Implement sending of heartbeats

node.py

@@ -0,0 +1,90 @@
+#! /usr/bin/env python3
+
+import hashlib, socket, sys, threading, time
+
+DEFAULT_PORT = 62039
+
+class Peer:
+    def __init__(self, ipv6, port, lifetime_counter):
+        self.ipv6 = ipv6
+        self.port = port
+        self.lifetime_counter = lifetime_counter
+
+class Node:
+    def __init__(self, node_socket, peers):
+        self.node_socket = node_socket
+        self.peers = peers
+
+def parse_address(addr_str):
+    if addr_str.startswith('['):
+        closing = addr_str.find(']:')
+        if closing == -1:
+            raise Exception(f'Not a valid address: {addr_str}')
+        ipv6 = addr_str[1:closing]
+        port = int(addr_str[closing+2:])
+    else:
+        ipv6 = addr_str
+        port = DEFAULT_PORT
+    return Peer(ipv6, port, 10)
+
+def wait_until(target_time):
+    duration = target_time - time.time()
+    if duration > 0:
+        time.sleep(duration)
+
+def empty_transaction_list_hash():
+    current_hash = 32 * b"\0"
+    for _ in range(1024):
+        entry = current_hash + 44 * b"\0"
+        current_hash = hashlib.sha256(entry).digest()
+    return current_hash
+
+def send_heartbeat(node, peer):
+    protocol_version = 2 * b"\0"
+    capable_version = 2 * b"\0"
+    msg_type = b"\0"
+    difficulty_sum = 32 * b"\0"
+    hash_value = empty_transaction_list_hash()
+    partner_ipv6 = 16 * b"\0"
+    partner_port = 2 * b"\0"
+
+    heartbeat_msg = protocol_version + capable_version + msg_type + \
+        difficulty_sum + hash_value + partner_ipv6 + partner_port
+    node.node_socket.sendto(heartbeat_msg, (peer.ipv6, peer.port))
+
+def heartbeat(node):
+    while True:
+        peer_count = len(node.peers)
+        start_time = time.time()
+        for i, peer in enumerate(node.peers):
+            wait_until(start_time + 60 * (i+1) / peer_count)
+            send_heartbeat(node, peer)
+
+def receiver(node):
+    pass
+
+def main():
+    address_arguments = sys.argv[1:]
+    peers = [parse_address(argument) for argument in address_arguments]
+
+    node_socket = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    try:
+        node_socket.bind(("::", DEFAULT_PORT))
+    except OSError as e:
+        if e.errno == 98:
+            node_socket.bind(("::", 0))
+            port = node_socket.getsockname()[1]
+            print(f"Default port {DEFAULT_PORT} is in use, listening on port {port} instead.")
+        else:
+            raise e
+
+    node = Node(node_socket, peers)
+    heartbeat_thread = threading.Thread(target = heartbeat, args = (node,))
+    receiving_thread = threading.Thread(target = receiver, args = (node,))
+    heartbeat_thread.start()
+    receiving_thread.start()
+    heartbeat_thread.join()
+    receiving_thread.join()
+
+if __name__ == '__main__':
+    main()