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\begin{verbatim}
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
/* A very basic TLS client.
*/
#define MAX_BUF 1024
#define CAFILE "ca.pem"
#define SA struct sockaddr
#define MSG "GET / HTTP/1.0\r\n\r\n"
/* Connects to the peer and returns a socket
* descriptor.
*/
int tcp_connect( void)
{
const char *PORT = "443";
const char *SERVER = "127.0.0.1";
int err, sd;
struct sockaddr_in sa;
/* connects to server
*/
sd = socket(AF_INET, SOCK_STREAM, 0);
memset(&sa, '\0', sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(atoi(PORT));
inet_pton(AF_INET, SERVER, &sa.sin_addr);
err = connect(sd, (SA *) & sa, sizeof(sa));
if (err < 0) {
fprintf(stderr, "Connect error\n");
exit(1);
}
return sd;
}
/* closes the given socket descriptor.
*/
void tcp_close( int sd)
{
shutdown(sd, SHUT_RDWR); /* no more receptions */
close(sd);
}
int main()
{
int ret, sd, ii;
gnutls_session_t session;
char buffer[MAX_BUF + 1];
gnutls_certificate_credentials_t xcred;
/* Allow connections to servers that have OpenPGP keys as well.
*/
const int cert_type_priority[3] = { GNUTLS_CRT_X509,
GNUTLS_CRT_OPENPGP, 0 };
gnutls_global_init();
/* X509 stuff */
gnutls_certificate_allocate_credentials(&xcred);
/* sets the trusted cas file
*/
gnutls_certificate_set_x509_trust_file(xcred, CAFILE, GNUTLS_X509_FMT_PEM);
/* Initialize TLS session
*/
gnutls_init(&session, GNUTLS_CLIENT);
/* Use default priorities */
gnutls_set_default_priority(session);
gnutls_certificate_type_set_priority(session, cert_type_priority);
/* put the x509 credentials to the current session
*/
gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred);
/* connect to the peer
*/
sd = tcp_connect();
gnutls_transport_set_ptr( session, (gnutls_transport_ptr_t)sd);
/* Perform the TLS handshake
*/
ret = gnutls_handshake( session);
if (ret < 0) {
fprintf(stderr, "*** Handshake failed\n");
gnutls_perror(ret);
goto end;
} else {
printf("- Handshake was completed\n");
}
gnutls_record_send( session, MSG, strlen(MSG));
ret = gnutls_record_recv( session, buffer, MAX_BUF);
if (ret == 0) {
printf("- Peer has closed the TLS connection\n");
goto end;
} else if (ret < 0) {
fprintf(stderr, "*** Error: %s\n", gnutls_strerror(ret));
goto end;
}
printf("- Received %d bytes: ", ret);
for (ii = 0; ii < ret; ii++) {
fputc(buffer[ii], stdout);
}
fputs("\n", stdout);
gnutls_bye( session, GNUTLS_SHUT_RDWR);
end:
tcp_close( sd);
gnutls_deinit(session);
gnutls_certificate_free_credentials(xcred);
gnutls_global_deinit();
return 0;
}
\end{verbatim}
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