Trying to connect() multiple times in TCP - c++

Question

I'm writing a client/server application where the client and server should send data to each other via a TCP socket. The client should connect to the server and if the connection fails, it should wait a few seconds and then try again to connect to it (up to a certain number of tries).
This is the code I currently have:
const int i_TRIES = 5;
time_t t_timeout = 3000;
int i_port = 5678;
int i_socket;
string s_IP = "127.0.0.1";
for(int i = 0; i < i_TRIES; i++)
{
if((i_socket = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
cout << "[Client]: Socket creation failed." << endl;
exit(EXIT_FAILURE);
}
memset(&server_address, '0', sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_port = htons(i_port);
if(inet_pton(AF_INET, s_IP.c_str(), &server_address.sin_addr) <= 0)
{
cout << "[Client]: Invalid IP address." << endl;
exit(EXIT_FAILURE);
}
if(connect(i_socket, (struct sockaddr *)&server_address, sizeof(server_address)) < 0)
{
if(i < i_TRIES - 2)
{
cout << "[Client]: Connection to server failed. Trying again in " << t_timeout << " ms." << endl;
close(i_socket);
sleep(t_timeout);
}
else
{
cout << "[Client]: Could not connect to server, exiting." << endl;
exit(EXIT_FAILURE);
}
}
else
{
cout << "[Client]: Successfully connected to server." << endl;
break;
}
}
// do stuff with socket
The issue I'm having is that the first call to connect() works as expected, it fails if there's no server and then the loop repeats, however, the second time connect() blocks forever (or at least for much longer than I want it to). Initially, my loop was just around the connect() if block (code below), and this also caused the same problem. After that I included the whole socket setup (the code above) in the loop, but that also didn't help. I also tried closing the socket after a failed connection, but this didn't help either.
Initial for loop:
// other stuff from above here
for(int i = 0; i < i_TRIES; i++)
{
if(connect(i_socket, (struct sockaddr *)&server_address, sizeof(server_address)) < 0)
{
if(i < i_TRIES - 2)
{
cout << "[Client]: Connection to server failed. Trying again in " << t_timeout << " ms." << endl;
sleep(t_timeout);
}
else
{
cout << "[Client]: Could not connect to server, exiting." << endl;
exit(EXIT_FAILURE);
}
}
else
{
cout << "[Client]: Successfully connected to server." << endl;
break;
}
}
// do stuff with socket
Can I force connect() to return after a certain amount of time has passed? Or is there a way to get the connect() function to try multiple times on it's own? Or is there something I need to do to the socket to reset everything before I can try again? I hope this isn't a dumb question, I couldn't find any information about how to connect multiple times.
Thanks in advance!

Answer 1

Can I force connect() to return after a certain amount of time has passed?
No. You must put the socket into non-blocking mode and then use select() or (e)poll() to provide timeout logic while you wait for the socket to connect. If the connection fails, or takes too long to connect, close the socket, create a new one, and try again.
Or is there a way to get the connect() function to try multiple times on it's own?
No. It can perform only 1 connection attempt per call.
Or is there something I need to do to the socket to reset everything before I can try again?
There is no guarantee that you can even call connect() multiple times on the same socket. On some platforms, you must destroy the socket and create a new socket before you call connect() again. You should get in the habit of doing that for all platforms.

Answer 2

Put the socket into non-blocking mode and use select() to implement the timeout. Select for writeability on the socket. Note that you can decrease the platform connect timeout by this means, but not increase it.
The sleep() is pointless, just literally a waste of time.