I have created simple TCP server which accepts connections and request and do some processing. I have referred following example and it is working fine. I send data to to connected client continuously and it is being printed on client side. Though after around period of 20-25 minutes, the client stops receiving any data. Also after such incident, the server shows running but now when I connect my client again to server, the server's connection accept handler doesnt get invoked. But I am able to telnet to the server's port and client is able to connect. Any idea what might be the problem?
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I am currently writing a server application that should instruct multiple clients.
I am unsure about the concept i have designed and would like to receive feedback on it.
There are several identical clients that record and process sensor data. In addition, the results are sent to the server so that the server can react if necessary and send new parameters to the client.
The client should continue to work after the connection has ended and try to reconnect at the same time. If there is no connection, data do not have to be transmitted subsequently.
My concept is as follows:
The client logs on to the server.
The client requests an initialization -> server ok.
The client requests parameter A -> server sends parameter
The client requests parameter B -> server sends parameter
...
The client requests parameter Z -> server sends parameter
The client sends initialization finished -> server says ok
endless loop
Server queries measured value X -> client sends measured value
Server sends parameter Y -> client says ok.
So first the client is the master and asks for the initialization parameters it needs, then the server and client swap roles and the server becomes the master.
Should the connection break, the client should reconnect to the server. but would then with the command:
The client sends initialization finished -> server says ok
start so that the initialization is skipped.
The request of parameters runs as follows:
Infinite loop
Send (command)
Timout = 1 second
Receive
if (! Timout)
break
so i send the command and wait a little, if no answer comes i send the command again. this is shown here in abbreviated form. I wrote it in c ++ and I use several state machines. The state machines naturally also catch errors when the connection is interrupted and jump back to the initialization status ...
Since this is a multi-client application, I find it a little difficult. it runs as a single client. I have a class client in which a state machine and a socket are stored. the instance runs in a separate thread.
My problem now is, if the connection is lost, how can I establish a new connection (from an old client) to its instance (state machine). i would do this over some id comparison. so that the client sends his id first of all. (maybe also mac address ???)
I currently keep the connections to all clients open at all times. is that state of the art? or should you send a command, wait for an answer and close the connection again and then reconnect if necessary?
Many Thanks
Once TCP connection is established
each side can send for data.
Just that you have to get write -> read sequence correct.
This can be easily implemented using non blocking socket IO.
"My problem now is, if the connection is lost, how can I establish a
new connection (from an old client) to its instance (state machine). i
would do this over some id comparison. so that the client sends his id
first of all. (maybe also mac address ???)"
One solution is each client has a UUID, Client must tell server every time it connects its ID , server can keep a map of UUID vs client socket connection.
If Client is lost server can delete the mapping. Both server & client can detect lost connection that should not be a problem.
We have the following configuration: Server, Client, DHCP-Server. The server runs on a static IP in "client mode". This means, that server has a list of all clients (hostnames) and builds TCP-connections. Clients have dynamic IPs.
How does it working: 1) Server creates a connection to a client and 2) Server waits for any data from a client (we use ACE framework and reactor-pattern). To have the list with clients up to date, we have added an additional timer, that sends a heartbeat to all clients.
And there is one strange behavior:
let's say a hostname "somehost.internal" has IP "10.10.100.50"
Time = t: connect to hostname "somehost.internal"
Time = t+1: change IP of the client to "10.10.100.60"
Time = t+2: heartbeat timer send data to an existing endpoint (10.10.100.50) and successfully returns (why??? this IP is not accessible)
in Wireshark I can see, that Retransmission packages
Time = t+5: some seconds later event handler returns with an error and the connection to the endpoint (10.10.100.50) will be closed
Do you have any advice, why a blocking send-function successfully returns when remote endpoint does not exist anymore?
I assume in step 3 you only send a heartbeat message to the client but do not actually wait for a response from the client on that heartbeat message.
The socket send() function only forwards the data to the OS. It does not mean that the data is actually transmitted or has been received by the peer.
The OS buffers data, transmits data over the network, waits for acknowledgements, retransmits data, etc.. This all takes time. Eventually the OS will decide that the other end no longer responds and marks the connection as invalid.
Only then when you perform a socket function on that connection is the application notified of any issues.
Writing a UDP client-server app in C++ (done that lots of times before in many languages in the past 15 years), but somehow this one is not working correctly.
I cannot post actual code nor minimal reproducible app at the moment but I am willing to pay for live help if anyone is available to help solve this quickly with screensharing.
I think this is a particularity with C++ sockets and the way I am using them in this specific app which is quite complex.
Basically the issue is that the packets sent from the server to the client are not received by the client, only when said client is on a separate nat.
When both in same local networking and using their local IP, everything works as expected.
Here is what I am doing :
Client sendto(...) packets through UDP to the server using a specific server host and port 12345 (and keeps sending these non-stop)
On another thread, client bind(...) on port 12345 and "0.0.0.0" and tries to poll() and recvfrom() in a loop (poll always returns 0 here when client is on a separate nat)
Server bind() on port 12345 and "0.0.0.0" then poll() and recvfrom() in a loop
Upon receiving the first UDP message from a client, it starts a thread for sending
UDP messages back to the client on a new socket, using the
sockaddr_in that it got from the recvfrom() to pass in the sendto() commands.
Result : Server perfectly receives ALL messages from all clients, and sends all messages back to all clients, but any client that is not on the same NAT will never receive any messages (poll() always returns 0).
As far as I understand it, when the client sends a UDP message to the server on a specific remote port (12345 in this case), it will punch a hole in its NAT so that it can receive messages back from the remote server on that port...
I tested five different client network configurations :
Local network with the server, using local IP addresses (WORKS)
Local network with the server while client is using a VPN thus going through a remote NAT (DOES NOT WORK)
Local network with the server but client is using the WAN ip address to connect to the server (DOES NOT WORK)
Client at an actual remote network from a friend's connection, behind a router (DOES NOT WORK)
Client going through a wifi hotspot created using my phone (DOES NOT WORK)
For all tests above, the server was correctly receiving all communications from clients.
I also tried forcing the port to 12345 for the sendto() instead of using the sockaddr_in as set from recvfrom(), same issue.
Am I doing anything wrong ?
If you want to help but need to see actual code, I can do that live with screen sharing and I will pay for the help.
Thanks.
Also, if anyone can point me to a great site where I can pay for VERY QUICK help, please let me know, I don't even bother searching google because I really want actual advice from people who tried these services, not ads trying to rip me off...
Only the original receiver socket is allowed to reply to the client, because it's the client request that opens the port in the NAT. So either use the same socket in the server to receive and reply, or get the port that the second server socket was bound to and transfer it with an initial message through the original server port, so that A can send to it and punch the hole.
It looks so strange to create two half duplex sockets when a socket is a full duplex communication object that I'd go with the first option.
sorry for the noobish question but I can't find any resources online clearly stating whether this should work or not, and all tutorials / sample code always use localhost ^^ Soooo...
I'm trying to setup a simple server / client using RakNet. I'm literally just following the first tutorial (http://www.jenkinssoftware.com/raknet/manual/tutorial.html), just trying to get the client to connect to the server and keep the connection alive for a bit.
It all works great as long as I use 127.0.0.1 or 192.168.0.XXX, I can start the server, then the client, the server detects the connection request and sends the reply to the client, the client receives the reply and prints out "connection accepted" and such, and I can exchange messages between the client and the server.
However if I try using my actual IP, the server does not seem to detect the connection request (if you look at the tutorial code, it doesn't print "incoming connection"), but the client still receives a reply from somewhere ("Our connection request has been accepted").
After this initial semi-successful connection, no more packets will be received by either server or client, and the client will inevitably get disconnected after a few seconds (I assume time out?).
Port is open on the router, and the app runs fine as long as I keep it on localhost.
So my question is: is it even possible to run a server and client on the same machine / IP which is sitting behind a router?
The RakNet documentation part about NAT punchthrough and UDP forwarding does mention no more than one client and server being able to run on the same machine, but I was under the impression that one server / one client would not be an issue?
Thanks in advance to anybody who can shed some light on this!!
Forgot to mention my firewall is disabled !
I have implemented a design in C++ that is:-
I parse an XML file which contain the ip and port of several servers,for each ip and port i first call the connect to server function in which i make a TCP socket connection with the server whether the connection is established or not i make a thread for each ip and port,if connection is not established i send the status of the server that connection is not established and if connection is established i then make a request to the server and receive response from the server in the thread.This is done after every minute for each thread.
Now the problem that i am facing is,if connection terminates or if the server power goes,how to again make a connection i mean after every one minute before sending request and receiving response from the server i have to check whether the connection is still there or not.
Can you please tell me how to do that?
You could have whatever it is that checks the connection status also do all of the communication for your other classes. Other classes pass a function pointer to it and in that method you test the connection, and if it's successful run the function you've been passed. If not stick it on a queue to be run once the connection is re-established.