blockchain.py

# Electrum - lightweight Bitcoin client
# Copyright (C) 2012 thomasv@ecdsa.org
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
import gzip
import threading
from time import sleep

from .equihash import is_gbp_valid
from . import util
from . import constants
from .bitcoin import *

blockchains = {}
'''
Postfork BTH headers are ~10x bigger, so we need compression.
This makes initial sync a bit slower but saves tons of storage.
'''
USE_COMPRESSSION = False
COMPRESSION_LEVEL = 1


# Encapsulated read/write to switch between non-compressed and compressed files by only changing USE_COMPRESSION flag
def read_file(filename, callback, lock):
    if callable(callback):
        with lock:
            if USE_COMPRESSSION:
                with gzip.open(filename, 'rb') as f:
                    return callback(f)
            else:
                with open(filename, 'rb') as f:
                    return callback(f)


def write_file(filename, callback, lock, mode='rb+'):
    if callable(callback):
        with lock:
            if USE_COMPRESSSION:
                with gzip.open(filename, 'wb', COMPRESSION_LEVEL) as f:
                    callback(f)
            else:
                with open(filename, mode) as f:
                    callback(f)


def serialize_header(header, legacy=False):
    s = int_to_hex(header.get('version'), 4) \
        + rev_hex(header.get('prev_block_hash')) \
        + rev_hex(header.get('merkle_root'))

    if not legacy:
        s += int_to_hex(header.get('block_height'), 4) \
            + rev_hex(header.get('reserved'))

    s += int_to_hex(header.get('timestamp'), 4) \
        + int_to_hex(header.get('bits'), 4)

    if legacy:
        s += rev_hex(header.get('nonce'))[:8]
    else:
        s += rev_hex(header.get('nonce')) \
             + rev_hex(header.get('solution'))

    return s


def deserialize_header(header, height):
    if not header:
        raise Exception('Invalid header: {}'.format(header))
    h = dict(
        block_height=height,
        version=hex_to_int(header[0:4]),
        prev_block_hash=hash_encode(header[4:36]),
        merkle_root=hash_encode(header[36:68]),
        reserved=hash_encode(header[72:100]),
        timestamp=hex_to_int(header[100:104]),
        bits=hex_to_int(header[104:108]),
        nonce=hash_encode(header[108:140]),
        solution=hash_encode(header[140:])
    )

    return h


def hash_header(header, height):
    if header is None:
        return '0' * 64
    if header.get('prev_block_hash') is None:
        header['prev_block_hash'] = '00'*32
    return hash_encode(Hash(bfh(serialize_header(header, (not is_post_bth_fork(height))))))


def read_blockchains(config):
    blockchains[0] = Blockchain(config, 0, None)
    fdir = os.path.join(util.get_headers_dir(config), 'forks')
    if not os.path.exists(fdir):
        os.mkdir(fdir)
    l = filter(lambda x: x.startswith('fork_'), os.listdir(fdir))
    l = sorted(l, key = lambda x: int(x.split('_')[1]))
    for filename in l:
        checkpoint = int(filename.split('_')[2])
        parent_id = int(filename.split('_')[1])
        b = Blockchain(config, checkpoint, parent_id)
        h = b.read_header(b.checkpoint)
        if b.parent().can_connect(h, check_height=False):
            blockchains[b.checkpoint] = b
        else:
            util.print_error("cannot connect", filename)
    return blockchains


def check_header(header):
    if type(header) is not dict:
        return False
    for b in blockchains.values():
        if b.check_header(header):
            return b
    return False


def can_connect(header):
    for b in blockchains.values():
        if b.can_connect(header):
            return b
    return False


class Blockchain(util.PrintError):
    """
    Manages blockchain headers and their verification
    """

    def __init__(self, config, checkpoint, parent_id):
        self.config = config
        # interface catching up
        self.catch_up = None
        self.checkpoint = checkpoint
        self.checkpoints = constants.net.CHECKPOINTS
        self.parent_id = parent_id
        self.lock = threading.Lock()
        self._size = 0
        self.update_size()
        util.set_verbosity(True)

    def parent(self):
        return blockchains[self.parent_id]

    def get_max_child(self):
        children = list(filter(lambda y: y.parent_id == self.checkpoint, blockchains.values()))
        return max([x.checkpoint for x in children]) if children else None

    def get_checkpoint(self):
        mc = self.get_max_child()
        return mc if mc is not None else self.checkpoint

    def get_branch_size(self):
        return self.height() - self.get_checkpoint() + 1

    def get_name(self):
        return self.get_hash(self.get_checkpoint()).lstrip('00')[0:10]

    def check_header(self, header):
        height = header.get('block_height')
        server_header_hash = hash_header(header, height)
        local_header_hash = self.get_hash(height)

        if server_header_hash != local_header_hash:
            self.print_error("Header hash mismatch " + "(" + str(height) + ") "
                             + server_header_hash + " != " + local_header_hash)

        return server_header_hash == local_header_hash

    def fork(parent, header):
        checkpoint = header.get('block_height')
        self = Blockchain(parent.config, checkpoint, parent.checkpoint)
        open(self.path(), 'w+').close()
        self.save_header(header)
        return self

    def height(self):
        return self.checkpoint + self.size() - 1

    def size(self):
        with self.lock:
            return self._size

    def update_size(self):
        p = self.path()
        if os.path.exists(p):
            def get_offset(f):
                return f.seek(0, 2)

            size = read_file(p, get_offset, self.lock)

            self._size = self.calculate_size(self.checkpoint, size)
        else:
            self._size = 0

    def calculate_size(self, checkpoint, size_in_bytes):
        # Pre-Fork
        prb = 0
        if not is_post_bth_fork(checkpoint):
            fork_byte_offset = constants.net.BTH_HEIGHT * constants.net.HEADER_SIZE_LEGACY
            offset = checkpoint * constants.net.HEADER_SIZE_LEGACY

            if offset + size_in_bytes > fork_byte_offset:
                prb = (fork_byte_offset - offset) // constants.net.HEADER_SIZE_LEGACY
                checkpoint = constants.net.BTH_HEIGHT
                size_in_bytes -= fork_byte_offset
            else:
                prb = size_in_bytes // constants.net.HEADER_SIZE_LEGACY

        # Post-fork
        pob = 0
        if is_post_bth_fork(checkpoint) and not is_post_equihash_fork(checkpoint):
            pob = (size_in_bytes // get_header_size(constants.net.BTH_HEIGHT))
            if is_post_equihash_fork((checkpoint + pob)):
                pob = constants.net.EQUIHASH_FORK_HEIGHT - checkpoint
                checkpoint = constants.net.EQUIHASH_FORK_HEIGHT
                size_in_bytes -= (pob * get_header_size(constants.net.BTH_HEIGHT))

        # Equihash-Fork
        peb = 0
        if is_post_equihash_fork(checkpoint):
            peb = size_in_bytes // get_header_size(constants.net.EQUIHASH_FORK_HEIGHT)

        return prb + pob + peb

    def verify_header(self, header, prev_hash, target):
        block_height = header.get('block_height')

        if prev_hash != header.get('prev_block_hash'):
            raise Exception("prev hash mismatch: %s vs %s" % (prev_hash, header.get('prev_block_hash')))
        bits = self.target_to_bits(target)
        if bits != header.get('bits'):
            raise Exception("bits mismatch: %s vs %s" % (bits, header.get('bits')))
        _hash = hash_header(header, block_height)
        if int('0x' + _hash, 16) > target:
            raise Exception("insufficient proof of work: %s vs target %s" % (int('0x' + _hash, 16), target))
        if is_post_bth_fork(block_height):
            header_bytes = bytes.fromhex(serialize_header(header))
            nonce = uint256_from_bytes(bfh(header.get('nonce'))[::-1])
            solution = bfh(header.get('solution'))[::-1]
            offset, length = var_int_read(solution, 0)
            solution = solution[offset:]

            params = get_equihash_params(block_height)

            if not is_gbp_valid(header_bytes, nonce, solution, params):
                raise Exception("Invalid equihash solution")

    def verify_chunk(self, height, data):
        size = len(data)
        offset = 0
        prev_hash = self.get_hash(height-1)

        headers = {}
        target = 0

        while offset < size:
            header_size = get_header_size(height)
            raw_header = data[offset:(offset + header_size)]
            header = deserialize_header(raw_header, height)
            headers[height] = header

            # Check retarget
            if needs_retarget(height) or target == 0:
                target = self.get_target(height, headers)

            self.verify_header(header, prev_hash, target)
            prev_hash = hash_header(header, height)
            offset += header_size
            height += 1

            # FIXME(wilson): Check why UI stalls. For now give it some processing time.
            sleep(0.001)

    def path(self):
        d = util.get_headers_dir(self.config)
        filename = 'blockchain_headers' if self.parent_id is None else os.path.join('forks', 'fork_%d_%d'%(self.parent_id, self.checkpoint))
        if USE_COMPRESSSION:
            filename += '.gz'
        return os.path.join(d, filename)

    def save_chunk(self, height, chunk):
        delta = height - self.checkpoint

        if delta < 0:
            chunk = chunk[-delta:]
            height = self.checkpoint

        offset = self.get_offset(self.checkpoint, height)

        self.write(chunk, offset, height // difficulty_adjustment_interval() > len(self.checkpoints))
        self.swap_with_parent()

    def swap_with_parent(self):
        if self.parent_id is None:
            return

        parent_branch_size = self.parent().height() - self.checkpoint + 1
        if parent_branch_size >= self.size():
            return

        self.print_error("swap", self.checkpoint, self.parent_id)
        parent_id = self.parent_id
        checkpoint = self.checkpoint
        parent = self.parent()

        def my_data_read(f):
            return f.read()

        my_data = read_file(self.path(), my_data_read, self.lock)

        offset = self.get_offset(parent.checkpoint, checkpoint)

        def parent_data_read(f):
            f.seek(offset)
            return f.read()

        parent_data = read_file(parent.path(), parent_data_read, parent.lock)

        self.write(parent_data, 0)
        parent.write(my_data, offset)

        # store file path
        for b in blockchains.values():
            b.old_path = b.path()
        # swap parameters
        self.parent_id = parent.parent_id
        parent.parent_id = parent_id

        self.checkpoint = parent.checkpoint
        parent.checkpoint = checkpoint

        self._size = parent._size
        parent._size = parent_branch_size

        # move files
        for b in blockchains.values():
            if b in [self, parent]:
                continue
            if b.old_path != b.path():
                self.print_error("renaming", b.old_path, b.path())
                os.rename(b.old_path, b.path())
        # update pointers
        blockchains[self.checkpoint] = self
        blockchains[parent.checkpoint] = parent

    def write(self, data, offset, truncate=True):
        filename = self.path()
        current_offset = self.get_offset(self.checkpoint, self.size())

        def write_data(f):
            if truncate and offset != current_offset:
                f.seek(offset)
                f.truncate()
            f.seek(offset)
            f.write(data)
            f.flush()
            os.fsync(f.fileno())

        write_file(filename, write_data, self.lock)

        self.update_size()

    def save_header(self, header):
        height = header.get('block_height')
        delta = height - self.checkpoint
        ser_header = serialize_header(header)

        offset = self.get_offset(self.checkpoint, height)
        header_size = get_header_size(height)
        data = bfh(ser_header)
        length = len(data)

        assert delta == self.size()
        assert length == header_size
        self.write(data, offset)

        self.swap_with_parent()

    def read_header(self, height):
        assert self.parent_id != self.checkpoint
        if height < 0:
            return
        if height < self.checkpoint:
            return self.parent().read_header(height)
        if height > self.height():
            return

        offset = self.get_offset(self.checkpoint, height)
        header_size = get_header_size(height)

        name = self.path()

        if os.path.exists(name):
            def get_header(f):
                f.seek(offset)
                return f.read(header_size)

            h = read_file(name, get_header, self.lock)
            if len(h) < header_size:
                raise Exception('Expected to read a full header. This was only {} bytes'.format(len(h)))
        elif not os.path.exists(util.get_headers_dir(self.config)):
            raise Exception('ElectrumBTH datadir does not exist. Was it deleted while running?')
        else:
            raise Exception('Cannot find headers file but datadir is there. Should be at {}'.format(name))
        if h == bytes([0])*header_size:
            return None
        return deserialize_header(h, height)

    def get_header(self, height, headers=None):
        if headers is None:
            headers = {}

        return headers[height] if height in headers else self.read_header(height)

    def get_hash(self, height):
        if height == -1:
            return '0000000000000000000000000000000000000000000000000000000000000000'
        elif height == 0:
            return constants.net.GENESIS
        elif height < len(self.checkpoints) * difficulty_adjustment_interval() and (height + 1) % difficulty_adjustment_interval() == 0:
            index = height // difficulty_adjustment_interval()
            h, t = self.checkpoints[index]
            return h
        else:
            return hash_header(self.read_header(height), height)

    def get_target(self, height, headers=None):
        if headers is None:
            headers = {}

        # Check for genesis
        if height == 0:
            new_target = constants.net.POW_LIMIT_LEGACY
        # Check for valid checkpoint
        elif height % difficulty_adjustment_interval() == 0 and 0 <= ((height // difficulty_adjustment_interval()) - 1) < len(self.checkpoints):
            h, t = self.checkpoints[((height // difficulty_adjustment_interval()) - 1)]
            new_target = t
        # Check for prefork
        elif height < constants.net.BTH_HEIGHT:
            new_target = self.get_legacy_target(height, headers)
        # Premine
        elif height < constants.net.BTH_HEIGHT + constants.net.PREMINE_SIZE:
            new_target = constants.net.POW_LIMIT
        # Initial start of BTH Fork (reduced difficulty)
        elif height < constants.net.BTH_HEIGHT + constants.net.PREMINE_SIZE + constants.net.DIGI_AVERAGING_WINDOW:
            new_target = constants.net.POW_LIMIT_START
        # Digishield
        elif height < constants.net.LWMA_HEIGHT:
            new_target = self.get_digishield_target(height, headers)
        # Zawy LWMA (old)
        elif height < constants.net.EQUIHASH_FORK_HEIGHT:
            new_target = self.get_lwma_target(height, headers, constants.net.LWMA_ADJUST_WEIGHT_LEGACY,
                                              constants.net.LWMA_MIN_DENOMINATOR_LEGACY)
        # Initial start of BTH Equihash Fork (reduced difficulty)
        elif height < constants.net.EQUIHASH_FORK_HEIGHT + constants.net.LWMA_AVERAGING_WINDOW:
            last = self.get_header((height - 1), headers)
            bits = last.get('bits')
            new_target = self.bits_to_target(bits)

            if height == constants.net.EQUIHASH_FORK_HEIGHT:
                # reduce diff
                new_target *= 100

                if new_target > constants.net.POW_LIMIT:
                    new_target = constants.net.POW_LIMIT
        # Zawy LWMA (new)
        else:
            new_target = self.get_lwma_target(height, headers, constants.net.LWMA_ADJUST_WEIGHT,
                                              constants.net.LWMA_MIN_DENOMINATOR)

        return new_target

    def get_legacy_target(self, height, headers):
        last_height = (height - 1)
        last = self.get_header(last_height, headers)

        if constants.net.REGTEST:
            new_target = self.bits_to_target(last.get('bits'))
        elif height % difficulty_adjustment_interval() != 0:
            if constants.net.TESTNET:
                cur = self.get_header(height, headers)

                # Special testnet handling
                if cur.get('timestamp') > last.get('timestamp') + constants.net.POW_TARGET_SPACING * 2:
                    new_target = constants.net.POW_LIMIT_LEGACY
                else:
                    # Return the last non-special-min-difficulty-rules-block
                    prev_height = last_height - 1
                    prev = self.get_header(prev_height, headers)

                    while prev is not None and last.get('block_height') % difficulty_adjustment_interval() != 0 \
                            and last.get('bits') == constants.net.POW_LIMIT:
                        last = prev
                        prev_height -= 1
                        prev = self.get_header(prev_height, headers)

                    new_target = self.bits_to_target(last.get('bits'))
            else:
                new_target = self.bits_to_target(last.get('bits'))
        else:
            first = self.read_header(height - difficulty_adjustment_interval())
            target = self.bits_to_target(last.get('bits'))

            actual_timespan = last.get('timestamp') - first.get('timestamp')
            target_timespan = constants.net.POW_TARGET_TIMESPAN_LEGACY
            actual_timespan = max(actual_timespan, target_timespan // 4)
            actual_timespan = min(actual_timespan, target_timespan * 4)

            new_target = min(constants.net.POW_LIMIT_LEGACY, (target * actual_timespan) // target_timespan)

        return new_target

    def get_lwma_target(self, height, headers, weight, denominator):
        cur = self.get_header(height, headers)
        last_height = (height - 1)
        last = self.get_header(last_height, headers)

        # Special testnet handling
        if constants.net.REGTEST:
            new_target = self.bits_to_target(last.get('bits'))
        elif constants.net.TESTNET and cur.get('timestamp') > last.get('timestamp') + constants.net.POW_TARGET_SPACING * 2:
            new_target = constants.net.POW_LIMIT
        else:
            total = 0
            t = 0
            j = 0

            assert (height - constants.net.LWMA_AVERAGING_WINDOW) > 0

            ts = 6 * constants.net.POW_TARGET_SPACING

            # Loop through N most recent blocks.  "< height", not "<=".
            # height-1 = most recently solved block
            for i in range(height - constants.net.LWMA_AVERAGING_WINDOW, height):
                cur = self.get_header(i, headers)
                prev_height = (i - 1)
                prev = self.get_header(prev_height, headers)

                solvetime = cur.get('timestamp') - prev.get('timestamp')

                if constants.net.LWMA_SOLVETIME_LIMITATION and solvetime > ts:
                    solvetime = ts

                j += 1
                t += solvetime * j
                total += self.bits_to_target(cur.get('bits')) // (weight * constants.net.LWMA_AVERAGING_WINDOW * constants.net.LWMA_AVERAGING_WINDOW)

            # Keep t reasonable in case strange solvetimes occurred.
            if t < constants.net.LWMA_AVERAGING_WINDOW * weight // denominator:
                t = constants.net.LWMA_AVERAGING_WINDOW * weight // denominator

            new_target = t * total

            if new_target > constants.net.POW_LIMIT:
                new_target = constants.net.POW_LIMIT

        return new_target

    def get_digishield_target(self, height, headers):
        pow_limit = constants.net.POW_LIMIT
        height -= 1
        last = self.get_header(height, headers)

        if last is None:
            new_target = pow_limit
        elif constants.net.REGTEST:
            new_target = self.bits_to_target(last.get('bits'))
        else:
            first = last
            total = 0
            i = 0

            while i < constants.net.DIGI_AVERAGING_WINDOW and first is not None:
                total += self.bits_to_target(first.get('bits'))
                prev_height = height - i - 1
                first = self.get_header(prev_height, headers)
                i += 1

            # This should never happen else we have a serious problem
            assert first is not None

            avg = total // constants.net.DIGI_AVERAGING_WINDOW
            actual_timespan = self.get_mediantime_past(headers, last.get('block_height')) \
                - self.get_mediantime_past(headers, first.get('block_height'))

            if actual_timespan < min_actual_timespan():
                actual_timespan = min_actual_timespan()

            if actual_timespan > max_actual_timespan():
                actual_timespan = max_actual_timespan()

            avg = avg // averaging_window_timespan()
            avg *= actual_timespan

            if avg > pow_limit:
                avg = pow_limit

            new_target = int(avg)

        return new_target

    def get_mediantime_past(self, headers, start_height):
        header = self.get_header(start_height, headers)

        times = []
        i = 0

        while i < 11 and header is not None:
            times.append(header.get('timestamp'))
            prev_height = start_height - i - 1
            header = self.get_header(prev_height, headers)
            i += 1

        times.sort()
        return times[(len(times) // 2)]

    def bits_to_target(self, bits):
        size = bits >> 24
        word = bits & 0x007fffff

        if size <= 3:
            word >>= 8 * (3 - size)
            ret = word
        else:
            ret = word
            ret <<= 8 * (size - 3)

        return ret

    def target_to_bits(self, target):
        assert target >= 0
        nsize = (target.bit_length() + 7) // 8
        if nsize <= 3:
            c = target << (8 * (3 - nsize))
        else:
            c = target >> (8 * (nsize - 3))
        if c & 0x00800000:
            c >>= 8
            nsize += 1
        assert (c & ~0x007fffff) == 0
        assert nsize < 256
        c |= nsize << 24
        return c

    def can_connect(self, header, check_height=True):
        if header is None:
            return False
        height = header['block_height']
        if check_height and self.height() != height - 1:
            self.print_error("cannot connect at height", height)
            return False
        if height == 0:
            return hash_header(header, height) == constants.net.GENESIS
        try:
            prev_hash = self.get_hash(height - 1)
        except:
            return False
        if prev_hash != header.get('prev_block_hash'):
            return False
        target = self.get_target(height, {height: header})
        try:
            self.verify_header(header, prev_hash, target)
        except BaseException as e:
            return False
        return True

    def connect_chunk(self, idx, hexdata):
        try:
            data = bfh(hexdata)
            self.verify_chunk(idx * constants.net.CHUNK_SIZE, data)
            self.print_error("validated chunk %d" % idx)
            self.save_chunk(idx * constants.net.CHUNK_SIZE, data)
            return True
        except BaseException as e:
            self.print_error('verify_chunk %d failed'%idx, str(e))
            return False

    def get_offset(self, checkpoint, height):
        # Pre-Fork
        prb = 0
        if not is_post_bth_fork(height):
            prb = height - checkpoint
        elif not is_post_bth_fork(checkpoint):
            prb = constants.net.BTH_HEIGHT - checkpoint

        # Equihash Fork
        peb = 0
        if is_post_equihash_fork(height):
            peb = height - max(checkpoint, constants.net.EQUIHASH_FORK_HEIGHT)

        # Post-fork
        pob = 0
        if is_post_bth_fork(height):
            pob = height - max(checkpoint, constants.net.BTH_HEIGHT) - peb

        offset = (prb * constants.net.HEADER_SIZE_LEGACY) \
            + (pob * get_header_size(constants.net.BTH_HEIGHT)) \
            + (peb * get_header_size(constants.net.EQUIHASH_FORK_HEIGHT))

        return offset

    def get_checkpoints(self):
        # for each chunk, store the hash of the last block and the target after the chunk
        cp = []
        diff_adj = difficulty_adjustment_interval()
        n = self.height() // diff_adj
        for index in range(n):
            height = (index + 1) * diff_adj

            if is_post_bth_fork(height):
                break

            h = self.get_hash(height - 1)
            target = self.get_target(height)
            cp.append((h, target))
        return cp