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Reading entire response through socket with good performance

I have written some code to get a webpage through a proxy using sockets. In essence, it works but reading the response has some strange behavior that is really tripping me up.
When I go to read the response after sending the GET command it is 0 bytes. It takes a few ticks before there is data to read. I don't want to hard code a delay in here as I am trying to write performant reliable code so I have coded a while loop that keeps reading the response until it more than 0.
This works for the first chunk but trying to read subsequent chunks is a problem. If i instantly try to read the response it will be 0 bytes so I need to check the subsequent reads also if they are greater than 0.
So to read the whole response I tried to check if the response is equal to the size of the buffer. If it is equal to the size of the buffer then I carry on and try to read another chunk. This has a few issues also. Sometimes the response will read less than the size of the buffer but there is still more to come, i guess I am reading it faster than they are sending it because if I add a Thread.Sleep() then the buffer will always be full but I don't think it is good practice to hardcode this because I don't know how fast they will be sending. This code will be used for multiple things and will be running on hundreds of threads so performance is everything.
Also if the last chunk just happens to be the size of my buffer then I think the loop will lock, This whole approach I have taken is horrible but I can't see how I should be reading it. I have seen the asynchronous examples but I think that will add to the overall complexity of my code as I just have 1 set process which I will run in many threads.
How do I efficiently read the response when I can't guarantee the next chunk will have data or be full even if there is more data to come?
Sorry for long text but I wanted to explain my thinking. Here is my code:
// Data buffer for incoming data.
byte[] bytes = new byte[1024];
// Connect to a remote device.
try
{
var proxyIpAddress = IPAddress.Parse("123.123.123.123"); //omitted
IPEndPoint remoteEP = new IPEndPoint(proxyIpAddress, 60099);
// Create a TCP/IP socket.
Socket sender = new Socket(proxyIpAddress.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());
sender.Send(Encoding.ASCII.GetBytes($"CONNECT google.com:80 HTTP/1.0\r\n\r\n"));
int bytesRec = 0;
while (bytesRec == 0)
{
// Receive the response from the remote device.
bytesRec = sender.Receive(bytes);
Console.WriteLine("{0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
}
//clear buffer
bytes = new byte[1024];
bytesRec = 0;
sender.Send(Encoding.ASCII.GetBytes("GET / HTTP/1.0\r\n\r\n"));
//wait for response
while (bytesRec == 0) //if i dont add this it returns before it actually gets data
{
// Receive the response from the remote device.
bytesRec = sender.Receive(bytes);
Console.WriteLine("{0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
}
if(bytes.Length == bytesRec) //full buffer so likely more but maybe not if final packet exactly 1024?
{
while (bytes.Length == bytesRec) //again if i miss this it returns too early
{
int subsequentBytes = 0;
while(subsequentBytes == 0) //this can get stuck if last packet exactly size of buffer i think
{
subsequentBytes = sender.Receive(bytes);
Console.WriteLine("{0}",
Encoding.ASCII.GetString(bytes, 0, subsequentBytes));
//this doesn't work. even when there are subsequent bytes sometimes it reads less
//than the size of the buffer so it exits prematurely. If I add a Thread.Sleep() here
// then it works but I don't want to hardcode the delay. How do I read this buffer properly?
Thread.Sleep(1000);
if (subsequentBytes > 0) bytesRec = subsequentBytes;
}
}
}
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (Exception e)
{
Console.WriteLine("Unexpected exception : {0}", e.ToString());
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
I understand this is difficult to follow and a lot of writing so if anyone perseveres with this they have my gratitude as the only option I can see is hardcoded pauses which will hurt performance and may still have issues.
EDIT
I have done some experiementing with different servers. If I ping the server then set a Thread.Sleep(pingValue) it works fine but if i set the sleep to lower than ping i get same issue.
Is there some good way with the .net libraries to account for this latency so I am not under/overestimating?

When I send a command to server from client , the client receives the response only if the request is sent twice

I am trying to send commands to the server , like for example requesting the server to send back the list of files in it's directory. The problem is that when I send the "list" command to the server, I have to send it twice in order for the server to send back the list of files to the client. I am sure that the server receives the command in both times as on the server side I print the result that is supposed to be sent to the client on the console and it appears both times.
I am using C# and TCPListeners to listen for incoming responses or commands, and TCPClient to send responses or commands between the server and the client.
The client code
private TcpListener tcpListener = new TcpListener(9090);
private void button3_Click(object sender, EventArgs e)
{
Byte[] bytesToSend = ASCIIEncoding.ASCII.GetBytes("list");
try
{
TcpClient clientSocket = new TcpClient(serverIPFinal, 8080);
if (clientSocket.Connected)
{
NetworkStream networkStream = clientSocket.GetStream();
networkStream.Write(bytesToSend, 0, bytesToSend.Length);
// networkStream.Close();
// clientSocket.Close();
thdListener = new Thread(new ThreadStart(listenerThreadList));
thdListener.Start();
}
}
catch
{
isConnectedLbl.Text = "Server not running";
}
}
//Listener Thread to receive list of files.
public void listenerThreadList()
{
tcpListener.Start();
while (true)
{
handlerSocket = tcpListener.AcceptSocket();
if (handlerSocket.Connected)
{
Control.CheckForIllegalCrossThreadCalls = false;
lock (this)
{
if (handlerSocket != null)
{
nSockets.Add(handlerSocket);
}
}
ThreadStart thdstHandler = new
ThreadStart(handlerThreadList);
Thread thdHandler = new Thread(thdstHandler);
thdHandler.Start();
}
}
}
//Handler Thread to receive list of files.
public void handlerThreadList()
{
Socket handlerSocketList = (Socket)nSockets[nSockets.Count - 1];
NetworkStream networkStreams = new NetworkStream(handlerSocketList);
int requestRead = 0;
string dataReceived;
byte[] buffer = new byte[1024];
//int iRx = soc.Receive(buffer);
requestRead = networkStreams.Read(buffer, 0, 1024);
char[] chars = new char[requestRead];
System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
int charLen = d.GetChars(buffer, 0, requestRead, chars, 0);
dataReceived = new System.String(chars);
Console.WriteLine(dataReceived);
MessageBox.Show(dataReceived);
//tcpListener.Stop();
thdListener.Abort();
}
The Server code:
TcpListener tcpListener = new TcpListener(8080);
public void listenerThreadCommands()
{
tcpListener.Start();
while (true)
{
handlerSocket = tcpListener.AcceptSocket();
if (handlerSocket.Connected)
{
Control.CheckForIllegalCrossThreadCalls = false;
connections.Items.Add(
handlerSocket.RemoteEndPoint.ToString() + " connected.");
// clientIP = handlerSocket.RemoteEndPoint.ToString();
lock (this)
{
nSockets.Add(handlerSocket);
}
ThreadStart thdstHandler = new
ThreadStart(handlerThreadCommands);
Thread thdHandler = new Thread(thdstHandler);
thdHandler.Start();
//tcpListener.Stop();
//handlerSocket.Close();
}
}
}
//Handler Thread to receive commands
public void handlerThreadCommands()
{
Socket handlerSocketCommands = (Socket)nSockets[nSockets.Count - 1];
NetworkStream networkStream = new NetworkStream(handlerSocketCommands);
int requestRead = 0;
string dataReceived;
byte[] buffer = new byte[1024];
requestRead = networkStream.Read(buffer, 0, 1024);
char[] chars = new char[requestRead];
System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
int charLen = d.GetChars(buffer, 0, requestRead, chars, 0);
dataReceived = new System.String(chars);
//connections.Items.Add(dataReceived);
if (dataReceived.Equals("list"))
{
localDate = DateTime.Now;
Files = Directory.GetFiles(System.IO.Directory.GetCurrentDirectory())
.Select(Path.GetFileName)
.ToArray();
String FilesString = "";
for (int i = 0; i < Files.Length; i++)
{
FilesString += Files[i] + "\n";
}
String clientIP = handlerSocketCommands.RemoteEndPoint.ToString();
int index = clientIP.IndexOf(":");
clientIP = clientIP.Substring(0, index);
WriteLogFile(logFilePath, clientIP, localDate.ToString(), " ", "list");
Console.WriteLine(clientIP);
Console.WriteLine(FilesString);
Byte[] bytesToSend = ASCIIEncoding.ASCII.GetBytes(FilesString);
try
{
WriteLogFile(logFilePath, clientIP, localDate.ToString(), " ", "list-response");
TcpClient clientSocket = new TcpClient(clientIP, 9090);
if (clientSocket.Connected)
{
NetworkStream networkStreamS = clientSocket.GetStream();
networkStreamS.Write(bytesToSend, 0, bytesToSend.Length);
networkStreamS.Close();
clientSocket.Close();
networkStream.Close();
//tcpListener.Stop();
// handlerSocketAuthenticate.Close();
}
}
catch
{
Console.WriteLine("Cant send");
}
}
else if (dataReceived.Equals("downloadfile"))
{
// handlerSocketAuthenticate.Close();
// tcpListener.Stop();
networkStream.Close();
thdListenerDownload = new Thread(new ThreadStart(listenerThreadDownloading));
thdListenerDownload.Start();
}
else
{
String clientIP1 = handlerSocketCommands.RemoteEndPoint.ToString();
int index = clientIP1.IndexOf(":");
clientIP1 = clientIP1.Substring(0, index);
// handlerSocketAuthenticate.Close();
CommandExecutor(dataReceived, clientIP1);
}
}

There are so many different things wrong with the code you posted, it's hard to know where to start, and it's impossible to have confidence that in the context of a Stack Overflow, one could sufficiently address all of the deficiencies. That said, in the interest of helping, it seems worth a try:
Sockets are bi-directional. There is no need for the client to use TcpListener at all. (By convention, the "server" is the endpoint that "listens" for new connections, and the "client" is the endpoint that initiates new connections, by connecting to a listening server.)You should just make a single connection from client to server, and then use that socket both for sending to and receiving from the server.
You are setting the CheckForIllegalCrossThreadCalls property to false. This is evil. The exceptions that occur are there to help you. Setting that property to false disables the exceptions, but does nothing to prevent the problems that the exceptions are designed to warn you about.You should use some mechanism to make sure that when you access UI objects, you do so only in the thread that owns those objects. The most primitive approach to this is to use Control.Invoke(). In modern C#, you are better off using async/await. With TcpClient, this is easy: you already are using GetStream() to get the NetworkStream object that represents the socket, so just use the asynchronous methods on that object, such as ReadAsync(), or if you wrap the stream in a StreamWriter and StreamReader, use the asynchronous methods on that object, such as ReadLineAsync().
You are checking the Connected property of the TcpClient object. This is pointless. When the Connect() method returns, you are connected. If you weren't, an exception would have been thrown.
You are not sufficiently synchronizing access to your nSockets object. In particular, you use its indexer in the handlerThreadList() method. This is safe when using the object concurrently only if you have guaranteed that no other thread is modifying the object, which is not the case in your code.
You are writing to the stream using ASCII encoding, but reading using UTF8 encoding. In practice, this is not really a problem, because ASCII includes only the code points 0-127, and those map exactly to the same character code points in UTF8. But it's really bad form. Pick one encoding, stick with it.
You are accepting using AcceptSocket(), but then just wrapping that in a NetworkStream anyway. Why not just use AcceptTcpClient() and call GetStream() on that? Both Socket and TcpClient are fine APIs, but it's a bit weird to mix and match in the same program, and will likely lead to some confusion later on, trying to keep straight which you're using where and why.
Your code assumes that the handlerThreadCommands() method will always be called in exactly the same order in which connections are accepted. That is, you retrieve the current socket with nSockets[nSockets.Count - 1]. But, due to the way Windows thread scheduling works, it is entirely possible that two or more connections could be accepted before any one of the threads meant to handle the connection is started, with the result that only the most recent connection is handled, and it is handled by those multiple threads.
You are assuming that command strings will be received as complete units. But this isn't how TCP works. TCP guarantees only that if you receive a byte, it will be in order relative to all the bytes sent before it. But you can receive any number of bytes. In particular, you can receive just a single byte, or you can receive multiple commands concatenated with each other, or you can receive half a command string, then the other half later, or the second half of one command and the first half of the next, etc. In practice, these problems don't show up in early testing because the server isn't operating under load, but later on they very well may be. And the code needs to be designed from the outset to work properly under these conditions; trying to patch bad code later is much more difficult.
I can't say that's the above are the only things wrong with the code, but they are most glaring, and in any case I think the above is sufficient food for thought for you at the moment.
Bottom line: you really should spend more time looking at good networking examples, and really getting to understand how they work and why they are written the way they do. You'll need to develop a good mental model for yourself of how the TCP protocol works, and make sure you are being very careful to follow the rules.
One resource I recommend highly is The Winsock Programmer's FAQ. It was written long ago, for a pre-.NET audience, but most of the information contained within is still very much relevant when using the higher-level networking APIs.
Alternatively, don't try to write low-level networking code yourself. There are a number of higher-level APIs that use various serialization techniques to encode whole objects and handle all of the lower-level network transport mechanics for you, allowing you to concentrate on the value-added features in your own program, instead of trying to reinvent the wheel.

Read unknown length by DataReader

I've been working with windows app store programming in c# recently, and I've come across a problem with sockets.
I need to be able to read data with an unknown length from a DataReader().
It sounds simple enough, but I've not been able to find a solution after a few days of searching.
Here's my current receiving code (A little sloppy, need to clean it up after I find a solution to this problem. And yes, a bit of this is from the Microsoft example)
DataReader reader = new DataReader(args.Socket.InputStream);
try
{
while (true)
{
// Read first 4 bytes (length of the subsequent string).
uint sizeFieldCount = await reader.LoadAsync(sizeof(uint));
if (sizeFieldCount != sizeof(uint))
{
// The underlying socket was closed before we were able to read the whole data.
return;
}
reader.InputStreamOptions
// Read the string.
uint stringLength = reader.ReadUInt32();
uint actualStringLength = await reader.LoadAsync(stringLength);
if (stringLength != actualStringLength)
{
// The underlying socket was closed before we were able to read the whole data.
return;
}
// Display the string on the screen. The event is invoked on a non-UI thread, so we need to marshal
// the text back to the UI thread.
//MessageBox.Show("Received data: " + reader.ReadString(actualStringLength));
MessageBox.updateList(reader.ReadString(actualStringLength));
}
}
catch (Exception exception)
{
// If this is an unknown status it means that the error is fatal and retry will likely fail.
if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown)
{
throw;
}
MessageBox.Show("Read stream failed with error: " + exception.Message);
}

You are going down the right lines - read the first INT to find out how many bytes are to be sent.
Franky Boyle is correct - without a signalling mechanism it is impossible to ever know the length of a stream. Thats why it is called a stream!
NO socket implementation (including the WinSock) will ever be clever enough to know when a client has finished sending data. The client could be having a cup of tea half way through sending the data!
Your server and its sockets will never know! What are they going to do? Wait forever? I suppose they could wait until the client had 'closed' the connection? But your client could have had a blue screen and the server will never get that TCP close packet, it will just be sitting there thinking it is getting more data one day?
I have never used a DataReader - i have never even heard of that class! Use NetworkStream instead.
From my memory I have written code like this in the past. I am just typing, no checking of syntax.
using(MemoryStream recievedData = new MemoryStream())
{
using(NetworkStream networkStream = new NetworkStream(connectedSocket))
{
int totalBytesToRead = networkStream.ReadByte();
// This is your mechanism to find out how many bytes
// the client wants to send.
byte[] readBuffer = new byte[1024]; // Up to you the length!
int totalBytesRead = 0;
int bytesReadInThisTcpWindow = 0;
// The length of the TCP window of the client is usually
// the number of bytes that will be pushed through
// to your server in one SOCKET.READ method call.
// For example, if the clients TCP window was 777 bytes, a:
// int bytesRead =
// networkStream.Read(readBuffer, 0, int.Max);
// bytesRead would be 777.
// If they were sending a large file, you would have to make
// it up from the many 777s.
// If it were a small file under 777 bytes, your bytesRead
// would be the total small length of say 500.
while
(
(
bytesReadInThisTcpWindow =
networkStream.Read(readBuffer, 0, readBuffer.Length)
) > 0
)
// If the bytesReadInThisTcpWindow = 0 then the client
// has disconnected or failed to send the promised number
// of bytes in your Windows server internals dictated timeout
// (important to kill it here to stop lots of waiting
// threads killing your server)
{
recievedData.Write(readBuffer, 0, bytesReadInThisTcpWindow);
totalBytesToRead = totalBytesToRead + bytesReadInThisTcpWindow;
}
if(totalBytesToRead == totalBytesToRead)
{
// We have our data!
}
}
}

How to create a TcpClient in C# that can recover from a lost network connection?

I am trying to write a TCP client thread that will connect to a server and continue to process data as it receives it. Sometimes the client will lose connection to the server. When the connection is re-established, the thread should resume/recover and automatically start processing data again. I can't seem to get this to work. The basic algorithm is below. My problem is that I just don't quite understand how the TcpClient behaves when the network connection is lost. How can I tell that the connection has been lost? Do I then need to close the connection? How do I reestablish the connection and continue on?
TcpClient _tcpClient;
IPEndPoint _ipEndPoint;
bool _cancelled = false;
bool _error = true;
while (!_cancelled)
{
try
{
if(_error)
{
_ipEndPoint = new IPEndPoint(_myAddress, _myPort);
_tcpClient.Connect(_ipEndPoint);
_networkStream = _tcpClient.GetStream();
_error = false;
}
else
{
_data = new byte[10025];
if(_networkStream.CanRead)
{
_bytesRead = _networkStream.Read(_data, 0, (int)_tcpClient.ReceiveBufferSize);
if(_bytesRead > 0)
{
...process the data...
}
else
{
_error = true;
}
}
else
{
_error = true;
}
}
}
catch(Exception ex)
{
...log error...
_error = true;
}
}

there is a Connected property on the TcpClient, but it is only updated when a Write or Read is executed on the NetworkStream.
I think you can just execute a Read(null,0,0) or Write(null,0,0) if you want to force a connectivity check. But in the example you have you can check the Connected or CanRead properties after your _networkStream.Read is completed.
As for reestablishing the link what you have will work. I would suggest Disposing of the old network stream before getting a new one. Something like this:
if(_networkStream != null)
{
_networkStream.Dispose();
}
_networkStream = _tcpClient.GetStream();
What I do is start a reconnect timer that will attempt to reconnect on a configured interval. Depending on the TcpHost your connecting to you may even want to start trying at a small interval 500-1000ms and increment is after a given number of failed retries so your not wasting a lot of time trying to connect to a host that is gone. Then after a max number of tries just give up unless the user explicitly requests to try again. But that also depends on what else your app is doing, if the connection is its sole purpose or if its just one piece.
The wrapper class I use to interact with TcpClient is around 700 lines of code and it handles reconnects, sending data as well as reading it. I work in a closed shop so i cant post it but if you have any other specific question I'd be happy to help.
Good luck.

Non blocking UDP socket .NET "A non-blocking socket operation could not be completed immediately" exception

I have written a small UDP client server class in C# that is used to provide comms between a Linux and a Windows machines.
The implementation of the UDP client and server in C# in Windows is a direct rewrite from C++ code I wrote for Linux originally.
I have no problems during run time between Linux machines but there is an intermittent problem that occasionally appears between Linux and Windows link.
Due to the application I need fast, non blocking operation of the UDP socket.
Since one client is Linux the code under C# I had to use some magic of marshalling.
Here is the code:
public bool Connect(string sIPAddr, int portNumber)
{
try
{
if (portNumber > 65535 && portNumber < 0)
{
this._isReady = false;
return this._isReady;
}
this._ipPort = portNumber;
this._ipAddress = IPAddress.Parse(sIPAddr);
IPEndPoint ipep = new IPEndPoint(this._ipAddress, this._ipPort);
this._myUDPClient = new Socket(ipep.Address.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
this._myUDPClient.Blocking = false;
this._myUDPClient.Connect(this._ipAddress, this._ipPort);
this._isReady = true;
return this._isReady;
}
catch (Exception)
{
this._isReady = false;
return this._isReady;
}
}
I use connect on UDP to simplify send and receive calls.
The problem happens when I try and read from the socket.
More code:
public bool NewMessageReceived()
{
try
{
if (this._newMessaageReceived)
{
return this._newMessaageReceived;
}
else
{
_messageBuffer = new byte[65507];
int numBytesRcvd = _myUDPClient.Receive(this._messageBuffer, 65507, SocketFlags.None);
Marshal.Copy(_messageBuffer, 0, _pmessageBuffer, 65507);
if (numBytesRcvd < 0)
{
this._newMessaageReceived = false;
// TODO: Add Socket Error Checking
}
else
{
this._newMessaageReceived = true;
}
Array.Clear(_messageBuffer, 0, _messageBuffer.GetLength(0));
return this._newMessaageReceived;
}
}
catch (Exception e)
{
System.Windows.Forms.MessageBox.Show(e.Message);
return false;
}
}
I have Wireshark running on both machines and I can see that the datagram sent from Linux machine arrives on Windows machine unharmed. However the UDP client Receive call throws and exception saying: "A non-blocking socket operation could not be completed
immediately" which from what I understand is a WSAEWOULDBLOCK error. However I explicitly set blocking option to false.
The sequence of events is the following:
Windows machine sends a datagram on port 2 and listens for acknowledge on port 1. I have a while loop which implements timeout
Code:
DateTime TimeAtStart = new DateTime();
TimeAtStart = DateTime.Now;
TimeSpan TimeOut = new TimeSpan(0,0,0,0,800);
IntPtr RecievedTelPtr = new IntPtr();
bool UnpackingResult;
while (TimeOut > (DateTime.Now - TimeAtStart))
{
if (!NackAckRecieveConnection.GetIsReady())
{
ErrorEventArguements.SetAllHmiNetworkEventArgs(ID, -3, 2);
return (false);
}
if (NackAckRecieveConnection.NewMessageReceived())
{
RecievedTelPtr = NackAckRecieveConnection.GetMessage();
UnpackingResult = UnpackHmiTelegram(RecievedTelPtr, AckNackType);
NackAckRecieveConnection.MessageRetrieved();
return (UnpackingResult);
}
}
//if escape loop return timeout err msg
ErrorEventArguements.SetAllHmiNetworkEventArgs(ID, -4, (AckNackType == 0) ? (1) : (3));
return (false);
I would like to be able to understand the issue and why the problem occurs and how can I fix it as I have fun out of ideas.
Thank you

I'm not answering the question, but I do need to point out something very important:
catch (Exception)
{
this._isReady = false;
return this._isReady;
}
Do NOT hide exceptions like that. When something fails you will have no chance what so ever to try to fix it, since you will never know why something failed. Do use proper exception handling.
Due to the application I need fast, non blocking operation of the UDP socket
That statement is not correct. Non-blocking sockets are not faster, they simply return before the operation has completed.
I do recommend that you switch back to blocking sockets, since you seem to be new to socket programming. Get the application running first, then try to optimize it.

You are setting the socket that you're reading messages from to non-blocking. This instructs the socket to NOT BLOCK if the operation cannot be completed immediately. What this means in practical terms is that if you attempt to read from the socket and there is nothing waiting to be read, the call will not return successfully.
I don't know how MessageReceived is being called, however I would assume that whatever is calling it is not checking that information is actually ready to be read from the socket, prior to the call.
As you're experiencing an intermittent problem, it would suggest that most of the time, the when MessageReceived is being called, there is data to be read from the socket.
If you want to continue to use non-blocking IO, you need to either change your logic, so that it catches the IO exception and retrys after a short delay (if you're sure there's going to be data there), or check to see if there is actually data available to be read from the socket, prior to attempting to perform the read.
One way to check if there is information available on the socket (prior to attempting to read from it) would be to use Socket.Poll. Something like:
if (_myUDPClient.Poll(myTimeoutInMicroSeconds, SelectMode.SelectRead)){
// Try to read the new messsage
} else {
continue; // go back to top of loop and try again
}
You may also need to check for SelectError state, to determine if the socket has a failure. Most of my socket programming has been from C++, so I'm not sure about the .Net specifics.