面试题：Python UDP服务器数据可靠性处理

实现思路

添加序列号：为每个发送的UDP数据包添加一个唯一的序列号。接收方根据序列号判断数据包是否按序到达，并且可以检测到丢失的数据包。
确认机制：接收方接收到数据包后，向发送方发送一个确认包（ACK），ACK包中包含接收到的数据包的序列号。
重传机制：发送方在发送数据包后，启动一个定时器。如果在定时器超时之前没有收到对应的ACK，就重传该数据包。
窗口机制：引入发送窗口，限制发送方在未收到ACK的情况下可以连续发送的数据包数量，避免过多重传导致网络拥塞。

关键代码片段

发送方代码

import socket
import time

# 创建UDP套接字
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
server_address = ('localhost', 10000)

# 发送窗口大小
window_size = 5
# 数据包序列号
sequence_number = 0
# 已发送但未确认的数据包
unacknowledged_packets = {}

def send_packet(data, seq_num):
    packet = f"{seq_num}:{data}".encode('utf-8')
    sock.sendto(packet, server_address)
    unacknowledged_packets[seq_num] = {
        'data': data,
      'sent_time': time.time()
    }

while True:
    while sequence_number - min(unacknowledged_packets.keys()) < window_size if unacknowledged_packets else True:
        data = input("Enter data to send (type 'exit' to quit): ")
        if data.lower() == 'exit':
            break
        send_packet(data, sequence_number)
        sequence_number += 1

    # 检查是否有超时的数据包需要重传
    current_time = time.time()
    for seq_num, packet_info in list(unacknowledged_packets.items()):
        if current_time - packet_info['sent_time'] > 1:  # 超时时间1秒
            print(f"Timeout for sequence number {seq_num}, retransmitting...")
            send_packet(packet_info['data'], seq_num)
            packet_info['sent_time'] = current_time

    try:
        sock.settimeout(0.1)  # 设置接收ACK的超时时间
        ack, _ = sock.recvfrom(1024)
        ack_seq_num = int(ack.decode('utf-8'))
        if ack_seq_num in unacknowledged_packets:
            del unacknowledged_packets[ack_seq_num]
            print(f"Received ACK for sequence number {ack_seq_num}")
    except socket.timeout:
        continue

    if data.lower() == 'exit':
        break

sock.close()

接收方代码

import socket

# 创建UDP套接字
sock = socket.socket(socket.AF_INET, socket.SOCK_DUDP)
server_address = ('localhost', 10000)
sock.bind(server_address)

expected_sequence_number = 0

while True:
    data, address = sock.recvfrom(1024)
    seq_num, received_data = data.decode('utf-8').split(':', 1)
    seq_num = int(seq_num)

    if seq_num == expected_sequence_number:
        print(f"Received data: {received_data}")
        ack = str(seq_num).encode('utf-8')
        sock.sendto(ack, address)
        expected_sequence_number += 1
    else:
        print(f"Received out - of - order packet with sequence number {seq_num}")

面试题：Python UDP服务器数据可靠性处理

知识考点

面试题答案

实现思路

关键代码片段

发送方代码

接收方代码