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 Blockchain(threading.Thread):
  26
  27     def __init__(self, config, network):
  28         threading.Thread.__init__(self)
  29         self.daemon = True
  30         self.config = config
  31         self.network = network
  32         self.lock = threading.Lock()
  33         self.local_height = 0
  34         self.running = False
  35         self.headers_url = 'http://headers.electrum.org/blockchain_headers'
  36         self.set_local_height()
  37         self.queue = Queue.Queue()
  38
  39
  40     def height(self):
  41         return self.local_height
  42
  43
  44     def stop(self):
  45         with self.lock: self.running = False
  46
  47
  48     def is_running(self):
  49         with self.lock: return self.running
  50
  51
  52     def run(self):
  53         self.init_headers_file()
  54         self.set_local_height()
  55         print_error( "blocks:", self.local_height )
  56
  57         with self.lock:
  58             self.running = True
  59
  60         while self.is_running():
  61
  62             try:
  63                 result = self.queue.get()
  64             except Queue.Empty:
  65                 continue
  66
  67             if not result: continue
  68
  69             i, header = result
  70             if not header: continue
  71
  72             height = header.get('block_height')
  73
  74             if height <= self.local_height:
  75                 continue
  76
  77             if height > self.local_height + 50:
  78                 if not self.get_and_verify_chunks(i, header, height):
  79                     continue
  80
  81             if height > self.local_height:
  82                 # get missing parts from interface (until it connects to my chain)
  83                 chain = self.get_chain( i, header )
  84
  85                 # skip that server if the result is not consistent
  86                 if not chain:
  87                     print_error('e')
  88                     continue
  89
  90                 # verify the chain
  91                 if self.verify_chain( chain ):
  92                     print_error("height:", height, i.server)
  93                     for header in chain:
  94                         self.save_header(header)
  95                 else:
  96                     print_error("error", i.server)
  97                     # todo: dismiss that server
  98                     continue
  99
 100
 101             self.network.new_blockchain_height(height, i)
 102
 103
 104
 105
 106     def verify_chain(self, chain):
 107
 108         first_header = chain[0]
 109         prev_header = self.read_header(first_header.get('block_height') -1)
 110
 111         for header in chain:
 112
 113             height = header.get('block_height')
 114
 115             prev_hash = self.hash_header(prev_header)
 116             bits, target = self.get_target(height/2016)
 117             _hash = self.hash_header(header)
 118             try:
 119                 assert prev_hash == header.get('prev_block_hash')
 120                 assert bits == header.get('bits')
 121                 assert eval('0x'+_hash) < target
 122             except:
 123                 return False
 124
 125             prev_header = header
 126
 127         return True
 128
 129
 130
 131     def verify_chunk(self, index, hexdata):
 132         data = hexdata.decode('hex')
 133         height = index*2016
 134         num = len(data)/80
 135
 136         if index == 0:
 137             previous_hash = ("0"*64)
 138         else:
 139             prev_header = self.read_header(index*2016-1)
 140             if prev_header is None: raise
 141             previous_hash = self.hash_header(prev_header)
 142
 143         bits, target = self.get_target(index)
 144
 145         for i in range(num):
 146             height = index*2016 + i
 147             raw_header = data[i*80:(i+1)*80]
 148             header = self.header_from_string(raw_header)
 149             _hash = self.hash_header(header)
 150             assert previous_hash == header.get('prev_block_hash')
 151             assert bits == header.get('bits')
 152             assert eval('0x'+_hash) < target
 153
 154             previous_header = header
 155             previous_hash = _hash
 156
 157         self.save_chunk(index, data)
 158         print_error("validated chunk %d"%height)
 159
 160
 161     def verify_header(self, header):
 162         # add header to the blockchain file
 163         # if there is a reorg, push it in a stack
 164
 165         height = header.get('block_height')
 166
 167         prev_header = self.read_header(height -1)
 168         if not prev_header:
 169             # return False to request previous header
 170             return False
 171
 172         prev_hash = self.hash_header(prev_header)
 173         bits, target = self.get_target(height/2016)
 174         _hash = self.hash_header(header)
 175         try:
 176             assert prev_hash == header.get('prev_block_hash')
 177             assert bits == header.get('bits')
 178             assert eval('0x'+_hash) < target
 179         except:
 180             # this can be caused by a reorg.
 181             print_error("verify header failed"+ repr(header))
 182             verifier.undo_verifications()
 183
 184             # return False to request previous header.
 185             return False
 186
 187         self.save_header(header)
 188         print_error("verify header:", _hash, height)
 189         return True
 190
 191
 192     def header_to_string(self, res):
 193         s = int_to_hex(res.get('version'),4) \
 194             + rev_hex(res.get('prev_block_hash')) \
 195             + rev_hex(res.get('merkle_root')) \
 196             + int_to_hex(int(res.get('timestamp')),4) \
 197             + int_to_hex(int(res.get('bits')),4) \
 198             + int_to_hex(int(res.get('nonce')),4)
 199         return s
 200
 201
 202     def header_from_string(self, s):
 203         hex_to_int = lambda s: eval('0x' + s[::-1].encode('hex'))
 204         h = {}
 205         h['version'] = hex_to_int(s[0:4])
 206         h['prev_block_hash'] = hash_encode(s[4:36])
 207         h['merkle_root'] = hash_encode(s[36:68])
 208         h['timestamp'] = hex_to_int(s[68:72])
 209         h['bits'] = hex_to_int(s[72:76])
 210         h['nonce'] = hex_to_int(s[76:80])
 211         return h
 212
 213     def hash_header(self, header):
 214         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 215
 216     def path(self):
 217         return os.path.join( self.config.path, 'blockchain_headers')
 218
 219     def init_headers_file(self):
 220         filename = self.path()
 221         if os.path.exists(filename):
 222             return
 223
 224         try:
 225             import urllib, socket
 226             socket.setdefaulttimeout(30)
 227             print_error("downloading ", self.headers_url )
 228             urllib.urlretrieve(self.headers_url, filename)
 229         except:
 230             print_error( "download failed. creating file", filename )
 231             open(filename,'wb+').close()
 232
 233     def save_chunk(self, index, chunk):
 234         filename = self.path()
 235         f = open(filename,'rb+')
 236         f.seek(index*2016*80)
 237         h = f.write(chunk)
 238         f.close()
 239         self.set_local_height()
 240
 241     def save_header(self, header):
 242         data = self.header_to_string(header).decode('hex')
 243         assert len(data) == 80
 244         height = header.get('block_height')
 245         filename = self.path()
 246         f = open(filename,'rb+')
 247         f.seek(height*80)
 248         h = f.write(data)
 249         f.close()
 250         self.set_local_height()
 251
 252
 253     def set_local_height(self):
 254         name = self.path()
 255         if os.path.exists(name):
 256             h = os.path.getsize(name)/80 - 1
 257             if self.local_height != h:
 258                 self.local_height = h
 259
 260
 261     def read_header(self, block_height):
 262         name = self.path()
 263         if os.path.exists(name):
 264             f = open(name,'rb')
 265             f.seek(block_height*80)
 266             h = f.read(80)
 267             f.close()
 268             if len(h) == 80:
 269                 h = self.header_from_string(h)
 270                 return h
 271
 272
 273     def get_target(self, index):
 274
 275         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 276         if index == 0: return 0x1d00ffff, max_target
 277
 278         first = self.read_header((index-1)*2016)
 279         last = self.read_header(index*2016-1)
 280
 281         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 282         nTargetTimespan = 14*24*60*60
 283         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 284         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 285
 286         bits = last.get('bits')
 287         # convert to bignum
 288         MM = 256*256*256
 289         a = bits%MM
 290         if a < 0x8000:
 291             a *= 256
 292         target = (a) * pow(2, 8 * (bits/MM - 3))
 293
 294         # new target
 295         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 296
 297         # convert it to bits
 298         c = ("%064X"%new_target)[2:]
 299         i = 31
 300         while c[0:2]=="00":
 301             c = c[2:]
 302             i -= 1
 303
 304         c = eval('0x'+c[0:6])
 305         if c > 0x800000:
 306             c /= 256
 307             i += 1
 308
 309         new_bits = c + MM * i
 310         return new_bits, new_target
 311
 312
 313     def request_header(self, i, h, queue):
 314         print_error("requesting header %d from %s"%(h, i.server))
 315         i.send([ ('blockchain.block.get_header',[h])], lambda i,r: queue.put((i,r)))
 316
 317     def retrieve_header(self, i, queue):
 318         while True:
 319             try:
 320                 ir = queue.get(timeout=1)
 321             except Queue.Empty:
 322                 print_error('timeout')
 323                 continue
 324
 325             if not ir:
 326                 continue
 327
 328             i, r = ir
 329
 330             if r.get('error'):
 331                 print_error('Verifier received an error:', r)
 332                 continue
 333
 334             # 3. handle response
 335             method = r['method']
 336             params = r['params']
 337             result = r['result']
 338
 339             if method == 'blockchain.block.get_header':
 340                 return result
 341
 342
 343
 344     def get_chain(self, interface, final_header):
 345
 346         header = final_header
 347         chain = [ final_header ]
 348         requested_header = False
 349         queue = Queue.Queue()
 350
 351         while self.is_running():
 352
 353             if requested_header:
 354                 header = self.retrieve_header(interface, queue)
 355                 if not header: return
 356                 chain = [ header ] + chain
 357                 requested_header = False
 358
 359             height = header.get('block_height')
 360             previous_header = self.read_header(height -1)
 361             if not previous_header:
 362                 self.request_header(interface, height - 1, queue)
 363                 requested_header = True
 364                 continue
 365
 366             # verify that it connects to my chain
 367             prev_hash = self.hash_header(previous_header)
 368             if prev_hash != header.get('prev_block_hash'):
 369                 print_error("reorg")
 370                 self.request_header(interface, height - 1, queue)
 371                 requested_header = True
 372                 continue
 373
 374             else:
 375                 # the chain is complete
 376                 return chain
 377
 378
 379     def get_and_verify_chunks(self, i, header, height):
 380         requested_chunks = []
 381         queue = Queue.Queue()
 382         min_index = (self.local_height + 1)/2016
 383         max_index = (height + 1)/2016
 384         for n in range(min_index, max_index + 1):
 385             print_error( "requesting chunk", n )
 386             i.send([ ('blockchain.block.get_chunk',[n])], lambda i,r:queue.put(r))
 387             requested_chunks.append(n)
 388             break
 389
 390         while requested_chunks:
 391             try:
 392                 r = queue.get(timeout=1)
 393             except Queue.Empty:
 394                 continue
 395             if not r: continue
 396
 397             if r.get('error'):
 398                 print_error('Verifier received an error:', r)
 399                 continue
 400
 401             # 3. handle response
 402             params = r['params']
 403             result = r['result']
 404
 405             index = params[0]
 406             try:
 407                 self.verify_chunk(index, result)
 408             except:
 409                 return False
 410             requested_chunks.remove(index)
 411
 412         return True
 413
 414
 415
 416
 417
 418
 419