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