用python编写客户端和服务端代码，写一个简单的chat程序 要求：1、传输服务能自由选择TCP或STP，在启动的时候配置，交互双方须统一； 2、能互发消息，互传文件； 3、简单测试一下分别采用TCP和STP时，程序的运行表现。 4、编程语言为python。

在Python中，我们可以使用socket库来编写简单的客户端和服务器端的聊天程序，支持TCP和UDP（User Datagram Protocol，用户数据报协议）。这里是一个简化的示例，展示如何创建一个基本的聊天系统：

**服务器端（server.py）：**

import socket
from threading import Thread

# 配置服务器地址和端口
if input("请选择通信协议（TCP/UDP）: ").lower() == 'tcp':
    family = socket.AF_INET
    proto = socket.SOCK_STREAM
else:
    family = socket.AF_INET
    proto = socket.SOCK_DGRAM

server_address = ('localhost', 9999)

if __name__ == "__main__":
    server = socket.socket(family, proto)
    
    if proto == socket.SOCK_STREAM:
        server.bind(server_address)
        print(f"Server started on {server_address} (TCP)")
    else:
        server.bind(("", 0))  # UDP server listens on any available port
        print(f"Server started on {server_address} (UDP)")

    if proto == socket.SOCK_STREAM:
        while True:
            client, addr = server.accept()
            print(f"Accepted connection from {addr}")
            client_handler = Thread(target=handle_client, args=(client,))
            client_handler.start()
    else:
        while True:
            data, addr = server.recvfrom(1024)
            print(f"Received message from {addr}: {data.decode('utf-8')}")
            server.sendto(data, addr)  # Echo back the message to sender

def handle_client(client):
    try:
        while True:
            msg = client.recv(1024)
            if not msg: break
            server.sendall(msg)  # Forward the message to all connected clients in UDP mode
    finally:
        client.close()

**客户端（client.py）：**

import socket
import os

if input("请选择通信协议（TCP/UDP）: ").lower() == 'tcp':
    family = socket.AF_INET
    proto = socket.SOCK_STREAM
else:
    family = socket.AF_INET
    proto = socket.SOCK_DGRAM

client_address = ('localhost', 9999)

if __name__ == "__main__":
    with socket.socket(family, proto) as sock:
        if proto == socket.SOCK_STREAM:
            sock.connect(server_address)
            print(f"Connected to {server_address} (TCP)")
        else:
            sock.sendto(b"Hello, Server!", server_address)
            print(f"Sent message to {server_address} (UDP)")

        while True:
            msg = input("Enter your message: ")
            if msg.lower() == "exit":
                break
            sock.send(msg.encode('utf-8'))
            if proto == socket.SOCK_STREAM:
                response = sock.recv(1024).decode('utf-8')
            else:
                response = None  # UDP doesn't guarantee message delivery

            if response:
                print(response)

sock.close()

要在不同协议下测试程序，你可以分别运行`server.py`（选择TCP或UDP）和`client.py`（也选择相同的协议），然后开始交流。注意，由于UDP是非连接的，它不保证消息的顺序和可靠性，所以在发送文件时可能会有丢失或乱序。