Develop Reference

How can I send multiple string messages from client to server using a single instance of TcpClient?

I have separate client and server console apps. I'm simply trying to send a string from the client to the server and have the server write the string to the console using TcpClient. I can send a single message just fine but when I throw a while loop into the client app to try and send multiple messages without closing the TcpClient, the server doesn't write anything to the console.
//Server
using (TcpClient client = listener.AcceptTcpClient())
{
NetworkStream ns = client.GetStream();
byte[] buffer = new byte[1024];
while (true)
{
if (ns.DataAvailable)
{
int bytesRead = 0;
string dataReceived = "";
do
{
bytesRead = ns.Read(buffer, 0, buffer.Length);
dataReceived += Encoding.UTF8.GetString(buffer, 0, bytesRead);
}
while (bytesRead > 0);
Console.WriteLine($"Message:{ dataReceived }\n");
}
}
}
//Client
using (TcpClient client = new TcpClient(hostname, port))
{
if (client.Connected)
{
Console.WriteLine("Connected to server");
NetworkStream ns = client.GetStream();
string message = "";
//Removing this while loop I can send a single message that the server will write to console
//but with the loop present the server does not write anything
while (true)
{
message = Console.ReadLine();
byte[] messageBytes = UTF8Encoding.UTF8.GetBytes(message);
ns.Write(messageBytes);
Console.WriteLine($"Message Sent! ({ messageBytes.Length } bytes)");
}
}
}
I'm interested in learning sockets and have been pouring over SO questions and MSDN docs for two days but cannot figure out why it's not working as I intend. I feel a bit silly even submitting a question because I'm sure it's something basic I'm not understanding. Could someone please drop some knowledge on me?
SOLUTION
//Server
using (TcpClient client = listener.AcceptTcpClient())
{
NetworkStream ns = client.GetStream();
StreamReader sr = new StreamReader(ns);
string message = "";
while (true)
{
message = sr.ReadLine();
Console.WriteLine(message);
}
}
//Client
using (TcpClient client = new TcpClient(hostname, port))
{
if (client.Connected)
{
Console.WriteLine("Connected to server");
NetworkStream ns = client.GetStream();
StreamWriter sw = new StreamWriter(ns) {Autoflush = true};
string message = "";
while (true)
{
message = Console.ReadLine();
sw.WriteLine(message);
}
}
}

If you debug your server, you'll see that it does receive data. You're just not displaying the data, because the only output your server does is after the loop when the byte count returned is 0: Console.WriteLine($"Message:{ dataReceived }\n");. The byte count will only be 0 when the underlying socket has been shutdown. That never happens because your client is stuck in an infinite loop.
A better approach, for a simple text-based client/server example like this, is to use StreamWriter and StreamReader with line-based messages, i.e. WriteLine() and ReadLine(). Then the line breaks serve as the message delimited, and your server can write the message each time it receives a new line.
Note also that in your example above, you are assuming that each chunk of data contains only complete characters. But you're using UTF8 where characters can be two or more bytes, and TCP doesn't guarantee how bytes that are sent are grouped. Using StreamWriter and StreamReader will fix this bug too, but if you wanted to do it explicitly yourself, you can use the Decoder class, which will buffer partial characters.
For some examples of how to correctly implement a simple client/server network program like that, see posts like these:
.NET Simple chat server example
C# multithreading chat server, handle disconnect
C# TcpClient: Send serialized objects using separators?

socat TCP listener with .NET Client

I have a socat TCP listener running on Linux (SLES 12). Any client that connects will pass a string to the socket and socat will execute a script which does some work with based on the string. The script echos some output which is passed back to client.
socat TCP-LISTEN:9996,fork EXEC:/home/abhishek/hello.sh
Below is the hello.sh script.
#!/bin/bash
read str
echo "[Hello] $str" | tee -a test.txt
When I run ncat client this works as expected. ncat is able to get the data back and output it.
echo abhishek | ncat 192.168.1.12 9996
[Hello] abhishek
Now I want to connect to socat through a .NET client written in C#. Below is the raw socket based code I have come up with.
IPAddress address = IPAddress.Parse("192.168.1.12");
IPEndPoint ipe = new IPEndPoint(address, 9996);
Socket client = new Socket(ipe.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
client.Connect(ipe);
byte[] msg = Encoding.ASCII.GetBytes("abhishek");
// Send the data through the socket.
int bytesSent = client.Send(msg);
Console.WriteLine("Sent {0} bytes.", bytesSent);
byte[] bytes = new byte[128];
int bytesRec = client.Receive(bytes); ;
Console.WriteLine("Response text = {0}", Encoding.ASCII.GetString(bytes, 0, bytesRec));
client.Shutdown(SocketShutdown.Both);
client.Close();
I get the line "Sent 8 bytes" but after that client hangs on Receive. The client data is received by hello.sh becaused test.txt contains new entry. When I kill the client (Ctrl+C) socat prints
2018/02/03 10:12:03 socat[21656] E write(4, 0xe530f0, 17): Broken pipe
How should I read the reply from socat in C#?
Thanks

I was able to use TcpClient to establish communication with socat and get the output from script. Below is the main part of code I implemented.
TcpClient client = new TcpClient("192.168.1.12", 9999);
NetworkStream stream = client.GetStream();
StreamWriter writer = new StreamWriter(stream) { AutoFlush = true };
StreamReader reader = new StreamReader(stream);
//Send message to socat.
writer.WriteLine(message);
//Receive reply from socat.
string reply = reader.ReadLine();
stream.close();
client.close();

c# tcpclient program writing to stream but client not receiving data

I have written a TCPClient program to run on my PC. It first initiates a TCP listener to listen on a specific port then reads/writes from/to multiple TCP clients on multiple threads.
I am able to read from the client but whenever I try to send data to it, the program displays that it has sent the data, but the client does not receive anything.
Here's the code:
TcpClient client = listener.AcceptTcpClient();
var childSocketThread = new Thread(() =>
{
if (client.Connected)
{
using (NetworkStream stream = client.GetStream())
{
Console.WriteLine("connected");
byte[] data = new byte[1000];
try
{
if (stream.CanRead)
{
stream.Read(data, 0, 1000);
string dataStr = Encoding.ASCII.GetString(data);
string dataa = dataStr.TrimEnd('\0');
//Console.WriteLine(dataa);
if (dataa.Length > 10)
{
deviceid = ParseRequest(dataa);
byte[] sendnow = Encoding.ASCII.GetBytes(reply[deviceid]);
Array.Clear(data, 0, 1000);
Console.WriteLine("Recieved data: " + dataa);
Console.WriteLine("Sending data");
using (StreamWriter writer = new StreamWriter(stream))
{
writer.AutoFlush = true;
writer.WriteLine(reply[deviceid]);
}
Console.WriteLine(reply[deviceid]);
Console.WriteLine("Sent");
}
Console.WriteLine();
}
}
catch (Exception es)
{
Console.WriteLine(es);
}
}
}
});
childSocketThread.Start();
The server device that I am using is a PLC. Also, things I have already tried:
1) sending directly using Socket.Send method.
2) sending directly using NetworkStream method.
3) accepting the TCP connection as sockets. (Socket device = listener.AcceptSocket).
None of these methods seem to send to the device, even though the program tells me that it had no issues sending data since it displays "Sent" after attempting to send data.
I downloaded another program from this link http://www.codeproject.com/Articles/488668/Csharp-TCP-Server. The test app they provide with it is able to send and receive data on the same port as my program running on the same PC.
I haven't been able to get any direction on how to diagnose and more importantly solve this issue. Any ideas?
Update 2015-08-10 11:18 a.m.:
Output of the Program is as follows:
Update 2015-08-10 11:32 a.m.:
Output of Syslog Console:
Update 2015-08-10 12:07 p.m.:
Output of Wireshark:

We need you to post both sides code. Nevertheless, here is some code that works just fine, you can use it to see if you are doing something wrong.
http://www.codeproject.com/Articles/1415/Introduction-to-TCP-client-server-in-C

.Net isn't deserializing stream when sent from Websockets

I'm making an application in PhoneGap, and I'm using HTML5 Websockets to send some info to another device (read: sending data to another user who has the app). Users are registered with ID and Username.
For this, I read that I have to make an TCP/Socket connection. I've tried to use an old socket-chat I once made in school with C#.
I'm connecting to the socket this way from the app:
var ws = new WebSocket("ws://127.0.0.1:7001");
ws.onopen = function()
{
// Web Socket is connected, send data using send()
ws.send("message");
};
And the server side looks like this (of course isn't the entire code, but the relevant parts)
private NetworkStream stream;
private IFormatter formatter = new BinaryFormatter();
private TcpListener server;
public TcpClient client;
private string username { get; set; }
private void StartServer()
{
int port = Convert.ToInt32(portUser);
server = new TcpListener(IPAddress.Parse(IP), port);
server.Start();
client = server.AcceptTcpClient();
stream = client.GetStream();
username = formatter.Deserialize(stream).ToString();
}
The last deserialize-line writes:
The input stream is not a valid binary format. The starting contents (in bytes) are: 47-45-54-20-2F-20-48-54-54-50-2F-31-2E-31-0D-0A-48 ...
Any other way to deserialize the stream? Or am I using a completely wrong way?
Edit: working C# way I used to send data between clients in the chatter
stream = client.GetStream();
formatter.Serialize(stream, messageobj);
stream.Flush();

Socket writing not working properly c#

I'm working on a biometry system with my C# application.
Sdk provices a connection via TCP/IP on port 2100, and works by receiving and sending strings to communicate .
My class:
class Biometry
{
private System.Net.Sockets.TcpClient _clientSocket = new System.Net.Sockets.TcpClient();
public Biometry() {
//connect to socket
_clientSocket.Connect("127.0.0.1", 2100);
_clientSocket.ReceiveTimeout = 9000;
}
public String identify(String msg) {
//get network stream
NetworkStream _serverStream = _clientSocket.GetStream();
//send an array of bites that represents a string(encoded)
System.Text.ASCIIEncoding ASCII = new System.Text.ASCIIEncoding();
byte[] outStream = System.Text.Encoding.ASCII.GetBytes(msg);
_serverStream.Write(outStream, 0, outStream.Length);
//reads the response from networkStream
byte[] inStream = new byte[10025];
_serverStream.Read(inStream, 0, (int)_clientSocket.ReceiveBufferSize);
string returndata = System.Text.Encoding.ASCII.GetString(inStream);
_serverStream.Close();
return returndata;
}
}
The problem is:
It is not working!! The biometry only works(SDK only understand my request) when I close the application(connection is closed).

You might need to flush the stream before your start reading using _serverStream.Flush().
Another problem might be that in your question you say you need to connect to port 21000, but in your code you connect to 2100, which might be a typo in either place, but should be fixed ;-)
In addition to flushing the stream, your server might also be waiting for an "end of message" indicator?