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257 lines
8.1 KiB
257 lines
8.1 KiB
#!/usr/bin/env python
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#
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# Electrum - lightweight Bitcoin client
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# Copyright (C) 2012 thomasv@ecdsa.org
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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import os
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import util
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from bitcoin import *
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class Blockchain():
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'''Manages blockchain headers and their verification'''
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def __init__(self, config, network):
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self.config = config
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self.network = network
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self.headers_url = 'https://headers.electrum.org/blockchain_headers'
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self.local_height = 0
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self.set_local_height()
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def print_error(self, *msg):
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util.print_error("[blockchain]", *msg)
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def height(self):
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return self.local_height
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def init(self):
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self.init_headers_file()
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self.set_local_height()
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self.print_error("%d blocks" % self.local_height)
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def verify_chain(self, chain):
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first_header = chain[0]
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prev_header = self.read_header(first_header.get('block_height') -1)
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for header in chain:
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height = header.get('block_height')
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prev_hash = self.hash_header(prev_header)
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bits, target = self.get_target(height/2016, chain)
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_hash = self.hash_header(header)
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try:
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assert prev_hash == header.get('prev_block_hash')
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assert bits == header.get('bits')
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assert int('0x'+_hash,16) < target
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except Exception:
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return False
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prev_header = header
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return True
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def verify_chunk(self, index, hexdata):
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data = hexdata.decode('hex')
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height = index*2016
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num = len(data)/80
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if index == 0:
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previous_hash = ("0"*64)
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else:
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prev_header = self.read_header(index*2016-1)
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if prev_header is None: raise
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previous_hash = self.hash_header(prev_header)
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bits, target = self.get_target(index)
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for i in range(num):
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height = index*2016 + i
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raw_header = data[i*80:(i+1)*80]
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header = self.header_from_string(raw_header)
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_hash = self.hash_header(header)
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assert previous_hash == header.get('prev_block_hash')
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assert bits == header.get('bits')
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assert int('0x'+_hash,16) < target
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previous_header = header
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previous_hash = _hash
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self.save_chunk(index, data)
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self.print_error("validated chunk %d to height %d" % (index, height))
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def header_to_string(self, res):
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s = int_to_hex(res.get('version'),4) \
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+ rev_hex(res.get('prev_block_hash')) \
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+ rev_hex(res.get('merkle_root')) \
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+ int_to_hex(int(res.get('timestamp')),4) \
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+ int_to_hex(int(res.get('bits')),4) \
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+ int_to_hex(int(res.get('nonce')),4)
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return s
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def header_from_string(self, s):
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hex_to_int = lambda s: int('0x' + s[::-1].encode('hex'), 16)
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h = {}
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h['version'] = hex_to_int(s[0:4])
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h['prev_block_hash'] = hash_encode(s[4:36])
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h['merkle_root'] = hash_encode(s[36:68])
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h['timestamp'] = hex_to_int(s[68:72])
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h['bits'] = hex_to_int(s[72:76])
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h['nonce'] = hex_to_int(s[76:80])
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return h
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def hash_header(self, header):
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return rev_hex(Hash(self.header_to_string(header).decode('hex')).encode('hex'))
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def path(self):
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return os.path.join(self.config.path, 'blockchain_headers')
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def init_headers_file(self):
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filename = self.path()
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if os.path.exists(filename):
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return
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try:
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import urllib, socket
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socket.setdefaulttimeout(30)
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self.print_error("downloading ", self.headers_url )
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urllib.urlretrieve(self.headers_url, filename)
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self.print_error("done.")
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except Exception:
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self.print_error( "download failed. creating file", filename )
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open(filename,'wb+').close()
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def save_chunk(self, index, chunk):
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filename = self.path()
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f = open(filename,'rb+')
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f.seek(index*2016*80)
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h = f.write(chunk)
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f.close()
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self.set_local_height()
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def save_header(self, header):
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data = self.header_to_string(header).decode('hex')
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assert len(data) == 80
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height = header.get('block_height')
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filename = self.path()
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f = open(filename,'rb+')
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f.seek(height*80)
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h = f.write(data)
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f.close()
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self.set_local_height()
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def set_local_height(self):
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name = self.path()
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if os.path.exists(name):
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h = os.path.getsize(name)/80 - 1
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if self.local_height != h:
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self.local_height = h
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def read_header(self, block_height):
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name = self.path()
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if os.path.exists(name):
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f = open(name,'rb')
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f.seek(block_height*80)
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h = f.read(80)
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f.close()
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if len(h) == 80:
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h = self.header_from_string(h)
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return h
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def get_target(self, index, chain=None):
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if chain is None:
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chain = [] # Do not use mutables as default values!
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max_target = 0x00000000FFFF0000000000000000000000000000000000000000000000000000
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if index == 0: return 0x1d00ffff, max_target
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first = self.read_header((index-1)*2016)
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last = self.read_header(index*2016-1)
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if last is None:
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for h in chain:
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if h.get('block_height') == index*2016-1:
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last = h
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nActualTimespan = last.get('timestamp') - first.get('timestamp')
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nTargetTimespan = 14*24*60*60
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nActualTimespan = max(nActualTimespan, nTargetTimespan/4)
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nActualTimespan = min(nActualTimespan, nTargetTimespan*4)
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bits = last.get('bits')
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# convert to bignum
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MM = 256*256*256
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a = bits%MM
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if a < 0x8000:
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a *= 256
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target = (a) * pow(2, 8 * (bits/MM - 3))
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# new target
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new_target = min( max_target, (target * nActualTimespan)/nTargetTimespan )
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# convert it to bits
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c = ("%064X"%new_target)[2:]
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i = 31
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while c[0:2]=="00":
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c = c[2:]
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i -= 1
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c = int('0x'+c[0:6],16)
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if c >= 0x800000:
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c /= 256
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i += 1
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new_bits = c + MM * i
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return new_bits, new_target
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def connect_header(self, chain, header):
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'''Builds a header chain until it connects. Returns True if it has
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successfully connected, False if verification failed, otherwise the
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height of the next header needed.'''
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chain.append(header) # Ordered by decreasing height
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previous_height = header['block_height'] - 1
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previous_header = self.read_header(previous_height)
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# Missing header, request it
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if not previous_header:
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return previous_height
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# Does it connect to my chain?
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prev_hash = self.hash_header(previous_header)
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if prev_hash != header.get('prev_block_hash'):
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self.print_error("reorg")
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return previous_height
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# The chain is complete. Reverse to order by increasing height
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chain.reverse()
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if self.verify_chain(chain):
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self.print_error("connected at height:", previous_height)
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for header in chain:
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self.save_header(header)
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return True
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return False
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def connect_chunk(self, idx, chunk):
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try:
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self.verify_chunk(idx, chunk)
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return idx + 1
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except Exception:
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self.print_error('verify_chunk failed')
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return idx - 1
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