Creating a Proxy Webserver in Python | Set 1 - GeeksforGeeks

15 Nov, 2017
Socket programming in python is very user friendly as compared to c. The programmer need not worry about minute details regarding sockets. In python, the user has more chance of focusing on the application layer rather than the network layer. In this tutorial we would be developing a simple multi-threaded proxy server capable of handling HTTP traffic. It would be mostly based on the basic socket programming ideas. If you are not sure about the basics then i would recommend that you brush them up before going through this tutorial.
This is a naive implementation of a proxy server. We would be gradually developing it into a quite useful server in the upcoming tutorials.
To begin with, we would achieve the process in 3 easy steps
1. Creating an incoming socketWe create a socket serverSocket in the __init__ method of the Server Class. This creates a socket for the incoming connections. We then bind the socket and then wait for the clients to connect.
def __init__(self, config):
    # Shutdown on Ctrl+C
    signal.signal(signal.SIGINT, self.shutdown) 

    # Create a TCP socket
    self.serverSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    # Re-use the socket
    self.serverSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

    # bind the socket to a public host, and a port   
    self.serverSocket.bind((config['HOST_NAME'], config['BIND_PORT']))
    
    self.serverSocket.listen(10) # become a server socket
    self.__clients = {}

2. Accept client and processThis is the easiest yet the most important of all the steps. We wait for the client’s connection request and once a successful connection is made, we dispatch the request in a separate thread, making ourselves available for the next request. This allows us to handle multiple requests simultaneously which boosts the performance of the server multifold times.
while True:

    # Establish the connection
    (clientSocket, client_address) = self.serverSocket.accept() 
    
    d = threading.Thread(name=self._getClientName(client_address), 
    target = self.proxy_thread, args=(clientSocket, client_address))
    d.setDaemon(True)
    d.start()

3. Redirecting the trafficThe main feature of a proxy server is to act as an intermediate between source and destination. Here, we would be fetching data from source and then pass it to the client.
First, we extract the URL from the received request data.
# get the request from browser
request = conn.recv(config['MAX_REQUEST_LEN']) 

# parse the first line
first_line = request.split('\n')[0]

# get url
url = first_line.split(' ')[1]
Then, we find the destination address of the request. Address is a tuple of (destination_ip_address, destination_port_no). We will be receiving data from this address.
http_pos = url.find("://") # find pos of ://
if (http_pos==-1):
    temp = url
else:
    temp = url[(http_pos+3):] # get the rest of url

port_pos = temp.find(":") # find the port pos (if any)

# find end of web server
webserver_pos = temp.find("/")
if webserver_pos == -1:
    webserver_pos = len(temp)

webserver = ""
port = -1
if (port_pos==-1 or webserver_pos < port_pos): 

    # default port 
    port = 80 
    webserver = temp[:webserver_pos] 

else: # specific port 
    port = int((temp[(port_pos+1):])[:webserver_pos-port_pos-1])
    webserver = temp[:port_pos] 

Now, we setup a new connection to the destination server (or remote server), and then send a copy of the original request to the server. The server will then respond with a response. All the response messages use the generic message format of RFC 822.
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
s.settimeout(config['CONNECTION_TIMEOUT'])
s.connect((webserver, port))
s.sendall(request)

We then redirect the server’s response to the client. conn is the original connection to the client. The response may be bigger then MAX_REQUEST_LEN that we are receiving in one call, so, a null response marks the end of the response.
while 1:
    # receive data from web server
    data = s.recv(config['MAX_REQUEST_LEN'])

    if (len(data) > 0):
        conn.send(data) # send to browser/client
    else:
        break

We then close the server connections appropriately and do the error handling to make sure the server works as expected.
How to test the server?1. Run the server on a terminal. Keep it running and switch to your favorite browser.2. Go to your browser’s proxy settings and change the proxy server to ‘localhost’ and port to ‘12345’.3. Now open any HTTP website (not HTTPS), for eg. geeksforgeeks.org and volla !! you should be able to access the content on the browser.
Once the server is running, we can monitor the requests coming to the client. We can use that data to monitor the content that is going or we can develop statistics based on the content.We can even restrict access to a website or blacklist an IP address. We would be dealing with more such features in the upcoming tutorials.What next?We would be adding the following features in our proxy server in the upcoming tutorials.– Blacklisting Domains– Content monitoring– Logging– HTTP WebServer + ProxyServer
The whole working source code of this tutorial is available here
Creating a Proxy Webserver in Python | Set 2
If you have any questions/comments then feel free to post them in the comments section.
About the Author:
Pinkesh Badjatiya hails from IIIT Hyderabad .He is a geek at heart with ample projects worth looking for. His project work can be seen here. 
If you also wish to showcase your blog here, please see GBlog for guest blog writing on GeeksforGeeks.
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