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