[rust-lightning] / lightning / src / ln / features.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Feature flag definitions for the Lightning protocol according to [BOLT #9].
//!
//! Lightning nodes advertise a supported set of operation through feature flags. Features are
//! applicable for a specific context as indicated in some [messages]. [`Features`] encapsulates
//! behavior for specifying and checking feature flags for a particular context. Each feature is
//! defined internally by a trait specifying the corresponding flags (i.e., even and odd bits). A
//! [`Context`] is used to parameterize [`Features`] and defines which features it can support.
//!
//! Whether a feature is considered "known" or "unknown" is relative to the implementation, whereas
//! the term "supports" is used in reference to a particular set of [`Features`]. That is, a node
//! supports a feature if it advertises the feature (as either required or optional) to its peers.
//! And the implementation can interpret a feature if the feature is known to it.
//!
//! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
//! [messages]: ../msgs/index.html
//! [`Features`]: struct.Features.html
//! [`Context`]: sealed/trait.Context.html

use std::{cmp, fmt};
use std::marker::PhantomData;

use ln::msgs::DecodeError;
use util::ser::{Readable, Writeable, Writer};

mod sealed {
        /// The context in which [`Features`] are applicable. Defines which features are required and
        /// which are optional for the context.
        ///
        /// [`Features`]: ../struct.Features.html
        pub trait Context {
                /// Features that are known to the implementation, where a required feature is indicated by
                /// its even bit and an optional feature is indicated by its odd bit.
                const KNOWN_FEATURE_FLAGS: &'static [u8];

                /// Bitmask for selecting features that are known to the implementation, regardless of
                /// whether each feature is required or optional.
                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.
        ///
        /// [`Context`]: trait.Context.html
        macro_rules! define_context {
                ($context: ident {
                        required_features: [$( $( $required_feature: ident )|*, )*],
                        optional_features: [$( $( $optional_feature: ident )|*, )*],
                }) => {
                        pub struct $context {}

                        impl Context for $context {
                                const KNOWN_FEATURE_FLAGS: &'static [u8] = &[
                                        // For each byte, use bitwise-OR to compute the applicable flags for known
                                        // required features `r_i` and optional features `o_j` for all `i` and `j` such
                                        // that the following slice is formed:
                                        //
                                        // [
                                        //  `r_0` | `r_1` | ... | `o_0` | `o_1` | ...,
                                        //  ...,
                                        // ]
                                        $(
                                                0b00_00_00_00 $(|
                                                        <Self as $required_feature>::REQUIRED_MASK)*
                                                $(|
                                                        <Self as $optional_feature>::OPTIONAL_MASK)*,
                                        )*
                                ];

                                const KNOWN_FEATURE_MASK: &'static [u8] = &[
                                        // Similar as above, but set both flags for each feature regardless of whether
                                        // the feature is required or optional.
                                        $(
                                                0b00_00_00_00 $(|
                                                        <Self as $required_feature>::REQUIRED_MASK |
                                                        <Self as $required_feature>::OPTIONAL_MASK)*
                                                $(|
                                                        <Self as $optional_feature>::REQUIRED_MASK |
                                                        <Self as $optional_feature>::OPTIONAL_MASK)*,
                                        )*
                                ];
                        }
                };
        }

        define_context!(InitContext {
                required_features: [
                        // Byte 0
                        ,
                        // Byte 1
                        StaticRemoteKey,
                        // Byte 2
                        ,
                        // Byte 3
                        ,
                ],
                optional_features: [
                        // Byte 0
                        DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
                        // Byte 1
                        VariableLengthOnion | PaymentSecret,
                        // Byte 2
                        BasicMPP,
                        // Byte 3
                        ShutdownAnySegwit,
                ],
        });
        define_context!(NodeContext {
                required_features: [
                        // Byte 0
                        ,
                        // Byte 1
                        StaticRemoteKey,
                        // Byte 2
                        ,
                        // Byte 3
                        ,
                ],
                optional_features: [
                        // Byte 0
                        DataLossProtect | UpfrontShutdownScript | GossipQueries,
                        // Byte 1
                        VariableLengthOnion | PaymentSecret,
                        // Byte 2
                        BasicMPP,
                        // Byte 3
                        ShutdownAnySegwit,
                ],
        });
        define_context!(ChannelContext {
                required_features: [],
                optional_features: [],
        });

        /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
        /// useful for manipulating feature flags.
        ///
        /// [`Context`]: trait.Context.html
        macro_rules! define_feature {
                ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr) => {
                        #[doc = $doc]
                        ///
                        /// See [BOLT #9] for details.
                        ///
                        /// [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
                        pub trait $feature: Context {
                                /// The bit used to signify that the feature is required.
                                const EVEN_BIT: usize = $odd_bit - 1;

                                /// The bit used to signify that the feature is optional.
                                const ODD_BIT: usize = $odd_bit;

                                /// Assertion that [`EVEN_BIT`] is actually even.
                                ///
                                /// [`EVEN_BIT`]: #associatedconstant.EVEN_BIT
                                const ASSERT_EVEN_BIT_PARITY: usize;

                                /// Assertion that [`ODD_BIT`] is actually odd.
                                ///
                                /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
                                const ASSERT_ODD_BIT_PARITY: usize;

                                /// The byte where the feature is set.
                                const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;

                                /// The bitmask for the feature's required flag relative to the [`BYTE_OFFSET`].
                                ///
                                /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
                                const REQUIRED_MASK: u8 = 1 << (Self::EVEN_BIT - 8 * Self::BYTE_OFFSET);

                                /// The bitmask for the feature's optional flag relative to the [`BYTE_OFFSET`].
                                ///
                                /// [`BYTE_OFFSET`]: #associatedconstant.BYTE_OFFSET
                                const OPTIONAL_MASK: u8 = 1 << (Self::ODD_BIT - 8 * Self::BYTE_OFFSET);

                                /// Returns whether the feature is required by the given flags.
                                #[inline]
                                fn requires_feature(flags: &Vec<u8>) -> bool {
                                        flags.len() > Self::BYTE_OFFSET &&
                                                (flags[Self::BYTE_OFFSET] & Self::REQUIRED_MASK) != 0
                                }

                                /// Returns whether the feature is supported by the given flags.
                                #[inline]
                                fn supports_feature(flags: &Vec<u8>) -> bool {
                                        flags.len() > Self::BYTE_OFFSET &&
                                                (flags[Self::BYTE_OFFSET] & (Self::REQUIRED_MASK | Self::OPTIONAL_MASK)) != 0
                                }

                                /// Sets the feature's required (even) bit in the given flags.
                                #[inline]
                                fn set_required_bit(flags: &mut Vec<u8>) {
                                        if flags.len() <= Self::BYTE_OFFSET {
                                                flags.resize(Self::BYTE_OFFSET + 1, 0u8);
                                        }

                                        flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
                                }

                                /// Sets the feature's optional (odd) bit in the given flags.
                                #[inline]
                                fn set_optional_bit(flags: &mut Vec<u8>) {
                                        if flags.len() <= Self::BYTE_OFFSET {
                                                flags.resize(Self::BYTE_OFFSET + 1, 0u8);
                                        }

                                        flags[Self::BYTE_OFFSET] |= Self::OPTIONAL_MASK;
                                }

                                /// Clears the feature's required (even) and optional (odd) bits from the given
                                /// flags.
                                #[inline]
                                fn clear_bits(flags: &mut Vec<u8>) {
                                        if flags.len() > Self::BYTE_OFFSET {
                                                flags[Self::BYTE_OFFSET] &= !Self::REQUIRED_MASK;
                                                flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
                                        }

                                        let last_non_zero_byte = flags.iter().rposition(|&byte| byte != 0);
                                        let size = if let Some(offset) = last_non_zero_byte { offset + 1 } else { 0 };
                                        flags.resize(size, 0u8);
                                }
                        }

                        $(
                                impl $feature for $context {
                                        // EVEN_BIT % 2 == 0
                                        const ASSERT_EVEN_BIT_PARITY: usize = 0 - (<Self as $feature>::EVEN_BIT % 2);

                                        // ODD_BIT % 2 == 1
                                        const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
                                }
                        )*
                }
        }

        define_feature!(1, DataLossProtect, [InitContext, NodeContext],
                "Feature flags for `option_data_loss_protect`.");
        // NOTE: Per Bolt #9, initial_routing_sync has no even bit.
        define_feature!(3, InitialRoutingSync, [InitContext],
                "Feature flags for `initial_routing_sync`.");
        define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
                "Feature flags for `option_upfront_shutdown_script`.");
        define_feature!(7, GossipQueries, [InitContext, NodeContext],
                "Feature flags for `gossip_queries`.");
        define_feature!(9, VariableLengthOnion, [InitContext, NodeContext],
                "Feature flags for `var_onion_optin`.");
        define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
                "Feature flags for `option_static_remotekey`.");
        define_feature!(15, PaymentSecret, [InitContext, NodeContext],
                "Feature flags for `payment_secret`.");
        define_feature!(17, BasicMPP, [InitContext, NodeContext],
                "Feature flags for `basic_mpp`.");
        define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
                "Feature flags for `opt_shutdown_anysegwit`.");

        #[cfg(test)]
        define_context!(TestingContext {
                required_features: [
                        // Byte 0
                        ,
                        // Byte 1
                        ,
                        // Byte 2
                        UnknownFeature,
                ],
                optional_features: [
                        // Byte 0
                        ,
                        // Byte 1
                        ,
                        // Byte 2
                        ,
                ],
        });

        #[cfg(test)]
        define_feature!(23, UnknownFeature, [TestingContext],
                "Feature flags for an unknown feature used in testing.");
}

/// Tracks the set of features which a node implements, templated by the context in which it
/// appears.
///
/// (C-not exported) as we map the concrete feature types below directly instead
pub struct Features<T: sealed::Context> {
        /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
        flags: Vec<u8>,
        mark: PhantomData<T>,
}

impl<T: sealed::Context> Clone for Features<T> {
        fn clone(&self) -> Self {
                Self {
                        flags: self.flags.clone(),
                        mark: PhantomData,
                }
        }
}
impl<T: sealed::Context> PartialEq for Features<T> {
        fn eq(&self, o: &Self) -> bool {
                self.flags.eq(&o.flags)
        }
}
impl<T: sealed::Context> fmt::Debug for Features<T> {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
                self.flags.fmt(fmt)
        }
}

/// Features used within an `init` message.
pub type InitFeatures = Features<sealed::InitContext>;
/// Features used within a `node_announcement` message.
pub type NodeFeatures = Features<sealed::NodeContext>;
/// Features used within a `channel_announcement` message.
pub type ChannelFeatures = Features<sealed::ChannelContext>;

impl InitFeatures {
        /// Writes all features present up to, and including, 13.
        pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
                let len = cmp::min(2, self.flags.len());
                w.size_hint(len + 2);
                (len as u16).write(w)?;
                for i in (0..len).rev() {
                        if i == 0 {
                                self.flags[i].write(w)?;
                        } else {
                                // On byte 1, we want up-to-and-including-bit-13, 0-indexed, which is
                                // up-to-and-including-bit-5, 0-indexed, on this byte:
                                (self.flags[i] & 0b00_11_11_11).write(w)?;
                        }
                }
                Ok(())
        }

        /// or's another InitFeatures into this one.
        pub(crate) fn or(mut self, o: InitFeatures) -> InitFeatures {
                let total_feature_len = cmp::max(self.flags.len(), o.flags.len());
                self.flags.resize(total_feature_len, 0u8);
                for (byte, o_byte) in self.flags.iter_mut().zip(o.flags.iter()) {
                        *byte |= *o_byte;
                }
                self
        }

        /// Converts `InitFeatures` to `Features<C>`. Only known `InitFeatures` relevant to context `C`
        /// are included in the result.
        pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
                self.to_context_internal()
        }
}

impl<T: sealed::Context> Features<T> {
        /// Create a blank Features with no features set
        pub fn empty() -> Self {
                Features {
                        flags: Vec::new(),
                        mark: PhantomData,
                }
        }

        /// Creates features known by the implementation as defined by [`T::KNOWN_FEATURE_FLAGS`].
        ///
        /// [`T::KNOWN_FEATURE_FLAGS`]: sealed/trait.Context.html#associatedconstant.KNOWN_FEATURE_FLAGS
        pub fn known() -> Self {
                Self {
                        flags: T::KNOWN_FEATURE_FLAGS.to_vec(),
                        mark: PhantomData,
                }
        }

        /// Converts `Features<T>` to `Features<C>`. Only known `T` features relevant to context `C` are
        /// included in the result.
        fn to_context_internal<C: sealed::Context>(&self) -> Features<C> {
                let byte_count = C::KNOWN_FEATURE_MASK.len();
                let mut flags = Vec::new();
                for (i, byte) in self.flags.iter().enumerate() {
                        if i < byte_count {
                                let known_source_features = T::KNOWN_FEATURE_MASK[i];
                                let known_target_features = C::KNOWN_FEATURE_MASK[i];
                                flags.push(byte & known_source_features & known_target_features);
                        }
                }
                Features::<C> { flags, mark: PhantomData, }
        }

        #[cfg(test)]
        /// Create a Features given a set of flags, in LE.
        pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
                Features {
                        flags,
                        mark: PhantomData,
                }
        }

        #[cfg(test)]
        /// Gets the underlying flags set, in LE.
        pub fn le_flags(&self) -> &Vec<u8> {
                &self.flags
        }

        pub(crate) fn requires_unknown_bits(&self) -> bool {
                // Bitwise AND-ing with all even bits set except for known features will select required
                // unknown features.
                let byte_count = T::KNOWN_FEATURE_MASK.len();
                self.flags.iter().enumerate().any(|(i, &byte)| {
                        let required_features = 0b01_01_01_01;
                        let unknown_features = if i < byte_count {
                                !T::KNOWN_FEATURE_MASK[i]
                        } else {
                                0b11_11_11_11
                        };
                        (byte & (required_features & unknown_features)) != 0
                })
        }

        pub(crate) fn supports_unknown_bits(&self) -> bool {
                // Bitwise AND-ing with all even and odd bits set except for known features will select
                // both required and optional unknown features.
                let byte_count = T::KNOWN_FEATURE_MASK.len();
                self.flags.iter().enumerate().any(|(i, &byte)| {
                        let unknown_features = if i < byte_count {
                                !T::KNOWN_FEATURE_MASK[i]
                        } else {
                                0b11_11_11_11
                        };
                        (byte & unknown_features) != 0
                })
        }

        /// The number of bytes required to represent the feature flags present. This does not include
        /// the length bytes which are included in the serialized form.
        pub(crate) fn byte_count(&self) -> usize {
                self.flags.len()
        }

        #[cfg(test)]
        pub(crate) fn set_required_unknown_bits(&mut self) {
                <sealed::TestingContext as sealed::UnknownFeature>::set_required_bit(&mut self.flags);
        }

        #[cfg(test)]
        pub(crate) fn set_optional_unknown_bits(&mut self) {
                <sealed::TestingContext as sealed::UnknownFeature>::set_optional_bit(&mut self.flags);
        }

        #[cfg(test)]
        pub(crate) fn clear_unknown_bits(&mut self) {
                <sealed::TestingContext as sealed::UnknownFeature>::clear_bits(&mut self.flags);
        }
}

impl<T: sealed::DataLossProtect> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_data_loss_protect(&self) -> bool {
                <T as sealed::DataLossProtect>::requires_feature(&self.flags)
        }
        pub(crate) fn supports_data_loss_protect(&self) -> bool {
                <T as sealed::DataLossProtect>::supports_feature(&self.flags)
        }
}

impl<T: sealed::UpfrontShutdownScript> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_upfront_shutdown_script(&self) -> bool {
                <T as sealed::UpfrontShutdownScript>::requires_feature(&self.flags)
        }
        pub(crate) fn supports_upfront_shutdown_script(&self) -> bool {
                <T as sealed::UpfrontShutdownScript>::supports_feature(&self.flags)
        }
        #[cfg(test)]
        pub(crate) fn clear_upfront_shutdown_script(mut self) -> Self {
                <T as sealed::UpfrontShutdownScript>::clear_bits(&mut self.flags);
                self
        }
}


impl<T: sealed::GossipQueries> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_gossip_queries(&self) -> bool {
                <T as sealed::GossipQueries>::requires_feature(&self.flags)
        }
        pub(crate) fn supports_gossip_queries(&self) -> bool {
                <T as sealed::GossipQueries>::supports_feature(&self.flags)
        }
        #[cfg(test)]
        pub(crate) fn clear_gossip_queries(mut self) -> Self {
                <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
                self
        }
}

impl<T: sealed::VariableLengthOnion> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_variable_length_onion(&self) -> bool {
                <T as sealed::VariableLengthOnion>::requires_feature(&self.flags)
        }
        pub(crate) fn supports_variable_length_onion(&self) -> bool {
                <T as sealed::VariableLengthOnion>::supports_feature(&self.flags)
        }
}

impl<T: sealed::StaticRemoteKey> Features<T> {
        pub(crate) fn supports_static_remote_key(&self) -> bool {
                <T as sealed::StaticRemoteKey>::supports_feature(&self.flags)
        }
        #[cfg(test)]
        pub(crate) fn requires_static_remote_key(&self) -> bool {
                <T as sealed::StaticRemoteKey>::requires_feature(&self.flags)
        }
}

impl<T: sealed::InitialRoutingSync> Features<T> {
        pub(crate) fn initial_routing_sync(&self) -> bool {
                <T as sealed::InitialRoutingSync>::supports_feature(&self.flags)
        }
        // We are no longer setting initial_routing_sync now that gossip_queries
        // is enabled. This feature is ignored by a peer when gossip_queries has 
        // been negotiated.
        #[cfg(test)]
        pub(crate) fn clear_initial_routing_sync(&mut self) {
                <T as sealed::InitialRoutingSync>::clear_bits(&mut self.flags)
        }
}

impl<T: sealed::PaymentSecret> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_payment_secret(&self) -> bool {
                <T as sealed::PaymentSecret>::requires_feature(&self.flags)
        }
        // Note that we never need to test this since what really matters is the invoice - iff the
        // invoice provides a payment_secret, we assume that we can use it (ie that the recipient
        // supports payment_secret).
        #[allow(dead_code)]
        pub(crate) fn supports_payment_secret(&self) -> bool {
                <T as sealed::PaymentSecret>::supports_feature(&self.flags)
        }
}

impl<T: sealed::BasicMPP> Features<T> {
        #[cfg(test)]
        pub(crate) fn requires_basic_mpp(&self) -> bool {
                <T as sealed::BasicMPP>::requires_feature(&self.flags)
        }
        // We currently never test for this since we don't actually *generate* multipath routes.
        #[allow(dead_code)]
        pub(crate) fn supports_basic_mpp(&self) -> bool {
                <T as sealed::BasicMPP>::supports_feature(&self.flags)
        }
}

impl<T: sealed::ShutdownAnySegwit> Features<T> {
        pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
                <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
        }
        #[cfg(test)]
        pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
                <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
                self
        }
}

impl<T: sealed::Context> Writeable for Features<T> {
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
                w.size_hint(self.flags.len() + 2);
                (self.flags.len() as u16).write(w)?;
                for f in self.flags.iter().rev() { // Swap back to big-endian
                        f.write(w)?;
                }
                Ok(())
        }
}

impl<T: sealed::Context> Readable for Features<T> {
        fn read<R: ::std::io::Read>(r: &mut R) -> Result<Self, DecodeError> {
                let mut flags: Vec<u8> = Readable::read(r)?;
                flags.reverse(); // Swap to little-endian
                Ok(Self {
                        flags,
                        mark: PhantomData,
                })
        }
}

#[cfg(test)]
mod tests {
        use super::{ChannelFeatures, InitFeatures, NodeFeatures};

        #[test]
        fn sanity_test_known_features() {
                assert!(!ChannelFeatures::known().requires_unknown_bits());
                assert!(!ChannelFeatures::known().supports_unknown_bits());
                assert!(!InitFeatures::known().requires_unknown_bits());
                assert!(!InitFeatures::known().supports_unknown_bits());
                assert!(!NodeFeatures::known().requires_unknown_bits());
                assert!(!NodeFeatures::known().supports_unknown_bits());

                assert!(InitFeatures::known().supports_upfront_shutdown_script());
                assert!(NodeFeatures::known().supports_upfront_shutdown_script());
                assert!(!InitFeatures::known().requires_upfront_shutdown_script());
                assert!(!NodeFeatures::known().requires_upfront_shutdown_script());

                assert!(InitFeatures::known().supports_gossip_queries());
                assert!(NodeFeatures::known().supports_gossip_queries());
                assert!(!InitFeatures::known().requires_gossip_queries());
                assert!(!NodeFeatures::known().requires_gossip_queries());

                assert!(InitFeatures::known().supports_data_loss_protect());
                assert!(NodeFeatures::known().supports_data_loss_protect());
                assert!(!InitFeatures::known().requires_data_loss_protect());
                assert!(!NodeFeatures::known().requires_data_loss_protect());

                assert!(InitFeatures::known().supports_variable_length_onion());
                assert!(NodeFeatures::known().supports_variable_length_onion());
                assert!(!InitFeatures::known().requires_variable_length_onion());
                assert!(!NodeFeatures::known().requires_variable_length_onion());

                assert!(InitFeatures::known().supports_static_remote_key());
                assert!(NodeFeatures::known().supports_static_remote_key());
                assert!(InitFeatures::known().requires_static_remote_key());
                assert!(NodeFeatures::known().requires_static_remote_key());

                assert!(InitFeatures::known().supports_payment_secret());
                assert!(NodeFeatures::known().supports_payment_secret());
                assert!(!InitFeatures::known().requires_payment_secret());
                assert!(!NodeFeatures::known().requires_payment_secret());

                assert!(InitFeatures::known().supports_basic_mpp());
                assert!(NodeFeatures::known().supports_basic_mpp());
                assert!(!InitFeatures::known().requires_basic_mpp());
                assert!(!NodeFeatures::known().requires_basic_mpp());

                assert!(InitFeatures::known().supports_shutdown_anysegwit());
                assert!(NodeFeatures::known().supports_shutdown_anysegwit());

                let mut init_features = InitFeatures::known();
                assert!(init_features.initial_routing_sync());
                init_features.clear_initial_routing_sync();
                assert!(!init_features.initial_routing_sync());
        }

        #[test]
        fn sanity_test_unknown_bits() {
                let mut features = ChannelFeatures::empty();
                assert!(!features.requires_unknown_bits());
                assert!(!features.supports_unknown_bits());

                features.set_required_unknown_bits();
                assert!(features.requires_unknown_bits());
                assert!(features.supports_unknown_bits());

                features.clear_unknown_bits();
                assert!(!features.requires_unknown_bits());
                assert!(!features.supports_unknown_bits());

                features.set_optional_unknown_bits();
                assert!(!features.requires_unknown_bits());
                assert!(features.supports_unknown_bits());
        }

        #[test]
        fn convert_to_context_with_relevant_flags() {
                let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
                assert!(init_features.initial_routing_sync());
                assert!(!init_features.supports_upfront_shutdown_script());
                assert!(!init_features.supports_gossip_queries());

                let node_features: NodeFeatures = init_features.to_context();
                {
                        // Check that the flags are as expected:
                        // - option_data_loss_protect
                        // - var_onion_optin | static_remote_key (req) | payment_secret
                        // - basic_mpp
                        // - opt_shutdown_anysegwit
                        assert_eq!(node_features.flags.len(), 4);
                        assert_eq!(node_features.flags[0], 0b00000010);
                        assert_eq!(node_features.flags[1], 0b10010010);
                        assert_eq!(node_features.flags[2], 0b00000010);
                        assert_eq!(node_features.flags[3], 0b00001000);
                }

                // Check that cleared flags are kept blank when converting back:
                // - initial_routing_sync was not applicable to NodeContext
                // - upfront_shutdown_script was cleared before converting
                // - gossip_queries was cleared before converting
                let features: InitFeatures = node_features.to_context_internal();
                assert!(!features.initial_routing_sync());
                assert!(!features.supports_upfront_shutdown_script());
                assert!(!init_features.supports_gossip_queries());
        }
}