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PingReply is null when using SendAsync

I am building a server selection screen and have a bunch of IP addresses that need to be pinged in order to know the remote hosts are reachable and to establish a TCP connection afterwards to request their data (like connected playerCount and MOTD, think of Minecraft Multiplayer Selection screen, you don't connect to the game, only requesting data from the endpoint).
The problem is that Ping is always unsuccessful, because the PingReply is null.
For generic use cases, I have wrapped the call with an event that gets fired when the Ping Reply is received back to the sender.
public static async void PingNET(string address, int timeOutMs, System.Action<PingReply> onCompleted)
{
await Task.Run(() => { //to continue unity main thread, start new thread
AutoResetEvent waiter = new AutoResetEvent(false);
var pingSender = new System.Net.NetworkInformation.Ping ();
// call handler when PingCompleted event is raised
pingSender.PingCompleted += (sender, e) =>
{
Debug.LogError ("Error and reply is always null! See: Error is null?: "
+ (e.Error == null) + " - Reply is null?: " + (e.Reply == null));
// If the operation was canceled, display a message to the user.
if (e.Cancelled) {
Debug.LogWarning("Ping canceled.");
}
// If an error occurred, display the exception to the user.
if (e.Error != null) {
Debug.LogError ("Ping failed:" + e.Error.ToString ());
}
if(onCompleted != null)
onCompleted(e.Reply);
};
// Send the ping asynchronously (uses internal new thread,
// so program does not freeze until reply received)
pingSender.SendAsync(address, timeOutMs, waiter);
});
}
Unity Test Runner Unit Test:
[Test]
public void PingTest(){
List<string> addresses = new List<string>(){
"127.0.0.1", "localhost", "www.stackoverflow.com", "www.google.com"
};
for (int i = 0; i < addresses.Count; i++)
{
Ping(addresses[i]);
}
}
private void Ping(string address){
NetworkUtils.PingNET(address, 10000, new System.Action<PingReply>((PingReply reply) => {
if (reply != null && reply.Status == IPStatus.Success)
{
Debug.Log($"Address: {reply.Address.ToString()}");
Debug.Log($"RoundTrip time: {reply.RoundtripTime}");
}
else //this gets called obviously
{
Debug.LogError("PING REPLY ERROR " + reply?.Status);
}
}));
}
Side Info: (Not directly tied to the question)
The reason why I use Ping in the first place is to prevent freeze (deadlock) on the client when the server goes offline while the connection is still tied to it and requesting data to the now unavailable remote host endpoint of the server. I could notify all connected clients that the server is shutting down, but this of course will not work when the server immediately lost connection to the internet.
So all in all, when the ping fails, it should handle in the UI logic to display the server is unreachable. Otherwise if it was successful, a TCP connection to the server is created to send a request. The server that listens on the same port sends a response with the data (playerCount, MOTD, etc.). After that, the client deseralizes the byte array to the datatypes and fires an event, which is subscribed by the UI to gather the deserealized data and display those.
The sending/receiving part with UI already works, just the ping not.
Is this process overcomplicated? Let me know if it could be simplified.
Any help is greatly appreciated.

Why isn't TcpListener listening?

We have a C++ v100 application that is processing every event in our system, listening on port 1705, running off the Hostname. (it works perfectly for the C++ app, and we don't want to change anything in the c++ code) We are trying to intercept some of those events into a C# 4.5.2 solution, simply to display specific events in our new web system.
I have coded the following, in an attempt to listen to port 1705 traffic... but I never receive any data. (I can create events that get sent to 1705)
The following code runs, and it makes it to 'Waiting for a connection', but never makes it to 'Connected!'. If you see any reason in the following code as to why I wouldn't be receiving data, please let me know:
private void PortListener()
{
TcpListener server = null;
try
{
// Set the TcpListener on port 13000.
var port = 1705;
var localAddr = IPAddress.Parse(Dns.GetHostAddresses(Environment.MachineName)[0].ToString());
server = new TcpListener(localAddr, port);
// Start listening for client requests.
server.Start();
// Buffer for reading data
var bytes = new byte[256];
// Enter the listening loop.
while (true)
{
Console.Write("Waiting for a connection... ");
// Perform a blocking call to accept requests.
// You could also user server.AcceptSocket() here.
var client = server.AcceptTcpClient();
Console.WriteLine("Connected!");
// Get a stream object for reading and writing
var stream = client.GetStream();
int i;
// Loop to receive all the data sent by the client.
while ((i = stream.Read(bytes, 0, bytes.Length)) != 0)
{
// Translate data bytes to a ASCII string.
var data = System.Text.Encoding.ASCII.GetString(bytes, 0, i);
Console.WriteLine("Received: {0}", data);
// Process the data sent by the client.
data = data.ToUpper();
//TODO: Process the data
}
// Shutdown and end connection
client.Close();
}
}
catch (SocketException e)
{
Console.WriteLine("SocketException: {0}", e);
}
finally
{
// Stop listening for new clients.
server?.Stop();
}
}

Make sure that you are binding/listening to the right ip-address. If you bind/listen on localhost (127.0.0.1) you can only connect from the same host.
Check what
Dns.GetHostAddresses(Environment.MachineName)[0].ToString());
really produces.

I'm doing this all wrong. In order to listen to an already opened Port, I need to use a TcpClient to connect and listen. Only a single TcpListener is allowed per port. Several TcpClients can connect at once. Sigh.

Why does my C# TcpClient fail to receive content from the server if the server sends before reading everything from the client?

In an application I'm working on I want to disconnect clients that are trying to send me packets that are too large.
Just before disconnecting them I want to send them a message informing them about the reason for disconnecting them.
The issue I am running into is that the client cannot receive this server message, if the server does not read everything the client has send him first. I do not understand why this is happening.
I've managed to narrow it down to a very small test setup where the problem is demonstrated.
The StreamUtil class is a simple wrapper class that helps to get around the TCP message boundary problem, basically on the sender side it sends the size of each message first and then the message itself, and on the receiver side it receives the size of the message first and then the message.
The client uses a ReadKey command to simulate some time between sending and receiving, seeing in my real application these two actions are not immediately back to back either.
Here is a test case that works:
Run server as shown below
Run client as shown below, it will show a "Press key message", WAIT do not press key yet
Turn off server since everything is already in the clients receive buffer anyway (I validated this using packet sniffer)
Press key on the client -> client correctly shows the messages from the server.
This is what I was expecting, so great so far no problem yet.
Now in the server code, comment out the 2nd receive call and repeat the steps above.
Step 1 and 2 complete successfully, no errors sending from client to server.
On step 3 however the client crashes on the read from the server, EVEN though the server reply HAS arrived on the client (again validated with packet sniffer).
If I do a partial shutdown (eg socket.Shutdown (...send...)) without closing the socket on the server, everything works.
1: I just cannot get my head around WHY not processing the line of text from the client on the server causes the client to fail on receiving the text send back from the server.
2: If I send content from server to client but STOP the server before actually closing the socket, this content never arrives, but the bytes have already been transmitted to the server side... (see ReadKey in server to simulate, basically I block there and then just quit the server)
If anyone could shed light on these two issues, I'd deeply appreciate it.
Client:
class TcpClientDemo
{
public static void Main (string[] args)
{
Console.WriteLine ("Starting....");
TcpClient client = new TcpClient();
try
{
client.Connect("localhost", 56789);
NetworkStream stream = client.GetStream();
StreamUtil.SendString(stream, "Client teststring...");
Console.WriteLine("Press key to initiate receive...");
Console.ReadKey();
Console.WriteLine("server reply:" + StreamUtil.ReceiveString(stream));
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
finally
{
client.Close();
}
Console.WriteLine("Client ended");
Console.ReadKey(true);
}
}
Server:
class TcpServerDemo
{
public static void Main (string[] args)
{
TcpListener listener = new TcpListener (IPAddress.Any, 56789);
listener.Start ();
Console.WriteLine ("Waiting for clients to serve...");
while (true)
{
TcpClient client = null;
NetworkStream stream = null;
try
{
client = listener.AcceptTcpClient();
stream = client.GetStream();
//question 1: Why does commenting this line prevent the client from receiving the server reply??
Console.WriteLine("client string:" + StreamUtil.ReceiveString(stream));
StreamUtil.SendString(stream, "...Server reply goes here...");
//question 2: If I close the server program without actually calling client.Close (while on this line), the client program crashes as well, why?
//Console.ReadKey();
}
catch (Exception e)
{
Console.WriteLine(e.Message);
break;
}
finally
{
if (stream != null) stream.Close();
if (client != null) client.Close();
Console.WriteLine("Done serving this client, everything closed.");
}
}
listener.Stop();
Console.WriteLine("Server ended.");
Console.ReadKey(true);
}
}
StreamUtil:
public class StreamUtil
{
public static byte[] ReadBytes (NetworkStream pStream, int byteCount) {
byte[] bytes = new byte[byteCount];
int bytesRead = 0;
int totalBytesRead = 0;
try {
while (
totalBytesRead != byteCount &&
(bytesRead = pStream.Read (bytes, totalBytesRead, byteCount - totalBytesRead)) > 0
) {
totalBytesRead += bytesRead;
Console.WriteLine("Read/Total:" + bytesRead + "/" + totalBytesRead);
}
} catch (Exception e) {
Console.WriteLine(e.Message);
}
return (totalBytesRead == byteCount) ? bytes : null;
}
public static void SendString (NetworkStream pStream, string pMessage) {
byte[] sendPacket = Encoding.ASCII.GetBytes (pMessage);
pStream.Write (BitConverter.GetBytes (sendPacket.Length), 0, 4);
pStream.Write (sendPacket, 0, sendPacket.Length);
}
public static string ReceiveString (NetworkStream pStream) {
int byteCountToRead = BitConverter.ToInt32(ReadBytes (pStream, 4), 0);
Console.WriteLine("Byte count to read:"+byteCountToRead);
byte[] receivePacket = ReadBytes (pStream, byteCountToRead);
return Encoding.ASCII.GetString (receivePacket);
}
}

The client fails because it detects the socket was already closed.
If C# socket operations detect a closed connection during earlier operations, an exception is thrown on the next operation which can mask data which would otherwise have been received
The StreamUtil class does a couple of things when the connection is closed before/during a read:
Exceptions from the reads are swallowed
A read of zero bytes isn't treated
These obfuscate what's happening when an unexpected close hits the client.
Changing ReadBytes not to swallow exceptions and to throw a mock socket-closed exception (e.g. if (bytesRead == 0) throw new SocketException(10053);) when it reads zero bytes I think makes the outcome more clear.
Edit
I missed something subtle in your examples - your first example causes a TCP RST flag to be sent as soon as the server closes connection, due to the socket being closed with data waiting to be read.
The RST flag results in a closedown that doesn't preserve pending data.
This blog has some discussion based on a very similar scenario (web server sending a HTTP error).
So I don't think there's an easy fix, options are:
As you already tried, shutdown the socket on the server before closing to force a FIN to be sent before the RST
Read the data in question but never process it (taking up bandwidth for no reason)

c# get post form data sent from browser by socket sometimes socket closes.why?

I have webserver receive data by async sockets:
var e = new SocketAsyncEventArgs();
e.Completed += new EventHandler<SocketAsyncEventArgs>(e_Completed);
while (true)
{ allDone.Reset();
mySocket.AcceptAsync(e);
allDone.WaitOne();
}
and the other method:
public void e_Completed(object sender, SocketAsyncEventArgs e)
{
var socket = (Socket)sender;
ThreadPool.QueueUserWorkItem(handleTcpRequest, e.AcceptSocket);
e.AcceptSocket = null;
socket.AcceptAsync(e);
}
this is the handleTcpRequest method.in this part I receive data from socket and do operation:
public void handleTcpRequest(object state)
{
string sBuffer = "";
string BufferTotal = "";
byte[] secureMessage;
Byte[] bReceive = new Byte[1024];
var mySocket = (Socket)state;
do
{
try
{
firstBufferRead = mySocket.Receive(bReceive, bReceive.Length, 0);
}
catch (Exception ex)
{
Console.WriteLine("Error Occurred (:))) " + ex.Message);
}
sBuffer += Encoding.GetEncoding(1252).GetString(bReceive, 0, firstBufferRead);
BufferTotal += Encoding.UTF8.GetString(bReceive, 0, firstBufferRead);
} while (mySocket.Available != 0);
.
.
.
.
mySocket.Close();
}
whats wrong?
sometimes connection resets and closes. this happens when distance is far or post data not multipart. but in multipart happens rarely. more with forms not in multipart.
when and where should I close socket?
when I work with socket in handleTcpRequest method its local. isn't it correct? I can't find the origin of the problem

The only way to know that you've received everything in a HTTP request is to understand the HTTP request. And to understand a HTTP request you have to choices:
Use a complete HTTP server
Create a HTTP parser
The reason to why your code fails for multi-part data is probably because the other party sends one part at a time, which means that your code manages to do a mySocket.Available != 0 before the rest is sent.
If you want to do the latter you have to read the HTTP header (in format headerName: headervalue, do note that there are also white space rules that you have to consider). Search for a header named content-length, parse it's value as an integer. Then wait for two line feeds in a row (\r\n\r\n). Finally start count bytes until you have received the number of bytes that was specified in the content-length header.
ohh.. ony more thing.. pray to God that Transfer-Encoding: Chunkedis not used.
My advice is that you give up on using sockets directly as it's apparent that you don't understand how they work or how to do research on them.

If response has a header of Connection: Close, then the socket closes automatically.

WP8 Socket ConnectAsync: Completed handler always returns Success?

I'm trying to connect to an ip/port from a WP8 via TCP/IP. I use socket.ConnectAsync() to initiate the Connection and specify a Completed Event like this
socketEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(delegate(object s, SocketAsyncEventArgs e)
{
lasterrorstring = e.SocketError.ToString();
if (e.SocketError != SocketError.Success)
{
:
}
});
Everything works. So I can talk to the other host correctly. However, the error case troubles me. For some reason, e.SocketError always returns Success. I even tried connecting to an ip that does not exist. It reports Success, too. Even the Send() afterwards report Success. What's wrong here?
For completeness, here is my whole Connection Setup code
Socket _socket = null;
DnsEndPoint hostEntry = new DnsEndPoint(hostName, portNumber);
// Create a stream-based, TCP socket using the InterNetwork Address Family.
_socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
// Create a SocketAsyncEventArgs object to be used in the connection request
SocketAsyncEventArgs socketEventArg = new SocketAsyncEventArgs();
socketEventArg.RemoteEndPoint = hostEntry;
// Inline event handler for the Completed event.
// Note: This event handler was implemented inline in order to make this method self-contained.
socketEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(delegate(object s, SocketAsyncEventArgs e)
{
// Retrieve the result of this request
lasterrorstring = e.SocketError.ToString();
if (e.SocketError != SocketError.Success)
{
res = 1;
}
});
// Make an asynchronous Connect request over the socket
_socket.ConnectAsync(socketEventArg);

This is an old question but anyway. It happens to me too and it seems until you send something by SendAsync method, it thinks it's connected. But on the Completed event of SendAsync e.SocketError does not return success. So you can send an empty data right after ConnectAsync returns success to know if it really is connected.