帮我写一个基于Socket实现UPD协议的文件上传到服务器和下载到本地的代码

在Python中，你可以使用`socket`模块来实现基于UDP的简单文件上传和下载。由于UDP是无连接的，所以在文件传输过程中，我们无法像TCP那样依赖确认和序列号。所以，对于文件上传和下载，我们将采取一种逐块传输的方式，每个文件分片作为一个单独的数据包发送。

以下是基本的代码实现：

# 客户端（Client.py）
import socket
import os

def send_file_to_server(file_path, server_address):
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    with open(file_path, 'rb') as file:
        total_size = os.path.getsize(file_path)
        chunk_size = 1024  # 每次发送的数据量
        for i in range(0, total_size, chunk_size):
            chunk = file.read(chunk_size)
            packet = {'index': i, 'data': chunk}
            encoded_packet = pickle.dumps(packet)
            server_socket.sendto(encoded_packet, server_address)
            print(f"Sent {i+chunk_size} bytes to server.")

def download_from_server(server_address, output_path):
    client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    request = b'start_download'
    client_socket.sendto(request, server_address)

    received_data = b''
    while True:
        data, addr = client_socket.recvfrom(1024)
        received_data += data
        if b'end_of_data' in data:
            break

    with open(output_path, 'wb') as file:
        unpickled_data = pickle.loads(received_data)
        index = unpickled_data['index']
        file.write(unpickled_data['data'][:index])
        print(f"Downloaded {index} bytes to local file.")

# 服务器端（Server.py）
import pickle
import socket

def handle_requests(server_socket):
    while True:
        data, addr = server_socket.recvfrom(1024)
        decoded_data = pickle.loads(data)

        if decoded_data.get('type') == 'file_upload':
            # 处理文件上传...
            pass

        elif decoded_data.get('type') == 'file_download':
            # 发送文件数据...
            data = pickle.dumps({'type': 'end_of_data'})
            server_socket.sendto(data, addr)

def main():
    server_address = ('localhost', 12345)
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    server_socket.bind(server_address)
    print(f"Server started at {server_address}")

    handle_requests(server_socket)

if __name__ == "__main__":
    main()

注意：以上代码仅作展示，未包含完整的文件处理逻辑，例如在服务器端对上传文件的存储管理和在客户端的下载过程中的分段合并。此外，为了简化示例，假设了文件大小可以整除`chunk_size`，在实际应用中，你需要更复杂的方式来处理文件边界。