Im building a multi client to server system using .Net for the client side and python for server side. Currently my python server socket simply echoes back the data sent to it without doing any extra processing:
from twisted.internet import reactor, protocol
class Echo(protocol.Protocol):
"""This is just about the simplest possible protocol"""
def dataReceived(self, data):
"As soon as any data is received, write it back."
self.transport.write(data)
print(str(data))
def main():
"""This runs the protocol on port 8000"""
factory = protocol.ServerFactory()
factory.protocol = Echo
reactor.listenTCP(8000,factory)
reactor.run()
# this only runs if the module was *not* imported
if __name__ == '__main__':
main()
Its built on the Twisted framework, and can be found on the examples page, at their website.
Im also using the Async TCP client for C# provided by MicroSoft found at:
https://msdn.microsoft.com/en-us/library/fx6588te%28v=vs.110%29.aspx
The problem is, the client sends the data successfully to the server - and the server receives it, and can echo it successfully, however the line:
self.transport.write(data)
Doesnt seem to send the data back correctly because the client never receives a reply back. Why is this happening? Is it a possible deadlock between reading streams?
Related
I am a junior programmer and it is my first time building a WebSocket application in C#.
I have been following the tutorial from this page:
https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_server
By sending messages from the client to the server, everything works well. However, I want to have a bidirectional connection, so that the server could send messages back to the client in order to see them in the browser.
I have tried the following method, by adding the following lines to the server code:
byte[] tosend = Encoding.ASCII.GetBytes("Message received by server");
stream.Write(tosend, 0, tosend.Length);
I thought the client would receive this message but unfortunately, it return an undefined error and closes the connection.
Could you explain why this method of sedning messages doesn't work and maybe give me a few suggestions?
Thanks!
I have a weird scenario and I'm not sure how to solve it.
I have a simple tcp chat server in nodejs and my clients are currently in native C#, and eventually will move to Unity. I have my own networking library which creates the TCP connection and handles messages etc, and works fine in some cases until it comes to disconnecting.
The server is running on an EC2 instance and I am loading two windows on my PC to test the multiple connections. When I close the window, I receive this error in the nodejs server console
Error: read ECONNRESET
at exports._errnoException (util.js:870:11)
at TCP.onread (net.js:544:26)
Which is fine, because this is the scenario where it works. I'm guessing this just means that the connection was abruptly closed (closing the window).
However problems arise when I instruct the socket to be shutdown.
I am porting my client to Unity and when closing the client, it does not produce this ECONNRESET error and the connection never closes abruptly (like I'd expect it to), so in this case I have to manually close the connection on the client which results in a different error.
Error: This socket has been ended by the other party
at Socket.writeAfterFIN [as write] (net.js:268:12)
at /opt/chat/chat.js:32:10
at Array.forEach (native)
at broadcast (/opt/chat/chat.js:31:10)
at Socket.<anonymous> (/opt/chat/chat.js:26:2)
at emitNone (events.js:72:20)
at Socket.emit (events.js:166:7)
at endReadableNT (_stream_readable.js:905:12)
at nextTickCallbackWith2Args (node.js:441:9)
at process._tickCallback (node.js:355:17)
When I receive this error on the server, the other connected clients can continue messaging the server, however they cannot receive messages from it.
My nodejs server was pulled from github here:
https://gist.github.com/creationix/707146
// Load the TCP Library
net = require('net');
// Keep track of the chat clients
var clients = [];
// Start a TCP Server
net.createServer(function (socket) {
// Identify this client
socket.name = socket.remoteAddress + ":" + socket.remotePort
// Put this new client in the list
clients.push(socket);
// Send a nice welcome message and announce
socket.write("Welcome " + socket.name + "\n");
broadcast(socket.name + " joined the chat\n", socket);
// Handle incoming messages from clients.
socket.on('data', function (data) {
broadcast(socket.name + "> " + data, socket);
});
// Remove the client from the list when it leaves
socket.on('end', function () {
clients.splice(clients.indexOf(socket), 1);
broadcast(socket.name + " left the chat.\n");
});
// Send a message to all clients
function broadcast(message, sender) {
clients.forEach(function (client) {
// Don't want to send it to sender
if (client === sender) return;
client.write(message);
});
// Log it to the server output too
process.stdout.write(message)
}
}).listen(5000);
// Put a friendly message on the terminal of the server.
console.log("Chat server running at port 5000\n");
Scenario
Let's assume we have CLIENT A on the left and CLIENT B on the right
On initial connection, they can both chat fine.
CLIENT B wishes to disconnect, and the code forces the disconnect by terminating the socket. The nodejs server receives the error "This socket has been ended by the other party" and broadcasts that this player has disconnected to CLIENT A
CLIENT A wishes to continue communicating, regardless that no one is connected. CLIENT A continues typing and sending messages, however the messages are not being received once CLIENT B has disconnected. However, the messages are indeed being sent to the server.
CLIENT A is NOT receiving his own messages.
CLIENT B wishes to reconnect to continue chatting and does so.
CLIENT A sends message 'hello'
CLIENT B sends message 'hello'
CLIENT B is seeing both messages, and experiencing a normal chat, however CLIENT A is not seeing any of the messages and is stuck on a blocking call trying to read data.
This is ONLY when I force the socket closed, and it works perfectly fine when I receive the ECONNRESET error. How can I replicate this error, or fix my issue?
EDIT
I have managed to reproduce the ECONNRESET error and now it works, but it still doesn't explain why it doesn't work with other errors.
The methods Close and GetStream().Close in C# TcpClient are not sufficient it seems to close a connection properly. Instead I had to access the socket directly and close that.
Closing the socket directly works in a native C# application but not in Unity.
To replicate this error in Unity I have to use
Shutdown(SocketShutdown.Receive);
I have a really weird issue with communication between server and client using UDP protocol. Client is written in Mono2x (I use Unity 3D as my client) and creates UdpClient class instance:
_udpClient = new UdpClient(9050);
_serverEP = new IPEndPoint(IPAddress.Parse(_serverIp), _serverPort);
My server is UWP application I want to run on Raspberry Pi that is using DatagramSocket:
_udpServer = new DatagramSocket();
_udpServer.MessageReceived += ClientCheck;
await _udpServer.BindServiceNameAsync(port.ToString());
I send data from client to server but with no luck. I checked with TCPView that data is send from my client application but never reaches the server. And now is the weird part. When I receive message from server first (I hardcode port to client), my client is able to send data with a success.
I am using same IPEndPoint to send data from client without any changes after receiving packet from server, it just starts working. Honestly, I have no idea what I could do wrong, so I will be thankful for any advice.
And now is the weird part. When I receive message from server first (I hardcode port to client), my client is able to send data with a success
This is a known issue which is filed based on this related question: https://stackoverflow.com/a/39767527/5254458
It includes the issue's description and temporary workaround.
The corresponding is team is investigating it and I can not guarantee that when the fix will be delivered.
I have a server and client listening with a while loop to process packets sent to each other.
But there are some functions on the client that I would like to send a packet and process the reply on the same function without having to receive the command on its while loop.
Example:
private static string GetMyEmailFromServer() => SendAndGetPacket("GetMyEmail");
The example above sends a packet to the server with the string "GetMyEmail" and waits until it receives a message back then returns the value. The function "SendAndGetPacket" is using an already existing connection to the server to make the request.
As of right now, I have been creating a secondary connection to the server on another port (instead of using the already open and auth connection). I considered creating a whole framework to manage the receiving packets into different channels, where just 1 of the channels are processed in the "while loop" in the client, but I would like to know if there is a high level command for it in C#. Also, if you have a better idea than channels or a guide to implementing an effective channel system, I would appreciate a link or book (doesn't have to be language specified).
Haribol
I'm writing a simple C++ client that should connect to a C# server. And, while the client runs throught fine and even states it sent a bunch of bites, the C# server never gets past listener.Acceppt():
Console.WriteLine("Waiting for a connection...");
// Program is suspended while waiting for an incoming connection.
Socket handler = listener.Accept();
I took the server source from here: Microsoft MSDN: Synchronous Server Socket Example
The client code I use can be found here: Microsoft MSDN: Complete Winsock Client Code
I also checked to server with the according C# client, which worked fine. I also checked the return values of the client, which also looked pretty plausible. So I'd guess the problem lies somewhere in how C++ / C# handle the details.
I tried Wireshark to find some hints, but mysteriously there was absolutely no trace of any communication on the used port (11000).
Where should I start looking to solve this issue?
Update: All communication at the moment runs just locally. I tried my IPAddress (from ipconfig) and 127.0.0.1 for both server and client.
I just have one network adapter installed, I use that IP adress. The client checks the getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result) and returns valid information (e.g. TCP as protocol). connect() returns 0, which should be ok.
Update 2:
I tried different combinations of C++/C# Server-Client-Setups:
C++-Server, C++ Client: Works
C++-Server, C# Client: Works
C#-Server, C# Client: Works
C#-Server, C++ Client: Does not work
C#-Server, putty: Works
Update 3: I tried Wireshark on the other Server-Client constellations, but neither of them did show any traffic on tcp.port == 11000, although they did work (see Update 2). It looks like Wireshark does not show any results, because everything is just local (see Wireshark localhost traffic capture)
I had the same problem.
The connection with winsock is asynchronous. And the example in C# that you are using is synchronous.
You have to use a Asynchronous example to get communication with your C++ code.
I used this two examples!
C Sharp server
https://msdn.microsoft.com/en-us/library/fx6588te(v=vs.110).aspx
C plus plus client
https://msdn.microsoft.com/en-us/library/windows/desktop/ms737591(v=vs.85).aspx