Merge branch 'master'
[oweals/gnunet.git] / src / util / client.c
index 7128a2de434fe9e87c79898ebe63dd65c99ff7ad..163ae6eb9f522c6e4fbbf35d5935cc13f7b03643 100644 (file)
@@ -1,6 +1,6 @@
 /*
      This file is part of GNUnet.
-     (C) 2001-2013 Christian Grothoff (and other contributing authors)
+     Copyright (C) 2001-2016 GNUnet e.V.
 
      GNUnet is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
@@ -14,8 +14,8 @@
 
      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
-     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-     Boston, MA 02111-1307, USA.
+     Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+     Boston, MA 02110-1301, USA.
 */
 
 /**
 #include "platform.h"
 #include "gnunet_protocols.h"
 #include "gnunet_util_lib.h"
+#include "gnunet_resolver_service.h"
+#include "gnunet_socks.h"
+
+
+#define LOG(kind,...) GNUNET_log_from (kind, "util-client",__VA_ARGS__)
 
 
 /**
- * How often do we re-try tranmsitting requests before giving up?
- * Note that if we succeeded transmitting a request but failed to read
- * a response, we do NOT re-try.
+ * Internal state for a client connected to a GNUnet service.
  */
-#define MAX_ATTEMPTS 50
+struct ClientState;
 
-#define LOG(kind,...) GNUNET_log_from (kind, "util",__VA_ARGS__)
 
 /**
- * Handle for a transmission request.
+ * During connect, we try multiple possible IP addresses
+ * to find out which one might work.
  */
-struct GNUNET_CLIENT_TransmitHandle
+struct AddressProbe
 {
-  /**
-   * Connection state.
-   */
-  struct GNUNET_CLIENT_Connection *client;
-
-  /**
-   * Function to call to get the data for transmission.
-   */
-  GNUNET_CONNECTION_TransmitReadyNotify notify;
 
   /**
-   * Closure for @e notify.
+   * This is a linked list.
    */
-  void *notify_cls;
+  struct AddressProbe *next;
 
   /**
-   * Handle to the transmission with the underlying
-   * connection.
+   * This is a doubly-linked list.
    */
-  struct GNUNET_CONNECTION_TransmitHandle *th;
+  struct AddressProbe *prev;
 
   /**
-   * If we are re-trying and are delaying to do so,
-   * handle to the scheduled task managing the delay.
+   * The address; do not free (allocated at the end of this struct).
    */
-  struct GNUNET_SCHEDULER_Task * reconnect_task;
+  const struct sockaddr *addr;
 
   /**
-   * Timeout for the operation overall.
+   * Underlying OS's socket.
    */
-  struct GNUNET_TIME_Absolute timeout;
+  struct GNUNET_NETWORK_Handle *sock;
 
   /**
-   * Number of bytes requested.
+   * Connection for which we are probing.
    */
-  size_t size;
+  struct ClientState *cstate;
 
   /**
-   * Are we allowed to re-try to connect without telling
-   * the user (of this API) about the connection troubles?
+   * Lenth of addr.
    */
-  int auto_retry;
+  socklen_t addrlen;
 
   /**
-   * Number of attempts left for transmitting the request.  We may
-   * fail the first time (say because the service is not yet up), in
-   * which case (if auto_retry is set) we wait a bit and re-try
-   * (timeout permitting).
+   * Task waiting for the connection to finish connecting.
    */
-  unsigned int attempts_left;
-
+  struct GNUNET_SCHEDULER_Task *task;
 };
 
 
 /**
- * Context for processing
- * "GNUNET_CLIENT_transmit_and_get_response" requests.
+ * Internal state for a client connected to a GNUnet service.
  */
-struct TransmitGetResponseContext
+struct ClientState
 {
-  /**
-   * Client handle.
-   */
-  struct GNUNET_CLIENT_Connection *client;
 
   /**
-   * Message to transmit; do not free, allocated
-   * right after this struct.
+   * The connection handle, NULL if not live
    */
-  const struct GNUNET_MessageHeader *hdr;
+  struct GNUNET_NETWORK_Handle *sock;
 
   /**
-   * Timeout to use.
+   * Handle to a pending DNS lookup request, NULL if DNS is finished.
    */
-  struct GNUNET_TIME_Absolute timeout;
+  struct GNUNET_RESOLVER_RequestHandle *dns_active;
 
   /**
-   * Function to call when done.
+   * Our configuration.
    */
-  GNUNET_CLIENT_MessageHandler rn;
+  const struct GNUNET_CONFIGURATION_Handle *cfg;
 
   /**
-   * Closure for @e rn.
+   * Linked list of sockets we are currently trying out
+   * (during connect).
    */
-  void *rn_cls;
-};
-
-/**
- * Struct to refer to a GNUnet TCP connection.
- * This is more than just a socket because if the server
- * drops the connection, the client automatically tries
- * to reconnect (and for that needs connection information).
- */
-struct GNUNET_CLIENT_Connection
-{
+  struct AddressProbe *ap_head;
 
   /**
-   * The connection handle, NULL if not live
+   * Linked list of sockets we are currently trying out
+   * (during connect).
    */
-  struct GNUNET_CONNECTION_Handle *connection;
+  struct AddressProbe *ap_tail;
 
   /**
-   * Our configuration.
+   * Name of the service we interact with.
    */
-  const struct GNUNET_CONFIGURATION_Handle *cfg;
+  char *service_name;
 
   /**
-   * Name of the service we interact with.
+   * Hostname, if any.
    */
-  char *service_name;
+  char *hostname;
 
   /**
-   * Context of a transmit_and_get_response operation, NULL
-   * if no such operation is pending.
+   * Next message to transmit to the service. NULL for none.
    */
-  struct TransmitGetResponseContext *tag;
+  const struct GNUNET_MessageHeader *msg;
 
   /**
-   * Handler for current receiver task.
+   * Task for trying to connect to the service.
    */
-  GNUNET_CLIENT_MessageHandler receiver_handler;
+  struct GNUNET_SCHEDULER_Task *retry_task;
 
   /**
-   * Closure for @e receiver_handler.
+   * Task for sending messages to the service.
    */
-  void *receiver_handler_cls;
+  struct GNUNET_SCHEDULER_Task *send_task;
 
   /**
-   * Handle for a pending transmission request, NULL if there is
-   * none pending.
+   * Task for sending messages to the service.
    */
-  struct GNUNET_CLIENT_TransmitHandle *th;
+  struct GNUNET_SCHEDULER_Task *recv_task;
 
   /**
-   * If we are re-trying and are delaying to do so,
-   * handle to the scheduled task managing the delay.
+   * Tokenizer for inbound messages.
    */
-  struct GNUNET_SCHEDULER_Task * receive_task;
+  struct GNUNET_MessageStreamTokenizer *mst;
 
   /**
-   * Buffer for received message.
+   * Message queue under our control.
    */
-  char *received_buf;
+  struct GNUNET_MQ_Handle *mq;
 
   /**
    * Timeout for receiving a response (absolute time).
@@ -201,1170 +171,717 @@ struct GNUNET_CLIENT_Connection
   struct GNUNET_TIME_Relative back_off;
 
   /**
-   * Number of bytes in received_buf that are valid.
-   */
-  size_t received_pos;
-
-  /**
-   * Size of received_buf.
-   */
-  unsigned int received_size;
-
-  /**
-   * Do we have a complete response in received_buf?
+   * TCP port (0 for disabled).
    */
-  int msg_complete;
+  unsigned long long port;
 
   /**
-   * Are we currently busy doing receive-processing?
-   * #GNUNET_YES if so, #GNUNET_NO if not.
+   * Offset in the message where we are for transmission.
    */
-  int in_receive;
+  size_t msg_off;
 
   /**
-   * Is this the first message we are sending to the service?
+   * How often have we tried to connect?
    */
-  int first_message;
+  unsigned int attempts;
 
   /**
-   * How often have we tried to connect?
+   * Are we supposed to die?  #GNUNET_SYSERR if destruction must be
+   * deferred, #GNUNET_NO by default, #GNUNET_YES if destruction was
+   * deferred.
    */
-  unsigned int attempts;
+  int in_destroy;
 
 };
 
 
-/**
- * Try connecting to the server using UNIX domain sockets.
- *
- * @param service_name name of service to connect to
- * @param cfg configuration to use
- * @return NULL on error, connection to UNIX otherwise
- */
-static struct GNUNET_CONNECTION_Handle *
-try_unixpath (const char *service_name,
-             const struct GNUNET_CONFIGURATION_Handle *cfg)
-{
-#if AF_UNIX
-  struct GNUNET_CONNECTION_Handle *connection;
-  char *unixpath;
-  struct sockaddr_un s_un;
-
-  unixpath = NULL;
-  if ((GNUNET_OK == GNUNET_CONFIGURATION_get_value_filename (cfg, service_name, "UNIXPATH", &unixpath)) &&
-      (0 < strlen (unixpath)))
-  {
-    /* We have a non-NULL unixpath, need to validate it */
-    if (strlen (unixpath) >= sizeof (s_un.sun_path))
-    {
-      LOG (GNUNET_ERROR_TYPE_WARNING,
-          _("UNIXPATH `%s' too long, maximum length is %llu\n"), unixpath,
-          (unsigned long long) sizeof (s_un.sun_path));
-      unixpath = GNUNET_NETWORK_shorten_unixpath (unixpath);
-      LOG (GNUNET_ERROR_TYPE_INFO,
-          _("Using `%s' instead\n"), unixpath);
-      if (NULL == unixpath)
-       return NULL;
-    }
-    connection = GNUNET_CONNECTION_create_from_connect_to_unixpath (cfg, unixpath);
-    if (NULL != connection)
-    {
-      LOG (GNUNET_ERROR_TYPE_DEBUG, "Connected to unixpath `%s'!\n",
-          unixpath);
-      GNUNET_free (unixpath);
-      return connection;
-    }
-  }
-  GNUNET_free_non_null (unixpath);
-#endif
-  return NULL;
-}
-
-
-/**
- * Test whether the configuration has proper values for connection
- * (UNIXPATH || (PORT && HOSTNAME)).
- *
- * @param service_name name of service to connect to
- * @param cfg configuration to use
- * @return #GNUNET_OK if the configuration is valid, #GNUNET_SYSERR if not
- */
-static int
-test_service_configuration (const char *service_name,
-                           const struct GNUNET_CONFIGURATION_Handle *cfg)
-{
-  int ret = GNUNET_SYSERR;
-  char *hostname = NULL;
-  unsigned long long port;
-#if AF_UNIX
-  char *unixpath = NULL;
-
-  if ((GNUNET_OK == GNUNET_CONFIGURATION_get_value_filename (cfg, service_name, "UNIXPATH", &unixpath)) &&
-      (0 < strlen (unixpath)))
-    ret = GNUNET_OK;
-  GNUNET_free_non_null (unixpath);
-#endif
-
-  if ( (GNUNET_YES ==
-       GNUNET_CONFIGURATION_have_value (cfg, service_name, "PORT")) &&
-       (GNUNET_OK ==
-       GNUNET_CONFIGURATION_get_value_number (cfg, service_name, "PORT", &port)) &&
-       (port <= 65535) && (0 != port) &&
-       (GNUNET_OK ==
-       GNUNET_CONFIGURATION_get_value_string (cfg, service_name, "HOSTNAME",
-                                              &hostname)) &&
-       (0 != strlen (hostname)) )
-    ret = GNUNET_OK;
-  GNUNET_free_non_null (hostname);
-  return ret;
-}
-
-
 /**
  * Try to connect to the service.
  *
- * @param service_name name of service to connect to
- * @param cfg configuration to use
- * @param attempt counter used to alternate between IP and UNIX domain sockets
- * @return NULL on error
- */
-static struct GNUNET_CONNECTION_Handle *
-do_connect (const char *service_name,
-            const struct GNUNET_CONFIGURATION_Handle *cfg,
-           unsigned int attempt)
-{
-  struct GNUNET_CONNECTION_Handle *connection;
-  char *hostname;
-  unsigned long long port;
-
-  connection = NULL;
-  if (0 == (attempt % 2))
-  {
-    /* on even rounds, try UNIX first */
-    connection = try_unixpath (service_name, cfg);
-    if (NULL != connection)
-      return connection;
-  }
-  if (GNUNET_YES ==
-      GNUNET_CONFIGURATION_have_value (cfg, service_name, "PORT"))
-  {
-    if ((GNUNET_OK !=
-        GNUNET_CONFIGURATION_get_value_number (cfg, service_name, "PORT", &port))
-       || (port > 65535) ||
-       (GNUNET_OK !=
-        GNUNET_CONFIGURATION_get_value_string (cfg, service_name, "HOSTNAME",
-                                               &hostname)))
-    {
-      LOG (GNUNET_ERROR_TYPE_WARNING,
-          _
-          ("Could not determine valid hostname and port for service `%s' from configuration.\n"),
-          service_name);
-      return NULL;
-    }
-    if (0 == strlen (hostname))
-    {
-      GNUNET_free (hostname);
-      LOG (GNUNET_ERROR_TYPE_WARNING,
-          _("Need a non-empty hostname for service `%s'.\n"), service_name);
-      return NULL;
-    }
-  }
-  else
-  {
-    /* unspecified means 0 (disabled) */
-    port = 0;
-    hostname = NULL;
-  }
-  if (0 == port)
-  {
-    /* if port is 0, try UNIX */
-    connection = try_unixpath (service_name, cfg);
-    if (NULL != connection)
-    {
-      GNUNET_free_non_null (hostname);
-      return connection;
-    }
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Port is 0 for service `%s', UNIXPATH did not work, returning NULL!\n",
-         service_name);
-    GNUNET_free_non_null (hostname);
-    return NULL;
-  }
-  connection = GNUNET_CONNECTION_create_from_connect (cfg, hostname, port);
-  GNUNET_free (hostname);
-  return connection;
-}
-
-
-/**
- * Get a connection with a service.
- *
- * @param service_name name of the service
- * @param cfg configuration to use
- * @return NULL on error (service unknown to configuration)
+ * @param cls the `struct ClientState` to try to connect to the service
  */
-struct GNUNET_CLIENT_Connection *
-GNUNET_CLIENT_connect (const char *service_name,
-                       const struct GNUNET_CONFIGURATION_Handle *cfg)
-{
-  struct GNUNET_CLIENT_Connection *client;
-  struct GNUNET_CONNECTION_Handle *connection;
-
-  if (GNUNET_OK !=
-      test_service_configuration (service_name,
-                                 cfg))
-    return NULL;
-  connection = do_connect (service_name, cfg, 0);
-  client = GNUNET_new (struct GNUNET_CLIENT_Connection);
-  client->first_message = GNUNET_YES;
-  client->attempts = 1;
-  client->connection = connection;
-  client->service_name = GNUNET_strdup (service_name);
-  client->cfg = cfg;
-  client->back_off = GNUNET_TIME_UNIT_MILLISECONDS;
-  return client;
-}
-
-
-/**
- * Destroy connection with the service.  This will automatically
- * cancel any pending "receive" request (however, the handler will
- * *NOT* be called, not even with a NULL message).  Any pending
- * transmission request will also be cancelled UNLESS the callback for
- * the transmission request has already been called, in which case the
- * transmission 'finish_pending_write' argument determines whether or
- * not the write is guaranteed to complete before the socket is fully
- * destroyed (unless, of course, there is an error with the server in
- * which case the message may still be lost).
- *
- * @param client handle to the service connection
- */
-void
-GNUNET_CLIENT_disconnect (struct GNUNET_CLIENT_Connection *client)
-{
-  if (GNUNET_YES == client->in_receive)
-  {
-    GNUNET_CONNECTION_receive_cancel (client->connection);
-    client->in_receive = GNUNET_NO;
-  }
-  if (NULL != client->th)
-  {
-    GNUNET_CLIENT_notify_transmit_ready_cancel (client->th);
-    client->th = NULL;
-  }
-  if (NULL != client->connection)
-  {
-    GNUNET_CONNECTION_destroy (client->connection);
-    client->connection = NULL;
-  }
-  if (NULL != client->receive_task)
-  {
-    GNUNET_SCHEDULER_cancel (client->receive_task);
-    client->receive_task = NULL;
-  }
-  if (NULL != client->tag)
-  {
-    GNUNET_free (client->tag);
-    client->tag = NULL;
-  }
-  client->receiver_handler = NULL;
-  GNUNET_array_grow (client->received_buf, client->received_size, 0);
-  GNUNET_free (client->service_name);
-  GNUNET_free (client);
-}
+static void
+start_connect (void *cls);
 
 
 /**
- * Check if message is complete.  Sets the "msg_complete" member
- * in the client struct.
+ * We've failed for good to establish a connection (timeout or
+ * no more addresses to try).
  *
- * @param client connection with the buffer to check
+ * @param cstate the connection we tried to establish
  */
 static void
-check_complete (struct GNUNET_CLIENT_Connection *client)
+connect_fail_continuation (struct ClientState *cstate)
 {
-  if ((client->received_pos >= sizeof (struct GNUNET_MessageHeader)) &&
-      (client->received_pos >=
-       ntohs (((const struct GNUNET_MessageHeader *) client->received_buf)->
-              size)))
-    client->msg_complete = GNUNET_YES;
+  GNUNET_break (NULL == cstate->ap_head);
+  GNUNET_break (NULL == cstate->ap_tail);
+  GNUNET_break (NULL == cstate->dns_active);
+  GNUNET_break (NULL == cstate->sock);
+  GNUNET_assert (NULL == cstate->send_task);
+  GNUNET_assert (NULL == cstate->recv_task);
+  // GNUNET_assert (NULL == cstate->proxy_handshake);
+
+  cstate->back_off = GNUNET_TIME_STD_BACKOFF (cstate->back_off);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Failed to establish connection to `%s', no further addresses to try, will try again in %s.\n",
+       cstate->service_name,
+       GNUNET_STRINGS_relative_time_to_string (cstate->back_off,
+                                               GNUNET_YES));
+  cstate->retry_task
+    = GNUNET_SCHEDULER_add_delayed (cstate->back_off,
+                                    &start_connect,
+                                    cstate);
 }
 
 
 /**
- * Callback function for data received from the network.  Note that
- * both @a available and @a errCode would be 0 if the read simply timed out.
+ * We are ready to send a message to the service.
  *
- * @param cls closure
- * @param buf pointer to received data
- * @param available number of bytes availabe in @a buf,
- *        possibly 0 (on errors)
- * @param addr address of the sender
- * @param addrlen size of @a addr
- * @param errCode value of errno (on errors receiving)
+ * @param cls the `struct ClientState` with the `msg` to transmit
  */
 static void
-receive_helper (void *cls, const void *buf, size_t available,
-                const struct sockaddr *addr, socklen_t addrlen, int errCode)
+transmit_ready (void *cls)
 {
-  struct GNUNET_CLIENT_Connection *client = cls;
-  struct GNUNET_TIME_Relative remaining;
-  GNUNET_CLIENT_MessageHandler receive_handler;
-  void *receive_handler_cls;
-
-  GNUNET_assert (GNUNET_NO == client->msg_complete);
-  GNUNET_assert (GNUNET_YES == client->in_receive);
-  client->in_receive = GNUNET_NO;
-  if ((0 == available) || (NULL == client->connection) || (0 != errCode))
-  {
-    /* signal timeout! */
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Timeout in receive_helper, available %u, client->connection %s, errCode `%s'\n",
-         (unsigned int) available, NULL == client->connection ? "NULL" : "non-NULL",
-         STRERROR (errCode));
-    if (NULL != (receive_handler = client->receiver_handler))
-    {
-      receive_handler_cls = client->receiver_handler_cls;
-      client->receiver_handler = NULL;
-      receive_handler (receive_handler_cls, NULL);
-    }
+  struct ClientState *cstate = cls;
+  ssize_t ret;
+  size_t len;
+  const char *pos;
+  int notify_in_flight;
+
+  cstate->send_task = NULL;
+  pos = (const char *) cstate->msg;
+  len = ntohs (cstate->msg->size);
+  GNUNET_assert (cstate->msg_off < len);
+ RETRY:
+  ret = GNUNET_NETWORK_socket_send (cstate->sock,
+                                    &pos[cstate->msg_off],
+                                    len - cstate->msg_off);
+  if (-1 == ret)
+  {
+    if (EINTR == errno)
+      goto RETRY;
+    GNUNET_MQ_inject_error (cstate->mq,
+                            GNUNET_MQ_ERROR_WRITE);
     return;
   }
-  /* FIXME: optimize for common fast case where buf contains the
-   * entire message and we need no copying... */
-
-  /* slow path: append to array */
-  if (client->received_size < client->received_pos + available)
-    GNUNET_array_grow (client->received_buf, client->received_size,
-                       client->received_pos + available);
-  memcpy (&client->received_buf[client->received_pos], buf, available);
-  client->received_pos += available;
-  check_complete (client);
-  /* check for timeout */
-  remaining = GNUNET_TIME_absolute_get_remaining (client->receive_timeout);
-  if (0 == remaining.rel_value_us)
-  {
-    /* signal timeout! */
-    if (NULL != (receive_handler = client->receiver_handler))
-    {
-      client->receiver_handler = NULL;
-      receive_handler (client->receiver_handler_cls, NULL);
-    }
+  notify_in_flight = (0 == cstate->msg_off);
+  cstate->msg_off += ret;
+  if (cstate->msg_off < len)
+  {
+    cstate->send_task
+      = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                        cstate->sock,
+                                        &transmit_ready,
+                                        cstate);
+    if (notify_in_flight)
+      GNUNET_MQ_impl_send_in_flight (cstate->mq);
     return;
   }
-  /* back to receive -- either for more data or to call callback! */
-  GNUNET_CLIENT_receive (client, client->receiver_handler,
-                         client->receiver_handler_cls, remaining);
+  cstate->msg = NULL;
+  GNUNET_MQ_impl_send_continue (cstate->mq);
 }
 
 
 /**
- * Continuation to call the receive callback.
+ * We have received a full message, pass to the MQ dispatcher.
+ * Called by the tokenizer via #receive_ready().
  *
- * @param cls  our handle to the client connection
- * @param tc scheduler context
+ * @param cls the `struct ClientState`
+ * @param msg message we received.
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR to stop further processing
  */
-static void
-receive_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
+static int
+recv_message (void *cls,
+              const struct GNUNET_MessageHeader *msg)
 {
-  struct GNUNET_CLIENT_Connection *client = cls;
-  GNUNET_CLIENT_MessageHandler handler = client->receiver_handler;
-  const struct GNUNET_MessageHeader *cmsg =
-      (const struct GNUNET_MessageHeader *) client->received_buf;
-  void *handler_cls = client->receiver_handler_cls;
-  uint16_t msize = ntohs (cmsg->size);
-  char mbuf[msize] GNUNET_ALIGN;
-  struct GNUNET_MessageHeader *msg = (struct GNUNET_MessageHeader *) mbuf;
+  struct ClientState *cstate = cls;
 
+  if (GNUNET_YES == cstate->in_destroy)
+    return GNUNET_SYSERR;
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Received message of type %u and size %u from %s service.\n",
-       ntohs (cmsg->type),
-       msize,
-       client->service_name);
-  client->receive_task = NULL;
-  GNUNET_assert (GNUNET_YES == client->msg_complete);
-  GNUNET_assert (client->received_pos >= msize);
-  memcpy (msg, cmsg, msize);
-  memmove (client->received_buf, &client->received_buf[msize],
-           client->received_pos - msize);
-  client->received_pos -= msize;
-  client->msg_complete = GNUNET_NO;
-  client->receiver_handler = NULL;
-  check_complete (client);
-  if (NULL != handler)
-    handler (handler_cls, msg);
+       "Received message of type %u and size %u from %s\n",
+       ntohs (msg->type),
+       ntohs (msg->size),
+       cstate->service_name);
+  GNUNET_MQ_inject_message (cstate->mq,
+                            msg);
+  if (GNUNET_YES == cstate->in_destroy)
+    return GNUNET_SYSERR;
+  return GNUNET_OK;
 }
 
 
 /**
- * Read from the service.
+ * Cancel all remaining connect attempts
  *
- * @param client the service
- * @param handler function to call with the message
- * @param handler_cls closure for @a handler
- * @param timeout how long to wait until timing out
+ * @param cstate handle of the client state to process
  */
-void
-GNUNET_CLIENT_receive (struct GNUNET_CLIENT_Connection *client,
-                       GNUNET_CLIENT_MessageHandler handler,
-                      void *handler_cls,
-                       struct GNUNET_TIME_Relative timeout)
-{
-  if (NULL == client->connection)
-  {
-    /* already disconnected, fail instantly! */
-    GNUNET_break (0);           /* this should not happen in well-written code! */
-    if (NULL != handler)
-      handler (handler_cls, NULL);
-    return;
-  }
-  client->receiver_handler = handler;
-  client->receiver_handler_cls = handler_cls;
-  client->receive_timeout = GNUNET_TIME_relative_to_absolute (timeout);
-  if (GNUNET_YES == client->msg_complete)
-  {
-    GNUNET_assert (NULL == client->receive_task);
-    client->receive_task = GNUNET_SCHEDULER_add_now (&receive_task, client);
-  }
-  else
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG, "calling GNUNET_CONNECTION_receive\n");
-    GNUNET_assert (GNUNET_NO == client->in_receive);
-    client->in_receive = GNUNET_YES;
-    GNUNET_CONNECTION_receive (client->connection, GNUNET_SERVER_MAX_MESSAGE_SIZE - 1,
-                               timeout, &receive_helper, client);
-  }
-}
-
-
-/**
- * Handle for a test to check if a service is running.
- */
-struct GNUNET_CLIENT_TestHandle
+static void
+cancel_aps (struct ClientState *cstate)
 {
-  /**
-   * Function to call with the result of the test.
-   */
-  GNUNET_CLIENT_TestResultCallback cb;
-
-  /**
-   * Closure for @e cb.
-   */
-  void *cb_cls;
-
-  /**
-   * Client connection we are using for the test, if any.
-   */
-  struct GNUNET_CLIENT_Connection *client;
-
-  /**
-   * Handle for the transmission request, if any.
-   */
-  struct GNUNET_CLIENT_TransmitHandle *th;
-
-  /**
-   * Deadline for calling @e cb.
-   */
-  struct GNUNET_TIME_Absolute test_deadline;
-
-  /**
-   * ID of task used for asynchronous operations.
-   */
-  struct GNUNET_SCHEDULER_Task * task;
-
-  /**
-   * Final result to report back (once known).
-   */
-  int result;
-};
+  struct AddressProbe *pos;
 
-
-/**
- * Abort testing for service.
- *
- * @param th test handle
- */
-void
-GNUNET_CLIENT_service_test_cancel (struct GNUNET_CLIENT_TestHandle *th)
-{
-  if (NULL != th->th)
-  {
-    GNUNET_CLIENT_notify_transmit_ready_cancel (th->th);
-    th->th = NULL;
-  }
-  if (NULL != th->client)
-  {
-    GNUNET_CLIENT_disconnect (th->client);
-    th->client = NULL;
-  }
-  if (NULL != th->task)
+  while (NULL != (pos = cstate->ap_head))
   {
-    GNUNET_SCHEDULER_cancel (th->task);
-    th->task = NULL;
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (pos->sock));
+    GNUNET_SCHEDULER_cancel (pos->task);
+    GNUNET_CONTAINER_DLL_remove (cstate->ap_head,
+                                cstate->ap_tail,
+                                pos);
+    GNUNET_free (pos);
   }
-  GNUNET_free (th);
 }
 
 
 /**
- * Task that reports back the result by calling the callback
- * and then cleans up.
+ * Implement the destruction of a message queue.  Implementations must
+ * not free @a mq, but should take care of @a impl_state.
  *
- * @param cls the `struct GNUNET_CLIENT_TestHandle`
- * @param tc scheduler context
+ * @param mq the message queue to destroy
+ * @param impl_state our `struct ClientState`
  */
 static void
-report_result (void *cls,
-              const struct GNUNET_SCHEDULER_TaskContext *tc)
+connection_client_destroy_impl (struct GNUNET_MQ_Handle *mq,
+                                void *impl_state)
 {
-  struct GNUNET_CLIENT_TestHandle *th = cls;
-
-  th->task = NULL;
-  th->cb (th->cb_cls, th->result);
-  GNUNET_CLIENT_service_test_cancel (th);
-}
-
+  struct ClientState *cstate = impl_state;
 
-/**
- * Report service test result asynchronously back to callback.
- *
- * @param th test handle with the result and the callback
- * @param result result to report
- */
-static void
-service_test_report (struct GNUNET_CLIENT_TestHandle *th,
-                    int result)
-{
-  th->result = result;
-  th->task = GNUNET_SCHEDULER_add_now (&report_result,
-                                      th);
+  if (GNUNET_SYSERR == cstate->in_destroy)
+  {
+    /* defer destruction */
+    cstate->in_destroy = GNUNET_YES;
+    cstate->mq = NULL;
+    return;
+  }
+  if (NULL != cstate->dns_active)
+    GNUNET_RESOLVER_request_cancel (cstate->dns_active);
+  if (NULL != cstate->send_task)
+    GNUNET_SCHEDULER_cancel (cstate->send_task);
+  if (NULL != cstate->recv_task)
+    GNUNET_SCHEDULER_cancel (cstate->recv_task);
+  if (NULL != cstate->retry_task)
+    GNUNET_SCHEDULER_cancel (cstate->retry_task);
+  if (NULL != cstate->sock)
+    GNUNET_NETWORK_socket_close (cstate->sock);
+  cancel_aps (cstate);
+  GNUNET_free (cstate->service_name);
+  GNUNET_free_non_null (cstate->hostname);
+  GNUNET_MST_destroy (cstate->mst);
+  GNUNET_free (cstate);
 }
 
 
 /**
- * Receive confirmation from test, service is up.
+ * This function is called once we have data ready to read.
  *
- * @param cls closure with the `struct GNUNET_CLIENT_TestHandle`
- * @param msg message received, NULL on timeout or fatal error
+ * @param cls `struct ClientState` with connection to read from
  */
 static void
-confirm_handler (void *cls, const struct GNUNET_MessageHeader *msg)
+receive_ready (void *cls)
 {
-  struct GNUNET_CLIENT_TestHandle *th = cls;
-
-  /* We may want to consider looking at the reply in more
-   * detail in the future, for example, is this the
-   * correct service? FIXME! */
-  if (NULL != msg)
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Received confirmation that service is running.\n");
-    service_test_report (th, GNUNET_YES);
+  struct ClientState *cstate = cls;
+  int ret;
+
+  cstate->recv_task = NULL;
+  cstate->in_destroy = GNUNET_SYSERR;
+  ret = GNUNET_MST_read (cstate->mst,
+                         cstate->sock,
+                         GNUNET_NO,
+                         GNUNET_NO);
+  if (GNUNET_SYSERR == ret)
+  {
+    if (NULL != cstate->mq)
+      GNUNET_MQ_inject_error (cstate->mq,
+                             GNUNET_MQ_ERROR_READ);
+    if (GNUNET_YES == cstate->in_destroy)
+      connection_client_destroy_impl (cstate->mq,
+                                     cstate);
+    return;
   }
-  else
+  if (GNUNET_YES == cstate->in_destroy)
   {
-    service_test_report (th, GNUNET_NO);
+    connection_client_destroy_impl (cstate->mq,
+                                    cstate);
+    return;
   }
+  cstate->in_destroy = GNUNET_NO;
+  cstate->recv_task
+    = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                     cstate->sock,
+                                     &receive_ready,
+                                     cstate);
 }
 
 
 /**
- * Send the 'TEST' message to the service.  If successful, prepare to
- * receive the reply.
+ * We've succeeded in establishing a connection.
  *
- * @param cls the `struct GNUNET_CLIENT_TestHandle` of the test
- * @param size number of bytes available in @a buf
- * @param buf where to write the message
- * @return number of bytes written to @a buf
+ * @param cstate the connection we tried to establish
  */
-static size_t
-write_test (void *cls, size_t size, void *buf)
+static void
+connect_success_continuation (struct ClientState *cstate)
 {
-  struct GNUNET_CLIENT_TestHandle *th = cls;
-  struct GNUNET_MessageHeader *msg;
-
-  th->th = NULL;
-  if (size < sizeof (struct GNUNET_MessageHeader))
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "Failed to transmit TEST request.\n");
-    service_test_report (th, GNUNET_NO);
-    return 0;                   /* client disconnected */
+  GNUNET_assert (NULL == cstate->recv_task);
+  cstate->recv_task
+    = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                     cstate->sock,
+                                     &receive_ready,
+                                     cstate);
+  if (NULL != cstate->msg)
+  {
+    GNUNET_assert (NULL == cstate->send_task);
+    cstate->send_task
+      = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                        cstate->sock,
+                                        &transmit_ready,
+                                        cstate);
   }
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Transmitting `%s' request.\n",
-       "TEST");
-  msg = (struct GNUNET_MessageHeader *) buf;
-  msg->type = htons (GNUNET_MESSAGE_TYPE_TEST);
-  msg->size = htons (sizeof (struct GNUNET_MessageHeader));
-  GNUNET_CLIENT_receive (th->client,
-                        &confirm_handler, th,
-                         GNUNET_TIME_absolute_get_remaining
-                         (th->test_deadline));
-  return sizeof (struct GNUNET_MessageHeader);
 }
 
 
 /**
- * Test if the service is running.  If we are given a UNIXPATH or a
- * local address, we do this NOT by trying to connect to the service,
- * but by trying to BIND to the same port.  If the BIND fails, we know
- * the service is running.
+ * Try connecting to the server using UNIX domain sockets.
  *
- * @param service name of the service to wait for
+ * @param service_name name of service to connect to
  * @param cfg configuration to use
- * @param timeout how long to wait at most
- * @param cb function to call with the result
- * @param cb_cls closure for @a cb
- * @return handle to cancel the test
+ * @return NULL on error, socket connected to UNIX otherwise
  */
-struct GNUNET_CLIENT_TestHandle *
-GNUNET_CLIENT_service_test (const char *service,
-                            const struct GNUNET_CONFIGURATION_Handle *cfg,
-                            struct GNUNET_TIME_Relative timeout,
-                            GNUNET_CLIENT_TestResultCallback cb,
-                           void *cb_cls)
+static struct GNUNET_NETWORK_Handle *
+try_unixpath (const char *service_name,
+             const struct GNUNET_CONFIGURATION_Handle *cfg)
 {
-  struct GNUNET_CLIENT_TestHandle *th;
-  char *hostname;
-  unsigned long long port;
+#if AF_UNIX
   struct GNUNET_NETWORK_Handle *sock;
+  char *unixpath;
+  struct sockaddr_un s_un;
 
-  th = GNUNET_new (struct GNUNET_CLIENT_TestHandle);
-  th->cb = cb;
-  th->cb_cls = cb_cls;
-  th->test_deadline = GNUNET_TIME_relative_to_absolute (timeout);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Testing if service `%s' is running.\n",
-       service);
-#ifdef AF_UNIX
+  unixpath = NULL;
+  if ((GNUNET_OK ==
+       GNUNET_CONFIGURATION_get_value_filename (cfg,
+                                                service_name,
+                                                "UNIXPATH",
+                                                &unixpath)) &&
+      (0 < strlen (unixpath)))
   {
-    /* probe UNIX support */
-    struct sockaddr_un s_un;
-    char *unixpath;
-    int abstract;
-
-    unixpath = NULL;
-    if ((GNUNET_OK ==
-        GNUNET_CONFIGURATION_get_value_filename (cfg,
-                                                 service,
-                                                 "UNIXPATH",
-                                                 &unixpath)) &&
-       (0 < strlen (unixpath)))  /* We have a non-NULL unixpath, does that mean it's valid? */
+    /* We have a non-NULL unixpath, need to validate it */
+    if (strlen (unixpath) >= sizeof (s_un.sun_path))
     {
-      if (strlen (unixpath) >= sizeof (s_un.sun_path))
-      {
-        LOG (GNUNET_ERROR_TYPE_WARNING,
-             _("UNIXPATH `%s' too long, maximum length is %llu\n"),
-            unixpath,
-             (unsigned long long) sizeof (s_un.sun_path));
-       unixpath = GNUNET_NETWORK_shorten_unixpath (unixpath);
-        LOG (GNUNET_ERROR_TYPE_INFO,
-             _("Using `%s' instead\n"), unixpath);
-      }
+      LOG (GNUNET_ERROR_TYPE_WARNING,
+          _("UNIXPATH `%s' too long, maximum length is %llu\n"),
+           unixpath,
+          (unsigned long long) sizeof (s_un.sun_path));
+      unixpath = GNUNET_NETWORK_shorten_unixpath (unixpath);
+      LOG (GNUNET_ERROR_TYPE_INFO,
+          _("Using `%s' instead\n"),
+           unixpath);
+      if (NULL == unixpath)
+       return NULL;
     }
+    memset (&s_un,
+            0,
+            sizeof (s_un));
+    s_un.sun_family = AF_UNIX;
+    strncpy (s_un.sun_path,
+             unixpath,
+             sizeof (s_un.sun_path) - 1);
 #ifdef LINUX
-    abstract = GNUNET_CONFIGURATION_get_value_yesno (cfg,
-                                                     "TESTING",
-                                                     "USE_ABSTRACT_SOCKETS");
-#else
-    abstract = GNUNET_NO;
-#endif
-    if ((NULL != unixpath) && (GNUNET_YES != abstract))
-    {
-      if (GNUNET_SYSERR == GNUNET_DISK_directory_create_for_file (unixpath))
-        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
-                                  "mkdir", unixpath);
-    }
-    if (NULL != unixpath)
     {
-      sock = GNUNET_NETWORK_socket_create (PF_UNIX, SOCK_STREAM, 0);
-      if (NULL != sock)
-      {
-       memset (&s_un, 0, sizeof (s_un));
-       s_un.sun_family = AF_UNIX;
-        strncpy (s_un.sun_path, unixpath, sizeof (s_un.sun_path) - 1);
-        if (GNUNET_YES == abstract)
-          s_un.sun_path[0] = '\0';
-#if HAVE_SOCKADDR_IN_SIN_LEN
-        s_un.sun_len = (u_char) sizeof (struct sockaddr_un);
-#endif
-       if (GNUNET_OK !=
-           GNUNET_NETWORK_socket_bind (sock, (const struct sockaddr *) &s_un,
-                                       sizeof (struct sockaddr_un)))
-        {
-         /* failed to bind => service must be running */
-         GNUNET_free (unixpath);
-         (void) GNUNET_NETWORK_socket_close (sock);
-         service_test_report (th, GNUNET_YES);
-         return th;
-       }
-       (void) GNUNET_NETWORK_socket_close (sock);
-        /* let's try IP */
-      }
-    }
-    GNUNET_free_non_null (unixpath);
-  }
-#endif
-
-  hostname = NULL;
-  if ((GNUNET_OK !=
-       GNUNET_CONFIGURATION_get_value_number (cfg, service, "PORT", &port)) ||
-      (port > 65535) ||
-      (GNUNET_OK !=
-       GNUNET_CONFIGURATION_get_value_string (cfg, service, "HOSTNAME",
-                                              &hostname)))
-  {
-    /* UNIXPATH failed (if possible) AND IP failed => error */
-    service_test_report (th, GNUNET_SYSERR);
-    return th;
-  }
+      int abstract;
 
-  if (0 == strcmp ("localhost", hostname)
-#if !LINUX
-      && 0
-#endif
-      )
-  {
-    /* can test using 'bind' */
-    struct sockaddr_in s_in;
-
-    memset (&s_in, 0, sizeof (s_in));
-#if HAVE_SOCKADDR_IN_SIN_LEN
-    s_in.sin_len = sizeof (struct sockaddr_in);
-#endif
-    s_in.sin_family = AF_INET;
-    s_in.sin_port = htons (port);
-
-    sock = GNUNET_NETWORK_socket_create (AF_INET, SOCK_STREAM, 0);
-    if (NULL != sock)
-    {
-      if (GNUNET_OK !=
-          GNUNET_NETWORK_socket_bind (sock, (const struct sockaddr *) &s_in,
-                                      sizeof (s_in)))
-      {
-        /* failed to bind => service must be running */
-        GNUNET_free (hostname);
-        (void) GNUNET_NETWORK_socket_close (sock);
-        service_test_report (th, GNUNET_YES);
-        return th;
-      }
-      (void) GNUNET_NETWORK_socket_close (sock);
+      abstract = GNUNET_CONFIGURATION_get_value_yesno (cfg,
+                                                       "TESTING",
+                                                       "USE_ABSTRACT_SOCKETS");
+      if (GNUNET_YES == abstract)
+        s_un.sun_path[0] = '\0';
     }
-  }
-
-  if (0 == strcmp ("ip6-localhost", hostname)
-#if !LINUX
-      && 0
 #endif
-      )
-  {
-    /* can test using 'bind' */
-    struct sockaddr_in6 s_in6;
-
-    memset (&s_in6, 0, sizeof (s_in6));
-#if HAVE_SOCKADDR_IN_SIN_LEN
-    s_in6.sin6_len = sizeof (struct sockaddr_in6);
+#if HAVE_SOCKADDR_UN_SUN_LEN
+    s_un.sun_len = (u_char) sizeof (struct sockaddr_un);
 #endif
-    s_in6.sin6_family = AF_INET6;
-    s_in6.sin6_port = htons (port);
-
-    sock = GNUNET_NETWORK_socket_create (AF_INET6, SOCK_STREAM, 0);
-    if (NULL != sock)
+    sock = GNUNET_NETWORK_socket_create (AF_UNIX,
+                                         SOCK_STREAM,
+                                         0);
+    if ( (NULL != sock) &&
+         ( (GNUNET_OK ==
+            GNUNET_NETWORK_socket_connect (sock,
+                                           (struct sockaddr *) &s_un,
+                                           sizeof (s_un))) ||
+           (EINPROGRESS == errno) ) )
     {
-      if (GNUNET_OK !=
-          GNUNET_NETWORK_socket_bind (sock, (const struct sockaddr *) &s_in6,
-                                      sizeof (s_in6)))
-      {
-        /* failed to bind => service must be running */
-        GNUNET_free (hostname);
-        (void) GNUNET_NETWORK_socket_close (sock);
-        service_test_report (th, GNUNET_YES);
-        return th;
-      }
-      (void) GNUNET_NETWORK_socket_close (sock);
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Successfully connected to unixpath `%s'!\n",
+          unixpath);
+      GNUNET_free (unixpath);
+      return sock;
     }
+    if (NULL != sock)
+      GNUNET_NETWORK_socket_close (sock);
   }
-
-  if (((0 == strcmp ("localhost", hostname)) ||
-       (0 == strcmp ("ip6-localhost", hostname)))
-#if !LINUX
-      && 0
+  GNUNET_free_non_null (unixpath);
 #endif
-      )
-  {
-    /* all binds succeeded => claim service not running right now */
-    GNUNET_free_non_null (hostname);
-    service_test_report (th, GNUNET_NO);
-    return th;
-  }
-  GNUNET_free_non_null (hostname);
-
-  /* non-localhost, try 'connect' method */
-  th->client = GNUNET_CLIENT_connect (service, cfg);
-  if (NULL == th->client)
-  {
-    LOG (GNUNET_ERROR_TYPE_INFO,
-         _("Could not connect to service `%s', configuration broken.\n"),
-         service);
-    service_test_report (th, GNUNET_SYSERR);
-    return th;
-  }
-  th->th = GNUNET_CLIENT_notify_transmit_ready (th->client,
-                                               sizeof (struct GNUNET_MessageHeader),
-                                               timeout, GNUNET_YES,
-                                               &write_test, th);
-  if (NULL == th->th)
-  {
-    LOG (GNUNET_ERROR_TYPE_WARNING,
-         _("Failure to transmit request to service `%s'\n"), service);
-    service_test_report (th, GNUNET_SYSERR);
-    return th;
-  }
-  return th;
+  return NULL;
 }
 
 
 /**
- * Connection notifies us about failure or success of
- * a transmission request.  Either pass it on to our
- * user or, if possible, retry.
+ * Scheduler let us know that we're either ready to write on the
+ * socket OR connect timed out.  Do the right thing.
  *
- * @param cls our `struct GNUNET_CLIENT_TransmissionHandle`
- * @param size number of bytes available for transmission
- * @param buf where to write them
- * @return number of bytes written to buf
+ * @param cls the `struct AddressProbe *` with the address that we are probing
  */
-static size_t
-client_notify (void *cls, size_t size, void *buf);
+static void
+connect_probe_continuation (void *cls)
+{
+  struct AddressProbe *ap = cls;
+  struct ClientState *cstate = ap->cstate;
+  const struct GNUNET_SCHEDULER_TaskContext *tc;
+  int error;
+  socklen_t len;
+
+  ap->task = NULL;
+  GNUNET_assert (NULL != ap->sock);
+  GNUNET_CONTAINER_DLL_remove (cstate->ap_head,
+                              cstate->ap_tail,
+                              ap);
+  len = sizeof (error);
+  error = 0;
+  tc = GNUNET_SCHEDULER_get_task_context ();
+  if ( (0 == (tc->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) ||
+       (GNUNET_OK !=
+       GNUNET_NETWORK_socket_getsockopt (ap->sock,
+                                         SOL_SOCKET,
+                                         SO_ERROR,
+                                         &error,
+                                         &len)) ||
+       (0 != error) )
+  {
+    GNUNET_break (GNUNET_OK ==
+                 GNUNET_NETWORK_socket_close (ap->sock));
+    GNUNET_free (ap);
+    if ( (NULL == cstate->ap_head) &&
+         //     (NULL == cstate->proxy_handshake) &&
+        (NULL == cstate->dns_active) )
+      connect_fail_continuation (cstate);
+    return;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Connection to `%s' succeeded!\n",
+       cstate->service_name);
+  /* trigger jobs that waited for the connection */
+  GNUNET_assert (NULL == cstate->sock);
+  cstate->sock = ap->sock;
+  GNUNET_free (ap);
+  cancel_aps (cstate);
+  connect_success_continuation (cstate);
+}
 
 
 /**
- * This task is run if we should re-try connection to the
- * service after a while.
+ * Try to establish a connection given the specified address.
+ * This function is called by the resolver once we have a DNS reply.
  *
- * @param cls our `struct GNUNET_CLIENT_TransmitHandle` of the request
- * @param tc unused
+ * @param cls our `struct ClientState *`
+ * @param addr address to try, NULL for "last call"
+ * @param addrlen length of @a addr
  */
 static void
-client_delayed_retry (void *cls,
-                     const struct GNUNET_SCHEDULER_TaskContext *tc)
+try_connect_using_address (void *cls,
+                           const struct sockaddr *addr,
+                           socklen_t addrlen)
 {
-  struct GNUNET_CLIENT_TransmitHandle *th = cls;
-  struct GNUNET_TIME_Relative delay;
+  struct ClientState *cstate = cls;
+  struct AddressProbe *ap;
 
-  th->reconnect_task = NULL;
-  if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
-  {
-    /* give up, was shutdown */
-    th->client->th = NULL;
-    th->notify (th->notify_cls, 0, NULL);
-    GNUNET_free (th);
-    return;
-  }
-  th->client->connection =
-    do_connect (th->client->service_name,
-               th->client->cfg,
-               th->client->attempts++);
-  th->client->first_message = GNUNET_YES;
-  if (NULL == th->client->connection)
+  if (NULL == addr)
   {
-    /* could happen if we're out of sockets */
-    delay = GNUNET_TIME_relative_min (GNUNET_TIME_absolute_get_remaining (th->timeout),
-                                      th->client->back_off);
-    th->client->back_off = GNUNET_TIME_STD_BACKOFF (th->client->back_off);
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Transmission failed %u times, trying again in %s.\n",
-         MAX_ATTEMPTS - th->attempts_left,
-         GNUNET_STRINGS_relative_time_to_string (delay, GNUNET_YES));
-    GNUNET_assert (NULL == th->reconnect_task);
-    th->reconnect_task =
-        GNUNET_SCHEDULER_add_delayed (delay, &client_delayed_retry, th);
+    cstate->dns_active = NULL;
+    if ( (NULL == cstate->ap_head) &&
+         //  (NULL == cstate->proxy_handshake) &&
+         (NULL == cstate->sock) )
+      connect_fail_continuation (cstate);
     return;
   }
-  th->th =
-      GNUNET_CONNECTION_notify_transmit_ready (th->client->connection, th->size,
-                                               GNUNET_TIME_absolute_get_remaining
-                                               (th->timeout), &client_notify,
-                                               th);
-  if (NULL == th->th)
-  {
+  if (NULL != cstate->sock)
+    return;                     /* already connected */
+  /* try to connect */
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Trying to connect using address `%s:%u'\n",
+       GNUNET_a2s (addr,
+                   addrlen),
+       cstate->port);
+  ap = GNUNET_malloc (sizeof (struct AddressProbe) + addrlen);
+  ap->addr = (const struct sockaddr *) &ap[1];
+  GNUNET_memcpy (&ap[1],
+                 addr,
+                 addrlen);
+  ap->addrlen = addrlen;
+  ap->cstate = cstate;
+
+  switch (ap->addr->sa_family)
+  {
+  case AF_INET:
+    ((struct sockaddr_in *) ap->addr)->sin_port = htons (cstate->port);
+    break;
+  case AF_INET6:
+    ((struct sockaddr_in6 *) ap->addr)->sin6_port = htons (cstate->port);
+    break;
+  default:
     GNUNET_break (0);
-    th->client->th = NULL;
-    th->notify (th->notify_cls, 0, NULL);
-    GNUNET_free (th);
+    GNUNET_free (ap);
+    return;                     /* not supported by us */
+  }
+  ap->sock = GNUNET_NETWORK_socket_create (ap->addr->sa_family,
+                                          SOCK_STREAM,
+                                           0);
+  if (NULL == ap->sock)
+  {
+    GNUNET_free (ap);
+    return;                     /* not supported by OS */
+  }
+  if ( (GNUNET_OK !=
+        GNUNET_NETWORK_socket_connect (ap->sock,
+                                       ap->addr,
+                                       ap->addrlen)) &&
+       (EINPROGRESS != errno) )
+  {
+    /* maybe refused / unsupported address, try next */
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_INFO,
+                         "connect");
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (ap->sock));
+    GNUNET_free (ap);
     return;
   }
+  GNUNET_CONTAINER_DLL_insert (cstate->ap_head,
+                               cstate->ap_tail,
+                               ap);
+  ap->task = GNUNET_SCHEDULER_add_write_net (GNUNET_CONNECTION_CONNECT_RETRY_TIMEOUT,
+                                            ap->sock,
+                                            &connect_probe_continuation,
+                                            ap);
 }
 
 
 /**
- * Connection notifies us about failure or success of a transmission
- * request.  Either pass it on to our user or, if possible, retry.
+ * Test whether the configuration has proper values for connection
+ * (UNIXPATH || (PORT && HOSTNAME)).
  *
- * @param cls our `struct GNUNET_CLIENT_TransmissionHandle`
- * @param size number of bytes available for transmission
- * @param buf where to write them
- * @return number of bytes written to @a buf
+ * @param service_name name of service to connect to
+ * @param cfg configuration to use
+ * @return #GNUNET_OK if the configuration is valid, #GNUNET_SYSERR if not
  */
-static size_t
-client_notify (void *cls, size_t size, void *buf)
+static int
+test_service_configuration (const char *service_name,
+                           const struct GNUNET_CONFIGURATION_Handle *cfg)
 {
-  struct GNUNET_CLIENT_TransmitHandle *th = cls;
-  struct GNUNET_CLIENT_Connection *client = th->client;
-  size_t ret;
-  struct GNUNET_TIME_Relative delay;
+  int ret = GNUNET_SYSERR;
+  char *hostname = NULL;
+  unsigned long long port;
+#if AF_UNIX
+  char *unixpath = NULL;
 
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "client_notify is running\n");
-  th->th = NULL;
-  client->th = NULL;
-  if (NULL == buf)
-  {
-    delay = GNUNET_TIME_absolute_get_remaining (th->timeout);
-    delay.rel_value_us /= 2;
-    if ((GNUNET_YES != th->auto_retry) || (0 == --th->attempts_left) ||
-        (delay.rel_value_us < 1)||
-       (0 != (GNUNET_SCHEDULER_get_reason() & GNUNET_SCHEDULER_REASON_SHUTDOWN)))
-    {
-      LOG (GNUNET_ERROR_TYPE_DEBUG,
-           "Transmission failed %u times, giving up.\n",
-           MAX_ATTEMPTS - th->attempts_left);
-      GNUNET_break (0 == th->notify (th->notify_cls, 0, NULL));
-      GNUNET_free (th);
-      return 0;
-    }
-    /* auto-retry */
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Failed to connect to `%s', automatically trying again.\n",
-         client->service_name);
-    if (GNUNET_YES == client->in_receive)
-    {
-      GNUNET_CONNECTION_receive_cancel (client->connection);
-      client->in_receive = GNUNET_NO;
-    }
-    GNUNET_CONNECTION_destroy (client->connection);
-    client->connection = NULL;
-    delay = GNUNET_TIME_relative_min (delay, client->back_off);
-    client->back_off =
-        GNUNET_TIME_relative_min (GNUNET_TIME_relative_multiply
-                                  (client->back_off, 2),
-                                  GNUNET_TIME_UNIT_SECONDS);
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Transmission failed %u times, trying again in %s.\n",
-         MAX_ATTEMPTS - th->attempts_left,
-         GNUNET_STRINGS_relative_time_to_string (delay, GNUNET_YES));
-    client->th = th;
-    GNUNET_assert (NULL == th->reconnect_task);
-    th->reconnect_task =
-        GNUNET_SCHEDULER_add_delayed (delay, &client_delayed_retry, th);
-    return 0;
-  }
-  GNUNET_assert (size >= th->size);
-  ret = th->notify (th->notify_cls, size, buf);
-  GNUNET_free (th);
-  if (sizeof (struct GNUNET_MessageHeader) <= ret)
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Transmitting message of type %u and size %u to %s service.\n",
-         ntohs (((struct GNUNET_MessageHeader *) buf)->type),
-         ntohs (((struct GNUNET_MessageHeader *) buf)->size),
-         client->service_name);
-  }
+  if ((GNUNET_OK ==
+       GNUNET_CONFIGURATION_get_value_filename (cfg,
+                                                service_name,
+                                                "UNIXPATH",
+                                                &unixpath)) &&
+      (0 < strlen (unixpath)))
+    ret = GNUNET_OK;
+  GNUNET_free_non_null (unixpath);
+#endif
+
+  if ( (GNUNET_YES ==
+       GNUNET_CONFIGURATION_have_value (cfg,
+                                         service_name,
+                                         "PORT")) &&
+       (GNUNET_OK ==
+       GNUNET_CONFIGURATION_get_value_number (cfg,
+                                               service_name,
+                                               "PORT",
+                                               &port)) &&
+       (port <= 65535) &&
+       (0 != port) &&
+       (GNUNET_OK ==
+       GNUNET_CONFIGURATION_get_value_string (cfg,
+                                               service_name,
+                                               "HOSTNAME",
+                                              &hostname)) &&
+       (0 != strlen (hostname)) )
+    ret = GNUNET_OK;
+  GNUNET_free_non_null (hostname);
   return ret;
 }
 
 
 /**
- * Ask the client to call us once the specified number of bytes
- * are free in the transmission buffer.  Will never call the @a notify
- * callback in this task, but always first go into the scheduler.
+ * Try to connect to the service.
  *
- * @param client connection to the service
- * @param size number of bytes to send
- * @param timeout after how long should we give up (and call
- *        notify with buf NULL and size 0)?
- * @param auto_retry if the connection to the service dies, should we
- *        automatically re-connect and retry (within the timeout period)
- *        or should we immediately fail in this case?  Pass GNUNET_YES
- *        if the caller does not care about temporary connection errors,
- *        for example because the protocol is stateless
- * @param notify function to call
- * @param notify_cls closure for @a notify
- * @return NULL if our buffer will never hold size bytes,
- *         a handle if the notify callback was queued (can be used to cancel)
+ * @param cls the `struct ClientState` to try to connect to the service
  */
-struct GNUNET_CLIENT_TransmitHandle *
-GNUNET_CLIENT_notify_transmit_ready (struct GNUNET_CLIENT_Connection *client,
-                                     size_t size,
-                                     struct GNUNET_TIME_Relative timeout,
-                                     int auto_retry,
-                                     GNUNET_CONNECTION_TransmitReadyNotify notify,
-                                    void *notify_cls)
+static void
+start_connect (void *cls)
 {
-  struct GNUNET_CLIENT_TransmitHandle *th;
+  struct ClientState *cstate = cls;
 
-  if (NULL != client->th)
+  cstate->retry_task = NULL;
+#if 0
+  /* Never use a local source if a proxy is configured */
+  if (GNUNET_YES ==
+      GNUNET_SOCKS_check_service (cstate->service_name,
+                                  cstate->cfg))
   {
-    /* If this breaks, you most likley called this function twice without waiting
-     * for completion or canceling the request */
-    GNUNET_break (0);
-    return NULL;
+    socks_connect (cstate);
+    return;
   }
-  th = GNUNET_new (struct GNUNET_CLIENT_TransmitHandle);
-  th->client = client;
-  th->size = size;
-  th->timeout = GNUNET_TIME_relative_to_absolute (timeout);
-  /* always auto-retry on first message to service */
-  th->auto_retry = (GNUNET_YES == client->first_message) ? GNUNET_YES : auto_retry;
-  client->first_message = GNUNET_NO;
-  th->notify = notify;
-  th->notify_cls = notify_cls;
-  th->attempts_left = MAX_ATTEMPTS;
-  client->th = th;
-  if (NULL == client->connection)
-  {
-    GNUNET_assert (NULL == th->reconnect_task);
-    th->reconnect_task =
-        GNUNET_SCHEDULER_add_delayed (client->back_off,
-                                      &client_delayed_retry,
-                                      th);
+#endif
 
-  }
-  else
+  if ( (0 == (cstate->attempts++ % 2)) ||
+       (0 == cstate->port) ||
+       (NULL == cstate->hostname) )
   {
-    th->th =
-        GNUNET_CONNECTION_notify_transmit_ready (client->connection, size, timeout,
-                                                 &client_notify, th);
-    if (NULL == th->th)
+    /* on even rounds, try UNIX first, or always
+       if we do not have a DNS name and TCP port. */
+    cstate->sock = try_unixpath (cstate->service_name,
+                                 cstate->cfg);
+    if (NULL != cstate->sock)
     {
-      GNUNET_break (0);
-      GNUNET_free (th);
-      client->th = NULL;
-      return NULL;
+      connect_success_continuation (cstate);
+      return;
     }
   }
-  return th;
+  if ( (NULL == cstate->hostname) ||
+       (0 == cstate->port) )
+  {
+    /* All options failed. Boo! */
+    connect_fail_continuation (cstate);
+    return;
+  }
+  cstate->dns_active
+    = GNUNET_RESOLVER_ip_get (cstate->hostname,
+                             AF_UNSPEC,
+                              GNUNET_CONNECTION_CONNECT_RETRY_TIMEOUT,
+                              &try_connect_using_address,
+                             cstate);
 }
 
 
 /**
- * Cancel a request for notification.
+ * Implements the transmission functionality of a message queue.
  *
- * @param th handle from the original request.
+ * @param mq the message queue
+ * @param msg the message to send
+ * @param impl_state our `struct ClientState`
  */
-void
-GNUNET_CLIENT_notify_transmit_ready_cancel (struct GNUNET_CLIENT_TransmitHandle *th)
+static void
+connection_client_send_impl (struct GNUNET_MQ_Handle *mq,
+                             const struct GNUNET_MessageHeader *msg,
+                             void *impl_state)
 {
-  if (NULL != th->reconnect_task)
-  {
-    GNUNET_assert (NULL == th->th);
-    GNUNET_SCHEDULER_cancel (th->reconnect_task);
-    th->reconnect_task = NULL;
-  }
-  else
-  {
-    GNUNET_assert (NULL != th->th);
-    GNUNET_CONNECTION_notify_transmit_ready_cancel (th->th);
-  }
-  th->client->th = NULL;
-  GNUNET_free (th);
+  struct ClientState *cstate = impl_state;
+
+  /* only one message at a time allowed */
+  GNUNET_assert (NULL == cstate->msg);
+  GNUNET_assert (NULL == cstate->send_task);
+  cstate->msg = msg;
+  cstate->msg_off = 0;
+  if (NULL == cstate->sock)
+    return; /* still waiting for connection */
+  cstate->send_task
+    = GNUNET_SCHEDULER_add_write_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                      cstate->sock,
+                                      &transmit_ready,
+                                      cstate);
 }
 
 
 /**
- * Function called to notify a client about the socket
- * begin ready to queue the message.  @a buf will be
- * NULL and @a size zero if the socket was closed for
- * writing in the meantime.
+ * Cancel the currently sent message.
  *
- * @param cls closure of type "struct TransmitGetResponseContext*"
- * @param size number of bytes available in @a buf
- * @param buf where the callee should write the message
- * @return number of bytes written to @a buf
+ * @param mq message queue
+ * @param impl_state our `struct ClientState`
  */
-static size_t
-transmit_for_response (void *cls,
-                      size_t size,
-                      void *buf)
+static void
+connection_client_cancel_impl (struct GNUNET_MQ_Handle *mq,
+                               void *impl_state)
 {
-  struct TransmitGetResponseContext *tc = cls;
-  uint16_t msize;
+  struct ClientState *cstate = impl_state;
 
-  tc->client->tag = NULL;
-  msize = ntohs (tc->hdr->size);
-  if (NULL == buf)
+  GNUNET_assert (NULL != cstate->msg);
+  GNUNET_assert (0 == cstate->msg_off);
+  cstate->msg = NULL;
+  if (NULL != cstate->send_task)
   {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         _("Could not submit request, not expecting to receive a response.\n"));
-    if (NULL != tc->rn)
-      tc->rn (tc->rn_cls, NULL);
-    GNUNET_free (tc);
-    return 0;
+    GNUNET_SCHEDULER_cancel (cstate->send_task);
+    cstate->send_task = NULL;
   }
-  GNUNET_assert (size >= msize);
-  memcpy (buf, tc->hdr, msize);
-  GNUNET_CLIENT_receive (tc->client, tc->rn, tc->rn_cls,
-                         GNUNET_TIME_absolute_get_remaining (tc->timeout));
-  GNUNET_free (tc);
-  return msize;
 }
 
 
 /**
- * Convenience API that combines sending a request
- * to the service and waiting for a response.
- * If either operation times out, the callback
- * will be called with a "NULL" response (in which
- * case the connection should probably be destroyed).
+ * Create a message queue to connect to a GNUnet service.
+ * If handlers are specfied, receive messages from the connection.
  *
- * @param client connection to use
- * @param hdr message to transmit
- * @param timeout when to give up (for both transmission
- *         and for waiting for a response)
- * @param auto_retry if the connection to the service dies, should we
- *        automatically re-connect and retry (within the timeout period)
- *        or should we immediately fail in this case?  Pass GNUNET_YES
- *        if the caller does not care about temporary connection errors,
- *        for example because the protocol is stateless
- * @param rn function to call with the response
- * @param rn_cls closure for @a rn
- * @return #GNUNET_OK on success, #GNUNET_SYSERR if a request
- *         is already pending
+ * @param cfg our configuration
+ * @param service_name name of the service to connect to
+ * @param handlers handlers for receiving messages, can be NULL
+ * @param error_handler error handler
+ * @param error_handler_cls closure for the @a error_handler
+ * @return the message queue, NULL on error
  */
-int
-GNUNET_CLIENT_transmit_and_get_response (struct GNUNET_CLIENT_Connection *client,
-                                         const struct GNUNET_MessageHeader *hdr,
-                                         struct GNUNET_TIME_Relative timeout,
-                                         int auto_retry,
-                                         GNUNET_CLIENT_MessageHandler rn,
-                                         void *rn_cls)
+struct GNUNET_MQ_Handle *
+GNUNET_CLIENT_connect (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                      const char *service_name,
+                      const struct GNUNET_MQ_MessageHandler *handlers,
+                      GNUNET_MQ_ErrorHandler error_handler,
+                      void *error_handler_cls)
 {
-  struct TransmitGetResponseContext *tc;
-  uint16_t msize;
+  struct ClientState *cstate;
 
-  if (NULL != client->th)
-    return GNUNET_SYSERR;
-  GNUNET_assert (NULL == client->tag);
-  msize = ntohs (hdr->size);
-  tc = GNUNET_malloc (sizeof (struct TransmitGetResponseContext) + msize);
-  tc->client = client;
-  tc->hdr = (const struct GNUNET_MessageHeader *) &tc[1];
-  memcpy (&tc[1], hdr, msize);
-  tc->timeout = GNUNET_TIME_relative_to_absolute (timeout);
-  tc->rn = rn;
-  tc->rn_cls = rn_cls;
-  if (NULL ==
-      GNUNET_CLIENT_notify_transmit_ready (client, msize, timeout, auto_retry,
-                                           &transmit_for_response, tc))
-  {
-    GNUNET_break (0);
-    GNUNET_free (tc);
-    return GNUNET_SYSERR;
+  if (GNUNET_OK !=
+      test_service_configuration (service_name,
+                                 cfg))
+    return NULL;
+  cstate = GNUNET_new (struct ClientState);
+  cstate->service_name = GNUNET_strdup (service_name);
+  cstate->cfg = cfg;
+  cstate->retry_task = GNUNET_SCHEDULER_add_now (&start_connect,
+                                                 cstate);
+  cstate->mst = GNUNET_MST_create (&recv_message,
+                                   cstate);
+  if (GNUNET_YES ==
+      GNUNET_CONFIGURATION_have_value (cfg,
+                                       service_name,
+                                       "PORT"))
+  {
+    if (! ( (GNUNET_OK !=
+            GNUNET_CONFIGURATION_get_value_number (cfg,
+                                                   service_name,
+                                                   "PORT",
+                                                   &cstate->port)) ||
+           (cstate->port > 65535) ||
+           (GNUNET_OK !=
+            GNUNET_CONFIGURATION_get_value_string (cfg,
+                                                   service_name,
+                                                   "HOSTNAME",
+                                                   &cstate->hostname)) ) &&
+       (0 == strlen (cstate->hostname)) )
+    {
+      GNUNET_free (cstate->hostname);
+      cstate->hostname = NULL;
+      LOG (GNUNET_ERROR_TYPE_WARNING,
+          _("Need a non-empty hostname for service `%s'.\n"),
+          service_name);
+    }
   }
-  client->tag = tc;
-  return GNUNET_OK;
+  cstate->mq = GNUNET_MQ_queue_for_callbacks (&connection_client_send_impl,
+                                             &connection_client_destroy_impl,
+                                             &connection_client_cancel_impl,
+                                             cstate,
+                                             handlers,
+                                             error_handler,
+                                             error_handler_cls);
+  return cstate->mq;
 }
 
-
-/*  end of client.c */
+/* end of client.c */