construct description of bitcoin block https://en.bitcoin.it/wiki/Protocol_specification

bcproto

'''Description of bitcoin binary protocol fragments'''

from construct import (Construct, ConstructError, Struct, Bytes, Array,
                       ULInt8, ULInt16, ULInt32, ULInt64)


class VarInt(Construct):
    def __init__(self, name):
        Construct.__init__(self, name)

    def _parse(self, stream, context):
        first = ULInt8('first')._parse(stream, context)

        if first < 0xfd:
            return first

        if first == 0xfd:
            return ULInt16('value')._parse(stream, context)

        if first == 0xfe:
            return ULInt32('value')._parse(stream, context)

        if first == 0xff:
            return ULInt64('value')._parse(stream, context)

        raise ConstructError('invalid value %r' % first)

    def _build(self, obj, stream, context):
        if obj < 0xfd:
            ULInt8('first')._build(obj, stream, context)

        elif obj < 2 ** 16:
            ULInt8('first')._build(0xfd, stream, context)
            ULInt16('value')._build(obj, stream, context)

        elif obj < 2 ** 32:
            ULInt8('first')._build(0xfe, stream, context)
            ULInt32('value')._build(obj, stream, context)

        else:
            ULInt8('first')._build(0xff, stream, context)
            ULInt64('value')._build(obj, stream, context)
            

TxInput = Struct(
    'txin',
    Bytes('prev_tx', 32),
    ULInt32('output_idx'),
    VarInt('script_length'),
    Bytes('script', lambda ctx: ctx.script_length),
    ULInt32('sequence')
)

TxOutput = Struct(
    'txout',
    ULInt64('value'),
    VarInt('script_length'),
    Bytes('script', lambda ctx: ctx.script_length)
)

Transaction = Struct(
    'tx',
    ULInt32('version'),
    VarInt('in_count'),
    Array(lambda ctx: ctx.in_count, TxInput),
    VarInt('out_count'),
    Array(lambda ctx: ctx.out_count, TxOutput),
    ULInt32('locktime')
)


Block = Struct(
    'block',
    ULInt32('version'),
    Bytes('prev_block', 32),
    Bytes('merkle_root', 32),
    ULInt32('unix_time'),
    ULInt32('difficulty'),
    ULInt32('nonce'),
    VarInt('tx_count'),
    Array(lambda ctx: ctx.tx_count, Transaction)
)