Develop Reference

Reopen Tcp socket on the same port

I have a socket that serves a single request-response purpose.
I set it up on port XXX let it wait for a connection, read the data and reply with some data.
I would like to open a new socket on the same port. As soon as the response was sent.
That is handled externally (there is a manager that is checking the state of the thread and if it was used it disposes it and creates a new one.
The problem is that it gets blocked on
_socket = _socket.Accept();
and when a new client tries to connect it never leaves this line. (And client gets no reply).
The socket is running in
new Thread(Run);
and here is my Run method:
private void Run()
{
var ipHostInfo = Dns.Resolve(Dns.GetHostName());
var ipAddress = ipHostInfo.AddressList[0];
var localEndPoint = new IPEndPoint(ipAddress, Port);
_socket = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
try
{
_socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
_socket.Bind(localEndPoint);
_socket.Listen(100);
_socket = _socket.Accept();
var data = string.Empty;
while (true)
{
var bytes = new byte[1024];
var bytesRec = _socket.Receive(bytes);
data += Encoding.UTF8.GetString(bytes, 0, bytesRec);
if (data.IndexOf("<EOF>", StringComparison.Ordinal) <= -1) continue;
var dataWithoutEof = data.Substring(0, data.IndexOf("<EOF>", StringComparison.Ordinal));
//TODO: do smt with the data
break;
}
var byteData = Encoding.UTF8.GetBytes("testResponse" + "<EOF>");
_socket.Send(byteData);
_socket.Shutdown(SocketShutdown.Both);
_socket.Close();
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
I suppose that I am not closing the existing socket correctly.

You code is wrong you should not expect this method to exit because you want your server up and running the whole time. I am assuming here you call run several times. Don't do that.
The code becomes then something like this :
_socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
_socket.Bind(localEndPoint);
_socket.Listen(100);
while (true)
{
var _servicingsocket = _socket.Accept();
....
_servicingsocket.close();
}
accept is a blocking call. That waits for a new connection.
_socket is a listening socket and must be kept during the lifetime of the server.
A TCP connection is based on the notion of a socket pair.
When the server starts you have a single socket that listens on port 100.
Suppose a connection is established, then accept returns what is called a servicing socket that is basically a clone from the listening socket. This means that it is also using source port 100, but because it is a servicing socket it belongs to a socket pair that identifies the connection. A socket pair is the combination of 2 sockets, your own socket and the peer. When a data comes in, TCP will iterate through the socket pairs to find the right socket.
An additional advantage of doing it this way is that you allow other connection attempts to queue up on the listening socket while you are processing the first request. Your _socket is overwritten with the servicing socket and you are then assuming that the listening socket is going to be garbage collected. I am not sure if this is going to happen because I haven't tried it like you are doing it in your code because it is a bad idea in the first place because it implements idisposable. (https://msdn.microsoft.com/en-us/library/system.net.sockets.socket%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396) If you really want to close the server you have to make sure to close both the servicing socket and the listening socket to make the code clean.

UDP Listener using sockets generating type error

Im new to Sockets and C# in general and am having a difficult time implementing a simple upd listener function. I've spent alot of time searching the web tying unsuccessfully to intergate any of the numerious examples online. So any suggestions, links, examples would be greatly appreciated!
At this point, I have a third party application broadcasting over port 6600 a general UPD message containing information about the location of the application server (ServerName, IP Address, etc.). I'd like to design my listener client application to capture the UPD broadcast and generate a collection of the available servers which can be used to future processing.
The problem I'm having is that when I attempt to create the listener using listener.Listen(0) if fails and generates a general type error. If I attempt to us the UdpClient class my application hangs and never returns any data. The Code for both examples is listed below:
namespace UDPListener
{
class Program
{
static void Main(string[] args)
{
Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
listener.Bind(new IPEndPoint(IPAddress.Any, 6600));
listener.Listen(6);
Socket socket = listener.Accept();
Stream netStream = new NetworkStream(socket);
StreamReader reader = new StreamReader(netStream);
string result = reader.ReadToEnd();
Console.WriteLine(result);
socket.Close();
listener.Close();
}
}
}
And the UdpClient:
private void IdentifyServer()
{
//Creates a UdpClient for reading incoming data.
UdpClient receivingUdpClient = new UdpClient(6600);
//Creates an IPEndPoint to record the IP Address and port number of the sender.
// The IPEndPoint will allow you to read datagrams sent from any source.
IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
try
{
// Blocks until a message returns on this socket from a remote host.
Byte[] receiveBytes = receivingUdpClient.Receive(ref RemoteIpEndPoint);
string returnData = Encoding.ASCII.GetString(receiveBytes);
Output.Text = ("This is the message you received " +
returnData.ToString());
Output.Text = ("This message was sent from " +
RemoteIpEndPoint.Address.ToString() +
" on their port number " +
RemoteIpEndPoint.Port.ToString());
}
catch (Exception e)
{
MessageBox.Show(e.ToString());
}

dtb was absolutely write! After much research and some help from a friend I realized that what I was actually looking for was a solution for Multicasting. I'll include the links below.
#dtb, thanks for helping point me in the right direction!
http://www.codeproject.com/Articles/1705/IP-Multicasting-in-C
http://codeidol.com/csharp/csharp-network/IP-Multicasting/Csharp-IP-Multicast-Support/

Unable to Read byte Stream in C#

I am building a client server application where a client has to send some byte stream and the server responds to it based on the bytes received from the Client. I am using the NetworkStream.Write and NetworkStream.Read methods to send and receive data. The client is able to create a TCP connection to the server. After accepting the connection, the server does NetworkStream.Read and waits for some input from the client. The Client sends the data using the NetworkStream.Write and also does NetworkStream.Flush. But the Server never wakes up from the Read.
Can you guys suggest me what could be the problem here or if you know any other methods to send Byte Stream over a TCP Connection in C# please let me know.
Thanks!

Smart-ass comments aside: even though you are only interested in 2 lines of code, I'm willing to bet your problem is someplace else in your code.
Using a modified version of the code found here, I constructed a simple example that works in my testing.
public static void Main()
{
TcpListener server = null;
try
{
// Set the TcpListener on port 13000.
Int32 port = 13000;
IPAddress localAddr = IPAddress.Parse("127.0.0.1");
// TcpListener server = new TcpListener(port);
server = new TcpListener(localAddr, port);
// Start listening for client requests.
server.Start();
// Buffer for reading data
Byte[] bytes = new Byte[256];
Console.Write("Waiting for a connection... ");
// Perform a blocking call to accept requests.
// You could also user server.AcceptSocket() here.
TcpClient client = server.AcceptTcpClient();
Console.WriteLine("Connected!");
// Get a stream object for reading and writing
NetworkStream stream = client.GetStream();
stream.Read(bytes, 0, bytes.Length);
Console.WriteLine(System.Text.Encoding.ASCII.GetString(bytes));
// Shutdown and end connection
client.Close();
}
catch (SocketException e)
{
Console.WriteLine("SocketException: {0}", e);
}
finally
{
// Stop listening for new clients.
server.Stop();
}
Console.WriteLine("\nHit enter to continue...");
Console.Read();
}
The read call will wait and return when I send it 1 byte with another program. We would need to see some code to figure out why this works and yours does not.

tcp/ip client server not working over internet

I'm going to setup a small client/server server in TCP/IP mode, I use VS2010,C# to develop my apps, I've googled a lot and could find some source codes, but none of them work in internet, I can get some answers in my own local system, i.e. I run my server, then listen for my own localhost (127.0.0.1) then send some data (for example using telnet), it works fine but when I do the same over internet I get nothing! I want to use port 80, as I want to send/receive http data, I have tested several source codes, here is the last code I have used (and it works on localhost with telnet)
//server code:
form_load()
IPAddress localAddress = IPAddress.Parse("127.0.0.1");
Socket listenSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
IPEndPoint ipEndpoint = new IPEndPoint(localAddress, 80);
// Bind the socket to the end point
listenSocket.Bind(ipEndpoint);
// Start listening, only allow 1 connection to queue at the same time
listenSocket.Listen(1);
listenSocket.BeginAccept(new AsyncCallback(ReceiveCallback), listenSocket);
Console.WriteLine("Server is waiting on socket {0}", listenSocket.LocalEndPoint);
// Start being important while the world rotates
while (true)
{
Console.WriteLine("Busy Waiting....");
Thread.Sleep(2000);
}
public static void ReceiveCallback(IAsyncResult AsyncCall)
{
System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
Byte[] message = encoding.GetBytes("I am a little busy, come back later!");
Socket listener = (Socket)AsyncCall.AsyncState;
Socket client = listener.EndAccept(AsyncCall);
Console.WriteLine("Received Connection from {0}", client.RemoteEndPoint);
client.Send(message);
Console.WriteLine("Ending the connection");
client.Close();
listener.BeginAccept(new AsyncCallback(ReceiveCallback), listener);
}
send data (client), of course I haven't used this code, is it right?
public static string SendData()
{
TcpClient client = new TcpClient();
client.Connect(IP, 80);
StreamWriter sw = new StreamWriter(client.GetStream());
StreamReader sr = new StreamReader(client.GetStream());
//if statement evalutes to see if the user has selected to update the server
//" " = update server
//"" = do not update the server
//if (updateData.Equals(""))
//{
// space = "";
//}
//else if (!updateData.Equals(""))
//{
// space = " ";
//}
//Refrences stream writer, username variable passed in from GUI
//space variable provides update function: "" = dont update. " " = update database.
sw.WriteLine("h");
sw.Flush();
//data send back from the server assigned to string variable
//string recieved = sr.ReadLine();
return "";
}
I'm going to have the server code in my Server (winserver 2008R2) but currently test it in normal PCs, what am I doing wrong? I want to send some http packet from a random system (with a random IP) to my server (which I know its IP), what should I do? is it possible with tcp/ip or I should do something else?
is it related to static IP? should I certainly have static IP? my web server has a static IP but my clients do not, is it a problem?
I think I have some problem in defining ports and IPs, how should I set them? my server has a specific IP, but I don't know IP of my clients, would you please explain it to me step by step?
thanks

The two most common problems in this scenario:
Ensure your server's router is using port forwarding to forward HTTP requests from the router to the server.
Ensure you are connecting to the server's public IP address, not its local network address.

getting 10060 (Connection Timed Out) when stress testing simple tcp server

I have created simple tcp server - it works pretty well.
the problems starts when we switch to the stress tests -since our server should handle many concurrent open sockets - we have created a stress test to check this.
unfortunately, looks like the server is choking and can not respond to new connection request in timely fashion when the number of the concurrent open sockets are around 100.
we already tried few types of server - and all produce the same behavior.
the server: can be something like the samples in this post(all produce the same behavior)
How to write a scalable Tcp/Ip based server
here is the code that we are using - when a client connects - the server will just hang in order to keep the socket alive.
enter code here
public class Server
{
private static readonly TcpListener listener = new TcpListener(IPAddress.Any, 2060);
public Server()
{
listener.Start();
Console.WriteLine("Started.");
while (true)
{
Console.WriteLine("Waiting for connection...");
var client = listener.AcceptTcpClient();
Console.WriteLine("Connected!");
// each connection has its own thread
new Thread(ServeData).Start(client);
}
}
private static void ServeData(object clientSocket)
{
Console.WriteLine("Started thread " + Thread.CurrentThread.ManagedThreadId);
var rnd = new Random();
try
{
var client = (TcpClient)clientSocket;
var stream = client.GetStream();
byte[] arr = new byte[1024];
stream.Read(arr, 0, 1024);
Thread.Sleep(int.MaxValue);
}
catch (SocketException e)
{
Console.WriteLine("Socket exception in thread {0}: {1}", Thread.CurrentThread.ManagedThreadId, e);
}
}
}
the stress test client: is a simple tcp client, that loop and open sokets, one after the other
class Program
{
static List<Socket> sockets;
static private void go(){
Socket newsock = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
IPEndPoint iep = new IPEndPoint(IPAddress.Parse("11.11.11.11"), 2060);
try
{
newsock.Connect(iep);
}
catch (SocketException ex)
{
Console.WriteLine(ex.Message );
}
lock (sockets)
{
sockets.Add(newsock);
}
}
static void Main(string[] args)
{
sockets = new List<Socket>();
//int start = 1;// Int32.Parse(Console.ReadLine());
for (int i = 1; i < 1000; i++)
{
go();
Thread.Sleep(200);
}
Console.WriteLine("press a key");
Console.ReadKey();
}
}
}
is there an easy way to explain this behavior? maybe c++ implementation if the TCP server will produce better results? maybe it is actually a client side problem?
Any comment will be welcomed !
ofer

Specify a huge listener backlog: http://msdn.microsoft.com/en-us/library/5kh8wf6s.aspx

Firstly a thread per connection design is unlikely to be especially scalable, you would do better to base your design on an asynchronous server model which uses IO Completion Ports under the hood. This, however, is unlikely to be the problem in this case as you're not really stressing the server that much.
Secondly the listen backlog is a red herring here. The listen backlog is used to provide a queue for connections that are waiting to be accepted. In this example your client uses a synchronous connect call which means that the client will never have more than 1 connect attempt outstanding at any one time. If you were using asynchronous connection attempts in the client then you would be right to look at tuning the listen backlog, perhaps.
Thirdly, given that the client code doesn't show that it sends any data, you can simply issue the read calls and remove the sleep that follows it, the read calls will block. The sleep just confuses matters.
Are you running the client and the server on the same machine?
Is this ALL the code in both client and server?
You might try and eliminate the client from the problem space by using my free TCP test client which is available here: http://www.lenholgate.com/blog/2005/11/windows-tcpip-server-performance.html
Likewise, you could test your test client against one of my simple free servers, like this one: http://www.lenholgate.com/blog/2005/11/simple-echo-servers.html
I can't see anything obviously wrong with the code (apart from the overall design).