src/connection.c

   1 /*
   2  * Handle connections.
   3  *
   4  * Copyright (C) 2011-2012  Simon Ruderich
   5  *
   6  * This program is free software: you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation, either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include "tlsproxy.h"
  21 #include "connection.h"
  22 #include "verify.h"
  23
  24 /* close() */
  25 #include <unistd.h>
  26 /* getaddrinfo() */
  27 #include <netdb.h>
  28 /* poll() */
  29 #include <poll.h>
  30 /* errno */
  31 #include <errno.h>
  32
  33
  34 /* Maximum length of a HTTP request line. Longer request lines are aborted
  35  * with an error. The standard doesn't specify a maximum line length but this
  36  * should be a good limit to make processing simpler. As HTTPS is used this
  37  * doesn't limit long GET requests. */
  38 #define MAX_REQUEST_LINE 4096
  39
  40 /* Format string used to send HTTP/1.0 error responses to the client.
  41  *
  42  * %s is used 4 times, first three are the error code (no %n$s!), the last is
  43  * the message. */
  44 #define HTTP_RESPONSE_FORMAT "HTTP/1.0 %s\r\n\
  45 Content-Type: text/html; charset=US-ASCII\r\n\
  46 \r\n\
  47 <!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\">\n\
  48 <html>\n\
  49 <head><title>%s</title></head>\n\
  50 <body>\n\
  51 <h1>%s</h1>\n\
  52 <p>%s</p>\n\
  53 </body>\n\
  54 </html>\n"
  55
  56
  57 static int initialize_tls_session_client(int peer_socket,
  58         const char *hostname,
  59         gnutls_session_t *session,
  60         gnutls_certificate_credentials_t *x509_cred);
  61 static int initialize_tls_session_server(int peer_socket,
  62         gnutls_session_t *session,
  63         gnutls_certificate_credentials_t *x509_cred);
  64
  65 static int read_http_request(FILE *client_fd, char *request, size_t length);
  66 static void send_bad_request(FILE *client_fd);
  67 static void send_forwarding_failure(FILE *client_fd);
  68 static void tls_send_invalid_cert_message(gnutls_session_t session);
  69
  70 static void transfer_data(int client, int server);
  71 static int read_from_write_to(int from, int to);
  72 static void transfer_data_tls(int client, int server,
  73                               gnutls_session_t client_session,
  74                               gnutls_session_t server_session);
  75 static int read_from_write_to_tls(gnutls_session_t from, gnutls_session_t to,
  76                                   size_t buffer_size);
  77
  78 static int connect_to_host(const char *hostname, const char *port);
  79
  80 static int parse_request(const char *buffer, char *host, char *port,
  81                                              int *version_minor);
  82
  83
  84 void handle_connection(int client_socket) {
  85     int server_socket;
  86     FILE *client_fd, *server_fd;
  87
  88     char buffer[MAX_REQUEST_LINE];
  89     char host[MAX_REQUEST_LINE];
  90     char port[5 + 1];
  91
  92     int version_minor; /* HTTP/1.x */
  93     int result;
  94
  95     /* client_x509_cred is used when talking to the client (acting as a TSL
  96      * server), server_x509_cred is used when talking to the server (acting as
  97      * a TSL client). */
  98     gnutls_certificate_credentials_t client_x509_cred, server_x509_cred;
  99
 100     gnutls_session_t client_session, server_session;
 101     /* initialize_tls_session_*() called? - used for goto out */
 102     int client_session_init, server_session_init;
 103     /* gnutls_handshake() called? - used for goto out */
 104     int client_session_started, server_session_started;
 105     /* Validation failed? If yes we need to send the special "invalid"
 106      * certificate. */
 107     int validation_failed;
 108
 109     LOG(LOG_DEBUG, "new connection");
 110
 111     server_socket = -1;
 112     client_fd = NULL;
 113     server_fd = NULL;
 114     client_session_init = 0;
 115     server_session_init = 0;
 116     client_session_started = 0;
 117     server_session_started = 0;
 118     validation_failed = 0;
 119
 120     client_fd = fdopen(client_socket, "a+");
 121     if (NULL == client_fd) {
 122         LOG_PERROR(LOG_WARNING, "fdopen(): client failed");
 123         goto out;
 124     }
 125
 126     /* Read request line (CONNECT ..) and headers (they are discarded). */
 127     result = read_http_request(client_fd, buffer, sizeof(buffer));
 128     if (-1 == result) {
 129         /* Read error. */
 130         LOG(LOG_WARNING, "read_http_request(): client read error");
 131         goto out;
 132     } else if (-2 == result) {
 133         /* EOF */
 134         LOG(LOG_WARNING, "read_http_request(): client EOF");
 135         send_bad_request(client_fd);
 136         goto out;
 137     }
 138
 139     if (0 != parse_request(buffer, host, port, &version_minor)) {
 140         LOG(LOG_WARNING, "bad request: %s", buffer);
 141         send_bad_request(client_fd);
 142         goto out;
 143     }
 144
 145     LOG(LOG_DEBUG, "target: %s:%s (HTTP 1.%d)", host, port, version_minor);
 146
 147     /* Connect to proxy server or directly to server. */
 148     if (NULL != global_proxy_host && NULL != global_proxy_port) {
 149         LOG(LOG_DEBUG, "connecting to %s:%s", global_proxy_host,
 150                                               global_proxy_port);
 151         server_socket = connect_to_host(global_proxy_host, global_proxy_port);
 152     } else {
 153         LOG(LOG_DEBUG, "connecting to %s:%s", host, port);
 154         server_socket = connect_to_host(host, port);
 155     }
 156
 157     if (-1 == server_socket) {
 158         LOG(LOG_WARNING, "failed to connect to server");
 159         send_forwarding_failure(client_fd);
 160         goto out;
 161     }
 162     server_fd = fdopen(server_socket, "a+");
 163     if (NULL == server_fd) {
 164         LOG_PERROR(LOG_WARNING, "fdopen(): server failed");
 165         send_forwarding_failure(client_fd);
 166         goto out;
 167     }
 168
 169     /* Connect to proxy if requested (command line option). */
 170     if (NULL != global_proxy_host && NULL != global_proxy_port) {
 171         fprintf(server_fd, "CONNECT %s:%s HTTP/1.0\r\n", host, port);
 172         fprintf(server_fd, "\r\n");
 173
 174         /* Read response line from proxy server. */
 175         result = read_http_request(server_fd, buffer, sizeof(buffer));
 176         if (-1 == result) {
 177             /* Read error. */
 178             LOG(LOG_WARNING, "read_http_request(): proxy read error");
 179             send_forwarding_failure(client_fd);
 180             goto out;
 181         } else if (-2 == result) {
 182             /* EOF */
 183             LOG(LOG_WARNING, "read_http_request(): proxy EOF");
 184             send_forwarding_failure(client_fd);
 185             goto out;
 186         }
 187
 188         /* Check response of proxy server. */
 189         if (0 != strncmp(buffer, "HTTP/1.0 200", 12)) {
 190             LOG(LOG_WARNING, "bad proxy response: %s", buffer);
 191             send_forwarding_failure(client_fd);
 192             goto out;
 193         }
 194     }
 195
 196     LOG(LOG_DEBUG, "connection to server established");
 197
 198     /* If the -u option is used and we don't know this hostname's server
 199      * certificate then just pass through the connection and let the client
 200      * verify the server certificate. */
 201     if (global_passthrough_unknown) {
 202         char path[TLSPROXY_MAX_PATH_LENGTH];
 203         FILE *file = NULL;
 204
 205         if (-2 == server_certificate_file(&file, host, path, sizeof(path))) {
 206             /* We've established a connection, tell the client. */
 207             fprintf(client_fd, "HTTP/1.0 200 Connection established\r\n");
 208             fprintf(client_fd, "\r\n");
 209             fflush(client_fd);
 210
 211             LOG(LOG_DEBUG, "transferring data");
 212
 213             /* Proxy data between client and server until one side is done
 214              * (EOF or error). */
 215             transfer_data(client_socket, server_socket);
 216
 217             LOG(LOG_DEBUG, "finished transferring data");
 218
 219             goto out;
 220         }
 221         /* server_certificate_file() may have opened the file, close it. */
 222         if (NULL != file) {
 223             fclose(file);
 224         }
 225     }
 226
 227     /* Initialize TLS client credentials to talk to the server. */
 228     result = initialize_tls_session_server(server_socket, &server_session,
 229                                                           &server_x509_cred);
 230     if (0 != result) {
 231         LOG(LOG_WARNING, "initialize_tls_session_server() failed");
 232         send_forwarding_failure(client_fd);
 233         goto out;
 234     }
 235     server_session_init = 1;
 236
 237     LOG(LOG_DEBUG, "starting server TLS handshake");
 238
 239     /* Try to establish TLS handshake between us and server. */
 240     result = gnutls_handshake(server_session);
 241     if (GNUTLS_E_SUCCESS != result) {
 242         LOG(LOG_WARNING, "server TLS handshake failed: %s",
 243                          gnutls_strerror(result));
 244         send_forwarding_failure(client_fd);
 245         goto out;
 246     }
 247     server_session_started = 1;
 248
 249     LOG(LOG_DEBUG, "server TLS handshake finished");
 250
 251     /* Make sure the server certificate is valid and known. */
 252     if (0 != verify_tls_connection(server_session, host)) {
 253         LOG(LOG_ERROR, "server certificate validation failed!");
 254         /* We send the error message over our TLS connection to the client,
 255          * but with an invalid certificate. No data is transfered from/to the
 256          * target server. */
 257         validation_failed = 1;
 258     }
 259
 260     /* Initialize TLS server credentials to talk to the client. */
 261     result = initialize_tls_session_client(client_socket,
 262                                            /* use a special host if the server
 263                                             * certificate was invalid */
 264                                            (validation_failed) ? "invalid"
 265                                                                : host,
 266                                            &client_session,
 267                                            &client_x509_cred);
 268     if (0 != result) {
 269         LOG(LOG_WARNING, "initialize_tls_session_client() failed");
 270         send_forwarding_failure(client_fd);
 271         goto out;
 272     }
 273     client_session_init = 1;
 274
 275     /* We've established a connection, tell the client. */
 276     fprintf(client_fd, "HTTP/1.0 200 Connection established\r\n");
 277     fprintf(client_fd, "\r\n");
 278     fflush(client_fd);
 279
 280     LOG(LOG_DEBUG, "starting client TLS handshake");
 281
 282     /* Try to establish TLS handshake between client and us. */
 283     result = gnutls_handshake(client_session);
 284     if (GNUTLS_E_SUCCESS != result) {
 285         LOG(LOG_WARNING, "client TLS handshake failed: %s",
 286                          gnutls_strerror(result));
 287         send_forwarding_failure(client_fd);
 288         goto out;
 289     }
 290     client_session_started = 1;
 291
 292     LOG(LOG_DEBUG, "client TLS handshake finished");
 293
 294     /* Tell the client that the verification failed. Shouldn't be necessary as
 295      * the client should terminate the connection because he received the
 296      * invalid certificate but better be sure. */
 297     if (validation_failed) {
 298         tls_send_invalid_cert_message(client_session);
 299         goto out;
 300     }
 301
 302     LOG(LOG_DEBUG, "transferring TLS data");
 303
 304     /* Proxy data between client and server until one side is done (EOF or
 305      * error). */
 306     transfer_data_tls(client_socket, server_socket,
 307                       client_session, server_session);
 308
 309     LOG(LOG_DEBUG, "finished transferring TLS data");
 310
 311 out:
 312     /* Close TLS sessions if necessary. Use GNUTLS_SHUT_RDWR so the data is
 313      * reliable transmitted. */
 314     if (0 != server_session_started) {
 315         gnutls_bye(server_session, GNUTLS_SHUT_RDWR);
 316     }
 317     if (0 != client_session_started) {
 318         gnutls_bye(client_session, GNUTLS_SHUT_RDWR);
 319     }
 320     if (0 != server_session_init) {
 321         gnutls_deinit(server_session);
 322         gnutls_certificate_free_credentials(server_x509_cred);
 323     }
 324     if (0 != client_session_init) {
 325         gnutls_deinit(client_session);
 326         gnutls_certificate_free_cas(client_x509_cred);
 327         gnutls_certificate_free_keys(client_x509_cred);
 328         gnutls_certificate_free_credentials(client_x509_cred);
 329     }
 330
 331     /* Close connection to server/proxy. */
 332     if (NULL != server_fd) {
 333         fclose(server_fd);
 334     } else if (-1 != server_socket) {
 335         close(server_socket);
 336     }
 337     LOG(LOG_DEBUG, "connection to server closed");
 338     /* Close connection to client. */
 339     if (NULL != client_fd) {
 340         fclose(client_fd);
 341     } else {
 342         close(client_socket);
 343     }
 344     LOG(LOG_DEBUG, "connection to client closed");
 345
 346     LOG(LOG_DEBUG, "connection finished");
 347 }
 348
 349
 350 static int initialize_tls_session_client(int peer_socket,
 351         const char *hostname,
 352         gnutls_session_t *session,
 353         gnutls_certificate_credentials_t *x509_cred) {
 354     int result;
 355     int use_invalid_cert;
 356     char path[TLSPROXY_MAX_PATH_LENGTH];
 357
 358     /* The "invalid" hostname is special. If it's used we send an invalid
 359      * certificate to let the client know something is wrong. */
 360     use_invalid_cert = (0 == strcmp(hostname, "invalid"));
 361
 362     if (0 != proxy_certificate_path(hostname, path, sizeof(path))) {
 363         LOG(LOG_ERROR,
 364             "initialize_tls_session_client(): \
 365 failed to get proxy certificate path");
 366         return -1;
 367     }
 368
 369     result = gnutls_certificate_allocate_credentials(x509_cred);
 370     if (GNUTLS_E_SUCCESS != result) {
 371         LOG(LOG_ERROR,
 372             "initialize_tls_session_client(): \
 373 gnutls_certificate_allocate_credentials(): %s",
 374             gnutls_strerror(result));
 375         return -1;
 376     }
 377
 378     /* Load proxy CA file, this CA "list" is send to the client. */
 379     if (!use_invalid_cert) {
 380         result = gnutls_certificate_set_x509_trust_file(*x509_cred,
 381                                                         PROXY_CA_FILE,
 382                                                         GNUTLS_X509_FMT_PEM);
 383         if (0 >= result) {
 384             LOG(LOG_ERROR,
 385                 "initialize_tls_session_client(): can't read CA file: '%s'",
 386                 PROXY_CA_FILE);
 387             gnutls_certificate_free_credentials(*x509_cred);
 388             return -1;
 389         }
 390     }
 391     /* If the invalid hostname was specified do nothing, we use a self-signed
 392      * certificate in this case. */
 393
 394     /* And certificate for this website and proxy's private key. */
 395     if (!use_invalid_cert) {
 396         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 397                                                       path, PROXY_KEY_FILE,
 398                                                       GNUTLS_X509_FMT_PEM);
 399     /* If the invalid hostname was specified load our special "invalid"
 400      * certificate. */
 401     } else {
 402         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 403                                                       PROXY_INVALID_CERT_FILE,
 404                                                       PROXY_KEY_FILE,
 405                                                       GNUTLS_X509_FMT_PEM);
 406     }
 407     if (GNUTLS_E_SUCCESS != result) {
 408         LOG(LOG_ERROR,
 409             "initialize_tls_session_client(): \
 410 can't read server certificate ('%s') or key file ('%s'): %s",
 411             path, PROXY_KEY_FILE, gnutls_strerror(result));
 412         gnutls_certificate_free_credentials(*x509_cred);
 413         /* Could be a missing certificate. */
 414         return -2;
 415     }
 416
 417     gnutls_certificate_set_dh_params(*x509_cred, global_tls_dh_params);
 418
 419     result = gnutls_init(session, GNUTLS_SERVER);
 420     if (GNUTLS_E_SUCCESS != result) {
 421         LOG(LOG_ERROR,
 422             "initialize_tls_session_client(): gnutls_init(): %s",
 423             gnutls_strerror(result));
 424         gnutls_certificate_free_credentials(*x509_cred);
 425         return -1;
 426     }
 427     result = gnutls_priority_set(*session, global_tls_priority_cache);
 428     if (GNUTLS_E_SUCCESS != result) {
 429         LOG(LOG_ERROR,
 430             "initialize_tls_session_client(): gnutls_priority_set(): %s",
 431             gnutls_strerror(result));
 432         gnutls_deinit(*session);
 433         gnutls_certificate_free_credentials(*x509_cred);
 434         return -1;
 435     }
 436     result = gnutls_credentials_set(*session,
 437                                     GNUTLS_CRD_CERTIFICATE, *x509_cred);
 438     if (GNUTLS_E_SUCCESS != result) {
 439         LOG(LOG_ERROR,
 440             "initialize_tls_session_client(): gnutls_credentials_set(): %s",
 441             gnutls_strerror(result));
 442         gnutls_deinit(*session);
 443         gnutls_certificate_free_credentials(*x509_cred);
 444         return -1;
 445     }
 446
 447     gnutls_transport_set_ptr(*session, (gnutls_transport_ptr_t)peer_socket);
 448
 449     return 0;
 450 }
 451 static int initialize_tls_session_server(int peer_socket,
 452         gnutls_session_t *session,
 453         gnutls_certificate_credentials_t *x509_cred) {
 454     int result;
 455
 456     result = gnutls_certificate_allocate_credentials(x509_cred);
 457     if (GNUTLS_E_SUCCESS != result) {
 458         LOG(LOG_ERROR,
 459             "initialize_tls_session_server(): \
 460 gnutls_certificate_allocate_credentials(): %s",
 461             gnutls_strerror(result));
 462         return -1;
 463     }
 464
 465     result = gnutls_init(session, GNUTLS_CLIENT);
 466     if (GNUTLS_E_SUCCESS != result) {
 467         LOG(LOG_ERROR,
 468             "initialize_tls_session_server(): gnutls_init(): %s",
 469             gnutls_strerror(result));
 470         gnutls_certificate_free_credentials(*x509_cred);
 471         return -1;
 472     }
 473     gnutls_priority_set(*session, global_tls_priority_cache);
 474     if (GNUTLS_E_SUCCESS != result) {
 475         LOG(LOG_ERROR,
 476             "initialize_tls_session_server(): gnutls_priority_set(): %s",
 477             gnutls_strerror(result));
 478         gnutls_deinit(*session);
 479         gnutls_certificate_free_credentials(*x509_cred);
 480         return -1;
 481     }
 482     result = gnutls_credentials_set(*session,
 483                                     GNUTLS_CRD_CERTIFICATE, *x509_cred);
 484     if (GNUTLS_E_SUCCESS != result) {
 485         LOG(LOG_ERROR,
 486             "initialize_tls_session_server(): gnutls_credentials_set(): %s",
 487             gnutls_strerror(result));
 488         gnutls_deinit(*session);
 489         gnutls_certificate_free_credentials(*x509_cred);
 490         return -1;
 491     }
 492
 493     gnutls_transport_set_ptr(*session, (gnutls_transport_ptr_t)peer_socket);
 494
 495     return 0;
 496 }
 497
 498
 499 /* Read HTTP request line and headers (ignored).
 500  *
 501  * On success 0 is returned, -1 on client error, -2 on unexpected EOF.
 502  */
 503 static int read_http_request(FILE *client_fd, char *request, size_t length) {
 504     char buffer[MAX_REQUEST_LINE];
 505
 506     if (NULL == fgets(request, (int)length, client_fd)) {
 507         if (ferror(client_fd)) {
 508             LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
 509             return -1;
 510         }
 511
 512         return -2;
 513     }
 514
 515     while (NULL != fgets(buffer, sizeof(buffer), client_fd)) {
 516         /* End of header. */
 517         if (0 == strcmp(buffer, "\n") || 0 == strcmp(buffer, "\r\n")) {
 518             break;
 519         }
 520     }
 521     if (ferror(client_fd)) {
 522         LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
 523         return -1;
 524     }
 525
 526     return 0;
 527 }
 528
 529 static void send_bad_request(FILE *client_fd) {
 530 #define RESPONSE_ERROR "400 Bad Request"
 531 #define RESPONSE_MSG   "Your browser sent an invalid request."
 532     fprintf(client_fd, HTTP_RESPONSE_FORMAT,
 533                        RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 534                        RESPONSE_MSG);
 535 #undef RESPONSE_ERROR
 536 #undef RESPONSE_MSG
 537 }
 538 static void send_forwarding_failure(FILE *client_fd) {
 539 #define RESPONSE_ERROR "503 Forwarding failure"
 540 #define RESPONSE_MSG   "Failed to connect to server, check logs."
 541     fprintf(client_fd, HTTP_RESPONSE_FORMAT,
 542                        RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 543                        RESPONSE_MSG);
 544 #undef RESPONSE_ERROR
 545 #undef RESPONSE_MSG
 546 }
 547 static void tls_send_invalid_cert_message(gnutls_session_t session) {
 548 #define RESPONSE_ERROR "500 Internal Server Error"
 549 #define RESPONSE_MSG   "Server certificate validation failed, check logs."
 550
 551     int result;
 552     char buffer[sizeof(HTTP_RESPONSE_FORMAT) - 1 /* '\0' */
 553                                              - 4 * 2 /* four %s */
 554                 + (sizeof(RESPONSE_ERROR) - 1 /* '\0' */) * 3
 555                 + sizeof(RESPONSE_MSG)    - 1 /* '\0' */
 556                 + 1 /* '\0' */];
 557
 558     result = snprintf(buffer, sizeof(buffer),
 559                       HTTP_RESPONSE_FORMAT,
 560                       RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 561                       RESPONSE_MSG);
 562     if (result < 0) {
 563         LOG_PERROR(LOG_ERROR,
 564                    "tls_send_invalid_cert_message(): snprintf failed");
 565         return;
 566     } else if ((size_t)result >= sizeof(buffer)) {
 567         LOG(LOG_ERROR,
 568             "tls_send_invalid_cert_message(): snprintf buffer too short");
 569         return;
 570     }
 571
 572     gnutls_record_send(session, buffer, sizeof(buffer) - 1);
 573                                         /* don't send trailing '\0' */
 574 #undef RESPONSE_ERROR
 575 #undef RESPONSE_MSG
 576 }
 577
 578
 579 /* Transfer data between client and server sockets until one closes the
 580  * connection. */
 581 static void transfer_data(int client, int server) {
 582     struct pollfd fds[2];
 583     fds[0].fd      = client;
 584     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 585     fds[0].revents = 0;
 586     fds[1].fd      = server;
 587     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 588     fds[1].revents = 0;
 589
 590     for (;;) {
 591         int result = poll(fds, 2, -1 /* no timeout */);
 592         if (result < 0) {
 593             LOG_PERROR(LOG_ERROR, "transfer_data(): poll()");
 594             return;
 595         }
 596
 597         /* Data available from client. */
 598         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 599             if (0 != read_from_write_to(client, server)) {
 600                 /* EOF (or other error) */
 601                 break;
 602             }
 603         }
 604         /* Data available from server. */
 605         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 606             if (0 != read_from_write_to(server, client)) {
 607                 /* EOF (or other error) */
 608                 break;
 609             }
 610         }
 611
 612         /* Client closed connection. */
 613         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 614             break;
 615         }
 616         /* Server closed connection. */
 617         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 618             break;
 619         }
 620     }
 621 }
 622
 623 /* Read available data from socket from and write it to socket to. At maximum
 624  * 4096 bytes are read/written. */
 625 static int read_from_write_to(int from, int to) {
 626     ssize_t size_read;
 627     ssize_t size_written;
 628     char buffer[4096];
 629
 630     LOG(LOG_DEBUG, "read_from_write_to(): %d -> %d", from, to);
 631
 632     size_read = read(from, buffer, sizeof(buffer));
 633     if (0 > size_read) {
 634         LOG_PERROR(LOG_WARNING, "read_from_write_to(): read()");
 635         return -1;
 636     }
 637     /* EOF */
 638     if (0 == size_read) {
 639         return -1;
 640     }
 641
 642     size_written = write(to, buffer, (size_t)size_read);
 643     if (0 > size_written) {
 644         LOG_PERROR(LOG_WARNING, "read_from_write_to(): write()");
 645         return -1;
 646     }
 647     if (size_read != size_written) {
 648         LOG(LOG_ERROR, "read_from_write_to(): only written %ld of %ld bytes!",
 649                        (long int)size_written, (long int)size_read);
 650         return -1;
 651     }
 652
 653     return 0;
 654 }
 655
 656 /* Transfer data between client and server TLS connection until one closes the
 657  * connection. */
 658 static void transfer_data_tls(int client, int server,
 659                               gnutls_session_t client_session,
 660                               gnutls_session_t server_session) {
 661     size_t buffer_size;
 662
 663     struct pollfd fds[2];
 664     fds[0].fd      = client;
 665     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 666     fds[0].revents = 0;
 667     fds[1].fd      = server;
 668     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 669     fds[1].revents = 0;
 670
 671     /* Get maximum possible buffer size. */
 672     buffer_size = gnutls_record_get_max_size(client_session);
 673     if (buffer_size > gnutls_record_get_max_size(server_session)) {
 674         buffer_size = gnutls_record_get_max_size(server_session);
 675     }
 676     LOG(LOG_DEBUG, "transfer_data_tls(): suggested buffer size: %ld",
 677                    (long int)buffer_size);
 678
 679     for (;;) {
 680         int result = poll(fds, 2, -1 /* no timeout */);
 681         if (result < 0) {
 682             LOG_PERROR(LOG_ERROR, "transfer_data(): poll()");
 683             return;
 684         }
 685
 686         /* Data available from client. */
 687         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 688             if (0 != read_from_write_to_tls(client_session, server_session,
 689                                             buffer_size)) {
 690                 /* EOF (or other error) */
 691                 break;
 692             }
 693         }
 694         /* Data available from server. */
 695         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 696             if (0 != read_from_write_to_tls(server_session, client_session,
 697                                             buffer_size)) {
 698                 /* EOF (or other error) */
 699                 break;
 700             }
 701         }
 702
 703         /* Client closed connection. */
 704         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 705             break;
 706         }
 707         /* Server closed connection. */
 708         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 709             break;
 710         }
 711     }
 712 }
 713
 714 /* Read available data from session from and write to session to. */
 715 static int read_from_write_to_tls(gnutls_session_t from,
 716                                   gnutls_session_t to,
 717                                   size_t buffer_size) {
 718     ssize_t size_read;
 719     ssize_t size_written;
 720     char buffer[16384];
 721
 722     if (buffer_size > sizeof(buffer)) {
 723         buffer_size = sizeof(buffer);
 724     }
 725     LOG(LOG_DEBUG, "read_from_write_to_tls(): used buffer size: %ld",
 726                    (long int)buffer_size);
 727
 728     size_read = gnutls_record_recv(from, buffer, buffer_size);
 729     if (0 > size_read) {
 730         LOG(LOG_WARNING, "read_from_write_to_tls(): gnutls_record_recv(): %s",
 731                          gnutls_strerror((int)size_read));
 732         return -1;
 733     }
 734     /* EOF */
 735     if (0 == size_read) {
 736         return -1;
 737     }
 738
 739     size_written = gnutls_record_send(to, buffer, (size_t)size_read);
 740     if (0 > size_written) {
 741         LOG(LOG_WARNING, "read_from_write_to_tls(): gnutls_record_send(): %s",
 742                          gnutls_strerror((int)size_written));
 743         return -1;
 744     }
 745     if (size_read != size_written) {
 746         LOG(LOG_ERROR, "read_from_write_to_tls(): only written %ld of %ld bytes!",
 747                        (long int)size_written, (long int)size_read);
 748         return -1;
 749     }
 750
 751     return 0;
 752 }
 753
 754
 755 static int connect_to_host(const char *hostname, const char *port) {
 756     struct addrinfo gai_hints;
 757     struct addrinfo *gai_result;
 758     int gai_return;
 759
 760     int server_socket;
 761     struct addrinfo *server;
 762
 763     if (NULL == hostname || NULL == port) {
 764         return -1;
 765     }
 766
 767     /* Get IP of hostname server. */
 768     memset(&gai_hints, 0, sizeof(gai_hints));
 769     gai_hints.ai_family   = AF_UNSPEC;
 770     gai_hints.ai_socktype = SOCK_STREAM;
 771     gai_hints.ai_protocol = 0;
 772     gai_hints.ai_flags    = AI_NUMERICSERV /* given port is numeric */
 773                           | AI_ADDRCONFIG  /* supported by this computer */
 774                           | AI_V4MAPPED;   /* support IPv4 through IPv6 */
 775     gai_return = getaddrinfo(hostname, port, &gai_hints, &gai_result);
 776     if (0 != gai_return) {
 777         LOG_PERROR(LOG_WARNING, "connect_to_host(): getaddrinfo()");
 778         return -1;
 779     }
 780
 781     /* Now try to connect to each server returned by getaddrinfo(), use the
 782      * first successful connect. */
 783     for (server = gai_result; NULL != server; server = server->ai_next) {
 784         server_socket = socket(server->ai_family,
 785                                server->ai_socktype,
 786                                server->ai_protocol);
 787         if (-1 == server_socket) {
 788             LOG_PERROR(LOG_DEBUG, "connect_to_host(): socket(), trying next");
 789             continue;
 790         }
 791
 792         if (-1 != connect(server_socket, server->ai_addr,
 793                                          server->ai_addrlen)) {
 794             break;
 795         }
 796         LOG_PERROR(LOG_DEBUG, "connect_to_host(): connect(), trying next");
 797
 798         close(server_socket);
 799     }
 800     /* Make sure we free the result from getaddrinfo(). */
 801     freeaddrinfo(gai_result);
 802
 803     if (NULL == server) {
 804         LOG_PERROR(LOG_WARNING, "connect_to_host(): no server found, abort");
 805         return -1;
 806     }
 807
 808     return server_socket;
 809 }
 810
 811
 812 /* Parse HTTP CONNECT request string and save its parameters.
 813  *
 814  * The following format is expected: "CONNECT host:port HTTP/1.x".
 815  *
 816  * request and host must have the same size! port must be at least 6 bytes
 817  * long (5 + '\0').
 818  */
 819 static int parse_request(const char *request, char *host, char *port,
 820                                               int *version_minor) {
 821     int port_unused; /* just used to verify the port is numeric */
 822     char *position;
 823
 824     /* scanf() doesn't check spaces. */
 825     if (0 != strncmp(request, "CONNECT ", 8)) {
 826         return -1;
 827     }
 828     /* Check request and extract data, "host:port" is not yet separated. */
 829     if (2 != sscanf(request, "CONNECT %s HTTP/1.%d",
 830                              host, version_minor)) {
 831         return -1;
 832     }
 833     /* Make sure ":port" is there. */
 834     if (NULL == (position = strchr(host, ':'))) {
 835         return -1;
 836     }
 837     /* Make sure port is numeric. */
 838     if (1 != sscanf(position + 1, "%d", &port_unused)) {
 839         return -1;
 840     }
 841     /* Store it in *port. */
 842     strncpy(port, position + 1, 5);
 843     port[5] = '\0';
 844     /* And remove port from host. */
 845     *position = '\0';
 846
 847     return 0;
 848 }