Implement Holder HTLC claim chunking for 0FC channels

Otherwise, we could hit the max 10_000vB size limit on V3 transactions
(BIP 431 rule 4).

Also introduce a `max_tx_weight` parameter to `select_confirmed_utxos`.
This constraint makes sure anchor and HTLC transactions in 0FC channels
satisfy the `TRUC_MAX_WEIGHT` and the `TRUC_CHILD_MAX_WEIGHT`
maximums.

Expand the coin-selection algorithm provided for any `T: WalletSource`
to satisfy this new constraint.

Author: tankyleo

lightning/src/chain/mod.rs

@@ -12,6 +12,8 @@
 use bitcoin::block::{Block, Header};
 use bitcoin::constants::genesis_block;
 use bitcoin::hash_types::{BlockHash, Txid};
+use bitcoin::hashes::sha256::Hash as Sha256;
+use bitcoin::hashes::{Hash, HashEngine};
 use bitcoin::network::Network;
 use bitcoin::script::{Script, ScriptBuf};
 use bitcoin::secp256k1::PublicKey;
@@ -21,6 +23,7 @@ use crate::chain::transaction::{OutPoint, TransactionData};
 use crate::impl_writeable_tlv_based;
 use crate::ln::types::ChannelId;
 use crate::sign::ecdsa::EcdsaChannelSigner;
+use crate::sign::HTLCDescriptor;
 
 #[allow(unused_imports)]
 use crate::prelude::*;
@@ -442,3 +445,14 @@ where
 /// This is not exported to bindings users as we just use [u8; 32] directly.
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
 pub struct ClaimId(pub [u8; 32]);
+
+impl ClaimId {
+	pub(crate) fn from_htlcs(htlcs: &[HTLCDescriptor]) -> ClaimId {
+		let mut engine = Sha256::engine();
+		for htlc in htlcs {
+			engine.input(&htlc.commitment_txid.to_byte_array());
+			engine.input(&htlc.htlc.transaction_output_index.unwrap().to_be_bytes());
+		}
+		ClaimId(Sha256::from_engine(engine).to_byte_array())
+	}
+}

lightning/src/chain/onchaintx.rs

@@ -14,8 +14,7 @@
 
 use bitcoin::amount::Amount;
 use bitcoin::hash_types::{BlockHash, Txid};
-use bitcoin::hashes::sha256::Hash as Sha256;
-use bitcoin::hashes::{Hash, HashEngine};
+use bitcoin::hashes::Hash;
 use bitcoin::locktime::absolute::LockTime;
 use bitcoin::script::{Script, ScriptBuf};
 use bitcoin::secp256k1;
@@ -882,12 +881,7 @@ impl<ChannelSigner: EcdsaChannelSigner> OnchainTxHandler<ChannelSigner> {
 								// claim, which will always be unique per request. Once a claim ID
 								// is generated, it is assigned and remains unchanged, even if the
 								// underlying set of HTLCs changes.
-								let mut engine = Sha256::engine();
-								for htlc in htlcs {
-									engine.input(&htlc.commitment_txid.to_byte_array());
-									engine.input(&htlc.htlc.transaction_output_index.unwrap().to_be_bytes());
-								}
-								ClaimId(Sha256::from_engine(engine).to_byte_array())
+								ClaimId::from_htlcs(htlcs)
 							},
 						};
 						debug_assert!(self.pending_claim_requests.get(&claim_id).is_none());