Server crash after client calls QtTcpSocket::disconnectFromHost();

Vadru

Hello!
I have a server running in linux and a client running in windows.
When the client close the application or lost connection everything works fine, but when the application runs the code:

void Network::disconnect()
{
   ...
    socket->disconnectFromHost();
 ...
}

The server will crash here::

void SendJSON(json j)
{
	vector <uint8_t> bson = json::to_bson(j);
	auto s = bson.size();

	vector <uint8_t> final;
	final.push_back(s >> 0);
	final.push_back(s >> 8);
	final.push_back(s >> 16);
	final.push_back(s >> 24);

	for (int i = 0; i < s; i++)
	{
		final.push_back(bson[i]);
	}

    if (write(client, &final.front(), final.size()) <= 0)  <- at this line the application will crash
	{
		connected = false;
		printf("connection failed\n");
		close(client);

		piThreadCreate(CheckForConnections);
	}
}

Is the problem that I'm using QtTcpSocket for the client and not for the server and if so, how can I disconnect in a safe way without crashing the server or closing the application?

SGaist

Hi and welcome to devnet,

What are you using of the server ?

Please provide the stack trace of your crash.

Vadru

I'm new to linux and I dont know how can I get the stack trace?

The server is running on a RaspberryPI.
The RaspberryPI is controlling my boiler and gathering some information like temperature, etc.
And the server is sending that information to the client so I can watch my boiler on my pc even when I'm not home.

SGaist

Use gdb to run your application.

Vadru

This is the stack trace:

Thread 5 "test" received signal SIGPIPE, Broken pipe.
[Switching to Thread 0xb4fff450 (LWP 7463)]
__GI___libc_write (nbytes=52, buf=0xb50008a0, fd=5)
    at ../sysdeps/unix/sysv/linux/write.c:26
26      ../sysdeps/unix/sysv/linux/write.c: No such file or directory.

Vadru

__libc_write (int fd, const void *buf, size_t nbytes)
{
  return SYSCALL_CANCEL (write, fd, buf, nbytes); <- this is that line of code
}

SGaist

Are you using a QTcpServer ?

SGaist

If not, are you handling that signal ? See here for some suggestions related to that.

Vadru

Such a simple mistake I have not used TCP in such a long time that I forgot all about signals.
I was getting so frustrated trying to solve it for several hours.
Now it works, thank you so much!

Vadru

Just of curiosity, why does disconnectFromHost() sends a sigpipe but when I close application it does not send a sigpipe?

SGaist

Sorry, I currently don't know although I am also intrigued.