I have been troubleshooting an issue that I encountered when using a library called AMQP .Net Lite (https://github.com/Azure/amqpnetlite) and have determined that it can be reproduced using a simple .NET Sockets client and server. My repro environment uses a client that sends simple text messages to the server based on some Microsoft samples (see below).
I have noticed after I sign into my company VPN that messages fail to transfer with the following error:
SocketException : System.Net.Sockets.SocketException (0x80004005): An existing connection was forcibly closed by the remote host
I am running both client and server locally on my machine when I encounter the issue.
I have read about this exception and learned that one cause is that the network link has gone down for some reason. This makes sense as logging into VPN must temporarily break the connection, thereby causing the exception. However, one interesting observation is that this problem only occurs when the server is hosting using IPv6. If I force it to use IPv4, then there is no loss of connectivity. Is there a simple explanation for that?
I am also wondering if there is some way to detect that the Socket is in a bad state without sending data? Are there some properties on the Socket I can inspect such that I can detect an issue and force a reconnect? If not, what do people typically do in this situation to ensure the failed messages are accounted for after reconnection?
Interestingly, with my test client, I have to send 2 messages before the exception is thrown, but neither message is received by the server (see picture below).
I am not a networking expert so bear with me if this is fundamental stuff.
Here is my client:
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;
public class SynchronousSocketClient
{
public static void StartClient()
{
// Data buffer for incoming data.
byte[] bytes = new byte[1024];
// Connect to a remote device.
try
{
// Establish the remote endpoint for the socket.
// This example uses port 11000 on the local computer.
IPHostEntry ipHostInfo = Dns.GetHostEntry(Environment.MachineName);
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, 11000);
// Create a TCP/IP socket.
Socket sender = new Socket(AddressFamily.InterNetworkV6,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes("This is a test");
Console.WriteLine("Press any key to send a message...");
int i = 0;
while (true)
{
Console.ReadLine();
// Send the data through the socket.
int bytesSent = sender.Send(msg);
Console.WriteLine(++i + " messages sent");
}
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (ArgumentNullException ane)
{
Console.WriteLine("ArgumentNullException : {0}", ane.ToString());
}
catch (SocketException se)
{
Console.WriteLine("SocketException : {0}", se.ToString());
}
catch (Exception e)
{
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.ReadLine();
}
public static int Main(String[] args)
{
StartClient();
return 0;
}
}
Here is my server:
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class SynchronousSocketListener
{
// Incoming data from the client.
public static string data = null;
public static void StartListening()
{
// Data buffer for incoming data.
byte[] bytes = new Byte[1024];
// Establish the local endpoint for the socket.
// Dns.GetHostName returns the name of the
// host running the application.
IPEndPoint localEndPoint = new IPEndPoint(IPAddress.IPv6Any, 11000);
// Create a TCP/IP socket.
Socket listener = new Socket(AddressFamily.InterNetworkV6,
SocketType.Stream, ProtocolType.Tcp);
// Bind the socket to the local endpoint and
// listen for incoming connections.
try
{
listener.Bind(localEndPoint);
listener.Listen(10);
// Start listening for connections.
while (true)
{
Console.WriteLine("Waiting for a connection...");
// Program is suspended while waiting for an incoming connection.
Socket handler = listener.Accept();
// An incoming connection needs to be processed.
while (true)
{
bytes = new byte[1024];
int bytesRec = handler.Receive(bytes);
data = Encoding.ASCII.GetString(bytes, 0, bytesRec);
Console.WriteLine(data);
}
// Show the data on the console.
Console.WriteLine("Text received : {0}", data);
// Echo the data back to the client.
byte[] msg = Encoding.ASCII.GetBytes(data);
handler.Send(msg);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.WriteLine("\nPress ENTER to continue...");
Console.Read();
}
public static int Main(String[] args)
{
StartListening();
return 0;
}
}
Here is a screenshot of the problem:
Related
i want to let 2 c# apps each one is on a separate computer and both connected to the same ADSL router to send messages to each other i know that we have to use Sockets and tried many solutions on the internet but they are all working at the same computer but not working on a separate computers.
i believe that the problem is in the ip addresses but i tried a lot with no good results
is there any simple code to help please
i tried this function on server side
public static void StartServer()
{
IPHostEntry host = Dns.GetHostEntry("DESKTOP-SBJHC7I");
IPAddress ipAddress = host.AddressList[0];
Console.WriteLine(ipAddress.ToString());
IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);
try
{
// Create a Socket that will use Tcp protocol
Socket listener = new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
// A Socket must be associated with an endpoint using the Bind method
listener.Bind(localEndPoint);
// Specify how many requests a Socket can listen before it gives Server busy response.
// We will listen 10 requests at a time
listener.Listen(10);
Console.WriteLine("Waiting for a connection...");
Socket handler = listener.Accept();
// Incoming data from the client.
string data = null;
byte[] bytes = null;
while (true)
{
bytes = new byte[1024];
int bytesRec = handler.Receive(bytes);
data += Encoding.ASCII.GetString(bytes, 0, bytesRec);
if (data.IndexOf("<EOF>") > -1)
{
break;
}
}
Console.WriteLine("Text received : {0}", data);
byte[] msg = Encoding.ASCII.GetBytes(data);
handler.Send(msg);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.WriteLine("\n Press any key to continue...");
Console.ReadKey();
}
and this function in the client side
public static void StartClient()
{
byte[] bytes = new byte[1024];
try
{
// Connect to a Remote server
// Get Host IP Address that is used to establish a connection
// In this case, we get one IP address of localhost that is IP : 127.0.0.1
// If a host has multiple addresses, you will get a list of addresses
IPHostEntry host = Dns.GetHostEntry("DESKTOP-SBJHC7I");
IPAddress ipAddress = host.AddressList[0];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, 11000);
// Create a TCP/IP socket.
Socket sender = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
// Connect to Remote EndPoint
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes("This is a test<EOF>");
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (ArgumentNullException ane)
{
Console.WriteLine("ArgumentNullException : {0}", ane.ToString());
}
catch (SocketException se)
{
Console.WriteLine("SocketException : {0}", se.ToString());
}
catch (Exception e)
{
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
please make sure that your client is connected to the same IP on which server is started. because it seems in your code that your client connecting to host which you getting it from localhost identity. For your testing purpose please hardcode the Server's IP address in your Remoteendpoint. if still the issue same then I will share code to test on a different networks.
My problem is weird and i was not able to find a resolution from referring to other threads regarding this. I am getting the error when i run the microsoft Synchronous Server Socket Example, Synchronous Client Socket Example, on two systems which are part of the domain but i do not get this error when i run the same code on two systems which are part of the network but they are not part of the domain! Anyone know what might be causing the issue?
The things i have done to try to resolve are I made sure the port was open, switched off the firewall and antivirus as suggested by others with similar problem.But it has not helped.
Server code:
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class SynchronousSocketListener {
// Incoming data from the client.
public static string data = null;
public static void StartListening() {
// Data buffer for incoming data.
byte[] bytes = new Byte[1024];
// Establish the local endpoint for the socket.
// Dns.GetHostName returns the name of the
// host running the application.
IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[0];
IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);
// Create a TCP/IP socket.
Socket listener = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp );
// Bind the socket to the local endpoint and
// listen for incoming connections.
try {
listener.Bind(localEndPoint);
listener.Listen(10);
// Start listening for connections.
while (true) {
Console.WriteLine("Waiting for a connection...");
// Program is suspended while waiting for an incoming connection.
Socket handler = listener.Accept();
data = null;
// An incoming connection needs to be processed.
while (true) {
int bytesRec = handler.Receive(bytes);
data += Encoding.ASCII.GetString(bytes,0,bytesRec);
if (data.IndexOf("<EOF>") > -1) {
break;
}
}
// Show the data on the console.
Console.WriteLine( "Text received : {0}", data);
// Echo the data back to the client.
byte[] msg = Encoding.ASCII.GetBytes(data);
handler.Send(msg);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
Console.WriteLine("\nPress ENTER to continue...");
Console.Read();
}
public static int Main(String[] args) {
StartListening();
return 0;
}
}
Client Code::
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class SynchronousSocketClient {
public static void StartClient() {
// Data buffer for incoming data.
byte[] bytes = new byte[1024];
// Connect to a remote device.
try {
// Establish the remote endpoint for the socket.
// This example uses port 11000 on the local computer.
IPAddress ipAddress = IPAddress.Parse("172.21.98.122");//Server IP
IPEndPoint remoteEP = new IPEndPoint(ipAddress,11000);
// Create a TCP/IP socket.
Socket sender = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp );
// Connect the socket to the remote endpoint. Catch any errors.
try {
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes("This is a test<EOF>");
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes,0,bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
} catch (ArgumentNullException ane) {
Console.WriteLine("ArgumentNullException : {0}",ane.ToString());
} catch (SocketException se) {
Console.WriteLine("SocketException : {0}",se.ToString());
} catch (Exception e) {
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
} catch (Exception e) {
Console.WriteLine( e.ToString());
}
}
public static int Main(String[] args) {
StartClient();
return 0;
}
}
Any help on the issue below would be highly appreciated. I'm using the StreamSocketListener Class to accept TCP/IP connection on my Raspberry Pi 3 running windows IoT 10 Core.
This is my server code so far:
static string _maintenancePort = "8888";
public async static void StartListening()
{
try
{
StreamSocketListener listener = new StreamSocketListener();
var currentSetting = listener.Control.QualityOfService;
listener.Control.QualityOfService = SocketQualityOfService.LowLatency;
listener.ConnectionReceived += SocketListener_ConnectionReceived;
listener.Control.KeepAlive = true;
await listener.BindServiceNameAsync(_maintenancePort);
}
catch (Exception e)
{
Log.WriteErrorLog(e);
}
}
private static async void SocketListener_ConnectionReceived(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args)
{
try
{
Log.WriteDebugLog("Incoming data...");
Stream inStream = args.Socket.InputStream.AsStreamForRead();
StreamReader reader = new StreamReader(inStream);
string request = await reader.ReadLineAsync();
if (request != null)
{
Log.WriteDebugLog("Received : " + request);
}
}
catch (Exception e)
{
Log.WriteErrorLog(e);
}
}
I wrote the following client code to connect to the socket. This code runs on another machine.
// ManualResetEvent instances signal completion.
private static ManualResetEvent connectDone = new ManualResetEvent(false);
private static ManualResetEvent sendDone = new ManualResetEvent(false);
private static ManualResetEvent receiveDone = new ManualResetEvent(false);
private static String response = String.Empty;
public static Socket client;
public static string SendMessageToClient(string ip, int port, string message, bool expectResponse)
{
// Connect to a remote device.
try
{
// Establish the remote endpoint for the socket.
IPAddress ipAddress = IPAddress.Parse(ip);
IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
// Create a TCP/IP socket.
client = new Socket(ipAddress.AddressFamily,SocketType.Stream, ProtocolType.Tcp);
// Connect to the remote endpoint.
client.BeginConnect(remoteEP, new AsyncCallback(ConnectCallback), client);
connectDone.WaitOne();
message += "^" + expectResponse.ToString();
// Send test data to the remote device.
Send(client, message);
sendDone.WaitOne();
// Receive the response from the remote device.
if (expectResponse)
{
Receive(client);
receiveDone.WaitOne();
}
// Release the socket.
client.Shutdown(SocketShutdown.Both);
client.Close();
return response;
}
catch (Exception e)
{
Log.Write(e, false);
return "";
}
}
private static void Send(Socket client, String data)
{
// Convert the string data to byte data using ASCII encoding.
byte[] byteData = Encoding.ASCII.GetBytes(data);
// Begin sending the data to the remote device.
client.BeginSend(byteData, 0, byteData.Length, 0, new AsyncCallback(SendCallback), client);
}
private static void SendCallback(IAsyncResult ar)
{
try
{
// Retrieve the socket from the state object.
Socket client = (Socket)ar.AsyncState;
// Complete sending the data to the remote device.
int bytesSent = client.EndSend(ar);
Log.WriteSingleMessage(String.Format("Sent {0} bytes to server.", bytesSent), false);
// Signal that all bytes have been sent.
sendDone.Set();
}
catch (Exception e)
{
Log.Write(e, false);
}
}
}
The client code is triggered by a button click event. The problem that I'm facing is that the server code above only works once. If I send a message to the server with the client code, the server processes the string perfect. However, if I hit the button a second time, the SocketListener_ConnectionReceived event is triggered but no data is coming in. I've tried several classes for ConnectionReceived but they all behave the same.
I checked with netstat on the Raspberry Pi if the server is listening and it is.
TCP 0.0.0.0:8888 0.0.0.0:0 LISTENING
Even child processes are created for handling the connection as you would expect from an Async calls. The client code closes the socket after it received a message that the data has been send (waitOne()) and the socket on the client machines changes to CLOSE_WAIT.
TCP 10.0.102.10:8888 10.0.100.11:31298 CLOSE_WAIT
TCP 10.0.102.10:8888 10.0.100.11:31299 ESTABLISHED
Can anyone help me out and point me in the right direction as to what I'm doing wrong. any help would be highly appreciated.
You can try to use synchronous methods instead asynchronous methods for socket client. It will work. Please refer to following code:
public void SendMessageToClientSync(string ip, int port, string message, bool expectResponse)
{
// Data buffer for incoming data.
byte[] bytes = new byte[1024];
// Connect to a remote device.
try
{
// Establish the remote endpoint for the socket.
// This example uses port 11000 on the local computer.
IPAddress ipAddress = IPAddress.Parse(ip);
IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
// Create a TCP/IP socket.
Socket sender = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes(message);
// Send the data through the socket.
int bytesSent = sender.Send(msg);
if(expectResponse)
{
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
}
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (ArgumentNullException ane)
{
Console.WriteLine("ArgumentNullException : {0}", ane.ToString());
}
catch (SocketException se)
{
Console.WriteLine("SocketException : {0}", se.ToString());
}
catch (Exception e)
{
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
I have an Android app (really Xamarin app) and I'm using Socket to listen on port 8888 on the Android app.
So, I want to connect to this port from another computer by tcp (from PC TO Android).
And, I receive the following error:
No connection could be made because the target machine actively refused it.
error 10061
My code (I got it from MS examples) works for two console apps. But if Android is server it doesn't work.
I try ping phone from pc, and it is OK.
My question: maybe should open a port? Or something else? How can I do this?
I will gladly to listen any ideas. Thanks.
My server code. C#, Xamarin.
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using Android.Runtime;
using Java.Lang;
using Byte = System.Byte;
using Exception = System.Exception;
using String = System.String;
using StringBuilder = System.Text.StringBuilder;
// State object for reading client data asynchronously
public class StateObject
{
// Client socket.
public Socket workSocket = null;
// Size of receive buffer.
public const int BufferSize = 1024;
// Receive buffer.
public byte[] buffer = new byte[BufferSize];
// Received data string.
public StringBuilder sb = new StringBuilder();
}
public class AsynchronousSocketListener
{
// Thread signal.
public static ManualResetEvent allDone = new ManualResetEvent(false);
public AsynchronousSocketListener()
{
}
public static void StartListening()
{
// Data buffer for incoming data.
byte[] bytes = new Byte[1024];
IPAddress ipAddress = new IPAddress(new byte[] { 127, 0, 0, 1 });
IPEndPoint remoteEP = new IPEndPoint(ipAddress, 8888);
// Create a TCP/IP socket.
Socket listener = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
// Bind the socket to the local endpoint and listen for incoming connections.
try
{
listener.Bind(remoteEP);
listener.Listen(100);
while (true)
{
// Set the event to nonsignaled state.
allDone.Reset();
// Start an asynchronous socket to listen for connections.
Console.WriteLine("Waiting for a connection...");
listener.BeginAccept(
new AsyncCallback(AcceptCallback),
listener);
// Wait until a connection is made before continuing.
allDone.WaitOne();
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.WriteLine("\nPress ENTER to continue...");
Console.Read();
}
public static void AcceptCallback(IAsyncResult ar)
{
// Signal the main thread to continue.
allDone.Set();
// Get the socket that handles the client request.
Socket listener = (Socket)ar.AsyncState;
Socket handler = listener.EndAccept(ar);
// Create the state object.
StateObject state = new StateObject();
state.workSocket = handler;
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);
}
public static void ReadCallback(IAsyncResult ar)
{
String content = String.Empty;
// Retrieve the state object and the handler socket
// from the asynchronous state object.
StateObject state = (StateObject)ar.AsyncState;
Socket handler = state.workSocket;
// Read data from the client socket.
int bytesRead = handler.EndReceive(ar);
if (bytesRead > 0)
{
// There might be more data, so store the data received so far.
state.sb.Append(Encoding.ASCII.GetString(
state.buffer, 0, bytesRead));
// Check for end-of-file tag. If it is not there, read
// more data.
content = state.sb.ToString();
if (content.IndexOf("<EOF>") > -1)
{
// All the data has been read from the
// client. Display it on the console.
Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",
content.Length, content);
// Echo the data back to the client.
Send(handler, content);
}
else
{
// Not all data received. Get more.
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);
}
}
}
private static void Send(Socket handler, String data)
{
// Convert the string data to byte data using ASCII encoding.
byte[] byteData = Encoding.ASCII.GetBytes(data);
// Begin sending the data to the remote device.
handler.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), handler);
}
private static void SendCallback(IAsyncResult ar)
{
try
{
// Retrieve the socket from the state object.
Socket handler = (Socket)ar.AsyncState;
// Complete sending the data to the remote device.
int bytesSent = handler.EndSend(ar);
Console.WriteLine("Sent {0} bytes to client.", bytesSent);
handler.Shutdown(SocketShutdown.Both);
handler.Close();
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
}
My client code. Just simple C# console app:
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class SynchronousSocketClient
{
public static void StartClient() {
// Data buffer for incoming data.
byte[] bytes = new byte[1024];
Console.WriteLine("Start!");
// Connect to a remote device.
try {
// Establish the remote endpoint for the socket.
// This example uses port 11000 on the local computer.
IPAddress ipAddress = new IPAddress(new byte[] { 10, 0, 1, 173 });
// IPAddress ipAddress = new IPAddress(new byte[] { 127, 0, 0, 1 });
IPEndPoint remoteEP = new IPEndPoint(ipAddress, 8888);
// Create a TCP/IP socket.
Socket sender = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp );
// Connect the socket to the remote endpoint. Catch any errors.
try {
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes("This is a test<EOF>");
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes,0,bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
} catch (ArgumentNullException ane) {
Console.WriteLine("ArgumentNullException : {0}",ane.ToString());
} catch (SocketException se) {
Console.WriteLine("SocketException : {0}",se.ErrorCode);
Console.WriteLine("SocketException : {0}",se.SocketErrorCode);
Console.WriteLine("SocketException : {0}",se.ToString());
} catch (Exception e) {
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
} catch (Exception e) {
Console.WriteLine( e.ToString());
}
}
}
There are two separate scenarios for socket-based data transport (in a typical local lan setting where there is an ordinary isp router in place):
Any client app (including browser) that connects to a well-known server endpoint (specific ip address and port) and just connects to establish a tcp session, and never listens. This is no problem. The router allows allows outgoing connection attempts.
Any client app that wants to connect to another client app that is listening. This is more difficult in that the router in a local lan setting does not typically allow any incoming connection attempts to a local host. Further the router is probably doing NAT translation so it has an addressable internet-facing ip address and has configured a specific external port to route to a specific internal host machine that is presumably listening at a local address and port.
There are several ways to determine what this endpoint addressing mapping configuration is but none of them are very convenient. The key point is that the router will only open an internal host to communications from the external internet if that host has previously tried to tcp connect to that external host (whether it be a server or a peer client app). This works for the browser/website server configuration because the client is always doing the connecting so the router opens the communication channel for that specific addressed external server and allows incoming data to be received by the client (browser). It is a similar situation for udp data transport. The router will only open the internal host to external incoming udp data if the internal client has recently sent a message to that specific peer. Http (a Tcp variant) provides the client/server protocol that uses this router convention for browser/website connectivity and communications. But for the peer client that wants to act as both a client and a server, there are significant barriers. Of course local lan socket communications are no problem, as local ip addresses are available for any internal lan peer.
I'm trying to develop a class that connect to iSeries (as400 - PGM Program) by sockets. The connection works fine but when I try to send data and receive it's get an error.
This is the code:
class Program
{
public static void StartClient()
{
byte[] bytes = new byte[1024];
string desaip = "10.112.2.11";
// Connect to a remote device.
try
{
IPAddress[] ipAddress = Dns.GetHostAddresses(desaip);
IPEndPoint remoteEP = new IPEndPoint(ipAddress[0], 42125);
// Create a TCP/IP socket.
Socket sender = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
sender.Connect(remoteEP);
Console.WriteLine("Socket connected to {0}",
sender.RemoteEndPoint.ToString());
#region forma A
// Encode the data string into a byte array.
byte[] msg = Encoding.ASCII.GetBytes("PRUEBAIB");
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Receive the response from the remote device.
sender.ReceiveTimeout = 10000;
int bytesRec = sender.Receive(bytes);
Console.WriteLine("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
#endregion forma A
}
catch (ArgumentNullException ane)
{
Console.WriteLine("ArgumentNullException : {0}", ane.ToString());
}
catch (SocketException se)
{
Console.WriteLine("SocketException : {0}", se.ToString());
}
catch (Exception e)
{
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
}
What could be wrong?
Check the software that is supposed to be listening to that port on the iSeries. Make sure that it is running, that it is listening to that port. Work with that job, and look at the job log to see what messages were sent. Check the program stack to see what statement it is on, which may help determine what has happened. The open files & I/O stats might also help.