Add message structs required for dual-funded channels
[rust-lightning] / lightning / src / ln / features.rs
index c978c61a3a563428e38f3368e557e544a6c623b9..8ccbf4166bbe71294a64309ed4832b9364845fa9 100644 (file)
 //!     (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).
+//! - `PaymentMetadata` - include additional data in invoices which is passed to recipients in the
+//!      onion.
+//!      (see [BOLT-11](https://github.com/lightning/bolts/blob/master/11-payment-encoding.md) for
+//!      more).
+//! - `ZeroConf` - supports accepting HTLCs and using channels prior to funding confirmation
+//!      (see
+//!      [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#the-channel_ready-message)
+//!      for more info).
 //! - `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 {io, io_extras};
-use prelude::*;
+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 ln::msgs::DecodeError;
-use util::ser::{Readable, Writeable, Writer};
+use crate::ln::msgs::DecodeError;
+use crate::util::ser::{Readable, WithoutLength, Writeable, Writer};
 
 mod sealed {
-       use prelude::*;
-       use ln::features::Features;
+       use crate::prelude::*;
+       use crate::ln::features::Features;
 
-       /// The context in which [`Features`] are applicable. Defines which features are required and
-       /// which are optional for the context.
+       /// 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 {
-               /// 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.
+               /// Bitmask for selecting features that are known to the implementation.
                const KNOWN_FEATURE_MASK: &'static [u8];
        }
 
@@ -82,41 +95,16 @@ mod sealed {
        /// are specified as a comma-separated list of bytes where each byte is a pipe-delimited list of
        /// feature identifiers.
        macro_rules! define_context {
-               ($context: ident {
-                       required_features: [$( $( $required_feature: ident )|*, )*],
-                       optional_features: [$( $( $optional_feature: ident )|*, )*],
-               }) => {
+               ($context: ident, [$( $( $known_feature: ident )|*, )*]) => {
                        #[derive(Eq, PartialEq)]
                        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)*,
+                                                       <Self as $known_feature>::REQUIRED_MASK |
+                                                       <Self as $known_feature>::OPTIONAL_MASK)*,
                                        )*
                                ];
                        }
@@ -125,17 +113,12 @@ mod sealed {
                                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 $optional_feature>::supports_feature(&self.flags) { "supported" }
+                                                       fmt.write_fmt(format_args!("{}: {}, ", stringify!($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" }
@@ -145,132 +128,84 @@ mod sealed {
                };
        }
 
-       define_context!(InitContext {
-               required_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       VariableLengthOnion | StaticRemoteKey | PaymentSecret,
-                       // Byte 2
-                       ,
-                       // Byte 3
-                       ,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       ,
-                       // Byte 6
-                       ,
-               ],
-               optional_features: [
-                       // Byte 0
-                       DataLossProtect | InitialRoutingSync | UpfrontShutdownScript | GossipQueries,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       BasicMPP | Wumbo,
-                       // Byte 3
-                       ShutdownAnySegwit,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       ChannelType | SCIDPrivacy,
-                       // Byte 6
-                       ZeroConf,
-               ],
-       });
-       define_context!(NodeContext {
-               required_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       VariableLengthOnion | StaticRemoteKey | PaymentSecret,
-                       // Byte 2
-                       ,
-                       // Byte 3
-                       ,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       ,
-                       // Byte 6
-                       ,
-               ],
-               optional_features: [
-                       // Byte 0
-                       DataLossProtect | UpfrontShutdownScript | GossipQueries,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       BasicMPP | Wumbo,
-                       // Byte 3
-                       ShutdownAnySegwit,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       ChannelType | SCIDPrivacy,
-                       // Byte 6
-                       ZeroConf | Keysend,
-               ],
-       });
-       define_context!(ChannelContext {
-               required_features: [],
-               optional_features: [],
-       });
-       define_context!(InvoiceContext {
-               required_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       VariableLengthOnion | PaymentSecret,
-                       // Byte 2
-                       ,
-               ],
-               optional_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       BasicMPP,
-               ],
-       });
+       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,
+               // Byte 3
+               ,
+               // Byte 4
+               ,
+               // Byte 5
+               ,
+               // Byte 6
+               PaymentMetadata,
+       ]);
+       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 {
-               required_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       StaticRemoteKey,
-                       // Byte 2
-                       ,
-                       // Byte 3
-                       ,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       SCIDPrivacy,
-                       // Byte 6
-                       ZeroConf,
-               ],
-               optional_features: [
-                       // Byte 0
-                       ,
-                       // Byte 1
-                       ,
-                       // Byte 2
-                       ,
-                       // Byte 3
-                       ,
-                       // Byte 4
-                       ,
-                       // Byte 5
-                       ,
-                       // Byte 6
-                       ,
-               ],
-       });
+       define_context!(ChannelTypeContext, [
+               // Byte 0
+               ,
+               // Byte 1
+               StaticRemoteKey,
+               // Byte 2
+               AnchorsZeroFeeHtlcTx,
+               // Byte 3
+               ,
+               // Byte 4
+               ,
+               // Byte 5
+               SCIDPrivacy,
+               // Byte 6
+               ZeroConf,
+       ]);
 
        /// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
        /// useful for manipulating feature flags.
@@ -299,6 +234,12 @@ mod sealed {
                                /// [`ODD_BIT`]: #associatedconstant.ODD_BIT
                                const ASSERT_ODD_BIT_PARITY: usize;
 
+                               /// Assertion that the bits are set in the context's [`KNOWN_FEATURE_MASK`].
+                               ///
+                               /// [`KNOWN_FEATURE_MASK`]: Context::KNOWN_FEATURE_MASK
+                               #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
+                               const ASSERT_BITS_IN_MASK: u8;
+
                                /// The byte where the feature is set.
                                const BYTE_OFFSET: usize = Self::EVEN_BIT / 8;
 
@@ -334,6 +275,7 @@ mod sealed {
                                        }
 
                                        flags[Self::BYTE_OFFSET] |= Self::REQUIRED_MASK;
+                                       flags[Self::BYTE_OFFSET] &= !Self::OPTIONAL_MASK;
                                }
 
                                /// Sets the feature's optional (odd) bit in the given flags.
@@ -385,6 +327,12 @@ mod sealed {
 
                                        // ODD_BIT % 2 == 1
                                        const ASSERT_ODD_BIT_PARITY: usize = (<Self as $feature>::ODD_BIT % 2) - 1;
+
+                                       // (byte & (REQUIRED_MASK | OPTIONAL_MASK)) >> (EVEN_BIT % 8) == 3
+                                       #[cfg(not(test))] // We violate this constraint with `UnknownFeature`
+                                       const ASSERT_BITS_IN_MASK: u8 =
+                                               ((<$context>::KNOWN_FEATURE_MASK[<Self as $feature>::BYTE_OFFSET] & (<Self as $feature>::REQUIRED_MASK | <Self as $feature>::OPTIONAL_MASK))
+                                                >> (<Self as $feature>::EVEN_BIT % 8)) - 3;
                                }
                        )*
                };
@@ -424,17 +372,18 @@ mod sealed {
        define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
                "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],
+       define_feature!(17, BasicMPP, [InitContext, NodeContext, InvoiceContext, Bolt12InvoiceContext],
                "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!(23, AnchorsZeroFeeHtlcTx, [InitContext, NodeContext, ChannelTypeContext],
+               "Feature flags for `option_anchors_zero_fee_htlc_tx`.", set_anchors_zero_fee_htlc_tx_optional,
+               set_anchors_zero_fee_htlc_tx_required, supports_anchors_zero_fee_htlc_tx, requires_anchors_zero_fee_htlc_tx);
        define_feature!(27, ShutdownAnySegwit, [InitContext, NodeContext],
                "Feature flags for `opt_shutdown_anysegwit`.", set_shutdown_any_segwit_optional,
                set_shutdown_any_segwit_required, supports_shutdown_anysegwit, requires_shutdown_anysegwit);
-       // We do not yet advertise the onion messages feature bit, but we need to detect when peers
-       // support it.
        define_feature!(39, OnionMessages, [InitContext, NodeContext],
                "Feature flags for `option_onion_messages`.", set_onion_messages_optional,
                set_onion_messages_required, supports_onion_messages, requires_onion_messages);
@@ -444,15 +393,20 @@ mod sealed {
        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!(49, PaymentMetadata, [InvoiceContext],
+               "Feature flags for payment metadata in invoices.", set_payment_metadata_optional,
+               set_payment_metadata_required, supports_payment_metadata, requires_payment_metadata);
        define_feature!(51, ZeroConf, [InitContext, NodeContext, ChannelTypeContext],
                "Feature flags for accepting channels with zero confirmations. Called `option_zeroconf` in the BOLTs",
                set_zero_conf_optional, set_zero_conf_required, supports_zero_conf, requires_zero_conf);
        define_feature!(55, Keysend, [NodeContext],
                "Feature flags for keysend payments.", set_keysend_optional, set_keysend_required,
                supports_keysend, requires_keysend);
+       // Note: update the module-level docs when a new feature bit is added!
 
        #[cfg(test)]
-       define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext, InvoiceContext],
+       define_feature!(123456789, UnknownFeature,
+               [NodeContext, ChannelContext, InvoiceContext, OfferContext, InvoiceRequestContext, Bolt12InvoiceContext, BlindedHopContext],
                "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
                set_unknown_feature_required, supports_unknown_test_feature, requires_unknown_test_feature);
 }
@@ -460,7 +414,7 @@ mod sealed {
 /// 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
+/// This is not exported to bindings users as we map the concrete feature types below directly instead
 #[derive(Eq)]
 pub struct Features<T: sealed::Context> {
        /// Note that, for convenience, flags is LITTLE endian (despite being big-endian on the wire)
@@ -468,6 +422,17 @@ pub struct Features<T: sealed::Context> {
        mark: PhantomData<T>,
 }
 
+impl <T: sealed::Context> Features<T> {
+       pub(crate) fn or(mut self, o: Self) -> Self {
+               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
+       }
+}
+
 impl<T: sealed::Context> Clone for Features<T> {
        fn clone(&self) -> Self {
                Self {
@@ -500,6 +465,14 @@ pub type NodeFeatures = Features<sealed::NodeContext>;
 pub type ChannelFeatures = Features<sealed::ChannelContext>;
 /// Features used within an invoice.
 pub type InvoiceFeatures = Features<sealed::InvoiceContext>;
+/// Features used within an `offer`.
+pub type OfferFeatures = Features<sealed::OfferContext>;
+/// Features used within an `invoice_request`.
+pub type InvoiceRequestFeatures = Features<sealed::InvoiceRequestContext>;
+/// Features used within an `invoice`.
+pub type Bolt12InvoiceFeatures = Features<sealed::Bolt12InvoiceContext>;
+/// Features used within BOLT 4 encrypted_data_tlv and BOLT 12 blinded_payinfo
+pub type BlindedHopFeatures = Features<sealed::BlindedHopContext>;
 
 /// Features used within the channel_type field in an OpenChannel message.
 ///
@@ -530,16 +503,6 @@ impl InitFeatures {
                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> {
@@ -570,10 +533,10 @@ impl InvoiceFeatures {
 }
 
 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();
+       // Maps the relevant `InitFeatures` to `ChannelTypeFeatures`. Any unknown features to
+       // `ChannelTypeFeatures` are not included in the result.
+       pub(crate) fn from_init(init: &InitFeatures) -> Self {
+               let mut ret = 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() {
@@ -662,14 +625,6 @@ impl<T: sealed::Context> Features<T> {
                }
        }
 
-       /// Creates a Features with the bits set which are known by the implementation
-       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> {
@@ -688,7 +643,8 @@ 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
+       ///
+       /// This is not exported to bindings users as we don't support export across multiple T
        pub fn from_le_bytes(flags: Vec<u8>) -> Features<T> {
                Features {
                        flags,
@@ -751,6 +707,24 @@ impl<T: sealed::Context> Features<T> {
                        (byte & unknown_features) != 0
                })
        }
+
+       // Returns true if the features within `self` are a subset of the features within `other`.
+       pub(crate) fn is_subset(&self, other: &Self) -> bool {
+               for (idx, byte) in self.flags.iter().enumerate() {
+                       if let Some(other_byte) = other.flags.get(idx) {
+                               if byte & other_byte != *byte {
+                                       // `self` has bits set that `other` doesn't.
+                                       return false;
+                               }
+                       } else {
+                               if *byte > 0 {
+                                       // `self` has a non-zero byte that `other` doesn't.
+                                       return false;
+                               }
+                       }
+               }
+               true
+       }
 }
 
 impl<T: sealed::UpfrontShutdownScript> Features<T> {
@@ -761,25 +735,6 @@ impl<T: sealed::UpfrontShutdownScript> Features<T> {
        }
 }
 
-
-impl<T: sealed::GossipQueries> Features<T> {
-       #[cfg(test)]
-       pub(crate) fn clear_gossip_queries(mut self) -> Self {
-               <T as sealed::GossipQueries>::clear_bits(&mut self.flags);
-               self
-       }
-}
-
-impl<T: sealed::InitialRoutingSync> Features<T> {
-       // 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::ShutdownAnySegwit> Features<T> {
        #[cfg(test)]
        pub(crate) fn clear_shutdown_anysegwit(mut self) -> Self {
@@ -796,6 +751,27 @@ impl<T: sealed::Wumbo> Features<T> {
        }
 }
 
+impl<T: sealed::SCIDPrivacy> Features<T> {
+       pub(crate) fn clear_scid_privacy(&mut self) {
+               <T as sealed::SCIDPrivacy>::clear_bits(&mut self.flags);
+       }
+}
+
+impl<T: sealed::AnchorsZeroFeeHtlcTx> Features<T> {
+       pub(crate) fn clear_anchors_zero_fee_htlc_tx(&mut self) {
+               <T as sealed::AnchorsZeroFeeHtlcTx>::clear_bits(&mut self.flags);
+       }
+}
+
+#[cfg(test)]
+impl<T: sealed::UnknownFeature> Features<T> {
+       pub(crate) fn unknown() -> Self {
+               let mut features = Self::empty();
+               features.set_unknown_feature_required();
+               features
+       }
+}
+
 macro_rules! impl_feature_len_prefixed_write {
        ($features: ident) => {
                impl Writeable for $features {
@@ -815,109 +791,47 @@ impl_feature_len_prefixed_write!(InitFeatures);
 impl_feature_len_prefixed_write!(ChannelFeatures);
 impl_feature_len_prefixed_write!(NodeFeatures);
 impl_feature_len_prefixed_write!(InvoiceFeatures);
+impl_feature_len_prefixed_write!(BlindedHopFeatures);
 
-// 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 {
+// Some features only appear inside of TLVs, so they don't have a length prefix when serialized.
+macro_rules! impl_feature_tlv_write {
+       ($features: ident) => {
+               impl Writeable for $features {
+                       fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+                               WithoutLength(self).write(w)
+                       }
+               }
+               impl Readable for $features {
+                       fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
+                               Ok(WithoutLength::<Self>::read(r)?.0)
+                       }
+               }
+       }
+}
+
+impl_feature_tlv_write!(ChannelTypeFeatures);
+
+// Some features may appear both in a TLV record and as part of a TLV subtype sequence. The latter
+// requires a length but the former does not.
+
+impl<T: sealed::Context> Writeable for WithoutLength<&Features<T>> {
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
-               self.write_be(w)
+               self.0.write_be(w)
        }
 }
-impl Readable for ChannelTypeFeatures {
+
+impl<T: sealed::Context> Readable for WithoutLength<Features<T>> {
        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))
+               Ok(WithoutLength(Features::<T>::from_be_bytes(v)))
        }
 }
 
 #[cfg(test)]
 mod tests {
-       use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, InvoiceFeatures, NodeFeatures};
+       use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, InvoiceFeatures, NodeFeatures, OfferFeatures, sealed};
        use bitcoin::bech32::{Base32Len, FromBase32, ToBase32, u5};
-
-       #[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!(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());
-               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!(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!(ChannelTypeFeatures::known().supports_scid_privacy());
-               assert!(!InitFeatures::known().requires_scid_privacy());
-               assert!(!NodeFeatures::known().requires_scid_privacy());
-               assert!(ChannelTypeFeatures::known().requires_scid_privacy());
-
-               assert!(InitFeatures::known().supports_wumbo());
-               assert!(NodeFeatures::known().supports_wumbo());
-               assert!(!InitFeatures::known().requires_wumbo());
-               assert!(!NodeFeatures::known().requires_wumbo());
-
-               assert!(InitFeatures::known().supports_zero_conf());
-               assert!(!InitFeatures::known().requires_zero_conf());
-               assert!(NodeFeatures::known().supports_zero_conf());
-               assert!(!NodeFeatures::known().requires_zero_conf());
-               assert!(ChannelTypeFeatures::known().supports_zero_conf());
-               assert!(ChannelTypeFeatures::known().requires_zero_conf());
-
-               let mut init_features = InitFeatures::known();
-               assert!(init_features.initial_routing_sync());
-               init_features.clear_initial_routing_sync();
-               assert!(!init_features.initial_routing_sync());
-       }
+       use crate::util::ser::{Readable, WithoutLength, Writeable};
 
        #[test]
        fn sanity_test_unknown_bits() {
@@ -938,7 +852,23 @@ mod tests {
 
        #[test]
        fn convert_to_context_with_relevant_flags() {
-               let init_features = InitFeatures::known().clear_upfront_shutdown_script().clear_gossip_queries();
+               let mut init_features = InitFeatures::empty();
+               // Set a bunch of features we use, plus initial_routing_sync_required (which shouldn't get
+               // converted as it's only relevant in an init context).
+               init_features.set_initial_routing_sync_required();
+               init_features.set_data_loss_protect_required();
+               init_features.set_variable_length_onion_required();
+               init_features.set_static_remote_key_required();
+               init_features.set_payment_secret_required();
+               init_features.set_basic_mpp_optional();
+               init_features.set_wumbo_optional();
+               init_features.set_shutdown_any_segwit_optional();
+               init_features.set_onion_messages_optional();
+               init_features.set_channel_type_optional();
+               init_features.set_scid_privacy_optional();
+               init_features.set_zero_conf_optional();
+               init_features.set_anchors_zero_fee_htlc_tx_optional();
+
                assert!(init_features.initial_routing_sync());
                assert!(!init_features.supports_upfront_shutdown_script());
                assert!(!init_features.supports_gossip_queries());
@@ -946,19 +876,19 @@ mod tests {
                let node_features: NodeFeatures = init_features.to_context();
                {
                        // Check that the flags are as expected:
-                       // - option_data_loss_protect
+                       // - option_data_loss_protect (req)
                        // - var_onion_optin (req) | static_remote_key (req) | payment_secret(req)
                        // - basic_mpp | wumbo
                        // - opt_shutdown_anysegwit
-                       // -
+                       // - onion_messages
                        // - option_channel_type | option_scid_alias
                        // - option_zeroconf
                        assert_eq!(node_features.flags.len(), 7);
-                       assert_eq!(node_features.flags[0], 0b00000010);
+                       assert_eq!(node_features.flags[0], 0b00000001);
                        assert_eq!(node_features.flags[1], 0b01010001);
-                       assert_eq!(node_features.flags[2], 0b00001010);
+                       assert_eq!(node_features.flags[2], 0b10001010);
                        assert_eq!(node_features.flags[3], 0b00001000);
-                       assert_eq!(node_features.flags[4], 0b00000000);
+                       assert_eq!(node_features.flags[4], 0b10000000);
                        assert_eq!(node_features.flags[5], 0b10100000);
                        assert_eq!(node_features.flags[6], 0b00001000);
                }
@@ -976,12 +906,13 @@ mod tests {
        #[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());
+               assert!(<sealed::ChannelContext as sealed::Context>::KNOWN_FEATURE_MASK.len() <
+                       <sealed::InvoiceContext as sealed::Context>::KNOWN_FEATURE_MASK.len());
+               let mut channel_features = ChannelFeatures::empty();
+               channel_features.set_unknown_feature_optional();
+               assert!(channel_features.supports_unknown_bits());
+               let invoice_features: InvoiceFeatures = channel_features.to_context_internal();
+               assert!(!invoice_features.supports_unknown_bits());
        }
 
        #[test]
@@ -995,6 +926,20 @@ mod tests {
                assert!(features.supports_payment_secret());
        }
 
+       #[test]
+       fn encodes_features_without_length() {
+               let features = OfferFeatures::from_le_bytes(vec![1, 2, 3, 4, 5, 42, 100, 101]);
+               assert_eq!(features.flags.len(), 8);
+
+               let mut serialized_features = Vec::new();
+               WithoutLength(&features).write(&mut serialized_features).unwrap();
+               assert_eq!(serialized_features.len(), 8);
+
+               let deserialized_features =
+                       WithoutLength::<OfferFeatures>::read(&mut &serialized_features[..]).unwrap().0;
+               assert_eq!(features, deserialized_features);
+       }
+
        #[test]
        fn invoice_features_encoding() {
                let features_as_u5s = vec![
@@ -1032,7 +977,7 @@ mod tests {
                // 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);
+               let converted_features = ChannelTypeFeatures::from_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());