the simplest bitcoin node

bitcoin_version_message.py

from binascii import hexlify, unhexlify
from hashlib import sha256
from io import BytesIO
import random
import socket
import struct
import time


user_agent_to_send = 'agentalex'
version = struct.pack("i", 70015) # corresponds to 0.15
services = struct.pack("Q", 0) # this "node" does nothing
timestamp = struct.pack("Q", (int(time.time())))
addr_recv_services = struct.pack("q", 0)
addr_recv_ip = struct.pack(">16s", b'127.0.0.1')
addr_recv_port = struct.pack(">H", 8333)
addr_trans_services = struct.pack("Q", 0)
addr_trans_ip = struct.pack(">16s", b'127.0.0.1')
addr_trans_port = struct.pack(">H", 8333)
nonce = struct.pack("Q", random.getrandbits(64))
user_agent_bytes = struct.pack("<B", len(user_agent_to_send))
user_agent = user_agent_to_send.encode()
starting_height = struct.pack("i", 0)
relay = struct.pack("?", False)

payload = version + services + timestamp + addr_recv_services + \
   addr_recv_ip + addr_recv_port + addr_trans_services + \
   addr_trans_ip + addr_trans_port + nonce + user_agent_bytes + \
   user_agent + starting_height + relay

network = unhexlify("F9BEB4D9") #mainnet
command = str.encode('version'.ljust(12, '\00'))
payload_size = struct.pack("I", len(payload))
checksum = sha256(sha256(payload).digest()).digest()[:4]

full_version_message = network + command + payload_size + checksum + payload


def read_a_message(sock):
    header = BytesIO(sock.recv(24))

    version = hexlify(header.read(4))
    command = header.read(12).decode().replace('\x00', '').upper()
    payload_size = struct.unpack("I", header.read(4))[0]
    checksum = hexlify(header.read(4))
    payload = sock.recv(payload_size)

    return {'message_type': command, 'payload': payload}


sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

try:
    some_existing_bitcoin_nodes = ["108.184.197.47", "87.140.70.14", "5.9.66.210"]
    sock.connect((random.choice(some_existing_bitcoin_nodes), 8333))
    sock.sendall(full_version_message)

    first_received_message = read_a_message(sock)
    print(f"omg you got a response from that node: {first_received_message}")

finally:
    sock.close()