OP_RETURN.py

# OP_RETURN.py
#
# Python script to generate and retrieve OP_RETURN bitcoin transactions
#
# Copyright (c) Coin Sciences Ltd
#
# 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.

from string import hexdigits
import codecs
import binascii
import hashlib
import json
import os.path
import random
import re
import struct
import subprocess
import time

basestring = str

# User-defined quasi-constants

OP_RETURN_BITCOIN_IP = '127.0.0.1'  # IP address of your bitcoin node
OP_RETURN_BITCOIN_USE_CMD = True  # use command-line instead of JSON-RPC?

if OP_RETURN_BITCOIN_USE_CMD:
    OP_RETURN_BITCOIN_PATH = '/usr/local/bin/dogecoin-cli'  # path to bitcoin-cli executable on this server

else:
    OP_RETURN_BITCOIN_PORT = ''  # leave empty to use default port for mainnet/testnet
    OP_RETURN_BITCOIN_USER = ''  # leave empty to read from ~/.dogecoin/dogecoin.conf (Unix only)
    OP_RETURN_BITCOIN_PASSWORD = ''  # leave empty to read from ~/.dogecoin/dogecoin.conf (Unix only)

OP_RETURN_BTC_FEE = 0.0001  # BTC fee to pay per transaction
OP_RETURN_BTC_DUST = 0.00001  # omit BTC outputs smaller than this

OP_RETURN_MAX_BYTES = 80  # maximum bytes in an OP_RETURN (80 as of Bitcoin 0.11)
OP_RETURN_MAX_BLOCKS = 10  # maximum number of blocks to try when retrieving data

OP_RETURN_NET_TIMEOUT = 10  # how long to time out (in seconds) when communicating with bitcoin node

SAT = 100000000  # coin divisible by how many satoshis


# User-facing functions

def OP_RETURN_send(send_address, send_amount, metadata, testnet=False):
    # Validate some parameters

    if not OP_RETURN_bitcoin_check(testnet):
        return {'error': 'Please check Bitcoin Core is running and OP_RETURN_BITCOIN_* constants are set correctly'}

    result = OP_RETURN_bitcoin_cmd('validateaddress', testnet, send_address)
    if not ('isvalid' in result and result['isvalid']):
        return {'error': 'Send address could not be validated: ' + send_address}

    if isinstance(metadata, basestring):
        metadata = metadata.encode('utf-8')  # convert to binary string

    metadata_len = len(metadata)

    if metadata_len > 65536:
        return {'error': 'This library only supports metadata up to 65536 bytes in size'}

    if metadata_len > OP_RETURN_MAX_BYTES:
        return {'error': 'Metadata has ' + str(metadata_len) + ' bytes but is limited to ' + str(
            OP_RETURN_MAX_BYTES) + ' (see OP_RETURN_MAX_BYTES)'}

    # Calculate amounts and choose inputs

    output_amount = send_amount + OP_RETURN_BTC_FEE

    inputs_spend = OP_RETURN_select_inputs(output_amount, testnet)

    if 'error' in inputs_spend:
        return {'error': inputs_spend['error']}

    change_amount = inputs_spend['total'] - output_amount

    # Build the raw transaction

    change_address = OP_RETURN_bitcoin_cmd('getrawchangeaddress', testnet)

    outputs = {send_address: send_amount}

    if change_amount >= OP_RETURN_BTC_DUST:
        outputs[change_address] = change_amount

    raw_txn = OP_RETURN_create_txn(inputs_spend['inputs'], outputs, metadata, len(outputs), testnet)

    # Sign and send the transaction, return result

    return OP_RETURN_sign_send_txn(raw_txn, testnet)


def OP_RETURN_store(data, testnet=False):
    # Data is stored in OP_RETURNs within a series of chained transactions.
    # If the OP_RETURN is followed by another output, the data continues in the transaction spending that output.
    # When the OP_RETURN is the last output, this also signifies the end of the data.

    # Validate parameters and get change address

    if not OP_RETURN_bitcoin_check(testnet):
        return {'error': 'Please check Bitcoin Core is running and OP_RETURN_BITCOIN_* constants are set correctly'}

    # if isinstance(data, basestring):
    #     data = data.encode('utf-8')  # convert to binary string

    len_data_in_bytes = len(data.encode('utf-8'))
    data_len = len(data)

    if data_len == 0:
        return {'error': 'Some data is required to be stored'}
    elif len_data_in_bytes > 80:
        return {'error': 'Data exceeds maximum size'}
    elif not all(it in hexdigits for it in data):
        data = binascii.hexlify(data.encode('utf-8'))
    else:
        data = data.encode()

    change_address = OP_RETURN_bitcoin_cmd('getrawchangeaddress', testnet)

    # Calculate amounts and choose first inputs to use

    output_amount = OP_RETURN_BTC_FEE * int(
        (data_len + OP_RETURN_MAX_BYTES - 1) / OP_RETURN_MAX_BYTES)  # number of transactions required

    inputs_spend = OP_RETURN_select_inputs(output_amount, testnet)
    if 'error' in inputs_spend:
        return {'error': inputs_spend['error']}

    inputs = inputs_spend['inputs']
    input_amount = inputs_spend['total']

    # Find the current blockchain height and mempool txids

    height = int(OP_RETURN_bitcoin_cmd('getblockcount', testnet))
    avoid_txids = OP_RETURN_bitcoin_cmd('getrawmempool', testnet)

    # Loop to build and send transactions

    result = {'txids': []}

    for data_ptr in range(0, data_len, OP_RETURN_MAX_BYTES):
        # Some preparation for this iteration

        last_txn = ((data_ptr + OP_RETURN_MAX_BYTES) >= data_len)  # is this the last tx in the chain?
        change_amount = (
                                int(input_amount * SAT) - int(OP_RETURN_BTC_FEE * SAT)
                        ) / SAT
        metadata = data[data_ptr:data_ptr + OP_RETURN_MAX_BYTES]

        # Build and send this transaction

        outputs = {}
        if change_amount >= OP_RETURN_BTC_DUST:  # might be skipped for last transaction
            outputs[change_address] = change_amount

        raw_txn = OP_RETURN_create_txn(inputs, outputs, metadata, len(outputs) if last_txn else 0, testnet)

        send_result = OP_RETURN_sign_send_txn(raw_txn, testnet)

        # Check for errors and collect the txid

        if 'error' in send_result:
            result['error'] = send_result['error']
            break

        result['txids'].append(send_result['txid'])

        if data_ptr == 0:
            result['ref'] = OP_RETURN_calc_ref(height, send_result['txid'], avoid_txids)

        # Prepare inputs for next iteration

        inputs = [{
            'txid': send_result['txid'],
            'vout': 1,
        }]

        input_amount = change_amount

    # Return the final result

    return result


def OP_RETURN_check(transaction_hash, testnet=False):
    if not OP_RETURN_bitcoin_check(testnet):
        return {'error': 'Please check Bitcoin Core is running and OP_RETURN_BITCOIN_* constants are set correctly'}

    try:
        raw_transaction = OP_RETURN_bitcoin_cmd('getrawtransaction', testnet, transaction_hash)
    except Exception as e:
        return {'error': f"Couldn't find the specified transaction. Cause: {e}"}
    try:
        transaction_data = OP_RETURN_bitcoin_cmd('decoderawtransaction', testnet, raw_transaction)
    except Exception as e:
        return {'error': f"Couldn't decode the specified transaction. Cause: {e}"}

    results = dict()

    for output in transaction_data['vout']:
        if 'OP_RETURN' in output['scriptPubKey']['asm']:
            op_return_data = output['scriptPubKey']['asm'].split(' ')[1]
            results[op_return_data] = codecs.decode(op_return_data, 'hex').decode('utf-8')

    if not bool(results):
        return {'error': 'No OP_RETURN data found'}
    else:
        return results


def OP_RETURN_retrieve(ref, max_results=1, testnet=False):
    # Validate parameters and get status of Bitcoin Core

    if not OP_RETURN_bitcoin_check(testnet):
        return {'error': 'Please check Bitcoin Core is running and OP_RETURN_BITCOIN_* constants are set correctly'}

    max_height = int(OP_RETURN_bitcoin_cmd('getblockcount', testnet))
    heights = OP_RETURN_get_ref_heights(ref, max_height)

    if not isinstance(heights, list):
        return {'error': 'Ref is not valid'}

    # Collect and return the results

    results = []

    for height in heights:
        if height == 0:
            txids = OP_RETURN_list_mempool_txns(testnet)  # if mempool, only get list for now (to save RPC calls)
            txns = None
        else:
            txns = OP_RETURN_get_block_txns(height, testnet)  # if block, get all fully unpacked
            txids = txns.keys()

        for txid in txids:
            if OP_RETURN_match_ref_txid(ref, txid):
                if height == 0:
                    txn_unpacked = OP_RETURN_get_mempool_txn(txid, testnet)
                else:
                    txn_unpacked = txns[txid]

                found = OP_RETURN_find_txn_data(txn_unpacked)

                if found:
                    # Collect data from txid which matches ref and contains an OP_RETURN

                    result = {
                        'txids': [str(txid)],
                        'data': found['op_return'],
                    }

                    key_heights = {height: True}

                    # Work out which other block heights / mempool we should try

                    if height == 0:
                        try_heights = []  # nowhere else to look if first still in mempool
                    else:
                        result['ref'] = OP_RETURN_calc_ref(height, txid, txns.keys())
                        try_heights = OP_RETURN_get_try_heights(height + 1, max_height, False)

                    # Collect the rest of the data, if appropriate

                    if height == 0:
                        this_txns = OP_RETURN_get_mempool_txns(testnet)  # now retrieve all to follow chain
                    else:
                        this_txns = txns

                    last_txid = txid
                    this_height = height

                    while found['index'] < (len(txn_unpacked['vout']) - 1):  # this means more data to come
                        next_txid = OP_RETURN_find_spent_txid(this_txns, last_txid, found['index'] + 1)

                        # If we found the next txid in the data chain

                        if next_txid:
                            result['txids'].append(str(next_txid))

                            txn_unpacked = this_txns[next_txid]
                            found = OP_RETURN_find_txn_data(txn_unpacked)

                            if found:
                                result['data'] += found['op_return']
                                key_heights[this_height] = True
                            else:
                                result['error'] = 'Data incomplete - missing OP_RETURN'
                                break

                            last_txid = next_txid

                        # Otherwise move on to the next height to keep looking

                        else:
                            if len(try_heights):
                                this_height = try_heights.pop(0)

                                if this_height == 0:
                                    this_txns = OP_RETURN_get_mempool_txns(testnet)
                                else:
                                    this_txns = OP_RETURN_get_block_txns(this_height, testnet)

                            else:
                                result['error'] = 'Data incomplete - could not find next transaction'
                                break

                    # Finish up the information about this result

                    result['heights'] = list(key_heights.keys())
                    results.append(result)

        if len(results) >= max_results:
            break  # stop if we have collected enough

    return results


# Utility functions

def OP_RETURN_select_inputs(total_amount, testnet):
    # List and sort unspent inputs by priority

    unspent_inputs = OP_RETURN_bitcoin_cmd('listunspent', testnet, 0)
    if not isinstance(unspent_inputs, list):
        return {'error': 'Could not retrieve list of unspent inputs'}

    unspent_inputs.sort(key=lambda unspent_input: unspent_input['amount'] * unspent_input['confirmations'],
                        reverse=True)

    # Identify which inputs should be spent

    inputs_spend = []
    input_amount = 0

    for unspent_input in unspent_inputs:
        inputs_spend.append(unspent_input)

        input_amount += unspent_input['amount']
        if input_amount >= total_amount:
            break  # stop when we have enough

    if input_amount < total_amount:
        return {'error': 'Not enough funds are available to cover the amount and fee'}

    # Return the successful result

    return {
        'inputs': inputs_spend,
        'total': input_amount,
    }


def OP_RETURN_create_txn(inputs, outputs, metadata, metadata_pos, testnet):
    raw_txn = OP_RETURN_bitcoin_cmd('createrawtransaction', testnet, inputs, outputs)

    txn_unpacked = OP_RETURN_unpack_txn(OP_RETURN_hex_to_bin(raw_txn))

    metadata_len = len(metadata)

    if metadata_len <= 75:
        payload = bytearray((metadata_len,)) + metadata  # length byte + data (https://en.bitcoin.it/wiki/Script)
    elif metadata_len <= 256:
        payload = b"\x4c" + bytearray((metadata_len,)) + metadata  # OP_PUSHDATA1 format
    else:
        payload = b"\x4d" + bytearray((metadata_len % 256,)) + bytearray(
            (int(metadata_len / 256),)) + metadata  # OP_PUSHDATA2 format

    metadata_pos = min(max(0, metadata_pos), len(txn_unpacked['vout']))  # constrain to valid values

    txn_unpacked['vout'][metadata_pos:metadata_pos] = [{
        'value': 0,
        'scriptPubKey': '6a' + OP_RETURN_bin_to_hex(payload)  # here's the OP_RETURN
    }]

    return OP_RETURN_bin_to_hex(OP_RETURN_pack_txn(txn_unpacked))


def OP_RETURN_sign_send_txn(raw_txn, testnet):
    signed_txn = OP_RETURN_bitcoin_cmd('signrawtransaction', testnet, raw_txn)
    if not ('complete' in signed_txn and signed_txn['complete']):
        return {'error': 'Could not sign the transaction'}

    send_txid = OP_RETURN_bitcoin_cmd('sendrawtransaction', testnet, signed_txn['hex'])
    if not (isinstance(send_txid, basestring) and len(send_txid) == 64):
        return {'error': 'Could not send the transaction'}

    return {'txid': str(send_txid)}


def OP_RETURN_list_mempool_txns(testnet):
    return OP_RETURN_bitcoin_cmd('getrawmempool', testnet)


def OP_RETURN_get_mempool_txn(txid, testnet):
    raw_txn = OP_RETURN_bitcoin_cmd('getrawtransaction', testnet, txid)
    return OP_RETURN_unpack_txn(OP_RETURN_hex_to_bin(raw_txn))


def OP_RETURN_get_mempool_txns(testnet):
    txids = OP_RETURN_list_mempool_txns(testnet)

    txns = {}
    for txid in txids:
        txns[txid] = OP_RETURN_get_mempool_txn(txid, testnet)

    return txns


def OP_RETURN_get_raw_block(height, testnet):
    block_hash = OP_RETURN_bitcoin_cmd('getblockhash', testnet, height)

    if not (isinstance(block_hash, basestring) and len(block_hash) == 64):
        return {'error': 'Block at height ' + str(height) + ' not found'}

    block_data = OP_RETURN_hex_to_bin(OP_RETURN_bitcoin_cmd('getblock', testnet, block_hash, 'false'))

    return {
        'block': block_data
    }


def OP_RETURN_get_block_txns(height, testnet):
    raw_block = OP_RETURN_get_raw_block(height, testnet)
    if 'error' in raw_block:
        return {'error': raw_block['error']}

    block = OP_RETURN_unpack_block(raw_block['block'])

    return block['txs']


# Talking to bitcoin-cli

def OP_RETURN_bitcoin_check(testnet):
    info = OP_RETURN_bitcoin_cmd('getinfo', testnet)

    return isinstance(info, dict) and 'balance' in info


def OP_RETURN_bitcoin_cmd(command, testnet, *args):  # more params are read from here
    if OP_RETURN_BITCOIN_USE_CMD:
        sub_args = [OP_RETURN_BITCOIN_PATH]
        if testnet:
            sub_args.append('-testnet')

        sub_args.append(command)

        for arg in args:
            sub_args.append(json.dumps(arg) if isinstance(arg, (dict, list, tuple)) else str(arg))

        raw_result = subprocess.check_output(sub_args).decode("utf-8").rstrip("\n")

        try:  # decode JSON if possible
            result = json.loads(raw_result)
        except ValueError:
            result = raw_result

    else:
        request = {
            'id': str(time.time()) + '-' + str(random.randint(100000, 999999)),
            'method': command,
            'params': args,
        }

        port = OP_RETURN_BITCOIN_PORT
        user = OP_RETURN_BITCOIN_USER
        password = OP_RETURN_BITCOIN_PASSWORD

        if not (len(port) and len(user) and len(password)):
            conf_lines = open(os.path.expanduser('~') + '/.dogecoin/dogecoin.conf').readlines()

            for conf_line in conf_lines:
                parts = conf_line.strip().split('=', 1)  # up to 2 parts

                if (parts[0] == 'rpcport') and not len(port):
                    port = int(parts[1])
                if (parts[0] == 'rpcuser') and not len(user):
                    user = parts[1]
                if (parts[0] == 'rpcpassword') and not len(password):
                    password = parts[1]

        if not len(port):
            port = 18332 if testnet else 8332

        if not (len(user) and len(password)):
            return None  # no point trying in this case

        url = 'http://' + OP_RETURN_BITCOIN_IP + ':' + str(port) + '/'

        try:
            from urllib2 import HTTPPasswordMgrWithDefaultRealm, HTTPBasicAuthHandler, build_opener, install_opener, \
                urlopen
        except ImportError:
            from urllib.request import HTTPPasswordMgrWithDefaultRealm, HTTPBasicAuthHandler, build_opener, \
                install_opener, urlopen

        passman = HTTPPasswordMgrWithDefaultRealm()
        passman.add_password(None, url, user, password)
        auth_handler = HTTPBasicAuthHandler(passman)
        opener = build_opener(auth_handler)
        install_opener(opener)
        raw_result = urlopen(url, json.dumps(request).encode('utf-8'), OP_RETURN_NET_TIMEOUT).read()

        result_array = json.loads(raw_result.decode('utf-8'))
        result = result_array['result']

    return result


# Working with data references

# The format of a data reference is: [estimated block height]-[partial txid] - where:

# [estimated block height] is the block where the first transaction might appear and following
# which all subsequent transactions are expected to appear. In the event of a weird blockchain
# reorg, it is possible the first transaction might appear in a slightly earlier block. When
# embedding data, we set [estimated block height] to 1+(the current block height).

# [partial txid] contains 2 adjacent bytes from the txid, at a specific position in the txid:
# 2*([partial txid] div 65536) gives the offset of the 2 adjacent bytes, between 0 and 28.
# ([partial txid] mod 256) is the byte of the txid at that offset.
# (([partial txid] mod 65536) div 256) is the byte of the txid at that offset plus one.
# Note that the txid is ordered according to user presentation, not raw data in the block.


def OP_RETURN_calc_ref(next_height, txid, avoid_txids):
    txid_binary = OP_RETURN_hex_to_bin(txid)

    for txid_offset in range(15):
        sub_txid = txid_binary[2 * txid_offset:2 * txid_offset + 2]
        clashed = False

        for avoid_txid in avoid_txids:
            avoid_txid_binary = OP_RETURN_hex_to_bin(avoid_txid)

            if (
                    (avoid_txid_binary[2 * txid_offset:2 * txid_offset + 2] == sub_txid) and
                    (txid_binary != avoid_txid_binary)
            ):
                clashed = True
                break

        if not clashed:
            break

    if clashed:  # could not find a good reference
        return None

    tx_ref = ord(txid_binary[2 * txid_offset:1 + 2 * txid_offset]) + 256 * ord(
        txid_binary[1 + 2 * txid_offset:2 + 2 * txid_offset]) + 65536 * txid_offset

    return '%06d-%06d' % (next_height, tx_ref)


def OP_RETURN_get_ref_parts(ref):
    if not re.search('^[0-9]+\-[0-9A-Fa-f]+$', ref):  # also support partial txid for second half
        return None

    parts = ref.split('-')

    if re.search('[A-Fa-f]', parts[1]):
        if len(parts[1]) >= 4:
            txid_binary = OP_RETURN_hex_to_bin(parts[1][0:4])
            parts[1] = ord(txid_binary[0:1]) + 256 * ord(txid_binary[1:2]) + 65536 * 0
        else:
            return None

    parts = list(map(int, parts))

    if parts[1] > 983039:  # 14*65536+65535
        return None

    return parts


def OP_RETURN_get_ref_heights(ref, max_height):
    parts = OP_RETURN_get_ref_parts(ref)
    if not parts:
        return None

    return OP_RETURN_get_try_heights(parts[0], max_height, True)


def OP_RETURN_get_try_heights(est_height, max_height, also_back):
    forward_height = est_height
    back_height = min(forward_height - 1, max_height)

    heights = []
    mempool = False
    try_height = 0

    while True:
        if also_back and ((try_height % 3) == 2):  # step back every 3 tries
            heights.append(back_height)
            back_height -= 1

        else:
            if forward_height > max_height:
                if not mempool:
                    heights.append(0)  # indicates to try mempool
                    mempool = True

                elif not also_back:
                    break  # nothing more to do here

            else:
                heights.append(forward_height)

            forward_height += 1

        if len(heights) >= OP_RETURN_MAX_BLOCKS:
            break

        try_height += 1

    return heights


def OP_RETURN_match_ref_txid(ref, txid):
    parts = OP_RETURN_get_ref_parts(ref)
    if not parts:
        return None

    txid_offset = int(parts[1] / 65536)
    txid_binary = OP_RETURN_hex_to_bin(txid)

    txid_part = txid_binary[2 * txid_offset:2 * txid_offset + 2]
    txid_match = bytearray([parts[1] % 256, int((parts[1] % 65536) / 256)])

    return txid_part == txid_match  # exact binary comparison


# Unpacking and packing bitcoin blocks and transactions	

def OP_RETURN_unpack_block(binary):
    buffer = OP_RETURN_buffer(binary)
    block = {}

    block['version'] = buffer.shift_unpack(4, '<L')
    block['hashPrevBlock'] = OP_RETURN_bin_to_hex(buffer.shift(32)[::-1])
    block['hashMerkleRoot'] = OP_RETURN_bin_to_hex(buffer.shift(32)[::-1])
    block['time'] = buffer.shift_unpack(4, '<L')
    block['bits'] = buffer.shift_unpack(4, '<L')
    block['nonce'] = buffer.shift_unpack(4, '<L')
    block['tx_count'] = buffer.shift_varint()

    block['txs'] = {}

    old_ptr = buffer.used()

    while buffer.remaining():
        transaction = OP_RETURN_unpack_txn_buffer(buffer)
        new_ptr = buffer.used()
        size = new_ptr - old_ptr

        raw_txn_binary = binary[old_ptr:old_ptr + size]
        txid = OP_RETURN_bin_to_hex(hashlib.sha256(hashlib.sha256(raw_txn_binary).digest()).digest()[::-1])

        old_ptr = new_ptr

        transaction['size'] = size
        block['txs'][txid] = transaction

    return block


def OP_RETURN_unpack_txn(binary):
    return OP_RETURN_unpack_txn_buffer(OP_RETURN_buffer(binary))


def OP_RETURN_unpack_txn_buffer(buffer):
    # see: https://en.bitcoin.it/wiki/Transactions

    txn = {
        'vin': [],
        'vout': [],
    }

    txn['version'] = buffer.shift_unpack(4, '<L')  # small-endian 32-bits

    inputs = buffer.shift_varint()
    if inputs > 100000:  # sanity check
        return None

    for _ in range(inputs):
        input = {}

        input['txid'] = OP_RETURN_bin_to_hex(buffer.shift(32)[::-1])
        input['vout'] = buffer.shift_unpack(4, '<L')
        length = buffer.shift_varint()
        input['scriptSig'] = OP_RETURN_bin_to_hex(buffer.shift(length))
        input['sequence'] = buffer.shift_unpack(4, '<L')

        txn['vin'].append(input)

    outputs = buffer.shift_varint()
    if outputs > 100000:  # sanity check
        return None

    for _ in range(outputs):
        output = {}

        output['value'] = float(buffer.shift_uint64()) / 100000000
        length = buffer.shift_varint()
        output['scriptPubKey'] = OP_RETURN_bin_to_hex(buffer.shift(length))

        txn['vout'].append(output)

    txn['locktime'] = buffer.shift_unpack(4, '<L')

    return txn


def OP_RETURN_find_spent_txid(txns, spent_txid, spent_vout):
    for txid, txn_unpacked in txns.items():
        for input in txn_unpacked['vin']:
            if (input['txid'] == spent_txid) and (input['vout'] == spent_vout):
                return txid

    return None


def OP_RETURN_find_txn_data(txn_unpacked):
    for index, output in enumerate(txn_unpacked['vout']):
        op_return = OP_RETURN_get_script_data(OP_RETURN_hex_to_bin(output['scriptPubKey']))

        if op_return:
            return {
                'index': index,
                'op_return': op_return,
            }

    return None


def OP_RETURN_get_script_data(scriptPubKeyBinary):
    op_return = None

    if scriptPubKeyBinary[0:1] == b'\x6a':
        first_ord = ord(scriptPubKeyBinary[1:2])

        if first_ord <= 75:
            op_return = scriptPubKeyBinary[2:2 + first_ord]
        elif first_ord == 0x4c:
            op_return = scriptPubKeyBinary[3:3 + ord(scriptPubKeyBinary[2:3])]
        elif first_ord == 0x4d:
            op_return = scriptPubKeyBinary[4:4 + ord(scriptPubKeyBinary[2:3]) + 256 * ord(scriptPubKeyBinary[3:4])]

    return op_return


def OP_RETURN_pack_txn(txn):
    binary = b''

    binary += struct.pack('<L', txn['version'])

    binary += OP_RETURN_pack_varint(len(txn['vin']))

    for input in txn['vin']:
        binary += OP_RETURN_hex_to_bin(input['txid'])[::-1]
        binary += struct.pack('<L', input['vout'])
        binary += OP_RETURN_pack_varint(int(len(input['scriptSig']) / 2))  # divide by 2 because it is currently in hex
        binary += OP_RETURN_hex_to_bin(input['scriptSig'])
        binary += struct.pack('<L', input['sequence'])

    binary += OP_RETURN_pack_varint(len(txn['vout']))

    for output in txn['vout']:
        binary += OP_RETURN_pack_uint64(int(round(output['value'] * 100000000)))
        binary += OP_RETURN_pack_varint(
            int(len(output['scriptPubKey']) / 2))  # divide by 2 because it is currently in hex
        binary += OP_RETURN_hex_to_bin(output['scriptPubKey'])

    binary += struct.pack('<L', txn['locktime'])

    return binary


def OP_RETURN_pack_varint(integer):
    if integer > 0xFFFFFFFF:
        packed = "\xFF" + OP_RETURN_pack_uint64(integer)
    elif integer > 0xFFFF:
        packed = "\xFE" + struct.pack('<L', integer)
    elif integer > 0xFC:
        packed = "\xFD".struct.pack('<H', integer)
    else:
        packed = struct.pack('B', integer)

    return packed


def OP_RETURN_pack_uint64(integer):
    upper = int(integer / 4294967296)
    lower = integer - upper * 4294967296

    return struct.pack('<L', lower) + struct.pack('<L', upper)


# Helper class for unpacking bitcoin binary data

class OP_RETURN_buffer():

    def __init__(self, data, ptr=0):
        self.data = data
        self.len = len(data)
        self.ptr = ptr

    def shift(self, chars):
        prefix = self.data[self.ptr:self.ptr + chars]
        self.ptr += chars

        return prefix

    def shift_unpack(self, chars, format):
        unpack = struct.unpack(format, self.shift(chars))

        return unpack[0]

    def shift_varint(self):
        value = self.shift_unpack(1, 'B')

        if value == 0xFF:
            value = self.shift_uint64()
        elif value == 0xFE:
            value = self.shift_unpack(4, '<L')
        elif value == 0xFD:
            value = self.shift_unpack(2, '<H')

        return value

    def shift_uint64(self):
        return self.shift_unpack(4, '<L') + 4294967296 * self.shift_unpack(4, '<L')

    def used(self):
        return min(self.ptr, self.len)

    def remaining(self):
        return max(self.len - self.ptr, 0)


# Converting binary <-> hexadecimal

def OP_RETURN_hex_to_bin(hex):
    try:
        raw = binascii.a2b_hex(hex)
    except Exception as e:
        print(e)
        return None

    return raw


def OP_RETURN_bin_to_hex(string):
    return binascii.b2a_hex(string).decode('utf-8')