src/connection.c

   1 /*
   2  * Handle connections.
   3  *
   4  * Copyright (C) 2011-2013  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 #include <errno.h>
  25 #include <netdb.h>
  26 #include <poll.h>
  27 #include <unistd.h>
  28
  29
  30 /* Maximum length of a HTTP request line. Longer request lines are aborted
  31  * with an error. The standard doesn't specify a maximum line length but this
  32  * should be a good limit to make processing simpler. As HTTPS is used this
  33  * doesn't limit long GET requests. */
  34 #define MAX_REQUEST_LINE 4096
  35
  36 /* Format string used to send HTTP/1.0 error responses to the client.
  37  *
  38  * %s is used 4 times, first three are the error code (no %n$s!), the last is
  39  * the message. */
  40 #define HTTP_RESPONSE_FORMAT "HTTP/1.0 %s\r\n\
  41 Content-Type: text/html; charset=US-ASCII\r\n\
  42 \r\n\
  43 <!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\">\n\
  44 <html>\n\
  45 <head><title>%s</title></head>\n\
  46 <body>\n\
  47 <h1>%s</h1>\n\
  48 <p>%s</p>\n\
  49 </body>\n\
  50 </html>\n"
  51
  52
  53 static int initialize_tls_session_client(int peer_socket,
  54         const char *hostname,
  55         gnutls_session_t *session,
  56         gnutls_certificate_credentials_t *x509_cred);
  57 static int initialize_tls_session_server(int peer_socket,
  58         gnutls_session_t *session,
  59         gnutls_certificate_credentials_t *x509_cred);
  60
  61 static int read_http_request(FILE *client_fd, char *request, size_t length);
  62 static void send_bad_request(FILE *client_fd);
  63 static void send_forwarding_failure(FILE *client_fd);
  64 static void tls_send_invalid_cert_message(gnutls_session_t session);
  65
  66 static void transfer_data(int client, int server);
  67 static int read_from_write_to(int from, int to);
  68 static void transfer_data_tls(int client, int server,
  69                               gnutls_session_t client_session,
  70                               gnutls_session_t server_session);
  71 static int read_from_write_to_tls(gnutls_session_t from, gnutls_session_t to,
  72                                   size_t buffer_size);
  73
  74 static int connect_to_host(const char *hostname, const char *port);
  75
  76 static int parse_request(const char *buffer, char *host, char *port,
  77                                              int *version_minor);
  78
  79
  80 void handle_connection(int client_socket) {
  81     int server_socket;
  82     FILE *client_fd, *server_fd;
  83
  84     char buffer[MAX_REQUEST_LINE];
  85     char host[MAX_REQUEST_LINE];
  86     char port[5 + 1];
  87
  88     int version_minor; /* x in HTTP/1.x */
  89     int result;
  90
  91     /* client_x509_cred is used when talking to the client (acting as a TSL
  92      * server), server_x509_cred is used when talking to the server (acting as
  93      * a TSL client). */
  94     gnutls_certificate_credentials_t client_x509_cred, server_x509_cred;
  95
  96     gnutls_session_t client_session, server_session;
  97     /* initialize_tls_session_*() called? - used for goto out */
  98     int client_session_init, server_session_init;
  99     /* gnutls_handshake() called? - used for goto out */
 100     int client_session_started, server_session_started;
 101     /* Validation failed? If yes we need to send the special "invalid"
 102      * certificate. */
 103     int validation_failed;
 104
 105     LOG(LOG_DEBUG, "new connection");
 106
 107     server_socket = -1;
 108     client_fd = NULL;
 109     server_fd = NULL;
 110     client_session_init = 0;
 111     server_session_init = 0;
 112     client_session_started = 0;
 113     server_session_started = 0;
 114     validation_failed = 0;
 115
 116     client_fd = fdopen(client_socket, "a+");
 117     if (client_fd == NULL) {
 118         LOG_PERROR(LOG_WARNING, "fdopen(): client failed");
 119         goto out;
 120     }
 121
 122     /* Read request line (CONNECT ..) and headers (they are discarded). */
 123     result = read_http_request(client_fd, buffer, sizeof(buffer));
 124     if (result == -1) {
 125         LOG(LOG_WARNING, "read_http_request(): client read error");
 126         goto out;
 127     } else if (result == -2) {
 128         LOG(LOG_WARNING, "read_http_request(): client EOF");
 129         send_bad_request(client_fd);
 130         goto out;
 131     }
 132
 133     if (parse_request(buffer, host, port, &version_minor) != 0) {
 134         LOG(LOG_WARNING, "bad request: %s", buffer);
 135         send_bad_request(client_fd);
 136         goto out;
 137     }
 138
 139     LOG(LOG_DEBUG, "target: %s:%s (HTTP 1.%d)", host, port, version_minor);
 140
 141     /* Connect to proxy server or directly to server. */
 142     if (global_proxy_host != NULL && global_proxy_port != NULL) {
 143         LOG(LOG_DEBUG, "connecting to %s:%s", global_proxy_host,
 144                                               global_proxy_port);
 145         server_socket = connect_to_host(global_proxy_host, global_proxy_port);
 146     } else {
 147         LOG(LOG_DEBUG, "connecting to %s:%s", host, port);
 148         server_socket = connect_to_host(host, port);
 149     }
 150
 151     if (server_socket == -1) {
 152         LOG(LOG_WARNING, "failed to connect to server");
 153         send_forwarding_failure(client_fd);
 154         goto out;
 155     }
 156     server_fd = fdopen(server_socket, "a+");
 157     if (server_fd == NULL) {
 158         LOG_PERROR(LOG_WARNING, "fdopen(): server failed");
 159         send_forwarding_failure(client_fd);
 160         goto out;
 161     }
 162
 163     /* Connect to proxy if requested (command line option). */
 164     if (global_proxy_host != NULL && global_proxy_port != NULL) {
 165         fprintf(server_fd, "CONNECT %s:%s HTTP/1.0\r\n", host, port);
 166         fprintf(server_fd, "\r\n");
 167
 168         /* Read response line from proxy server. */
 169         result = read_http_request(server_fd, buffer, sizeof(buffer));
 170         if (result == -1) {
 171             LOG(LOG_WARNING, "read_http_request(): proxy read error");
 172             send_forwarding_failure(client_fd);
 173             goto out;
 174         } else if (result == -2) {
 175             LOG(LOG_WARNING, "read_http_request(): proxy EOF");
 176             send_forwarding_failure(client_fd);
 177             goto out;
 178         }
 179
 180         /* Check response of proxy server. */
 181         if (strncmp(buffer, "HTTP/1.0 200", 12)) {
 182             LOG(LOG_WARNING, "bad proxy response: %s", buffer);
 183             send_forwarding_failure(client_fd);
 184             goto out;
 185         }
 186     }
 187
 188     LOG(LOG_DEBUG, "connection to server established");
 189
 190     /* If the -u option is used and we don't know this hostname's server
 191      * certificate then just pass through the connection and let the client
 192      * verify the server certificate. */
 193     if (global_passthrough_unknown) {
 194         char path[TLSPROXY_MAX_PATH_LENGTH];
 195         FILE *file = NULL;
 196
 197         if (server_certificate_file(&file, host, path, sizeof(path)) == -2) {
 198             /* We've established a connection, tell the client. */
 199             fprintf(client_fd, "HTTP/1.0 200 Connection established\r\n");
 200             fprintf(client_fd, "\r\n");
 201             fflush(client_fd);
 202
 203             LOG(LOG_DEBUG, "transferring data");
 204
 205             /* Proxy data between client and server until one side is done
 206              * (EOF or error). */
 207             transfer_data(client_socket, server_socket);
 208
 209             LOG(LOG_DEBUG, "finished transferring data");
 210
 211             goto out;
 212         }
 213         /* server_certificate_file() may have opened the file, close it. */
 214         if (file != NULL) {
 215             fclose(file);
 216         }
 217     }
 218
 219     /* Initialize TLS client credentials to talk to the server. */
 220     result = initialize_tls_session_server(server_socket, &server_session,
 221                                                           &server_x509_cred);
 222     if (result != 0) {
 223         LOG(LOG_WARNING, "initialize_tls_session_server() failed");
 224         send_forwarding_failure(client_fd);
 225         goto out;
 226     }
 227     server_session_init = 1;
 228
 229     LOG(LOG_DEBUG, "starting server TLS handshake");
 230
 231     /* Try to establish TLS handshake between us and server. */
 232     result = gnutls_handshake(server_session);
 233     if (result != GNUTLS_E_SUCCESS) {
 234         LOG(LOG_WARNING, "server TLS handshake failed: %s",
 235                          gnutls_strerror(result));
 236         send_forwarding_failure(client_fd);
 237         goto out;
 238     }
 239     server_session_started = 1;
 240
 241     LOG(LOG_DEBUG, "server TLS handshake finished");
 242
 243     /* Make sure the server certificate is valid and known. */
 244     if (verify_tls_connection(server_session, host) != 0) {
 245         LOG(LOG_ERROR, "server certificate validation failed!");
 246         /* We'll send the error message over our TLS connection to the client,
 247          * but with an invalid certificate. No data is transfered from/to the
 248          * target server. */
 249         validation_failed = 1;
 250     }
 251
 252     /* Initialize TLS server credentials to talk to the client. */
 253     result = initialize_tls_session_client(client_socket,
 254                                            /* use a special host if the server
 255                                             * certificate was invalid */
 256                                            (validation_failed) ? "invalid"
 257                                                                : host,
 258                                            &client_session,
 259                                            &client_x509_cred);
 260     if (result != 0) {
 261         LOG(LOG_WARNING, "initialize_tls_session_client() failed");
 262         send_forwarding_failure(client_fd);
 263         goto out;
 264     }
 265     client_session_init = 1;
 266
 267     /* We've established a connection, tell the client. */
 268     fprintf(client_fd, "HTTP/1.0 200 Connection established\r\n");
 269     fprintf(client_fd, "\r\n");
 270     fflush(client_fd);
 271
 272     LOG(LOG_DEBUG, "starting client TLS handshake");
 273
 274     /* Try to establish TLS handshake between client and us. */
 275     result = gnutls_handshake(client_session);
 276     if (result != GNUTLS_E_SUCCESS) {
 277         LOG(LOG_WARNING, "client TLS handshake failed: %s",
 278                          gnutls_strerror(result));
 279         send_forwarding_failure(client_fd);
 280         goto out;
 281     }
 282     client_session_started = 1;
 283
 284     LOG(LOG_DEBUG, "client TLS handshake finished");
 285
 286     /* Tell the client that the verification failed. Shouldn't be necessary as
 287      * the client should terminate the connection because he received the
 288      * invalid certificate but better be sure. */
 289     if (validation_failed) {
 290         tls_send_invalid_cert_message(client_session);
 291         goto out;
 292     }
 293
 294     LOG(LOG_DEBUG, "transferring TLS data");
 295
 296     /* Proxy data between client and server until one side is done (EOF or
 297      * error). */
 298     transfer_data_tls(client_socket, server_socket,
 299                       client_session, server_session);
 300
 301     LOG(LOG_DEBUG, "finished transferring TLS data");
 302
 303 out:
 304     /* Close TLS sessions if necessary. Use GNUTLS_SHUT_RDWR so the data is
 305      * reliable transmitted. */
 306     if (server_session_started) {
 307         gnutls_bye(server_session, GNUTLS_SHUT_RDWR);
 308     }
 309     if (client_session_started) {
 310         gnutls_bye(client_session, GNUTLS_SHUT_RDWR);
 311     }
 312     if (server_session_init) {
 313         gnutls_deinit(server_session);
 314         gnutls_certificate_free_credentials(server_x509_cred);
 315     }
 316     if (client_session_init) {
 317         gnutls_deinit(client_session);
 318         gnutls_certificate_free_cas(client_x509_cred);
 319         gnutls_certificate_free_keys(client_x509_cred);
 320         gnutls_certificate_free_credentials(client_x509_cred);
 321     }
 322
 323     /* Close connection to server/proxy. */
 324     if (server_fd != NULL) {
 325         fclose(server_fd);
 326     } else if (server_socket != -1) {
 327         close(server_socket);
 328     }
 329     LOG(LOG_DEBUG, "connection to server closed");
 330     /* Close connection to client. */
 331     if (client_fd != NULL) {
 332         fclose(client_fd);
 333     } else {
 334         close(client_socket);
 335     }
 336     LOG(LOG_DEBUG, "connection to client closed");
 337
 338     LOG(LOG_DEBUG, "connection finished");
 339 }
 340
 341
 342 static int initialize_tls_session_client(int peer_socket,
 343         const char *hostname,
 344         gnutls_session_t *session,
 345         gnutls_certificate_credentials_t *x509_cred) {
 346     int result;
 347     int use_invalid_cert;
 348     char path[TLSPROXY_MAX_PATH_LENGTH];
 349
 350     /* The "invalid" hostname is special. If it's used we send an invalid
 351      * certificate to let the client know something is wrong. */
 352     use_invalid_cert = (!strcmp(hostname, "invalid"));
 353
 354     if (proxy_certificate_path(hostname, path, sizeof(path)) != 0) {
 355         LOG(LOG_ERROR,
 356             "initialize_tls_session_client(): \
 357 failed to get proxy certificate path");
 358         return -1;
 359     }
 360
 361     result = gnutls_certificate_allocate_credentials(x509_cred);
 362     if (result != GNUTLS_E_SUCCESS) {
 363         LOG(LOG_ERROR,
 364             "initialize_tls_session_client(): \
 365 gnutls_certificate_allocate_credentials(): %s",
 366             gnutls_strerror(result));
 367         return -1;
 368     }
 369
 370     /* Load proxy CA file, this CA "list" is send to the client. */
 371     if (!use_invalid_cert) {
 372         result = gnutls_certificate_set_x509_trust_file(*x509_cred,
 373                                                         PROXY_CA_FILE,
 374                                                         GNUTLS_X509_FMT_PEM);
 375         if (result <= 0) {
 376             LOG(LOG_ERROR,
 377                 "initialize_tls_session_client(): can't read CA file: '%s'",
 378                 PROXY_CA_FILE);
 379             gnutls_certificate_free_credentials(*x509_cred);
 380             return -1;
 381         }
 382     }
 383     /* If the invalid hostname was specified do nothing, we use a self-signed
 384      * certificate in this case. */
 385
 386     /* And certificate for this website and proxy's private key. */
 387     if (!use_invalid_cert) {
 388         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 389                                                       path, PROXY_KEY_FILE,
 390                                                       GNUTLS_X509_FMT_PEM);
 391     /* If the invalid hostname was specified load our special "invalid"
 392      * certificate. */
 393     } else {
 394         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 395                                                       PROXY_INVALID_CERT_FILE,
 396                                                       PROXY_KEY_FILE,
 397                                                       GNUTLS_X509_FMT_PEM);
 398     }
 399     if (result != GNUTLS_E_SUCCESS) {
 400         LOG(LOG_ERROR,
 401             "initialize_tls_session_client(): \
 402 can't read server certificate ('%s') or key file ('%s'): %s",
 403             path, PROXY_KEY_FILE, gnutls_strerror(result));
 404         gnutls_certificate_free_credentials(*x509_cred);
 405         /* Could be a missing certificate. */
 406         return -2;
 407     }
 408
 409     gnutls_certificate_set_dh_params(*x509_cred, global_tls_dh_params);
 410
 411     result = gnutls_init(session, GNUTLS_SERVER);
 412     if (result != GNUTLS_E_SUCCESS) {
 413         LOG(LOG_ERROR,
 414             "initialize_tls_session_client(): gnutls_init(): %s",
 415             gnutls_strerror(result));
 416         gnutls_certificate_free_credentials(*x509_cred);
 417         return -1;
 418     }
 419     result = gnutls_priority_set(*session, global_tls_priority_cache);
 420     if (result != GNUTLS_E_SUCCESS) {
 421         LOG(LOG_ERROR,
 422             "initialize_tls_session_client(): gnutls_priority_set(): %s",
 423             gnutls_strerror(result));
 424         gnutls_deinit(*session);
 425         gnutls_certificate_free_credentials(*x509_cred);
 426         return -1;
 427     }
 428     result = gnutls_credentials_set(*session,
 429                                     GNUTLS_CRD_CERTIFICATE, *x509_cred);
 430     if (result != GNUTLS_E_SUCCESS) {
 431         LOG(LOG_ERROR,
 432             "initialize_tls_session_client(): gnutls_credentials_set(): %s",
 433             gnutls_strerror(result));
 434         gnutls_deinit(*session);
 435         gnutls_certificate_free_credentials(*x509_cred);
 436         return -1;
 437     }
 438
 439     gnutls_transport_set_ptr(*session, (gnutls_transport_ptr_t)peer_socket);
 440
 441     return 0;
 442 }
 443 static int initialize_tls_session_server(int peer_socket,
 444         gnutls_session_t *session,
 445         gnutls_certificate_credentials_t *x509_cred) {
 446     int result;
 447
 448     result = gnutls_certificate_allocate_credentials(x509_cred);
 449     if (result != GNUTLS_E_SUCCESS) {
 450         LOG(LOG_ERROR,
 451             "initialize_tls_session_server(): \
 452 gnutls_certificate_allocate_credentials(): %s",
 453             gnutls_strerror(result));
 454         return -1;
 455     }
 456
 457     result = gnutls_init(session, GNUTLS_CLIENT);
 458     if (result != GNUTLS_E_SUCCESS) {
 459         LOG(LOG_ERROR,
 460             "initialize_tls_session_server(): gnutls_init(): %s",
 461             gnutls_strerror(result));
 462         gnutls_certificate_free_credentials(*x509_cred);
 463         return -1;
 464     }
 465     result = gnutls_priority_set(*session, global_tls_priority_cache);
 466     if (result != GNUTLS_E_SUCCESS) {
 467         LOG(LOG_ERROR,
 468             "initialize_tls_session_server(): gnutls_priority_set(): %s",
 469             gnutls_strerror(result));
 470         gnutls_deinit(*session);
 471         gnutls_certificate_free_credentials(*x509_cred);
 472         return -1;
 473     }
 474     result = gnutls_credentials_set(*session,
 475                                     GNUTLS_CRD_CERTIFICATE, *x509_cred);
 476     if (result != GNUTLS_E_SUCCESS) {
 477         LOG(LOG_ERROR,
 478             "initialize_tls_session_server(): gnutls_credentials_set(): %s",
 479             gnutls_strerror(result));
 480         gnutls_deinit(*session);
 481         gnutls_certificate_free_credentials(*x509_cred);
 482         return -1;
 483     }
 484
 485     gnutls_transport_set_ptr(*session, (gnutls_transport_ptr_t)peer_socket);
 486
 487     return 0;
 488 }
 489
 490
 491 /* Read HTTP request line and headers (ignored).
 492  *
 493  * On success 0 is returned, -1 on client error, -2 on unexpected EOF.
 494  */
 495 static int read_http_request(FILE *client_fd, char *request, size_t length) {
 496     char buffer[MAX_REQUEST_LINE];
 497
 498     if (fgets(request, (int)length, client_fd) == NULL) {
 499         if (ferror(client_fd)) {
 500             LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
 501             return -1;
 502         }
 503         /* EOF */
 504         return -2;
 505     }
 506
 507     while (fgets(buffer, sizeof(buffer), client_fd) != NULL) {
 508         /* End of header. */
 509         if (!strcmp(buffer, "\n") || !strcmp(buffer, "\r\n")) {
 510             break;
 511         }
 512     }
 513     if (ferror(client_fd)) {
 514         LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
 515         return -1;
 516     }
 517
 518     return 0;
 519 }
 520
 521 static void send_bad_request(FILE *client_fd) {
 522 #define RESPONSE_ERROR "400 Bad Request"
 523 #define RESPONSE_MSG   "Your browser sent an invalid request."
 524     fprintf(client_fd, HTTP_RESPONSE_FORMAT,
 525                        RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 526                        RESPONSE_MSG);
 527 #undef RESPONSE_ERROR
 528 #undef RESPONSE_MSG
 529 }
 530 static void send_forwarding_failure(FILE *client_fd) {
 531 #define RESPONSE_ERROR "503 Forwarding failure"
 532 #define RESPONSE_MSG   "Failed to connect to server, check logs."
 533     fprintf(client_fd, HTTP_RESPONSE_FORMAT,
 534                        RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 535                        RESPONSE_MSG);
 536 #undef RESPONSE_ERROR
 537 #undef RESPONSE_MSG
 538 }
 539 static void tls_send_invalid_cert_message(gnutls_session_t session) {
 540 #define RESPONSE_ERROR "500 Internal Server Error"
 541 #define RESPONSE_MSG   "Server certificate validation failed, check logs."
 542
 543     int result;
 544     char buffer[sizeof(HTTP_RESPONSE_FORMAT) - 1 /* '\0' */
 545                                              - 4 * 2 /* four %s */
 546                 + (sizeof(RESPONSE_ERROR) - 1 /* '\0' */) * 3
 547                 + sizeof(RESPONSE_MSG)    - 1 /* '\0' */
 548                 + 1 /* '\0' */];
 549
 550     result = snprintf(buffer, sizeof(buffer),
 551                       HTTP_RESPONSE_FORMAT,
 552                       RESPONSE_ERROR, RESPONSE_ERROR, RESPONSE_ERROR,
 553                       RESPONSE_MSG);
 554     if (result < 0) {
 555         LOG_PERROR(LOG_ERROR,
 556                    "tls_send_invalid_cert_message(): snprintf failed");
 557         return;
 558     } else if ((size_t)result >= sizeof(buffer)) {
 559         LOG(LOG_ERROR,
 560             "tls_send_invalid_cert_message(): snprintf buffer too short");
 561         return;
 562     }
 563
 564     gnutls_record_send(session, buffer, sizeof(buffer) - 1);
 565                                         /* don't send trailing '\0' */
 566 #undef RESPONSE_ERROR
 567 #undef RESPONSE_MSG
 568 }
 569
 570
 571 /* Transfer data between client and server sockets until one closes the
 572  * connection. */
 573 static void transfer_data(int client, int server) {
 574     struct pollfd fds[2];
 575     fds[0].fd      = client;
 576     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 577     fds[0].revents = 0;
 578     fds[1].fd      = server;
 579     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 580     fds[1].revents = 0;
 581
 582     for (;;) {
 583         int result = poll(fds, 2 /* fd count */, -1 /* no timeout */);
 584         if (result < 0) {
 585             LOG_PERROR(LOG_ERROR, "transfer_data(): poll()");
 586             return;
 587         }
 588
 589         /* Data available from client. */
 590         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 591             if (read_from_write_to(client, server) != 0) {
 592                 /* EOF (or other error) */
 593                 break;
 594             }
 595         }
 596         /* Data available from server. */
 597         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 598             if (read_from_write_to(server, client) != 0) {
 599                 /* EOF (or other error) */
 600                 break;
 601             }
 602         }
 603
 604         /* Client closed connection. */
 605         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 606             break;
 607         }
 608         /* Server closed connection. */
 609         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 610             break;
 611         }
 612     }
 613 }
 614
 615 /* Read available data from socket from and write it to socket to. At maximum
 616  * 4096 bytes are read/written. */
 617 static int read_from_write_to(int from, int to) {
 618     ssize_t size_read;
 619     ssize_t size_written;
 620     char buffer[4096];
 621
 622     LOG(LOG_DEBUG, "read_from_write_to(): %d -> %d", from, to);
 623
 624     size_read = read(from, buffer, sizeof(buffer));
 625     if (size_read < 0) {
 626         LOG_PERROR(LOG_WARNING, "read_from_write_to(): read()");
 627         return -1;
 628     /* EOF */
 629     } else if (size_read == 0) {
 630         return -1;
 631     }
 632
 633     size_written = write(to, buffer, (size_t)size_read);
 634     if (size_written < 0) {
 635         LOG_PERROR(LOG_WARNING, "read_from_write_to(): write()");
 636         return -1;
 637     }
 638     if (size_read != size_written) {
 639         LOG(LOG_ERROR, "read_from_write_to(): only written %ld of %ld bytes!",
 640                        (long int)size_written, (long int)size_read);
 641         return -1;
 642     }
 643
 644     return 0;
 645 }
 646
 647 /* Transfer data between client and server TLS connection until one closes the
 648  * connection. */
 649 static void transfer_data_tls(int client, int server,
 650                               gnutls_session_t client_session,
 651                               gnutls_session_t server_session) {
 652     size_t buffer_size;
 653
 654     struct pollfd fds[2];
 655     fds[0].fd      = client;
 656     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 657     fds[0].revents = 0;
 658     fds[1].fd      = server;
 659     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 660     fds[1].revents = 0;
 661
 662     /* Get maximum possible buffer size. */
 663     buffer_size = gnutls_record_get_max_size(client_session);
 664     if (gnutls_record_get_max_size(server_session) < buffer_size) {
 665         buffer_size = gnutls_record_get_max_size(server_session);
 666     }
 667     LOG(LOG_DEBUG, "transfer_data_tls(): suggested buffer size: %ld",
 668                    (long int)buffer_size);
 669
 670     for (;;) {
 671         int result = poll(fds, 2 /* fd count */, -1 /* no timeout */);
 672         if (result < 0) {
 673             LOG_PERROR(LOG_ERROR, "transfer_data(): poll()");
 674             return;
 675         }
 676
 677         /* Data available from client. */
 678         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 679             if (read_from_write_to_tls(client_session, server_session,
 680                                        buffer_size) != 0) {
 681                 /* EOF (or other error) */
 682                 break;
 683             }
 684         }
 685         /* Data available from server. */
 686         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 687             if (read_from_write_to_tls(server_session, client_session,
 688                                        buffer_size) != 0) {
 689                 /* EOF (or other error) */
 690                 break;
 691             }
 692         }
 693
 694         /* Client closed connection. */
 695         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 696             break;
 697         }
 698         /* Server closed connection. */
 699         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 700             break;
 701         }
 702     }
 703 }
 704
 705 /* Read available data from session from and write to session to. */
 706 static int read_from_write_to_tls(gnutls_session_t from,
 707                                   gnutls_session_t to,
 708                                   size_t buffer_size) {
 709     ssize_t size_read;
 710     ssize_t size_written;
 711     char buffer[16384];
 712
 713     if (buffer_size > sizeof(buffer)) {
 714         buffer_size = sizeof(buffer);
 715     }
 716     LOG(LOG_DEBUG, "read_from_write_to_tls(): used buffer size: %ld",
 717                    (long int)buffer_size);
 718
 719     size_read = gnutls_record_recv(from, buffer, buffer_size);
 720     if (size_read < 0) {
 721         LOG(LOG_WARNING, "read_from_write_to_tls(): gnutls_record_recv(): %s",
 722                          gnutls_strerror((int)size_read));
 723         return -1;
 724     /* EOF */
 725     } else if (size_read == 0) {
 726         return -1;
 727     }
 728
 729     size_written = gnutls_record_send(to, buffer, (size_t)size_read);
 730     if (size_written < 0) {
 731         LOG(LOG_WARNING, "read_from_write_to_tls(): gnutls_record_send(): %s",
 732                          gnutls_strerror((int)size_written));
 733         return -1;
 734     }
 735     if (size_read != size_written) {
 736         LOG(LOG_ERROR, "read_from_write_to_tls(): only written %ld of %ld bytes!",
 737                        (long int)size_written, (long int)size_read);
 738         return -1;
 739     }
 740
 741     return 0;
 742 }
 743
 744
 745 static int connect_to_host(const char *hostname, const char *port) {
 746     struct addrinfo gai_hints;
 747     struct addrinfo *gai_result;
 748     int gai_return;
 749
 750     int server_socket;
 751     struct addrinfo *server;
 752
 753     if (hostname == NULL || port == NULL) {
 754         return -1;
 755     }
 756
 757     /* Get IP of hostname server. */
 758     memset(&gai_hints, 0, sizeof(gai_hints));
 759     gai_hints.ai_family   = AF_UNSPEC;
 760     gai_hints.ai_socktype = SOCK_STREAM;
 761     gai_hints.ai_protocol = 0;
 762     gai_hints.ai_flags    = AI_NUMERICSERV /* given port is numeric */
 763                           | AI_ADDRCONFIG  /* supported by this computer */
 764                           | AI_V4MAPPED;   /* support IPv4 through IPv6 */
 765     gai_return = getaddrinfo(hostname, port, &gai_hints, &gai_result);
 766     if (gai_return != 0) {
 767         if (gai_return == EAI_SYSTEM) {
 768             LOG_PERROR(LOG_WARNING, "connect_to_host(): getaddrinfo()");
 769         } else {
 770             LOG(LOG_WARNING, "connect_to_host(): getaddrinfo(): %s",
 771                              gai_strerror(gai_return));
 772         }
 773         return -1;
 774     }
 775
 776     /* Now try to connect to each server returned by getaddrinfo(), use the
 777      * first successful connect. */
 778     for (server = gai_result; server != NULL; server = server->ai_next) {
 779         server_socket = socket(server->ai_family,
 780                                server->ai_socktype,
 781                                server->ai_protocol);
 782         if (server_socket == -1) {
 783             LOG_PERROR(LOG_DEBUG, "connect_to_host(): socket(), trying next");
 784             continue;
 785         }
 786
 787         if (connect(server_socket, server->ai_addr, server->ai_addrlen) != -1) {
 788             break;
 789         }
 790         LOG_PERROR(LOG_DEBUG, "connect_to_host(): connect(), trying next");
 791
 792         close(server_socket);
 793     }
 794     /* Make sure we free the result from getaddrinfo(). */
 795     freeaddrinfo(gai_result);
 796
 797     if (server == NULL) {
 798         LOG_PERROR(LOG_WARNING, "connect_to_host(): no server found, abort");
 799         return -1;
 800     }
 801
 802     return server_socket;
 803 }
 804
 805
 806 /* Parse HTTP CONNECT request string and save its parameters.
 807  *
 808  * The following format is expected: "CONNECT host:port HTTP/1.x".
 809  *
 810  * request and host must have the same size! port must be at least 6 bytes
 811  * long (5 + '\0').
 812  */
 813 static int parse_request(const char *request, char *host, char *port,
 814                                               int *version_minor) {
 815     int port_unused; /* just used to verify the port is numeric */
 816     char *position;
 817
 818     /* scanf() doesn't check spaces. */
 819     if (strncmp(request, "CONNECT ", 8)) {
 820         return -1;
 821     }
 822     /* Check request and extract data, "host:port" is not yet separated. */
 823     if (sscanf(request, "CONNECT %s HTTP/1.%d", host, version_minor) != 2) {
 824         return -1;
 825     }
 826     /* Make sure ":port" is there. */
 827     if ((position = strchr(host, ':')) == NULL) {
 828         return -1;
 829     }
 830     /* Make sure port is numeric. */
 831     if (sscanf(position + 1, "%d", &port_unused) != 1) {
 832         return -1;
 833     }
 834     /* Store it in *port. */
 835     strncpy(port, position + 1, 5);
 836     port[5] = '\0';
 837     /* And remove port from host. */
 838     *position = '\0';
 839
 840     return 0;
 841 }