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_merkle = []
  57         requested_chunks = []
  58         requested_headers = []
  59         all_chunks = False
  60
  61         # subscribe to block headers
  62         self.interface.send([ ('blockchain.headers.subscribe',[])], 'verifier')
  63
  64         while self.is_running():
  65             # request missing chunks
  66             if not all_chunks and self.height and not requested_chunks:
  67
  68                 if self.local_height + 50 < self.height:
  69                     min_index = (self.local_height + 1)/2016
  70                     max_index = (self.height + 1)/2016
  71                     for i in range(min_index, max_index + 1):
  72                         print_error( "requesting chunk", i )
  73                         self.interface.send([ ('blockchain.block.get_chunk',[i])], 'verifier')
  74                         requested_chunks.append(i)
  75                         break
  76                 else:
  77                     all_chunks = True
  78                     print_error("downloaded all chunks")
  79
  80
  81             # process pending headers
  82             if self.pending_headers and all_chunks:
  83                 done = []
  84                 for header in self.pending_headers:
  85                     if self.verify_header(header):
  86                         done.append(header)
  87                     else:
  88                         # request previous header
  89                         i = header.get('block_height') - 1
  90                         if i not in requested_headers:
  91                             print_error("requesting header %d"%i)
  92                             self.interface.send([ ('blockchain.block.get_header',[i])], 'verifier')
  93                             requested_headers.append(i)
  94                         # no point continuing
  95                         break
  96                 if done:
  97                     self.interface.trigger_callback('updated')
  98                     for header in done:
  99                         self.pending_headers.remove(header)
 100
 101             try:
 102                 r = self.interface.get_response('verifier',timeout=1)
 103             except Queue.Empty:
 104                 continue
 105             if not r: continue
 106
 107             if r.get('error'):
 108                 print_error('Verifier received an error:', r)
 109                 continue
 110
 111             # 3. handle response
 112             method = r['method']
 113             params = r['params']
 114             result = r['result']
 115
 116             if method == 'blockchain.block.get_chunk':
 117                 index = params[0]
 118                 self.verify_chunk(index, result)
 119                 requested_chunks.remove(index)
 120
 121             elif method in ['blockchain.headers.subscribe', 'blockchain.block.get_header']:
 122
 123                 self.pending_headers.append(result)
 124                 if method == 'blockchain.block.get_header':
 125                     requested_headers.remove(result.get('block_height'))
 126                 else:
 127                     self.height = result.get('block_height')
 128                     ## fixme # self.interface.poke('synchronizer')
 129
 130                 self.pending_headers.sort(key=lambda x: x.get('block_height'))
 131                 # print "pending headers", map(lambda x: x.get('block_height'), self.pending_headers)
 132
 133
 134
 135
 136
 137     def verify_chunk(self, index, hexdata):
 138         data = hexdata.decode('hex')
 139         height = index*2016
 140         num = len(data)/80
 141         print_error("validating headers %d"%height)
 142
 143         if index == 0:
 144             previous_hash = ("0"*64)
 145         else:
 146             prev_header = self.read_header(index*2016-1)
 147             if prev_header is None: raise
 148             previous_hash = self.hash_header(prev_header)
 149
 150         bits, target = self.get_target(index)
 151
 152         for i in range(num):
 153             height = index*2016 + i
 154             raw_header = data[i*80:(i+1)*80]
 155             header = self.header_from_string(raw_header)
 156             _hash = self.hash_header(header)
 157             assert previous_hash == header.get('prev_block_hash')
 158             assert bits == header.get('bits')
 159             assert eval('0x'+_hash) < target
 160
 161             previous_header = header
 162             previous_hash = _hash
 163
 164         self.save_chunk(index, data)
 165
 166
 167     def verify_header(self, header):
 168         # add header to the blockchain file
 169         # if there is a reorg, push it in a stack
 170
 171         height = header.get('block_height')
 172
 173         prev_header = self.read_header(height -1)
 174         if not prev_header:
 175             # return False to request previous header
 176             return False
 177
 178         prev_hash = self.hash_header(prev_header)
 179         bits, target = self.get_target(height/2016)
 180         _hash = self.hash_header(header)
 181         try:
 182             assert prev_hash == header.get('prev_block_hash')
 183             assert bits == header.get('bits')
 184             assert eval('0x'+_hash) < target
 185         except:
 186             # this can be caused by a reorg.
 187             print_error("verify header failed"+ repr(header))
 188             # undo verifications
 189             with self.lock:
 190                 items = self.verified_tx.items()[:]
 191             for tx_hash, item in items:
 192                 tx_height, timestamp, pos = item
 193                 if tx_height >= height:
 194                     print_error("redoing", tx_hash)
 195                     with self.lock:
 196                         self.verified_tx.pop(tx_hash)
 197                         if tx_hash in self.merkle_roots:
 198                             self.merkle_roots.pop(tx_hash)
 199             # return False to request previous header.
 200             return False
 201
 202         self.save_header(header)
 203         print_error("verify header:", _hash, height)
 204         return True
 205
 206
 207
 208
 209     def header_to_string(self, res):
 210         s = int_to_hex(res.get('version'),4) \
 211             + rev_hex(res.get('prev_block_hash')) \
 212             + rev_hex(res.get('merkle_root')) \
 213             + int_to_hex(int(res.get('timestamp')),4) \
 214             + int_to_hex(int(res.get('bits')),4) \
 215             + int_to_hex(int(res.get('nonce')),4)
 216         return s
 217
 218
 219     def header_from_string(self, s):
 220         hex_to_int = lambda s: eval('0x' + s[::-1].encode('hex'))
 221         h = {}
 222         h['version'] = hex_to_int(s[0:4])
 223         h['prev_block_hash'] = hash_encode(s[4:36])
 224         h['merkle_root'] = hash_encode(s[36:68])
 225         h['timestamp'] = hex_to_int(s[68:72])
 226         h['bits'] = hex_to_int(s[72:76])
 227         h['nonce'] = hex_to_int(s[76:80])
 228         return h
 229
 230     def hash_header(self, header):
 231         return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
 232
 233     def path(self):
 234         wdir = self.config.get('blockchain_headers_path', user_dir())
 235         if wdir and not os.path.exists( wdir ): os.mkdir(wdir)
 236         return os.path.join( wdir, 'blockchain_headers')
 237
 238     def init_headers_file(self):
 239         filename = self.path()
 240         if os.path.exists(filename):
 241             return
 242
 243         try:
 244             import urllib, socket
 245             socket.setdefaulttimeout(30)
 246             print_error("downloading ", self.headers_url )
 247             urllib.urlretrieve(self.headers_url, filename)
 248         except:
 249             print_error( "download failed. creating file", filename )
 250             open(filename,'wb+').close()
 251
 252     def save_chunk(self, index, chunk):
 253         filename = self.path()
 254         f = open(filename,'rb+')
 255         f.seek(index*2016*80)
 256         h = f.write(chunk)
 257         f.close()
 258         self.set_local_height()
 259
 260     def save_header(self, header):
 261         data = self.header_to_string(header).decode('hex')
 262         assert len(data) == 80
 263         height = header.get('block_height')
 264         filename = self.path()
 265         f = open(filename,'rb+')
 266         f.seek(height*80)
 267         h = f.write(data)
 268         f.close()
 269         self.set_local_height()
 270
 271
 272     def set_local_height(self):
 273         name = self.path()
 274         if os.path.exists(name):
 275             h = os.path.getsize(name)/80 - 1
 276             if self.local_height != h:
 277                 self.local_height = h
 278
 279
 280     def read_header(self, block_height):
 281         name = self.path()
 282         if os.path.exists(name):
 283             f = open(name,'rb')
 284             f.seek(block_height*80)
 285             h = f.read(80)
 286             f.close()
 287             if len(h) == 80:
 288                 h = self.header_from_string(h)
 289                 return h
 290
 291
 292     def get_target(self, index):
 293
 294         max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
 295         if index == 0: return 0x1d00ffff, max_target
 296
 297         first = self.read_header((index-1)*2016)
 298         last = self.read_header(index*2016-1)
 299
 300         nActualTimespan = last.get('timestamp') - first.get('timestamp')
 301         nTargetTimespan = 14*24*60*60
 302         nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
 303         nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
 304
 305         bits = last.get('bits')
 306         # convert to bignum
 307         MM = 256*256*256
 308         a = bits%MM
 309         if a < 0x8000:
 310             a *= 256
 311         target = (a) * pow(2, 8 * (bits/MM - 3))
 312
 313         # new target
 314         new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
 315
 316         # convert it to bits
 317         c = ("%064X"%new_target)[2:]
 318         i = 31
 319         while c[0:2]=="00":
 320             c = c[2:]
 321             i -= 1
 322
 323         c = eval('0x'+c[0:6])
 324         if c > 0x800000:
 325             c /= 256
 326             i += 1
 327
 328         new_bits = c + MM * i
 329         return new_bits, new_target
 330