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, chain)
 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 int('0x'+_hash,16) < target
 122             except Exception:
 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 int('0x'+_hash,16) < 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
 162     def header_to_string(self, res):
 163         s = int_to_hex(res.get('version'),4) \
 164             + rev_hex(res.get('prev_block_hash')) \
 165             + rev_hex(res.get('merkle_root')) \
 166             + int_to_hex(int(res.get('timestamp')),4) \
 167             + int_to_hex(int(res.get('bits')),4) \
 168             + int_to_hex(int(res.get('nonce')),4)
 169         return s
 170
 171
 172     def header_from_string(self, s):
 173         hex_to_int = lambda s: int('0x' + s[::-1].encode('hex'), 16)
 174         h = {}
 175         h['version'] = hex_to_int(s[0:4])
 176         h['prev_block_hash'] = hash_encode(s[4:36])
 177         h['merkle_root'] = hash_encode(s[36:68])
 178         h['timestamp'] = hex_to_int(s[68:72])
 179         h['bits'] = hex_to_int(s[72:76])
 180         h['nonce'] = hex_to_int(s[76:80])
 181         return h
 182
 183     def hash_header(self, header):
 184         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 185
 186     def path(self):
 187         return os.path.join( self.config.path, 'blockchain_headers')
 188
 189     def init_headers_file(self):
 190         filename = self.path()
 191         if os.path.exists(filename):
 192             return
 193
 194         try:
 195             import urllib, socket
 196             socket.setdefaulttimeout(30)
 197             print_error("downloading ", self.headers_url )
 198             urllib.urlretrieve(self.headers_url, filename)
 199             print_error("done.")
 200         except Exception:
 201             print_error( "download failed. creating file", filename )
 202             open(filename,'wb+').close()
 203
 204     def save_chunk(self, index, chunk):
 205         filename = self.path()
 206         f = open(filename,'rb+')
 207         f.seek(index*2016*80)
 208         h = f.write(chunk)
 209         f.close()
 210         self.set_local_height()
 211
 212     def save_header(self, header):
 213         data = self.header_to_string(header).decode('hex')
 214         assert len(data) == 80
 215         height = header.get('block_height')
 216         filename = self.path()
 217         f = open(filename,'rb+')
 218         f.seek(height*80)
 219         h = f.write(data)
 220         f.close()
 221         self.set_local_height()
 222
 223
 224     def set_local_height(self):
 225         name = self.path()
 226         if os.path.exists(name):
 227             h = os.path.getsize(name)/80 - 1
 228             if self.local_height != h:
 229                 self.local_height = h
 230
 231
 232     def read_header(self, block_height):
 233         name = self.path()
 234         if os.path.exists(name):
 235             f = open(name,'rb')
 236             f.seek(block_height*80)
 237             h = f.read(80)
 238             f.close()
 239             if len(h) == 80:
 240                 h = self.header_from_string(h)
 241                 return h
 242
 243
 244     def get_target(self, index, chain=None):
 245         if chain is None:
 246             chain = []  # Do not use mutables as default values!
 247
 248         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 249         if index == 0: return 0x1d00ffff, max_target
 250
 251         first = self.read_header((index-1)*2016)
 252         last = self.read_header(index*2016-1)
 253         if last is None:
 254             for h in chain:
 255                 if h.get('block_height') == index*2016-1:
 256                     last = h
 257
 258         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 259         nTargetTimespan = 14*24*60*60
 260         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 261         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 262
 263         bits = last.get('bits')
 264         # convert to bignum
 265         MM = 256*256*256
 266         a = bits%MM
 267         if a < 0x8000:
 268             a *= 256
 269         target = (a) * pow(2, 8 * (bits/MM - 3))
 270
 271         # new target
 272         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 273
 274         # convert it to bits
 275         c = ("%064X"%new_target)[2:]
 276         i = 31
 277         while c[0:2]=="00":
 278             c = c[2:]
 279             i -= 1
 280
 281         c = int('0x'+c[0:6],16)
 282         if c >= 0x800000:
 283             c /= 256
 284             i += 1
 285
 286         new_bits = c + MM * i
 287         return new_bits, new_target
 288
 289
 290     def request_header(self, i, h, queue):
 291         print_error("requesting header %d from %s"%(h, i.server))
 292         i.send([ ('blockchain.block.get_header',[h])], lambda i,r: queue.put((i,r)))
 293
 294     def retrieve_header(self, i, queue):
 295         while True:
 296             try:
 297                 ir = queue.get(timeout=1)
 298             except Queue.Empty:
 299                 print_error('timeout')
 300                 continue
 301
 302             if not ir:
 303                 continue
 304
 305             i, r = ir
 306
 307             if r.get('error'):
 308                 print_error('Verifier received an error:', r)
 309                 continue
 310
 311             # 3. handle response
 312             method = r['method']
 313             params = r['params']
 314             result = r['result']
 315
 316             if method == 'blockchain.block.get_header':
 317                 return result
 318
 319
 320
 321     def get_chain(self, interface, final_header):
 322
 323         header = final_header
 324         chain = [ final_header ]
 325         requested_header = False
 326         queue = Queue.Queue()
 327
 328         while self.is_running():
 329
 330             if requested_header:
 331                 header = self.retrieve_header(interface, queue)
 332                 if not header: return
 333                 chain = [ header ] + chain
 334                 requested_header = False
 335
 336             height = header.get('block_height')
 337             previous_header = self.read_header(height -1)
 338             if not previous_header:
 339                 self.request_header(interface, height - 1, queue)
 340                 requested_header = True
 341                 continue
 342
 343             # verify that it connects to my chain
 344             prev_hash = self.hash_header(previous_header)
 345             if prev_hash != header.get('prev_block_hash'):
 346                 print_error("reorg")
 347                 self.request_header(interface, height - 1, queue)
 348                 requested_header = True
 349                 continue
 350
 351             else:
 352                 # the chain is complete
 353                 return chain
 354
 355
 356     def get_and_verify_chunks(self, i, header, height):
 357
 358         queue = Queue.Queue()
 359         min_index = (self.local_height + 1)/2016
 360         max_index = (height + 1)/2016
 361         n = min_index
 362         while n < max_index + 1:
 363             print_error( "Requesting chunk:", n )
 364             r = i.synchronous_get([ ('blockchain.block.get_chunk',[n])])[0]
 365             if not r:
 366                 continue
 367             try:
 368                 self.verify_chunk(n, r)
 369                 n = n + 1
 370             except Exception:
 371                 print_error('Verify chunk failed!')
 372                 n = n - 1
 373                 if n < 0:
 374                     return False
 375
 376         return True
 377