+//! The following features are currently supported in the LDK:
+//! - `DataLossProtect` - requires/supports that a node which has somehow fallen behind, e.g., has been restored from an old backup,
+//! can detect that it has fallen behind
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
+//! - `InitialRoutingSync` - requires/supports that the sending node needs a complete routing information dump
+//! (see [BOLT-7](https://github.com/lightning/bolts/blob/master/07-routing-gossip.md#initial-sync) for more information).
+//! - `UpfrontShutdownScript` - commits to a shutdown scriptpubkey when opening a channel
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-open_channel-message) for more information).
+//! - `GossipQueries` - requires/supports more sophisticated gossip control
+//! (see [BOLT-7](https://github.com/lightning/bolts/blob/master/07-routing-gossip.md) for more information).
+//! - `PaymentSecret` - requires/supports that a node supports payment_secret field
+//! (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md) for more information).
+//! - `BasicMPP` - requires/supports that a node can receive basic multi-part payments
+//! (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md#basic-multi-part-payments) for more information).
+//! - `Wumbo` - requires/supports that a node create large channels. Called `option_support_large_channel` in the spec.
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-open_channel-message) for more information).
+//! - `ShutdownAnySegwit` - requires/supports that future segwit versions are allowed in `shutdown`
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
+//! - `OnionMessages` - requires/supports forwarding onion messages
+//! (see [BOLT-7](https://github.com/lightning/bolts/pull/759/files) for more information).
+//! TODO: update link
+//! - `ChannelType` - node supports the channel_type field in open/accept
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
+//! - `SCIDPrivacy` - supply channel aliases for routing
+//! (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
+//! - `Keysend` - send funds to a node without an invoice
+//! (see the [`Keysend` feature assignment proposal](https://github.com/lightning/bolts/issues/605#issuecomment-606679798) for more information).
+//! - `AnchorsZeroFeeHtlcTx` - requires/supports that commitment transactions include anchor outputs
+//! and HTLC transactions are pre-signed with zero fee (see
+//! [BOLT-3](https://github.com/lightning/bolts/blob/master/03-transactions.md) for more
+//! information).
+//!
+//! [BOLT #9]: https://github.com/lightning/bolts/blob/master/09-features.md
+//! [messages]: crate::ln::msgs
+
+use crate::{io, io_extras};
+use crate::prelude::*;
+use core::{cmp, fmt};
+use core::hash::{Hash, Hasher};
+use core::marker::PhantomData;
+
+use bitcoin::bech32;
+use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5, WriteBase32};
+use crate::ln::msgs::DecodeError;
+use crate::util::ser::{Readable, WithoutLength, Writeable, Writer};
+
+mod sealed {
+ use crate::prelude::*;
+ use crate::ln::features::Features;
+
+ /// The context in which [`Features`] are applicable. Defines which features are known to the
+ /// implementation, though specification of them as required or optional is up to the code
+ /// constructing a features object.
+ pub trait Context {
+ /// Bitmask for selecting features that are known to the implementation.
+ const KNOWN_FEATURE_MASK: &'static [u8];
+ }
+
+ /// Defines a [`Context`] by stating which features it requires and which are optional. Features
+ /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
+ /// feature identifiers.
+ macro_rules! define_context {
+ ($context: ident, [$( $( $known_feature: ident )|*, )*]) => {
+ #[derive(Eq, PartialEq)]
+ pub struct $context {}
+
+ impl Context for $context {
+ const KNOWN_FEATURE_MASK: &'static [u8] = &[
+ $(
+ 0b00_00_00_00 $(|
+ <Self as $known_feature>::REQUIRED_MASK |
+ <Self as $known_feature>::OPTIONAL_MASK)*,
+ )*
+ ];
+ }
+
+ impl alloc::fmt::Display for Features<$context> {
+ fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
+ $(
+ $(
+ fmt.write_fmt(format_args!("{}: {}, ", stringify!($known_feature),
+ if <$context as $known_feature>::requires_feature(&self.flags) { "required" }
+ else if <$context as $known_feature>::supports_feature(&self.flags) { "supported" }
+ else { "not supported" }))?;
+ )*
+ {} // Rust gets mad if we only have a $()* block here, so add a dummy {}
+ )*
+ fmt.write_fmt(format_args!("unknown flags: {}",
+ if self.requires_unknown_bits() { "required" }
+ else if self.supports_unknown_bits() { "supported" } else { "none" }))
+ }
+ }
+ };
+ }
+
+ define_context!(InitContext, [
+ // Byte 0
+ DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
+ // Byte 1
+ VariableLengthOnion | StaticRemoteKey | PaymentSecret,
+ // Byte 2
+ BasicMPP | Wumbo | AnchorsZeroFeeHtlcTx,
+ // Byte 3
+ ShutdownAnySegwit,
+ // Byte 4
+ OnionMessages,
+ // Byte 5
+ ChannelType | SCIDPrivacy,
+ // Byte 6
+ ZeroConf,
+ ]);
+ define_context!(NodeContext, [
+ // Byte 0
+ DataLossProtect | UpfrontShutdownScript | GossipQueries,
+ // Byte 1
+ VariableLengthOnion | StaticRemoteKey | PaymentSecret,
+ // Byte 2
+ BasicMPP | Wumbo | AnchorsZeroFeeHtlcTx,
+ // Byte 3
+ ShutdownAnySegwit,
+ // Byte 4
+ OnionMessages,
+ // Byte 5
+ ChannelType | SCIDPrivacy,
+ // Byte 6
+ ZeroConf | Keysend,
+ ]);
+ define_context!(ChannelContext, []);
+ define_context!(InvoiceContext, [
+ // Byte 0
+ ,
+ // Byte 1
+ VariableLengthOnion | PaymentSecret,
+ // Byte 2
+ BasicMPP,
+ ]);
+ define_context!(OfferContext, []);
+ define_context!(InvoiceRequestContext, []);
+ define_context!(Bolt12InvoiceContext, [
+ // Byte 0
+ ,
+ // Byte 1
+ ,
+ // Byte 2
+ BasicMPP,
+ ]);
+ define_context!(BlindedHopContext, []);
+ // This isn't a "real" feature context, and is only used in the channel_type field in an
+ // `OpenChannel` message.
+ define_context!(ChannelTypeContext, [
+ // Byte 0
+ ,
+ // Byte 1
+ StaticRemoteKey,
+ // Byte 2
+ AnchorsZeroFeeHtlcTx,
+ // Byte 3
+ ,
+ // Byte 4
+ ,
+ // Byte 5
+ SCIDPrivacy,
+ // Byte 6
+ ZeroConf,
+ ]);