Enable wumbo channels to be created
[rust-lightning] / lightning / src / ln / features.rs
index 36f29ada14e4609709777d3594a3cfc9b7c2dd7a..2580874640e438e611bea9b88ddda0384dc9db5d 100644 (file)
 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
 //! [messages]: crate::ln::msgs
 
-use std::{cmp, fmt};
-use std::marker::PhantomData;
+use {io, io_extras};
+use 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};
@@ -31,6 +34,7 @@ use ln::msgs::DecodeError;
 use util::ser::{Readable, Writeable, Writer};
 
 mod sealed {
+       use prelude::*;
        use ln::features::Features;
 
        /// The context in which [`Features`] are applicable. Defines which features are required and
@@ -87,6 +91,28 @@ mod sealed {
                                        )*
                                ];
                        }
+
+                       impl alloc::fmt::Display for Features<$context> {
+                               fn fmt(&self, fmt: &mut alloc::fmt::Formatter) -> Result<(), alloc::fmt::Error> {
+                                       $(
+                                               $(
+                                                       fmt.write_fmt(format_args!("{}: {}, ", stringify!($required_feature),
+                                                               if <$context as $required_feature>::requires_feature(&self.flags) { "required" }
+                                                               else if <$context as $required_feature>::supports_feature(&self.flags) { "supported" }
+                                                               else { "not supported" }))?;
+                                               )*
+                                               $(
+                                                       fmt.write_fmt(format_args!("{}: {}, ", stringify!($optional_feature),
+                                                               if <$context as $optional_feature>::requires_feature(&self.flags) { "required" }
+                                                               else if <$context as $optional_feature>::supports_feature(&self.flags) { "supported" }
+                                                               else { "not supported" }))?;
+                                               )*
+                                       )*
+                                       fmt.write_fmt(format_args!("unknown flags: {}",
+                                               if self.requires_unknown_bits() { "required" }
+                                               else if self.supports_unknown_bits() { "supported" } else { "none" }))
+                               }
+                       }
                };
        }
 
@@ -95,21 +121,29 @@ mod sealed {
                        // Byte 0
                        ,
                        // Byte 1
-                       StaticRemoteKey,
+                       VariableLengthOnion | StaticRemoteKey | PaymentSecret,
                        // Byte 2
                        ,
                        // Byte 3
                        ,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       ,
                ],
                optional_features: [
                        // Byte 0
                        DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
                        // Byte 1
-                       VariableLengthOnion | PaymentSecret,
+                       ,
                        // Byte 2
-                       BasicMPP,
+                       BasicMPP | Wumbo,
                        // Byte 3
                        ShutdownAnySegwit,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       ChannelType | SCIDPrivacy,
                ],
        });
        define_context!(NodeContext {
@@ -117,21 +151,33 @@ mod sealed {
                        // Byte 0
                        ,
                        // Byte 1
-                       StaticRemoteKey,
+                       VariableLengthOnion | StaticRemoteKey | PaymentSecret,
                        // Byte 2
                        ,
                        // Byte 3
                        ,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       ,
+                       // Byte 6
+                       ,
                ],
                optional_features: [
                        // Byte 0
                        DataLossProtect | UpfrontShutdownScript | GossipQueries,
                        // Byte 1
-                       VariableLengthOnion | PaymentSecret,
+                       ,
                        // Byte 2
-                       BasicMPP,
+                       BasicMPP | Wumbo,
                        // Byte 3
                        ShutdownAnySegwit,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       ChannelType | SCIDPrivacy,
+                       // Byte 6
+                       Keysend,
                ],
        });
        define_context!(ChannelContext {
@@ -139,22 +185,61 @@ mod sealed {
                optional_features: [],
        });
        define_context!(InvoiceContext {
-               required_features: [,,,],
-               optional_features: [
+               required_features: [
                        // Byte 0
                        ,
                        // Byte 1
                        VariableLengthOnion | PaymentSecret,
                        // Byte 2
+                       ,
+               ],
+               optional_features: [
+                       // Byte 0
+                       ,
+                       // Byte 1
+                       ,
+                       // Byte 2
                        BasicMPP,
                ],
        });
+       // This isn't a "real" feature context, and is only used in the channel_type field in an
+       // `OpenChannel` message.
+       define_context!(ChannelTypeContext {
+               required_features: [
+                       // Byte 0
+                       ,
+                       // Byte 1
+                       StaticRemoteKey,
+                       // Byte 2
+                       ,
+                       // Byte 3
+                       ,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       SCIDPrivacy,
+               ],
+               optional_features: [
+                       // Byte 0
+                       ,
+                       // Byte 1
+                       ,
+                       // Byte 2
+                       ,
+                       // Byte 3
+                       ,
+                       // Byte 4
+                       ,
+                       // Byte 5
+                       ,
+               ],
+       });
 
        /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
        /// useful for manipulating feature flags.
        macro_rules! define_feature {
                ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
-                $required_setter: ident) => {
+                $required_setter: ident, $supported_getter: ident) => {
                        #[doc = $doc]
                        ///
                        /// See [BOLT #9] for details.
@@ -241,15 +326,18 @@ mod sealed {
 
                        impl <T: $feature> Features<T> {
                                /// Set this feature as optional.
-                               pub fn $optional_setter(mut self) -> Self {
+                               pub fn $optional_setter(&mut self) {
                                        <T as $feature>::set_optional_bit(&mut self.flags);
-                                       self
                                }
 
                                /// Set this feature as required.
-                               pub fn $required_setter(mut self) -> Self {
+                               pub fn $required_setter(&mut self) {
                                        <T as $feature>::set_required_bit(&mut self.flags);
-                                       self
+                               }
+
+                               /// Checks if this feature is supported.
+                               pub fn $supported_getter(&self) -> bool {
+                                       <T as $feature>::supports_feature(&self.flags)
                                }
                        }
 
@@ -262,59 +350,67 @@ mod sealed {
                                        const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
                                }
                        )*
-
+               };
+               ($odd_bit: expr, $feature: ident, [$($context: ty),+], $doc: expr, $optional_setter: ident,
+                $required_setter: ident, $supported_getter: ident, $required_getter: ident) => {
+                       define_feature!($odd_bit, $feature, [$($context),+], $doc, $optional_setter, $required_setter, $supported_getter);
+                       impl <T: $feature> Features<T> {
+                               /// Checks if this feature is required.
+                               pub fn $required_getter(&self) -> bool {
+                                       <T as $feature>::requires_feature(&self.flags)
+                               }
+                       }
                }
        }
 
        define_feature!(1, DataLossProtect, [InitContext, NodeContext],
                "Feature flags for `option_data_loss_protect`.", set_data_loss_protect_optional,
-               set_data_loss_protect_required);
+               set_data_loss_protect_required, supports_data_loss_protect, requires_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`.",
-               set_initial_routing_sync_optional, set_initial_routing_sync_required);
+               set_initial_routing_sync_optional, set_initial_routing_sync_required,
+               initial_routing_sync);
        define_feature!(5, UpfrontShutdownScript, [InitContext, NodeContext],
                "Feature flags for `option_upfront_shutdown_script`.", set_upfront_shutdown_script_optional,
-               set_upfront_shutdown_script_required);
+               set_upfront_shutdown_script_required, supports_upfront_shutdown_script,
+               requires_upfront_shutdown_script);
        define_feature!(7, GossipQueries, [InitContext, NodeContext],
-               "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required);
+               "Feature flags for `gossip_queries`.", set_gossip_queries_optional, set_gossip_queries_required,
+               supports_gossip_queries, requires_gossip_queries);
        define_feature!(9, VariableLengthOnion, [InitContext, NodeContext, InvoiceContext],
                "Feature flags for `var_onion_optin`.", set_variable_length_onion_optional,
-               set_variable_length_onion_required);
-       define_feature!(13, StaticRemoteKey, [InitContext, NodeContext],
+               set_variable_length_onion_required, supports_variable_length_onion,
+               requires_variable_length_onion);
+       define_feature!(13, StaticRemoteKey, [InitContext, NodeContext, ChannelTypeContext],
                "Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
-               set_static_remote_key_required);
+               set_static_remote_key_required, supports_static_remote_key, requires_static_remote_key);
        define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
-               "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required);
+               "Feature flags for `payment_secret`.", set_payment_secret_optional, set_payment_secret_required,
+               supports_payment_secret, requires_payment_secret);
        define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext],
-               "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required);
+               "Feature flags for `basic_mpp`.", set_basic_mpp_optional, set_basic_mpp_required,
+               supports_basic_mpp, requires_basic_mpp);
+       define_feature!(19, Wumbo, [InitContext, NodeContext],
+               "Feature flags for `option_support_large_channel` (aka wumbo channels).", set_wumbo_optional, set_wumbo_required,
+               supports_wumbo, requires_wumbo);
        define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
                "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
-               set_shutdown_any_segwit_required);
-
-       #[cfg(test)]
-       define_context!(TestingContext {
-               required_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       UnknownFeature,
-               ],
-               optional_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       ,
-               ],
-       });
+               set_shutdown_any_segwit_required, supports_shutdown_anysegwit, requires_shutdown_anysegwit);
+       define_feature!(45, ChannelType, [InitContext, NodeContext],
+               "Feature flags for `option_channel_type`.", set_channel_type_optional,
+               set_channel_type_required, supports_channel_type, requires_channel_type);
+       define_feature!(47, SCIDPrivacy, [InitContext, NodeContext, ChannelTypeContext],
+               "Feature flags for only forwarding with SCID aliasing. Called `option_scid_alias` in the BOLTs",
+               set_scid_privacy_optional, set_scid_privacy_required, supports_scid_privacy, requires_scid_privacy);
+
+       define_feature!(55, Keysend, [NodeContext],
+               "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required,
+               supports_keysend, requires_keysend);
 
        #[cfg(test)]
-       define_feature!(23, UnknownFeature, [TestingContext],
+       define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext, InvoiceContext],
                "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
-               set_unknown_feature_required);
+               set_unknown_feature_required, supports_unknown_test_feature, requires_unknown_test_feature);
 }
 
 /// Tracks the set of features which a node implements, templated by the context in which it
@@ -336,6 +432,11 @@ impl<T: sealed::Context> Clone for Features<T> {
                }
        }
 }
+impl<T: sealed::Context> Hash for Features<T> {
+       fn hash<H: Hasher>(&self, hasher: &mut H) {
+               self.flags.hash(hasher);
+       }
+}
 impl<T: sealed::Context> PartialEq for Features<T> {
        fn eq(&self, o: &Self) -> bool {
                self.flags.eq(&o.flags)
@@ -356,11 +457,22 @@ pub type ChannelFeatures = Features<sealed::ChannelContext>;
 /// Features used within an invoice.
 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
 
+/// Features used within the channel_type field in an OpenChannel message.
+///
+/// A channel is always of some known "type", describing the transaction formats used and the exact
+/// semantics of our interaction with our peer.
+///
+/// Note that because a channel is a specific type which is proposed by the opener and accepted by
+/// the counterparty, only required features are allowed here.
+///
+/// This is serialized differently from other feature types - it is not prefixed by a length, and
+/// thus must only appear inside a TLV where its length is known in advance.
+pub type ChannelTypeFeatures = Features<sealed::ChannelTypeContext>;
+
 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> {
+       pub(crate) fn write_up_to_13<W: Writer>(&self, w: &mut W) -> Result<(), 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 {
@@ -397,6 +509,42 @@ impl InvoiceFeatures {
        pub(crate) fn to_context<C: sealed::Context>(&self) -> Features<C> {
                self.to_context_internal()
        }
+
+       /// Getting a route for a keysend payment to a private node requires providing the payee's
+       /// features (since they were not announced in a node announcement). However, keysend payments
+       /// don't have an invoice to pull the payee's features from, so this method is provided for use in
+       /// [`PaymentParameters::for_keysend`], thus omitting the need for payers to manually construct an
+       /// `InvoiceFeatures` for [`find_route`].
+       ///
+       /// [`PaymentParameters::for_keysend`]: crate::routing::router::PaymentParameters::for_keysend
+       /// [`find_route`]: crate::routing::router::find_route
+       pub(crate) fn for_keysend() -> InvoiceFeatures {
+               let mut res = InvoiceFeatures::empty();
+               res.set_variable_length_onion_optional();
+               res
+       }
+}
+
+impl ChannelTypeFeatures {
+       /// Constructs the implicit channel type based on the common supported types between us and our
+       /// counterparty
+       pub(crate) fn from_counterparty_init(counterparty_init: &InitFeatures) -> Self {
+               let mut ret = counterparty_init.to_context_internal();
+               // ChannelTypeFeatures must only contain required bits, so we OR the required forms of all
+               // optional bits and then AND out the optional ones.
+               for byte in ret.flags.iter_mut() {
+                       *byte |= (*byte & 0b10_10_10_10) >> 1;
+                       *byte &= 0b01_01_01_01;
+               }
+               ret
+       }
+
+       /// Constructs a ChannelTypeFeatures with only static_remotekey set
+       pub(crate) fn only_static_remote_key() -> Self {
+               let mut ret = Self::empty();
+               <sealed::ChannelTypeContext as sealed::StaticRemoteKey>::set_required_bit(&mut ret.flags);
+               ret
+       }
 }
 
 impl ToBase32 for InvoiceFeatures {
@@ -481,13 +629,14 @@ impl<T: sealed::Context> Features<T> {
        /// 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 from_byte_count = T::KNOWN_FEATURE_MASK.len();
+               let to_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);
+                       if i < from_byte_count && i < to_byte_count {
+                               let from_known_features = T::KNOWN_FEATURE_MASK[i];
+                               let to_known_features = C::KNOWN_FEATURE_MASK[i];
+                               flags.push(byte & from_known_features & to_known_features);
                        }
                }
                Features::<C> { flags, mark: PhantomData, }
@@ -495,6 +644,7 @@ impl<T: sealed::Context> Features<T> {
 
        /// Create a Features given a set of flags, in little-endian. This is in reverse byte order from
        /// most on-the-wire encodings.
+       /// (C-not exported) as we don't support export across multiple T
        pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
                Features {
                        flags,
@@ -508,7 +658,28 @@ impl<T: sealed::Context> Features<T> {
                &self.flags
        }
 
-       pub(crate) fn requires_unknown_bits(&self) -> bool {
+       fn write_be<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+               for f in self.flags.iter().rev() { // Swap back to big-endian
+                       f.write(w)?;
+               }
+               Ok(())
+       }
+
+       fn from_be_bytes(mut flags: Vec<u8>) -> Features<T> {
+               flags.reverse(); // Swap to little-endian
+               Self {
+                       flags,
+                       mark: PhantomData,
+               }
+       }
+
+       pub(crate) fn supports_any_optional_bits(&self) -> bool {
+               self.flags.iter().any(|&byte| (byte & 0b10_10_10_10) != 0)
+       }
+
+       /// Returns true if this `Features` object contains unknown feature flags which are set as
+       /// "required".
+       pub 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();
@@ -536,47 +707,9 @@ impl<T: sealed::Context> Features<T> {
                        (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);
@@ -586,13 +719,6 @@ impl<T: sealed::UpfrontShutdownScript> Features<T> {
 
 
 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);
@@ -600,30 +726,7 @@ impl<T: sealed::GossipQueries> Features<T> {
        }
 }
 
-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.
@@ -633,67 +736,60 @@ impl<T: sealed::InitialRoutingSync> Features<T> {
        }
 }
 
-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> {
+impl<T: sealed::ShutdownAnySegwit> 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.
-       pub(crate) fn supports_basic_mpp(&self) -> bool {
-               <T as sealed::BasicMPP>::supports_feature(&self.flags)
+       pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
+               <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
+               self
        }
 }
 
-impl<T: sealed::ShutdownAnySegwit> Features<T> {
-       pub(crate) fn supports_shutdown_anysegwit(&self) -> bool {
-               <T as sealed::ShutdownAnySegwit>::supports_feature(&self.flags)
-       }
+impl<T: sealed::Wumbo> Features<T> {
        #[cfg(test)]
-       pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
-               <T as sealed::ShutdownAnySegwit>::clear_bits(&mut self.flags);
+       pub(crate) fn clear_wumbo(mut self) -> Self {
+               <T as sealed::Wumbo>::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)?;
+macro_rules! impl_feature_len_prefixed_write {
+       ($features: ident) => {
+               impl Writeable for $features {
+                       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+                               (self.flags.len() as u16).write(w)?;
+                               self.write_be(w)
+                       }
+               }
+               impl Readable for $features {
+                       fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
+                               Ok(Self::from_be_bytes(Vec::<u8>::read(r)?))
+                       }
                }
-               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,
-               })
+impl_feature_len_prefixed_write!(InitFeatures);
+impl_feature_len_prefixed_write!(ChannelFeatures);
+impl_feature_len_prefixed_write!(NodeFeatures);
+impl_feature_len_prefixed_write!(InvoiceFeatures);
+
+// Because ChannelTypeFeatures only appears inside of TLVs, it doesn't have a length prefix when
+// serialized. Thus, we can't use `impl_feature_len_prefixed_write`, above, and have to write our
+// own serialization.
+impl Writeable for ChannelTypeFeatures {
+       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+               self.write_be(w)
+       }
+}
+impl Readable for ChannelTypeFeatures {
+       fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
+               let v = io_extras::read_to_end(r)?;
+               Ok(Self::from_be_bytes(v))
        }
 }
 
 #[cfg(test)]
 mod tests {
-       use super::{ChannelFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
+       use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
        use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
 
        #[test]
@@ -722,8 +818,10 @@ mod tests {
 
                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!(InvoiceFeatures::known().supports_variable_length_onion());
+               assert!(InitFeatures::known().requires_variable_length_onion());
+               assert!(NodeFeatures::known().requires_variable_length_onion());
+               assert!(InvoiceFeatures::known().requires_variable_length_onion());
 
                assert!(InitFeatures::known().supports_static_remote_key());
                assert!(NodeFeatures::known().supports_static_remote_key());
@@ -732,17 +830,36 @@ mod tests {
 
                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!(InvoiceFeatures::known().supports_payment_secret());
+               assert!(InitFeatures::known().requires_payment_secret());
+               assert!(NodeFeatures::known().requires_payment_secret());
+               assert!(InvoiceFeatures::known().requires_payment_secret());
 
                assert!(InitFeatures::known().supports_basic_mpp());
                assert!(NodeFeatures::known().supports_basic_mpp());
+               assert!(InvoiceFeatures::known().supports_basic_mpp());
                assert!(!InitFeatures::known().requires_basic_mpp());
                assert!(!NodeFeatures::known().requires_basic_mpp());
+               assert!(!InvoiceFeatures::known().requires_basic_mpp());
+
+               assert!(InitFeatures::known().supports_channel_type());
+               assert!(NodeFeatures::known().supports_channel_type());
+               assert!(!InitFeatures::known().requires_channel_type());
+               assert!(!NodeFeatures::known().requires_channel_type());
 
                assert!(InitFeatures::known().supports_shutdown_anysegwit());
                assert!(NodeFeatures::known().supports_shutdown_anysegwit());
 
+               assert!(InitFeatures::known().supports_scid_privacy());
+               assert!(NodeFeatures::known().supports_scid_privacy());
+               assert!(!InitFeatures::known().requires_scid_privacy());
+               assert!(!NodeFeatures::known().requires_scid_privacy());
+
+               assert!(InitFeatures::known().supports_wumbo());
+               assert!(NodeFeatures::known().supports_wumbo());
+               assert!(!InitFeatures::known().requires_wumbo());
+               assert!(!NodeFeatures::known().requires_wumbo());
+
                let mut init_features = InitFeatures::known();
                assert!(init_features.initial_routing_sync());
                init_features.clear_initial_routing_sync();
@@ -751,19 +868,17 @@ mod tests {
 
        #[test]
        fn sanity_test_unknown_bits() {
-               let mut features = ChannelFeatures::empty();
+               let features = ChannelFeatures::empty();
                assert!(!features.requires_unknown_bits());
                assert!(!features.supports_unknown_bits());
 
-               features.set_required_unknown_bits();
+               let mut features = ChannelFeatures::empty();
+               features.set_unknown_feature_required();
                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();
+               let mut features = ChannelFeatures::empty();
+               features.set_unknown_feature_optional();
                assert!(!features.requires_unknown_bits());
                assert!(features.supports_unknown_bits());
        }
@@ -779,14 +894,18 @@ mod tests {
                {
                        // Check that the flags are as expected:
                        // - option_data_loss_protect
-                       // - var_onion_optin | static_remote_key (req) | payment_secret
-                       // - basic_mpp
+                       // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
+                       // - basic_mpp | wumbo
                        // - opt_shutdown_anysegwit
-                       assert_eq!(node_features.flags.len(), 4);
+                       // -
+                       // - option_channel_type | option_scid_alias
+                       assert_eq!(node_features.flags.len(), 6);
                        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[1], 0b01010001);
+                       assert_eq!(node_features.flags[2], 0b00001010);
                        assert_eq!(node_features.flags[3], 0b00001000);
+                       assert_eq!(node_features.flags[4], 0b00000000);
+                       assert_eq!(node_features.flags[5], 0b10100000);
                }
 
                // Check that cleared flags are kept blank when converting back:
@@ -799,11 +918,22 @@ mod tests {
                assert!(!init_features.supports_gossip_queries());
        }
 
+       #[test]
+       fn convert_to_context_with_unknown_flags() {
+               // Ensure the `from` context has fewer known feature bytes than the `to` context.
+               assert!(InvoiceFeatures::known().flags.len() < NodeFeatures::known().flags.len());
+               let mut invoice_features = InvoiceFeatures::known();
+               invoice_features.set_unknown_feature_optional();
+               assert!(invoice_features.supports_unknown_bits());
+               let node_features: NodeFeatures = invoice_features.to_context();
+               assert!(!node_features.supports_unknown_bits());
+       }
+
        #[test]
        fn set_feature_bits() {
-               let features = InvoiceFeatures::empty()
-                       .set_basic_mpp_optional()
-                       .set_payment_secret_required();
+               let mut features = InvoiceFeatures::empty();
+               features.set_basic_mpp_optional();
+               features.set_payment_secret_required();
                assert!(features.supports_basic_mpp());
                assert!(!features.requires_basic_mpp());
                assert!(features.requires_payment_secret());
@@ -840,4 +970,16 @@ mod tests {
                let features_deserialized = InvoiceFeatures::from_base32(&features_as_u5s).unwrap();
                assert_eq!(features, features_deserialized);
        }
+
+       #[test]
+       fn test_channel_type_mapping() {
+               // If we map an InvoiceFeatures with StaticRemoteKey optional, it should map into a
+               // required-StaticRemoteKey ChannelTypeFeatures.
+               let mut init_features = InitFeatures::empty();
+               init_features.set_static_remote_key_optional();
+               let converted_features = ChannelTypeFeatures::from_counterparty_init(&init_features);
+               assert_eq!(converted_features, ChannelTypeFeatures::only_static_remote_key());
+               assert!(!converted_features.supports_any_optional_bits());
+               assert!(converted_features.requires_static_remote_key());
+       }
 }