Setting a timeout when using connect() in C++

Question

I'm using sockets in c++ on linux to connect to a server using connect(), but it doesn't seem to have a timeout value. What would be the easiest/best way to give it a timeout of a few seconds. I'll post the code I have up to, and including, the blocking call to connect():

using namespace std; int main( int argc, char* argv[] ) { // Interpret the command line arguments string uri_string = "";

if ( argc != 2 )
{
 cerr << "Usage: " << argv[0];
 cerr << " <URI>" << endl;
 return 1;
}
else
{
 uri_string = argv[1];
}

// Create URI object and have it parse the uri_string
URI *uri = URI::Parse(uri_string);

if ( uri == NULL )
{
 cerr << "Error: Cannot parse URI." << endl;
 return 2;
}

// Check the port number specified, if none use port 80
unsigned port = 80;
if ( uri->Is_port_defined() )
{
 port = uri->Get_port();
}

// Create TCP socket and connect to server
int tcp_sock = socket( AF_INET, SOCK_STREAM, 0 );
if ( tcp_sock < 0 )
{
 cerr << "Unable to create TCP socket." << endl;
 return 3;
}

sockaddr_in server;
socklen_t slen = sizeof(server);

server.sin_family = AF_INET;
server.sin_port = htons( port );
cout << "Resolving " << uri->Get_host() << "... ";
hostent *hostp = gethostbyname( uri->Get_host().c_str() );
memcpy( &server.sin_addr, hostp->h_addr, hostp->h_length );

struct in_addr **pptr;
pptr = (struct in_addr **)hostp->h_addr_list;

string ip_addr = "";
while( *pptr != NULL ) {
 ip_addr += inet_ntoa(**(pptr++));
}
cout << ip_addr << endl;

cout << "Connecting to " << uri->Get_host() << "|" << ip_addr << "|:";
cout << port << "... ";
if ( connect( tcp_sock, (sockaddr*)&server, slen ) < 0 )
{
 cerr << "Unable to connect to server via TCP." << endl;
 close( tcp_sock );
 return 4;
}
cout << "connected." << endl;

// rest of code

Answer 1

Take a look at this newsgroup post, with details and sample code for how to put a timeout on socket connections in Lunux. The basic idea is to use non-blocking sockets, and then wait for a connection.

Answer 2

Make the socket a non-blocking socket, and then use select() or poll() with a timeout value to check for writability. If the select() returns with a timeout you did not connect in time, and you can close the socket and deal with the connection failure. If it returns with a completion, everything is fine and you can proceed.

Answer 3

set non-blocking mode for your socket and use select to check whether connection established. here is the sample

Answer 4

Another way to do non-blocking without the pain of select() is to check GetLastError() for EWOULDBLOCK.

// set socket as nonblocking
unsigned long value = 1;
if (ioctlsocket(yourSocket, FIONBIO, &value) == SOCKET_ERROR)
 return SOCKET_ERROR;

// (call connect here)

// check if connect would block
if (GetLastError() == EWOULDBLOCK)
    return TIMEOUT;