_ 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 //! The following features are currently required in the LDK:
  23 //! - `VariableLengthOnion` - requires/supports variable-length routing onion payloads
  24 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md) for more information).
  25 //! - `StaticRemoteKey` - requires/supports static key for remote output
  26 //!     (see [BOLT-3](https://github.com/lightning/bolts/blob/master/03-transactions.md) for more information).
  27 //!
  28 //! The following features are currently supported in the LDK:
  29 //! - `DataLossProtect` - requires/supports that a node which has somehow fallen behind, e.g., has been restored from an old backup,
  30 //!     can detect that it has fallen behind
  31 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
  32 //! - `InitialRoutingSync` - requires/supports that the sending node needs a complete routing information dump
  33 //!     (see [BOLT-7](https://github.com/lightning/bolts/blob/master/07-routing-gossip.md#initial-sync) for more information).
  34 //! - `UpfrontShutdownScript` - commits to a shutdown scriptpubkey when opening a channel
  35 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-open_channel-message) for more information).
  36 //! - `GossipQueries` - requires/supports more sophisticated gossip control
  37 //!     (see [BOLT-7](https://github.com/lightning/bolts/blob/master/07-routing-gossip.md) for more information).
  38 //! - `PaymentSecret` - requires/supports that a node supports payment_secret field
  39 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md) for more information).
  40 //! - `BasicMPP` - requires/supports that a node can receive basic multi-part payments
  41 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md#basic-multi-part-payments) for more information).
  42 //! - `Wumbo` - requires/supports that a node create large channels. Called `option_support_large_channel` in the spec.
  43 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-open_channel-message) for more information).
  44 //! - `ShutdownAnySegwit` - requires/supports that future segwit versions are allowed in `shutdown`
  45 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
  46 //! - `OnionMessages` - requires/supports forwarding onion messages
  47 //!     (see [BOLT-7](https://github.com/lightning/bolts/pull/759/files) for more information).
  48 //!     TODO: update link
  49 //! - `ChannelType` - node supports the channel_type field in open/accept
  50 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
  51 //! - `SCIDPrivacy` - supply channel aliases for routing
  52 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
  53 //! - `Keysend` - send funds to a node without an invoice
  54 //!     (see the [`Keysend` feature assignment proposal](https://github.com/lightning/bolts/issues/605#issuecomment-606679798) for more information).
  55 //!
  56 //! [BOLT #9]: https://github.com/lightning/bolts/blob/master/09-features.md
  57 //! [messages]: crate::ln::msgs
  58
  59 use crate::{io, io_extras};
  60 use crate::prelude::*;
  61 use core::{cmp, fmt};
  62 use core::hash::{Hash, Hasher};
  63 use core::marker::PhantomData;
  64
  65 use bitcoin::bech32;
  66 use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5, WriteBase32};
  67 use crate::ln::msgs::DecodeError;
  68 use crate::util::ser::{Readable, Writeable, Writer};
  69
  70 mod sealed {
  71         use crate::prelude::*;
  72         use crate::ln::features::Features;
  73
  74         /// The context in which [`Features`] are applicable. Defines which features are known to the
  75         /// implementation, though specification of them as required or optional is up to the code
  76         /// constructing a features object.
  77         pub trait Context {
  78                 /// Bitmask for selecting features that are known to the implementation.
  79                 const KNOWN_FEATURE_MASK: &'static [u8];
  80         }
  81
  82         /// Defines a [`Context`] by stating which features it requires and which are optional. Features
  83         /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
  84         /// feature identifiers.
  85         macro_rules! define_context {
  86                 ($context: ident, [$( $( $known_feature: ident )|*, )*]) => {
  87                         #[derive(Eq, PartialEq)]
  88                         pub struct $context {}
  89
  90                         impl Context for $context {
  91                                 const KNOWN_FEATURE_MASK: &'static [u8] = &[
  92                                         $(
  93                                                 0b00_00_00_00 $(|
  94                                                         <Self as $known_feature>::REQUIRED_MASK |
  95                                                         <Self as $known_feature>::OPTIONAL_MASK)*,
  96                                         )*
  97                                 ];
  98                         }
  99
 100                         impl alloc::fmt::Display for Features<$context> {
 101                                 fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
 102                                         $(
 103                                                 $(
 104                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($known_feature),
 105                                                                 if <$context as $known_feature>::requires_feature(&self.flags) { "required" }
 106                                                                 else if <$context as $known_feature>::supports_feature(&self.flags) { "supported" }
 107                                                                 else { "not supported" }))?;
 108                                                 )*
 109                                                 {} // Rust gets mad if we only have a $()* block here, so add a dummy {}
 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                 // Byte 0
 121                 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
 122                 // Byte 1
 123                 VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 124                 // Byte 2
 125                 BasicMPP | Wumbo,
 126                 // Byte 3
 127                 ShutdownAnySegwit,
 128                 // Byte 4
 129                 OnionMessages,
 130                 // Byte 5
 131                 ChannelType | SCIDPrivacy,
 132                 // Byte 6
 133                 ZeroConf,
 134         ]);
 135         define_context!(NodeContext, [
 136                 // Byte 0
 137                 DataLossProtect | UpfrontShutdownScript | GossipQueries,
 138                 // Byte 1
 139                 VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 140                 // Byte 2
 141                 BasicMPP | Wumbo,
 142                 // Byte 3
 143                 ShutdownAnySegwit,
 144                 // Byte 4
 145                 OnionMessages,
 146                 // Byte 5
 147                 ChannelType | SCIDPrivacy,
 148                 // Byte 6
 149                 ZeroConf | Keysend,
 150         ]);
 151         define_context!(ChannelContext, []);
 152         define_context!(InvoiceContext, [
 153                 // Byte 0
 154                 ,
 155                 // Byte 1
 156                 VariableLengthOnion | PaymentSecret,
 157                 // Byte 2
 158                 BasicMPP,
 159         ]);
 160         define_context!(OfferContext, []);
 161         define_context!(InvoiceRequestContext, []);
 162         // This isn't a "real" feature context, and is only used in the channel_type field in an
 163         // `OpenChannel` message.
 164         define_context!(ChannelTypeContext, [
 165                 // Byte 0
 166                 ,
 167                 // Byte 1
 168                 StaticRemoteKey,
 169                 // Byte 2
 170                 ,
 171                 // Byte 3
 172                 ,
 173                 // Byte 4
 174                 ,
 175                 // Byte 5
 176                 SCIDPrivacy,
 177                 // Byte 6
 178                 ZeroConf,
 179         ]);
 180
 181         /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
 182         /// useful for manipulating feature flags.
 183         macro_rules! define_feature {
 184                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 185                  $required_setter: ident, $supported_getter: ident) => {
 186                         #[doc = $doc]
 187                         ///
 188                         /// See [BOLT #9] for details.
 189                         ///
 190                         /// [BOLT #9]: https://github.com/lightning/bolts/blob/master/09-features.md
 191                         pub trait $feature: Context {
 192                                 /// The bit used to signify that the feature is required.
 193                                 const EVEN_BIT: usize = $odd_bit - 1;
 194
 195                                 /// The bit used to signify that the feature is optional.
 196                                 const ODD_BIT: usize = $odd_bit;
 197
 198                                 /// Assertion that [`EVEN_BIT`] is actually even.
 199                                 ///
 200                                 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
 201                                 const ASSERT_EVEN_BIT_PARITY: usize;
 202
 203                                 /// Assertion that [`ODD_BIT`] is actually odd.
 204                                 ///
 205                                 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
 206                                 const ASSERT_ODD_BIT_PARITY: usize;
 207
 208                                 /// Assertion that the bits are set in the context's [`KNOWN_FEATURE_MASK`].
 209                                 ///
 210                                 /// [`KNOWN_FEATURE_MASK`]: Context::KNOWN_FEATURE_MASK
 211                                 #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
 212                                 const ASSERT_BITS_IN_MASK: u8;
 213
 214                                 /// The byte where the feature is set.
 215                                 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
 216
 217                                 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
 218                                 ///
 219                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 220                                 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
 221
 222                                 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
 223                                 ///
 224                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 225                                 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
 226
 227                                 /// Returns whether the feature is required by the given flags.
 228                                 #[inline]
 229                                 fn requires_feature(flags: &Vec<u8>) -> bool {
 230                                         flags.len() > Self::BYTE_OFFSET &&
 231                                                 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
 232                                 }
 233
 234                                 /// Returns whether the feature is supported by the given flags.
 235                                 #[inline]
 236                                 fn supports_feature(flags: &Vec<u8>) -> bool {
 237                                         flags.len() > Self::BYTE_OFFSET &&
 238                                                 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
 239                                 }
 240
 241                                 /// Sets the feature's required (even) bit in the given flags.
 242                                 #[inline]
 243                                 fn set_required_bit(flags: &mut Vec<u8>) {
 244                                         if flags.len() <= Self::BYTE_OFFSET {
 245                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 246                                         }
 247
 248                                         flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
 249                                 }
 250
 251                                 /// Sets the feature's optional (odd) bit in the given flags.
 252                                 #[inline]
 253                                 fn set_optional_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::OPTIONAL_MASK;
 259                                 }
 260
 261                                 /// Clears the feature's required (even) and optional (odd) bits from the given
 262                                 /// flags.
 263                                 #[inline]
 264                                 fn clear_bits(flags: &mut Vec<u8>) {
 265                                         if flags.len() > Self::BYTE_OFFSET {
 266                                                 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
 267                                                 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
 268                                         }
 269
 270                                         let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
 271                                         let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
 272                                         flags.resize(size, 0u8);
 273                                 }
 274                         }
 275
 276                         impl <T: $feature> Features<T> {
 277                                 /// Set this feature as optional.
 278                                 pub fn $optional_setter(&mut self) {
 279                                         <T as $feature>::set_optional_bit(&mut self.flags);
 280                                 }
 281
 282                                 /// Set this feature as required.
 283                                 pub fn $required_setter(&mut self) {
 284                                         <T as $feature>::set_required_bit(&mut self.flags);
 285                                 }
 286
 287                                 /// Checks if this feature is supported.
 288                                 pub fn $supported_getter(&self) -> bool {
 289                                         <T as $feature>::supports_feature(&self.flags)
 290                                 }
 291                         }
 292
 293                         $(
 294                                 impl $feature for $context {
 295                                         // EVEN_BIT % 2 == 0
 296                                         const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
 297
 298                                         // ODD_BIT % 2 == 1
 299                                         const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
 300
 301                                         // (byte & (REQUIRED_MASK | OPTIONAL_MASK)) >> (EVEN_BIT % 8) == 3
 302                                         #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
 303                                         const ASSERT_BITS_IN_MASK: u8 =
 304                                                 ((<$context>::KNOWN_FEATURE_MASK[<Self as $feature>::BYTE_OFFSET] & (<Self as $feature>::REQUIRED_MASK | <Self as $feature>::OPTIONAL_MASK))
 305                                                  >> (<Self as $feature>::EVEN_BIT % 8)) - 3;
 306                                 }
 307                         )*
 308                 };
 309                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 310                  $required_setter: ident, $supported_getter: ident, $required_getter: ident) => {
 311                         define_feature!($odd_bit, $feature, [$($context),+], $doc, $optional_setter, $required_setter, $supported_getter);
 312                         impl <T: $feature> Features<T> {
 313                                 /// Checks if this feature is required.
 314                                 pub fn $required_getter(&self) -> bool {
 315                                         <T as $feature>::requires_feature(&self.flags)
 316                                 }
 317                         }
 318                 }
 319         }
 320
 321         define_feature!(1, DataLossProtect, [InitContext, NodeContext],
 322                 "Feature flags for `option_data_loss_protect`.", set_data_loss_protect_optional,
 323                 set_data_loss_protect_required, supports_data_loss_protect, requires_data_loss_protect);
 324         // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
 325         define_feature!(3, InitialRoutingSync, [InitContext], "Feature flags for `initial_routing_sync`.",
 326                 set_initial_routing_sync_optional, set_initial_routing_sync_required,
 327                 initial_routing_sync);
 328         define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
 329                 "Feature flags for `option_upfront_shutdown_script`.", set_upfront_shutdown_script_optional,
 330                 set_upfront_shutdown_script_required, supports_upfront_shutdown_script,
 331                 requires_upfront_shutdown_script);
 332         define_feature!(7, GossipQueries, [InitContext, NodeContext],
 333                 "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required,
 334                 supports_gossip_queries, requires_gossip_queries);
 335         define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
 336                 "Feature flags for `var_onion_optin`.", set_variable_length_onion_optional,
 337                 set_variable_length_onion_required, supports_variable_length_onion,
 338                 requires_variable_length_onion);
 339         define_feature!(13, StaticRemoteKey, [InitContext, NodeContext, ChannelTypeContext],
 340                 "Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
 341                 set_static_remote_key_required, supports_static_remote_key, requires_static_remote_key);
 342         define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
 343                 "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required,
 344                 supports_payment_secret, requires_payment_secret);
 345         define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext],
 346                 "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required,
 347                 supports_basic_mpp, requires_basic_mpp);
 348         define_feature!(19, Wumbo, [InitContext, NodeContext],
 349                 "Feature flags for `option_support_large_channel` (aka wumbo channels).", set_wumbo_optional, set_wumbo_required,
 350                 supports_wumbo, requires_wumbo);
 351         define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
 352                 "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
 353                 set_shutdown_any_segwit_required, supports_shutdown_anysegwit, requires_shutdown_anysegwit);
 354         define_feature!(39, OnionMessages, [InitContext, NodeContext],
 355                 "Feature flags for `option_onion_messages`.", set_onion_messages_optional,
 356                 set_onion_messages_required, supports_onion_messages, requires_onion_messages);
 357         define_feature!(45, ChannelType, [InitContext, NodeContext],
 358                 "Feature flags for `option_channel_type`.", set_channel_type_optional,
 359                 set_channel_type_required, supports_channel_type, requires_channel_type);
 360         define_feature!(47, SCIDPrivacy, [InitContext, NodeContext, ChannelTypeContext],
 361                 "Feature flags for only forwarding with SCID aliasing. Called `option_scid_alias` in the BOLTs",
 362                 set_scid_privacy_optional, set_scid_privacy_required, supports_scid_privacy, requires_scid_privacy);
 363         define_feature!(51, ZeroConf, [InitContext, NodeContext, ChannelTypeContext],
 364                 "Feature flags for accepting channels with zero confirmations. Called `option_zeroconf` in the BOLTs",
 365                 set_zero_conf_optional, set_zero_conf_required, supports_zero_conf, requires_zero_conf);
 366         define_feature!(55, Keysend, [NodeContext],
 367                 "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required,
 368                 supports_keysend, requires_keysend);
 369
 370         #[cfg(test)]
 371         define_feature!(123456789, UnknownFeature,
 372                 [NodeContext, ChannelContext, InvoiceContext, OfferContext, InvoiceRequestContext],
 373                 "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
 374                 set_unknown_feature_required, supports_unknown_test_feature, requires_unknown_test_feature);
 375 }
 376
 377 /// Tracks the set of features which a node implements, templated by the context in which it
 378 /// appears.
 379 ///
 380 /// (C-not exported) as we map the concrete feature types below directly instead
 381 #[derive(Eq)]
 382 pub struct Features<T: sealed::Context> {
 383         /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
 384         flags: Vec<u8>,
 385         mark: PhantomData<T>,
 386 }
 387
 388 impl <T: sealed::Context> Features<T> {
 389         pub(crate) fn or(mut self, o: Self) -> Self {
 390                 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
 391                 self.flags.resize(total_feature_len, 0u8);
 392                 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
 393                         *byte |= *o_byte;
 394                 }
 395                 self
 396         }
 397 }
 398
 399 impl<T: sealed::Context> Clone for Features<T> {
 400         fn clone(&self) -> Self {
 401                 Self {
 402                         flags: self.flags.clone(),
 403                         mark: PhantomData,
 404                 }
 405         }
 406 }
 407 impl<T: sealed::Context> Hash for Features<T> {
 408         fn hash<H: Hasher>(&self, hasher: &mut H) {
 409                 self.flags.hash(hasher);
 410         }
 411 }
 412 impl<T: sealed::Context> PartialEq for Features<T> {
 413         fn eq(&self, o: &Self) -> bool {
 414                 self.flags.eq(&o.flags)
 415         }
 416 }
 417 impl<T: sealed::Context> fmt::Debug for Features<T> {
 418         fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 419                 self.flags.fmt(fmt)
 420         }
 421 }
 422
 423 /// Features used within an `init` message.
 424 pub type InitFeatures = Features<sealed::InitContext>;
 425 /// Features used within a `node_announcement` message.
 426 pub type NodeFeatures = Features<sealed::NodeContext>;
 427 /// Features used within a `channel_announcement` message.
 428 pub type ChannelFeatures = Features<sealed::ChannelContext>;
 429 /// Features used within an invoice.
 430 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
 431 /// Features used within an `offer`.
 432 pub type OfferFeatures = Features<sealed::OfferContext>;
 433 /// Features used within an `invoice_request`.
 434 pub type InvoiceRequestFeatures = Features<sealed::InvoiceRequestContext>;
 435
 436 /// Features used within the channel_type field in an OpenChannel message.
 437 ///
 438 /// A channel is always of some known "type", describing the transaction formats used and the exact
 439 /// semantics of our interaction with our peer.
 440 ///
 441 /// Note that because a channel is a specific type which is proposed by the opener and accepted by
 442 /// the counterparty, only required features are allowed here.
 443 ///
 444 /// This is serialized differently from other feature types - it is not prefixed by a length, and
 445 /// thus must only appear inside a TLV where its length is known in advance.
 446 pub type ChannelTypeFeatures = Features<sealed::ChannelTypeContext>;
 447
 448 impl InitFeatures {
 449         /// Writes all features present up to, and including, 13.
 450         pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 451                 let len = cmp::min(2, self.flags.len());
 452                 (len as u16).write(w)?;
 453                 for i in (0..len).rev() {
 454                         if i == 0 {
 455                                 self.flags[i].write(w)?;
 456                         } else {
 457                                 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
 458                                 // up-to-and-including-bit-5, 0-indexed, on this byte:
 459                                 (self.flags[i] & 0b00_11_11_11).write(w)?;
 460                         }
 461                 }
 462                 Ok(())
 463         }
 464
 465         /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
 466         /// are included in the result.
 467         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 468                 self.to_context_internal()
 469         }
 470 }
 471
 472 impl InvoiceFeatures {
 473         /// Converts `InvoiceFeatures` to `Features<C>`. Only known `InvoiceFeatures` relevant to
 474         /// context `C` are included in the result.
 475         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 476                 self.to_context_internal()
 477         }
 478
 479         /// Getting a route for a keysend payment to a private node requires providing the payee's
 480         /// features (since they were not announced in a node announcement). However, keysend payments
 481         /// don't have an invoice to pull the payee's features from, so this method is provided for use in
 482         /// [`PaymentParameters::for_keysend`], thus omitting the need for payers to manually construct an
 483         /// `InvoiceFeatures` for [`find_route`].
 484         ///
 485         /// [`PaymentParameters::for_keysend`]: crate::routing::router::PaymentParameters::for_keysend
 486         /// [`find_route`]: crate::routing::router::find_route
 487         pub(crate) fn for_keysend() -> InvoiceFeatures {
 488                 let mut res = InvoiceFeatures::empty();
 489                 res.set_variable_length_onion_optional();
 490                 res
 491         }
 492 }
 493
 494 impl ChannelTypeFeatures {
 495         /// Constructs the implicit channel type based on the common supported types between us and our
 496         /// counterparty
 497         pub(crate) fn from_counterparty_init(counterparty_init: &InitFeatures) -> Self {
 498                 let mut ret = counterparty_init.to_context_internal();
 499                 // ChannelTypeFeatures must only contain required bits, so we OR the required forms of all
 500                 // optional bits and then AND out the optional ones.
 501                 for byte in ret.flags.iter_mut() {
 502                         *byte |= (*byte & 0b10_10_10_10) >> 1;
 503                         *byte &= 0b01_01_01_01;
 504                 }
 505                 ret
 506         }
 507
 508         /// Constructs a ChannelTypeFeatures with only static_remotekey set
 509         pub(crate) fn only_static_remote_key() -> Self {
 510                 let mut ret = Self::empty();
 511                 <sealed::ChannelTypeContext as sealed::StaticRemoteKey>::set_required_bit(&mut ret.flags);
 512                 ret
 513         }
 514 }
 515
 516 impl ToBase32 for InvoiceFeatures {
 517         fn write_base32<W: WriteBase32>(&self, writer: &mut W) -> Result<(), <W as WriteBase32>::Err> {
 518                 // Explanation for the "4": the normal way to round up when dividing is to add the divisor
 519                 // minus one before dividing
 520                 let length_u5s = (self.flags.len() * 8 + 4) / 5 as usize;
 521                 let mut res_u5s: Vec<u5> = vec![u5::try_from_u8(0).unwrap(); length_u5s];
 522                 for (byte_idx, byte) in self.flags.iter().enumerate() {
 523                         let bit_pos_from_left_0_indexed = byte_idx * 8;
 524                         let new_u5_idx = length_u5s - (bit_pos_from_left_0_indexed / 5) as usize - 1;
 525                         let new_bit_pos = bit_pos_from_left_0_indexed % 5;
 526                         let shifted_chunk_u16 = (*byte as u16) << new_bit_pos;
 527                         let curr_u5_as_u8 = res_u5s[new_u5_idx].to_u8();
 528                         res_u5s[new_u5_idx] = u5::try_from_u8(curr_u5_as_u8 | ((shifted_chunk_u16 & 0x001f) as u8)).unwrap();
 529                         if new_u5_idx > 0 {
 530                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 1].to_u8();
 531                                 res_u5s[new_u5_idx - 1] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 5) & 0x001f) as u8)).unwrap();
 532                         }
 533                         if new_u5_idx > 1 {
 534                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 2].to_u8();
 535                                 res_u5s[new_u5_idx - 2] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 10) & 0x001f) as u8)).unwrap();
 536                         }
 537                 }
 538                 // Trim the highest feature bits.
 539                 while !res_u5s.is_empty() && res_u5s[0] == u5::try_from_u8(0).unwrap() {
 540                         res_u5s.remove(0);
 541                 }
 542                 writer.write(&res_u5s)
 543         }
 544 }
 545
 546 impl Base32Len for InvoiceFeatures {
 547         fn base32_len(&self) -> usize {
 548                 self.to_base32().len()
 549         }
 550 }
 551
 552 impl FromBase32 for InvoiceFeatures {
 553         type Err = bech32::Error;
 554
 555         fn from_base32(field_data: &[u5]) -> Result<InvoiceFeatures, bech32::Error> {
 556                 // Explanation for the "7": the normal way to round up when dividing is to add the divisor
 557                 // minus one before dividing
 558                 let length_bytes = (field_data.len() * 5 + 7) / 8 as usize;
 559                 let mut res_bytes: Vec<u8> = vec![0; length_bytes];
 560                 for (u5_idx, chunk) in field_data.iter().enumerate() {
 561                         let bit_pos_from_right_0_indexed = (field_data.len() - u5_idx - 1) * 5;
 562                         let new_byte_idx = (bit_pos_from_right_0_indexed / 8) as usize;
 563                         let new_bit_pos = bit_pos_from_right_0_indexed % 8;
 564                         let chunk_u16 = chunk.to_u8() as u16;
 565                         res_bytes[new_byte_idx] |= ((chunk_u16 << new_bit_pos) & 0xff) as u8;
 566                         if new_byte_idx != length_bytes - 1 {
 567                                 res_bytes[new_byte_idx + 1] |= ((chunk_u16 >> (8-new_bit_pos)) & 0xff) as u8;
 568                         }
 569                 }
 570                 // Trim the highest feature bits.
 571                 while !res_bytes.is_empty() && res_bytes[res_bytes.len() - 1] == 0 {
 572                         res_bytes.pop();
 573                 }
 574                 Ok(InvoiceFeatures::from_le_bytes(res_bytes))
 575         }
 576 }
 577
 578 impl<T: sealed::Context> Features<T> {
 579         /// Create a blank Features with no features set
 580         pub fn empty() -> Self {
 581                 Features {
 582                         flags: Vec::new(),
 583                         mark: PhantomData,
 584                 }
 585         }
 586
 587         /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
 588         /// included in the result.
 589         fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
 590                 let from_byte_count = T::KNOWN_FEATURE_MASK.len();
 591                 let to_byte_count = C::KNOWN_FEATURE_MASK.len();
 592                 let mut flags = Vec::new();
 593                 for (i, byte) in self.flags.iter().enumerate() {
 594                         if i < from_byte_count && i < to_byte_count {
 595                                 let from_known_features = T::KNOWN_FEATURE_MASK[i];
 596                                 let to_known_features = C::KNOWN_FEATURE_MASK[i];
 597                                 flags.push(byte & from_known_features & to_known_features);
 598                         }
 599                 }
 600                 Features::<C> { flags, mark: PhantomData, }
 601         }
 602
 603         /// Create a Features given a set of flags, in little-endian. This is in reverse byte order from
 604         /// most on-the-wire encodings.
 605         /// (C-not exported) as we don't support export across multiple T
 606         pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
 607                 Features {
 608                         flags,
 609                         mark: PhantomData,
 610                 }
 611         }
 612
 613         #[cfg(test)]
 614         /// Gets the underlying flags set, in LE.
 615         pub fn le_flags(&self) -> &Vec<u8> {
 616                 &self.flags
 617         }
 618
 619         fn write_be<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 620                 for f in self.flags.iter().rev() { // Swap back to big-endian
 621                         f.write(w)?;
 622                 }
 623                 Ok(())
 624         }
 625
 626         fn from_be_bytes(mut flags: Vec<u8>) -> Features<T> {
 627                 flags.reverse(); // Swap to little-endian
 628                 Self {
 629                         flags,
 630                         mark: PhantomData,
 631                 }
 632         }
 633
 634         pub(crate) fn supports_any_optional_bits(&self) -> bool {
 635                 self.flags.iter().any(|&byte| (byte & 0b10_10_10_10) != 0)
 636         }
 637
 638         /// Returns true if this `Features` object contains unknown feature flags which are set as
 639         /// "required".
 640         pub fn requires_unknown_bits(&self) -> bool {
 641                 // Bitwise AND-ing with all even bits set except for known features will select required
 642                 // unknown features.
 643                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 644                 self.flags.iter().enumerate().any(|(i, &byte)| {
 645                         let required_features = 0b01_01_01_01;
 646                         let unknown_features = if i < byte_count {
 647                                 !T::KNOWN_FEATURE_MASK[i]
 648                         } else {
 649                                 0b11_11_11_11
 650                         };
 651                         (byte & (required_features & unknown_features)) != 0
 652                 })
 653         }
 654
 655         pub(crate) fn supports_unknown_bits(&self) -> bool {
 656                 // Bitwise AND-ing with all even and odd bits set except for known features will select
 657                 // both required and optional unknown features.
 658                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 659                 self.flags.iter().enumerate().any(|(i, &byte)| {
 660                         let unknown_features = if i < byte_count {
 661                                 !T::KNOWN_FEATURE_MASK[i]
 662                         } else {
 663                                 0b11_11_11_11
 664                         };
 665                         (byte & unknown_features) != 0
 666                 })
 667         }
 668 }
 669
 670 impl<T: sealed::UpfrontShutdownScript> Features<T> {
 671         #[cfg(test)]
 672         pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
 673                 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
 674                 self
 675         }
 676 }
 677
 678 impl<T: sealed::ShutdownAnySegwit> Features<T> {
 679         #[cfg(test)]
 680         pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
 681                 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
 682                 self
 683         }
 684 }
 685
 686 impl<T: sealed::Wumbo> Features<T> {
 687         #[cfg(test)]
 688         pub(crate) fn clear_wumbo(mut self) -> Self {
 689                 <T as sealed::Wumbo>::clear_bits(&mut self.flags);
 690                 self
 691         }
 692 }
 693
 694 #[cfg(test)]
 695 impl<T: sealed::UnknownFeature> Features<T> {
 696         pub(crate) fn unknown() -> Self {
 697                 let mut features = Self::empty();
 698                 features.set_unknown_feature_required();
 699                 features
 700         }
 701 }
 702
 703 macro_rules! impl_feature_len_prefixed_write {
 704         ($features: ident) => {
 705                 impl Writeable for $features {
 706                         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 707                                 (self.flags.len() as u16).write(w)?;
 708                                 self.write_be(w)
 709                         }
 710                 }
 711                 impl Readable for $features {
 712                         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 713                                 Ok(Self::from_be_bytes(Vec::<u8>::read(r)?))
 714                         }
 715                 }
 716         }
 717 }
 718 impl_feature_len_prefixed_write!(InitFeatures);
 719 impl_feature_len_prefixed_write!(ChannelFeatures);
 720 impl_feature_len_prefixed_write!(NodeFeatures);
 721 impl_feature_len_prefixed_write!(InvoiceFeatures);
 722
 723 // Some features only appear inside of TLVs, so they don't have a length prefix when serialized.
 724 macro_rules! impl_feature_tlv_write {
 725         ($features: ident) => {
 726                 impl Writeable for $features {
 727                         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 728                                 self.write_be(w)
 729                         }
 730                 }
 731                 impl Readable for $features {
 732                         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 733                                 let v = io_extras::read_to_end(r)?;
 734                                 Ok(Self::from_be_bytes(v))
 735                         }
 736                 }
 737         }
 738 }
 739
 740 impl_feature_tlv_write!(ChannelTypeFeatures);
 741 impl_feature_tlv_write!(OfferFeatures);
 742 impl_feature_tlv_write!(InvoiceRequestFeatures);
 743
 744 #[cfg(test)]
 745 mod tests {
 746         use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, InvoiceFeatures, NodeFeatures, sealed};
 747         use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
 748
 749         #[test]
 750         fn sanity_test_unknown_bits() {
 751                 let features = ChannelFeatures::empty();
 752                 assert!(!features.requires_unknown_bits());
 753                 assert!(!features.supports_unknown_bits());
 754
 755                 let mut features = ChannelFeatures::empty();
 756                 features.set_unknown_feature_required();
 757                 assert!(features.requires_unknown_bits());
 758                 assert!(features.supports_unknown_bits());
 759
 760                 let mut features = ChannelFeatures::empty();
 761                 features.set_unknown_feature_optional();
 762                 assert!(!features.requires_unknown_bits());
 763                 assert!(features.supports_unknown_bits());
 764         }
 765
 766         #[test]
 767         fn convert_to_context_with_relevant_flags() {
 768                 let mut init_features = InitFeatures::empty();
 769                 // Set a bunch of features we use, plus initial_routing_sync_required (which shouldn't get
 770                 // converted as it's only relevant in an init context).
 771                 init_features.set_initial_routing_sync_required();
 772                 init_features.set_data_loss_protect_optional();
 773                 init_features.set_variable_length_onion_required();
 774                 init_features.set_static_remote_key_required();
 775                 init_features.set_payment_secret_required();
 776                 init_features.set_basic_mpp_optional();
 777                 init_features.set_wumbo_optional();
 778                 init_features.set_shutdown_any_segwit_optional();
 779                 init_features.set_onion_messages_optional();
 780                 init_features.set_channel_type_optional();
 781                 init_features.set_scid_privacy_optional();
 782                 init_features.set_zero_conf_optional();
 783
 784                 assert!(init_features.initial_routing_sync());
 785                 assert!(!init_features.supports_upfront_shutdown_script());
 786                 assert!(!init_features.supports_gossip_queries());
 787
 788                 let node_features: NodeFeatures = init_features.to_context();
 789                 {
 790                         // Check that the flags are as expected:
 791                         // - option_data_loss_protect
 792                         // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
 793                         // - basic_mpp | wumbo
 794                         // - opt_shutdown_anysegwit
 795                         // - onion_messages
 796                         // - option_channel_type | option_scid_alias
 797                         // - option_zeroconf
 798                         assert_eq!(node_features.flags.len(), 7);
 799                         assert_eq!(node_features.flags[0], 0b00000010);
 800                         assert_eq!(node_features.flags[1], 0b01010001);
 801                         assert_eq!(node_features.flags[2], 0b00001010);
 802                         assert_eq!(node_features.flags[3], 0b00001000);
 803                         assert_eq!(node_features.flags[4], 0b10000000);
 804                         assert_eq!(node_features.flags[5], 0b10100000);
 805                         assert_eq!(node_features.flags[6], 0b00001000);
 806                 }
 807
 808                 // Check that cleared flags are kept blank when converting back:
 809                 // - initial_routing_sync was not applicable to NodeContext
 810                 // - upfront_shutdown_script was cleared before converting
 811                 // - gossip_queries was cleared before converting
 812                 let features: InitFeatures = node_features.to_context_internal();
 813                 assert!(!features.initial_routing_sync());
 814                 assert!(!features.supports_upfront_shutdown_script());
 815                 assert!(!init_features.supports_gossip_queries());
 816         }
 817
 818         #[test]
 819         fn convert_to_context_with_unknown_flags() {
 820                 // Ensure the `from` context has fewer known feature bytes than the `to` context.
 821                 assert!(<sealed::InvoiceContext as sealed::Context>::KNOWN_FEATURE_MASK.len() <
 822                         <sealed::NodeContext as sealed::Context>::KNOWN_FEATURE_MASK.len());
 823                 let mut invoice_features = InvoiceFeatures::empty();
 824                 invoice_features.set_unknown_feature_optional();
 825                 assert!(invoice_features.supports_unknown_bits());
 826                 let node_features: NodeFeatures = invoice_features.to_context();
 827                 assert!(!node_features.supports_unknown_bits());
 828         }
 829
 830         #[test]
 831         fn set_feature_bits() {
 832                 let mut features = InvoiceFeatures::empty();
 833                 features.set_basic_mpp_optional();
 834                 features.set_payment_secret_required();
 835                 assert!(features.supports_basic_mpp());
 836                 assert!(!features.requires_basic_mpp());
 837                 assert!(features.requires_payment_secret());
 838                 assert!(features.supports_payment_secret());
 839         }
 840
 841         #[test]
 842         fn invoice_features_encoding() {
 843                 let features_as_u5s = vec![
 844                         u5::try_from_u8(6).unwrap(),
 845                         u5::try_from_u8(10).unwrap(),
 846                         u5::try_from_u8(25).unwrap(),
 847                         u5::try_from_u8(1).unwrap(),
 848                         u5::try_from_u8(10).unwrap(),
 849                         u5::try_from_u8(0).unwrap(),
 850                         u5::try_from_u8(20).unwrap(),
 851                         u5::try_from_u8(2).unwrap(),
 852                         u5::try_from_u8(0).unwrap(),
 853                         u5::try_from_u8(6).unwrap(),
 854                         u5::try_from_u8(0).unwrap(),
 855                         u5::try_from_u8(16).unwrap(),
 856                         u5::try_from_u8(1).unwrap(),
 857                 ];
 858                 let features = InvoiceFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
 859
 860                 // Test length calculation.
 861                 assert_eq!(features.base32_len(), 13);
 862
 863                 // Test serialization.
 864                 let features_serialized = features.to_base32();
 865                 assert_eq!(features_as_u5s, features_serialized);
 866
 867                 // Test deserialization.
 868                 let features_deserialized = InvoiceFeatures::from_base32(&features_as_u5s).unwrap();
 869                 assert_eq!(features, features_deserialized);
 870         }
 871
 872         #[test]
 873         fn test_channel_type_mapping() {
 874                 // If we map an InvoiceFeatures with StaticRemoteKey optional, it should map into a
 875                 // required-StaticRemoteKey ChannelTypeFeatures.
 876                 let mut init_features = InitFeatures::empty();
 877                 init_features.set_static_remote_key_optional();
 878                 let converted_features = ChannelTypeFeatures::from_counterparty_init(&init_features);
 879                 assert_eq!(converted_features, ChannelTypeFeatures::only_static_remote_key());
 880                 assert!(!converted_features.supports_any_optional_bits());
 881                 assert!(converted_features.requires_static_remote_key());
 882         }
 883 }