Define anchor channel reserve requirements

This change defines anchor reserve requirements by calculating weights
and fees for the transactions that need to be confirmed on-chain in the
event of a unilateral closure. The calculation is given a set of
parameters as input, including the expected fee rate and number of
in-flight HTLCs.

lightning/src/chain/channelmonitor.rs

@@ -34,6 +34,7 @@ use bitcoin::secp256k1::{self, SecretKey, PublicKey, Secp256k1, ecdsa::Signature
 
 use crate::ln::channel::INITIAL_COMMITMENT_NUMBER;
 use crate::ln::types::ChannelId;
+use crate::types::features::ChannelTypeFeatures;
 use crate::types::payment::{PaymentHash, PaymentPreimage};
 use crate::ln::msgs::DecodeError;
 use crate::ln::channel_keys::{DelayedPaymentKey, DelayedPaymentBasepoint, HtlcBasepoint, HtlcKey, RevocationKey, RevocationBasepoint};
@@ -1571,6 +1572,11 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitor<Signer> {
 		self.inner.lock().unwrap().channel_id()
 	}
 
+	/// Gets the channel type of the corresponding channel.
+	pub fn channel_type_features(&self) -> ChannelTypeFeatures {
+		self.inner.lock().unwrap().channel_type_features()
+	}
+
 	/// Gets a list of txids, with their output scripts (in the order they appear in the
 	/// transaction), which we must learn about spends of via block_connected().
 	pub fn get_outputs_to_watch(&self) -> Vec<(Txid, Vec<(u32, ScriptBuf)>)> {
@@ -4692,6 +4698,10 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 			self.onchain_events_awaiting_threshold_conf.push(entry);
 		}
 	}
+
+	fn channel_type_features(&self) -> ChannelTypeFeatures {
+		self.onchain_tx_handler.channel_type_features().clone()
+	}
 }
 
 impl<Signer: EcdsaChannelSigner, T: Deref, F: Deref, L: Deref> chain::Listen for (ChannelMonitor<Signer>, T, F, L)