SSL_connect for non blocking socket

Question

I use a non blocking socket. For a normal TCP connect I do as in here: Non blocking socket - how to check if a connection was successful?

But for the SSL_connect call I cannot get it to work.

I understand it as I should: 1. Repeatedly call SSL_connect. 2. Check if SSL_get_error is SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. 3. If so, then I am not 100% sure what to do next. Should I call SSL_connect until I don't get that? Or should I do as with a normal socket, check the socket with select using read_fds or write_fds and check with FD_ISSET and if so check getsockopt with SO_ERROR?

Basically, for SSL_connect and a non-blocking socket, what tells me that the connection has succeeded? I have looked at other examples but none are clear enough.

Your guess is right: you should wait for appropriate socket events with poll or select api according to operation result. And repeat operation. — Valeri Atamaniouk
But should I call SSL_connect only once ever? What am I waiting for with select? if read or write is set for my socket, what does it mean? WHat should I do? Do I call getsockopt or not? — Soft Ware
Usually you give a connected socket to SSL_connect. This function is not for lower-level connect operation, but for security protocol setup. — Valeri Atamaniouk
Yes I know. I can do SSL_connect with blocking sockets. But I am unsure about nonblocking ones. Some pseudocode for the whole process is what I need. — Soft Ware

Valeri Atamaniouk Valeri Atamaniouk · Accepted Answer · 2015-02-13T21:07:20

Here is an algorithm:

int s = socket(...);
fcntl(s, ...); // make it non-blocking
while (-1 == connect(s,...))
{
   fd_set fds;
   FD_ZERO(&fds);
   FD_SET(s, &fds);
   select(s + 1, NULL, &fds, NULL, NULL);
}

... // initialize all SSL stuff
SSL_set_fd(ctx, s);
while (-1 == SSL_connect(ssl))
{
   fd_set fds;
   FD_ZERO(&fds);
   FD_SET(s, &fds);

   switch (SSL_get_error())
   {
   case SSL_ERROR_WANT_READ:
       select(s + 1, &fds, NULL, NULL, NULL);
       break;
   case SSL_ERROR_WANT_WRITE:
       select(s + 1, NULL, &fds, NULL, NULL);
       break;
   default: abort();
   }
}
// done...

SSL_connect for non blocking socket

2 Answers