].to_u8();
 452                         res_u5s[new_u5_idx] = u5::try_from_u8(curr_u5_as_u8 | ((shifted_chunk_u16 & 0x001f) as u8)).unwrap();
 453                         if new_u5_idx > 0 {
 454                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 1].to_u8();
 455                                 res_u5s[new_u5_idx - 1] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 5) & 0x001f) as u8)).unwrap();
 456                         }
 457                         if new_u5_idx > 1 {
 458                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 2].to_u8();
 459                                 res_u5s[new_u5_idx - 2] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 10) & 0x001f) as u8)).unwrap();
 460                         }
 461                 }
 462                 // Trim the highest feature bits.
 463                 while !res_u5s.is_empty() && res_u5s[0] == u5::try_from_u8(0).unwrap() {
 464                         res_u5s.remove(0);
 465                 }
 466                 writer.write(&res_u5s)
 467         }
 468 }
 469
 470 impl Base32Len for InvoiceFeatures {
 471         fn base32_len(&self) -> usize {
 472                 self.to_base32().len()
 473         }
 474 }
 475
 476 impl FromBase32 for InvoiceFeatures {
 477         type Err = bech32::Error;
 478
 479         fn from_base32(field_data: &[u5]) -> Result<InvoiceFeatures, bech32::Error> {
 480                 // Explanation for the "7": the normal way to round up when dividing is to add the divisor
 481                 // minus one before dividing
 482                 let length_bytes = (field_data.len() * 5 + 7) / 8 as usize;
 483                 let mut res_bytes: Vec<u8> = vec![0; length_bytes];
 484                 for (u5_idx, chunk) in field_data.iter().enumerate() {
 485                         let bit_pos_from_right_0_indexed = (field_data.len() - u5_idx - 1) * 5;
 486                         let new_byte_idx = (bit_pos_from_right_0_indexed / 8) as usize;
 487                         let new_bit_pos = bit_pos_from_right_0_indexed % 8;
 488                         let chunk_u16 = chunk.to_u8() as u16;
 489                         res_bytes[new_byte_idx] |= ((chunk_u16 << new_bit_pos) & 0xff) as u8;
 490                         if new_byte_idx != length_bytes - 1 {
 491                                 res_bytes[new_byte_idx + 1] |= ((chunk_u16 >> (8-new_bit_pos)) & 0xff) as u8;
 492                         }
 493                 }
 494                 // Trim the highest feature bits.
 495                 while !res_bytes.is_empty() && res_bytes[res_bytes.len() - 1] == 0 {
 496                         res_bytes.pop();
 497                 }
 498                 Ok(InvoiceFeatures::from_le_bytes(res_bytes))
 499         }
 500 }
 501
 502 impl<T: sealed::Context> Features<T> {
 503         /// Create a blank Features with no features set
 504         pub fn empty() -> Self {
 505                 Features {
 506                         flags: Vec::new(),
 507                         mark: PhantomData,
 508                 }
 509         }
 510
 511         /// Creates a Features with the bits set which are known by the implementation
 512         pub fn known() -> Self {
 513                 Self {
 514                         flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
 515                         mark: PhantomData,
 516                 }
 517         }
 518
 519         /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
 520         /// included in the result.
 521         fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
 522                 let from_byte_count = T::KNOWN_FEATURE_MASK.len();
 523                 let to_byte_count = C::KNOWN_FEATURE_MASK.len();
 524                 let mut flags = Vec::new();
 525                 for (i, byte) in self.flags.iter().enumerate() {
 526                         if i < from_byte_count && i < to_byte_count {
 527                                 let from_known_features = T::KNOWN_FEATURE_MASK[i];
 528                                 let to_known_features = C::KNOWN_FEATURE_MASK[i];
 529                                 flags.push(byte & from_known_features & to_known_features);
 530                         }
 531                 }
 532                 Features::<C> { flags, mark: PhantomData, }
 533         }
 534
 535         /// Create a Features given a set of flags, in little-endian. This is in reverse byte order from
 536         /// most on-the-wire encodings.
 537         /// (C-not exported) as we don't support export across multiple T
 538         pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
 539                 Features {
 540                         flags,
 541                         mark: PhantomData,
 542                 }
 543         }
 544
 545         #[cfg(test)]
 546         /// Gets the underlying flags set, in LE.
 547         pub fn le_flags(&self) -> &Vec<u8> {
 548                 &self.flags
 549         }
 550
 551         pub(crate) fn requires_unknown_bits(&self) -> bool {
 552                 // Bitwise AND-ing with all even bits set except for known features will select required
 553                 // unknown features.
 554                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 555                 self.flags.iter().enumerate().any(|(i, &byte)| {
 556                         let required_features = 0b01_01_01_01;
 557                         let unknown_features = if i < byte_count {
 558                                 !T::KNOWN_FEATURE_MASK[i]
 559                         } else {
 560                                 0b11_11_11_11
 561                         };
 562                         (byte & (required_features & unknown_features)) != 0
 563                 })
 564         }
 565
 566         pub(crate) fn supports_unknown_bits(&self) -> bool {
 567                 // Bitwise AND-ing with all even and odd bits set except for known features will select
 568                 // both required and optional unknown features.
 569                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 570                 self.flags.iter().enumerate().any(|(i, &byte)| {
 571                         let unknown_features = if i < byte_count {
 572                                 !T::KNOWN_FEATURE_MASK[i]
 573                         } else {
 574                                 0b11_11_11_11
 575                         };
 576                         (byte & unknown_features) != 0
 577                 })
 578         }
 579
 580         /// The number of bytes required to represent the feature flags present. This does not include
 581         /// the length bytes which are included in the serialized form.
 582         pub(crate) fn byte_count(&self) -> usize {
 583                 self.flags.len()
 584         }
 585 }
 586
 587 impl<T: sealed::DataLossProtect> Features<T> {
 588         #[cfg(test)]
 589         pub(crate) fn requires_data_loss_protect(&self) -> bool {
 590                 <T as sealed::DataLossProtect>::requires_feature(&self.flags)
 591         }
 592         #[cfg(test)]
 593         pub(crate) fn supports_data_loss_protect(&self) -> bool {
 594                 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
 595         }
 596 }
 597
 598 impl<T: sealed::UpfrontShutdownScript> Features<T> {
 599         #[cfg(test)]
 600         pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
 601                 <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
 602         }
 603         pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
 604                 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
 605         }
 606         #[cfg(test)]
 607         pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
 608                 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
 609                 self
 610         }
 611 }
 612
 613
 614 impl<T: sealed::GossipQueries> Features<T> {
 615         #[cfg(test)]
 616         pub(crate) fn requires_gossip_queries(&self) -> bool {
 617                 <T as sealed::GossipQueries>::requires_feature(&self.flags)
 618         }
 619         pub(crate) fn supports_gossip_queries(&self) -> bool {
 620                 <T as sealed::GossipQueries>::supports_feature(&self.flags)
 621         }
 622         #[cfg(test)]
 623         pub(crate) fn clear_gossip_queries(mut self) -> Self {
 624                 <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
 625                 self
 626         }
 627 }
 628
 629 impl<T: sealed::VariableLengthOnion> Features<T> {
 630         #[cfg(test)]
 631         pub(crate) fn requires_variable_length_onion(&self) -> bool {
 632                 <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
 633         }
 634         pub(crate) fn supports_variable_length_onion(&self) -> bool {
 635                 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
 636         }
 637 }
 638
 639 impl<T: sealed::StaticRemoteKey> Features<T> {
 640         pub(crate) fn supports_static_remote_key(&self) -> bool {
 641                 <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
 642         }
 643         #[cfg(test)]
 644         pub(crate) fn requires_static_remote_key(&self) -> bool {
 645                 <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
 646         }
 647 }
 648
 649 impl<T: sealed::InitialRoutingSync> Features<T> {
 650         pub(crate) fn initial_routing_sync(&self) -> bool {
 651                 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
 652         }
 653         // We are no longer setting initial_routing_sync now that gossip_queries
 654         // is enabled. This feature is ignored by a peer when gossip_queries has
 655         // been negotiated.
 656         #[cfg(test)]
 657         pub(crate) fn clear_initial_routing_sync(&mut self) {
 658                 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
 659         }
 660 }
 661
 662 impl<T: sealed::PaymentSecret> Features<T> {
 663         #[cfg(test)]
 664         pub(crate) fn requires_payment_secret(&self) -> bool {
 665                 <T as sealed::PaymentSecret>::requires_feature(&self.flags)
 666         }
 667         /// Returns whether the `payment_secret` feature is supported.
 668         pub fn supports_payment_secret(&self) -> bool {
 669                 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
 670         }
 671 }
 672
 673 impl<T: sealed::BasicMPP> Features<T> {
 674         #[cfg(test)]
 675         pub(crate) fn requires_basic_mpp(&self) -> bool {
 676                 <T as sealed::BasicMPP>::requires_feature(&self.flags)
 677         }
 678         // We currently never test for this since we don't actually *generate* multipath routes.
 679         pub(crate) fn supports_basic_mpp(&self) -> bool {
 680                 <T as sealed::BasicMPP>::supports_feature(&self.flags)
 681         }
 682 }
 683
 684 impl<T: sealed::ShutdownAnySegwit> Features<T> {
 685         pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
 686                 <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
 687         }
 688         #[cfg(test)]
 689         pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
 690                 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
 691                 self
 692         }
 693 }
 694
 695 impl<T: sealed::Context> Writeable for Features<T> {
 696         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 697                 w.size_hint(self.flags.len() + 2);
 698                 (self.flags.len() as u16).write(w)?;
 699                 for f in self.flags.iter().rev() { // Swap back to big-endian
 700                         f.write(w)?;
 701                 }
 702                 Ok(())
 703         }
 704 }
 705
 706 impl<T: sealed::Context> Readable for Features<T> {
 707         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 708                 let mut flags: Vec<u8> = Readable::read(r)?;
 709                 flags.reverse(); // Swap to little-endian
 710                 Ok(Self {
 711                         flags,
 712                         mark: PhantomData,
 713                 })
 714         }
 715 }
 716
 717 #[cfg(test)]
 718 mod tests {
 719         use super::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
 720         use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
 721
 722         #[test]
 723         fn sanity_test_known_features() {
 724                 assert!(!ChannelFeatures::known().requires_unknown_bits());
 725                 assert!(!ChannelFeatures::known().supports_unknown_bits());
 726                 assert!(!InitFeatures::known().requires_unknown_bits());
 727                 assert!(!InitFeatures::known().supports_unknown_bits());
 728                 assert!(!NodeFeatures::known().requires_unknown_bits());
 729                 assert!(!NodeFeatures::known().supports_unknown_bits());
 730
 731                 assert!(InitFeatures::known().supports_upfront_shutdown_script());
 732                 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
 733                 assert!(!InitFeatures::known().requires_upfront_shutdown_script());
 734                 assert!(!NodeFeatures::known().requires_upfront_shutdown_script());
 735
 736                 assert!(InitFeatures::known().supports_gossip_queries());
 737                 assert!(NodeFeatures::known().supports_gossip_queries());
 738                 assert!(!InitFeatures::known().requires_gossip_queries());
 739                 assert!(!NodeFeatures::known().requires_gossip_queries());
 740
 741                 assert!(InitFeatures::known().supports_data_loss_protect());
 742                 assert!(NodeFeatures::known().supports_data_loss_protect());
 743                 assert!(!InitFeatures::known().requires_data_loss_protect());
 744                 assert!(!NodeFeatures::known().requires_data_loss_protect());
 745
 746                 assert!(InitFeatures::known().supports_variable_length_onion());
 747                 assert!(NodeFeatures::known().supports_variable_length_onion());
 748                 assert!(InvoiceFeatures::known().supports_variable_length_onion());
 749                 assert!(InitFeatures::known().requires_variable_length_onion());
 750                 assert!(NodeFeatures::known().requires_variable_length_onion());
 751                 assert!(InvoiceFeatures::known().requires_variable_length_onion());
 752
 753                 assert!(InitFeatures::known().supports_static_remote_key());
 754                 assert!(NodeFeatures::known().supports_static_remote_key());
 755                 assert!(InitFeatures::known().requires_static_remote_key());
 756                 assert!(NodeFeatures::known().requires_static_remote_key());
 757
 758                 assert!(InitFeatures::known().supports_payment_secret());
 759                 assert!(NodeFeatures::known().supports_payment_secret());
 760                 assert!(InvoiceFeatures::known().supports_payment_secret());
 761                 assert!(InitFeatures::known().requires_payment_secret());
 762                 assert!(NodeFeatures::known().requires_payment_secret());
 763                 assert!(InvoiceFeatures::known().requires_payment_secret());
 764
 765                 assert!(InitFeatures::known().supports_basic_mpp());
 766                 assert!(NodeFeatures::known().supports_basic_mpp());
 767                 assert!(InvoiceFeatures::known().supports_basic_mpp());
 768                 assert!(!InitFeatures::known().requires_basic_mpp());
 769                 assert!(!NodeFeatures::known().requires_basic_mpp());
 770                 assert!(!InvoiceFeatures::known().requires_basic_mpp());
 771
 772                 assert!(InitFeatures::known().supports_shutdown_anysegwit());
 773                 assert!(NodeFeatures::known().supports_shutdown_anysegwit());
 774
 775                 let mut init_features = InitFeatures::known();
 776                 assert!(init_features.initial_routing_sync());
 777                 init_features.clear_initial_routing_sync();
 778                 assert!(!init_features.initial_routing_sync());
 779         }
 780
 781         #[test]
 782         fn sanity_test_unknown_bits() {
 783                 let features = ChannelFeatures::empty();
 784                 assert!(!features.requires_unknown_bits());
 785                 assert!(!features.supports_unknown_bits());
 786
 787                 let features = ChannelFeatures::empty().set_unknown_feature_required();
 788                 assert!(features.requires_unknown_bits());
 789                 assert!(features.supports_unknown_bits());
 790
 791                 let features = ChannelFeatures::empty().set_unknown_feature_optional();
 792                 assert!(!features.requires_unknown_bits());
 793                 assert!(features.supports_unknown_bits());
 794         }
 795
 796         #[test]
 797         fn convert_to_context_with_relevant_flags() {
 798                 let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
 799                 assert!(init_features.initial_routing_sync());
 800                 assert!(!init_features.supports_upfront_shutdown_script());
 801                 assert!(!init_features.supports_gossip_queries());
 802
 803                 let node_features: NodeFeatures = init_features.to_context();
 804                 {
 805                         // Check that the flags are as expected:
 806                         // - option_data_loss_protect
 807                         // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
 808                         // - basic_mpp
 809                         // - opt_shutdown_anysegwit
 810                         assert_eq!(node_features.flags.len(), 4);
 811                         assert_eq!(node_features.flags[0], 0b00000010);
 812                         assert_eq!(node_features.flags[1], 0b01010001);
 813                         assert_eq!(node_features.flags[2], 0b00000010);
 814                         assert_eq!(node_features.flags[3], 0b00001000);
 815                 }
 816
 817                 // Check that cleared flags are kept blank when converting back:
 818                 // - initial_routing_sync was not applicable to NodeContext
 819                 // - upfront_shutdown_script was cleared before converting
 820                 // - gossip_queries was cleared before converting
 821                 let features: InitFeatures = node_features.to_context_internal();
 822                 assert!(!features.initial_routing_sync());
 823                 assert!(!features.supports_upfront_shutdown_script());
 824                 assert!(!init_features.supports_gossip_queries());
 825         }
 826
 827         #[test]
 828         fn convert_to_context_with_unknown_flags() {
 829                 // Ensure the `from` context has fewer known feature bytes than the `to` context.
 830                 assert!(InvoiceFeatures::known().byte_count() < NodeFeatures::known().byte_count());
 831                 let invoice_features = InvoiceFeatures::known().set_unknown_feature_optional();
 832                 assert!(invoice_features.supports_unknown_bits());
 833                 let node_features: NodeFeatures = invoice_features.to_context();
 834                 assert!(!node_features.supports_unknown_bits());
 835         }
 836
 837         #[test]
 838         fn set_feature_bits() {
 839                 let features = InvoiceFeatures::empty()
 840                         .set_basic_mpp_optional()
 841                         .set_payment_secret_required();
 842                 assert!(features.supports_basic_mpp());
 843                 assert!(!features.requires_basic_mpp());
 844                 assert!(features.requires_payment_secret());
 845                 assert!(features.supports_payment_secret());
 846         }
 847
 848         #[test]
 849         fn invoice_features_encoding() {
 850                 let features_as_u5s = vec![
 851                         u5::try_from_u8(6).unwrap(),
 852                         u5::try_from_u8(10).unwrap(),
 853                         u5::try_from_u8(25).unwrap(),
 854                         u5::try_from_u8(1).unwrap(),
 855                         u5::try_from_u8(10).unwrap(),
 856                         u5::try_from_u8(0).unwrap(),
 857                         u5::try_from_u8(20).unwrap(),
 858                         u5::try_from_u8(2).unwrap(),
 859                         u5::try_from_u8(0).unwrap(),
 860                         u5::try_from_u8(6).unwrap(),
 861                         u5::try_from_u8(0).unwrap(),
 862                         u5::try_from_u8(16).unwrap(),
 863                         u5::try_from_u8(1).unwrap(),
 864                 ];
 865                 let features = InvoiceFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
 866
 867                 // Test length calculation.
 868                 assert_eq!(features.base32_len(), 13);
 869
 870                 // Test serialization.
 871                 let features_serialized = features.to_base32();
 872                 assert_eq!(features_as_u5s, features_serialized);
 873
 874                 // Test deserialization.
 875                 let features_deserialized = InvoiceFeatures::from_base32(&features_as_u5s).unwrap();
 876                 assert_eq!(features, features_deserialized);
 877         }
 878 }