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bitcoin: count the witness script when weighing an anchors to_remote input #57

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Merged
kwsantiago merged 1 commit into from
Oct 19, 2026
Merged

bitcoin: count the witness script when weighing an anchors to_remote input #57

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5 changes: 3 additions & 2 deletions bitcoin/tx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -935,8 +935,9 @@ size_t bitcoin_tx_input_witness_weight(enum utxotype utxotype)
* to `1` and witness: <remote_sig>
* Otherwise, this output is a simple P2WPKH to `remotepubkey`.
*/
/* In practice, these predate anchors, so: */
return 1 + 1 + bitcoin_tx_input_sig_weight();
/* Only the anchors form is P2WSH, so the witness is the sig
* and that script: 37 bytes, or up to 39 with a lease's csv. */
return bitcoin_tx_input_sig_weight() + 1 + 39;
case UTXO_P2TR:
/* Unified Schnorr signatures include an explicit sighash byte. */
return 1 + 64 + !is_elements(chainparams);
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26 changes: 26 additions & 0 deletions tests/test_wallet.py
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Expand Up @@ -2948,3 +2948,29 @@ def mock_fail_sendrawtx(r):
bitcoind.generate_block(1)
sync_blockheight(bitcoind, [l1])
assert l1.db_query('SELECT COUNT(*) as c FROM outputs WHERE status=0')[0]['c'] == 0


@unittest.skipIf(TEST_NETWORK != 'regtest', 'elementsd anchors not supported')
def test_withdraw_anchor_to_remote_min_feerate(node_factory, bitcoind):
"""The to_remote output of an anchor channel's unilateral close is spent
at the minimum feerate: its weight estimate covers the witness script."""
l1, l2 = node_factory.line_graph(2)
l1.pay(l2, 200000000)
l1.rpc.dev_fail(l2.info['id'])
l1.wait_for_channel_onchain(l2.info['id'])
bitcoind.generate_block(1, wait_for_mempool=1)
sync_blockheight(bitcoind, [l2])

wait_for(lambda: [o for o in l2.rpc.listfunds()['outputs']
if o['scriptpubkey'].startswith('0020')] != [])
utxo = only_one([o for o in l2.rpc.listfunds()['outputs']
if o['scriptpubkey'].startswith('0020')])
# Its csv lock is one block.
bitcoind.generate_block(1)
sync_blockheight(bitcoind, [l2])

out = l2.rpc.withdraw(bitcoind.rpc.getnewaddress(), 'all', '253perkw',
utxos=['{}:{}'.format(utxo['txid'], utxo['output'])])
tx = bitcoind.rpc.getrawtransaction(out['txid'], True)
fee = bitcoind.rpc.getmempoolentry(out['txid'])['fees']['base']
assert fee * 10**8 * 1000 / tx['weight'] >= 250
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