[Computer Network] 套接字编程作业4：代理服务器 Proxy Server 提高要求-POST

Porxy Server

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本作业的基本要求可参考: https://blog.csdn.net/young_cr7/article/details/104703586

1. 原理介绍

   (1) POST请求一般用于向服务器发送数据，而代理服务器可将客户端发送的数据缓存。若存在历史数据则进行比对，两者一致则无需向服务器发送该数据(此处假设由客户端发送POST请求，经代理服务器到达服务器，是服务器获取数据的唯一方式)。两者不一致或不存在历史数据时，则由代理服务器通过POST请求方式向服务器发送数据，同时将该数据缓存。当发送数据成功时，则向客户端发送响应报文"OK"

   (2) 接受POST请求的服务器可利用Python的flask进行编写

   from flask import Flask, request
   app = Flask(__name__)
   
   
   @app.route('/simulator/gridConnect/', methods=['GET', 'POST'])
   def set_grid_connect():
       recv_data = request.get_json()
       print(request)
       if recv_data:
           grid_connect = recv_data['grid_connected']
       return "OK"
   

   (3) 可借助Postman软件向代理服务器发送POST请求

2. Source code

from socket import *
import traceback

tcpSerSock = socket(AF_INET, SOCK_STREAM)
server_port = 22500
tcpSerSock.bind(('', server_port))
tcpSerSock.listen(1)

while True:
    print('Ready to serve...')
    tcpCliSock, addr = tcpSerSock.accept()
    print('Received a connection from:', addr)
    message = tcpCliSock.recv(1024).decode(encoding="utf-8")
    print(message)
    request_method = message.split()[0]
    # Extract the filename from the given message
    filename = message.split()[1].partition("//")[2].replace('/', '_').replace(':', '_')
    print(filename)
    fileExist = "false"
    if request_method == "GET":
        # 省略
    elif request_method == "POST":
        try:
            post_data = ''.join(message[message.index('{') + 1:message.index('}')].split())
            print(post_data)
            f = open(filename, "r")
            outputdata = f.read()
            print(outputdata)
            if post_data != outputdata:
                raise ValueError
            tcpCliSock.sendall("HTTP/1.1 200 OK\r\n".encode(encoding="utf-8"))
            tcpCliSock.sendall("Content-Type:text/html\r\n".encode(encoding="utf-8"))
            tcpCliSock.sendall("\r\nOK\r\n".encode(encoding="utf-8"))
            print('Not modified')
        except IOError:
            print(traceback.format_exc())
            tmpFile = open("./" + filename, "w")
            tmpFile.writelines(post_data)
            tmpFile.close()
            c = socket(AF_INET, SOCK_STREAM)
            host_address = message.split()[1].partition("//")[2].partition("/")[0].replace("www.", "", 1)
            hostname = host_address.partition(":")[0]
            host_port = int(host_address.partition(":")[2])
            try:
                c.connect((hostname, host_port))
                old_url = message.split()[1]
                new_url = ''.join(old_url.partition("//")[2].partition("/")[1:])
                message = message.replace(old_url, new_url)
                c.send(message.encode(encoding="utf-8"))
                buff = c.recv(1024).decode(encoding="utf-8")
                print(buff)
                tcpCliSock.send("HTTP/1.1 200 OK\r\n".encode(encoding="utf-8"))
                tcpCliSock.send("Content-Type:text/html\r\n".encode(encoding="utf-8"))
                tcpCliSock.send("\r\nOK\r\n".encode(encoding="utf-8"))
            except:
                print("Illegal request")
    tcpCliSock.close()
tcpSerSock.close()

3. 客户端
   
   ​ 向服务器发送grid_connected数据(数据为json格式)，响应报文为OK

4. 代理服务器

   (1) 代理服务器没有该数据的缓存时，向服务器发送POST请求

   POST http://localhost:9000/simulator/gridConnect/ HTTP/1.1
   Content-Type: application/json
   User-Agent: PostmanRuntime/7.22.0
   Accept: */*
   Cache-Control: no-cache
   Postman-Token: 39ae1a6d-1547-4ce6-afbe-b29d2eff9a06
   Host: localhost:9000
   Accept-Encoding: gzip, deflate, br
   Content-Length: 35
   Connection: keep-alive
   
   {
       "grid_connected": true	
   }
   
   localhost_9000_simulator_gridConnect_
   "grid_connected":true
   Traceback (most recent call last):
     File "D:/Pycharm-project/Computer Network/Socket/Proxy Server/proxyServer.py", line 61, in <module>
       f = open(filename, "r")
   FileNotFoundError: [Errno 2] No such file or directory: 'localhost_9000_simulator_gridConnect_'
   
   HTTP/1.0 200 OK
   

   (2) 代理服务器有了该数据的缓存，当客户端发送数据与历史数据一致时，代理服务器打印Not modified，不再向服务器发送请求

   POST http://localhost:9000/simulator/gridConnect/ HTTP/1.1
   Content-Type: application/json
   User-Agent: PostmanRuntime/7.22.0
   Accept: */*
   Cache-Control: no-cache
   Postman-Token: 6347322c-7f21-4c82-9866-a71a7ace662d
   Host: localhost:9000
   Accept-Encoding: gzip, deflate, br
   Content-Length: 35
   Connection: keep-alive
   
   {
       "grid_connected": true	
   }
   
   localhost_9000_simulator_gridConnect_
   "grid_connected":true
   "grid_connected":true
   Not modified
   

​