Implement channel_type negotiation

lightning-background-processor/src/lib.rs

@@ -154,7 +154,7 @@ impl BackgroundProcessor {
 	/// functionality implemented by other handlers.
 	/// * [`NetGraphMsgHandler`] if given will update the [`NetworkGraph`] based on payment failures.
 	///
-	/// [top-level documentation]: Self
+	/// [top-level documentation]: BackgroundProcessor
 	/// [`join`]: Self::join
 	/// [`stop`]: Self::stop
 	/// [`ChannelManager`]: lightning::ln::channelmanager::ChannelManager

lightning/src/ln/channel.rs

@@ -23,7 +23,7 @@ use bitcoin::secp256k1::{Secp256k1,Signature};
 use bitcoin::secp256k1;
 
 use ln::{PaymentPreimage, PaymentHash};
-use ln::features::{ChannelFeatures, InitFeatures};
+use ln::features::{ChannelFeatures, ChannelTypeFeatures, InitFeatures};
 use ln::msgs;
 use ln::msgs::{DecodeError, OptionalField, DataLossProtect};
 use ln::script::{self, ShutdownScript};
@@ -550,6 +550,9 @@ pub(super) struct Channel<Signer: Sign> {
 	// is fine, but as a sanity check in our failure to generate the second claim, we check here
 	// that the original was a claim, and that we aren't now trying to fulfill a failed HTLC.
 	historical_inbound_htlc_fulfills: HashSet<u64>,
+
+	/// This channel's type, as negotiated during channel open
+	channel_type: ChannelTypeFeatures,
 }
 
 #[cfg(any(test, feature = "fuzztarget"))]
@@ -775,6 +778,11 @@ impl<Signer: Sign> Channel<Signer> {
 
 			#[cfg(any(test, feature = "fuzztarget"))]
 			historical_inbound_htlc_fulfills: HashSet::new(),
+
+			// We currently only actually support one channel type, so don't retry with new types
+			// on error messages. When we support more we'll need fallback support (assuming we
+			// want to support old types).
+			channel_type: ChannelTypeFeatures::only_static_remote_key(),
 		})
 	}
 
@@ -803,6 +811,23 @@ impl<Signer: Sign> Channel<Signer> {
 		where K::Target: KeysInterface<Signer = Signer>,
           F::Target: FeeEstimator
 	{
+		// First check the channel type is known, failing before we do anything else if we don't
+		// support this channel type.
+		let channel_type = if let Some(channel_type) = &msg.channel_type {
+			if channel_type.supports_any_optional_bits() {
+				return Err(ChannelError::Close("Channel Type field contained optional bits - this is not allowed".to_owned()));
+			}
+			if *channel_type != ChannelTypeFeatures::only_static_remote_key() {
+				return Err(ChannelError::Close("Channel Type was not understood".to_owned()));
+			}
+			channel_type.clone()
+		} else {
+			ChannelTypeFeatures::from_counterparty_init(&their_features)
+		};
+		if !channel_type.supports_static_remote_key() {
+			return Err(ChannelError::Close("Channel Type was not understood - we require static remote key".to_owned()));
+		}
+
 		let holder_signer = keys_provider.get_channel_signer(true, msg.funding_satoshis);
 		let pubkeys = holder_signer.pubkeys().clone();
 		let counterparty_pubkeys = ChannelPublicKeys {
@@ -1043,6 +1068,8 @@ impl<Signer: Sign> Channel<Signer> {
 
 			#[cfg(any(test, feature = "fuzztarget"))]
 			historical_inbound_htlc_fulfills: HashSet::new(),
+
+			channel_type,
 		};
 
 		Ok(chan)
@@ -4283,6 +4310,7 @@ impl<Signer: Sign> Channel<Signer> {
 				Some(script) => script.clone().into_inner(),
 				None => Builder::new().into_script(),
 			}),
+			channel_type: Some(self.channel_type.clone()),
 		}
 	}
 
@@ -5240,6 +5268,7 @@ impl<Signer: Sign> Writeable for Channel<Signer> {
 			(7, self.shutdown_scriptpubkey, option),
 			(9, self.target_closing_feerate_sats_per_kw, option),
 			(11, self.monitor_pending_finalized_fulfills, vec_type),
+			(13, self.channel_type, required),
 		});
 
 		Ok(())
@@ -5474,6 +5503,9 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 		let mut announcement_sigs = None;
 		let mut target_closing_feerate_sats_per_kw = None;
 		let mut monitor_pending_finalized_fulfills = Some(Vec::new());
+		// Prior to supporting channel type negotiation, all of our channels were static_remotekey
+		// only, so we default to that if none was written.
+		let mut channel_type = Some(ChannelTypeFeatures::only_static_remote_key());
 		read_tlv_fields!(reader, {
 			(0, announcement_sigs, option),
 			(1, minimum_depth, option),
@@ -5482,8 +5514,16 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 			(7, shutdown_scriptpubkey, option),
 			(9, target_closing_feerate_sats_per_kw, option),
 			(11, monitor_pending_finalized_fulfills, vec_type),
+			(13, channel_type, option),
 		});
 
+		let chan_features = channel_type.as_ref().unwrap();
+		if chan_features.supports_unknown_bits() || chan_features.requires_unknown_bits() {
+			// If the channel was written by a new version and negotiated with features we don't
+			// understand yet, refuse to read it.
+			return Err(DecodeError::UnknownRequiredFeature);
+		}
+
 		let mut secp_ctx = Secp256k1::new();
 		secp_ctx.seeded_randomize(&keys_source.get_secure_random_bytes());
 
@@ -5576,6 +5616,8 @@ impl<'a, Signer: Sign, K: Deref> ReadableArgs<&'a K> for Channel<Signer>
 
 			#[cfg(any(test, feature = "fuzztarget"))]
 			historical_inbound_htlc_fulfills,
+
+			channel_type: channel_type.unwrap(),
 		})
 	}
 }

lightning/src/ln/features.rs

@@ -22,7 +22,7 @@
 //! [BOLT #9]: https://github.com/lightningnetwork/lightning-rfc/blob/master/09-features.md
 //! [messages]: crate::ln::msgs
 
-use io;
+use {io, io_extras};
 use prelude::*;
 use core::{cmp, fmt};
 use core::hash::{Hash, Hasher};
@@ -194,6 +194,30 @@ mod sealed {
 			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
+			,
+		],
+		optional_features: [
+			// Byte 0
+			,
+			// Byte 1
+			,
+			// Byte 2
+			,
+			// Byte 3
+			,
+		],
+	});
 
 	/// Defines a feature with the given bits for the specified [`Context`]s. The generated trait is
 	/// useful for manipulating feature flags.
@@ -325,7 +349,7 @@ mod sealed {
 	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],
+	define_feature!(13, StaticRemoteKey, [InitContext, NodeContext, ChannelTypeContext],
 		"Feature flags for `option_static_remotekey`.", set_static_remote_key_optional,
 		set_static_remote_key_required);
 	define_feature!(15, PaymentSecret, [InitContext, NodeContext, InvoiceContext],
@@ -388,6 +412,18 @@ 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<(), io::Error> {
@@ -442,6 +478,28 @@ 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();
+		// 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 {
 	fn write_base32<W: WriteBase32>(&self, writer: &mut W) -> Result<(), <W as WriteBase32>::Err> {
 		// Explanation for the "4": the normal way to round up when dividing is to add the divisor
@@ -553,6 +611,25 @@ impl<T: sealed::Context> Features<T> {
 		&self.flags
 	}
 
+	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 {
@@ -692,31 +769,44 @@ impl<T: sealed::ShutdownAnySegwit> Features<T> {
 		self
 	}
 }
-
-impl<T: sealed::Context> Writeable for Features<T> {
-	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
-		(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> {
+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 mut flags: Vec<u8> = Readable::read(r)?;
-		flags.reverse(); // Swap to little-endian
-		Ok(Self {
-			flags,
-			mark: PhantomData,
-		})
+		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]
@@ -875,4 +965,15 @@ 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 init_features = InitFeatures::empty().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());
+	}
 }