SSL BIO example

ssl_bio.c

#include <openssl/ssl.h>

/**
 * This example demonstrates how to set up a simple SSL BIO filter on an
 * existing connect BIO. This is useful in sutiations where cleartext
 * communication is upgraded to ciphertext communication.
 *
 * Compile with:
 *    gcc ssl_bio.c -lcrypto -lssl -o ssl_bio
 */

void
handle_error (const char *msg)
{
	fprintf (stderr, "%s\n", msg);
	ERR_print_errors_fp (stderr);
	exit (1);
}

int
main (void)
{
	SSL_load_error_strings ();
	SSL_library_init ();

	SSL_CTX *ssl_ctx = SSL_CTX_new (SSLv23_client_method ());
	if (!ssl_ctx)
		handle_error ("Failed creating SSL context");

	SSL *ssl = SSL_new (ssl_ctx);
	if (!ssl)
		handle_error ("Failed allocating SSL structure");

	SSL_set_connect_state (ssl);

	/* Create SSL filter BIO. Data that passes through this filter will be
	 * encrypted. Also handles handshake when needed.
	 */
	BIO *ssl_bio = BIO_new (BIO_f_ssl ());
	if (!ssl_bio)
		handle_error ("Failed creating SSL BIO");

	BIO_set_ssl (ssl_bio, ssl, BIO_CLOSE);

	/* Creates a BIO of method BIO_s_connect and sets hostname and port. */
	BIO *bio = BIO_new_connect ("example.com:https");
	if (!bio)
		handle_error ("Failed creating connect BIO");

	/* Create a BIO of method BIO_s_file, for writing to stdout. */
	BIO *out = BIO_new_fp (stdout, BIO_NOCLOSE);
	if (!out)
		handle_error ("Failed creating file BIO");

	if (BIO_do_connect (bio) <= 0)
		handle_error ("Error connecting to server");

	BIO_push (ssl_bio, bio);

	if (BIO_puts (ssl_bio, "GET https://www.example.com/ HTTP/1.1\n\n") <= 0)
		handle_error ("Failed writing request");

	char buf[1024];
	for (;;) {
		int len = BIO_read (ssl_bio, buf, sizeof (buf));

		if (len == 0)
			break;

		if (len < 0)
			handle_error ("Failed reading response data");

		BIO_write (out, buf, len);
	}

	BIO_free (bio);
	BIO_free (ssl_bio);
	BIO_free (out);

	SSL_CTX_free (ssl_ctx);
	ERR_free_strings ();

	return 0;
}