_ 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::hash::{Hash, Hasher};
  29 use core::marker::PhantomData;
  30
  31 use bitcoin::bech32;
  32 use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5, WriteBase32};
  33 use ln::msgs::DecodeError;
  34 use util::ser::{Readable, Writeable, Writer};
  35
  36 mod sealed {
  37         use prelude::*;
  38         use ln::features::Features;
  39
  40         /// The context in which [`Features`] are applicable. Defines which features are required and
  41         /// which are optional for the context.
  42         pub trait Context {
  43                 /// Features that are known to the implementation, where a required feature is indicated by
  44                 /// its even bit and an optional feature is indicated by its odd bit.
  45                 const KNOWN_FEATURE_FLAGS: &'static [u8];
  46
  47                 /// Bitmask for selecting features that are known to the implementation, regardless of
  48                 /// whether each feature is required or optional.
  49                 const KNOWN_FEATURE_MASK: &'static [u8];
  50         }
  51
  52         /// Defines a [`Context`] by stating which features it requires and which are optional. Features
  53         /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
  54         /// feature identifiers.
  55         macro_rules! define_context {
  56                 ($context: ident {
  57                         required_features: [$( $( $required_feature: ident )|*, )*],
  58                         optional_features: [$( $( $optional_feature: ident )|*, )*],
  59                 }) => {
  60                         #[derive(Eq, PartialEq)]
  61                         pub struct $context {}
  62
  63                         impl Context for $context {
  64                                 const KNOWN_FEATURE_FLAGS: &'static [u8] = &[
  65                                         // For each byte, use bitwise-OR to compute the applicable flags for known
  66                                         // required features `r_i` and optional features `o_j` for all `i` and `j` such
  67                                         // that the following slice is formed:
  68                                         //
  69                                         // [
  70                                         //  `r_0` | `r_1` | ... | `o_0` | `o_1` | ...,
  71                                         //  ...,
  72                                         // ]
  73                                         $(
  74                                                 0b00_00_00_00 $(|
  75                                                         <Self as $required_feature>::REQUIRED_MASK)*
  76                                                 $(|
  77                                                         <Self as $optional_feature>::OPTIONAL_MASK)*,
  78                                         )*
  79                                 ];
  80
  81                                 const KNOWN_FEATURE_MASK: &'static [u8] = &[
  82                                         // Similar as above, but set both flags for each feature regardless of whether
  83                                         // the feature is required or optional.
  84                                         $(
  85                                                 0b00_00_00_00 $(|
  86                                                         <Self as $required_feature>::REQUIRED_MASK |
  87                                                         <Self as $required_feature>::OPTIONAL_MASK)*
  88                                                 $(|
  89                                                         <Self as $optional_feature>::REQUIRED_MASK |
  90                                                         <Self as $optional_feature>::OPTIONAL_MASK)*,
  91                                         )*
  92                                 ];
  93                         }
  94
  95                         impl alloc::fmt::Display for Features<$context> {
  96                                 fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
  97                                         $(
  98                                                 $(
  99                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($required_feature),
 100                                                                 if <$context as $required_feature>::requires_feature(&self.flags) { "required" }
 101                                                                 else if <$context as $required_feature>::supports_feature(&self.flags) { "supported" }
 102                                                                 else { "not supported" }))?;
 103                                                 )*
 104                                                 $(
 105                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($optional_feature),
 106                                                                 if <$context as $optional_feature>::requires_feature(&self.flags) { "required" }
 107                                                                 else if <$context as $optional_feature>::supports_feature(&self.flags) { "supported" }
 108                                                                 else { "not supported" }))?;
 109                                                 )*
 110                                         )*
 111                                         fmt.write_fmt(format_args!("unknown flags: {}",
 112                                                 if self.requires_unknown_bits() { "required" }
 113                                                 else if self.supports_unknown_bits() { "supported" } else { "none" }))
 114                                 }
 115                         }
 116                 };
 117         }
 118
 119         define_context!(InitContext {
 120                 required_features: [
 121                         // Byte 0
 122                         ,
 123                         // Byte 1
 124                         VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 125                         // Byte 2
 126                         ,
 127                         // Byte 3
 128                         ,
 129                 ],
 130                 optional_features: [
 131                         // Byte 0
 132                         DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
 133                         // Byte 1
 134                         ,
 135                         // Byte 2
 136                         BasicMPP,
 137                         // Byte 3
 138                         ShutdownAnySegwit,
 139                 ],
 140         });
 141         define_context!(NodeContext {
 142                 required_features: [
 143                         // Byte 0
 144                         ,
 145                         // Byte 1
 146                         VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 147                         // Byte 2
 148                         ,
 149                         // Byte 3
 150                         ,
 151                         // Byte 4
 152                         ,
 153                         // Byte 5
 154                         ,
 155                         // Byte 6
 156                         ,
 157                 ],
 158                 optional_features: [
 159                         // Byte 0
 160                         DataLossProtect | UpfrontShutdownScript | GossipQueries,
 161                         // Byte 1
 162                         ,
 163                         // Byte 2
 164                         BasicMPP,
 165                         // Byte 3
 166                         ShutdownAnySegwit,
 167                         // Byte 4
 168                         ,
 169                         // Byte 5
 170                         ,
 171                         // Byte 6
 172                         Keysend,
 173                 ],
 174         });
 175         define_context!(ChannelContext {
 176                 required_features: [],
 177                 optional_features: [],
 178         });
 179         define_context!(InvoiceContext {
 180                 required_features: [
 181                         // Byte 0
 182                         ,
 183                         // Byte 1
 184                         VariableLengthOnion | PaymentSecret,
 185                         // Byte 2
 186                         ,
 187                 ],
 188                 optional_features: [
 189                         // Byte 0
 190                         ,
 191                         // Byte 1
 192                         ,
 193                         // Byte 2
 194                         BasicMPP,
 195                 ],
 196         });
 197
 198         /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
 199         /// useful for manipulating feature flags.
 200         macro_rules! define_feature {
 201                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 202                  $required_setter: ident) => {
 203                         #[doc = $doc]
 204                         ///
 205                         /// See [BOLT #9] for details.
 206                         ///
 207                         /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
 208                         pub trait $feature: Context {
 209                                 /// The bit used to signify that the feature is required.
 210                                 const EVEN_BIT: usize = $odd_bit - 1;
 211
 212                                 /// The bit used to signify that the feature is optional.
 213                                 const ODD_BIT: usize = $odd_bit;
 214
 215                                 /// Assertion that [`EVEN_BIT`] is actually even.
 216                                 ///
 217                                 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
 218                                 const ASSERT_EVEN_BIT_PARITY: usize;
 219
 220                                 /// Assertion that [`ODD_BIT`] is actually odd.
 221                                 ///
 222                                 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
 223                                 const ASSERT_ODD_BIT_PARITY: usize;
 224
 225                                 /// The byte where the feature is set.
 226                                 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
 227
 228                                 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
 229                                 ///
 230                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 231                                 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
 232
 233                                 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
 234                                 ///
 235                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 236                                 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
 237
 238                                 /// Returns whether the feature is required by the given flags.
 239                                 #[inline]
 240                                 fn requires_feature(flags: &Vec<u8>) -> bool {
 241                                         flags.len() > Self::BYTE_OFFSET &&
 242                                                 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
 243                                 }
 244
 245                                 /// Returns whether the feature is supported by the given flags.
 246                                 #[inline]
 247                                 fn supports_feature(flags: &Vec<u8>) -> bool {
 248                                         flags.len() > Self::BYTE_OFFSET &&
 249                                                 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
 250                                 }
 251
 252                                 /// Sets the feature's required (even) bit in the given flags.
 253                                 #[inline]
 254                                 fn set_required_bit(flags: &mut Vec<u8>) {
 255                                         if flags.len() <= Self::BYTE_OFFSET {
 256                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 257                                         }
 258
 259                                         flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
 260                                 }
 261
 262                                 /// Sets the feature's optional (odd) bit in the given flags.
 263                                 #[inline]
 264                                 fn set_optional_bit(flags: &mut Vec<u8>) {
 265                                         if flags.len() <= Self::BYTE_OFFSET {
 266                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 267                                         }
 268
 269                                         flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
 270                                 }
 271
 272                                 /// Clears the feature's required (even) and optional (odd) bits from the given
 273                                 /// flags.
 274                                 #[inline]
 275                                 fn clear_bits(flags: &mut Vec<u8>) {
 276                                         if flags.len() > Self::BYTE_OFFSET {
 277                                                 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
 278                                                 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
 279                                         }
 280
 281                                         let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
 282                                         let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
 283                                         flags.resize(size, 0u8);
 284                                 }
 285                         }
 286
 287                         impl <T: $feature> Features<T> {
 288                                 /// Set this feature as optional.
 289                                 pub fn $optional_setter(mut self) -> Self {
 290                                         <T as $feature>::set_optional_bit(&mut self.flags);
 291                                         self
 292                                 }
 293
 294                                 /// Set this feature as required.
 295                                 pub fn $required_setter(mut self) -> Self {
 296                                         <T as $feature>::set_required_bit(&mut self.flags);
 297                                         self
 298                                 }
 299                         }
 300
 301                         $(
 302                                 impl $feature for $context {
 303                                         // EVEN_BIT % 2 == 0
 304                                         const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
 305
 306                                         // ODD_BIT % 2 == 1
 307                                         const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
 308                                 }
 309                         )*
 310
 311                 }
 312         }
 313
 314         define_feature!(1, DataLossProtect, [InitContext, NodeContext],
 315                 "Feature flags for `option_data_loss_protect`.", set_data_loss_protect_optional,
 316                 set_data_loss_protect_required);
 317         // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
 318         define_feature!(3, InitialRoutingSync, [InitContext], "Feature flags for `initial_routing_sync`.",
 319                 set_initial_routing_sync_optional, set_initial_routing_sync_required);
 320         define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
 321                 "Feature flags for `option_upfront_shutdown_script`.", set_upfront_shutdown_script_optional,
 322                 set_upfront_shutdown_script_required);
 323         define_feature!(7, GossipQueries, [InitContext, NodeContext],
 324                 "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required);
 325         define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
 326                 "Feature flags for `var_onion_optin`.", set_variable_length_onion_optional,
 327                 set_variable_length_onion_required);
 328         define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
 329                 "Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
 330                 set_static_remote_key_required);
 331         define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
 332                 "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required);
 333         define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext],
 334                 "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required);
 335         define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
 336                 "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
 337                 set_shutdown_any_segwit_required);
 338         define_feature!(55, Keysend, [NodeContext],
 339                 "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required);
 340
 341         #[cfg(test)]
 342         define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext, InvoiceContext],
 343                 "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
 344                 set_unknown_feature_required);
 345 }
 346
 347 /// Tracks the set of features which a node implements, templated by the context in which it
 348 /// appears.
 349 ///
 350 /// (C-not exported) as we map the concrete feature types below directly instead
 351 #[derive(Eq)]
 352 pub struct Features<T: sealed::Context> {
 353         /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
 354         flags: Vec<u8>,
 355         mark: PhantomData<T>,
 356 }
 357
 358 impl<T: sealed::Context> Clone for Features<T> {
 359         fn clone(&self) -> Self {
 360                 Self {
 361                         flags: self.flags.clone(),
 362                         mark: PhantomData,
 363                 }
 364         }
 365 }
 366 impl<T: sealed::Context> Hash for Features<T> {
 367         fn hash<H: Hasher>(&self, hasher: &mut H) {
 368                 self.flags.hash(hasher);
 369         }
 370 }
 371 impl<T: sealed::Context> PartialEq for Features<T> {
 372         fn eq(&self, o: &Self) -> bool {
 373                 self.flags.eq(&o.flags)
 374         }
 375 }
 376 impl<T: sealed::Context> fmt::Debug for Features<T> {
 377         fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 378                 self.flags.fmt(fmt)
 379         }
 380 }
 381
 382 /// Features used within an `init` message.
 383 pub type InitFeatures = Features<sealed::InitContext>;
 384 /// Features used within a `node_announcement` message.
 385 pub type NodeFeatures = Features<sealed::NodeContext>;
 386 /// Features used within a `channel_announcement` message.
 387 pub type ChannelFeatures = Features<sealed::ChannelContext>;
 388 /// Features used within an invoice.
 389 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
 390
 391 impl InitFeatures {
 392         /// Writes all features present up to, and including, 13.
 393         pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 394                 let len = cmp::min(2, self.flags.len());
 395                 w.size_hint(len + 2);
 396                 (len as u16).write(w)?;
 397                 for i in (0..len).rev() {
 398                         if i == 0 {
 399                                 self.flags[i].write(w)?;
 400                         } else {
 401                                 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
 402                                 // up-to-and-including-bit-5, 0-indexed, on this byte:
 403                                 (self.flags[i] & 0b00_11_11_11).write(w)?;
 404                         }
 405                 }
 406                 Ok(())
 407         }
 408
 409         /// or's another InitFeatures into this one.
 410         pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
 411                 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
 412                 self.flags.resize(total_feature_len, 0u8);
 413                 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
 414                         *byte |= *o_byte;
 415                 }
 416                 self
 417         }
 418
 419         /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
 420         /// are included in the result.
 421         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 422                 self.to_context_internal()
 423         }
 424 }
 425
 426 impl InvoiceFeatures {
 427         /// Converts `InvoiceFeatures` to `Features<C>`. Only known `InvoiceFeatures` relevant to
 428         /// context `C` are included in the result.
 429         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 430                 self.to_context_internal()
 431         }
 432
 433         /// Getting a route for a keysend payment to a private node requires providing the payee's
 434         /// features (since they were not announced in a node announcement). However, keysend payments
 435         /// don't have an invoice to pull the payee's features from, so this method is provided for use in
 436         /// [`get_keysend_route`], thus omitting the need for payers to manually construct an
 437         /// `InvoiceFeatures` for [`get_route`].
 438         ///
 439         /// [`get_keysend_route`]: crate::routing::router::get_keysend_route
 440         /// [`get_route`]: crate::routing::router::get_route
 441         pub(crate) fn for_keysend() -> InvoiceFeatures {
 442                 InvoiceFeatures::empty().set_variable_length_onion_optional()
 443         }
 444 }
 445
 446 impl ToBase32 for InvoiceFeatures {
 447         fn write_base32<W: WriteBase32>(&self, writer: &mut W) -> Result<(), <W as WriteBase32>::Err> {
 448                 // Explanation for the "4": the normal way to round up when dividing is to add the divisor
 449                 // minus one before dividing
 450                 let length_u5s = (self.flags.len() * 8 + 4) / 5 as usize;
 451                 let mut res_u5s: Vec<u5> = vec![u5::try_from_u8(0).unwrap(); length_u5s];
 452                 for (byte_idx, byte) in self.flags.iter().enumerate() {
 453                         let bit_pos_from_left_0_indexed = byte_idx * 8;
 454                         let new_u5_idx = length_u5s - (bit_pos_from_left_0_indexed / 5) as usize - 1;
 455                         let new_bit_pos = bit_pos_from_left_0_indexed % 5;
 456                         let shifted_chunk_u16 = (*byte as u16) << new_bit_pos;
 457                         let curr_u5_as_u8 = res_u5s[new_u5_idx].to_u8();
 458                         res_u5s[new_u5_idx] = u5::try_from_u8(curr_u5_as_u8 | ((shifted_chunk_u16 & 0x001f) as u8)).unwrap();
 459                         if new_u5_idx > 0 {
 460                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 1].to_u8();
 461                                 res_u5s[new_u5_idx - 1] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 5) & 0x001f) as u8)).unwrap();
 462                         }
 463                         if new_u5_idx > 1 {
 464                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 2].to_u8();
 465                                 res_u5s[new_u5_idx - 2] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 10) & 0x001f) as u8)).unwrap();
 466                         }
 467                 }
 468                 // Trim the highest feature bits.
 469                 while !res_u5s.is_empty() && res_u5s[0] == u5::try_from_u8(0).unwrap() {
 470                         res_u5s.remove(0);
 471                 }
 472                 writer.write(&res_u5s)
 473         }
 474 }
 475
 476 impl Base32Len for InvoiceFeatures {
 477         fn base32_len(&self) -> usize {
 478                 self.to_base32().len()
 479         }
 480 }
 481
 482 impl FromBase32 for InvoiceFeatures {
 483         type Err = bech32::Error;
 484
 485         fn from_base32(field_data: &[u5]) -> Result<InvoiceFeatures, bech32::Error> {
 486                 // Explanation for the "7": the normal way to round up when dividing is to add the divisor
 487                 // minus one before dividing
 488                 let length_bytes = (field_data.len() * 5 + 7) / 8 as usize;
 489                 let mut res_bytes: Vec<u8> = vec![0; length_bytes];
 490                 for (u5_idx, chunk) in field_data.iter().enumerate() {
 491                         let bit_pos_from_right_0_indexed = (field_data.len() - u5_idx - 1) * 5;
 492                         let new_byte_idx = (bit_pos_from_right_0_indexed / 8) as usize;
 493                         let new_bit_pos = bit_pos_from_right_0_indexed % 8;
 494                         let chunk_u16 = chunk.to_u8() as u16;
 495                         res_bytes[new_byte_idx] |= ((chunk_u16 << new_bit_pos) & 0xff) as u8;
 496                         if new_byte_idx != length_bytes - 1 {
 497                                 res_bytes[new_byte_idx + 1] |= ((chunk_u16 >> (8-new_bit_pos)) & 0xff) as u8;
 498                         }
 499                 }
 500                 // Trim the highest feature bits.
 501                 while !res_bytes.is_empty() && res_bytes[res_bytes.len() - 1] == 0 {
 502                         res_bytes.pop();
 503                 }
 504                 Ok(InvoiceFeatures::from_le_bytes(res_bytes))
 505         }
 506 }
 507
 508 impl<T: sealed::Context> Features<T> {
 509         /// Create a blank Features with no features set
 510         pub fn empty() -> Self {
 511                 Features {
 512                         flags: Vec::new(),
 513                         mark: PhantomData,
 514                 }
 515         }
 516
 517         /// Creates a Features with the bits set which are known by the implementation
 518         pub fn known() -> Self {
 519                 Self {
 520                         flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
 521                         mark: PhantomData,
 522                 }
 523         }
 524
 525         /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
 526         /// included in the result.
 527         fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
 528                 let from_byte_count = T::KNOWN_FEATURE_MASK.len();
 529                 let to_byte_count = C::KNOWN_FEATURE_MASK.len();
 530                 let mut flags = Vec::new();
 531                 for (i, byte) in self.flags.iter().enumerate() {
 532                         if i < from_byte_count && i < to_byte_count {
 533                                 let from_known_features = T::KNOWN_FEATURE_MASK[i];
 534                                 let to_known_features = C::KNOWN_FEATURE_MASK[i];
 535                                 flags.push(byte & from_known_features & to_known_features);
 536                         }
 537                 }
 538                 Features::<C> { flags, mark: PhantomData, }
 539         }
 540
 541         /// Create a Features given a set of flags, in little-endian. This is in reverse byte order from
 542         /// most on-the-wire encodings.
 543         /// (C-not exported) as we don't support export across multiple T
 544         pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
 545                 Features {
 546                         flags,
 547                         mark: PhantomData,
 548                 }
 549         }
 550
 551         #[cfg(test)]
 552         /// Gets the underlying flags set, in LE.
 553         pub fn le_flags(&self) -> &Vec<u8> {
 554                 &self.flags
 555         }
 556
 557         /// Returns true if this `Features` object contains unknown feature flags which are set as
 558         /// "required".
 559         pub fn requires_unknown_bits(&self) -> bool {
 560                 // Bitwise AND-ing with all even bits set except for known features will select required
 561                 // unknown features.
 562                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 563                 self.flags.iter().enumerate().any(|(i, &byte)| {
 564                         let required_features = 0b01_01_01_01;
 565                         let unknown_features = if i < byte_count {
 566                                 !T::KNOWN_FEATURE_MASK[i]
 567                         } else {
 568                                 0b11_11_11_11
 569                         };
 570                         (byte & (required_features & unknown_features)) != 0
 571                 })
 572         }
 573
 574         pub(crate) fn supports_unknown_bits(&self) -> bool {
 575                 // Bitwise AND-ing with all even and odd bits set except for known features will select
 576                 // both required and optional unknown features.
 577                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 578                 self.flags.iter().enumerate().any(|(i, &byte)| {
 579                         let unknown_features = if i < byte_count {
 580                                 !T::KNOWN_FEATURE_MASK[i]
 581                         } else {
 582                                 0b11_11_11_11
 583                         };
 584                         (byte & unknown_features) != 0
 585                 })
 586         }
 587
 588         /// The number of bytes required to represent the feature flags present. This does not include
 589         /// the length bytes which are included in the serialized form.
 590         pub(crate) fn byte_count(&self) -> usize {
 591                 self.flags.len()
 592         }
 593 }
 594
 595 impl<T: sealed::DataLossProtect> Features<T> {
 596         #[cfg(test)]
 597         pub(crate) fn requires_data_loss_protect(&self) -> bool {
 598                 <T as sealed::DataLossProtect>::requires_feature(&self.flags)
 599         }
 600         #[cfg(test)]
 601         pub(crate) fn supports_data_loss_protect(&self) -> bool {
 602                 <T as sealed::DataLossProtect>::supports_feature(&self.flags)
 603         }
 604 }
 605
 606 impl<T: sealed::UpfrontShutdownScript> Features<T> {
 607         #[cfg(test)]
 608         pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
 609                 <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
 610         }
 611         pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
 612                 <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
 613         }
 614         #[cfg(test)]
 615         pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
 616                 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
 617                 self
 618         }
 619 }
 620
 621
 622 impl<T: sealed::GossipQueries> Features<T> {
 623         #[cfg(test)]
 624         pub(crate) fn requires_gossip_queries(&self) -> bool {
 625                 <T as sealed::GossipQueries>::requires_feature(&self.flags)
 626         }
 627         pub(crate) fn supports_gossip_queries(&self) -> bool {
 628                 <T as sealed::GossipQueries>::supports_feature(&self.flags)
 629         }
 630         #[cfg(test)]
 631         pub(crate) fn clear_gossip_queries(mut self) -> Self {
 632                 <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
 633                 self
 634         }
 635 }
 636
 637 impl<T: sealed::VariableLengthOnion> Features<T> {
 638         #[cfg(test)]
 639         pub(crate) fn requires_variable_length_onion(&self) -> bool {
 640                 <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
 641         }
 642         pub(crate) fn supports_variable_length_onion(&self) -> bool {
 643                 <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
 644         }
 645 }
 646
 647 impl<T: sealed::StaticRemoteKey> Features<T> {
 648         pub(crate) fn supports_static_remote_key(&self) -> bool {
 649                 <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
 650         }
 651         #[cfg(test)]
 652         pub(crate) fn requires_static_remote_key(&self) -> bool {
 653                 <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
 654         }
 655 }
 656
 657 impl<T: sealed::InitialRoutingSync> Features<T> {
 658         pub(crate) fn initial_routing_sync(&self) -> bool {
 659                 <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
 660         }
 661         // We are no longer setting initial_routing_sync now that gossip_queries
 662         // is enabled. This feature is ignored by a peer when gossip_queries has
 663         // been negotiated.
 664         #[cfg(test)]
 665         pub(crate) fn clear_initial_routing_sync(&mut self) {
 666                 <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
 667         }
 668 }
 669
 670 impl<T: sealed::PaymentSecret> Features<T> {
 671         #[cfg(test)]
 672         pub(crate) fn requires_payment_secret(&self) -> bool {
 673                 <T as sealed::PaymentSecret>::requires_feature(&self.flags)
 674         }
 675         /// Returns whether the `payment_secret` feature is supported.
 676         pub fn supports_payment_secret(&self) -> bool {
 677                 <T as sealed::PaymentSecret>::supports_feature(&self.flags)
 678         }
 679 }
 680
 681 impl<T: sealed::BasicMPP> Features<T> {
 682         #[cfg(test)]
 683         pub(crate) fn requires_basic_mpp(&self) -> bool {
 684                 <T as sealed::BasicMPP>::requires_feature(&self.flags)
 685         }
 686         // We currently never test for this since we don't actually *generate* multipath routes.
 687         pub(crate) fn supports_basic_mpp(&self) -> bool {
 688                 <T as sealed::BasicMPP>::supports_feature(&self.flags)
 689         }
 690 }
 691
 692 impl<T: sealed::ShutdownAnySegwit> Features<T> {
 693         pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
 694                 <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
 695         }
 696         #[cfg(test)]
 697         pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
 698                 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
 699                 self
 700         }
 701 }
 702
 703 impl<T: sealed::Context> Writeable for Features<T> {
 704         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 705                 w.size_hint(self.flags.len() + 2);
 706                 (self.flags.len() as u16).write(w)?;
 707                 for f in self.flags.iter().rev() { // Swap back to big-endian
 708                         f.write(w)?;
 709                 }
 710                 Ok(())
 711         }
 712 }
 713
 714 impl<T: sealed::Context> Readable for Features<T> {
 715         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 716                 let mut flags: Vec<u8> = Readable::read(r)?;
 717                 flags.reverse(); // Swap to little-endian
 718                 Ok(Self {
 719                         flags,
 720                         mark: PhantomData,
 721                 })
 722         }
 723 }
 724
 725 #[cfg(test)]
 726 mod tests {
 727         use super::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
 728         use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
 729
 730         #[test]
 731         fn sanity_test_known_features() {
 732                 assert!(!ChannelFeatures::known().requires_unknown_bits());
 733                 assert!(!ChannelFeatures::known().supports_unknown_bits());
 734                 assert!(!InitFeatures::known().requires_unknown_bits());
 735                 assert!(!InitFeatures::known().supports_unknown_bits());
 736                 assert!(!NodeFeatures::known().requires_unknown_bits());
 737                 assert!(!NodeFeatures::known().supports_unknown_bits());
 738
 739                 assert!(InitFeatures::known().supports_upfront_shutdown_script());
 740                 assert!(NodeFeatures::known().supports_upfront_shutdown_script());
 741                 assert!(!InitFeatures::known().requires_upfront_shutdown_script());
 742                 assert!(!NodeFeatures::known().requires_upfront_shutdown_script());
 743
 744                 assert!(InitFeatures::known().supports_gossip_queries());
 745                 assert!(NodeFeatures::known().supports_gossip_queries());
 746                 assert!(!InitFeatures::known().requires_gossip_queries());
 747                 assert!(!NodeFeatures::known().requires_gossip_queries());
 748
 749                 assert!(InitFeatures::known().supports_data_loss_protect());
 750                 assert!(NodeFeatures::known().supports_data_loss_protect());
 751                 assert!(!InitFeatures::known().requires_data_loss_protect());
 752                 assert!(!NodeFeatures::known().requires_data_loss_protect());
 753
 754                 assert!(InitFeatures::known().supports_variable_length_onion());
 755                 assert!(NodeFeatures::known().supports_variable_length_onion());
 756                 assert!(InvoiceFeatures::known().supports_variable_length_onion());
 757                 assert!(InitFeatures::known().requires_variable_length_onion());
 758                 assert!(NodeFeatures::known().requires_variable_length_onion());
 759                 assert!(InvoiceFeatures::known().requires_variable_length_onion());
 760
 761                 assert!(InitFeatures::known().supports_static_remote_key());
 762                 assert!(NodeFeatures::known().supports_static_remote_key());
 763                 assert!(InitFeatures::known().requires_static_remote_key());
 764                 assert!(NodeFeatures::known().requires_static_remote_key());
 765
 766                 assert!(InitFeatures::known().supports_payment_secret());
 767                 assert!(NodeFeatures::known().supports_payment_secret());
 768                 assert!(InvoiceFeatures::known().supports_payment_secret());
 769                 assert!(InitFeatures::known().requires_payment_secret());
 770                 assert!(NodeFeatures::known().requires_payment_secret());
 771                 assert!(InvoiceFeatures::known().requires_payment_secret());
 772
 773                 assert!(InitFeatures::known().supports_basic_mpp());
 774                 assert!(NodeFeatures::known().supports_basic_mpp());
 775                 assert!(InvoiceFeatures::known().supports_basic_mpp());
 776                 assert!(!InitFeatures::known().requires_basic_mpp());
 777                 assert!(!NodeFeatures::known().requires_basic_mpp());
 778                 assert!(!InvoiceFeatures::known().requires_basic_mpp());
 779
 780                 assert!(InitFeatures::known().supports_shutdown_anysegwit());
 781                 assert!(NodeFeatures::known().supports_shutdown_anysegwit());
 782
 783                 let mut init_features = InitFeatures::known();
 784                 assert!(init_features.initial_routing_sync());
 785                 init_features.clear_initial_routing_sync();
 786                 assert!(!init_features.initial_routing_sync());
 787         }
 788
 789         #[test]
 790         fn sanity_test_unknown_bits() {
 791                 let features = ChannelFeatures::empty();
 792                 assert!(!features.requires_unknown_bits());
 793                 assert!(!features.supports_unknown_bits());
 794
 795                 let features = ChannelFeatures::empty().set_unknown_feature_required();
 796                 assert!(features.requires_unknown_bits());
 797                 assert!(features.supports_unknown_bits());
 798
 799                 let features = ChannelFeatures::empty().set_unknown_feature_optional();
 800                 assert!(!features.requires_unknown_bits());
 801                 assert!(features.supports_unknown_bits());
 802         }
 803
 804         #[test]
 805         fn convert_to_context_with_relevant_flags() {
 806                 let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
 807                 assert!(init_features.initial_routing_sync());
 808                 assert!(!init_features.supports_upfront_shutdown_script());
 809                 assert!(!init_features.supports_gossip_queries());
 810
 811                 let node_features: NodeFeatures = init_features.to_context();
 812                 {
 813                         // Check that the flags are as expected:
 814                         // - option_data_loss_protect
 815                         // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
 816                         // - basic_mpp
 817                         // - opt_shutdown_anysegwit
 818                         assert_eq!(node_features.flags.len(), 4);
 819                         assert_eq!(node_features.flags[0], 0b00000010);
 820                         assert_eq!(node_features.flags[1], 0b01010001);
 821                         assert_eq!(node_features.flags[2], 0b00000010);
 822                         assert_eq!(node_features.flags[3], 0b00001000);
 823                 }
 824
 825                 // Check that cleared flags are kept blank when converting back:
 826                 // - initial_routing_sync was not applicable to NodeContext
 827                 // - upfront_shutdown_script was cleared before converting
 828                 // - gossip_queries was cleared before converting
 829                 let features: InitFeatures = node_features.to_context_internal();
 830                 assert!(!features.initial_routing_sync());
 831                 assert!(!features.supports_upfront_shutdown_script());
 832                 assert!(!init_features.supports_gossip_queries());
 833         }
 834
 835         #[test]
 836         fn convert_to_context_with_unknown_flags() {
 837                 // Ensure the `from` context has fewer known feature bytes than the `to` context.
 838                 assert!(InvoiceFeatures::known().byte_count() < NodeFeatures::known().byte_count());
 839                 let invoice_features = InvoiceFeatures::known().set_unknown_feature_optional();
 840                 assert!(invoice_features.supports_unknown_bits());
 841                 let node_features: NodeFeatures = invoice_features.to_context();
 842                 assert!(!node_features.supports_unknown_bits());
 843         }
 844
 845         #[test]
 846         fn set_feature_bits() {
 847                 let features = InvoiceFeatures::empty()
 848                         .set_basic_mpp_optional()
 849                         .set_payment_secret_required();
 850                 assert!(features.supports_basic_mpp());
 851                 assert!(!features.requires_basic_mpp());
 852                 assert!(features.requires_payment_secret());
 853                 assert!(features.supports_payment_secret());
 854         }
 855
 856         #[test]
 857         fn invoice_features_encoding() {
 858                 let features_as_u5s = vec![
 859                         u5::try_from_u8(6).unwrap(),
 860                         u5::try_from_u8(10).unwrap(),
 861                         u5::try_from_u8(25).unwrap(),
 862                         u5::try_from_u8(1).unwrap(),
 863                         u5::try_from_u8(10).unwrap(),
 864                         u5::try_from_u8(0).unwrap(),
 865                         u5::try_from_u8(20).unwrap(),
 866                         u5::try_from_u8(2).unwrap(),
 867                         u5::try_from_u8(0).unwrap(),
 868                         u5::try_from_u8(6).unwrap(),
 869                         u5::try_from_u8(0).unwrap(),
 870                         u5::try_from_u8(16).unwrap(),
 871                         u5::try_from_u8(1).unwrap(),
 872                 ];
 873                 let features = InvoiceFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
 874
 875                 // Test length calculation.
 876                 assert_eq!(features.base32_len(), 13);
 877
 878                 // Test serialization.
 879                 let features_serialized = features.to_base32();
 880                 assert_eq!(features_as_u5s, features_serialized);
 881
 882                 // Test deserialization.
 883                 let features_deserialized = InvoiceFeatures::from_base32(&features_as_u5s).unwrap();
 884                 assert_eq!(features, features_deserialized);
 885         }
 886 }