[Computer Network] 套接字编程作业4：代理服务器 Proxy Server

Porxy Server

source code

# proxyServer.py
from socket import *

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)
    # Extract the filename from the given message
    filename = message.split()[1].partition("//")[2].replace('/', '_')
    print(filename)
    fileExist = "false"
    try:
        # Check whether the file exist in the cache
        f = open(filename, "r")
        outputdata = f.readlines()
        outputdata = outputdata[outputdata.index("<html>\n")-1:]
        fileExist = "true"
        # ProxyServer finds a cache hit and generates a response message
        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"))
        print(outputdata)
        for line in outputdata:
            tcpCliSock.send(line.encode(encoding="utf-8"))
        print('Read from cache')
    # Error handling for file not found in cache
    except IOError:
        if fileExist == "false":
            # Create a socket on the proxy server
            c = socket(AF_INET, SOCK_STREAM)
            hostname = message.split()[1].partition("//")[2].partition("/")[0].replace("www.", "", 1)
            print("Host name:", hostname)
            try:
                # Connect to the socket to port 80
                c.connect((hostname, 80))
                c.send(message.encode(encoding="utf-8"))
                buff = c.recv(1024).decode(encoding="utf-8")          
                # Create a new file in the cache for the requested file.
                # Also send the response in the buffer to client socket and the corresponding file in the cache
                tcpCliSock.send(buff.encode(encoding="utf-8"))
                tmpFile = open("./" + filename, "w")
                tmpFile.writelines(buff)
                tmpFile.close()
            except:
                print("Illegal request")
        else:
            # HTTP response message for file not found
            tcpCliSock.send("404 Found".encode(encoding="utf-8"))
    tcpCliSock.close()
tcpSerSock.close()

搜索中输入代理服务器，打开系统设置的代理服务器设置，地址设为http://localhost，端口设置为程序中的server_port
访问http://gaia.cs.umass.edu/wireshark-labs/INTRO-wireshark-file1.html，通过代理服务器请求html对象

由于代理服务器没有缓存，因此代理服务器会向服务器gaia.cs.umass.edu请求该对象，见图中Host name: gaia.cs.umass.edu，并将该文件对象存在代理服务器的文件夹中，结果如下
再次访问该网页，通过代理服务器请求对象

由于代理服务器有该对象的缓存，因此直接从缓存中取出对象发送给浏览器，见图中Read from cache

![proxy5](proxy5.png)// 代理服务器缓存的文件，除html外还包括响应报文的状态行和首部行

HTTP/1.1 200 OK

Date: Fri, 06 Mar 2020 07:35:34 GMT

Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips PHP/5.4.16 mod_perl/2.0.11 Perl/v5.16.3

Last-Modified: Fri, 06 Mar 2020 06:59:02 GMT

ETag: "51-5a02a3045f9f3"

Accept-Ranges: bytes

Content-Length: 81

Content-Type: text/html; charset=UTF-8



<html>
	Congratulations!  You've downloaded the first Wireshark lab file!
</html>

值得一提的是，该文件除包含响应报文的entity body，即html部分内容外，还包状态行、首部行等，若直接显示则会出现
在这里插入图片描述

可对该对象进行一定的处理后再发送给浏览器，保证只显示有用信息，或在保存该文件对象时便对其进行处理

outputdata = f.readlines()
outputdata = outputdata[outputdata.index("<html>\n")-1:]

其他注意事项

代理服务器运行在本机时，若将IP地址设为127.0.0.1，可能无法正常运行

解决方法：直接输入空字符，使用默认值localhost
```
# tcpSerSock.bind(('127.0.0.1', server_port))
tcpSerSock.bind(('', server_port))
```

young_cr7

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[Computer Network] 套接字编程作业4：代理服务器 Proxy Server

Porxy Server

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