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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)

/* 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));

        /* One could use specific priority strings such as "PERFORMANCE:%SERVER_PRECEDENCE"
         * especially if they are read from a configuration file; otherwise, it
         * is recommended to use the defaults as shown here. */
        CHECK(gnutls_priority_init(&priority_cache, NULL, NULL));

#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);

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

}

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