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.interface = interface
  33         self.interface.register_channel('verifier')
  34         self.lock = threading.Lock()
  35         self.pending_headers = [] # headers that have not been verified
  36         self.height = 0
  37         self.local_height = 0
  38         self.running = False
  39         self.headers_url = 'http://headers.electrum.org/blockchain_headers'
  40
  41
  42     def stop(self):
  43         with self.lock: self.running = False
  44         self.interface.poke('verifier')
  45
  46     def is_running(self):
  47         with self.lock: return self.running
  48
  49     def run(self):
  50
  51         self.init_headers_file()
  52         self.set_local_height()
  53
  54         with self.lock:
  55             self.running = True
  56         requested_chunks = []
  57         requested_headers = []
  58         all_chunks = False
  59
  60         # subscribe to block headers
  61         self.interface.send([ ('blockchain.headers.subscribe',[])], 'verifier')
  62
  63         while self.is_running():
  64             # request missing chunks
  65             if not all_chunks and self.height and not requested_chunks:
  66
  67                 if self.local_height + 50 < self.height:
  68                     min_index = (self.local_height + 1)/2016
  69                     max_index = (self.height + 1)/2016
  70                     for i in range(min_index, max_index + 1):
  71                         print_error( "requesting chunk", i )
  72                         self.interface.send([ ('blockchain.block.get_chunk',[i])], 'verifier')
  73                         requested_chunks.append(i)
  74                         break
  75                 else:
  76                     all_chunks = True
  77                     print_error("downloaded all chunks")
  78
  79
  80             # process pending headers
  81             if self.pending_headers and all_chunks:
  82                 done = []
  83                 for header in self.pending_headers:
  84                     if self.verify_header(header):
  85                         done.append(header)
  86                     else:
  87                         # request previous header
  88                         i = header.get('block_height') - 1
  89                         if i not in requested_headers:
  90                             print_error("requesting header %d"%i)
  91                             self.interface.send([ ('blockchain.block.get_header',[i])], 'verifier')
  92                             requested_headers.append(i)
  93                         # no point continuing
  94                         break
  95                 if done:
  96                     self.interface.trigger_callback('updated')
  97                     for header in done:
  98                         self.pending_headers.remove(header)
  99
 100             try:
 101                 r = self.interface.get_response('verifier',timeout=1)
 102             except Queue.Empty:
 103                 continue
 104             if not r: continue
 105
 106             if r.get('error'):
 107                 print_error('Verifier received an error:', r)
 108                 continue
 109
 110             # 3. handle response
 111             method = r['method']
 112             params = r['params']
 113             result = r['result']
 114
 115             if method == 'blockchain.block.get_chunk':
 116                 index = params[0]
 117                 self.verify_chunk(index, result)
 118                 requested_chunks.remove(index)
 119
 120             elif method in ['blockchain.headers.subscribe', 'blockchain.block.get_header']:
 121
 122                 self.pending_headers.append(result)
 123                 if method == 'blockchain.block.get_header':
 124                     requested_headers.remove(result.get('block_height'))
 125                 else:
 126                     self.height = result.get('block_height')
 127                     ## fixme # self.interface.poke('synchronizer')
 128
 129                 self.pending_headers.sort(key=lambda x: x.get('block_height'))
 130                 # print "pending headers", map(lambda x: x.get('block_height'), self.pending_headers)
 131
 132
 133
 134
 135
 136     def verify_chunk(self, index, hexdata):
 137         data = hexdata.decode('hex')
 138         height = index*2016
 139         num = len(data)/80
 140         print_error("validating headers %d"%height)
 141
 142         if index == 0:
 143             previous_hash = ("0"*64)
 144         else:
 145             prev_header = self.read_header(index*2016-1)
 146             if prev_header is None: raise
 147             previous_hash = self.hash_header(prev_header)
 148
 149         bits, target = self.get_target(index)
 150
 151         for i in range(num):
 152             height = index*2016 + i
 153             raw_header = data[i*80:(i+1)*80]
 154             header = self.header_from_string(raw_header)
 155             _hash = self.hash_header(header)
 156             assert previous_hash == header.get('prev_block_hash')
 157             assert bits == header.get('bits')
 158             assert eval('0x'+_hash) < target
 159
 160             previous_header = header
 161             previous_hash = _hash
 162
 163         self.save_chunk(index, data)
 164
 165
 166     def verify_header(self, header):
 167         # add header to the blockchain file
 168         # if there is a reorg, push it in a stack
 169
 170         height = header.get('block_height')
 171
 172         prev_header = self.read_header(height -1)
 173         if not prev_header:
 174             # return False to request previous header
 175             return False
 176
 177         prev_hash = self.hash_header(prev_header)
 178         bits, target = self.get_target(height/2016)
 179         _hash = self.hash_header(header)
 180         try:
 181             assert prev_hash == header.get('prev_block_hash')
 182             assert bits == header.get('bits')
 183             assert eval('0x'+_hash) < target
 184         except:
 185             # this can be caused by a reorg.
 186             print_error("verify header failed"+ repr(header))
 187             # undo verifications
 188             with self.lock:
 189                 items = self.verified_tx.items()[:]
 190             for tx_hash, item in items:
 191                 tx_height, timestamp, pos = item
 192                 if tx_height >= height:
 193                     print_error("redoing", tx_hash)
 194                     with self.lock:
 195                         self.verified_tx.pop(tx_hash)
 196                         if tx_hash in self.merkle_roots:
 197                             self.merkle_roots.pop(tx_hash)
 198             # return False to request previous header.
 199             return False
 200
 201         self.save_header(header)
 202         print_error("verify header:", _hash, height)
 203         return True
 204
 205
 206
 207
 208     def header_to_string(self, res):
 209         s = int_to_hex(res.get('version'),4) \
 210             + rev_hex(res.get('prev_block_hash')) \
 211             + rev_hex(res.get('merkle_root')) \
 212             + int_to_hex(int(res.get('timestamp')),4) \
 213             + int_to_hex(int(res.get('bits')),4) \
 214             + int_to_hex(int(res.get('nonce')),4)
 215         return s
 216
 217
 218     def header_from_string(self, s):
 219         hex_to_int = lambda s: eval('0x' + s[::-1].encode('hex'))
 220         h = {}
 221         h['version'] = hex_to_int(s[0:4])
 222         h['prev_block_hash'] = hash_encode(s[4:36])
 223         h['merkle_root'] = hash_encode(s[36:68])
 224         h['timestamp'] = hex_to_int(s[68:72])
 225         h['bits'] = hex_to_int(s[72:76])
 226         h['nonce'] = hex_to_int(s[76:80])
 227         return h
 228
 229     def hash_header(self, header):
 230         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 231
 232     def path(self):
 233         return os.path.join( self.config.path, 'blockchain_headers')
 234
 235     def init_headers_file(self):
 236         filename = self.path()
 237         if os.path.exists(filename):
 238             return
 239
 240         try:
 241             import urllib, socket
 242             socket.setdefaulttimeout(30)
 243             print_error("downloading ", self.headers_url )
 244             urllib.urlretrieve(self.headers_url, filename)
 245         except:
 246             print_error( "download failed. creating file", filename )
 247             open(filename,'wb+').close()
 248
 249     def save_chunk(self, index, chunk):
 250         filename = self.path()
 251         f = open(filename,'rb+')
 252         f.seek(index*2016*80)
 253         h = f.write(chunk)
 254         f.close()
 255         self.set_local_height()
 256
 257     def save_header(self, header):
 258         data = self.header_to_string(header).decode('hex')
 259         assert len(data) == 80
 260         height = header.get('block_height')
 261         filename = self.path()
 262         f = open(filename,'rb+')
 263         f.seek(height*80)
 264         h = f.write(data)
 265         f.close()
 266         self.set_local_height()
 267
 268
 269     def set_local_height(self):
 270         name = self.path()
 271         if os.path.exists(name):
 272             h = os.path.getsize(name)/80 - 1
 273             if self.local_height != h:
 274                 self.local_height = h
 275
 276
 277     def read_header(self, block_height):
 278         name = self.path()
 279         if os.path.exists(name):
 280             f = open(name,'rb')
 281             f.seek(block_height*80)
 282             h = f.read(80)
 283             f.close()
 284             if len(h) == 80:
 285                 h = self.header_from_string(h)
 286                 return h
 287
 288
 289     def get_target(self, index):
 290
 291         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 292         if index == 0: return 0x1d00ffff, max_target
 293
 294         first = self.read_header((index-1)*2016)
 295         last = self.read_header(index*2016-1)
 296
 297         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 298         nTargetTimespan = 14*24*60*60
 299         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 300         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 301
 302         bits = last.get('bits')
 303         # convert to bignum
 304         MM = 256*256*256
 305         a = bits%MM
 306         if a < 0x8000:
 307             a *= 256
 308         target = (a) * pow(2, 8 * (bits/MM - 3))
 309
 310         # new target
 311         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 312
 313         # convert it to bits
 314         c = ("%064X"%new_target)[2:]
 315         i = 31
 316         while c[0:2]=="00":
 317             c = c[2:]
 318             i -= 1
 319
 320         c = eval('0x'+c[0:6])
 321         if c > 0x800000:
 322             c /= 256
 323             i += 1
 324
 325         new_bits = c + MM * i
 326         return new_bits, new_target
 327
 328
 329