Re: RRe: A simple proxy server in C# - C# Discussion Boards

Re: A simple proxy server in C#

12-Aug-12 1:41

I have written a simple and minimalist HTTP proxy server that runs on command line. In the Start() method, a TcpListener blocks until it gets a client request and creates a new thread (ThreadHandleClient method) that processes this client, fetches its url and relays data.

The trouble is in the relay logic that I want to refine. In the first inner loop, I receive all webserver data and send it to client until zero bytes are left. In second inner loop, I do vice-versa: receive all client data and send to web-server until zero bytes left. However, the code gets blocked in the beginning of second inner-loop at client.receive(). This is what I'm basically doing:

Any help will be truly appreciated. Thanks in advance.

public void Start(IPAddress ip, int port)
    {
    try
    {
    TcpListener listener = new TcpListener(ip, port);
    listener.Start(100);
    while (!stopFlag)
    {
    Socket client = listener.AcceptSocket();
    IPEndPoint rep = (IPEndPoint)client.RemoteEndPoint;
    Thread th = new Thread(ThreadHandleClient);
    th.Start(client);
    }
    listener.Stop();
    }
    catch (Exception ex)
    {
    Debug.Print("START: " + ex.Message);
    }
    }
    public void ThreadHandleClient(object o)
    {
    try
    {
    Socket client = (Socket)o;
    NetworkStream ns = new NetworkStream(client);
    //RECEIVE CLIENT DATA
    byte[] buffer = new byte[2048];
    int rec = 0, sent = 0, transferred = 0, rport = 0;
    string data = "";
    do
    {
    rec = ns.Read(buffer, 0, buffer.Length);
    data += Encoding.ASCII.GetString(buffer, 0, rec);
    } while (rec == buffer.Length);
    //PARSE DESTINATION AND SEND REQUEST
    string line = data.Replace("\r\n", "\n").Split(new string[] { "\n" }, StringSplitOptions.None)[0];
    Uri uri = new Uri(line.Split(new string[] { " " }, StringSplitOptions.None)[1]);
    Debug.Print("CLIENT REQUEST RECEIVED: " + uri.OriginalString);
    if (uri.Scheme == "https")
    {
    rport = 443;
    Debug.Print("HTTPS - 443");
    }
    else
    {
    rport = 80;
    Debug.Print("HTTP - 443");
    }
    IPHostEntry rh = Dns.GetHostEntry(uri.Host);
    Socket webserver = new Socket(rh.AddressList[0].AddressFamily, SocketType.Stream, ProtocolType.IP);
    webserver.Connect(new IPEndPoint(rh.AddressList[0], rport));
    byte[] databytes = Encoding.ASCII.GetBytes(data);
    webserver.Send(databytes, databytes.Length, SocketFlags.None);
    Debug.Print("SENT TO SERVER. WILL NOW RELAY: " + data);
    //START RELAY
    buffer = new byte[2048];
    rec = 0;
    data = "";
    do
    {
    transferred = 0;
    do
    {
    rec = webserver.Receive(buffer, buffer.Length, SocketFlags.None);
    Debug.Print("RECEIVED FROM WEBSERVER[" + rec.ToString() + "]: " + Encoding.ASCII.GetString(buffer, 0, rec));
    sent = client.Send(buffer, rec, SocketFlags.None);
    Debug.Print("SENT TO CLIENT[" + sent.ToString() + "]: " + Encoding.ASCII.GetString(buffer, 0, rec));
    transferred += rec;
    //data += Encoding.ASCII.GetString(serverbytes, 0, rec);
    } while (rec == buffer.Length);
    Debug.Print("loop-1 finished");
    if (transferred == 0)
    break;
    transferred = 0;
    do
    {
    rec = client.Receive(buffer, buffer.Length, SocketFlags.None);
    Debug.Print("RECEIVED FROM CLIENT: " + Encoding.ASCII.GetString(buffer, 0, rec));
    sent = webserver.Send(buffer, rec, SocketFlags.None);
    Debug.Print("SENT TO WEBSERVER[" + sent.ToString() + "]: " + Encoding.ASCII.GetString(buffer, 0, rec));
    transferred += rec;
    } while (rec == buffer.Length);
    Debug.Print("loop-2 finished");
    } while (transferred > 0);
    Debug.Print("LOOP ENDS. EXITING THREAD");
    }
    catch (Exception ex)
    {
    Debug.Print("Error occured: " + ex.Message);
    }

Richard Andrew x6412-Aug-12 4:17

Richard Andrew x64

12-Aug-12 4:17

If no data has arrived, then Receive is going to block. If this is not what you want, then use BeginReceive.

The difficult we do right away...
...the impossible takes slightly longer.

RRe: A simple proxy server in C#

Prahlad Yeri12-Aug-12 5:07

12-Aug-12 5:07

Thanks Richard. For reasons of simplicity, I don't want to create anync calls and handle everything in thant one thread only. Is there no way to do this using the sync Receive() method ?

Richard Andrew x6412-Aug-12 5:25

Richard Andrew x64

12-Aug-12 5:25

If you want, you could call Receive on a background worker thread, but that would entail multiple threads.

The bottom line is that Receive will behave synchronously, meaning it will block when there is no data.

The difficult we do right away...
...the impossible takes slightly longer.

Prahlad Yeri12-Aug-12 5:31

12-Aug-12 5:31

Is there a way to check the data in the socket and call Receive() only when data is available for receiving. This way it should not block, right?

Richard Andrew x6412-Aug-12 5:36

Richard Andrew x64

12-Aug-12 5:36

I see that Socket has a method called Poll. Take a look:

Socket.Poll[^]

The difficult we do right away...
...the impossible takes slightly longer.

Prahlad Yeri12-Aug-12 6:18

XDocument.Save() reversing attribute order

12-Aug-12 6:18

Thanks. The Poll() method really helped. I'm now polling for three seconds before receiving for both client and the server. However, there is still some logical issue with my code:

if (client.Poll(3000 * 1000, SelectMode.SelectRead))
{
    rec = client.Receive(buffer, buffer.Length, SocketFlags.None);
    Debug.Print("RECEIVED FROM CLIENT: " + Encoding.ASCII.GetString(buffer, 0, rec));

    sent = webserver.Send(buffer, rec, SocketFlags.None);
    Debug.Print("SENT TO WEBSERVER[" + sent.ToString() + "]: " + Encoding.ASCII.GetString(buffer, 0, rec));
    transferred += rec;
}
else
{
    Debug.Print("No data polled from client");
}

As I said, one logical fault still remains. In the proxy client machine, I'm able to open google.com. Then performed a search that also went fine. However, when I click on a search result, the proxy again gives me google.com!! What am I missing?

Tracking system

kipchirchir11-Aug-12 20:52

kipchirchir

11-Aug-12 20:52

If i want a simple server to client communication as a background service on windows Os, that would only send ISP infor to a hosted domain, WHERE would i start? C# or VB.net or other? Which has an example or godd start?

Experience is the best teacher

Re: Tracking system

OriginalGriff11-Aug-12 21:17

OriginalGriff

11-Aug-12 21:17

kipchirchir wrote:
WHERE would i start?

By explaining that in terms we can understand?

kipchirchir wrote:
C# or VB.net or other?

Whichever you know and are comfortable with.
VB and C# are interchangeable, pretty much, anything you can do in one, you can do in the other.

Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water

Re: Tracking system

Richard MacCutchan11-Aug-12 21:46

Richard MacCutchan

11-Aug-12 21:46

See my answer in the .NET forum; BTW, please do not post the same question in multiple forums.

One of these days I'm going to think of a really clever signature.

Nukeman3311-Aug-12 2:03

Nukeman33

11-Aug-12 2:03

If I do something like this

XElement root = new XElement("Root",
new XAttribute("Att1", "a"),
new XAttribute("Att2", "b"),
new XAttribute("Att3", "c"));
XDocument document = new XDocument(root);
document.Save("file.xml");

Instead of it writing

Root Att1="a" Att2="b" Att3="c"/

it writes Root Att3="c" Att2="b" Att1="a"/

Even in debugging mode when I look at the XML contents of document it appears to be in the proper order, but when it writes to file it reverses them. Can anyone tell me why it is doing this?

Eddy Vluggen11-Aug-12 2:22

Eddy Vluggen

11-Aug-12 2:22

Efficiency, I guess. Does the order matter?

Bastard Programmer from Hell Suspicious | :suss:

if you can't read my code, try converting it here[^]

Dave Kreskowiak11-Aug-12 4:13

Dave Kreskowiak

11-Aug-12 4:13

Considering XML doesn't give a rats ass about the order of attributes, what's the problem?

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

jschell11-Aug-12 7:35

jschell

11-Aug-12 7:35

Nukeman33 wrote:
Can anyone tell me why it is doing this?

You have a bug either in implementation and/or requirements if you think that the order matters.