We have a framework that communicates via native WinAPI sockets (WSASend , CompletionPorts, etc) via TCP.
Recently, we've added some classes to this framework that also async sends and receives some messages via UDP, but these classes use Boost.ASIO (io_context etc).
Since then, we noticed that WinSocks connect function fails, with the following error:
A connection attempt failed because the connected party did not
properly respond after a period of time, or established connection
failed because connected host has failed to respond. The thread 0x3038
has exited with code 0 (0x0)
This only fails when connecting to a remote computer, not locally.
When reverting to an older version without these Boost classes, everything works fine (ruling out firewall issues)
When the Boost.ASIO classes our used outside of the framework, they work fine.
We are unsure what causes this issue. My hunch is that it is a conflict on OS level between winsock and boost.ASIO.
Did anyone run into something similar? Any ideas or pointers would be really appreciated.
Ben
Related
I'm trying to enhance some client C++ code using gRPC to support failover between 2 LAN connections.
I'm unsure if I found a bug in gRPC, or more likely that I'm doing something wrong.
Both the server and client machines are on the same network with dual LAN connections, I'll call LAN-A and LAN-B.
The server is listening on 0.0.0.0:5214, so accepts connections on both LANs.
I tried creating the channel on the client with both IPs, and using various load balancing options, ex:
string all_endpoints = "ipv4:172.24.1.12:5214,10.23.50.123:5214";
grpc::ChannelArguments args;
args.SetLoadBalancingPolicyName("pick_first");
_chan = grpc::CreateCustomChannel(all_endpoints,
grpc::InsecureChannelCredentials(),
args);
_stub = std::move(Service::NewStub(_chan));
When I startup the client and server with all LAN connections functioning, everything works perfectly. However, if I kill one of the connections or startup the client with one of the connections down, gRPC seems to be blocking forever on that subchannel. I would expect it to use the subchannel that is still functioning.
As an experiment, I implemented some code to only try to connect on 1 channel (the non-functioning one in this case), and then wait 5 seconds for a connection. If the deadline is exceeded, then we create a new channel and stub.
if(!_chan->WaitForConnected(std::chrono::system_clock::now() +
std::chrono::milliseconds(5000)))
{
lan_failover();
}
The stub is a unique_ptr so should be destroyed, the channel is a shared_ptr. What I see is that I can successfully connect on my new channel but when my code returns, gRPC ends up taking over and indefinitely blocking on what appears to be trying to connect on the old channel. I would expect gRPC would be closing/deleting this no longer used channel. I don't see any functions available in the cpp version that I can call on the channel or globally that would for the shutdown/closure of the channel.
I'm at a loss on how to get gRPC to stop trying to connect on failed channels, any help would be greatly appreciated.
Thanks!
Here is some grpc debug output I see when I startup with the first load balancing implementation I mention, and 1 of the 2 LANs is not functioning (blocking forever):
https://pastebin.com/S5s9E4fA
You can enable keepaliaves. Example usage: https://github.com/grpc/grpc/blob/master/test/cpp/end2end/flaky_network_test.cc#L354-L358
Just wanted to let anyone know the problem wasn't with gRCP, but the way our systems were configured with a SAN that was being written too. A SAN was mounted through the LAN connection I was using the test failover through and the process was actually blocking because it was trying to access that SAN. The stack trace was misleading because it showed the gRPC thread.
I am trying to use ZeroMQ to connect to a historical data server written in Python while I connect to Interactive Brokers' Trader Workstation (TWS) using C++ through UNIX socket in Linux. But I can't seem to get both to work at the same time. I tried to connect to the Python server using ZeroMQ first, and then to TWS once the connection is established. But after I connect to TWS, I can't seem to interact with my original ZeroMQ connection in any way. The connection with TWS would always lose whenever I provide the ZeroMQ socket to call zmq::poll. But if I don't include the ZeroMQ socket, zmq::poll works just fine with the file descriptor from the connection to TWS. I am not too experienced with either UNIX sockets or ZeroMQ, but is it true that I can't use ZeroMQ and sockets API in the same thread? I thought it would be simple to add ZeroMQ to the original Interactive Brokers socket client, but it is more complicated than I expected. Any suggestions would be greatly appreciated.
I'm testing out using DBus for inter process communication for an QT C++ project (Linux).
I'm not using the bus daemon and i'm using unix paths / sockets.
After navigating my way through the mysterious world that is QT DBUS all seemed to be going well, until i wanted to test the robustness of one of my interfaces.
After killing the server process en restarting it, the connection times out.. i cleanup the connection objects (client-side) and i try to re-connect to the server.
The client does not seem to be able to reconnect and i get the following errors:
errName: org.freedesktop.DBus.Error.NoServer
errMesage: Failed to connect to socket /tmp/abcd: Connection refused
Ive tried:
- QDBusConnection::disconnectFromPeer(addr);
- cleaning up all related object, so no references to the connection exist.
When i restart the client, it has no problems connecting to the (restarted) server.
Problem found!
Seems to be a bug in Qt 4.8.x:
https://bugreports.qt.io/browse/QTBUG-27973
https://codereview.qt-project.org/#/c/60709/
QDBusConnection::disconnectFromBus and QDBusConnection::disconnectFromPeer does not remove invalid connection
I made a simple program in c++ for connecting to a site and loading a page HTML code or send data using GET/POST requests.
But now I want the program to connect and send/receive data through proxy.
You probably know software like NextVpn and proxifier. when they are running any application which tries to communicate through internet will have to go through these apps.
The problem is that my program connects and communicates directly and my proxy software doesn't interfere.
Communication is done by the socket programming routins (SOCKET class) like this
SOCKET sck=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
connect(sck,(SOCKADDR*)(&SockAddr),sizeof(SockAddr));
send(sck,myRequest,strlen(myRequest),0);
Any solution?
EDIT: The problem was from NextVPN not the Proxifier itself. It seems that NextVPN lacks functionality in hooking into some programs. First NextVPN finds the program which is trying to connect to a remote address then redirects it to its portable version of proxifier with something named "compose.ns" . Unfortunately it was unable or couldn't detect my app connecting to internet. Instead I used Proxifier itself and it successfully detected my app as it was showing in its connection list.
A chat program would be a good enough example.
Just need a server that can accept multiple connections from the clients, and the server needs to be able to send messages to individual clients.
I plan to turn this into a distributed computing program to work with multiple Neural Networks.
Asio is the Boost library that handles networking. There's a chat server example listed here.
I cannot give you an example progam. But to write a server things that you have to do:
1. server will listen at a port for connection
2. thread pool which will accept the connection and serve request
3. write the server code in thread safe manner
You have to use socket programming A good link for that http://beej.us/guide/bgnet/
you can use win32 api in windows and posix for linux