_ 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 //! - `AnchorsZeroFeeHtlcTx` - requires/supports that commitment transactions include anchor outputs
  56 //!   and HTLC transactions are pre-signed with zero fee (see
  57 //!   [BOLT-3](https://github.com/lightning/bolts/blob/master/03-transactions.md) for more
  58 //!   information).
  59 //!
  60 //! [BOLT #9]: https://github.com/lightning/bolts/blob/master/09-features.md
  61 //! [messages]: crate::ln::msgs
  62
  63 use crate::{io, io_extras};
  64 use crate::prelude::*;
  65 use core::{cmp, fmt};
  66 use core::hash::{Hash, Hasher};
  67 use core::marker::PhantomData;
  68
  69 use bitcoin::bech32;
  70 use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5, WriteBase32};
  71 use crate::ln::msgs::DecodeError;
  72 use crate::util::ser::{Readable, WithoutLength, Writeable, Writer};
  73
  74 mod sealed {
  75         use crate::prelude::*;
  76         use crate::ln::features::Features;
  77
  78         /// The context in which [`Features`] are applicable. Defines which features are known to the
  79         /// implementation, though specification of them as required or optional is up to the code
  80         /// constructing a features object.
  81         pub trait Context {
  82                 /// Bitmask for selecting features that are known to the implementation.
  83                 const KNOWN_FEATURE_MASK: &'static [u8];
  84         }
  85
  86         /// Defines a [`Context`] by stating which features it requires and which are optional. Features
  87         /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
  88         /// feature identifiers.
  89         macro_rules! define_context {
  90                 ($context: ident, [$( $( $known_feature: ident )|*, )*]) => {
  91                         #[derive(Eq, PartialEq)]
  92                         pub struct $context {}
  93
  94                         impl Context for $context {
  95                                 const KNOWN_FEATURE_MASK: &'static [u8] = &[
  96                                         $(
  97                                                 0b00_00_00_00 $(|
  98                                                         <Self as $known_feature>::REQUIRED_MASK |
  99                                                         <Self as $known_feature>::OPTIONAL_MASK)*,
 100                                         )*
 101                                 ];
 102                         }
 103
 104                         impl alloc::fmt::Display for Features<$context> {
 105                                 fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
 106                                         $(
 107                                                 $(
 108                                                         fmt.write_fmt(format_args!("{}: {}, ", stringify!($known_feature),
 109                                                                 if <$context as $known_feature>::requires_feature(&self.flags) { "required" }
 110                                                                 else if <$context as $known_feature>::supports_feature(&self.flags) { "supported" }
 111                                                                 else { "not supported" }))?;
 112                                                 )*
 113                                                 {} // Rust gets mad if we only have a $()* block here, so add a dummy {}
 114                                         )*
 115                                         fmt.write_fmt(format_args!("unknown flags: {}",
 116                                                 if self.requires_unknown_bits() { "required" }
 117                                                 else if self.supports_unknown_bits() { "supported" } else { "none" }))
 118                                 }
 119                         }
 120                 };
 121         }
 122
 123         define_context!(InitContext, [
 124                 // Byte 0
 125                 DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
 126                 // Byte 1
 127                 VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 128                 // Byte 2
 129                 BasicMPP | Wumbo | AnchorsZeroFeeHtlcTx,
 130                 // Byte 3
 131                 ShutdownAnySegwit,
 132                 // Byte 4
 133                 OnionMessages,
 134                 // Byte 5
 135                 ChannelType | SCIDPrivacy,
 136                 // Byte 6
 137                 ZeroConf,
 138         ]);
 139         define_context!(NodeContext, [
 140                 // Byte 0
 141                 DataLossProtect | UpfrontShutdownScript | GossipQueries,
 142                 // Byte 1
 143                 VariableLengthOnion | StaticRemoteKey | PaymentSecret,
 144                 // Byte 2
 145                 BasicMPP | Wumbo | AnchorsZeroFeeHtlcTx,
 146                 // Byte 3
 147                 ShutdownAnySegwit,
 148                 // Byte 4
 149                 OnionMessages,
 150                 // Byte 5
 151                 ChannelType | SCIDPrivacy,
 152                 // Byte 6
 153                 ZeroConf | Keysend,
 154         ]);
 155         define_context!(ChannelContext, []);
 156         define_context!(InvoiceContext, [
 157                 // Byte 0
 158                 ,
 159                 // Byte 1
 160                 VariableLengthOnion | PaymentSecret,
 161                 // Byte 2
 162                 BasicMPP,
 163                 // Byte 3
 164                 ,
 165                 // Byte 4
 166                 ,
 167                 // Byte 5
 168                 ,
 169                 // Byte 6
 170                 PaymentMetadata,
 171         ]);
 172         define_context!(OfferContext, []);
 173         define_context!(InvoiceRequestContext, []);
 174         define_context!(Bolt12InvoiceContext, [
 175                 // Byte 0
 176                 ,
 177                 // Byte 1
 178                 ,
 179                 // Byte 2
 180                 BasicMPP,
 181         ]);
 182         define_context!(BlindedHopContext, []);
 183         // This isn't a "real" feature context, and is only used in the channel_type field in an
 184         // `OpenChannel` message.
 185         define_context!(ChannelTypeContext, [
 186                 // Byte 0
 187                 ,
 188                 // Byte 1
 189                 StaticRemoteKey,
 190                 // Byte 2
 191                 AnchorsZeroFeeHtlcTx,
 192                 // Byte 3
 193                 ,
 194                 // Byte 4
 195                 ,
 196                 // Byte 5
 197                 SCIDPrivacy,
 198                 // Byte 6
 199                 ZeroConf,
 200         ]);
 201
 202         /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
 203         /// useful for manipulating feature flags.
 204         macro_rules! define_feature {
 205                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 206                  $required_setter: ident, $supported_getter: ident) => {
 207                         #[doc = $doc]
 208                         ///
 209                         /// See [BOLT #9] for details.
 210                         ///
 211                         /// [BOLT #9]: https://github.com/lightning/bolts/blob/master/09-features.md
 212                         pub trait $feature: Context {
 213                                 /// The bit used to signify that the feature is required.
 214                                 const EVEN_BIT: usize = $odd_bit - 1;
 215
 216                                 /// The bit used to signify that the feature is optional.
 217                                 const ODD_BIT: usize = $odd_bit;
 218
 219                                 /// Assertion that [`EVEN_BIT`] is actually even.
 220                                 ///
 221                                 /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
 222                                 const ASSERT_EVEN_BIT_PARITY: usize;
 223
 224                                 /// Assertion that [`ODD_BIT`] is actually odd.
 225                                 ///
 226                                 /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
 227                                 const ASSERT_ODD_BIT_PARITY: usize;
 228
 229                                 /// Assertion that the bits are set in the context's [`KNOWN_FEATURE_MASK`].
 230                                 ///
 231                                 /// [`KNOWN_FEATURE_MASK`]: Context::KNOWN_FEATURE_MASK
 232                                 #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
 233                                 const ASSERT_BITS_IN_MASK: u8;
 234
 235                                 /// The byte where the feature is set.
 236                                 const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
 237
 238                                 /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
 239                                 ///
 240                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 241                                 const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);
 242
 243                                 /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
 244                                 ///
 245                                 /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
 246                                 const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);
 247
 248                                 /// Returns whether the feature is required by the given flags.
 249                                 #[inline]
 250                                 fn requires_feature(flags: &Vec<u8>) -> bool {
 251                                         flags.len() > Self::BYTE_OFFSET &&
 252                                                 (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
 253                                 }
 254
 255                                 /// Returns whether the feature is supported by the given flags.
 256                                 #[inline]
 257                                 fn supports_feature(flags: &Vec<u8>) -> bool {
 258                                         flags.len() > Self::BYTE_OFFSET &&
 259                                                 (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
 260                                 }
 261
 262                                 /// Sets the feature's required (even) bit in the given flags.
 263                                 #[inline]
 264                                 fn set_required_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::REQUIRED_MASK;
 270                                 }
 271
 272                                 /// Sets the feature's optional (odd) bit in the given flags.
 273                                 #[inline]
 274                                 fn set_optional_bit(flags: &mut Vec<u8>) {
 275                                         if flags.len() <= Self::BYTE_OFFSET {
 276                                                 flags.resize(Self::BYTE_OFFSET + 1, 0u8);
 277                                         }
 278
 279                                         flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
 280                                 }
 281
 282                                 /// Clears the feature's required (even) and optional (odd) bits from the given
 283                                 /// flags.
 284                                 #[inline]
 285                                 fn clear_bits(flags: &mut Vec<u8>) {
 286                                         if flags.len() > Self::BYTE_OFFSET {
 287                                                 flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
 288                                                 flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
 289                                         }
 290
 291                                         let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
 292                                         let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
 293                                         flags.resize(size, 0u8);
 294                                 }
 295                         }
 296
 297                         impl <T: $feature> Features<T> {
 298                                 /// Set this feature as optional.
 299                                 pub fn $optional_setter(&mut self) {
 300                                         <T as $feature>::set_optional_bit(&mut self.flags);
 301                                 }
 302
 303                                 /// Set this feature as required.
 304                                 pub fn $required_setter(&mut self) {
 305                                         <T as $feature>::set_required_bit(&mut self.flags);
 306                                 }
 307
 308                                 /// Checks if this feature is supported.
 309                                 pub fn $supported_getter(&self) -> bool {
 310                                         <T as $feature>::supports_feature(&self.flags)
 311                                 }
 312                         }
 313
 314                         $(
 315                                 impl $feature for $context {
 316                                         // EVEN_BIT % 2 == 0
 317                                         const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);
 318
 319                                         // ODD_BIT % 2 == 1
 320                                         const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
 321
 322                                         // (byte & (REQUIRED_MASK | OPTIONAL_MASK)) >> (EVEN_BIT % 8) == 3
 323                                         #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
 324                                         const ASSERT_BITS_IN_MASK: u8 =
 325                                                 ((<$context>::KNOWN_FEATURE_MASK[<Self as $feature>::BYTE_OFFSET] & (<Self as $feature>::REQUIRED_MASK | <Self as $feature>::OPTIONAL_MASK))
 326                                                  >> (<Self as $feature>::EVEN_BIT % 8)) - 3;
 327                                 }
 328                         )*
 329                 };
 330                 ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
 331                  $required_setter: ident, $supported_getter: ident, $required_getter: ident) => {
 332                         define_feature!($odd_bit, $feature, [$($context),+], $doc, $optional_setter, $required_setter, $supported_getter);
 333                         impl <T: $feature> Features<T> {
 334                                 /// Checks if this feature is required.
 335                                 pub fn $required_getter(&self) -> bool {
 336                                         <T as $feature>::requires_feature(&self.flags)
 337                                 }
 338                         }
 339                 }
 340         }
 341
 342         define_feature!(1, DataLossProtect, [InitContext, NodeContext],
 343                 "Feature flags for `option_data_loss_protect`.", set_data_loss_protect_optional,
 344                 set_data_loss_protect_required, supports_data_loss_protect, requires_data_loss_protect);
 345         // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
 346         define_feature!(3, InitialRoutingSync, [InitContext], "Feature flags for `initial_routing_sync`.",
 347                 set_initial_routing_sync_optional, set_initial_routing_sync_required,
 348                 initial_routing_sync);
 349         define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
 350                 "Feature flags for `option_upfront_shutdown_script`.", set_upfront_shutdown_script_optional,
 351                 set_upfront_shutdown_script_required, supports_upfront_shutdown_script,
 352                 requires_upfront_shutdown_script);
 353         define_feature!(7, GossipQueries, [InitContext, NodeContext],
 354                 "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required,
 355                 supports_gossip_queries, requires_gossip_queries);
 356         define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
 357                 "Feature flags for `var_onion_optin`.", set_variable_length_onion_optional,
 358                 set_variable_length_onion_required, supports_variable_length_onion,
 359                 requires_variable_length_onion);
 360         define_feature!(13, StaticRemoteKey, [InitContext, NodeContext, ChannelTypeContext],
 361                 "Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
 362                 set_static_remote_key_required, supports_static_remote_key, requires_static_remote_key);
 363         define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
 364                 "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required,
 365                 supports_payment_secret, requires_payment_secret);
 366         define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext, Bolt12InvoiceContext],
 367                 "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required,
 368                 supports_basic_mpp, requires_basic_mpp);
 369         define_feature!(19, Wumbo, [InitContext, NodeContext],
 370                 "Feature flags for `option_support_large_channel` (aka wumbo channels).", set_wumbo_optional, set_wumbo_required,
 371                 supports_wumbo, requires_wumbo);
 372         define_feature!(23, AnchorsZeroFeeHtlcTx, [InitContext, NodeContext, ChannelTypeContext],
 373                 "Feature flags for `option_anchors_zero_fee_htlc_tx`.", set_anchors_zero_fee_htlc_tx_optional,
 374                 set_anchors_zero_fee_htlc_tx_required, supports_anchors_zero_fee_htlc_tx, requires_anchors_zero_fee_htlc_tx);
 375         define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
 376                 "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
 377                 set_shutdown_any_segwit_required, supports_shutdown_anysegwit, requires_shutdown_anysegwit);
 378         define_feature!(39, OnionMessages, [InitContext, NodeContext],
 379                 "Feature flags for `option_onion_messages`.", set_onion_messages_optional,
 380                 set_onion_messages_required, supports_onion_messages, requires_onion_messages);
 381         define_feature!(45, ChannelType, [InitContext, NodeContext],
 382                 "Feature flags for `option_channel_type`.", set_channel_type_optional,
 383                 set_channel_type_required, supports_channel_type, requires_channel_type);
 384         define_feature!(47, SCIDPrivacy, [InitContext, NodeContext, ChannelTypeContext],
 385                 "Feature flags for only forwarding with SCID aliasing. Called `option_scid_alias` in the BOLTs",
 386                 set_scid_privacy_optional, set_scid_privacy_required, supports_scid_privacy, requires_scid_privacy);
 387         define_feature!(49, PaymentMetadata, [InvoiceContext],
 388                 "Feature flags for payment metadata in invoices.", set_payment_metadata_optional,
 389                 set_payment_metadata_required, supports_payment_metadata, requires_payment_metadata);
 390         define_feature!(51, ZeroConf, [InitContext, NodeContext, ChannelTypeContext],
 391                 "Feature flags for accepting channels with zero confirmations. Called `option_zeroconf` in the BOLTs",
 392                 set_zero_conf_optional, set_zero_conf_required, supports_zero_conf, requires_zero_conf);
 393         define_feature!(55, Keysend, [NodeContext],
 394                 "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required,
 395                 supports_keysend, requires_keysend);
 396
 397         #[cfg(test)]
 398         define_feature!(123456789, UnknownFeature,
 399                 [NodeContext, ChannelContext, InvoiceContext, OfferContext, InvoiceRequestContext, Bolt12InvoiceContext, BlindedHopContext],
 400                 "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
 401                 set_unknown_feature_required, supports_unknown_test_feature, requires_unknown_test_feature);
 402 }
 403
 404 /// Tracks the set of features which a node implements, templated by the context in which it
 405 /// appears.
 406 ///
 407 /// This is not exported to bindings users as we map the concrete feature types below directly instead
 408 #[derive(Eq)]
 409 pub struct Features<T: sealed::Context> {
 410         /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
 411         flags: Vec<u8>,
 412         mark: PhantomData<T>,
 413 }
 414
 415 impl <T: sealed::Context> Features<T> {
 416         pub(crate) fn or(mut self, o: Self) -> Self {
 417                 let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
 418                 self.flags.resize(total_feature_len, 0u8);
 419                 for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
 420                         *byte |= *o_byte;
 421                 }
 422                 self
 423         }
 424 }
 425
 426 impl<T: sealed::Context> Clone for Features<T> {
 427         fn clone(&self) -> Self {
 428                 Self {
 429                         flags: self.flags.clone(),
 430                         mark: PhantomData,
 431                 }
 432         }
 433 }
 434 impl<T: sealed::Context> Hash for Features<T> {
 435         fn hash<H: Hasher>(&self, hasher: &mut H) {
 436                 self.flags.hash(hasher);
 437         }
 438 }
 439 impl<T: sealed::Context> PartialEq for Features<T> {
 440         fn eq(&self, o: &Self) -> bool {
 441                 self.flags.eq(&o.flags)
 442         }
 443 }
 444 impl<T: sealed::Context> fmt::Debug for Features<T> {
 445         fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
 446                 self.flags.fmt(fmt)
 447         }
 448 }
 449
 450 /// Features used within an `init` message.
 451 pub type InitFeatures = Features<sealed::InitContext>;
 452 /// Features used within a `node_announcement` message.
 453 pub type NodeFeatures = Features<sealed::NodeContext>;
 454 /// Features used within a `channel_announcement` message.
 455 pub type ChannelFeatures = Features<sealed::ChannelContext>;
 456 /// Features used within an invoice.
 457 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
 458 /// Features used within an `offer`.
 459 pub type OfferFeatures = Features<sealed::OfferContext>;
 460 /// Features used within an `invoice_request`.
 461 pub type InvoiceRequestFeatures = Features<sealed::InvoiceRequestContext>;
 462 /// Features used within an `invoice`.
 463 pub type Bolt12InvoiceFeatures = Features<sealed::Bolt12InvoiceContext>;
 464 /// Features used within BOLT 4 encrypted_data_tlv and BOLT 12 blinded_payinfo
 465 pub type BlindedHopFeatures = Features<sealed::BlindedHopContext>;
 466
 467 /// Features used within the channel_type field in an OpenChannel message.
 468 ///
 469 /// A channel is always of some known "type", describing the transaction formats used and the exact
 470 /// semantics of our interaction with our peer.
 471 ///
 472 /// Note that because a channel is a specific type which is proposed by the opener and accepted by
 473 /// the counterparty, only required features are allowed here.
 474 ///
 475 /// This is serialized differently from other feature types - it is not prefixed by a length, and
 476 /// thus must only appear inside a TLV where its length is known in advance.
 477 pub type ChannelTypeFeatures = Features<sealed::ChannelTypeContext>;
 478
 479 impl InitFeatures {
 480         /// Writes all features present up to, and including, 13.
 481         pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 482                 let len = cmp::min(2, self.flags.len());
 483                 (len as u16).write(w)?;
 484                 for i in (0..len).rev() {
 485                         if i == 0 {
 486                                 self.flags[i].write(w)?;
 487                         } else {
 488                                 // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
 489                                 // up-to-and-including-bit-5, 0-indexed, on this byte:
 490                                 (self.flags[i] & 0b00_11_11_11).write(w)?;
 491                         }
 492                 }
 493                 Ok(())
 494         }
 495
 496         /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
 497         /// are included in the result.
 498         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 499                 self.to_context_internal()
 500         }
 501 }
 502
 503 impl InvoiceFeatures {
 504         /// Converts `InvoiceFeatures` to `Features<C>`. Only known `InvoiceFeatures` relevant to
 505         /// context `C` are included in the result.
 506         pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
 507                 self.to_context_internal()
 508         }
 509
 510         /// Getting a route for a keysend payment to a private node requires providing the payee's
 511         /// features (since they were not announced in a node announcement). However, keysend payments
 512         /// don't have an invoice to pull the payee's features from, so this method is provided for use in
 513         /// [`PaymentParameters::for_keysend`], thus omitting the need for payers to manually construct an
 514         /// `InvoiceFeatures` for [`find_route`].
 515         ///
 516         /// [`PaymentParameters::for_keysend`]: crate::routing::router::PaymentParameters::for_keysend
 517         /// [`find_route`]: crate::routing::router::find_route
 518         pub(crate) fn for_keysend() -> InvoiceFeatures {
 519                 let mut res = InvoiceFeatures::empty();
 520                 res.set_variable_length_onion_optional();
 521                 res
 522         }
 523 }
 524
 525 impl ChannelTypeFeatures {
 526         // Maps the relevant `InitFeatures` to `ChannelTypeFeatures`. Any unknown features to
 527         // `ChannelTypeFeatures` are not included in the result.
 528         pub(crate) fn from_init(init: &InitFeatures) -> Self {
 529                 let mut ret = init.to_context_internal();
 530                 // ChannelTypeFeatures must only contain required bits, so we OR the required forms of all
 531                 // optional bits and then AND out the optional ones.
 532                 for byte in ret.flags.iter_mut() {
 533                         *byte |= (*byte & 0b10_10_10_10) >> 1;
 534                         *byte &= 0b01_01_01_01;
 535                 }
 536                 ret
 537         }
 538
 539         /// Constructs a ChannelTypeFeatures with only static_remotekey set
 540         pub(crate) fn only_static_remote_key() -> Self {
 541                 let mut ret = Self::empty();
 542                 <sealed::ChannelTypeContext as sealed::StaticRemoteKey>::set_required_bit(&mut ret.flags);
 543                 ret
 544         }
 545 }
 546
 547 impl ToBase32 for InvoiceFeatures {
 548         fn write_base32<W: WriteBase32>(&self, writer: &mut W) -> Result<(), <W as WriteBase32>::Err> {
 549                 // Explanation for the "4": the normal way to round up when dividing is to add the divisor
 550                 // minus one before dividing
 551                 let length_u5s = (self.flags.len() * 8 + 4) / 5 as usize;
 552                 let mut res_u5s: Vec<u5> = vec![u5::try_from_u8(0).unwrap(); length_u5s];
 553                 for (byte_idx, byte) in self.flags.iter().enumerate() {
 554                         let bit_pos_from_left_0_indexed = byte_idx * 8;
 555                         let new_u5_idx = length_u5s - (bit_pos_from_left_0_indexed / 5) as usize - 1;
 556                         let new_bit_pos = bit_pos_from_left_0_indexed % 5;
 557                         let shifted_chunk_u16 = (*byte as u16) << new_bit_pos;
 558                         let curr_u5_as_u8 = res_u5s[new_u5_idx].to_u8();
 559                         res_u5s[new_u5_idx] = u5::try_from_u8(curr_u5_as_u8 | ((shifted_chunk_u16 & 0x001f) as u8)).unwrap();
 560                         if new_u5_idx > 0 {
 561                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 1].to_u8();
 562                                 res_u5s[new_u5_idx - 1] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 5) & 0x001f) as u8)).unwrap();
 563                         }
 564                         if new_u5_idx > 1 {
 565                                 let curr_u5_as_u8 = res_u5s[new_u5_idx - 2].to_u8();
 566                                 res_u5s[new_u5_idx - 2] = u5::try_from_u8(curr_u5_as_u8 | (((shifted_chunk_u16 >> 10) & 0x001f) as u8)).unwrap();
 567                         }
 568                 }
 569                 // Trim the highest feature bits.
 570                 while !res_u5s.is_empty() && res_u5s[0] == u5::try_from_u8(0).unwrap() {
 571                         res_u5s.remove(0);
 572                 }
 573                 writer.write(&res_u5s)
 574         }
 575 }
 576
 577 impl Base32Len for InvoiceFeatures {
 578         fn base32_len(&self) -> usize {
 579                 self.to_base32().len()
 580         }
 581 }
 582
 583 impl FromBase32 for InvoiceFeatures {
 584         type Err = bech32::Error;
 585
 586         fn from_base32(field_data: &[u5]) -> Result<InvoiceFeatures, bech32::Error> {
 587                 // Explanation for the "7": the normal way to round up when dividing is to add the divisor
 588                 // minus one before dividing
 589                 let length_bytes = (field_data.len() * 5 + 7) / 8 as usize;
 590                 let mut res_bytes: Vec<u8> = vec![0; length_bytes];
 591                 for (u5_idx, chunk) in field_data.iter().enumerate() {
 592                         let bit_pos_from_right_0_indexed = (field_data.len() - u5_idx - 1) * 5;
 593                         let new_byte_idx = (bit_pos_from_right_0_indexed / 8) as usize;
 594                         let new_bit_pos = bit_pos_from_right_0_indexed % 8;
 595                         let chunk_u16 = chunk.to_u8() as u16;
 596                         res_bytes[new_byte_idx] |= ((chunk_u16 << new_bit_pos) & 0xff) as u8;
 597                         if new_byte_idx != length_bytes - 1 {
 598                                 res_bytes[new_byte_idx + 1] |= ((chunk_u16 >> (8-new_bit_pos)) & 0xff) as u8;
 599                         }
 600                 }
 601                 // Trim the highest feature bits.
 602                 while !res_bytes.is_empty() && res_bytes[res_bytes.len() - 1] == 0 {
 603                         res_bytes.pop();
 604                 }
 605                 Ok(InvoiceFeatures::from_le_bytes(res_bytes))
 606         }
 607 }
 608
 609 impl<T: sealed::Context> Features<T> {
 610         /// Create a blank Features with no features set
 611         pub fn empty() -> Self {
 612                 Features {
 613                         flags: Vec::new(),
 614                         mark: PhantomData,
 615                 }
 616         }
 617
 618         /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
 619         /// included in the result.
 620         fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
 621                 let from_byte_count = T::KNOWN_FEATURE_MASK.len();
 622                 let to_byte_count = C::KNOWN_FEATURE_MASK.len();
 623                 let mut flags = Vec::new();
 624                 for (i, byte) in self.flags.iter().enumerate() {
 625                         if i < from_byte_count && i < to_byte_count {
 626                                 let from_known_features = T::KNOWN_FEATURE_MASK[i];
 627                                 let to_known_features = C::KNOWN_FEATURE_MASK[i];
 628                                 flags.push(byte & from_known_features & to_known_features);
 629                         }
 630                 }
 631                 Features::<C> { flags, mark: PhantomData, }
 632         }
 633
 634         /// Create a Features given a set of flags, in little-endian. This is in reverse byte order from
 635         /// most on-the-wire encodings.
 636         ///
 637         /// This is not exported to bindings users as we don't support export across multiple T
 638         pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
 639                 Features {
 640                         flags,
 641                         mark: PhantomData,
 642                 }
 643         }
 644
 645         #[cfg(test)]
 646         /// Gets the underlying flags set, in LE.
 647         pub fn le_flags(&self) -> &Vec<u8> {
 648                 &self.flags
 649         }
 650
 651         fn write_be<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 652                 for f in self.flags.iter().rev() { // Swap back to big-endian
 653                         f.write(w)?;
 654                 }
 655                 Ok(())
 656         }
 657
 658         fn from_be_bytes(mut flags: Vec<u8>) -> Features<T> {
 659                 flags.reverse(); // Swap to little-endian
 660                 Self {
 661                         flags,
 662                         mark: PhantomData,
 663                 }
 664         }
 665
 666         pub(crate) fn supports_any_optional_bits(&self) -> bool {
 667                 self.flags.iter().any(|&byte| (byte & 0b10_10_10_10) != 0)
 668         }
 669
 670         /// Returns true if this `Features` object contains unknown feature flags which are set as
 671         /// "required".
 672         pub fn requires_unknown_bits(&self) -> bool {
 673                 // Bitwise AND-ing with all even bits set except for known features will select required
 674                 // unknown features.
 675                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 676                 self.flags.iter().enumerate().any(|(i, &byte)| {
 677                         let required_features = 0b01_01_01_01;
 678                         let unknown_features = if i < byte_count {
 679                                 !T::KNOWN_FEATURE_MASK[i]
 680                         } else {
 681                                 0b11_11_11_11
 682                         };
 683                         (byte & (required_features & unknown_features)) != 0
 684                 })
 685         }
 686
 687         pub(crate) fn supports_unknown_bits(&self) -> bool {
 688                 // Bitwise AND-ing with all even and odd bits set except for known features will select
 689                 // both required and optional unknown features.
 690                 let byte_count = T::KNOWN_FEATURE_MASK.len();
 691                 self.flags.iter().enumerate().any(|(i, &byte)| {
 692                         let unknown_features = if i < byte_count {
 693                                 !T::KNOWN_FEATURE_MASK[i]
 694                         } else {
 695                                 0b11_11_11_11
 696                         };
 697                         (byte & unknown_features) != 0
 698                 })
 699         }
 700
 701         // Returns true if the features within `self` are a subset of the features within `other`.
 702         pub(crate) fn is_subset(&self, other: &Self) -> bool {
 703                 for (idx, byte) in self.flags.iter().enumerate() {
 704                         if let Some(other_byte) = other.flags.get(idx) {
 705                                 if byte & other_byte != *byte {
 706                                         // `self` has bits set that `other` doesn't.
 707                                         return false;
 708                                 }
 709                         } else {
 710                                 if *byte > 0 {
 711                                         // `self` has a non-zero byte that `other` doesn't.
 712                                         return false;
 713                                 }
 714                         }
 715                 }
 716                 true
 717         }
 718 }
 719
 720 impl<T: sealed::UpfrontShutdownScript> Features<T> {
 721         #[cfg(test)]
 722         pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
 723                 <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
 724                 self
 725         }
 726 }
 727
 728 impl<T: sealed::ShutdownAnySegwit> Features<T> {
 729         #[cfg(test)]
 730         pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
 731                 <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
 732                 self
 733         }
 734 }
 735
 736 impl<T: sealed::Wumbo> Features<T> {
 737         #[cfg(test)]
 738         pub(crate) fn clear_wumbo(mut self) -> Self {
 739                 <T as sealed::Wumbo>::clear_bits(&mut self.flags);
 740                 self
 741         }
 742 }
 743
 744 impl<T: sealed::SCIDPrivacy> Features<T> {
 745         pub(crate) fn clear_scid_privacy(&mut self) {
 746                 <T as sealed::SCIDPrivacy>::clear_bits(&mut self.flags);
 747         }
 748 }
 749
 750 impl<T: sealed::AnchorsZeroFeeHtlcTx> Features<T> {
 751         pub(crate) fn clear_anchors_zero_fee_htlc_tx(&mut self) {
 752                 <T as sealed::AnchorsZeroFeeHtlcTx>::clear_bits(&mut self.flags);
 753         }
 754 }
 755
 756 #[cfg(test)]
 757 impl<T: sealed::UnknownFeature> Features<T> {
 758         pub(crate) fn unknown() -> Self {
 759                 let mut features = Self::empty();
 760                 features.set_unknown_feature_required();
 761                 features
 762         }
 763 }
 764
 765 macro_rules! impl_feature_len_prefixed_write {
 766         ($features: ident) => {
 767                 impl Writeable for $features {
 768                         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 769                                 (self.flags.len() as u16).write(w)?;
 770                                 self.write_be(w)
 771                         }
 772                 }
 773                 impl Readable for $features {
 774                         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 775                                 Ok(Self::from_be_bytes(Vec::<u8>::read(r)?))
 776                         }
 777                 }
 778         }
 779 }
 780 impl_feature_len_prefixed_write!(InitFeatures);
 781 impl_feature_len_prefixed_write!(ChannelFeatures);
 782 impl_feature_len_prefixed_write!(NodeFeatures);
 783 impl_feature_len_prefixed_write!(InvoiceFeatures);
 784 impl_feature_len_prefixed_write!(BlindedHopFeatures);
 785
 786 // Some features only appear inside of TLVs, so they don't have a length prefix when serialized.
 787 macro_rules! impl_feature_tlv_write {
 788         ($features: ident) => {
 789                 impl Writeable for $features {
 790                         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 791                                 WithoutLength(self).write(w)
 792                         }
 793                 }
 794                 impl Readable for $features {
 795                         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 796                                 Ok(WithoutLength::<Self>::read(r)?.0)
 797                         }
 798                 }
 799         }
 800 }
 801
 802 impl_feature_tlv_write!(ChannelTypeFeatures);
 803
 804 // Some features may appear both in a TLV record and as part of a TLV subtype sequence. The latter
 805 // requires a length but the former does not.
 806
 807 impl<T: sealed::Context> Writeable for WithoutLength<&Features<T>> {
 808         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 809                 self.0.write_be(w)
 810         }
 811 }
 812
 813 impl<T: sealed::Context> Readable for WithoutLength<Features<T>> {
 814         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 815                 let v = io_extras::read_to_end(r)?;
 816                 Ok(WithoutLength(Features::<T>::from_be_bytes(v)))
 817         }
 818 }
 819
 820 #[cfg(test)]
 821 mod tests {
 822         use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, InvoiceFeatures, NodeFeatures, OfferFeatures, sealed};
 823         use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
 824         use crate::util::ser::{Readable, WithoutLength, Writeable};
 825
 826         #[test]
 827         fn sanity_test_unknown_bits() {
 828                 let features = ChannelFeatures::empty();
 829                 assert!(!features.requires_unknown_bits());
 830                 assert!(!features.supports_unknown_bits());
 831
 832                 let mut features = ChannelFeatures::empty();
 833                 features.set_unknown_feature_required();
 834                 assert!(features.requires_unknown_bits());
 835                 assert!(features.supports_unknown_bits());
 836
 837                 let mut features = ChannelFeatures::empty();
 838                 features.set_unknown_feature_optional();
 839                 assert!(!features.requires_unknown_bits());
 840                 assert!(features.supports_unknown_bits());
 841         }
 842
 843         #[test]
 844         fn convert_to_context_with_relevant_flags() {
 845                 let mut init_features = InitFeatures::empty();
 846                 // Set a bunch of features we use, plus initial_routing_sync_required (which shouldn't get
 847                 // converted as it's only relevant in an init context).
 848                 init_features.set_initial_routing_sync_required();
 849                 init_features.set_data_loss_protect_optional();
 850                 init_features.set_variable_length_onion_required();
 851                 init_features.set_static_remote_key_required();
 852                 init_features.set_payment_secret_required();
 853                 init_features.set_basic_mpp_optional();
 854                 init_features.set_wumbo_optional();
 855                 init_features.set_shutdown_any_segwit_optional();
 856                 init_features.set_onion_messages_optional();
 857                 init_features.set_channel_type_optional();
 858                 init_features.set_scid_privacy_optional();
 859                 init_features.set_zero_conf_optional();
 860                 init_features.set_anchors_zero_fee_htlc_tx_optional();
 861
 862                 assert!(init_features.initial_routing_sync());
 863                 assert!(!init_features.supports_upfront_shutdown_script());
 864                 assert!(!init_features.supports_gossip_queries());
 865
 866                 let node_features: NodeFeatures = init_features.to_context();
 867                 {
 868                         // Check that the flags are as expected:
 869                         // - option_data_loss_protect
 870                         // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
 871                         // - basic_mpp | wumbo
 872                         // - opt_shutdown_anysegwit
 873                         // - onion_messages
 874                         // - option_channel_type | option_scid_alias
 875                         // - option_zeroconf
 876                         assert_eq!(node_features.flags.len(), 7);
 877                         assert_eq!(node_features.flags[0], 0b00000010);
 878                         assert_eq!(node_features.flags[1], 0b01010001);
 879                         assert_eq!(node_features.flags[2], 0b10001010);
 880                         assert_eq!(node_features.flags[3], 0b00001000);
 881                         assert_eq!(node_features.flags[4], 0b10000000);
 882                         assert_eq!(node_features.flags[5], 0b10100000);
 883                         assert_eq!(node_features.flags[6], 0b00001000);
 884                 }
 885
 886                 // Check that cleared flags are kept blank when converting back:
 887                 // - initial_routing_sync was not applicable to NodeContext
 888                 // - upfront_shutdown_script was cleared before converting
 889                 // - gossip_queries was cleared before converting
 890                 let features: InitFeatures = node_features.to_context_internal();
 891                 assert!(!features.initial_routing_sync());
 892                 assert!(!features.supports_upfront_shutdown_script());
 893                 assert!(!init_features.supports_gossip_queries());
 894         }
 895
 896         #[test]
 897         fn convert_to_context_with_unknown_flags() {
 898                 // Ensure the `from` context has fewer known feature bytes than the `to` context.
 899                 assert!(<sealed::ChannelContext as sealed::Context>::KNOWN_FEATURE_MASK.len() <
 900                         <sealed::InvoiceContext as sealed::Context>::KNOWN_FEATURE_MASK.len());
 901                 let mut channel_features = ChannelFeatures::empty();
 902                 channel_features.set_unknown_feature_optional();
 903                 assert!(channel_features.supports_unknown_bits());
 904                 let invoice_features: InvoiceFeatures = channel_features.to_context_internal();
 905                 assert!(!invoice_features.supports_unknown_bits());
 906         }
 907
 908         #[test]
 909         fn set_feature_bits() {
 910                 let mut features = InvoiceFeatures::empty();
 911                 features.set_basic_mpp_optional();
 912                 features.set_payment_secret_required();
 913                 assert!(features.supports_basic_mpp());
 914                 assert!(!features.requires_basic_mpp());
 915                 assert!(features.requires_payment_secret());
 916                 assert!(features.supports_payment_secret());
 917         }
 918
 919         #[test]
 920         fn encodes_features_without_length() {
 921                 let features = OfferFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
 922                 assert_eq!(features.flags.len(), 8);
 923
 924                 let mut serialized_features = Vec::new();
 925                 WithoutLength(&features).write(&mut serialized_features).unwrap();
 926                 assert_eq!(serialized_features.len(), 8);
 927
 928                 let deserialized_features =
 929                         WithoutLength::<OfferFeatures>::read(&mut &serialized_features[..]).unwrap().0;
 930                 assert_eq!(features, deserialized_features);
 931         }
 932
 933         #[test]
 934         fn invoice_features_encoding() {
 935                 let features_as_u5s = vec![
 936                         u5::try_from_u8(6).unwrap(),
 937                         u5::try_from_u8(10).unwrap(),
 938                         u5::try_from_u8(25).unwrap(),
 939                         u5::try_from_u8(1).unwrap(),
 940                         u5::try_from_u8(10).unwrap(),
 941                         u5::try_from_u8(0).unwrap(),
 942                         u5::try_from_u8(20).unwrap(),
 943                         u5::try_from_u8(2).unwrap(),
 944                         u5::try_from_u8(0).unwrap(),
 945                         u5::try_from_u8(6).unwrap(),
 946                         u5::try_from_u8(0).unwrap(),
 947                         u5::try_from_u8(16).unwrap(),
 948                         u5::try_from_u8(1).unwrap(),
 949                 ];
 950                 let features = InvoiceFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
 951
 952                 // Test length calculation.
 953                 assert_eq!(features.base32_len(), 13);
 954
 955                 // Test serialization.
 956                 let features_serialized = features.to_base32();
 957                 assert_eq!(features_as_u5s, features_serialized);
 958
 959                 // Test deserialization.
 960                 let features_deserialized = InvoiceFeatures::from_base32(&features_as_u5s).unwrap();
 961                 assert_eq!(features, features_deserialized);
 962         }
 963
 964         #[test]
 965         fn test_channel_type_mapping() {
 966                 // If we map an InvoiceFeatures with StaticRemoteKey optional, it should map into a
 967                 // required-StaticRemoteKey ChannelTypeFeatures.
 968                 let mut init_features = InitFeatures::empty();
 969                 init_features.set_static_remote_key_optional();
 970                 let converted_features = ChannelTypeFeatures::from_init(&init_features);
 971                 assert_eq!(converted_features, ChannelTypeFeatures::only_static_remote_key());
 972                 assert!(!converted_features.supports_any_optional_bits());
 973                 assert!(converted_features.requires_static_remote_key());
 974         }
 975 }