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