How to make non-blocking OpenSSL connection? - c

Question

I want make a non-blocking OpenSSL connection
On this connection - if no data available for read, then entire program execution flow make stop on SSL_read(). I want so that if no data available for read it give me the returns values like WANT_READ and i know no more data available.
char *sslRead (connection *c)
{
const int readSize = 1024;
char *rc = NULL;
int r;
int received, count = 0;
int ReallocSize = 0;
char buffer[1024];
if (c)
{
while (1)
{
if (!rc)
{
rc = malloc (readSize + 1);
if (rc == NULL)
printf("the major error have happen. leave program\n");
}
else
{
ReallocSize = (count + 1) * (readSize + 1);
rc = realloc (rc, ReallocSize);
}
// if i have no data available for read after reading data,
// this call will not return anything and wait for more data
// i want change this non blocking connections
received = SSL_read (c->sslHandle, buffer, readSize);
buffer[received] = '\0';
if (received <= 0)
{
printf(" received equal to or less than 0\n");
switch (SSL_get_error(c->sslHandle, r))
{
case SSL_ERROR_NONE:
printf("SSL_ERROR_NONE\n");
break;
case SSL_ERROR_ZERO_RETURN:
printf("SSL_ERROR_ZERO_RETURN\n");
break;
case SSL_ERROR_WANT_READ:
printf("SSL_ERROR_WANT_READ\n");
break;
default:
printf("error happens %i\n", r);
}
break;
}
count++;
}
}
return rc;
}
here is how i make connection
connection *sslConnect (void)
{
connection *c;
c = malloc (sizeof (connection));
c->sslHandle = NULL;
c->sslContext = NULL;
c->socket = tcpConnect ();
if (c->socket)
{
// Register the error strings for libcrypto & libssl
SSL_load_error_strings ();
// Register the available ciphers and digests
SSL_library_init ();
// New context saying we are a client, and using SSL 2 or 3
c->sslContext = SSL_CTX_new (SSLv23_client_method ());
if (c->sslContext == NULL)
ERR_print_errors_fp (stderr);
// Create an SSL struct for the connection
c->sslHandle = SSL_new (c->sslContext);
if (c->sslHandle == NULL)
ERR_print_errors_fp (stderr);
// Connect the SSL struct to our connection
if (!SSL_set_fd (c->sslHandle, c->socket))
ERR_print_errors_fp (stderr);
// Initiate SSL handshake
if (SSL_connect (c->sslHandle) != 1)
ERR_print_errors_fp (stderr);
}
else
{
perror ("Connect failed");
}
return c;
}
thanks you very much.

Answer 1

Creating a non-blocking socket is a pre-requisite to a non-blocking connect...
The following steps summarize: (see complete description in site linked below)
1) Call the fcntl() API to retrieve the socket descriptor's current flag settings into a local variable.
2) In that local variable, set the O_NONBLOCK (non-blocking) flag on. (being careful not to tamper with the other flags)
3) Call the fcntl() API to set the flags for the descriptor to the value in our local variable.
( read more on non-blocking sockets techniques here )
Assuming an existing socket, the following implements the steps outlined above:
BOOL SetSocketBlockingEnabled(SOCKET fd, BOOL blocking)
{
if (fd < 0) return FALSE;
#ifdef WIN32
unsigned long mode = blocking ? 0 : 1;
return (ioctlsocket(fd, FIONBIO, &mode) == 0) ? TRUE : FALSE;
#else
int flags = fcntl(fd, F_GETFL, 0);
if (flags < 0) return false;
flags = blocking ? (flags&~O_NONBLOCK) : (flags|O_NONBLOCK);
return (fcntl(fd, F_SETFL, flags) == 0) ? TRUE : FALSE;
#endif
}
Once you have a non-blocking socket, then see this post explaining how to do a non-blocking connect