Python UDP 文件传输：高效与可靠性的权衡369

UDP (用户数据报协议) 是一种无连接的传输层协议，它提供了一种快速、低开销的数据传输方式。与 TCP (传输控制协议) 不同，UDP 不保证数据的可靠性或顺序性。这意味着数据包可能丢失、失序或重复到达。然而，正是这种“不靠谱”的特点，在某些情况下使其成为优于 TCP 的选择，例如实时视频流或在线游戏，因为UDP的低延迟更重要。本文将深入探讨如何在 Python 中使用 UDP 协议进行文件传输，并着重讨论如何处理 UDP 的不稳定性以提高传输的可靠性。

虽然 UDP 不提供内置的可靠性机制，但我们可以通过编程手段来弥补这一不足。一个常用的方法是实现自定义的确认机制和重传机制。发送端发送数据包后，需要等待接收端的确认。如果没有收到确认，则需要重传该数据包。此外，还需要对接收到的数据包进行排序，以确保数据完整性。

以下是一个 Python 代码示例，演示了如何使用 UDP 传输文件： ```python
import socket
import os
import struct
def send_file(filename, server_address):
"""发送文件到指定的服务器地址。"""
sock = (socket.AF_INET, socket.SOCK_DGRAM)
with open(filename, 'rb') as f:
data = (1024) #每次读取1024字节
sequence_number = 0
while data:
packet = ('!I', sequence_number) + data #添加序列号
(packet, server_address)
# 等待确认 (简化版本，实际应用中需要更复杂的确认机制)
try:
(1) #设置超时时间
ack, address = (1024)
if ack == b'ACK':
sequence_number += 1
print(f"Packet {sequence_number-1} sent successfully")
else:
print(f"Error receiving ACK for packet {sequence_number}")
except :
print(f"Timeout waiting for ACK for packet {sequence_number}. Resending...")
#重发
continue

data = (1024)
()
print("File transfer complete.")

def receive_file(filename, server_address):
"""接收文件并保存到本地。"""
sock = (socket.AF_INET, socket.SOCK_DGRAM)
(server_address)
received_packets = {}
expected_sequence = 0
while True:
try:
data, address = (1024)
sequence_number = ('!I', data[:4])[0]
packet_data = data[4:]
received_packets[sequence_number] = packet_data
#检查是否接收到所有的包
if sequence_number == expected_sequence:
with open(filename, 'ab') as f:
(packet_data)
expected_sequence += 1
(b'ACK', address) #发送确认
print(f"Packet {sequence_number} received successfully")
#判断是否接收完成
all_received = True
for i in range(expected_sequence):
if i not in received_packets:
all_received = False
break
if all_received:
break
else:
print(f"Packet {sequence_number} received out of order or duplicated, ignoring.")
except Exception as e:
print(f"Error receiving packet: {e}")
break

()
print("File transfer complete.")

if __name__ == "__main__":
server_address = ('127.0.0.1', 12345) #服务器IP和端口
filename = '' #要传输的文件
# 发送文件
send_file(filename, server_address)
# 接收文件 (在另一台机器或同一机器的另一个终端运行)
receive_file('received_' + filename, server_address)
```