How to establish a connection to the bitcoin manually. Peer discovery + connecting and sending version message

bitcoin_connection.py

# Import requests and regex library
import requests
import re

def get_external_ip():
    # Make a request to checkip.dyndns.org as proposed
    # in https://en.bitcoin.it/wiki/Satoshi_Client_Node_Discovery#DNS_Addresses
    response = requests.get('http://checkip.dyndns.org').text

    # Filter the response with a regex for an IPv4 address
    ip = re.search("(?:[0-9]{1,3}\.){3}[0-9]{1,3}", response).group()
    return ip

external_ip = get_external_ip()
print(external_ip)

# Import socket and time library
import socket
import time

def get_node_addresses():
    # The list of seeds as hardcoded in a Bitcoin client
    # view https://en.bitcoin.it/wiki/Satoshi_Client_Node_Discovery#DNS_Addresses
    dns_seeds = [
        ("seed.bitcoin.sipa.be", 8333),
        ("dnsseed.bluematt.me", 8333),
        ("dnsseed.bitcoin.dashjr.org", 8333),
        ("seed.bitcoinstats.com", 8333),
        ("seed.bitnodes.io", 8333),
        ("bitseed.xf2.org", 8333),
    ]

    # The list where we store our found peers
    found_peers = []
    try:
        # Loop our seed list
        for (ip_address, port) in dns_seeds:
            index = 0
            # Connect to a dns address and get the A records
            for info in socket.getaddrinfo(ip_address, port,
                                           socket.AF_INET, socket.SOCK_STREAM,
                                           socket.IPPROTO_TCP):
                # The IP address and port is at index [4][0]
                # for example: ('13.250.46.106', 8333)
                found_peers.append((info[4][0], info[4][1]))
    except Exception:
        return found_peers

peers = get_node_addresses()
print(peers)

import struct
import random
import hashlib

# Create a streaming socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to the first responding peer from our dns list
def connect(peer_index):
    try:
        print("Trying to connect to ", peers[peer_index])
        err = sock.connect(peers[peer_index])
        return peer_index
    except Exception:
        # Sidenote: Recursive call to test the next peer
        # You would it not do like this in a real world, but it is for educational purposes only
        return connect(peer_index+1)

peer_index = connect(0)

def create_version_message():
    # Encode all values to the right binary representation on https://bitcoin.org/en/developer-reference#version
    # And https://docs.python.org/3/library/struct.html#format-characters

    # The current protocol version, look it up under https://bitcoin.org/en/developer-reference#protocol-versions
    version = struct.pack("i", 70015)

    # Services that we support, can be either full-node (1) or not full-node (0)
    services = struct.pack("Q", 0)

    # The current timestamp
    timestamp = struct.pack("q", int(time.time()))

    # Services that receiver supports
    add_recv_services = struct.pack("Q", 0)

    # The receiver's IP, we got it from the DNS example above
    add_recv_ip = struct.pack(">16s", bytes(peers[peer_index][0], 'utf-8'))

    # The receiver's port (Bitcoin default is 8333)
    add_recv_port = struct.pack(">H", 8333)

    # Should be identical to services, was added later by the protocol
    add_trans_services = struct.pack("Q", 0)
    # Our ip or 127.0.0.1
    add_trans_ip = struct.pack(">16s", bytes("127.0.0.1", 'utf-8'))
    # Our port
    add_trans_port = struct.pack(">H", 8333)

    # A nonce to detect connections to ourself
    # If we receive the same nonce that we sent, we want to connect to oursel
    nonce = struct.pack("Q", random.getrandbits(64))
    # Can be a user agent like Satoshi:0.15.1, we leave it empty
    user_agent_bytes = struct.pack("B", 0)
    # The block starting height, you can find the latest on http://blockchain.info/
    starting_height = struct.pack("i", 525453)
    # We do not relay data and thus want to prevent to get tx messages
    relay = struct.pack("?", False)

    # Let's combine everything to our payload
    payload = version + services + timestamp + add_recv_services + add_recv_ip + add_recv_port + \
              add_trans_services + add_trans_ip + add_trans_port + nonce + user_agent_bytes + starting_height + relay

    # To meet the protocol specifications, we also have to create a header
    # The general header format is described here https://en.bitcoin.it/wiki/Protocol_documentation#Message_structure

    # The magic bytes, indicate the initiating network (Mainnet or Testned)
    # The known values can be found here https://en.bitcoin.it/wiki/Protocol_documentation#Common_structures
    magic = bytes.fromhex("F9BEB4D9")

    # The command we want to send e.g. version message
    # This must be null padded to reach 12 bytes in total (version = 7 Bytes + 5 zero bytes)
    command = b"version" + 5 * b"\00"
    # The payload length
    length = struct.pack("I", len(payload))
    # The checksum, combuted as described in https://en.bitcoin.it/wiki/Protocol_documentation#Message_structure
    checksum = hashlib.sha256(hashlib.sha256(payload).digest()).digest()[:4]

    # Build up the message
    return magic + command + length + checksum + payload

# Send out our version message
sock.send(create_version_message())

def encode_received_message(recv_message):
    # Encode the magic number
    recv_magic = recv_message[:4].hex()
    # Encode the command (should be version)
    recv_command = recv_message[4:16]

    # Encode the payload length
    recv_length = struct.unpack("I", recv_message[16:20])

    # Encode the checksum
    recv_checksum = recv_message[20:24]

    # Encode the payload (the rest)
    recv_payload = recv_message[24:]

    # Encode the version of the other peer
    recv_version = struct.unpack("i", recv_payload[:4])
    return (recv_magic, recv_command, recv_length, recv_checksum, recv_payload, recv_version)


time.sleep(1)

# Receive the message
encoded_values = encode_received_message(sock.recv(8192))
print("Version: ", encoded_values[-1])