src/util/client.c

   1 /*
   2      This file is part of GNUnet.
   3      Copyright (C) 2001-2016 GNUnet e.V.
   4
   5      GNUnet is free software; you can redistribute it and/or modify
   6      it under the terms of the GNU General Public License as published
   7      by the Free Software Foundation; either version 3, or (at your
   8      option) any later version.
   9
  10      GNUnet is distributed in the hope that it will be useful, but
  11      WITHOUT ANY WARRANTY; without even the implied warranty of
  12      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13      General Public License for more details.
  14
  15      You should have received a copy of the GNU General Public License
  16      along with GNUnet; see the file COPYING.  If not, write to the
  17      Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  18      Boston, MA 02110-1301, USA.
  19 */
  20
  21 /**
  22  * @file util/client.c
  23  * @brief code for access to services
  24  * @author Christian Grothoff
  25  *
  26  * Generic TCP code for reliable, record-oriented TCP
  27  * connections between clients and service providers.
  28  */
  29 #include "platform.h"
  30 #include "gnunet_protocols.h"
  31 #include "gnunet_util_lib.h"
  32 #include "gnunet_resolver_service.h"
  33 #include "gnunet_socks.h"
  34
  35
  36 #define LOG(kind,...) GNUNET_log_from (kind, "util",__VA_ARGS__)
  37
  38
  39 /**
  40  * Internal state for a client connected to a GNUnet service.
  41  */
  42 struct ClientState;
  43
  44
  45 /**
  46  * During connect, we try multiple possible IP addresses
  47  * to find out which one might work.
  48  */
  49 struct AddressProbe
  50 {
  51
  52   /**
  53    * This is a linked list.
  54    */
  55   struct AddressProbe *next;
  56
  57   /**
  58    * This is a doubly-linked list.
  59    */
  60   struct AddressProbe *prev;
  61
  62   /**
  63    * The address; do not free (allocated at the end of this struct).
  64    */
  65   const struct sockaddr *addr;
  66
  67   /**
  68    * Underlying OS's socket.
  69    */
  70   struct GNUNET_NETWORK_Handle *sock;
  71
  72   /**
  73    * Connection for which we are probing.
  74    */
  75   struct ClientState *cstate;
  76
  77   /**
  78    * Lenth of addr.
  79    */
  80   socklen_t addrlen;
  81
  82   /**
  83    * Task waiting for the connection to finish connecting.
  84    */
  85   struct GNUNET_SCHEDULER_Task *task;
  86 };
  87
  88
  89 /**
  90  * Internal state for a client connected to a GNUnet service.
  91  */
  92 struct ClientState
  93 {
  94
  95   /**
  96    * The connection handle, NULL if not live
  97    */
  98   struct GNUNET_NETWORK_Handle *sock;
  99
 100   /**
 101    * Handle to a pending DNS lookup request, NULL if DNS is finished.
 102    */
 103   struct GNUNET_RESOLVER_RequestHandle *dns_active;
 104
 105   /**
 106    * Our configuration.
 107    */
 108   const struct GNUNET_CONFIGURATION_Handle *cfg;
 109
 110   /**
 111    * Linked list of sockets we are currently trying out
 112    * (during connect).
 113    */
 114   struct AddressProbe *ap_head;
 115
 116   /**
 117    * Linked list of sockets we are currently trying out
 118    * (during connect).
 119    */
 120   struct AddressProbe *ap_tail;
 121
 122   /**
 123    * Name of the service we interact with.
 124    */
 125   char *service_name;
 126
 127   /**
 128    * Hostname, if any.
 129    */
 130   char *hostname;
 131
 132   /**
 133    * Next message to transmit to the service. NULL for none.
 134    */
 135   const struct GNUNET_MessageHeader *msg;
 136
 137   /**
 138    * Task for trying to connect to the service.
 139    */
 140   struct GNUNET_SCHEDULER_Task *retry_task;
 141
 142   /**
 143    * Task for sending messages to the service.
 144    */
 145   struct GNUNET_SCHEDULER_Task *send_task;
 146
 147   /**
 148    * Task for sending messages to the service.
 149    */
 150   struct GNUNET_SCHEDULER_Task *recv_task;
 151
 152   /**
 153    * Tokenizer for inbound messages.
 154    */
 155   struct GNUNET_MessageStreamTokenizer *mst;
 156
 157   /**
 158    * Message queue under our control.
 159    */
 160   struct GNUNET_MQ_Handle *mq;
 161
 162   /**
 163    * Timeout for receiving a response (absolute time).
 164    */
 165   struct GNUNET_TIME_Absolute receive_timeout;
 166
 167   /**
 168    * Current value for our incremental back-off (for
 169    * connect re-tries).
 170    */
 171   struct GNUNET_TIME_Relative back_off;
 172
 173   /**
 174    * TCP port (0 for disabled).
 175    */
 176   unsigned long long port;
 177
 178   /**
 179    * Offset in the message where we are for transmission.
 180    */
 181   size_t msg_off;
 182
 183   /**
 184    * How often have we tried to connect?
 185    */
 186   unsigned int attempts;
 187
 188   /**
 189    * Are we supposed to die?  #GNUNET_SYSERR if destruction must be
 190    * deferred, #GNUNET_NO by default, #GNUNET_YES if destruction was
 191    * deferred.
 192    */
 193   int in_destroy;
 194
 195 };
 196
 197
 198 /**
 199  * Try to connect to the service.
 200  *
 201  * @param cls the `struct ClientState` to try to connect to the service
 202  */
 203 static void
 204 start_connect (void *cls);
 205
 206
 207 /**
 208  * We've failed for good to establish a connection (timeout or
 209  * no more addresses to try).
 210  *
 211  * @param cstate the connection we tried to establish
 212  */
 213 static void
 214 connect_fail_continuation (struct ClientState *cstate)
 215 {
 216   GNUNET_break (NULL == cstate->ap_head);
 217   GNUNET_break (NULL == cstate->ap_tail);
 218   GNUNET_break (NULL == cstate->dns_active);
 219   GNUNET_break (NULL == cstate->sock);
 220   GNUNET_assert (NULL == cstate->send_task);
 221   GNUNET_assert (NULL == cstate->recv_task);
 222   // GNUNET_assert (NULL == cstate->proxy_handshake);
 223
 224   cstate->back_off = GNUNET_TIME_STD_BACKOFF (cstate->back_off);
 225   LOG (GNUNET_ERROR_TYPE_DEBUG,
 226        "Failed to establish connection to `%s', no further addresses to try, will try again in %s.\n",
 227        cstate->service_name,
 228        GNUNET_STRINGS_relative_time_to_string (cstate->back_off,
 229                                                GNUNET_YES));
 230   cstate->retry_task
 231     = GNUNET_SCHEDULER_add_delayed (cstate->back_off,
 232                                     &start_connect,
 233                                     cstate);
 234 }
 235
 236
 237 /**
 238  * We are ready to send a message to the service.
 239  *
 240  * @param cls the `struct ClientState` with the `msg` to transmit
 241  */
 242 static void
 243 transmit_ready (void *cls)
 244 {
 245   struct ClientState *cstate = cls;
 246   ssize_t ret;
 247   size_t len;
 248   const char *pos;
 249   int notify_in_flight;
 250
 251   cstate->send_task = NULL;
 252   pos = (const char *) cstate->msg;
 253   len = ntohs (cstate->msg->size);
 254   GNUNET_assert (cstate->msg_off < len);
 255  RETRY:
 256   ret = GNUNET_NETWORK_socket_send (cstate->sock,
 257                                     &pos[cstate->msg_off],
 258                                     len - cstate->msg_off);
 259   if (-1 == ret)
 260   {
 261     if (EINTR == errno)
 262       goto RETRY;
 263     GNUNET_MQ_inject_error (cstate->mq,
 264                             GNUNET_MQ_ERROR_WRITE);
 265     return;
 266   }
 267   notify_in_flight = (0 == cstate->msg_off);
 268   cstate->msg_off += ret;
 269   if (cstate->msg_off < len)
 270   {
 271     cstate->send_task
 272       = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
 273                                         cstate->sock,
 274                                         &transmit_ready,
 275                                         cstate);
 276     if (notify_in_flight)
 277       GNUNET_MQ_impl_send_in_flight (cstate->mq);
 278     return;
 279   }
 280   cstate->msg = NULL;
 281   GNUNET_MQ_impl_send_continue (cstate->mq);
 282 }
 283
 284
 285 /**
 286  * We have received a full message, pass to the MQ dispatcher.
 287  * Called by the tokenizer via #receive_ready().
 288  *
 289  * @param cls the `struct ClientState`
 290  * @param msg message we received.
 291  * @return #GNUNET_OK on success, #GNUNET_SYSERR to stop further processing
 292  */
 293 static int
 294 recv_message (void *cls,
 295               const struct GNUNET_MessageHeader *msg)
 296 {
 297   struct ClientState *cstate = cls;
 298
 299   if (GNUNET_YES == cstate->in_destroy)
 300     return GNUNET_SYSERR;
 301   GNUNET_MQ_inject_message (cstate->mq,
 302                             msg);
 303   if (GNUNET_YES == cstate->in_destroy)
 304     return GNUNET_SYSERR;
 305   return GNUNET_OK;
 306 }
 307
 308
 309 /**
 310  * Cancel all remaining connect attempts
 311  *
 312  * @param cstate handle of the client state to process
 313  */
 314 static void
 315 cancel_aps (struct ClientState *cstate)
 316 {
 317   struct AddressProbe *pos;
 318
 319   while (NULL != (pos = cstate->ap_head))
 320   {
 321     GNUNET_break (GNUNET_OK ==
 322                   GNUNET_NETWORK_socket_close (pos->sock));
 323     GNUNET_SCHEDULER_cancel (pos->task);
 324     GNUNET_CONTAINER_DLL_remove (cstate->ap_head,
 325                                  cstate->ap_tail,
 326                                  pos);
 327     GNUNET_free (pos);
 328   }
 329 }
 330
 331
 332 /**
 333  * Implement the destruction of a message queue.  Implementations must
 334  * not free @a mq, but should take care of @a impl_state.
 335  *
 336  * @param mq the message queue to destroy
 337  * @param impl_state our `struct ClientState`
 338  */
 339 static void
 340 connection_client_destroy_impl (struct GNUNET_MQ_Handle *mq,
 341                                 void *impl_state)
 342 {
 343   struct ClientState *cstate = impl_state;
 344
 345   if (GNUNET_SYSERR == cstate->in_destroy)
 346   {
 347     /* defer destruction */
 348     cstate->in_destroy = GNUNET_YES;
 349     cstate->mq = NULL;
 350     return;
 351   }
 352   if (NULL != cstate->dns_active)
 353     GNUNET_RESOLVER_request_cancel (cstate->dns_active);
 354   if (NULL != cstate->send_task)
 355     GNUNET_SCHEDULER_cancel (cstate->send_task);
 356   if (NULL != cstate->recv_task)
 357     GNUNET_SCHEDULER_cancel (cstate->recv_task);
 358   if (NULL != cstate->retry_task)
 359     GNUNET_SCHEDULER_cancel (cstate->retry_task);
 360   if (NULL != cstate->sock)
 361     GNUNET_NETWORK_socket_close (cstate->sock);
 362   cancel_aps (cstate);
 363   GNUNET_free (cstate->service_name);
 364   GNUNET_free_non_null (cstate->hostname);
 365   GNUNET_MST_destroy (cstate->mst);
 366   GNUNET_free (cstate);
 367 }
 368
 369
 370 /**
 371  * This function is called once we have data ready to read.
 372  *
 373  * @param cls `struct ClientState` with connection to read from
 374  */
 375 static void
 376 receive_ready (void *cls)
 377 {
 378   struct ClientState *cstate = cls;
 379   int ret;
 380
 381   cstate->recv_task = NULL;
 382   cstate->in_destroy = GNUNET_SYSERR;
 383   ret = GNUNET_MST_read (cstate->mst,
 384                          cstate->sock,
 385                          GNUNET_NO,
 386                          GNUNET_NO);
 387   if (GNUNET_SYSERR == ret)
 388   {
 389     if (NULL != cstate->mq)
 390       GNUNET_MQ_inject_error (cstate->mq,
 391                               GNUNET_MQ_ERROR_READ);
 392     if (GNUNET_YES == cstate->in_destroy)
 393       connection_client_destroy_impl (cstate->mq,
 394                                       cstate);
 395     return;
 396   }
 397   if (GNUNET_YES == cstate->in_destroy)
 398   {
 399     connection_client_destroy_impl (cstate->mq,
 400                                     cstate);
 401     return;
 402   }
 403   cstate->in_destroy = GNUNET_NO;
 404   cstate->recv_task
 405     = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
 406                                      cstate->sock,
 407                                      &receive_ready,
 408                                      cstate);
 409 }
 410
 411
 412 /**
 413  * We've succeeded in establishing a connection.
 414  *
 415  * @param cstate the connection we tried to establish
 416  */
 417 static void
 418 connect_success_continuation (struct ClientState *cstate)
 419 {
 420   GNUNET_assert (NULL == cstate->recv_task);
 421   cstate->recv_task
 422     = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
 423                                      cstate->sock,
 424                                      &receive_ready,
 425                                      cstate);
 426   if (NULL != cstate->msg)
 427   {
 428     GNUNET_assert (NULL == cstate->send_task);
 429     cstate->send_task
 430       = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
 431                                         cstate->sock,
 432                                         &transmit_ready,
 433                                         cstate);
 434   }
 435 }
 436
 437
 438 /**
 439  * Try connecting to the server using UNIX domain sockets.
 440  *
 441  * @param service_name name of service to connect to
 442  * @param cfg configuration to use
 443  * @return NULL on error, socket connected to UNIX otherwise
 444  */
 445 static struct GNUNET_NETWORK_Handle *
 446 try_unixpath (const char *service_name,
 447               const struct GNUNET_CONFIGURATION_Handle *cfg)
 448 {
 449 #if AF_UNIX
 450   struct GNUNET_NETWORK_Handle *sock;
 451   char *unixpath;
 452   struct sockaddr_un s_un;
 453
 454   unixpath = NULL;
 455   if ((GNUNET_OK ==
 456        GNUNET_CONFIGURATION_get_value_filename (cfg,
 457                                                 service_name,
 458                                                 "UNIXPATH",
 459                                                 &unixpath)) &&
 460       (0 < strlen (unixpath)))
 461   {
 462     /* We have a non-NULL unixpath, need to validate it */
 463     if (strlen (unixpath) >= sizeof (s_un.sun_path))
 464     {
 465       LOG (GNUNET_ERROR_TYPE_WARNING,
 466            _("UNIXPATH `%s' too long, maximum length is %llu\n"),
 467            unixpath,
 468            (unsigned long long) sizeof (s_un.sun_path));
 469       unixpath = GNUNET_NETWORK_shorten_unixpath (unixpath);
 470       LOG (GNUNET_ERROR_TYPE_INFO,
 471            _("Using `%s' instead\n"),
 472            unixpath);
 473       if (NULL == unixpath)
 474         return NULL;
 475     }
 476     memset (&s_un,
 477             0,
 478             sizeof (s_un));
 479     s_un.sun_family = AF_UNIX;
 480     strncpy (s_un.sun_path,
 481              unixpath,
 482              sizeof (s_un.sun_path) - 1);
 483 #ifdef LINUX
 484     {
 485       int abstract;
 486
 487       abstract = GNUNET_CONFIGURATION_get_value_yesno (cfg,
 488                                                        "TESTING",
 489                                                        "USE_ABSTRACT_SOCKETS");
 490       if (GNUNET_YES == abstract)
 491         s_un.sun_path[0] = '\0';
 492     }
 493 #endif
 494 #if HAVE_SOCKADDR_IN_SIN_LEN
 495     un.sun_len = (u_char) sizeof (struct sockaddr_un);
 496 #endif
 497     sock = GNUNET_NETWORK_socket_create (AF_UNIX,
 498                                          SOCK_STREAM,
 499                                          0);
 500     if ( (NULL != sock) &&
 501          ( (GNUNET_OK ==
 502             GNUNET_NETWORK_socket_connect (sock,
 503                                            (struct sockaddr *) &s_un,
 504                                            sizeof (s_un))) ||
 505            (EINPROGRESS == errno) ) )
 506     {
 507       LOG (GNUNET_ERROR_TYPE_DEBUG,
 508            "Successfully connected to unixpath `%s'!\n",
 509            unixpath);
 510       GNUNET_free (unixpath);
 511       return sock;
 512     }
 513   }
 514   GNUNET_free_non_null (unixpath);
 515 #endif
 516   return NULL;
 517 }
 518
 519
 520 /**
 521  * Scheduler let us know that we're either ready to write on the
 522  * socket OR connect timed out.  Do the right thing.
 523  *
 524  * @param cls the `struct AddressProbe *` with the address that we are probing
 525  */
 526 static void
 527 connect_probe_continuation (void *cls)
 528 {
 529   struct AddressProbe *ap = cls;
 530   struct ClientState *cstate = ap->cstate;
 531   const struct GNUNET_SCHEDULER_TaskContext *tc;
 532   int error;
 533   socklen_t len;
 534
 535   ap->task = NULL;
 536   GNUNET_assert (NULL != ap->sock);
 537   GNUNET_CONTAINER_DLL_remove (cstate->ap_head,
 538                                cstate->ap_tail,
 539                                ap);
 540   len = sizeof (error);
 541   error = 0;
 542   tc = GNUNET_SCHEDULER_get_task_context ();
 543   if ( (0 == (tc->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) ||
 544        (GNUNET_OK !=
 545         GNUNET_NETWORK_socket_getsockopt (ap->sock,
 546                                           SOL_SOCKET,
 547                                           SO_ERROR,
 548                                           &error,
 549                                           &len)) ||
 550        (0 != error) )
 551   {
 552     GNUNET_break (GNUNET_OK ==
 553                   GNUNET_NETWORK_socket_close (ap->sock));
 554     GNUNET_free (ap);
 555     if ( (NULL == cstate->ap_head) &&
 556          //      (NULL == cstate->proxy_handshake) &&
 557          (NULL == cstate->dns_active) )
 558       connect_fail_continuation (cstate);
 559     return;
 560   }
 561   LOG (GNUNET_ERROR_TYPE_DEBUG,
 562        "Connection to `%s' succeeded!\n",
 563        cstate->service_name);
 564   /* trigger jobs that waited for the connection */
 565   GNUNET_assert (NULL == cstate->sock);
 566   cstate->sock = ap->sock;
 567   GNUNET_free (ap);
 568   cancel_aps (cstate);
 569   connect_success_continuation (cstate);
 570 }
 571
 572
 573 /**
 574  * Try to establish a connection given the specified address.
 575  * This function is called by the resolver once we have a DNS reply.
 576  *
 577  * @param cls our `struct ClientState *`
 578  * @param addr address to try, NULL for "last call"
 579  * @param addrlen length of @a addr
 580  */
 581 static void
 582 try_connect_using_address (void *cls,
 583                            const struct sockaddr *addr,
 584                            socklen_t addrlen)
 585 {
 586   struct ClientState *cstate = cls;
 587   struct AddressProbe *ap;
 588
 589   if (NULL == addr)
 590   {
 591     cstate->dns_active = NULL;
 592     if ( (NULL == cstate->ap_head) &&
 593          //  (NULL == cstate->proxy_handshake) &&
 594          (NULL == cstate->sock) )
 595       connect_fail_continuation (cstate);
 596     return;
 597   }
 598   if (NULL != cstate->sock)
 599     return;                     /* already connected */
 600   /* try to connect */
 601   LOG (GNUNET_ERROR_TYPE_DEBUG,
 602        "Trying to connect using address `%s:%u'\n",
 603        GNUNET_a2s (addr,
 604                    addrlen),
 605        cstate->port);
 606   ap = GNUNET_malloc (sizeof (struct AddressProbe) + addrlen);
 607   ap->addr = (const struct sockaddr *) &ap[1];
 608   GNUNET_memcpy (&ap[1],
 609                  addr,
 610                  addrlen);
 611   ap->addrlen = addrlen;
 612   ap->cstate = cstate;
 613
 614   switch (ap->addr->sa_family)
 615   {
 616   case AF_INET:
 617     ((struct sockaddr_in *) ap->addr)->sin_port = htons (cstate->port);
 618     break;
 619   case AF_INET6:
 620     ((struct sockaddr_in6 *) ap->addr)->sin6_port = htons (cstate->port);
 621     break;
 622   default:
 623     GNUNET_break (0);
 624     GNUNET_free (ap);
 625     return;                     /* not supported by us */
 626   }
 627   ap->sock = GNUNET_NETWORK_socket_create (ap->addr->sa_family,
 628                                            SOCK_STREAM,
 629                                            0);
 630   if (NULL == ap->sock)
 631   {
 632     GNUNET_free (ap);
 633     return;                     /* not supported by OS */
 634   }
 635   if ( (GNUNET_OK !=
 636         GNUNET_NETWORK_socket_connect (ap->sock,
 637                                        ap->addr,
 638                                        ap->addrlen)) &&
 639        (EINPROGRESS != errno) )
 640   {
 641     /* maybe refused / unsupported address, try next */
 642     GNUNET_log_strerror (GNUNET_ERROR_TYPE_INFO,
 643                          "connect");
 644     GNUNET_break (GNUNET_OK ==
 645                   GNUNET_NETWORK_socket_close (ap->sock));
 646     GNUNET_free (ap);
 647     return;
 648   }
 649   GNUNET_CONTAINER_DLL_insert (cstate->ap_head,
 650                                cstate->ap_tail,
 651                                ap);
 652   ap->task = GNUNET_SCHEDULER_add_write_net (GNUNET_CONNECTION_CONNECT_RETRY_TIMEOUT,
 653                                              ap->sock,
 654                                              &connect_probe_continuation,
 655                                              ap);
 656 }
 657
 658
 659 /**
 660  * Test whether the configuration has proper values for connection
 661  * (UNIXPATH || (PORT && HOSTNAME)).
 662  *
 663  * @param service_name name of service to connect to
 664  * @param cfg configuration to use
 665  * @return #GNUNET_OK if the configuration is valid, #GNUNET_SYSERR if not
 666  */
 667 static int
 668 test_service_configuration (const char *service_name,
 669                             const struct GNUNET_CONFIGURATION_Handle *cfg)
 670 {
 671   int ret = GNUNET_SYSERR;
 672   char *hostname = NULL;
 673   unsigned long long port;
 674 #if AF_UNIX
 675   char *unixpath = NULL;
 676
 677   if ((GNUNET_OK ==
 678        GNUNET_CONFIGURATION_get_value_filename (cfg,
 679                                                 service_name,
 680                                                 "UNIXPATH",
 681                                                 &unixpath)) &&
 682       (0 < strlen (unixpath)))
 683     ret = GNUNET_OK;
 684   GNUNET_free_non_null (unixpath);
 685 #endif
 686
 687   if ( (GNUNET_YES ==
 688         GNUNET_CONFIGURATION_have_value (cfg,
 689                                          service_name,
 690                                          "PORT")) &&
 691        (GNUNET_OK ==
 692         GNUNET_CONFIGURATION_get_value_number (cfg,
 693                                                service_name,
 694                                                "PORT",
 695                                                &port)) &&
 696        (port <= 65535) &&
 697        (0 != port) &&
 698        (GNUNET_OK ==
 699         GNUNET_CONFIGURATION_get_value_string (cfg,
 700                                                service_name,
 701                                                "HOSTNAME",
 702                                                &hostname)) &&
 703        (0 != strlen (hostname)) )
 704     ret = GNUNET_OK;
 705   GNUNET_free_non_null (hostname);
 706   return ret;
 707 }
 708
 709
 710 /**
 711  * Try to connect to the service.
 712  *
 713  * @param cls the `struct ClientState` to try to connect to the service
 714  */
 715 static void
 716 start_connect (void *cls)
 717 {
 718   struct ClientState *cstate = cls;
 719
 720   cstate->retry_task = NULL;
 721 #if 0
 722   /* Never use a local source if a proxy is configured */
 723   if (GNUNET_YES ==
 724       GNUNET_SOCKS_check_service (cstate->service_name,
 725                                   cstate->cfg))
 726   {
 727     socks_connect (cstate);
 728     return;
 729   }
 730 #endif
 731
 732   if ( (0 == (cstate->attempts++ % 2)) ||
 733        (0 == cstate->port) ||
 734        (NULL == cstate->hostname) )
 735   {
 736     /* on even rounds, try UNIX first, or always
 737        if we do not have a DNS name and TCP port. */
 738     cstate->sock = try_unixpath (cstate->service_name,
 739                                  cstate->cfg);
 740     if (NULL != cstate->sock)
 741     {
 742       connect_success_continuation (cstate);
 743       return;
 744     }
 745   }
 746   if ( (NULL == cstate->hostname) ||
 747        (0 == cstate->port) )
 748   {
 749     /* All options failed. Boo! */
 750     connect_fail_continuation (cstate);
 751     return;
 752   }
 753   cstate->dns_active
 754     = GNUNET_RESOLVER_ip_get (cstate->hostname,
 755                               AF_UNSPEC,
 756                               GNUNET_CONNECTION_CONNECT_RETRY_TIMEOUT,
 757                               &try_connect_using_address,
 758                               cstate);
 759 }
 760
 761
 762 /**
 763  * Implements the transmission functionality of a message queue.
 764  *
 765  * @param mq the message queue
 766  * @param msg the message to send
 767  * @param impl_state our `struct ClientState`
 768  */
 769 static void
 770 connection_client_send_impl (struct GNUNET_MQ_Handle *mq,
 771                              const struct GNUNET_MessageHeader *msg,
 772                              void *impl_state)
 773 {
 774   struct ClientState *cstate = impl_state;
 775
 776   /* only one message at a time allowed */
 777   GNUNET_assert (NULL == cstate->msg);
 778   GNUNET_assert (NULL == cstate->send_task);
 779   cstate->msg = msg;
 780   cstate->msg_off = 0;
 781   if (NULL == cstate->sock)
 782     return; /* still waiting for connection */
 783   cstate->send_task
 784     = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
 785                                       cstate->sock,
 786                                       &transmit_ready,
 787                                       cstate);
 788 }
 789
 790
 791 /**
 792  * Cancel the currently sent message.
 793  *
 794  * @param mq message queue
 795  * @param impl_state our `struct ClientState`
 796  */
 797 static void
 798 connection_client_cancel_impl (struct GNUNET_MQ_Handle *mq,
 799                                void *impl_state)
 800 {
 801   struct ClientState *cstate = impl_state;
 802
 803   GNUNET_assert (NULL != cstate->msg);
 804   GNUNET_assert (0 == cstate->msg_off);
 805   cstate->msg = NULL;
 806   if (NULL != cstate->send_task)
 807   {
 808     GNUNET_SCHEDULER_cancel (cstate->send_task);
 809     cstate->send_task = NULL;
 810   }
 811 }
 812
 813
 814 /**
 815  * Create a message queue to connect to a GNUnet service.
 816  * If handlers are specfied, receive messages from the connection.
 817  *
 818  * @param cfg our configuration
 819  * @param service_name name of the service to connect to
 820  * @param handlers handlers for receiving messages, can be NULL
 821  * @param error_handler error handler
 822  * @param error_handler_cls closure for the @a error_handler
 823  * @return the message queue, NULL on error
 824  */
 825 struct GNUNET_MQ_Handle *
 826 GNUNET_CLIENT_connect (const struct GNUNET_CONFIGURATION_Handle *cfg,
 827                        const char *service_name,
 828                        const struct GNUNET_MQ_MessageHandler *handlers,
 829                        GNUNET_MQ_ErrorHandler error_handler,
 830                        void *error_handler_cls)
 831 {
 832   struct ClientState *cstate;
 833
 834   if (GNUNET_OK !=
 835       test_service_configuration (service_name,
 836                                   cfg))
 837     return NULL;
 838   cstate = GNUNET_new (struct ClientState);
 839   cstate->service_name = GNUNET_strdup (service_name);
 840   cstate->cfg = cfg;
 841   cstate->retry_task = GNUNET_SCHEDULER_add_now (&start_connect,
 842                                                  cstate);
 843   cstate->mst = GNUNET_MST_create (&recv_message,
 844                                    cstate);
 845   if (GNUNET_YES ==
 846       GNUNET_CONFIGURATION_have_value (cfg,
 847                                        service_name,
 848                                        "PORT"))
 849   {
 850     if (! ( (GNUNET_OK !=
 851              GNUNET_CONFIGURATION_get_value_number (cfg,
 852                                                     service_name,
 853                                                     "PORT",
 854                                                     &cstate->port)) ||
 855             (cstate->port > 65535) ||
 856             (GNUNET_OK !=
 857              GNUNET_CONFIGURATION_get_value_string (cfg,
 858                                                     service_name,
 859                                                     "HOSTNAME",
 860                                                     &cstate->hostname)) ) &&
 861         (0 == strlen (cstate->hostname)) )
 862     {
 863       GNUNET_free (cstate->hostname);
 864       cstate->hostname = NULL;
 865       LOG (GNUNET_ERROR_TYPE_WARNING,
 866            _("Need a non-empty hostname for service `%s'.\n"),
 867            service_name);
 868     }
 869   }
 870   cstate->mq = GNUNET_MQ_queue_for_callbacks (&connection_client_send_impl,
 871                                               &connection_client_destroy_impl,
 872                                               &connection_client_cancel_impl,
 873                                               cstate,
 874                                               handlers,
 875                                               error_handler,
 876                                               error_handler_cls);
 877   return cstate->mq;
 878 }
 879
 880 /* end of client_new.c */