Server Program

Build a Python server socket that binds to this computer, accepts one client, reads a short request, sends one reply, and closes both sockets.

Example

import socket
import threading

def serve(ready):
    server = socket.socket()
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server.bind(("127.0.0.1", 5050))
    server.listen(1)
    ready.append(5050)
    server.settimeout(3)
    client, address = server.accept()
    try:
        message = client.recv(1024).decode()
        print("request", message, "from", address[0])
        client.send(("Desk " + message).encode())
    finally:
        client.close()
        server.close()

ready = []
worker = threading.Thread(target=serve, args=(ready,))
worker.start()
while not ready:
    worker.join(0.01)
client = socket.socket()
try:
    client.connect(("127.0.0.1", 5050))
    client.send("Avery".encode())
    print(client.recv(1024).decode())
finally:
    client.close()
worker.join()

The server prints request Avery from 127.0.0.1, and the client prints Desk Avery. bind uses this computer only. listen(1) queues one waiting client. accept returns the connection and the address pair. The reply is encoded before send. Both sockets close in finally. The server function runs on a thread only so this one file can also run the client and then exit. Two real programs would be two files, with the same bind, listen, accept, recv, and send steps. The playground does not call accept, because that call waits. It shows the same request and reply as bytes.

Key takeaways

• Import socket, create the server socket, then bind and listen

• accept waits for one client and returns the connection plus the address

• recv(1024).decode() is the request text

• send the reply only after encode()

• Close the client socket and the server socket

• Next: Client Program — connect, send one request, and read the reply

• Previous: Socket Calls