7.2.1 Echo server with X.509 authentication

This example is a very simple echo server which supports X.509 authentication.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <assert.h>

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define CRLFILE "crl.pem"

#define CHECK(x) assert((x) >= 0)
#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

/* The OCSP status file contains up to date information about revocation
 * of the server's certificate. That can be periodically be updated
 * using:
 * $ ocsptool --ask --load-cert your_cert.pem --load-issuer your_issuer.pem
 *            --load-signer your_issuer.pem --outfile ocsp-status.der
 */
#define OCSP_STATUS_FILE "ocsp-status.der"

/* This is a sample TLS 1.0 echo server, using X.509 authentication and
 * OCSP stapling support.
 */

#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

int main(void)
{
	int listen_sd;
	int sd, ret;
	gnutls_certificate_credentials_t x509_cred;
	gnutls_priority_t priority_cache;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	int optval = 1;

	/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

	CHECK(gnutls_certificate_allocate_credentials(&x509_cred));

	CHECK(gnutls_certificate_set_x509_trust_file(x509_cred, CAFILE,
						     GNUTLS_X509_FMT_PEM));

	CHECK(gnutls_certificate_set_x509_crl_file(x509_cred, CRLFILE,
						   GNUTLS_X509_FMT_PEM));

	/* The following code sets the certificate key pair as well as, 
	 * an OCSP response which corresponds to it. It is possible
	 * to set multiple key-pairs and multiple OCSP status responses
	 * (the latter since 3.5.6). See the manual pages of the individual
	 * functions for more information.
	 */
	CHECK(gnutls_certificate_set_x509_key_file(x509_cred, CERTFILE, KEYFILE,
						   GNUTLS_X509_FMT_PEM));

	CHECK(gnutls_certificate_set_ocsp_status_request_file(
		x509_cred, OCSP_STATUS_FILE, 0));

	CHECK(gnutls_priority_init(&priority_cache, NULL, NULL));

	/* Instead of the default options as shown above one could specify
	 * additional options such as server precedence in ciphersuite selection
	 * as follows:
	 * gnutls_priority_init2(&priority_cache,
	 *                       "%SERVER_PRECEDENCE",
	 *                       NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND);
	 */

#if GNUTLS_VERSION_NUMBER >= 0x030506
	/* only available since GnuTLS 3.5.6, on previous versions see
	 * gnutls_certificate_set_dh_params(). */
	gnutls_certificate_set_known_dh_params(x509_cred,
					       GNUTLS_SEC_PARAM_MEDIUM);
#endif

	/* Socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);

	memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

	setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

	bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));

	listen(listen_sd, 1024);

	printf("Server ready. Listening to port '%d'.\n\n", PORT);

	client_len = sizeof(sa_cli);
	for (;;) {
		CHECK(gnutls_init(&session, GNUTLS_SERVER));
		CHECK(gnutls_priority_set(session, priority_cache));
		CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
					     x509_cred));

		/* We don't request any certificate from the client.
		 * If we did we would need to verify it. One way of
		 * doing that is shown in the "Verifying a certificate"
		 * example.
		 */
		gnutls_certificate_server_set_request(session,
						      GNUTLS_CERT_IGNORE);
		gnutls_handshake_set_timeout(session,
					     GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

		sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

		printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

		gnutls_transport_set_int(session, sd);

		LOOP_CHECK(ret, gnutls_handshake(session));
		if (ret < 0) {
			close(sd);
			gnutls_deinit(session);
			fprintf(stderr, "*** Handshake has failed (%s)\n\n",
				gnutls_strerror(ret));
			continue;
		}
		printf("- Handshake was completed\n");

		/* see the Getting peer's information example */
		/* print_info(session); */

		for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv(session, buffer,
							   MAX_BUF));

			if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				CHECK(gnutls_record_send(session, buffer, ret));
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection.
		 */
		LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));

		close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

	gnutls_certificate_free_credentials(x509_cred);
	gnutls_priority_deinit(priority_cache);

	gnutls_global_deinit();

	return 0;
}