lib/blockchain.py

   1 #!/usr/bin/env python
   2 #
   3 # Electrum - lightweight Bitcoin client
   4 # Copyright (C) 2012 thomasv@ecdsa.org
   5 #
   6 # This program is free software: you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation, either version 3 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14 # GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program. If not, see <http://www.gnu.org/licenses/>.
  18
  19
  20 import threading, time, Queue, os, sys, shutil
  21 from util import user_dir, appdata_dir, print_error
  22 from bitcoin import *
  23
  24
  25 class BlockchainVerifier(threading.Thread):
  26     """ Simple Payment Verification """
  27
  28     def __init__(self, interface, config):
  29         threading.Thread.__init__(self)
  30         self.daemon = True
  31         self.config = config
  32         self.lock = threading.Lock()
  33         self.height = 0
  34         self.local_height = 0
  35         self.running = False
  36         self.headers_url = 'http://headers.electrum.org/blockchain_headers'
  37         self.interface = interface
  38         interface.register_channel('verifier')
  39         self.set_local_height()
  40
  41
  42
  43     def start_interfaces(self):
  44         import interface
  45         servers = interface.DEFAULT_SERVERS
  46         servers = interface.filter_protocol(servers,'s')
  47         print_error("using %d servers"% len(servers))
  48         self.interfaces = map ( lambda server: interface.Interface({'server':server} ), servers )
  49
  50         for i in self.interfaces:
  51             i.start()
  52             # subscribe to block headers
  53             i.register_channel('verifier')
  54             i.register_channel('get_header')
  55             i.send([ ('blockchain.headers.subscribe',[])], 'verifier')
  56             # note: each interface should send its results directly to a queue, instead of channels
  57             # pass the queue to the interface, so that several can share the same queue
  58
  59
  60     def get_new_response(self):
  61         # listen to interfaces, forward to verifier using the queue
  62         while 1:
  63             for i in self.interfaces:
  64                 try:
  65                     r = i.get_response('verifier',timeout=0)
  66                 except Queue.Empty:
  67                     continue
  68
  69                 result = r.get('result')
  70                 if result:
  71                     return (i,result)
  72
  73             time.sleep(1)
  74
  75
  76
  77
  78     def stop(self):
  79         with self.lock: self.running = False
  80         #self.interface.poke('verifier')
  81
  82     def is_running(self):
  83         with self.lock: return self.running
  84
  85
  86     def request_header(self, i, h):
  87         print_error("requesting header %d from %s"%(h, i.server))
  88         i.send([ ('blockchain.block.get_header',[h])], 'get_header')
  89
  90     def retrieve_header(self, i):
  91         while True:
  92             try:
  93                 r = i.get_response('get_header',timeout=1)
  94             except Queue.Empty:
  95                 print_error('timeout')
  96                 continue
  97
  98             if r.get('error'):
  99                 print_error('Verifier received an error:', r)
 100                 continue
 101
 102             # 3. handle response
 103             method = r['method']
 104             params = r['params']
 105             result = r['result']
 106
 107             if method == 'blockchain.block.get_header':
 108                 return result
 109
 110
 111     def get_chain(self, interface, final_header):
 112
 113         header = final_header
 114         chain = [ final_header ]
 115         requested_header = False
 116
 117         while self.is_running():
 118
 119             if requested_header:
 120                 header = self.retrieve_header(interface)
 121                 if not header: return
 122                 chain = [ header ] + chain
 123                 requested_header = False
 124
 125             height = header.get('block_height')
 126             previous_header = self.read_header(height -1)
 127             if not previous_header:
 128                 self.request_header(interface, height - 1)
 129                 requested_header = True
 130                 continue
 131
 132             # verify that it connects to my chain
 133             prev_hash = self.hash_header(previous_header)
 134             if prev_hash != header.get('prev_block_hash'):
 135                 print_error("reorg")
 136                 self.request_header(interface, height - 1)
 137                 requested_header = True
 138                 continue
 139
 140             else:
 141                 # the chain is complete
 142                 return chain
 143
 144
 145     def verify_chain(self, chain):
 146
 147         first_header = chain[0]
 148         prev_header = self.read_header(first_header.get('block_height') -1)
 149
 150         for header in chain:
 151
 152             height = header.get('block_height')
 153
 154             prev_hash = self.hash_header(prev_header)
 155             bits, target = self.get_target(height/2016)
 156             _hash = self.hash_header(header)
 157             try:
 158                 assert prev_hash == header.get('prev_block_hash')
 159                 assert bits == header.get('bits')
 160                 assert eval('0x'+_hash) < target
 161             except:
 162                 return False
 163
 164             prev_header = header
 165
 166         return True
 167
 168
 169
 170
 171     def verify_chunk(self, index, hexdata):
 172         data = hexdata.decode('hex')
 173         height = index*2016
 174         num = len(data)/80
 175         print_error("validating headers %d"%height)
 176
 177         if index == 0:
 178             previous_hash = ("0"*64)
 179         else:
 180             prev_header = self.read_header(index*2016-1)
 181             if prev_header is None: raise
 182             previous_hash = self.hash_header(prev_header)
 183
 184         bits, target = self.get_target(index)
 185
 186         for i in range(num):
 187             height = index*2016 + i
 188             raw_header = data[i*80:(i+1)*80]
 189             header = self.header_from_string(raw_header)
 190             _hash = self.hash_header(header)
 191             assert previous_hash == header.get('prev_block_hash')
 192             assert bits == header.get('bits')
 193             assert eval('0x'+_hash) < target
 194
 195             previous_header = header
 196             previous_hash = _hash
 197
 198         self.save_chunk(index, data)
 199
 200
 201     def verify_header(self, header):
 202         # add header to the blockchain file
 203         # if there is a reorg, push it in a stack
 204
 205         height = header.get('block_height')
 206
 207         prev_header = self.read_header(height -1)
 208         if not prev_header:
 209             # return False to request previous header
 210             return False
 211
 212         prev_hash = self.hash_header(prev_header)
 213         bits, target = self.get_target(height/2016)
 214         _hash = self.hash_header(header)
 215         try:
 216             assert prev_hash == header.get('prev_block_hash')
 217             assert bits == header.get('bits')
 218             assert eval('0x'+_hash) < target
 219         except:
 220             # this can be caused by a reorg.
 221             print_error("verify header failed"+ repr(header))
 222             verifier.undo_verifications()
 223
 224             # return False to request previous header.
 225             return False
 226
 227         self.save_header(header)
 228         print_error("verify header:", _hash, height)
 229         return True
 230
 231
 232
 233
 234     def header_to_string(self, res):
 235         s = int_to_hex(res.get('version'),4) \
 236             + rev_hex(res.get('prev_block_hash')) \
 237             + rev_hex(res.get('merkle_root')) \
 238             + int_to_hex(int(res.get('timestamp')),4) \
 239             + int_to_hex(int(res.get('bits')),4) \
 240             + int_to_hex(int(res.get('nonce')),4)
 241         return s
 242
 243
 244     def header_from_string(self, s):
 245         hex_to_int = lambda s: eval('0x' + s[::-1].encode('hex'))
 246         h = {}
 247         h['version'] = hex_to_int(s[0:4])
 248         h['prev_block_hash'] = hash_encode(s[4:36])
 249         h['merkle_root'] = hash_encode(s[36:68])
 250         h['timestamp'] = hex_to_int(s[68:72])
 251         h['bits'] = hex_to_int(s[72:76])
 252         h['nonce'] = hex_to_int(s[76:80])
 253         return h
 254
 255     def hash_header(self, header):
 256         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 257
 258     def path(self):
 259         return os.path.join( self.config.path, 'blockchain_headers')
 260
 261     def init_headers_file(self):
 262         filename = self.path()
 263         if os.path.exists(filename):
 264             return
 265
 266         try:
 267             import urllib, socket
 268             socket.setdefaulttimeout(30)
 269             print_error("downloading ", self.headers_url )
 270             urllib.urlretrieve(self.headers_url, filename)
 271         except:
 272             print_error( "download failed. creating file", filename )
 273             open(filename,'wb+').close()
 274
 275     def save_chunk(self, index, chunk):
 276         filename = self.path()
 277         f = open(filename,'rb+')
 278         f.seek(index*2016*80)
 279         h = f.write(chunk)
 280         f.close()
 281         self.set_local_height()
 282
 283     def save_header(self, header):
 284         data = self.header_to_string(header).decode('hex')
 285         assert len(data) == 80
 286         height = header.get('block_height')
 287         filename = self.path()
 288         f = open(filename,'rb+')
 289         f.seek(height*80)
 290         h = f.write(data)
 291         f.close()
 292         self.set_local_height()
 293
 294
 295     def set_local_height(self):
 296         name = self.path()
 297         if os.path.exists(name):
 298             h = os.path.getsize(name)/80 - 1
 299             if self.local_height != h:
 300                 self.local_height = h
 301                 self.height = self.local_height
 302
 303
 304     def read_header(self, block_height):
 305         name = self.path()
 306         if os.path.exists(name):
 307             f = open(name,'rb')
 308             f.seek(block_height*80)
 309             h = f.read(80)
 310             f.close()
 311             if len(h) == 80:
 312                 h = self.header_from_string(h)
 313                 return h
 314
 315
 316     def get_target(self, index):
 317
 318         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 319         if index == 0: return 0x1d00ffff, max_target
 320
 321         first = self.read_header((index-1)*2016)
 322         last = self.read_header(index*2016-1)
 323
 324         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 325         nTargetTimespan = 14*24*60*60
 326         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 327         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 328
 329         bits = last.get('bits')
 330         # convert to bignum
 331         MM = 256*256*256
 332         a = bits%MM
 333         if a < 0x8000:
 334             a *= 256
 335         target = (a) * pow(2, 8 * (bits/MM - 3))
 336
 337         # new target
 338         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 339
 340         # convert it to bits
 341         c = ("%064X"%new_target)[2:]
 342         i = 31
 343         while c[0:2]=="00":
 344             c = c[2:]
 345             i -= 1
 346
 347         c = eval('0x'+c[0:6])
 348         if c > 0x800000:
 349             c /= 256
 350             i += 1
 351
 352         new_bits = c + MM * i
 353         return new_bits, new_target
 354
 355
 356
 357
 358     def run(self):
 359         self.start_interfaces()
 360
 361         self.init_headers_file()
 362         self.set_local_height()
 363         print_error( "blocks:", self.local_height )
 364
 365         with self.lock:
 366             self.running = True
 367
 368         while self.is_running():
 369
 370             i, header = self.get_new_response()
 371
 372             height = header.get('block_height')
 373
 374             if height > self.local_height:
 375                 # get missing parts from interface (until it connects to my chain)
 376                 chain = self.get_chain( i, header )
 377
 378                 # skip that server if the result is not consistent
 379                 if not chain: continue
 380
 381                 # verify the chain
 382                 if self.verify_chain( chain ):
 383                     print_error("height:", height, i.server)
 384                     for header in chain:
 385                         self.save_header(header)
 386                         self.height = height
 387                 else:
 388                     print_error("error", i.server)
 389                     # todo: dismiss that server
 390
 391
 392
 393
 394
 395 if __name__ == "__main__":
 396     import interface, simple_config
 397
 398     config = simple_config.SimpleConfig({'verbose':True})
 399
 400     i0 = interface.Interface()
 401     i0.start()
 402
 403     bv = BlockchainVerifier(i0, config)
 404     bv.start()
 405
 406
 407     # listen to interfaces, forward to verifier using the queue
 408     while 1:
 409         time.sleep(1)
 410
 411
 412