jason-me/mypowp2pcoin.py

## mypowp2pcoin.py
"""
POW Syndacoin

Usage:
  pow_syndacoin.py.py serve
  pow_syndacoin.py.py ping [--node <node>]
  pow_syndacoin.py.py tx <from> <to> <amount> [--node <node>]
  pow_syndacoin.py.py balance <name> [--node <node>]

Options:
  -h --help      Show this screen.
  --node=<node>  Hostname of node [default: node0]
"""

import uuid, socketserver, socket, sys, argparse, time, os, logging, threading, hashlib, random

from docopt import docopt
from copy import deepcopy
from ecdsa import SigningKey, SECP256k1
from utils import serialize, deserialize

PORT = 10000
BLOCK_SUBSIDY = 50
node = None

logging.basicConfig(level="INFO", format='%(threadName)-6s | %(message)s')
logger = logging.getLogger(__name__)


def spend_message(tx, index):
    outpoint = tx.tx_ins[index].outpoint
    return serialize(outpoint) + serialize(tx.tx_outs)

class Tx:

    def __init__(self, id, tx_ins, tx_outs):
        self.id = id
        self.tx_ins = tx_ins
        self.tx_outs = tx_outs

    def sign_input(self, index, private_key):
        message = spend_message(self, index)
        signature = private_key.sign(message)
        self.tx_ins[index].signature = signature

    def verify_input(self, index, public_key):
        tx_in = self.tx_ins[index]
        message = spend_message(self, index)
        return public_key.verify(tx_in.signature, message)

    @property
    def is_coinbase(self):
        return self.tx_ins[0].tx_id is None

    def __eq__(self, other):
        return self.id == other.id

class TxIn:

    def __init__(self, tx_id, index, signature=None):
        self.tx_id = tx_id
        self.index = index
        self.signature = signature

    @property
    def outpoint(self):
        return (self.tx_id, self.index)

class TxOut:

    def __init__(self, tx_id, index, amount, public_key):
        self.tx_id = tx_id
        self.index = index
        self.amount = amount
        self.public_key = public_key

    @property
    def outpoint(self):
        return (self.tx_id, self.index)

class Block:

    def __init__(self, txns, prev_id, nonce):
        self.txns = txns
        self.prev_id = prev_id
        self.nonce = nonce

    @property
    def header(self):
        return serialize(self)

    @property
    def id(self):
        return hashlib.sha256(self.header).hexdigest()

    @property
    def proof(self):
        return int(self.id, 16)

    def __repr__(self):
        return f"Block(prev_id={self.prev_id[:10]}... id={self.id[:10]}...)"


class Node:

    def __init__(self, address):
        self.blocks = []
        self.utxo_set = {}
        self.mempool = []
        self.peers = []
        self.pending_peers = []
        self.address = address

    def connect(self, peer):
        if peer not in self.peers and peer != self.address:
            logger.info(f'(handshake) Sent "connect" to {peer[0]}')
            try:
                send_message(peer, "connect", None)
                self.pending_peers.append(peer)
            except:
                logger.info(f'(handshake) Node {peer[0]} offline')

    @property
    def mempool_outpoints(self):
        return [tx_in.outpoint for tx in self.mempool for tx_in in tx.tx_ins]

    def fetch_utxos(self, public_key):
        return [tx_out for tx_out in self.utxo_set.values()
                if tx_out.public_key == public_key]

    def update_utxo_set(self, tx):
        # Remove utxos that were just spent
        if not tx.is_coinbase:
            for tx_in in tx.tx_ins:
                del self.utxo_set[tx_in.outpoint]

        # Save utxos which were just created
        for tx_out in tx.tx_outs:
            self.utxo_set[tx_out.outpoint] = tx_out

    def fetch_balance(self, public_key):
        # Fetch utxos associated with this public key
        utxos = self.fetch_utxos(public_key)
        # Sum the amounts
        return sum([tx_out.amount for tx_out in utxos])

    def validate_tx(self, tx):
        in_sum = 0
        out_sum = 0
        for index, tx_in in enumerate(tx.tx_ins):
            # TxIn spending an unspent output
            assert tx_in.outpoint in self.utxo_set

            # No pending transactions spending this same output
            assert tx_in.outpoint not in self.mempool_outpoints

            # Grab the tx_out
            tx_out = self.utxo_set[tx_in.outpoint]

            # Verify signature using public key of TxOut we're spending
            public_key = tx_out.public_key
            tx.verify_input(index, public_key)

            # Sum up the total inputs
            amount = tx_out.amount
            in_sum += amount

        for tx_out in tx.tx_outs:
            # Sum up the total outpouts
            out_sum += tx_out.amount

        # Check no value created or destroyed
        assert in_sum == out_sum

    def validate_coinbase(self, tx):
        assert len(tx.tx_ins) == len(tx.tx_outs) == 1
        assert tx.tx_outs[0].amount == BLOCK_SUBSIDY

    def handle_tx(self, tx):
        if tx not in self.mempool:
            self.validate_tx(tx)
            self.mempool.append(tx)

        # Propagate transaction
        for peer in self.peers:
            send_message(peer, "tx", tx)

    def validate_block(self, block):
        assert block.proof < POW_TARGET, "Insufficient Proof-of-Work"
        assert block.prev_id == self.blocks[-1].id

    def handle_block(self, block):
        # Check work, chain ordering
        self.validate_block(block)

        # Validate coinbase separately
        self.validate_coinbase(block.txns[0])

        # Check the transactions are valid
        for tx in block.txns[1:]:
            self.validate_tx(tx)

        # If they're all good, update self.blocks and self.utxo_set
        for tx in block.txns:
            self.update_utxo_set(tx)

        # Add the block to our chain
        self.blocks.append(block)

        logger.info(f"Block accepted: height={len(self.blocks) - 1}")

        # Block propogation
        for peer in self.peers:
            send_message(peer, "block", block)

def prepare_simple_tx(utxos, sender_private_key, recipient_public_key, amount):
    sender_public_key = sender_private_key.get_verifying_key()

    # Construct tx.tx_outs
    tx_ins = []
    tx_in_sum = 0
    for tx_out in utxos:
        tx_ins.append(TxIn(tx_id=tx_out.tx_id, index=tx_out.index, signature=None))
        tx_in_sum += tx_out.amount
        if tx_in_sum > amount:
            break

    # Make sure sender can afford it
    assert tx_in_sum >= amount

    # Construct tx.tx_outs
    tx_id = uuid.uuid4()
    change = tx_in_sum - amount
    tx_outs = [
        TxOut(tx_id=tx_id, index=0, amount=amount, public_key=recipient_public_key),
        TxOut(tx_id=tx_id, index=1, amount=change, public_key=sender_public_key),
    ]

    # Construct tx and sign inputs
    tx = Tx(id=tx_id, tx_ins=tx_ins, tx_outs=tx_outs)
    for i in range(len(tx.tx_ins)):
        tx.sign_input(i, sender_private_key)

        return tx

def prepare_coinbase(public_key, tx_id=None):
    if tx_id is None:
        tx_id = uuid.uuid4()
    return Tx(
        id=tx_id,
        tx_ins=[
            TxIn(None, None, None),
        ],
        tx_outs=[
            TxOut(tx_id=tx_id, index=0, amount=BLOCK_SUBSIDY,
                  public_key=public_key)
        ],
    )

##########
# Mining #
##########

DIFFICULTY_BITS = 15
POW_TARGET = 2 ** (256 - DIFFICULTY_BITS)
mining_interrupt = threading.Event()


def mine_block(block):
    while block.proof >= POW_TARGET:
        # TODO: accept interrupts here if tip changes
        if mining_interrupt.is_set():
            logger.info("Mining interrupted")
            mining_interrupt.clear()
            return
        block.nonce += 1
    return block


def mine_forever(public_key):
    logging.info("Starting miner")
    while True:
        coinbase = prepare_coinbase(public_key)
        unmined_block = Block(
            txns=[coinbase] + node.mempool,
            prev_id=node.blocks[-1].id,
            nonce=random.randint(0, 1000000000),
        )
        mined_block = mine_block(unmined_block)

        if mined_block:
            logger.info("")
            logger.info("Mined a block")
            node.handle_block(mined_block)

def mine_genesis_block(public_key):
    global node
    coinbase = prepare_coinbase(public_key, tx_id="abcd1234")
    unmined_block = Block(txns=[coinbase], prev_id=None, nonce=0)
    mined_block = mine_block(unmined_block)
    node.blocks.append(mined_block)
    node.update_utxo_set(coinbase)

##############
# Networking #
##############

def prepare_message(command, data):
    return {
        "command": command,
        "data": data,
    }

class TCPHandler(socketserver.BaseRequestHandler):

    def get_canonical_peer_address(self):
        ip = self.client_address[0]
        try:
            hostname = socket.gethostbyaddr(ip)
            hostname = re.search(r"_(.*?)_", hostname[0]).group(1)
        except:
            hostname = ip
        return (hostname, PORT)

    def respond(self, command, data):
        response = prepare_message(command, data)
        return self.request.sendall(serialize(response))

    def handle(self):
        message_bytes = self.request.recv(1024*4).strip()
        message = deserialize(message_bytes)
        command = message["command"]
        data = message["data"]

        # logger.info(f"received {command}")
        peer = self.get_canonical_peer_address()

        # Handshake / Authentication
        if command == "connect":
            if peer not in node.pending_peers and peer not in node.peers:
                node.pending_peers.append(peer)
                logger.info(f'(handshake) Accepted "connect" request from \
"{peer[0]}"')
                send_message(peer, "connect-response", None)

        elif command == "connect-response":
            if peer in node.pending_peers and peer not in node.peers:
                node.pending_peers.remove(peer)
                node.peers.append(peer)
                logger.info(f'(handshake) Connected to "{peer[0]}"')
                send_message(peer, "connect-response", None)

                # Request their peers
                send_message(peer, "peers", None)

        else:
            assert peer in node.peers, \
                f"Rejecting {command} from unconnected {peer[0]}"


        # Business Logic

        if command == "peers":
            send_message(peer, "peers-response", node.peers)

        if command == "peers-response":
            for peer in data:
                node.connect(peer)

        if command == "ping":
            self.respond(command="pong", data="")

        if command == "block":
            if data.prev_id == node.blocks[-1].id:
                node.handle_block(data)
                # Interrupt mining thread
                mining_interrupt.set()

        if command == "tx":
            node.handle_tx(data)

        if command == "balance":
            balance = node.fetch_balance(data)
            self.respond(command="balance-response", data=balance)

        if command == "utxos":
            utxos = node.fetch_utxos(data)
            self.respond(command="utxos-response", data=utxos)

def external_address(node):
    i = int(node[-1])
    port = PORT + i
    return ('localhost', port)

def serve():
    logger.info("Starting server")
    server = socketserver.TCPServer(("0.0.0.0", PORT), TCPHandler)
    server.serve_forever()

def send_message(address, command, data, response=False):
    message = prepare_message(command, data)
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect(address)
        s.sendall(serialize(message))
        if response:
            return deserialize(s.recv(5000))


#######
# CLI #
#######

def lookup_private_key(name):
    exponent = {
        "alice": 1, "bob": 2, "node0": 3, "node1": 4, "node2": 5
    }[name]
    return SigningKey.from_secret_exponent(exponent, curve=SECP256k1)

def lookup_public_key(name):
    return lookup_private_key(name).get_verifying_key()

def main(args):
    if args["serve"]:
        threading.current_thread().name = "main"
        name = os.environ["NAME"]

        global node
        node = Node(address=(name, PORT))

        # Alice is Satoshi!!!
        mine_genesis_block(lookup_public_key("alice"))

        # Start server thread
        server_thread = threading.Thread(target=serve, name="server")
        server_thread.start()

        # Join the network
        peers = [(p, PORT) for p in os.environ['PEERS'].split(',')]
        for peer in peers:
            node.connect(peer)

        # Start miner thread
        miner_public_key = lookup_public_key(name)
        miner_thread = threading.Thread(target=mine_forever,
                args=[miner_public_key], name="miner")
        miner_thread.start()

    elif args["ping"]:
        address = address_from_host(args["--node"])
        send_message(address, "ping", "")
    elif args["balance"]:
        public_key = lookup_public_key(args["<name>"])
        address = external_address(args["--node"])
        response = send_message(address, "balance", public_key, response=True)
        print(response["data"])
    elif args["tx"]:
        # Grab parameters
        sender_private_key = lookup_private_key(args["<from>"])
        sender_public_key = sender_private_key.get_verifying_key()
        recipient_private_key = lookup_private_key(args["<to>"])
        recipient_public_key = recipient_private_key.get_verifying_key()
        amount = int(args["<amount>"])
        address = external_address(args["--node"])

        # Fetch utxos available to spend
        response = send_message(address, "utxos", sender_public_key, response=True)
        utxos = response["data"]

        # Prepare transaction
        tx = prepare_simple_tx(utxos, sender_private_key, recipient_public_key, amount)

        # send to node
        send_message(address, "tx", tx)
    else:
        print("Invalid command")


if __name__ == '__main__':
    main(docopt(__doc__))
	"""
	POW Syndacoin

	Usage:
	pow_syndacoin.py.py serve
	pow_syndacoin.py.py ping [--node <node>]
	pow_syndacoin.py.py tx <from> <to> <amount> [--node <node>]
	pow_syndacoin.py.py balance <name> [--node <node>]

	Options:
	-h --help Show this screen.
	--node=<node> Hostname of node [default: node0]
	"""

	import uuid, socketserver, socket, sys, argparse, time, os, logging, threading, hashlib, random

	from docopt import docopt
	from copy import deepcopy
	from ecdsa import SigningKey, SECP256k1
	from utils import serialize, deserialize

	PORT = 10000
	BLOCK_SUBSIDY = 50
	node = None

	logging.basicConfig(level="INFO", format='%(threadName)-6s \| %(message)s')
	logger = logging.getLogger(__name__)


	def spend_message(tx, index):
	outpoint = tx.tx_ins[index].outpoint
	return serialize(outpoint) + serialize(tx.tx_outs)

	class Tx:

	def __init__(self, id, tx_ins, tx_outs):
	self.id = id
	self.tx_ins = tx_ins
	self.tx_outs = tx_outs

	def sign_input(self, index, private_key):
	message = spend_message(self, index)
	signature = private_key.sign(message)
	self.tx_ins[index].signature = signature

	def verify_input(self, index, public_key):
	tx_in = self.tx_ins[index]
	message = spend_message(self, index)
	return public_key.verify(tx_in.signature, message)

	@property
	def is_coinbase(self):
	return self.tx_ins[0].tx_id is None

	def __eq__(self, other):
	return self.id == other.id

	class TxIn:

	def __init__(self, tx_id, index, signature=None):
	self.tx_id = tx_id
	self.index = index
	self.signature = signature

	@property
	def outpoint(self):
	return (self.tx_id, self.index)

	class TxOut:

	def __init__(self, tx_id, index, amount, public_key):
	self.tx_id = tx_id
	self.index = index
	self.amount = amount
	self.public_key = public_key

	@property
	def outpoint(self):
	return (self.tx_id, self.index)

	class Block:

	def __init__(self, txns, prev_id, nonce):
	self.txns = txns
	self.prev_id = prev_id
	self.nonce = nonce

	@property
	def header(self):
	return serialize(self)

	@property
	def id(self):
	return hashlib.sha256(self.header).hexdigest()

	@property
	def proof(self):
	return int(self.id, 16)

	def __repr__(self):
	return f"Block(prev_id={self.prev_id[:10]}... id={self.id[:10]}...)"


	class Node:

	def __init__(self, address):
	self.blocks = []
	self.utxo_set = {}
	self.mempool = []
	self.peers = []
	self.pending_peers = []
	self.address = address

	def connect(self, peer):
	if peer not in self.peers and peer != self.address:
	logger.info(f'(handshake) Sent "connect" to {peer[0]}')
	try:
	send_message(peer, "connect", None)
	self.pending_peers.append(peer)
	except:
	logger.info(f'(handshake) Node {peer[0]} offline')

	@property
	def mempool_outpoints(self):
	return [tx_in.outpoint for tx in self.mempool for tx_in in tx.tx_ins]

	def fetch_utxos(self, public_key):
	return [tx_out for tx_out in self.utxo_set.values()
	if tx_out.public_key == public_key]

	def update_utxo_set(self, tx):
	# Remove utxos that were just spent
	if not tx.is_coinbase:
	for tx_in in tx.tx_ins:
	del self.utxo_set[tx_in.outpoint]

	# Save utxos which were just created
	for tx_out in tx.tx_outs:
	self.utxo_set[tx_out.outpoint] = tx_out

	def fetch_balance(self, public_key):
	# Fetch utxos associated with this public key
	utxos = self.fetch_utxos(public_key)
	# Sum the amounts
	return sum([tx_out.amount for tx_out in utxos])

	def validate_tx(self, tx):
	in_sum = 0
	out_sum = 0
	for index, tx_in in enumerate(tx.tx_ins):
	# TxIn spending an unspent output
	assert tx_in.outpoint in self.utxo_set

	# No pending transactions spending this same output
	assert tx_in.outpoint not in self.mempool_outpoints

	# Grab the tx_out
	tx_out = self.utxo_set[tx_in.outpoint]

	# Verify signature using public key of TxOut we're spending
	public_key = tx_out.public_key
	tx.verify_input(index, public_key)

	# Sum up the total inputs
	amount = tx_out.amount
	in_sum += amount

	for tx_out in tx.tx_outs:
	# Sum up the total outpouts
	out_sum += tx_out.amount

	# Check no value created or destroyed
	assert in_sum == out_sum

	def validate_coinbase(self, tx):
	assert len(tx.tx_ins) == len(tx.tx_outs) == 1
	assert tx.tx_outs[0].amount == BLOCK_SUBSIDY

	def handle_tx(self, tx):
	if tx not in self.mempool:
	self.validate_tx(tx)
	self.mempool.append(tx)

	# Propagate transaction
	for peer in self.peers:
	send_message(peer, "tx", tx)

	def validate_block(self, block):
	assert block.proof < POW_TARGET, "Insufficient Proof-of-Work"
	assert block.prev_id == self.blocks[-1].id

	def handle_block(self, block):
	# Check work, chain ordering
	self.validate_block(block)

	# Validate coinbase separately
	self.validate_coinbase(block.txns[0])

	# Check the transactions are valid
	for tx in block.txns[1:]:
	self.validate_tx(tx)

	# If they're all good, update self.blocks and self.utxo_set
	for tx in block.txns:
	self.update_utxo_set(tx)

	# Add the block to our chain
	self.blocks.append(block)

	logger.info(f"Block accepted: height={len(self.blocks) - 1}")

	# Block propogation
	for peer in self.peers:
	send_message(peer, "block", block)

	def prepare_simple_tx(utxos, sender_private_key, recipient_public_key, amount):
	sender_public_key = sender_private_key.get_verifying_key()

	# Construct tx.tx_outs
	tx_ins = []
	tx_in_sum = 0
	for tx_out in utxos:
	tx_ins.append(TxIn(tx_id=tx_out.tx_id, index=tx_out.index, signature=None))
	tx_in_sum += tx_out.amount
	if tx_in_sum > amount:
	break

	# Make sure sender can afford it
	assert tx_in_sum >= amount

	# Construct tx.tx_outs
	tx_id = uuid.uuid4()
	change = tx_in_sum - amount
	tx_outs = [
	TxOut(tx_id=tx_id, index=0, amount=amount, public_key=recipient_public_key),
	TxOut(tx_id=tx_id, index=1, amount=change, public_key=sender_public_key),
	]

	# Construct tx and sign inputs
	tx = Tx(id=tx_id, tx_ins=tx_ins, tx_outs=tx_outs)
	for i in range(len(tx.tx_ins)):
	tx.sign_input(i, sender_private_key)

	return tx

	def prepare_coinbase(public_key, tx_id=None):
	if tx_id is None:
	tx_id = uuid.uuid4()
	return Tx(
	id=tx_id,
	tx_ins=[
	TxIn(None, None, None),
	],
	tx_outs=[
	TxOut(tx_id=tx_id, index=0, amount=BLOCK_SUBSIDY,
	public_key=public_key)
	],
	)

	##########
	# Mining #
	##########

	DIFFICULTY_BITS = 15
	POW_TARGET = 2 ** (256 - DIFFICULTY_BITS)
	mining_interrupt = threading.Event()


	def mine_block(block):
	while block.proof >= POW_TARGET:
	# TODO: accept interrupts here if tip changes
	if mining_interrupt.is_set():
	logger.info("Mining interrupted")
	mining_interrupt.clear()
	return
	block.nonce += 1
	return block


	def mine_forever(public_key):
	logging.info("Starting miner")
	while True:
	coinbase = prepare_coinbase(public_key)
	unmined_block = Block(
	txns=[coinbase] + node.mempool,
	prev_id=node.blocks[-1].id,
	nonce=random.randint(0, 1000000000),
	)
	mined_block = mine_block(unmined_block)

	if mined_block:
	logger.info("")
	logger.info("Mined a block")
	node.handle_block(mined_block)

	def mine_genesis_block(public_key):
	global node
	coinbase = prepare_coinbase(public_key, tx_id="abcd1234")
	unmined_block = Block(txns=[coinbase], prev_id=None, nonce=0)
	mined_block = mine_block(unmined_block)
	node.blocks.append(mined_block)
	node.update_utxo_set(coinbase)

	##############
	# Networking #
	##############

	def prepare_message(command, data):
	return {
	"command": command,
	"data": data,
	}

	class TCPHandler(socketserver.BaseRequestHandler):

	def get_canonical_peer_address(self):
	ip = self.client_address[0]
	try:
	hostname = socket.gethostbyaddr(ip)
	hostname = re.search(r"_(.*?)_", hostname[0]).group(1)
	except:
	hostname = ip
	return (hostname, PORT)

	def respond(self, command, data):
	response = prepare_message(command, data)
	return self.request.sendall(serialize(response))

	def handle(self):
	message_bytes = self.request.recv(1024*4).strip()
	message = deserialize(message_bytes)
	command = message["command"]
	data = message["data"]

	# logger.info(f"received {command}")
	peer = self.get_canonical_peer_address()

	# Handshake / Authentication
	if command == "connect":
	if peer not in node.pending_peers and peer not in node.peers:
	node.pending_peers.append(peer)
	logger.info(f'(handshake) Accepted "connect" request from \
	"{peer[0]}"')
	send_message(peer, "connect-response", None)

	elif command == "connect-response":
	if peer in node.pending_peers and peer not in node.peers:
	node.pending_peers.remove(peer)
	node.peers.append(peer)
	logger.info(f'(handshake) Connected to "{peer[0]}"')
	send_message(peer, "connect-response", None)

	# Request their peers
	send_message(peer, "peers", None)

	else:
	assert peer in node.peers, \
	f"Rejecting {command} from unconnected {peer[0]}"


	# Business Logic

	if command == "peers":
	send_message(peer, "peers-response", node.peers)

	if command == "peers-response":
	for peer in data:
	node.connect(peer)

	if command == "ping":
	self.respond(command="pong", data="")

	if command == "block":
	if data.prev_id == node.blocks[-1].id:
	node.handle_block(data)
	# Interrupt mining thread
	mining_interrupt.set()

	if command == "tx":
	node.handle_tx(data)

	if command == "balance":
	balance = node.fetch_balance(data)
	self.respond(command="balance-response", data=balance)

	if command == "utxos":
	utxos = node.fetch_utxos(data)
	self.respond(command="utxos-response", data=utxos)

	def external_address(node):
	i = int(node[-1])
	port = PORT + i
	return ('localhost', port)

	def serve():
	logger.info("Starting server")
	server = socketserver.TCPServer(("0.0.0.0", PORT), TCPHandler)
	server.serve_forever()

	def send_message(address, command, data, response=False):
	message = prepare_message(command, data)
	with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
	s.connect(address)
	s.sendall(serialize(message))
	if response:
	return deserialize(s.recv(5000))


	#######
	# CLI #
	#######

	def lookup_private_key(name):
	exponent = {
	"alice": 1, "bob": 2, "node0": 3, "node1": 4, "node2": 5
	}[name]
	return SigningKey.from_secret_exponent(exponent, curve=SECP256k1)

	def lookup_public_key(name):
	return lookup_private_key(name).get_verifying_key()

	def main(args):
	if args["serve"]:
	threading.current_thread().name = "main"
	name = os.environ["NAME"]

	global node
	node = Node(address=(name, PORT))

	# Alice is Satoshi!!!
	mine_genesis_block(lookup_public_key("alice"))

	# Start server thread
	server_thread = threading.Thread(target=serve, name="server")
	server_thread.start()

	# Join the network
	peers = [(p, PORT) for p in os.environ['PEERS'].split(',')]
	for peer in peers:
	node.connect(peer)

	# Start miner thread
	miner_public_key = lookup_public_key(name)
	miner_thread = threading.Thread(target=mine_forever,
	args=[miner_public_key], name="miner")
	miner_thread.start()

	elif args["ping"]:
	address = address_from_host(args["--node"])
	send_message(address, "ping", "")
	elif args["balance"]:
	public_key = lookup_public_key(args["<name>"])
	address = external_address(args["--node"])
	response = send_message(address, "balance", public_key, response=True)
	print(response["data"])
	elif args["tx"]:
	# Grab parameters
	sender_private_key = lookup_private_key(args["<from>"])
	sender_public_key = sender_private_key.get_verifying_key()
	recipient_private_key = lookup_private_key(args["<to>"])
	recipient_public_key = recipient_private_key.get_verifying_key()
	amount = int(args["<amount>"])
	address = external_address(args["--node"])

	# Fetch utxos available to spend
	response = send_message(address, "utxos", sender_public_key, response=True)
	utxos = response["data"]

	# Prepare transaction
	tx = prepare_simple_tx(utxos, sender_private_key, recipient_public_key, amount)

	# send to node
	send_message(address, "tx", tx)
	else:
	print("Invalid command")


	if __name__ == '__main__':
	main(docopt(__doc__))