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 self.is_running():
  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     def get_chunks(self, i, header, height):
 170         requested_chunks = []
 171         min_index = (self.local_height + 1)/2016
 172         max_index = (height + 1)/2016
 173         for n in range(min_index, max_index + 1):
 174             print_error( "requesting chunk", n )
 175             i.send([ ('blockchain.block.get_chunk',[n])], 'get_header')
 176             requested_chunks.append(n)
 177             break
 178
 179         while requested_chunks:
 180             try:
 181                 r = i.get_response('get_header',timeout=1)
 182             except Queue.Empty:
 183                 continue
 184             if not r: continue
 185
 186             if r.get('error'):
 187                 print_error('Verifier received an error:', r)
 188                 continue
 189
 190             # 3. handle response
 191             method = r['method']
 192             params = r['params']
 193             result = r['result']
 194
 195             if method == 'blockchain.block.get_chunk':
 196                 index = params[0]
 197                 self.verify_chunk(index, result)
 198                 requested_chunks.remove(index)
 199
 200
 201     def verify_chunk(self, index, hexdata):
 202         data = hexdata.decode('hex')
 203         height = index*2016
 204         num = len(data)/80
 205
 206         if index == 0:
 207             previous_hash = ("0"*64)
 208         else:
 209             prev_header = self.read_header(index*2016-1)
 210             if prev_header is None: raise
 211             previous_hash = self.hash_header(prev_header)
 212
 213         bits, target = self.get_target(index)
 214
 215         for i in range(num):
 216             height = index*2016 + i
 217             raw_header = data[i*80:(i+1)*80]
 218             header = self.header_from_string(raw_header)
 219             _hash = self.hash_header(header)
 220             assert previous_hash == header.get('prev_block_hash')
 221             assert bits == header.get('bits')
 222             assert eval('0x'+_hash) < target
 223
 224             previous_header = header
 225             previous_hash = _hash
 226
 227         self.save_chunk(index, data)
 228         print_error("validated chunk %d"%height)
 229
 230
 231     def verify_header(self, header):
 232         # add header to the blockchain file
 233         # if there is a reorg, push it in a stack
 234
 235         height = header.get('block_height')
 236
 237         prev_header = self.read_header(height -1)
 238         if not prev_header:
 239             # return False to request previous header
 240             return False
 241
 242         prev_hash = self.hash_header(prev_header)
 243         bits, target = self.get_target(height/2016)
 244         _hash = self.hash_header(header)
 245         try:
 246             assert prev_hash == header.get('prev_block_hash')
 247             assert bits == header.get('bits')
 248             assert eval('0x'+_hash) < target
 249         except:
 250             # this can be caused by a reorg.
 251             print_error("verify header failed"+ repr(header))
 252             verifier.undo_verifications()
 253
 254             # return False to request previous header.
 255             return False
 256
 257         self.save_header(header)
 258         print_error("verify header:", _hash, height)
 259         return True
 260
 261
 262
 263
 264     def header_to_string(self, res):
 265         s = int_to_hex(res.get('version'),4) \
 266             + rev_hex(res.get('prev_block_hash')) \
 267             + rev_hex(res.get('merkle_root')) \
 268             + int_to_hex(int(res.get('timestamp')),4) \
 269             + int_to_hex(int(res.get('bits')),4) \
 270             + int_to_hex(int(res.get('nonce')),4)
 271         return s
 272
 273
 274     def header_from_string(self, s):
 275         hex_to_int = lambda s: eval('0x' + s[::-1].encode('hex'))
 276         h = {}
 277         h['version'] = hex_to_int(s[0:4])
 278         h['prev_block_hash'] = hash_encode(s[4:36])
 279         h['merkle_root'] = hash_encode(s[36:68])
 280         h['timestamp'] = hex_to_int(s[68:72])
 281         h['bits'] = hex_to_int(s[72:76])
 282         h['nonce'] = hex_to_int(s[76:80])
 283         return h
 284
 285     def hash_header(self, header):
 286         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 287
 288     def path(self):
 289         return os.path.join( self.config.path, 'blockchain_headers')
 290
 291     def init_headers_file(self):
 292         filename = self.path()
 293         if os.path.exists(filename):
 294             return
 295
 296         try:
 297             import urllib, socket
 298             socket.setdefaulttimeout(30)
 299             print_error("downloading ", self.headers_url )
 300             urllib.urlretrieve(self.headers_url, filename)
 301         except:
 302             print_error( "download failed. creating file", filename )
 303             open(filename,'wb+').close()
 304
 305     def save_chunk(self, index, chunk):
 306         filename = self.path()
 307         f = open(filename,'rb+')
 308         f.seek(index*2016*80)
 309         h = f.write(chunk)
 310         f.close()
 311         self.set_local_height()
 312
 313     def save_header(self, header):
 314         data = self.header_to_string(header).decode('hex')
 315         assert len(data) == 80
 316         height = header.get('block_height')
 317         filename = self.path()
 318         f = open(filename,'rb+')
 319         f.seek(height*80)
 320         h = f.write(data)
 321         f.close()
 322         self.set_local_height()
 323
 324
 325     def set_local_height(self):
 326         name = self.path()
 327         if os.path.exists(name):
 328             h = os.path.getsize(name)/80 - 1
 329             if self.local_height != h:
 330                 self.local_height = h
 331                 self.height = self.local_height
 332
 333
 334     def read_header(self, block_height):
 335         name = self.path()
 336         if os.path.exists(name):
 337             f = open(name,'rb')
 338             f.seek(block_height*80)
 339             h = f.read(80)
 340             f.close()
 341             if len(h) == 80:
 342                 h = self.header_from_string(h)
 343                 return h
 344
 345
 346     def get_target(self, index):
 347
 348         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 349         if index == 0: return 0x1d00ffff, max_target
 350
 351         first = self.read_header((index-1)*2016)
 352         last = self.read_header(index*2016-1)
 353
 354         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 355         nTargetTimespan = 14*24*60*60
 356         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 357         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 358
 359         bits = last.get('bits')
 360         # convert to bignum
 361         MM = 256*256*256
 362         a = bits%MM
 363         if a < 0x8000:
 364             a *= 256
 365         target = (a) * pow(2, 8 * (bits/MM - 3))
 366
 367         # new target
 368         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 369
 370         # convert it to bits
 371         c = ("%064X"%new_target)[2:]
 372         i = 31
 373         while c[0:2]=="00":
 374             c = c[2:]
 375             i -= 1
 376
 377         c = eval('0x'+c[0:6])
 378         if c > 0x800000:
 379             c /= 256
 380             i += 1
 381
 382         new_bits = c + MM * i
 383         return new_bits, new_target
 384
 385
 386
 387
 388     def run(self):
 389         self.start_interfaces()
 390
 391         self.init_headers_file()
 392         self.set_local_height()
 393         print_error( "blocks:", self.local_height )
 394
 395         with self.lock:
 396             self.running = True
 397
 398         while self.is_running():
 399
 400             i, header = self.get_new_response()
 401
 402             height = header.get('block_height')
 403
 404             if height > self.local_height + 50:
 405                 self.get_chunks(i, header, height)
 406
 407
 408             if height > self.local_height:
 409
 410                 # get missing parts from interface (until it connects to my chain)
 411                 chain = self.get_chain( i, header )
 412
 413                 # skip that server if the result is not consistent
 414                 if not chain: continue
 415
 416                 # verify the chain
 417                 if self.verify_chain( chain ):
 418                     print_error("height:", height, i.server)
 419                     for header in chain:
 420                         self.save_header(header)
 421                         self.height = height
 422                 else:
 423                     print_error("error", i.server)
 424                     # todo: dismiss that server
 425
 426
 427
 428
 429
 430 if __name__ == "__main__":
 431     import interface, simple_config
 432
 433     config = simple_config.SimpleConfig({'verbose':True})
 434
 435     i0 = interface.Interface()
 436     i0.start()
 437
 438     bv = BlockchainVerifier(i0, config)
 439     bv.start()
 440
 441
 442     # listen to interfaces, forward to verifier using the queue
 443     while 1:
 444         time.sleep(1)
 445
 446
 447