7.3.11 Echo server with anonymous authentication

This example server supports anonymous authentication, and could be used to serve the example client for anonymous 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>

/* This is a sample TLS 1.0 echo server, for anonymous authentication only.
 */

#define SOCKET_ERR(err, s)  \
	if (err == -1) {    \
		perror(s);  \
		return (1); \
	}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

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

	if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

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

	gnutls_anon_allocate_server_credentials(&anoncred);

	gnutls_anon_set_server_known_dh_params(anoncred,
					       GNUTLS_SEC_PARAM_MEDIUM);

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

	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));

	err = bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));
	SOCKET_ERR(err, "bind");
	err = listen(listen_sd, 1024);
	SOCKET_ERR(err, "listen");

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

	client_len = sizeof(sa_cli);
	for (;;) {
		gnutls_init(&session, GNUTLS_SERVER);
		gnutls_priority_set_direct(session,
					   "NORMAL:+ANON-ECDH:+ANON-DH", NULL);
		gnutls_credentials_set(session, GNUTLS_CRD_ANON, anoncred);

		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);

		do {
			ret = gnutls_handshake(session);
		} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

		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 (;;) {
			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
				 */
				gnutls_record_send(session, buffer, ret);
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection.
		 */
		gnutls_bye(session, GNUTLS_SHUT_WR);

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

	gnutls_anon_free_server_credentials(anoncred);

	gnutls_global_deinit();

	return 0;
}