p2pool/data.py

   1 from __future__ import division
   2
   3 import hashlib
   4 import os
   5 import random
   6 import time
   7
   8 from twisted.python import log
   9
  10 import p2pool
  11 from p2pool.bitcoin import data as bitcoin_data, script, sha256
  12 from p2pool.util import math, forest, pack
  13
  14 # hashlink
  15
  16 hash_link_type = pack.ComposedType([
  17     ('state', pack.FixedStrType(32)),
  18     ('extra_data', pack.FixedStrType(0)), # bit of a hack, but since the donation script is at the end, const_ending is long enough to always make this empty
  19     ('length', pack.VarIntType()),
  20 ])
  21
  22 def prefix_to_hash_link(prefix, const_ending=''):
  23     assert prefix.endswith(const_ending), (prefix, const_ending)
  24     x = sha256.sha256(prefix)
  25     return dict(state=x.state, extra_data=x.buf[:max(0, len(x.buf)-len(const_ending))], length=x.length//8)
  26
  27 def check_hash_link(hash_link, data, const_ending=''):
  28     extra_length = hash_link['length'] % (512//8)
  29     assert len(hash_link['extra_data']) == max(0, extra_length - len(const_ending))
  30     extra = (hash_link['extra_data'] + const_ending)[len(hash_link['extra_data']) + len(const_ending) - extra_length:]
  31     assert len(extra) == extra_length
  32     return pack.IntType(256).unpack(hashlib.sha256(sha256.sha256(data, (hash_link['state'], extra, 8*hash_link['length'])).digest()).digest())
  33
  34 # shares
  35
  36 small_block_header_type = pack.ComposedType([
  37     ('version', pack.VarIntType()), # XXX must be constrained to 32 bits
  38     ('previous_block', pack.PossiblyNoneType(0, pack.IntType(256))),
  39     ('timestamp', pack.IntType(32)),
  40     ('bits', bitcoin_data.FloatingIntegerType()),
  41     ('nonce', pack.IntType(32)),
  42 ])
  43
  44 share_data_type = pack.ComposedType([
  45     ('previous_share_hash', pack.PossiblyNoneType(0, pack.IntType(256))),
  46     ('coinbase', pack.VarStrType()),
  47     ('nonce', pack.IntType(32)),
  48     ('pubkey_hash', pack.IntType(160)),
  49     ('subsidy', pack.IntType(64)),
  50     ('donation', pack.IntType(16)),
  51     ('stale_info', pack.IntType(8)), # 0 nothing, 253 orphan, 254 doa
  52 ])
  53
  54 share_info_type = pack.ComposedType([
  55     ('share_data', share_data_type),
  56     ('max_bits', bitcoin_data.FloatingIntegerType()),
  57     ('bits', bitcoin_data.FloatingIntegerType()),
  58     ('timestamp', pack.IntType(32)),
  59 ])
  60
  61 share1a_type = pack.ComposedType([
  62     ('min_header', small_block_header_type),
  63     ('share_info', share_info_type),
  64     ('hash_link', hash_link_type),
  65     ('merkle_branch', bitcoin_data.merkle_branch_type),
  66 ])
  67
  68 share1b_type = pack.ComposedType([
  69     ('min_header', small_block_header_type),
  70     ('share_info', share_info_type),
  71     ('hash_link', hash_link_type),
  72     ('other_txs', pack.ListType(bitcoin_data.tx_type)),
  73 ])
  74
  75
  76 # type:
  77 # 2: share1a
  78 # 3: share1b
  79
  80 share_type = pack.ComposedType([
  81     ('type', pack.VarIntType()),
  82     ('contents', pack.VarStrType()),
  83 ])
  84
  85
  86 def get_pool_attempts_per_second(tracker, previous_share_hash, dist, min_work=False, integer=False):
  87     assert dist >= 2
  88     near = tracker.shares[previous_share_hash]
  89     far = tracker.shares[tracker.get_nth_parent_hash(previous_share_hash, dist - 1)]
  90     attempts = tracker.get_work(near.hash) - tracker.get_work(far.hash) if not min_work else tracker.get_delta(near.hash).min_work - tracker.get_delta(far.hash).min_work
  91     time = near.timestamp - far.timestamp
  92     if time <= 0:
  93         time = 1
  94     if integer:
  95         return attempts//time
  96     return attempts/time
  97
  98 def get_average_stale_prop(tracker, share_hash, lookbehind):
  99     stales = sum(1 for share in tracker.get_chain(share_hash, lookbehind) if share.share_data['stale_info'] in [253, 254])
 100     return stales/(lookbehind + stales)
 101
 102 DONATION_SCRIPT = '4104ffd03de44a6e11b9917f3a29f9443283d9871c9d743ef30d5eddcd37094b64d1b3d8090496b53256786bf5c82932ec23c3b74d9f05a6f95a8b5529352656664bac'.decode('hex')
 103
 104 ref_type = pack.ComposedType([
 105     ('identifier', pack.FixedStrType(64//8)),
 106     ('share_info', share_info_type),
 107 ])
 108
 109 gentx_before_refhash = pack.VarStrType().pack(DONATION_SCRIPT) + pack.IntType(64).pack(0) + pack.VarStrType().pack('\x20' + pack.IntType(256).pack(0))[:2]
 110
 111 def generate_transaction(tracker, share_data, block_target, desired_timestamp, desired_target, net):
 112     previous_share = tracker.shares[share_data['previous_share_hash']] if share_data['previous_share_hash'] is not None else None
 113
 114     height, last = tracker.get_height_and_last(share_data['previous_share_hash'])
 115     assert height >= net.REAL_CHAIN_LENGTH or last is None
 116     if height < net.TARGET_LOOKBEHIND:
 117         pre_target3 = net.MAX_TARGET
 118     else:
 119         attempts_per_second = get_pool_attempts_per_second(tracker, share_data['previous_share_hash'], net.TARGET_LOOKBEHIND, min_work=True, integer=True)
 120         pre_target = 2**256//(net.SHARE_PERIOD*attempts_per_second) - 1 if attempts_per_second else 2**256-1
 121         pre_target2 = math.clip(pre_target, (previous_share.max_target*9//10, previous_share.max_target*11//10))
 122         pre_target3 = math.clip(pre_target2, (0, net.MAX_TARGET))
 123     max_bits = bitcoin_data.FloatingInteger.from_target_upper_bound(pre_target3)
 124     bits = bitcoin_data.FloatingInteger.from_target_upper_bound(math.clip(desired_target, (pre_target3//10, pre_target3)))
 125
 126     weights, total_weight, donation_weight = tracker.get_cumulative_weights(share_data['previous_share_hash'],
 127         min(height, net.REAL_CHAIN_LENGTH),
 128         65535*net.SPREAD*bitcoin_data.target_to_average_attempts(block_target),
 129     )
 130     assert total_weight == sum(weights.itervalues()) + donation_weight, (total_weight, sum(weights.itervalues()) + donation_weight)
 131
 132     amounts = dict((script, share_data['subsidy']*(199*weight)//(200*total_weight)) for script, weight in weights.iteritems()) # 99.5% goes according to weights prior to this share
 133     this_script = bitcoin_data.pubkey_hash_to_script2(share_data['pubkey_hash'])
 134     amounts[this_script] = amounts.get(this_script, 0) + share_data['subsidy']//200 # 0.5% goes to block finder
 135     amounts[DONATION_SCRIPT] = amounts.get(DONATION_SCRIPT, 0) + share_data['subsidy'] - sum(amounts.itervalues()) # all that's left over is the donation weight and some extra satoshis due to rounding
 136
 137     if sum(amounts.itervalues()) != share_data['subsidy'] or any(x < 0 for x in amounts.itervalues()):
 138         raise ValueError()
 139
 140     dests = sorted(amounts.iterkeys(), key=lambda script: (script == DONATION_SCRIPT, amounts[script], script))[-4000:] # block length limit, unlikely to ever be hit
 141
 142     share_info = dict(
 143         share_data=share_data,
 144         max_bits=max_bits,
 145         bits=bits,
 146         timestamp=math.clip(desired_timestamp, (
 147             (previous_share.timestamp + net.SHARE_PERIOD) - (net.SHARE_PERIOD - 1), # = previous_share.timestamp + 1
 148             (previous_share.timestamp + net.SHARE_PERIOD) + (net.SHARE_PERIOD - 1),
 149         )) if previous_share is not None else desired_timestamp,
 150     )
 151
 152     return share_info, dict(
 153         version=1,
 154         tx_ins=[dict(
 155             previous_output=None,
 156             sequence=None,
 157             script=share_data['coinbase'].ljust(2, '\x00'),
 158         )],
 159         tx_outs=[dict(value=amounts[script], script=script) for script in dests if amounts[script]] + [dict(
 160             value=0,
 161             script='\x20' + pack.IntType(256).pack(bitcoin_data.hash256(ref_type.pack(dict(
 162                 identifier=net.IDENTIFIER,
 163                 share_info=share_info,
 164             )))),
 165         )],
 166         lock_time=0,
 167     )
 168
 169 def get_expected_payouts(tracker, best_share_hash, block_target, subsidy, net):
 170     weights, total_weight, donation_weight = tracker.get_cumulative_weights(best_share_hash, min(tracker.get_height(best_share_hash), net.REAL_CHAIN_LENGTH), 65535*net.SPREAD*bitcoin_data.target_to_average_attempts(block_target))
 171     res = dict((script, subsidy*weight//total_weight) for script, weight in weights.iteritems())
 172     res[DONATION_SCRIPT] = res.get(DONATION_SCRIPT, 0) + subsidy - sum(res.itervalues())
 173     return res
 174
 175 class Share(object):
 176     __slots__ = 'net min_header share_info hash_link merkle_branch other_txs hash share_data max_target target timestamp previous_hash new_script gentx_hash header pow_hash header_hash time_seen peer'.split(' ')
 177
 178     @classmethod
 179     def from_share(cls, share, net, peer):
 180         if share['type'] in [0, 1]:
 181             from p2pool import p2p
 182             raise p2p.PeerMisbehavingError('sent an obsolete share')
 183         elif share['type'] == 2:
 184             return cls(net, peer, other_txs=None, **share1a_type.unpack(share['contents']))
 185         elif share['type'] == 3:
 186             share1b = share1b_type.unpack(share['contents'])
 187             return cls(net, peer, merkle_branch=bitcoin_data.calculate_merkle_branch([0] + [bitcoin_data.hash256(bitcoin_data.tx_type.pack(x)) for x in share1b['other_txs']], 0), **share1b)
 188         else:
 189             raise ValueError('unknown share type: %r' % (share['type'],))
 190
 191     def __init__(self, net, peer, min_header, share_info, hash_link, merkle_branch, other_txs):
 192         if len(share_info['share_data']['coinbase']) > 100:
 193             raise ValueError('''coinbase too large! %i bytes''' % (len(self.share_data['coinbase']),))
 194
 195         if len(merkle_branch) > 16:
 196             raise ValueError('merkle_branch too long!')
 197
 198         if p2pool.DEBUG and other_txs is not None and bitcoin_data.calculate_merkle_branch([0] + [bitcoin_data.hash256(bitcoin_data.tx_type.pack(x)) for x in other_txs], 0) != merkle_branch:
 199             raise ValueError('merkle_branch and other_txs do not match')
 200
 201         assert not hash_link['extra_data'], repr(hash_link['extra_data'])
 202
 203         self.net = net
 204         self.peer = peer
 205         self.min_header = min_header
 206         self.share_info = share_info
 207         self.hash_link = hash_link
 208         self.merkle_branch = merkle_branch
 209         self.other_txs = other_txs
 210
 211         self.share_data = self.share_info['share_data']
 212         self.max_target = self.share_info['max_bits'].target
 213         self.target = self.share_info['bits'].target
 214         self.timestamp = self.share_info['timestamp']
 215         self.previous_hash = self.share_data['previous_share_hash']
 216         self.new_script = bitcoin_data.pubkey_hash_to_script2(self.share_data['pubkey_hash'])
 217
 218         self.gentx_hash = check_hash_link(
 219             hash_link,
 220             pack.IntType(256).pack(bitcoin_data.hash256(ref_type.pack(dict(
 221                 identifier=net.IDENTIFIER,
 222                 share_info=share_info,
 223             )))) + pack.IntType(32).pack(0),
 224             gentx_before_refhash,
 225         )
 226         merkle_root = bitcoin_data.check_merkle_branch(self.gentx_hash, 0, merkle_branch)
 227         self.header = dict(min_header, merkle_root=merkle_root)
 228         self.pow_hash = net.PARENT.POW_FUNC(bitcoin_data.block_header_type.pack(self.header))
 229         self.header_hash = bitcoin_data.hash256(bitcoin_data.block_header_type.pack(self.header))
 230
 231         if self.pow_hash > self.target:
 232             raise p2p.PeerMisbehavingError('share PoW invalid')
 233
 234         if other_txs is not None and not self.pow_hash <= self.header['bits'].target:
 235             raise ValueError('other_txs provided when not a block solution')
 236         if other_txs is None and self.pow_hash <= self.header['bits'].target:
 237             raise ValueError('other_txs not provided when a block solution')
 238
 239         self.hash = bitcoin_data.hash256(share_type.pack(self.as_share()))
 240
 241         # XXX eww
 242         self.time_seen = time.time()
 243
 244     def __repr__(self):
 245         return '<Share %s>' % (' '.join('%s=%r' % (k, getattr(self, k)) for k in self.__slots__),)
 246
 247     def check(self, tracker):
 248         share_info, gentx = generate_transaction(tracker, self.share_info['share_data'], self.header['bits'].target, self.share_info['timestamp'], self.share_info['bits'].target, self.net)
 249         if share_info != self.share_info:
 250             raise ValueError('share difficulty invalid')
 251         if bitcoin_data.hash256(bitcoin_data.tx_type.pack(gentx)) != self.gentx_hash:
 252             raise ValueError('''gentx doesn't match hash_link''')
 253
 254     def as_share(self):
 255         if not self.pow_hash <= self.header['bits'].target: # share1a
 256             return dict(type=2, contents=share1a_type.pack(dict(min_header=self.min_header, share_info=self.share_info, hash_link=self.hash_link, merkle_branch=self.merkle_branch)))
 257         else: # share1b
 258             return dict(type=3, contents=share1b_type.pack(dict(min_header=self.min_header, share_info=self.share_info, hash_link=self.hash_link, other_txs=self.other_txs)))
 259
 260     def as_block(self, tracker):
 261         if self.other_txs is None:
 262             raise ValueError('share does not contain all txs')
 263
 264         share_info, gentx = generate_transaction(tracker, self.share_info['share_data'], self.header['bits'].target, self.share_info['timestamp'], self.share_info['bits'].target, self.net)
 265         assert share_info == self.share_info
 266
 267         return dict(header=self.header, txs=[gentx] + self.other_txs)
 268
 269 class WeightsSkipList(forest.TrackerSkipList):
 270     # share_count, weights, total_weight
 271
 272     def get_delta(self, element):
 273         from p2pool.bitcoin import data as bitcoin_data
 274         share = self.tracker.shares[element]
 275         att = bitcoin_data.target_to_average_attempts(share.target)
 276         return 1, {share.new_script: att*(65535-share.share_data['donation'])}, att*65535, att*share.share_data['donation']
 277
 278     def combine_deltas(self, (share_count1, weights1, total_weight1, total_donation_weight1), (share_count2, weights2, total_weight2, total_donation_weight2)):
 279         return share_count1 + share_count2, math.add_dicts(weights1, weights2), total_weight1 + total_weight2, total_donation_weight1 + total_donation_weight2
 280
 281     def initial_solution(self, start, (max_shares, desired_weight)):
 282         assert desired_weight % 65535 == 0, divmod(desired_weight, 65535)
 283         return 0, None, 0, 0
 284
 285     def apply_delta(self, (share_count1, weights_list, total_weight1, total_donation_weight1), (share_count2, weights2, total_weight2, total_donation_weight2), (max_shares, desired_weight)):
 286         if total_weight1 + total_weight2 > desired_weight and share_count2 == 1:
 287             assert (desired_weight - total_weight1) % 65535 == 0
 288             script, = weights2.iterkeys()
 289             new_weights = dict(script=(desired_weight - total_weight1)//65535*weights2[script]//(total_weight2//65535))
 290             return share_count1 + share_count2, (weights_list, new_weights), desired_weight, total_donation_weight1 + (desired_weight - total_weight1)//65535*total_donation_weight2//(total_weight2//65535)
 291         return share_count1 + share_count2, (weights_list, weights2), total_weight1 + total_weight2, total_donation_weight1 + total_donation_weight2
 292
 293     def judge(self, (share_count, weights_list, total_weight, total_donation_weight), (max_shares, desired_weight)):
 294         if share_count > max_shares or total_weight > desired_weight:
 295             return 1
 296         elif share_count == max_shares or total_weight == desired_weight:
 297             return 0
 298         else:
 299             return -1
 300
 301     def finalize(self, (share_count, weights_list, total_weight, total_donation_weight), (max_shares, desired_weight)):
 302         assert share_count <= max_shares and total_weight <= desired_weight
 303         assert share_count == max_shares or total_weight == desired_weight
 304         return math.add_dicts(*math.flatten_linked_list(weights_list)), total_weight, total_donation_weight
 305
 306 class OkayTracker(forest.Tracker):
 307     def __init__(self, net, my_share_hashes, my_doa_share_hashes):
 308         forest.Tracker.__init__(self, delta_type=forest.get_attributedelta_type(dict(forest.AttributeDelta.attrs,
 309             work=lambda share: bitcoin_data.target_to_average_attempts(share.target),
 310             min_work=lambda share: bitcoin_data.target_to_average_attempts(share.max_target),
 311         )))
 312         self.net = net
 313         self.verified = forest.Tracker(delta_type=forest.get_attributedelta_type(dict(forest.AttributeDelta.attrs,
 314             work=lambda share: bitcoin_data.target_to_average_attempts(share.target),
 315             my_count=lambda share: 1 if share.hash in my_share_hashes else 0,
 316             my_doa_count=lambda share: 1 if share.hash in my_doa_share_hashes else 0,
 317             my_orphan_announce_count=lambda share: 1 if share.hash in my_share_hashes and share.share_data['stale_info'] == 253 else 0,
 318             my_dead_announce_count=lambda share: 1 if share.hash in my_share_hashes and share.share_data['stale_info'] == 254 else 0,
 319         )))
 320         self.verified.get_nth_parent_hash = self.get_nth_parent_hash # self is a superset of self.verified
 321
 322         self.get_cumulative_weights = WeightsSkipList(self)
 323
 324     def attempt_verify(self, share):
 325         if share.hash in self.verified.shares:
 326             return True
 327         height, last = self.get_height_and_last(share.hash)
 328         if height < self.net.CHAIN_LENGTH + 1 and last is not None:
 329             raise AssertionError()
 330         try:
 331             share.check(self)
 332         except:
 333             log.err(None, 'Share check failed:')
 334             return False
 335         else:
 336             self.verified.add(share)
 337             return True
 338
 339     def think(self, block_rel_height_func, previous_block, bits):
 340         desired = set()
 341
 342         # O(len(self.heads))
 343         #   make 'unverified heads' set?
 344         # for each overall head, attempt verification
 345         # if it fails, attempt on parent, and repeat
 346         # if no successful verification because of lack of parents, request parent
 347         bads = set()
 348         for head in set(self.heads) - set(self.verified.heads):
 349             head_height, last = self.get_height_and_last(head)
 350
 351             for share in self.get_chain(head, head_height if last is None else min(5, max(0, head_height - self.net.CHAIN_LENGTH))):
 352                 if self.attempt_verify(share):
 353                     break
 354                 if share.hash in self.heads:
 355                     bads.add(share.hash)
 356             else:
 357                 if last is not None:
 358                     desired.add((
 359                         self.shares[random.choice(list(self.reverse_shares[last]))].peer,
 360                         last,
 361                         max(x.timestamp for x in self.get_chain(head, min(head_height, 5))),
 362                         min(x.target for x in self.get_chain(head, min(head_height, 5))),
 363                     ))
 364         for bad in bads:
 365             assert bad not in self.verified.shares
 366             assert bad in self.heads
 367             if p2pool.DEBUG:
 368                 print "BAD", bad
 369             self.remove(bad)
 370
 371         # try to get at least CHAIN_LENGTH height for each verified head, requesting parents if needed
 372         for head in list(self.verified.heads):
 373             head_height, last_hash = self.verified.get_height_and_last(head)
 374             last_height, last_last_hash = self.get_height_and_last(last_hash)
 375             # XXX review boundary conditions
 376             want = max(self.net.CHAIN_LENGTH - head_height, 0)
 377             can = max(last_height - 1 - self.net.CHAIN_LENGTH, 0) if last_last_hash is not None else last_height
 378             get = min(want, can)
 379             #print 'Z', head_height, last_hash is None, last_height, last_last_hash is None, want, can, get
 380             for share in self.get_chain(last_hash, get):
 381                 if not self.attempt_verify(share):
 382                     break
 383             if head_height < self.net.CHAIN_LENGTH and last_last_hash is not None:
 384                 desired.add((
 385                     self.shares[random.choice(list(self.verified.reverse_shares[last_hash]))].peer,
 386                     last_last_hash,
 387                     max(x.timestamp for x in self.get_chain(head, min(head_height, 5))),
 388                     min(x.target for x in self.get_chain(head, min(head_height, 5))),
 389                 ))
 390
 391         # decide best tree
 392         decorated_tails = sorted((self.score(max(self.verified.tails[tail_hash], key=self.verified.get_work), block_rel_height_func), tail_hash) for tail_hash in self.verified.tails)
 393         if p2pool.DEBUG:
 394             print len(decorated_tails), 'tails:'
 395             for score, tail_hash in decorated_tails:
 396                 print format_hash(tail_hash), score
 397         best_tail_score, best_tail = decorated_tails[-1] if decorated_tails else (None, None)
 398
 399         # decide best verified head
 400         decorated_heads = sorted(((
 401             self.verified.get_work(self.verified.get_nth_parent_hash(h, min(5, self.verified.get_height(h)))),
 402             #self.shares[h].peer is None,
 403             self.shares[h].pow_hash <= self.shares[h].header['bits'].target, # is block solution
 404             (self.shares[h].header['previous_block'], self.shares[h].header['bits']) == (previous_block, bits) or self.shares[h].peer is None,
 405             -self.shares[h].time_seen,
 406         ), h) for h in self.verified.tails.get(best_tail, []))
 407         if p2pool.DEBUG:
 408             print len(decorated_heads), 'heads. Top 10:'
 409             for score, head_hash in decorated_heads[-10:]:
 410                 print '   ', format_hash(head_hash), format_hash(self.shares[head_hash].previous_hash), score
 411         best_head_score, best = decorated_heads[-1] if decorated_heads else (None, None)
 412
 413         # eat away at heads
 414         if decorated_heads:
 415             for i in xrange(1000):
 416                 to_remove = set()
 417                 for share_hash, tail in self.heads.iteritems():
 418                     if share_hash in [head_hash for score, head_hash in decorated_heads[-5:]]:
 419                         #print 1
 420                         continue
 421                     if self.shares[share_hash].time_seen > time.time() - 300:
 422                         #print 2
 423                         continue
 424                     if share_hash not in self.verified.shares and max(self.shares[after_tail_hash].time_seen for after_tail_hash in self.reverse_shares.get(tail)) > time.time() - 120: # XXX stupid
 425                         #print 3
 426                         continue
 427                     to_remove.add(share_hash)
 428                 if not to_remove:
 429                     break
 430                 for share_hash in to_remove:
 431                     self.remove(share_hash)
 432                     if share_hash in self.verified.shares:
 433                         self.verified.remove(share_hash)
 434                 #print "_________", to_remove
 435
 436         # drop tails
 437         for i in xrange(1000):
 438             to_remove = set()
 439             for tail, heads in self.tails.iteritems():
 440                 if min(self.get_height(head) for head in heads) < 2*self.net.CHAIN_LENGTH + 10:
 441                     continue
 442                 for aftertail in self.reverse_shares.get(tail, set()):
 443                     if len(self.reverse_shares[self.shares[aftertail].previous_hash]) > 1: # XXX
 444                         print "raw"
 445                         continue
 446                     to_remove.add(aftertail)
 447             if not to_remove:
 448                 break
 449             # if removed from this, it must be removed from verified
 450             #start = time.time()
 451             for aftertail in to_remove:
 452                 if self.shares[aftertail].previous_hash not in self.tails:
 453                     print "erk", aftertail, self.shares[aftertail].previous_hash
 454                     continue
 455                 self.remove(aftertail)
 456                 if aftertail in self.verified.shares:
 457                     self.verified.remove(aftertail)
 458             #end = time.time()
 459             #print "removed! %i %f" % (len(to_remove), (end - start)/len(to_remove))
 460
 461         if best is not None:
 462             best_share = self.shares[best]
 463             if (best_share.header['previous_block'], best_share.header['bits']) != (previous_block, bits) and best_share.header_hash != previous_block and best_share.peer is not None:
 464                 if p2pool.DEBUG:
 465                     print 'Stale detected! %x < %x' % (best_share.header['previous_block'], previous_block)
 466                 best = best_share.previous_hash
 467
 468             timestamp_cutoff = min(int(time.time()), best_share.timestamp) - 3600
 469             target_cutoff = 2**256//(self.net.SHARE_PERIOD*best_tail_score[1] + 1) * 2 if best_tail_score[1] is not None else 2**256-1
 470         else:
 471             timestamp_cutoff = int(time.time()) - 24*60*60
 472             target_cutoff = 2**256-1
 473
 474         if p2pool.DEBUG:
 475             print 'Desire %i shares. Cutoff: %s old diff>%.2f' % (len(desired), math.format_dt(time.time() - timestamp_cutoff), bitcoin_data.target_to_difficulty(target_cutoff))
 476             for peer, hash, ts, targ in desired:
 477                 print '   ', '%s:%i' % peer.addr if peer is not None else None, format_hash(hash), math.format_dt(time.time() - ts), bitcoin_data.target_to_difficulty(targ), ts >= timestamp_cutoff, targ <= target_cutoff
 478
 479         return best, [(peer, hash) for peer, hash, ts, targ in desired if ts >= timestamp_cutoff and targ <= target_cutoff]
 480
 481     def score(self, share_hash, block_rel_height_func):
 482         # returns approximate lower bound on chain's hashrate in the last self.net.CHAIN_LENGTH*15//16*self.net.SHARE_PERIOD time
 483
 484         head_height = self.verified.get_height(share_hash)
 485         if head_height < self.net.CHAIN_LENGTH:
 486             return head_height, None
 487
 488         end_point = self.verified.get_nth_parent_hash(share_hash, self.net.CHAIN_LENGTH*15//16)
 489
 490         block_height = max(block_rel_height_func(share.header['previous_block']) for share in
 491             self.verified.get_chain(end_point, self.net.CHAIN_LENGTH//16))
 492
 493         return self.net.CHAIN_LENGTH, (self.verified.get_work(share_hash) - self.verified.get_work(end_point))//((0 - block_height + 1)*self.net.PARENT.BLOCK_PERIOD)
 494
 495 def format_hash(x):
 496     if x is None:
 497         return 'xxxxxxxx'
 498     return '%08x' % (x % 2**32)
 499
 500 class ShareStore(object):
 501     def __init__(self, prefix, net):
 502         self.filename = prefix
 503         self.dirname = os.path.dirname(os.path.abspath(prefix))
 504         self.filename = os.path.basename(os.path.abspath(prefix))
 505         self.net = net
 506         self.known = None # will be filename -> set of share hashes, set of verified hashes
 507         self.known_desired = None
 508
 509     def get_shares(self):
 510         if self.known is not None:
 511             raise AssertionError()
 512         known = {}
 513         filenames, next = self.get_filenames_and_next()
 514         for filename in filenames:
 515             share_hashes, verified_hashes = known.setdefault(filename, (set(), set()))
 516             with open(filename, 'rb') as f:
 517                 for line in f:
 518                     try:
 519                         type_id_str, data_hex = line.strip().split(' ')
 520                         type_id = int(type_id_str)
 521                         if type_id == 0:
 522                             pass
 523                         elif type_id == 1:
 524                             pass
 525                         elif type_id == 2:
 526                             verified_hash = int(data_hex, 16)
 527                             yield 'verified_hash', verified_hash
 528                             verified_hashes.add(verified_hash)
 529                         elif type_id == 5:
 530                             raw_share = share_type.unpack(data_hex.decode('hex'))
 531                             if raw_share['type'] in [0, 1]:
 532                                 continue
 533                             share = Share.from_share(raw_share, self.net, None)
 534                             yield 'share', share
 535                             share_hashes.add(share.hash)
 536                         else:
 537                             raise NotImplementedError("share type %i" % (type_id,))
 538                     except Exception:
 539                         log.err(None, "Error while reading saved shares, continuing where left off:")
 540         self.known = known
 541         self.known_desired = dict((k, (set(a), set(b))) for k, (a, b) in known.iteritems())
 542
 543     def _add_line(self, line):
 544         filenames, next = self.get_filenames_and_next()
 545         if filenames and os.path.getsize(filenames[-1]) < 10e6:
 546             filename = filenames[-1]
 547         else:
 548             filename = next
 549
 550         with open(filename, 'ab') as f:
 551             f.write(line + '\n')
 552
 553         return filename
 554
 555     def add_share(self, share):
 556         for filename, (share_hashes, verified_hashes) in self.known.iteritems():
 557             if share.hash in share_hashes:
 558                 break
 559         else:
 560             filename = self._add_line("%i %s" % (5, share_type.pack(share.as_share()).encode('hex')))
 561             share_hashes, verified_hashes = self.known.setdefault(filename, (set(), set()))
 562             share_hashes.add(share.hash)
 563         share_hashes, verified_hashes = self.known_desired.setdefault(filename, (set(), set()))
 564         share_hashes.add(share.hash)
 565
 566     def add_verified_hash(self, share_hash):
 567         for filename, (share_hashes, verified_hashes) in self.known.iteritems():
 568             if share_hash in verified_hashes:
 569                 break
 570         else:
 571             filename = self._add_line("%i %x" % (2, share_hash))
 572             share_hashes, verified_hashes = self.known.setdefault(filename, (set(), set()))
 573             verified_hashes.add(share_hash)
 574         share_hashes, verified_hashes = self.known_desired.setdefault(filename, (set(), set()))
 575         verified_hashes.add(share_hash)
 576
 577     def get_filenames_and_next(self):
 578         suffixes = sorted(int(x[len(self.filename):]) for x in os.listdir(self.dirname) if x.startswith(self.filename) and x[len(self.filename):].isdigit())
 579         return [os.path.join(self.dirname, self.filename + str(suffix)) for suffix in suffixes], os.path.join(self.dirname, self.filename + (str(suffixes[-1] + 1) if suffixes else str(0)))
 580
 581     def forget_share(self, share_hash):
 582         for filename, (share_hashes, verified_hashes) in self.known_desired.iteritems():
 583             if share_hash in share_hashes:
 584                 share_hashes.remove(share_hash)
 585         self.check_remove()
 586
 587     def forget_verified_share(self, share_hash):
 588         for filename, (share_hashes, verified_hashes) in self.known_desired.iteritems():
 589             if share_hash in verified_hashes:
 590                 verified_hashes.remove(share_hash)
 591         self.check_remove()
 592
 593     def check_remove(self):
 594         to_remove = set()
 595         for filename, (share_hashes, verified_hashes) in self.known_desired.iteritems():
 596             #print filename, len(share_hashes) + len(verified_hashes)
 597             if not share_hashes and not verified_hashes:
 598                 to_remove.add(filename)
 599         for filename in to_remove:
 600             self.known.pop(filename)
 601             self.known_desired.pop(filename)
 602             os.remove(filename)
 603             print "REMOVED", filename