Use constants from ln crate

lightning/src/events/bump_transaction.rs

@@ -37,11 +37,11 @@ use bitcoin::secp256k1;
 use bitcoin::secp256k1::{PublicKey, Secp256k1};
 use bitcoin::secp256k1::ecdsa::Signature;
 
-const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
+pub(crate) const EMPTY_SCRIPT_SIG_WEIGHT: u64 = 1 /* empty script_sig */ * WITNESS_SCALE_FACTOR as u64;
 
 const BASE_INPUT_SIZE: u64 = 32 /* txid */ + 4 /* vout */ + 4 /* sequence */;
 
-const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
+pub(crate) const BASE_INPUT_WEIGHT: u64 = BASE_INPUT_SIZE * WITNESS_SCALE_FACTOR as u64;
 
 /// The parameters required to derive a channel signer via [`SignerProvider`].
 #[derive(Clone, Debug, PartialEq, Eq)]

lightning/src/ln/interactivetxs.rs

@@ -21,6 +21,7 @@ use crate::sign::EntropySource;
 use core::ops::Deref;
 use std::io::sink;
 use bitcoin::consensus::Encodable;
+use crate::events::bump_transaction::{BASE_INPUT_WEIGHT, EMPTY_SCRIPT_SIG_WEIGHT};
 use crate::util::ser::TransactionU16LenLimited;
 
 /// The number of received `tx_add_input` messages during a negotiation at which point the
@@ -320,11 +321,8 @@ impl NegotiationContext {
 			return Err(AbortReason::TransactionTooLarge);
 		}
 
-		// TODO:
-		// - Use existing rust-lightning/rust-bitcoin constants.
-		// - How do we enforce their fees cover the witness without knowing its expected length?
-		// 	 - Read eclair's code to see if they do this?
-		const INPUT_WEIGHT: u64 = (32 + 4 + 4) * WITNESS_SCALE_FACTOR as u64;
+		// TODO: How do we enforce their fees cover the witness without knowing its expected length?
+		const INPUT_WEIGHT: u64 = BASE_INPUT_WEIGHT + EMPTY_SCRIPT_SIG_WEIGHT;
 
 		// - the peer's paid feerate does not meet or exceed the agreed feerate (based on the minimum fee).
 		let counterparty_output_weight_contributed: u64 = counterparty_outputs_contributed.clone().map(|output|