branch and bound based coin selection with random draw fallback
This commit is contained in:
Lex Berezhny
Jack Robison
parent
7161a0edb9
commit
dcd8a6bb0e
3 changed files with 244 additions and 313 deletions
151
lbrynet/tests/unit/wallet/test_coinselection.py
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151
lbrynet/tests/unit/wallet/test_coinselection.py
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@ -0,0 +1,151 @@
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import unittest
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from lbrynet.wallet.constants import CENT, MAXIMUM_FEE_PER_BYTE
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from lbrynet.wallet.transaction import Transaction, Output
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from lbrynet.wallet.coinselection import CoinSelector, MAXIMUM_TRIES
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from lbrynet.wallet.manager import WalletManager
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from lbrynet.wallet import set_wallet_manager
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NULL_HASH = '\x00'*32
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def search(*args, **kwargs):
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selection = CoinSelector(*args, **kwargs).branch_and_bound()
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return [o.amount for o in selection] if selection else selection
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def utxo(amount):
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return Output.pay_pubkey_hash(Transaction(), 0, amount, NULL_HASH)
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class TestCoinSelectionTests(unittest.TestCase):
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def setUp(self):
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set_wallet_manager(WalletManager({'fee_per_byte': MAXIMUM_FEE_PER_BYTE}))
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def test_empty_coins(self):
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self.assertIsNone(CoinSelector([], 0, 0).select())
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def test_skip_binary_search_if_total_not_enough(self):
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fee = utxo(CENT).spend(fake=True).fee
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big_pool = [utxo(CENT+fee) for _ in range(100)]
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selector = CoinSelector(big_pool, 101 * CENT, 0)
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self.assertIsNone(selector.select())
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self.assertEqual(selector.tries, 0) # Never tried.
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# check happy path
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selector = CoinSelector(big_pool, 100 * CENT, 0)
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self.assertEqual(len(selector.select()), 100)
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self.assertEqual(selector.tries, 201)
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def test_exact_match(self):
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fee = utxo(CENT).spend(fake=True).fee
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utxo_pool = [
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utxo(CENT + fee),
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utxo(CENT),
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utxo(CENT - fee),
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]
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selector = CoinSelector(utxo_pool, CENT, 0)
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match = selector.select()
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self.assertEqual([CENT + fee], [c.amount for c in match])
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self.assertTrue(selector.exact_match)
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def test_random_draw(self):
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utxo_pool = [
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utxo(2 * CENT),
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utxo(3 * CENT),
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utxo(4 * CENT),
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]
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selector = CoinSelector(utxo_pool, CENT, 0, 1)
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match = selector.select()
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self.assertEqual([2 * CENT], [c.amount for c in match])
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self.assertFalse(selector.exact_match)
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class TestOfficialBitcoinCoinSelectionTests(unittest.TestCase):
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# Bitcoin implementation:
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# https://github.com/bitcoin/bitcoin/blob/master/src/wallet/coinselection.cpp
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#
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# Bitcoin implementation tests:
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# https://github.com/bitcoin/bitcoin/blob/master/src/wallet/test/coinselector_tests.cpp
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#
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# Branch and Bound coin selection white paper:
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# https://murch.one/wp-content/uploads/2016/11/erhardt2016coinselection.pdf
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def setUp(self):
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set_wallet_manager(WalletManager({'fee_per_byte': 0}))
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def make_hard_case(self, utxos):
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target = 0
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utxo_pool = []
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for i in range(utxos):
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amount = 1 << (utxos+i)
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target += amount
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utxo_pool.append(utxo(amount))
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utxo_pool.append(utxo(amount + (1 << (utxos-1-i))))
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return utxo_pool, target
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def test_branch_and_bound_coin_selection(self):
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utxo_pool = [
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utxo(1 * CENT),
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utxo(2 * CENT),
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utxo(3 * CENT),
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utxo(4 * CENT)
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]
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# Select 1 Cent
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self.assertEqual([1 * CENT], search(utxo_pool, 1 * CENT, 0.5 * CENT))
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# Select 2 Cent
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self.assertEqual([2 * CENT], search(utxo_pool, 2 * CENT, 0.5 * CENT))
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# Select 5 Cent
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self.assertEqual([3 * CENT, 2 * CENT], search(utxo_pool, 5 * CENT, 0.5 * CENT))
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# Select 11 Cent, not possible
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self.assertIsNone(search(utxo_pool, 11 * CENT, 0.5 * CENT))
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# Select 10 Cent
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utxo_pool += [utxo(5 * CENT)]
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self.assertEqual(
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[4 * CENT, 3 * CENT, 2 * CENT, 1 * CENT],
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search(utxo_pool, 10 * CENT, 0.5 * CENT)
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)
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# Negative effective value
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# Select 10 Cent but have 1 Cent not be possible because too small
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# TODO: bitcoin has [5, 3, 2]
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self.assertEqual(
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[4 * CENT, 3 * CENT, 2 * CENT, 1 * CENT],
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search(utxo_pool, 10 * CENT, 5000)
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)
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# Select 0.25 Cent, not possible
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self.assertIsNone(search(utxo_pool, 0.25 * CENT, 0.5 * CENT))
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# Iteration exhaustion test
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utxo_pool, target = self.make_hard_case(17)
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selector = CoinSelector(utxo_pool, target, 0)
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self.assertIsNone(selector.branch_and_bound())
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self.assertEqual(selector.tries, MAXIMUM_TRIES) # Should exhaust
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utxo_pool, target = self.make_hard_case(14)
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self.assertIsNotNone(search(utxo_pool, target, 0)) # Should not exhaust
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# Test same value early bailout optimization
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utxo_pool = [
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utxo(7 * CENT),
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utxo(7 * CENT),
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utxo(7 * CENT),
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utxo(7 * CENT),
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utxo(2 * CENT)
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] + [utxo(5 * CENT)]*50000
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self.assertEqual(
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[7 * CENT, 7 * CENT, 7 * CENT, 7 * CENT, 2 * CENT],
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search(utxo_pool, 30 * CENT, 5000)
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)
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# Select 1 Cent with pool of only greater than 5 Cent
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utxo_pool = [utxo(i * CENT) for i in range(5, 21)]
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for _ in range(100):
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self.assertIsNone(search(utxo_pool, 1 * CENT, 2 * CENT))
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@ -1,313 +0,0 @@
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import struct
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import logging
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from collections import defaultdict, namedtuple
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from math import floor, log10
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from .hashing import sha256
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from .constants import COIN, TYPE_ADDRESS
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from .transaction import Transaction
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from .errors import NotEnoughFunds
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log = logging.getLogger()
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class PRNG(object):
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"""
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A simple deterministic PRNG. Used to deterministically shuffle a
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set of coins - the same set of coins should produce the same output.
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Although choosing UTXOs "randomly" we want it to be deterministic,
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so if sending twice from the same UTXO set we choose the same UTXOs
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to spend. This prevents attacks on users by malicious or stale
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servers.
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"""
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def __init__(self, seed):
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self.sha = sha256(seed)
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self.pool = bytearray()
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def get_bytes(self, n):
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while len(self.pool) < n:
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self.pool.extend(self.sha)
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self.sha = sha256(self.sha)
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result, self.pool = self.pool[:n], self.pool[n:]
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return result
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def random(self):
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# Returns random double in [0, 1)
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four = self.get_bytes(4)
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return struct.unpack("I", four)[0] / 4294967296.0
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def randint(self, start, end):
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# Returns random integer in [start, end)
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return start + int(self.random() * (end - start))
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def choice(self, seq):
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return seq[int(self.random() * len(seq))]
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def shuffle(self, x):
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for i in reversed(xrange(1, len(x))):
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# pick an element in x[:i+1] with which to exchange x[i]
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j = int(self.random() * (i + 1))
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x[i], x[j] = x[j], x[i]
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Bucket = namedtuple('Bucket', ['desc', 'size', 'value', 'coins'])
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def strip_unneeded(bkts, sufficient_funds):
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'''Remove buckets that are unnecessary in achieving the spend amount'''
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bkts = sorted(bkts, key=lambda bkt: bkt.value)
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for i in range(len(bkts)):
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if not sufficient_funds(bkts[i + 1:]):
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return bkts[i:]
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# Shouldn't get here
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return bkts
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class CoinChooserBase:
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def keys(self, coins):
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raise NotImplementedError
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def bucketize_coins(self, coins):
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keys = self.keys(coins)
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buckets = defaultdict(list)
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for key, coin in zip(keys, coins):
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buckets[key].append(coin)
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def make_Bucket(desc, coins):
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size = sum(Transaction.estimated_input_size(coin)
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for coin in coins)
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value = sum(coin['value'] for coin in coins)
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return Bucket(desc, size, value, coins)
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return map(make_Bucket, buckets.keys(), buckets.values())
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def penalty_func(self, tx):
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def penalty(candidate):
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return 0
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return penalty
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def change_amounts(self, tx, count, fee_estimator, dust_threshold):
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# Break change up if bigger than max_change
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output_amounts = [o[2] for o in tx.outputs()]
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# Don't split change of less than 0.02 BTC
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max_change = max(max(output_amounts) * 1.25, 0.02 * COIN)
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# Use N change outputs
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for n in range(1, count + 1):
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# How much is left if we add this many change outputs?
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change_amount = max(0, tx.get_fee() - fee_estimator(n))
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if change_amount // n <= max_change:
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break
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# Get a handle on the precision of the output amounts; round our
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# change to look similar
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def trailing_zeroes(val):
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s = str(val)
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return len(s) - len(s.rstrip('0'))
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zeroes = map(trailing_zeroes, output_amounts)
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min_zeroes = min(zeroes)
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max_zeroes = max(zeroes)
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zeroes = range(max(0, min_zeroes - 1), (max_zeroes + 1) + 1)
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# Calculate change; randomize it a bit if using more than 1 output
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remaining = change_amount
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amounts = []
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while n > 1:
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average = remaining // n
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amount = self.p.randint(int(average * 0.7), int(average * 1.3))
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precision = min(self.p.choice(zeroes), int(floor(log10(amount))))
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amount = int(round(amount, -precision))
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amounts.append(amount)
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remaining -= amount
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n -= 1
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# Last change output. Round down to maximum precision but lose
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# no more than 100 satoshis to fees (2dp)
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N = pow(10, min(2, zeroes[0]))
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amount = (remaining // N) * N
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amounts.append(amount)
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assert sum(amounts) <= change_amount
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return amounts
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def change_outputs(self, tx, change_addrs, fee_estimator, dust_threshold):
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amounts = self.change_amounts(tx, len(change_addrs), fee_estimator,
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dust_threshold)
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assert min(amounts) >= 0
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assert len(change_addrs) >= len(amounts)
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# If change is above dust threshold after accounting for the
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# size of the change output, add it to the transaction.
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dust = sum(amount for amount in amounts if amount < dust_threshold)
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amounts = [amount for amount in amounts if amount >= dust_threshold]
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change = [(TYPE_ADDRESS, addr, amount)
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for addr, amount in zip(change_addrs, amounts)]
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log.debug('change: %s', change)
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if dust:
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log.debug('not keeping dust %s', dust)
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return change
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def make_tx(self, coins, outputs, change_addrs, fee_estimator,
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dust_threshold, abandon_txid=None):
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'''Select unspent coins to spend to pay outputs. If the change is
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greater than dust_threshold (after adding the change output to
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the transaction) it is kept, otherwise none is sent and it is
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added to the transaction fee.'''
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# Deterministic randomness from coins
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utxos = [c['prevout_hash'] + str(c['prevout_n']) for c in coins]
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self.p = PRNG(''.join(sorted(utxos)))
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# Copy the ouputs so when adding change we don't modify "outputs"
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tx = Transaction.from_io([], outputs[:])
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# Size of the transaction with no inputs and no change
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base_size = tx.estimated_size()
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spent_amount = tx.output_value()
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claim_coin = None
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if abandon_txid is not None:
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claim_coins = [coin for coin in coins if coin['is_claim']]
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assert len(claim_coins) >= 1
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claim_coin = claim_coins[0]
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spent_amount -= claim_coin['value']
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coins = [coin for coin in coins if not coin['is_claim']]
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def sufficient_funds(buckets):
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'''Given a list of buckets, return True if it has enough
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value to pay for the transaction'''
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total_input = sum(bucket.value for bucket in buckets)
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total_size = sum(bucket.size for bucket in buckets) + base_size
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return total_input >= spent_amount + fee_estimator(total_size)
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# Collect the coins into buckets, choose a subset of the buckets
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buckets = self.bucketize_coins(coins)
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buckets = self.choose_buckets(buckets, sufficient_funds,
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self.penalty_func(tx))
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if claim_coin is not None:
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tx.add_inputs([claim_coin])
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tx.add_inputs([coin for b in buckets for coin in b.coins])
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tx_size = base_size + sum(bucket.size for bucket in buckets)
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# This takes a count of change outputs and returns a tx fee;
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# each pay-to-bitcoin-address output serializes as 34 bytes
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def fee(count):
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return fee_estimator(tx_size + count * 34)
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change = self.change_outputs(tx, change_addrs, fee, dust_threshold)
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tx.add_outputs(change)
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log.debug("using %i inputs", len(tx.inputs()))
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log.info("using buckets: %s", [bucket.desc for bucket in buckets])
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return tx
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class CoinChooserOldestFirst(CoinChooserBase):
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'''Maximize transaction priority. Select the oldest unspent
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transaction outputs in your wallet, that are sufficient to cover
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the spent amount. Then, remove any unneeded inputs, starting with
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the smallest in value.
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'''
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def keys(self, coins):
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return [coin['prevout_hash'] + ':' + str(coin['prevout_n'])
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for coin in coins]
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def choose_buckets(self, buckets, sufficient_funds, penalty_func):
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'''Spend the oldest buckets first.'''
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# Unconfirmed coins are young, not old
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def adj_height(height):
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return 99999999 if height == 0 else height
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buckets.sort(key=lambda b: max(adj_height(coin['height'])
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for coin in b.coins))
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selected = []
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for bucket in buckets:
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selected.append(bucket)
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if sufficient_funds(selected):
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return strip_unneeded(selected, sufficient_funds)
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raise NotEnoughFunds()
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class CoinChooserRandom(CoinChooserBase):
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def keys(self, coins):
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return [coin['prevout_hash'] + ':' + str(coin['prevout_n'])
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for coin in coins]
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def bucket_candidates(self, buckets, sufficient_funds):
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'''Returns a list of bucket sets.'''
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candidates = set()
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# Add all singletons
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for n, bucket in enumerate(buckets):
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if sufficient_funds([bucket]):
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candidates.add((n,))
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# And now some random ones
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attempts = min(100, (len(buckets) - 1) * 10 + 1)
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permutation = range(len(buckets))
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for i in range(attempts):
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# Get a random permutation of the buckets, and
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# incrementally combine buckets until sufficient
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self.p.shuffle(permutation)
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bkts = []
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for count, index in enumerate(permutation):
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bkts.append(buckets[index])
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if sufficient_funds(bkts):
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candidates.add(tuple(sorted(permutation[:count + 1])))
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break
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else:
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raise NotEnoughFunds()
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candidates = [[buckets[n] for n in c] for c in candidates]
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return [strip_unneeded(c, sufficient_funds) for c in candidates]
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def choose_buckets(self, buckets, sufficient_funds, penalty_func):
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candidates = self.bucket_candidates(buckets, sufficient_funds)
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penalties = [penalty_func(cand) for cand in candidates]
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winner = candidates[penalties.index(min(penalties))]
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log.debug("Bucket sets: %i", len(buckets))
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log.debug("Winning penalty: %s", min(penalties))
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return winner
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class CoinChooserPrivacy(CoinChooserRandom):
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'''Attempts to better preserve user privacy. First, if any coin is
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spent from a user address, all coins are. Compared to spending
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from other addresses to make up an amount, this reduces
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information leakage about sender holdings. It also helps to
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reduce blockchain UTXO bloat, and reduce future privacy loss that
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would come from reusing that address' remaining UTXOs. Second, it
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penalizes change that is quite different to the sent amount.
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Third, it penalizes change that is too big.'''
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def keys(self, coins):
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return [coin['address'] for coin in coins]
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def penalty_func(self, tx):
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min_change = min(o[2] for o in tx.outputs()) * 0.75
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max_change = max(o[2] for o in tx.outputs()) * 1.33
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spent_amount = sum(o[2] for o in tx.outputs())
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def penalty(buckets):
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badness = len(buckets) - 1
|
||||
total_input = sum(bucket.value for bucket in buckets)
|
||||
change = float(total_input - spent_amount)
|
||||
# Penalize change not roughly in output range
|
||||
if change < min_change:
|
||||
badness += (min_change - change) / (min_change + 10000)
|
||||
elif change > max_change:
|
||||
badness += (change - max_change) / (max_change + 10000)
|
||||
# Penalize large change; 5 BTC excess ~= using 1 more input
|
||||
badness += change / (COIN * 5)
|
||||
return badness
|
||||
|
||||
return penalty
|
||||
|
||||
|
||||
COIN_CHOOSERS = {'Priority': CoinChooserOldestFirst,
|
||||
'Privacy': CoinChooserPrivacy}
|
||||
93
lbrynet/wallet/coinselection.py
Normal file
93
lbrynet/wallet/coinselection.py
Normal file
|
|
@ -0,0 +1,93 @@
|
|||
from __future__ import print_function
|
||||
from random import Random
|
||||
|
||||
MAXIMUM_TRIES = 100000
|
||||
|
||||
|
||||
class CoinSelector:
|
||||
|
||||
def __init__(self, coins, target, cost_of_change, seed=None, debug=False):
|
||||
self.coins = coins
|
||||
self.target = target
|
||||
self.cost_of_change = cost_of_change
|
||||
self.exact_match = False
|
||||
self.tries = 0
|
||||
self.available = sum(c.effective_amount for c in self.coins)
|
||||
self.debug = debug
|
||||
self.random = Random(seed)
|
||||
debug and print(target)
|
||||
debug and print([c.effective_amount for c in self.coins])
|
||||
|
||||
def select(self):
|
||||
if self.target > self.available:
|
||||
return
|
||||
if not self.coins:
|
||||
return
|
||||
return self.branch_and_bound() or self.single_random_draw()
|
||||
|
||||
def single_random_draw(self):
|
||||
self.random.shuffle(self.coins)
|
||||
selection = []
|
||||
amount = 0
|
||||
for coin in self.coins:
|
||||
selection.append(coin)
|
||||
amount += coin.effective_amount
|
||||
if amount >= self.target+self.cost_of_change:
|
||||
return selection
|
||||
|
||||
def branch_and_bound(self):
|
||||
# see bitcoin implementation for more info:
|
||||
# https://github.com/bitcoin/bitcoin/blob/master/src/wallet/coinselection.cpp
|
||||
|
||||
self.coins.sort(reverse=True)
|
||||
|
||||
current_value = 0
|
||||
current_available_value = self.available
|
||||
current_selection = []
|
||||
best_waste = self.cost_of_change
|
||||
best_selection = []
|
||||
|
||||
while self.tries < MAXIMUM_TRIES:
|
||||
self.tries += 1
|
||||
|
||||
backtrack = False
|
||||
if current_value + current_available_value < self.target or \
|
||||
current_value > self.target + self.cost_of_change:
|
||||
backtrack = True
|
||||
elif current_value >= self.target:
|
||||
new_waste = current_value - self.target
|
||||
if new_waste <= best_waste:
|
||||
best_waste = new_waste
|
||||
best_selection = current_selection[:]
|
||||
backtrack = True
|
||||
|
||||
if backtrack:
|
||||
while current_selection and not current_selection[-1]:
|
||||
current_selection.pop()
|
||||
current_available_value += self.coins[len(current_selection)].effective_amount
|
||||
|
||||
if not current_selection:
|
||||
break
|
||||
|
||||
current_selection[-1] = False
|
||||
utxo = self.coins[len(current_selection)-1]
|
||||
current_value -= utxo.effective_amount
|
||||
|
||||
else:
|
||||
utxo = self.coins[len(current_selection)]
|
||||
current_available_value -= utxo.effective_amount
|
||||
previous_utxo = self.coins[len(current_selection)-1] if current_selection else None
|
||||
if current_selection and not current_selection[-1] and \
|
||||
utxo.effective_amount == previous_utxo.effective_amount and \
|
||||
utxo.fee == previous_utxo.fee:
|
||||
current_selection.append(False)
|
||||
else:
|
||||
current_selection.append(True)
|
||||
current_value += utxo.effective_amount
|
||||
self.debug and print(current_selection)
|
||||
|
||||
if best_selection:
|
||||
self.exact_match = True
|
||||
return [
|
||||
self.coins[i] for i, include in enumerate(best_selection) if include
|
||||
]
|
||||
Loading…
Reference in a new issue