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[oweals/gnunet.git] / src / transport / plugin_transport_tcp.c

/*
  This file is part of GNUnet
  (C) 2002--2014 Christian Grothoff (and other contributing authors)

  GNUnet is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published
  by the Free Software Foundation; either version 3, or (at your
  option) any later version.

  GNUnet is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License for more details.

  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.
 */
/**
 * @file transport/plugin_transport_tcp.c
 * @brief Implementation of the TCP transport service
 * @author Christian Grothoff
 */
#include "platform.h"
#include "gnunet_hello_lib.h"
#include "gnunet_constants.h"
#include "gnunet_util_lib.h"
#include "gnunet_nat_lib.h"
#include "gnunet_protocols.h"
#include "gnunet_resolver_service.h"
#include "gnunet_signatures.h"
#include "gnunet_statistics_service.h"
#include "gnunet_transport_service.h"
#include "gnunet_transport_plugin.h"
#include "transport.h"

#define LOG(kind,...) GNUNET_log_from (kind, "transport-tcp",__VA_ARGS__)

#define PLUGIN_NAME "tcp"

/**
 * How long until we give up on establishing an NAT connection?
 * Must be > 4 RTT
 */
#define NAT_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 10)

GNUNET_NETWORK_STRUCT_BEGIN


/**
 * Initial handshake message for a session.
 */
struct WelcomeMessage
{
  /**
   * Type is #GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_WELCOME.
   */
  struct GNUNET_MessageHeader header;

  /**
   * Identity of the node connecting (TCP client)
   */
  struct GNUNET_PeerIdentity clientIdentity;

};

/**
 * Basically a WELCOME message, but with the purpose
 * of giving the waiting peer a client handle to use
 */
struct TCP_NAT_ProbeMessage
{
  /**
   * Type is #GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_NAT_PROBE.
   */
  struct GNUNET_MessageHeader header;

  /**
   * Identity of the sender of the message.
   */
  struct GNUNET_PeerIdentity clientIdentity;

};
GNUNET_NETWORK_STRUCT_END

/**
 * Context for sending a NAT probe via TCP.
 */
struct TCPProbeContext
{

  /**
   * Active probes are kept in a DLL.
   */
  struct TCPProbeContext *next;

  /**
   * Active probes are kept in a DLL.
   */
  struct TCPProbeContext *prev;

  /**
   * Probe connection.
   */
  struct GNUNET_CONNECTION_Handle *sock;

  /**
   * Message to be sent.
   */
  struct TCP_NAT_ProbeMessage message;

  /**
   * Handle to the transmission.
   */
  struct GNUNET_CONNECTION_TransmitHandle *transmit_handle;

  /**
   * Transport plugin handle.
   */
  struct Plugin *plugin;
};

GNUNET_NETWORK_STRUCT_BEGIN

/**
 * Network format for IPv4 addresses.
 */
struct IPv4TcpAddress
{
  /**
   * Optional options and flags for this address
   */
  uint32_t options;

  /**
   * IPv4 address, in network byte order.
   */
  uint32_t ipv4_addr GNUNET_PACKED;

  /**
   * Port number, in network byte order.
   */
  uint16_t t4_port GNUNET_PACKED;

};

/**
 * Network format for IPv6 addresses.
 */
struct IPv6TcpAddress
{
  /**
   * Optional flags for this address
   */
  uint32_t options;

  /**
   * IPv6 address.
   */
  struct in6_addr ipv6_addr GNUNET_PACKED;

  /**
   * Port number, in network byte order.
   */
  uint16_t t6_port GNUNET_PACKED;

};
GNUNET_NETWORK_STRUCT_END

/**
 * Encapsulation of all of the state of the plugin.
 */
struct Plugin;

/**
 * Information kept for each message that is yet to
 * be transmitted.
 */
struct PendingMessage
{

  /**
   * This is a doubly-linked list.
   */
  struct PendingMessage *next;

  /**
   * This is a doubly-linked list.
   */
  struct PendingMessage *prev;

  /**
   * The pending message
   */
  const char *msg;

  /**
   * Continuation function to call once the message
   * has been sent.  Can be NULL if there is no
   * continuation to call.
   */
  GNUNET_TRANSPORT_TransmitContinuation transmit_cont;

  /**
   * Closure for transmit_cont.
   */
  void *transmit_cont_cls;

  /**
   * Timeout value for the pending message.
   */
  struct GNUNET_TIME_Absolute timeout;

  /**
   * So that the gnunet-service-transport can group messages together,
   * these pending messages need to accept a message buffer and size
   * instead of just a GNUNET_MessageHeader.
   */
  size_t message_size;

};

/**
 * Session handle for TCP connections.
 */
struct Session
{
  /**
   * To whom are we talking to (set to our identity
   * if we are still waiting for the welcome message)
   */
  struct GNUNET_PeerIdentity target;

  /**
   * Pointer to the global plugin struct.
   */
  struct Plugin *plugin;

  /**
   * The client (used to identify this connection)
   */
  struct GNUNET_SERVER_Client *client;

  /**
   * Task cleaning up a NAT client connection establishment attempt;
   */
  GNUNET_SCHEDULER_TaskIdentifier nat_connection_timeout;

  /**
   * Messages currently pending for transmission
   * to this peer, if any.
   */
  struct PendingMessage *pending_messages_head;

  /**
   * Messages currently pending for transmission
   * to this peer, if any.
   */
  struct PendingMessage *pending_messages_tail;

  /**
   * Handle for pending transmission request.
   */
  struct GNUNET_SERVER_TransmitHandle *transmit_handle;

  /**
   * Address of the other peer.
   */
  struct GNUNET_HELLO_Address *address;

  /**
   * ID of task used to delay receiving more to throttle sender.
   */
  GNUNET_SCHEDULER_TaskIdentifier receive_delay_task;

  /**
   * Session timeout task
   */
  GNUNET_SCHEDULER_TaskIdentifier timeout_task;

  /**
   * When will this session time out?
   */
  struct GNUNET_TIME_Absolute timeout;

  /**
   * When will we continue to read from the socket?
   * (used to enforce inbound quota).
   */
  struct GNUNET_TIME_Absolute receive_delay;

  /**
   * Last activity on this connection.  Used to select preferred
   * connection.
   */
  struct GNUNET_TIME_Absolute last_activity;

  /**
   * Number of bytes waiting for transmission to this peer.
   */
  unsigned long long bytes_in_queue;

  /**
   * Number of messages waiting for transmission to this peer.
   */
  unsigned int msgs_in_queue;

  /**
   * Are we still expecting the welcome message? (#GNUNET_YES/#GNUNET_NO)
   */
  int expecting_welcome;

  /**
   * Was this session created using NAT traversal?
   */
  int is_nat;

  /**
   * ATS network type in NBO
   */
  enum GNUNET_ATS_Network_Type ats_address_network_type;
};

/**
 * Encapsulation of all of the state of the plugin.
 */
struct Plugin
{
  /**
   * Our environment.
   */
  struct GNUNET_TRANSPORT_PluginEnvironment *env;

  /**
   * The listen socket.
   */
  struct GNUNET_CONNECTION_Handle *lsock;

  /**
   * Our handle to the NAT module.
   */
  struct GNUNET_NAT_Handle *nat;

  /**
   * Map from peer identities to sessions for the given peer.
   */
  struct GNUNET_CONTAINER_MultiPeerMap *sessionmap;

  /**
   * Handle to the network service.
   */
  struct GNUNET_SERVICE_Context *service;

  /**
   * Handle to the server for this service.
   */
  struct GNUNET_SERVER_Handle *server;

  /**
   * Copy of the handler array where the closures are
   * set to this struct's instance.
   */
  struct GNUNET_SERVER_MessageHandler *handlers;

  /**
   * Map of peers we have tried to contact behind a NAT
   */
  struct GNUNET_CONTAINER_MultiPeerMap *nat_wait_conns;

  /**
   * List of active TCP probes.
   */
  struct TCPProbeContext *probe_head;

  /**
   * List of active TCP probes.
   */
  struct TCPProbeContext *probe_tail;

  /**
   * Handle for (DYN)DNS lookup of our external IP.
   */
  struct GNUNET_RESOLVER_RequestHandle *ext_dns;

  /**
   * Function to call about session status changes.
   */
  GNUNET_TRANSPORT_SessionInfoCallback sic;

  /**
   * Closure for @e sic.
   */
  void *sic_cls;

  /**
   * How many more TCP sessions are we allowed to open right now?
   */
  unsigned long long max_connections;

  /**
   * How many more TCP sessions do we have right now?
   */
  unsigned long long cur_connections;

  /**
   * ID of task used to update our addresses when one expires.
   */
  GNUNET_SCHEDULER_TaskIdentifier address_update_task;

  /**
   * Address options
   */
  uint32_t myoptions;

  /**
   * Port that we are actually listening on.
   */
  uint16_t open_port;

  /**
   * Port that the user said we would have visible to the
   * rest of the world.
   */
  uint16_t adv_port;

};


/**
 * If a session monitor is attached, notify it about the new
 * session state.
 *
 * @param plugin our plugin
 * @param session session that changed state
 * @param state new state of the session
 */
static void
notify_session_monitor (struct Plugin *plugin,
                        struct Session *session,
                        enum GNUNET_TRANSPORT_SessionState state)
{
  struct GNUNET_TRANSPORT_SessionInfo info;

  if (NULL == plugin->sic)
    return;
  memset (&info, 0, sizeof (info));
  info.state = state;
  info.is_inbound = GNUNET_SYSERR; /* hard to say */
  info.num_msg_pending = session->msgs_in_queue;
  info.num_bytes_pending = session->bytes_in_queue;
  if (GNUNET_SCHEDULER_NO_TASK != session->receive_delay_task)
    info.receive_delay = session->receive_delay;
  info.session_timeout = session->timeout;
  info.address = session->address;
  plugin->sic (plugin->sic_cls,
               session,
               &info);
}


/**
 * Function called for a quick conversion of the binary address to
 * a numeric address.  Note that the caller must not free the
 * address and that the next call to this function is allowed
 * to override the address again.
 *
 * @param cls closure ('struct Plugin*')
 * @param addr binary address
 * @param addrlen length of the address
 * @return string representing the same address
 */
static const char *
tcp_plugin_address_to_string (void *cls,
                              const void *addr,
                              size_t addrlen);


/**
 * Function to check if an inbound connection is acceptable.
 * Mostly used to limit the total number of open connections
 * we can have.
 *
 * @param cls the `struct Plugin`
 * @param ucred credentials, if available, otherwise NULL
 * @param addr address
 * @param addrlen length of address
 * @return #GNUNET_YES to allow, #GNUNET_NO to deny, #GNUNET_SYSERR
 *   for unknown address family (will be denied).
 */
static int
plugin_tcp_access_check (void *cls,
                         const struct GNUNET_CONNECTION_Credentials *ucred,
                         const struct sockaddr *addr,
                         socklen_t addrlen)
{
  struct Plugin *plugin = cls;

  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Accepting new incoming TCP connection from `%s'\n",
       GNUNET_a2s (addr, addrlen));
  if (plugin->cur_connections >= plugin->max_connections)
    return GNUNET_NO;
  plugin->cur_connections++;
  return GNUNET_YES;
}


/**
 * Our external IP address/port mapping has changed.
 *
 * @param cls closure, the `struct Plugin`
 * @param add_remove #GNUNET_YES to mean the new public IP address, #GNUNET_NO to mean
 *     the previous (now invalid) one
 * @param addr either the previous or the new public IP address
 * @param addrlen actual length of @a addr
 */
static void
tcp_nat_port_map_callback (void *cls,
                           int add_remove,
                           const struct sockaddr *addr,
                           socklen_t addrlen)
{
  struct Plugin *plugin = cls;
  struct GNUNET_HELLO_Address *address;
  struct IPv4TcpAddress t4;
  struct IPv6TcpAddress t6;
  void *arg;
  size_t args;

  LOG(GNUNET_ERROR_TYPE_INFO, "NAT notification to %s address `%s'\n",
      (GNUNET_YES == add_remove) ? "add" : "remove",
      GNUNET_a2s (addr, addrlen));
  /* convert 'addr' to our internal format */
  switch (addr->sa_family)
  {
  case AF_INET:
    GNUNET_assert(addrlen == sizeof(struct sockaddr_in));
    memset (&t4, 0, sizeof(t4));
    t4.options = htonl (plugin->myoptions);
    t4.ipv4_addr = ((struct sockaddr_in *) addr)->sin_addr.s_addr;
    t4.t4_port = ((struct sockaddr_in *) addr)->sin_port;
    arg = &t4;
    args = sizeof (t4);
    break;
  case AF_INET6:
    GNUNET_assert(addrlen == sizeof(struct sockaddr_in6));
    memset (&t6, 0, sizeof(t6));
    memcpy (&t6.ipv6_addr, &((struct sockaddr_in6 *) addr)->sin6_addr,
        sizeof(struct in6_addr));
    t6.options = htonl (plugin->myoptions);
    t6.t6_port = ((struct sockaddr_in6 *) addr)->sin6_port;
    arg = &t6;
    args = sizeof (t6);
    break;
  default:
    GNUNET_break(0);
    return;
  }
  /* modify our published address list */
  GNUNET_assert ((args == sizeof (struct IPv4TcpAddress)) ||
      (args == sizeof (struct IPv6TcpAddress)));
  address = GNUNET_HELLO_address_allocate (plugin->env->my_identity,
      PLUGIN_NAME, arg, args, GNUNET_HELLO_ADDRESS_INFO_NONE);
  plugin->env->notify_address (plugin->env->cls, add_remove, address);
  GNUNET_HELLO_address_free(address);
}


/**
 * Function called for a quick conversion of the binary address to
 * a numeric address.  Note that the caller must not free the
 * address and that the next call to this function is allowed
 * to override the address again.
 *
 * @param cls closure (`struct Plugin*`)
 * @param addr binary address
 * @param addrlen length of @a addr
 * @return string representing the same address
 */
static const char *
tcp_plugin_address_to_string (void *cls,
                       const void *addr,
                       size_t addrlen)
{
  static char rbuf[INET6_ADDRSTRLEN + 12];
  char buf[INET6_ADDRSTRLEN];
  const void *sb;
  struct in_addr a4;
  struct in6_addr a6;
  const struct IPv4TcpAddress *t4;
  const struct IPv6TcpAddress *t6;
  int af;
  uint16_t port;
  uint32_t options;

  switch (addrlen)
  {
  case sizeof(struct IPv6TcpAddress):
    t6 = addr;
    af = AF_INET6;
    port = ntohs (t6->t6_port);
    options = ntohl (t6->options);
    memcpy (&a6, &t6->ipv6_addr, sizeof(a6));
    sb = &a6;
    break;
  case sizeof(struct IPv4TcpAddress):
    t4 = addr;
    af = AF_INET;
    port = ntohs (t4->t4_port);
    options = ntohl (t4->options);
    memcpy (&a4, &t4->ipv4_addr, sizeof(a4));
    sb = &a4;
    break;
  default:
    LOG (GNUNET_ERROR_TYPE_WARNING,
         _("Unexpected address length: %u bytes\n"),
         (unsigned int) addrlen);
    return NULL ;
  }
  if (NULL == inet_ntop (af, sb, buf, INET6_ADDRSTRLEN))
  {
    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
                         "inet_ntop");
    return NULL ;
  }
  GNUNET_snprintf (rbuf, sizeof(rbuf),
                   (af == AF_INET6) ? "%s.%u.[%s]:%u" : "%s.%u.%s:%u",
                   PLUGIN_NAME,
                   options,
                   buf,
                   port);
  return rbuf;
}


/**
 * Function called to convert a string address to
 * a binary address.
 *
 * @param cls closure (`struct Plugin*`)
 * @param addr string address
 * @param addrlen length of the address
 * @param buf location to store the buffer
 * @param added location to store the number of bytes in the buffer.
 *        If the function returns #GNUNET_SYSERR, its contents are undefined.
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
 */
static int
tcp_plugin_string_to_address (void *cls,
                              const char *addr,
                              uint16_t addrlen,
                              void **buf,
                              size_t *added)
{
  struct sockaddr_storage socket_address;
  char *address;
  char *plugin;
  char *optionstr;
  uint32_t options;

  /* Format tcp.options.address:port */
  address = NULL;
  plugin = NULL;
  optionstr = NULL;
  if ((NULL == addr) || (addrlen == 0))
  {
    GNUNET_break(0);
    return GNUNET_SYSERR;
  }
  if ('\0' != addr[addrlen - 1])
  {
    GNUNET_break(0);
    return GNUNET_SYSERR;
  }
  if (strlen (addr) != addrlen - 1)
  {
    GNUNET_break(0);
    return GNUNET_SYSERR;
  }
  plugin = GNUNET_strdup (addr);
  optionstr = strchr (plugin, '.');
  if (NULL == optionstr)
  {
    GNUNET_break(0);
    GNUNET_free(plugin);
    return GNUNET_SYSERR;
  }
  optionstr[0] = '\0';
  optionstr++;
  options = atol (optionstr);
  address = strchr (optionstr, '.');
  if (NULL == address)
  {
    GNUNET_break(0);
    GNUNET_free(plugin);
    return GNUNET_SYSERR;
  }
  address[0] = '\0';
  address++;

  if (GNUNET_OK
      != GNUNET_STRINGS_to_address_ip (address, strlen (address),
          &socket_address))
  {
    GNUNET_break(0);
    GNUNET_free(plugin);
    return GNUNET_SYSERR;
  }

  GNUNET_free(plugin);
  switch (socket_address.ss_family)
  {
  case AF_INET:
  {
    struct IPv4TcpAddress *t4;
    struct sockaddr_in *in4 = (struct sockaddr_in *) &socket_address;
    t4 = GNUNET_new (struct IPv4TcpAddress);
    t4->options = htonl (options);
    t4->ipv4_addr = in4->sin_addr.s_addr;
    t4->t4_port = in4->sin_port;
    *buf = t4;
    *added = sizeof(struct IPv4TcpAddress);
    return GNUNET_OK;
  }
  case AF_INET6:
  {
    struct IPv6TcpAddress *t6;
    struct sockaddr_in6 *in6 = (struct sockaddr_in6 *) &socket_address;
    t6 = GNUNET_new (struct IPv6TcpAddress);
    t6->options = htonl (options);
    t6->ipv6_addr = in6->sin6_addr;
    t6->t6_port = in6->sin6_port;
    *buf = t6;
    *added = sizeof(struct IPv6TcpAddress);
    return GNUNET_OK;
  }
  default:
    return GNUNET_SYSERR;
  }
}


/**
 * Find the session handle for the given client.
 * Currently uses both the hashmap and the client
 * context, as the client context is new and the
 * logic still needs to be tested.
 *
 * @param plugin the plugin
 * @param client which client to find the session handle for
 * @return NULL if no matching session exists
 */
static struct Session *
lookup_session_by_client (struct Plugin *plugin,
                          struct GNUNET_SERVER_Client *client)
{
  return GNUNET_SERVER_client_get_user_context (client, struct Session);
}


/**
 * Functions with this signature are called whenever we need
 * to close a session due to a disconnect or failure to
 * establish a connection.
 *
 * @param cls the `struct Plugin`
 * @param session session to close down
 * @return #GNUNET_OK on success
 */
static int
tcp_plugin_disconnect_session (void *cls,
                               struct Session *session)
{
  struct Plugin *plugin = cls;
  struct PendingMessage *pm;

  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Disconnecting session of peer `%s' address `%s'\n",
       GNUNET_i2s (&session->target),
       tcp_plugin_address_to_string (NULL,
                             session->address->address,
                             session->address->address_length));

  if (GNUNET_SCHEDULER_NO_TASK != session->timeout_task)
  {
    GNUNET_SCHEDULER_cancel (session->timeout_task);
    session->timeout_task = GNUNET_SCHEDULER_NO_TASK;
    session->timeout = GNUNET_TIME_UNIT_ZERO_ABS;
  }

  if (GNUNET_YES ==
      GNUNET_CONTAINER_multipeermap_remove (plugin->sessionmap,
                                            &session->target,
                                            session))
  {
    GNUNET_STATISTICS_update (session->plugin->env->stats,
        gettext_noop ("# TCP sessions active"), -1, GNUNET_NO);
  }
  else
  {
    GNUNET_assert(GNUNET_YES ==
                  GNUNET_CONTAINER_multipeermap_remove (plugin->nat_wait_conns,
                                                        &session->target,
                                                        session));
  }
  if (NULL != session->client)
    GNUNET_SERVER_client_set_user_context (session->client,
                                           (void *) NULL);

  /* clean up state */
  if (NULL != session->transmit_handle)
  {
    GNUNET_SERVER_notify_transmit_ready_cancel (session->transmit_handle);
    session->transmit_handle = NULL;
  }
  plugin->env->unregister_quota_notification (plugin->env->cls,
                                              &session->target,
                                              PLUGIN_NAME,
                                              session);
  session->plugin->env->session_end (session->plugin->env->cls,
                                     session->address,
                                     session);

  if (GNUNET_SCHEDULER_NO_TASK != session->nat_connection_timeout)
  {
    GNUNET_SCHEDULER_cancel (session->nat_connection_timeout);
    session->nat_connection_timeout = GNUNET_SCHEDULER_NO_TASK;
  }

  while (NULL != (pm = session->pending_messages_head))
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         (NULL != pm->transmit_cont)
         ? "Could not deliver message to `%4s'.\n"
         : "Could not deliver message to `%4s', notifying.\n",
         GNUNET_i2s (&session->target));
    GNUNET_STATISTICS_update (session->plugin->env->stats,
                              gettext_noop ("# bytes currently in TCP buffers"),
                              -(int64_t) pm->message_size, GNUNET_NO);
    GNUNET_STATISTICS_update (session->plugin->env->stats,
                              gettext_noop ("# bytes discarded by TCP (disconnect)"),
                              pm->message_size,
                              GNUNET_NO);
    GNUNET_CONTAINER_DLL_remove (session->pending_messages_head,
                                 session->pending_messages_tail,
                                 pm);
    GNUNET_assert (0 < session->msgs_in_queue);
    session->msgs_in_queue--;
    GNUNET_assert (pm->message_size <= session->bytes_in_queue);
    session->bytes_in_queue -= pm->message_size;
    if (NULL != pm->transmit_cont)
      pm->transmit_cont (pm->transmit_cont_cls,
                         &session->target,
                         GNUNET_SYSERR,
                         pm->message_size,
                         0);
    GNUNET_free (pm);
  }
  GNUNET_assert (0 == session->msgs_in_queue);
  GNUNET_assert (0 == session->bytes_in_queue);
  notify_session_monitor (session->plugin,
                          session,
                          GNUNET_TRANSPORT_SS_UP);

  if (session->receive_delay_task != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (session->receive_delay_task);
    if (NULL != session->client)
      GNUNET_SERVER_receive_done (session->client, GNUNET_SYSERR);
  }
  if (NULL != session->client)
  {
    GNUNET_SERVER_client_disconnect (session->client);
    GNUNET_SERVER_client_drop (session->client);
    session->client = NULL;
  }
  GNUNET_HELLO_address_free (session->address);
  GNUNET_assert(NULL == session->transmit_handle);
  GNUNET_free(session);
  return GNUNET_OK;
}


/**
 * Function that is called to get the keepalive factor.
 * #GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT is divided by this number to
 * calculate the interval between keepalive packets.
 *
 * @param cls closure with the `struct Plugin`
 * @return keepalive factor
 */
static unsigned int
tcp_plugin_query_keepalive_factor (void *cls)
{
  return 3;
}


/**
 * Session was idle, so disconnect it
 *
 * @param cls the `struct Session` of the idle session
 * @param tc scheduler context
 */
static void
session_timeout (void *cls,
                 const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Session *s = cls;
  struct GNUNET_TIME_Relative left;

  s->timeout_task = GNUNET_SCHEDULER_NO_TASK;
  left = GNUNET_TIME_absolute_get_remaining (s->timeout);
  if (0 != left.rel_value_us)
  {
    /* not actually our turn yet, but let's at least update
       the monitor, it may think we're about to die ... */
    notify_session_monitor (s->plugin,
                            s,
                            GNUNET_TRANSPORT_SS_UP);
    s->timeout_task = GNUNET_SCHEDULER_add_delayed (left,
                                                    &session_timeout,
                                                    s);
    return;
  }
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Session %p was idle for %s, disconnecting\n",
       s,
       GNUNET_STRINGS_relative_time_to_string (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
                                               GNUNET_YES));
  /* call session destroy function */
  tcp_plugin_disconnect_session (s->plugin, s);
}


/**
 * Increment session timeout due to activity
 *
 * @param s session to increment timeout for
 */
static void
reschedule_session_timeout (struct Session *s)
{
  GNUNET_assert(GNUNET_SCHEDULER_NO_TASK != s->timeout_task);
  s->timeout = GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
}


/**
 * Create a new session.  Also queues a welcome message.
 *
 * @param plugin the plugin
 * @param address the address to create the session for
 * @param client client to use, reference counter must have already been increased
 * @param is_nat this a NAT session, we should wait for a client to
 *               connect to us from an address, then assign that to
 *               the session
 * @return new session object
 */
static struct Session *
create_session (struct Plugin *plugin,
                const struct GNUNET_HELLO_Address *address,
                struct GNUNET_SERVER_Client *client,
                int is_nat)
{
  struct Session *session;
  struct PendingMessage *pm;
  struct WelcomeMessage welcome;

  if (GNUNET_YES != is_nat)
    GNUNET_assert (NULL != client);
  else
    GNUNET_assert (NULL == client);

  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Creating new session for peer `%4s'\n",
       GNUNET_i2s (&address->peer));
  session = GNUNET_new (struct Session);
  session->last_activity = GNUNET_TIME_absolute_get ();
  session->plugin = plugin;
  session->is_nat = is_nat;
  session->client = client;
  session->address = GNUNET_HELLO_address_copy (address);
  session->target = address->peer;
  session->expecting_welcome = GNUNET_YES;
  session->ats_address_network_type = GNUNET_ATS_NET_UNSPECIFIED;
  pm = GNUNET_malloc (sizeof (struct PendingMessage) +
      sizeof (struct WelcomeMessage));
  pm->msg = (const char *) &pm[1];
  pm->message_size = sizeof(struct WelcomeMessage);
  welcome.header.size = htons (sizeof(struct WelcomeMessage));
  welcome.header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_WELCOME);
  welcome.clientIdentity = *plugin->env->my_identity;
  memcpy (&pm[1], &welcome, sizeof(welcome));
  pm->timeout = GNUNET_TIME_UNIT_FOREVER_ABS;
  GNUNET_STATISTICS_update (plugin->env->stats,
      gettext_noop ("# bytes currently in TCP buffers"), pm->message_size,
      GNUNET_NO);
  GNUNET_CONTAINER_DLL_insert (session->pending_messages_head,
                               session->pending_messages_tail,
                               pm);
  session->msgs_in_queue++;
  session->bytes_in_queue += pm->message_size;
  session->timeout = GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  session->timeout_task = GNUNET_SCHEDULER_add_delayed (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
                                                        &session_timeout,
                                                        session);
  if (GNUNET_YES != is_nat)
  {
    GNUNET_STATISTICS_update (plugin->env->stats,
                              gettext_noop ("# TCP sessions active"),
                              1,
                              GNUNET_NO);
    notify_session_monitor (session->plugin,
                            session,
                            GNUNET_TRANSPORT_SS_UP);
  }
  else
  {
    notify_session_monitor (session->plugin,
                            session,
                            GNUNET_TRANSPORT_SS_HANDSHAKE);
  }
  plugin->env->register_quota_notification (plugin->env->cls,
                                            &address->peer,
                                            PLUGIN_NAME,
                                            session);
  return session;
}


/**
 * If we have pending messages, ask the server to
 * transmit them (schedule the respective tasks, etc.)
 *
 * @param session for which session should we do this
 */
static void
process_pending_messages (struct Session *session);


/**
 * Function called to notify a client about the socket
 * being ready to queue more data.  "buf" will be
 * NULL and "size" zero if the socket was closed for
 * writing in the meantime.
 *
 * @param cls closure
 * @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
 */
static size_t
do_transmit (void *cls, size_t size, void *buf)
{
  struct Session *session = cls;
  struct GNUNET_PeerIdentity pid;
  struct Plugin *plugin;
  struct PendingMessage *pos;
  struct PendingMessage *hd;
  struct PendingMessage *tl;
  struct GNUNET_TIME_Absolute now;
  char *cbuf;
  size_t ret;

  session->transmit_handle = NULL;
  plugin = session->plugin;
  if (NULL == buf)
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Timeout trying to transmit to peer `%4s', discarding message queue.\n",
         GNUNET_i2s (&session->target));
    /* timeout; cancel all messages that have already expired */
    hd = NULL;
    tl = NULL;
    ret = 0;
    now = GNUNET_TIME_absolute_get ();
    while ((NULL != (pos = session->pending_messages_head))
        && (pos->timeout.abs_value_us <= now.abs_value_us))
    {
      GNUNET_CONTAINER_DLL_remove (session->pending_messages_head,
                                   session->pending_messages_tail,
                                   pos);
      GNUNET_assert (0 < session->msgs_in_queue);
      session->msgs_in_queue--;
      GNUNET_assert (pos->message_size <= session->bytes_in_queue);
      session->bytes_in_queue -= pos->message_size;
      LOG (GNUNET_ERROR_TYPE_DEBUG,
           "Failed to transmit %u byte message to `%4s'.\n",
           pos->message_size,
           GNUNET_i2s (&session->target));
      ret += pos->message_size;
      GNUNET_CONTAINER_DLL_insert_after (hd, tl, tl, pos);
    }
    /* do this call before callbacks (so that if callbacks destroy
     * session, they have a chance to cancel actions done by this
     * call) */
    process_pending_messages (session);
    pid = session->target;
    /* no do callbacks and do not use session again since
     * the callbacks may abort the session */
    while (NULL != (pos = hd))
    {
      GNUNET_CONTAINER_DLL_remove (hd, tl, pos);
      if (pos->transmit_cont != NULL)
        pos->transmit_cont (pos->transmit_cont_cls,
                            &pid,
                            GNUNET_SYSERR,
                            pos->message_size, 0);
      GNUNET_free (pos);
    }
    GNUNET_STATISTICS_update (plugin->env->stats,
                              gettext_noop ("# bytes currently in TCP buffers"), -(int64_t) ret,
                              GNUNET_NO);
    GNUNET_STATISTICS_update (plugin->env->stats,
                              gettext_noop ("# bytes discarded by TCP (timeout)"),
                              ret,
                              GNUNET_NO);
    if (0 < ret)
      notify_session_monitor (session->plugin,
                              session,
                              GNUNET_TRANSPORT_SS_UP);
    return 0;
  }
  /* copy all pending messages that would fit */
  ret = 0;
  cbuf = buf;
  hd = NULL;
  tl = NULL;
  while (NULL != (pos = session->pending_messages_head))
  {
    if (ret + pos->message_size > size)
      break;
    GNUNET_CONTAINER_DLL_remove (session->pending_messages_head,
                                 session->pending_messages_tail,
                                 pos);
    GNUNET_assert (0 < session->msgs_in_queue);
    session->msgs_in_queue--;
    GNUNET_assert (pos->message_size <= session->bytes_in_queue);
    session->bytes_in_queue -= pos->message_size;
    GNUNET_assert(size >= pos->message_size);
    LOG(GNUNET_ERROR_TYPE_DEBUG,
        "Transmitting message of type %u size %u\n",
        ntohs (((struct GNUNET_MessageHeader *) pos->msg)->type),
        pos->message_size);
    /* FIXME: this memcpy can be up to 7% of our total runtime */
    memcpy (cbuf, pos->msg, pos->message_size);
    cbuf += pos->message_size;
    ret += pos->message_size;
    size -= pos->message_size;
    GNUNET_CONTAINER_DLL_insert_tail (hd, tl, pos);
  }
  notify_session_monitor (session->plugin,
                          session,
                          GNUNET_TRANSPORT_SS_UP);
  /* schedule 'continuation' before callbacks so that callbacks that
   * cancel everything don't cause us to use a session that no longer
   * exists... */
  process_pending_messages (session);
  session->last_activity = GNUNET_TIME_absolute_get ();
  pid = session->target;
  /* we'll now call callbacks that may cancel the session; hence
   * we should not use 'session' after this point */
  while (NULL != (pos = hd))
  {
    GNUNET_CONTAINER_DLL_remove (hd, tl, pos);
    if (pos->transmit_cont != NULL)
      pos->transmit_cont (pos->transmit_cont_cls,
                          &pid,
                          GNUNET_OK,
                          pos->message_size,
                          pos->message_size); /* FIXME: include TCP overhead */
    GNUNET_free(pos);
  }
  GNUNET_assert (NULL == hd);
  GNUNET_assert (NULL == tl);
  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Transmitting %u bytes\n",
      ret);
  GNUNET_STATISTICS_update (plugin->env->stats,
                            gettext_noop ("# bytes currently in TCP buffers"),
                            - (int64_t) ret,
                            GNUNET_NO);
  GNUNET_STATISTICS_update (plugin->env->stats,
                            gettext_noop ("# bytes transmitted via TCP"),
                            ret,
                            GNUNET_NO);
  return ret;
}


/**
 * If we have pending messages, ask the server to
 * transmit them (schedule the respective tasks, etc.)
 *
 * @param session for which session should we do this
 */
static void
process_pending_messages (struct Session *session)
{
  struct PendingMessage *pm;

  GNUNET_assert (NULL != session->client);
  if (NULL != session->transmit_handle)
    return;
  if (NULL == (pm = session->pending_messages_head))
    return;

  session->transmit_handle = GNUNET_SERVER_notify_transmit_ready (session->client,
                                                                  pm->message_size,
                                                                  GNUNET_TIME_absolute_get_remaining (pm->timeout),
                                                                  &do_transmit,
                                                                  session);
}


/**
 * Function that can be used by the transport service to transmit
 * a message using the plugin.   Note that in the case of a
 * peer disconnecting, the continuation MUST be called
 * prior to the disconnect notification itself.  This function
 * will be called with this peer's HELLO message to initiate
 * a fresh connection to another peer.
 *
 * @param cls closure
 * @param session which session must be used
 * @param msgbuf the message to transmit
 * @param msgbuf_size number of bytes in 'msgbuf'
 * @param priority how important is the message (most plugins will
 *                 ignore message priority and just FIFO)
 * @param to how long to wait at most for the transmission (does not
 *                require plugins to discard the message after the timeout,
 *                just advisory for the desired delay; most plugins will ignore
 *                this as well)
 * @param cont continuation to call once the message has
 *        been transmitted (or if the transport is ready
 *        for the next transmission call; or if the
 *        peer disconnected...); can be NULL
 * @param cont_cls closure for @a cont
 * @return number of bytes used (on the physical network, with overheads);
 *         -1 on hard errors (i.e. address invalid); 0 is a legal value
 *         and does NOT mean that the message was not transmitted (DV)
 */
static ssize_t
tcp_plugin_send (void *cls,
                 struct Session *session,
                 const char *msgbuf,
                 size_t msgbuf_size,
                 unsigned int priority,
                 struct GNUNET_TIME_Relative to,
                 GNUNET_TRANSPORT_TransmitContinuation cont,
                 void *cont_cls)
{
  struct Plugin * plugin = cls;
  struct PendingMessage *pm;

  /* create new message entry */
  pm = GNUNET_malloc (sizeof (struct PendingMessage) + msgbuf_size);
  pm->msg = (const char *) &pm[1];
  memcpy (&pm[1], msgbuf, msgbuf_size);
  pm->message_size = msgbuf_size;
  pm->timeout = GNUNET_TIME_relative_to_absolute (to);
  pm->transmit_cont = cont;
  pm->transmit_cont_cls = cont_cls;

  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Asked to transmit %u bytes to `%s', added message to list.\n",
      msgbuf_size, GNUNET_i2s (&session->target));

  if (GNUNET_YES ==
      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessionmap,
                                                    &session->target,
                                                    session))
  {
    GNUNET_assert (NULL != session->client);
    GNUNET_SERVER_client_set_timeout (session->client,
        GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
    GNUNET_STATISTICS_update (plugin->env->stats,
        gettext_noop ("# bytes currently in TCP buffers"), msgbuf_size,
        GNUNET_NO);

    /* append pm to pending_messages list */
    GNUNET_CONTAINER_DLL_insert_tail (session->pending_messages_head,
                                      session->pending_messages_tail,
                                      pm);
    notify_session_monitor (session->plugin,
                            session,
                            GNUNET_TRANSPORT_SS_UP);
    session->msgs_in_queue++;
    session->bytes_in_queue += pm->message_size;
    process_pending_messages (session);
    return msgbuf_size;
  }
  else if (GNUNET_YES ==
           GNUNET_CONTAINER_multipeermap_contains_value (plugin->nat_wait_conns,
                                                         &session->target,
                                                         session))
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "This NAT WAIT session for peer `%s' is not yet ready!\n",
         GNUNET_i2s (&session->target));
    GNUNET_STATISTICS_update (plugin->env->stats,
                              gettext_noop ("# bytes currently in TCP buffers"), msgbuf_size,
                              GNUNET_NO);
    /* append pm to pending_messages list */
    GNUNET_CONTAINER_DLL_insert_tail (session->pending_messages_head,
                                      session->pending_messages_tail,
                                      pm);
    session->msgs_in_queue++;
    session->bytes_in_queue += pm->message_size;
    notify_session_monitor (session->plugin,
                            session,
                            GNUNET_TRANSPORT_SS_HANDSHAKE);
    return msgbuf_size;
  }
  else
  {
    LOG(GNUNET_ERROR_TYPE_ERROR,
        "Invalid session %p\n",
        session);
    if (NULL != cont)
      cont (cont_cls,
            &session->target,
            GNUNET_SYSERR,
            pm->message_size,
            0);
    GNUNET_break (0);
    GNUNET_free (pm);
    return GNUNET_SYSERR; /* session does not exist here */
  }
}

/**
 * Closure for #session_lookup_it().
 */
struct SessionItCtx
{
  /**
   * Address we are looking for.
   */
  const struct GNUNET_HELLO_Address *address;

  /**
   * Where to store the session (if we found it).
   */
  struct Session *result;

};


/**
 * Look for a session by address.
 *
 * @param cls the `struct SessionItCtx`
 * @param key unused
 * @param value a `struct Session`
 * @return #GNUNET_YES to continue looking, #GNUNET_NO if we found the session
 */
static int
session_lookup_it (void *cls,
                   const struct GNUNET_PeerIdentity *key,
                   void *value)
{
  struct SessionItCtx * si_ctx = cls;
  struct Session * session = value;

  if (0 != GNUNET_HELLO_address_cmp (si_ctx->address, session->address))
    return GNUNET_YES;
  /* Found existing session */
  si_ctx->result = session;
  return GNUNET_NO;
}


/**
 * Task cleaning up a NAT connection attempt after timeout
 *
 * @param cls the `struct Session`
 * @param tc scheduler context (unused)
 */
static void
nat_connect_timeout (void *cls,
                     const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Session *session = cls;

  session->nat_connection_timeout = GNUNET_SCHEDULER_NO_TASK;
  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "NAT WAIT connection to `%4s' at `%s' could not be established, removing session\n",
      GNUNET_i2s (&session->target),
      tcp_plugin_address_to_string (NULL,
                             session->address->address,
                             session->address->address_length));
  tcp_plugin_disconnect_session (session->plugin,
                                 session);
}


/**
 * Function that will be called whenever the transport service wants to
 * notify the plugin that a session is still active and in use and
 * therefore the session timeout for this session has to be updated
 *
 * @param cls closure
 * @param peer which peer was the session for
 * @param session which session is being updated
 */
static void
tcp_plugin_update_session_timeout (void *cls,
                                   const struct GNUNET_PeerIdentity *peer,
                                   struct Session *session)
{
  reschedule_session_timeout (session);
}


/**
 * Task to signal the server that we can continue
 * receiving from the TCP client now.
 *
 * @param cls the `struct Session*`
 * @param tc task context (unused)
 */
static void
delayed_done (void *cls,
              const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Session *session = cls;

  session->receive_delay_task = GNUNET_SCHEDULER_NO_TASK;
  reschedule_session_timeout (session);

  GNUNET_SERVER_receive_done (session->client, GNUNET_OK);
}


/**
 * Function that will be called whenever the transport service wants to
 * notify the plugin that the inbound quota changed and that the plugin
 * should update it's delay for the next receive value
 *
 * @param cls closure
 * @param peer which peer was the session for
 * @param session which session is being updated
 * @param delay new delay to use for receiving
 */
static void
tcp_plugin_update_inbound_delay (void *cls,
                                 const struct GNUNET_PeerIdentity *peer,
                                 struct Session *session,
                                 struct GNUNET_TIME_Relative delay)
{
  if (GNUNET_SCHEDULER_NO_TASK == session->receive_delay_task)
    return;
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "New inbound delay %s\n",
       GNUNET_STRINGS_relative_time_to_string (delay,
                                               GNUNET_NO));
  session->receive_delay = GNUNET_TIME_relative_to_absolute (delay);
  GNUNET_SCHEDULER_cancel (session->receive_delay_task);
  session->receive_delay_task = GNUNET_SCHEDULER_add_delayed (delay,
                                                              &delayed_done,
                                                              session);
}


/**
 * Create a new session to transmit data to the target
 * This session will used to send data to this peer and the plugin will
 * notify us by calling the env->session_end function
 *
 * @param cls closure
 * @param address the address to use
 * @return the session if the address is valid, NULL otherwise
 */
static struct Session *
tcp_plugin_get_session (void *cls,
                        const struct GNUNET_HELLO_Address *address)
{
  struct Plugin *plugin = cls;
  struct Session *session = NULL;
  int af;
  const void *sb;
  size_t sbs;
  struct GNUNET_CONNECTION_Handle *sa;
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  const struct IPv4TcpAddress *t4;
  const struct IPv6TcpAddress *t6;
  struct GNUNET_ATS_Information ats;
  unsigned int is_natd = GNUNET_NO;
  size_t addrlen;

  addrlen = address->address_length;
  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Trying to get session for `%s' address of peer `%s'\n",
      tcp_plugin_address_to_string(NULL, address->address, address->address_length),
      GNUNET_i2s (&address->peer));

  if (GNUNET_HELLO_address_check_option(address, GNUNET_HELLO_ADDRESS_INFO_INBOUND))
  {
    GNUNET_break (0);
    return NULL;
  }

  /* look for existing session */
  if (GNUNET_YES == GNUNET_CONTAINER_multipeermap_contains (plugin->sessionmap,
          &address->peer))
  {
    struct SessionItCtx si_ctx;

    si_ctx.address = address;
    si_ctx.result = NULL;

    GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessionmap,
        &address->peer, &session_lookup_it, &si_ctx);
    if (si_ctx.result != NULL)
    {
      session = si_ctx.result;
      LOG(GNUNET_ERROR_TYPE_DEBUG,
          "Found existing session for `%s' address `%s' session %p\n",
          GNUNET_i2s (&address->peer),
          tcp_plugin_address_to_string(NULL, address->address, address->address_length),
          session);
      return session;
    }
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Existing sessions did not match address `%s' or peer `%s'\n",
         tcp_plugin_address_to_string (NULL,
                                       address->address,
                                       address->address_length),
        GNUNET_i2s (&address->peer));
  }

  if (addrlen == sizeof(struct IPv6TcpAddress))
  {
    GNUNET_assert(NULL != address->address); /* make static analysis happy */
    t6 = address->address;
    af = AF_INET6;
    memset (&a6, 0, sizeof(a6));
#if HAVE_SOCKADDR_IN_SIN_LEN
    a6.sin6_len = sizeof (a6);
#endif
    a6.sin6_family = AF_INET6;
    a6.sin6_port = t6->t6_port;
    if (t6->t6_port == 0)
      is_natd = GNUNET_YES;
    memcpy (&a6.sin6_addr, &t6->ipv6_addr, sizeof(struct in6_addr));
    sb = &a6;
    sbs = sizeof(a6);
  }
  else if (addrlen == sizeof(struct IPv4TcpAddress))
  {
    GNUNET_assert(NULL != address->address); /* make static analysis happy */
    t4 = address->address;
    af = AF_INET;
    memset (&a4, 0, sizeof(a4));
#if HAVE_SOCKADDR_IN_SIN_LEN
    a4.sin_len = sizeof (a4);
#endif
    a4.sin_family = AF_INET;
    a4.sin_port = t4->t4_port;
    if (t4->t4_port == 0)
      is_natd = GNUNET_YES;
    a4.sin_addr.s_addr = t4->ipv4_addr;
    sb = &a4;
    sbs = sizeof(a4);
  }
  else
  {
    GNUNET_STATISTICS_update (plugin->env->stats, gettext_noop
    ("# requests to create session with invalid address"), 1, GNUNET_NO);
    return NULL ;
  }

  ats = plugin->env->get_address_type (plugin->env->cls, sb, sbs);

  if ((is_natd == GNUNET_YES) && (addrlen == sizeof(struct IPv6TcpAddress)))
  {
    /* NAT client only works with IPv4 addresses */
    return NULL ;
  }

  if (plugin->cur_connections >= plugin->max_connections)
  {
    /* saturated */
    return NULL ;
  }

  if ((is_natd == GNUNET_YES)
      && (GNUNET_YES
          == GNUNET_CONTAINER_multipeermap_contains (plugin->nat_wait_conns,
              &address->peer)))
  {
    /* Only do one NAT punch attempt per peer identity */
    return NULL ;
  }

  if ((is_natd == GNUNET_YES) && (NULL != plugin->nat) &&
      (GNUNET_NO == GNUNET_CONTAINER_multipeermap_contains (plugin->nat_wait_conns,
              &address->peer)))
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
        "Found valid IPv4 NAT address (creating session)!\n");
    session = create_session (plugin, address, NULL, GNUNET_YES);
    session->ats_address_network_type = (enum GNUNET_ATS_Network_Type) ntohl (
        ats.value);
    GNUNET_break(
        session->ats_address_network_type != GNUNET_ATS_NET_UNSPECIFIED);
    session->nat_connection_timeout = GNUNET_SCHEDULER_add_delayed (NAT_TIMEOUT,
        &nat_connect_timeout, session);
    GNUNET_assert(session != NULL);
    GNUNET_assert(GNUNET_OK == GNUNET_CONTAINER_multipeermap_put (plugin->nat_wait_conns,
        &session->target, session, GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));

    LOG(GNUNET_ERROR_TYPE_DEBUG,
        "Created NAT WAIT connection to `%4s' at `%s'\n",
        GNUNET_i2s (&session->target), GNUNET_a2s (sb, sbs));

    if (GNUNET_OK == GNUNET_NAT_run_client (plugin->nat, &a4))
      return session;
    else
    {
      LOG(GNUNET_ERROR_TYPE_DEBUG,
          "Running NAT client for `%4s' at `%s' failed\n",
          GNUNET_i2s (&session->target),
          GNUNET_a2s (sb, sbs));
      tcp_plugin_disconnect_session (plugin,
                                     session);
      return NULL;
    }
  }

  /* create new outbound session */
  GNUNET_assert(plugin->cur_connections <= plugin->max_connections);
  sa = GNUNET_CONNECTION_create_from_sockaddr (af, sb, sbs);
  if (NULL == sa)
  {
    LOG(GNUNET_ERROR_TYPE_DEBUG,
        "Failed to create connection to `%4s' at `%s'\n",
        GNUNET_i2s (&address->peer), GNUNET_a2s (sb, sbs));
    return NULL ;
  }
  plugin->cur_connections++;
  if (plugin->cur_connections == plugin->max_connections)
    GNUNET_SERVER_suspend (plugin->server); /* Maximum number of connections rechead */

  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Asked to transmit to `%4s', creating fresh session using address `%s'.\n",
      GNUNET_i2s (&address->peer), GNUNET_a2s (sb, sbs));

  session = create_session (plugin, address,
      GNUNET_SERVER_connect_socket (plugin->server, sa), GNUNET_NO);
  session->ats_address_network_type = (enum GNUNET_ATS_Network_Type) ntohl (
      ats.value);
  GNUNET_break(session->ats_address_network_type != GNUNET_ATS_NET_UNSPECIFIED);
  GNUNET_SERVER_client_set_user_context(session->client, session);
  GNUNET_CONTAINER_multipeermap_put (plugin->sessionmap, &session->target,
      session, GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Creating new session for `%s' address `%s' session %p\n",
      GNUNET_i2s (&address->peer),
      tcp_plugin_address_to_string(NULL, address->address, address->address_length),
      session);
  /* Send TCP Welcome */
  process_pending_messages (session);

  return session;
}


static int
session_disconnect_it (void *cls,
                       const struct GNUNET_PeerIdentity *key,
                       void *value)
{
  struct Plugin *plugin = cls;
  struct Session *session = value;

  GNUNET_STATISTICS_update (session->plugin->env->stats,
                            gettext_noop ("# transport-service disconnect requests for TCP"),
                            1,
                            GNUNET_NO);
  tcp_plugin_disconnect_session (plugin,
                                 session);
  return GNUNET_YES;
}


/**
 * Function that can be called to force a disconnect from the
 * specified neighbour.  This should also cancel all previously
 * scheduled transmissions.  Obviously the transmission may have been
 * partially completed already, which is OK.  The plugin is supposed
 * to close the connection (if applicable) and no longer call the
 * transmit continuation(s).
 *
 * Finally, plugin MUST NOT call the services's receive function to
 * notify the service that the connection to the specified target was
 * closed after a getting this call.
 *
 * @param cls closure
 * @param target peer for which the last transmission is
 *        to be cancelled
 */
static void
tcp_plugin_disconnect (void *cls,
                       const struct GNUNET_PeerIdentity *target)
{
  struct Plugin *plugin = cls;

  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Disconnecting peer `%4s'\n",
      GNUNET_i2s (target));
  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessionmap,
                                              target,
                                              &session_disconnect_it,
                                              plugin);
  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->nat_wait_conns,
                                              target,
                                              &session_disconnect_it,
                                              plugin);
}


/**
 * Running pretty printers: head
 */
static struct PrettyPrinterContext *ppc_dll_head;

/**
 * Running pretty printers: tail
 */
static struct PrettyPrinterContext *ppc_dll_tail;

/**
 * Context for address to string conversion, closure
 * for #append_port().
 */
struct PrettyPrinterContext
{
  /**
   * DLL
   */
  struct PrettyPrinterContext *next;

  /**
   * DLL
   */
  struct PrettyPrinterContext *prev;

  /**
   * Timeout task
   */
  GNUNET_SCHEDULER_TaskIdentifier timeout_task;

  /**
   * Resolver handle
   */
  struct GNUNET_RESOLVER_RequestHandle *resolver_handle;

  /**
   * Function to call with the result.
   */
  GNUNET_TRANSPORT_AddressStringCallback asc;

  /**
   * Clsoure for @e asc.
   */
  void *asc_cls;

  /**
   * Port to add after the IP address.
   */
  uint16_t port;

  /**
   * IPv6 address
   */
  int ipv6;

  /**
   * Options
   */
  uint32_t options;
};


/**
 * Append our port and forward the result.
 *
 * @param cls the `struct PrettyPrinterContext *`
 * @param hostname hostname part of the address
 */
static void
append_port (void *cls,
             const char *hostname)
{
  struct PrettyPrinterContext *ppc = cls;
  char *ret;

  if (NULL == hostname)
  {
    /* Final call, done */
    ppc->resolver_handle = NULL;
    GNUNET_CONTAINER_DLL_remove (ppc_dll_head,
                                 ppc_dll_tail,
                                 ppc);
    ppc->asc (ppc->asc_cls,
              NULL,
              GNUNET_OK);
    GNUNET_free (ppc);
    return;
  }
  if (GNUNET_YES == ppc->ipv6)
    GNUNET_asprintf (&ret,
                     "%s.%u.[%s]:%d",
                     PLUGIN_NAME,
                     ppc->options,
                     hostname,
                     ppc->port);
  else
    GNUNET_asprintf (&ret,
                     "%s.%u.%s:%d",
                     PLUGIN_NAME,
                     ppc->options,
                     hostname,
                     ppc->port);
  ppc->asc (ppc->asc_cls,
            ret,
            GNUNET_OK);
  GNUNET_free (ret);
}


/**
 * Convert the transports address to a nice, human-readable
 * format.
 *
 * @param cls closure
 * @param type name of the transport that generated the address
 * @param addr one of the addresses of the host, NULL for the last address
 *        the specific address format depends on the transport
 * @param addrlen length of the @a addr
 * @param numeric should (IP) addresses be displayed in numeric form?
 * @param timeout after how long should we give up?
 * @param asc function to call on each string
 * @param asc_cls closure for @a asc
 */
static void
tcp_plugin_address_pretty_printer (void *cls,
                                   const char *type,
                                   const void *addr,
                                   size_t addrlen,
                                   int numeric,
                                   struct GNUNET_TIME_Relative timeout,
                                   GNUNET_TRANSPORT_AddressStringCallback asc,
                                   void *asc_cls)
{
  struct PrettyPrinterContext *ppc;
  const void *sb;
  size_t sbs;
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  const struct IPv4TcpAddress *t4;
  const struct IPv6TcpAddress *t6;
  uint16_t port;
  uint32_t options;

  if (sizeof(struct IPv6TcpAddress) == addrlen)
  {
    t6 = addr;
    memset (&a6, 0, sizeof(a6));
    a6.sin6_family = AF_INET6;
    a6.sin6_port = t6->t6_port;
    memcpy (&a6.sin6_addr, &t6->ipv6_addr, sizeof(struct in6_addr));
    port = ntohs (t6->t6_port);
    options = ntohl (t6->options);
    sb = &a6;
    sbs = sizeof(a6);
  }
  else if (sizeof(struct IPv4TcpAddress) == addrlen)
  {
    t4 = addr;
    memset (&a4, 0, sizeof(a4));
    a4.sin_family = AF_INET;
    a4.sin_port = t4->t4_port;
    a4.sin_addr.s_addr = t4->ipv4_addr;
    port = ntohs (t4->t4_port);
    options = ntohl (t4->options);
    sb = &a4;
    sbs = sizeof(a4);
  }
  else
  {
    /* invalid address */
    asc (asc_cls, NULL, GNUNET_SYSERR);
    asc (asc_cls, NULL, GNUNET_OK);
    return;
  }
  ppc = GNUNET_new (struct PrettyPrinterContext);
  if (addrlen == sizeof(struct IPv6TcpAddress))
    ppc->ipv6 = GNUNET_YES;
  else
    ppc->ipv6 = GNUNET_NO;
  ppc->asc = asc;
  ppc->asc_cls = asc_cls;
  ppc->port = port;
  ppc->options = options;
  ppc->resolver_handle = GNUNET_RESOLVER_hostname_get (sb,
                                                       sbs,
                                                       ! numeric,
                                                       timeout,
                                                       &append_port, ppc);
  if (NULL == ppc->resolver_handle)
  {
    GNUNET_break (0);
    GNUNET_free (ppc);
    return;
  }
  GNUNET_CONTAINER_DLL_insert (ppc_dll_head,
                               ppc_dll_tail,
                               ppc);
}


/**
 * Check if the given port is plausible (must be either our listen
 * port or our advertised port), or any port if we are behind NAT
 * and do not have a port open.  If it is neither, we return
 * #GNUNET_SYSERR.
 *
 * @param plugin global variables
 * @param in_port port number to check
 * @return #GNUNET_OK if port is either open_port or adv_port
 */
static int
check_port (struct Plugin *plugin, uint16_t in_port)
{
  if ((in_port == plugin->adv_port) || (in_port == plugin->open_port))
    return GNUNET_OK;
  return GNUNET_SYSERR;
}

/**
 * Function that will be called to check if a binary address for this
 * plugin is well-formed and corresponds to an address for THIS peer
 * (as per our configuration).  Naturally, if absolutely necessary,
 * plugins can be a bit conservative in their answer, but in general
 * plugins should make sure that the address does not redirect
 * traffic to a 3rd party that might try to man-in-the-middle our
 * traffic.
 *
 * @param cls closure, our `struct Plugin *`
 * @param addr pointer to the address
 * @param addrlen length of addr
 * @return #GNUNET_OK if this is a plausible address for this peer
 *         and transport, #GNUNET_SYSERR if not
 */
static int
tcp_plugin_check_address (void *cls, const void *addr, size_t addrlen)
{
  struct Plugin *plugin = cls;
  struct IPv4TcpAddress *v4;
  struct IPv6TcpAddress *v6;

  if ((addrlen != sizeof(struct IPv4TcpAddress))
      && (addrlen != sizeof(struct IPv6TcpAddress)))
  {
    GNUNET_break_op(0);
    return GNUNET_SYSERR;
  }

  if (addrlen == sizeof(struct IPv4TcpAddress))
  {
    v4 = (struct IPv4TcpAddress *) addr;
    if (0 != memcmp (&v4->options,
                     &plugin->myoptions,
                     sizeof(uint32_t)))
    {
      GNUNET_break(0);
      return GNUNET_SYSERR;
    }
    if (GNUNET_OK != check_port (plugin, ntohs (v4->t4_port)))
      return GNUNET_SYSERR;
    if (GNUNET_OK
        != GNUNET_NAT_test_address (plugin->nat, &v4->ipv4_addr,
            sizeof(struct in_addr)))
      return GNUNET_SYSERR;
  }
  else
  {
    v6 = (struct IPv6TcpAddress *) addr;
    if (IN6_IS_ADDR_LINKLOCAL (&v6->ipv6_addr))
    {
      GNUNET_break_op(0);
      return GNUNET_SYSERR;
    }
    if (0 != memcmp (&v6->options,
                     &plugin->myoptions,
                     sizeof (uint32_t)))
    {
      GNUNET_break(0);
      return GNUNET_SYSERR;
    }
    if (GNUNET_OK != check_port (plugin, ntohs (v6->t6_port)))
      return GNUNET_SYSERR;
    if (GNUNET_OK
        != GNUNET_NAT_test_address (plugin->nat, &v6->ipv6_addr,
            sizeof(struct in6_addr)))
      return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}

/**
 * We've received a nat probe from this peer via TCP.  Finish
 * creating the client session and resume sending of queued
 * messages.
 *
 * @param cls closure
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_tcp_nat_probe (void *cls,
                      struct GNUNET_SERVER_Client *client,
                      const struct GNUNET_MessageHeader *message)
{
  struct Plugin *plugin = cls;
  struct Session *session;
  const struct TCP_NAT_ProbeMessage *tcp_nat_probe;
  size_t alen;
  void *vaddr;
  struct IPv4TcpAddress *t4;
  struct IPv6TcpAddress *t6;
  const struct sockaddr_in *s4;
  const struct sockaddr_in6 *s6;

  LOG(GNUNET_ERROR_TYPE_DEBUG, "Received NAT probe\n");
  /* We have received a TCP NAT probe, meaning we (hopefully) initiated
   * a connection to this peer by running gnunet-nat-client.  This peer
   * received the punch message and now wants us to use the new connection
   * as the default for that peer.  Do so and then send a WELCOME message
   * so we can really be connected!
   */
  if (ntohs (message->size) != sizeof(struct TCP_NAT_ProbeMessage))
  {
    GNUNET_break_op(0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }

  tcp_nat_probe = (const struct TCP_NAT_ProbeMessage *) message;
  if (0 == memcmp (&tcp_nat_probe->clientIdentity, plugin->env->my_identity,
          sizeof(struct GNUNET_PeerIdentity)))
  {
    /* refuse connections from ourselves */
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }

  session = GNUNET_CONTAINER_multipeermap_get (plugin->nat_wait_conns,
      &tcp_nat_probe->clientIdentity);
  if (session == NULL)
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Did NOT find session for NAT probe!\n");
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
    return;
  }
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Found session for NAT probe!\n");

  if (session->nat_connection_timeout != GNUNET_SCHEDULER_NO_TASK)
  {
    GNUNET_SCHEDULER_cancel (session->nat_connection_timeout);
    session->nat_connection_timeout = GNUNET_SCHEDULER_NO_TASK;
  }

  if (GNUNET_OK != GNUNET_SERVER_client_get_address (client, &vaddr, &alen))
  {
    GNUNET_break(0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    tcp_plugin_disconnect_session (plugin,
                                   session);
    return;
  }
  GNUNET_assert(
      GNUNET_CONTAINER_multipeermap_remove (plugin->nat_wait_conns, &tcp_nat_probe->clientIdentity, session) == GNUNET_YES);
  GNUNET_SERVER_client_set_user_context(client, session);
  GNUNET_CONTAINER_multipeermap_put (plugin->sessionmap, &session->target,
      session, GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  session->last_activity = GNUNET_TIME_absolute_get ();
  LOG(GNUNET_ERROR_TYPE_DEBUG, "Found address `%s' for incoming connection\n",
      GNUNET_a2s (vaddr, alen));
  switch (((const struct sockaddr *) vaddr)->sa_family)
  {
  case AF_INET:
    s4 = vaddr;
    t4 = GNUNET_new (struct IPv4TcpAddress);
    t4->options = htonl(0);
    t4->t4_port = s4->sin_port;
    t4->ipv4_addr = s4->sin_addr.s_addr;
    session->address = GNUNET_HELLO_address_allocate (
        &tcp_nat_probe->clientIdentity, PLUGIN_NAME, &t4,
        sizeof(struct IPv4TcpAddress),
        GNUNET_HELLO_ADDRESS_INFO_NONE);
    break;
  case AF_INET6:
    s6 = vaddr;
    t6 = GNUNET_new (struct IPv6TcpAddress);
    t6->options = htonl(0);
    t6->t6_port = s6->sin6_port;
    memcpy (&t6->ipv6_addr, &s6->sin6_addr, sizeof(struct in6_addr));
    session->address = GNUNET_HELLO_address_allocate (
        &tcp_nat_probe->clientIdentity,
        PLUGIN_NAME, &t6, sizeof(struct IPv6TcpAddress),
        GNUNET_HELLO_ADDRESS_INFO_NONE);
    break;
  default:
    GNUNET_break_op(0);
    LOG(GNUNET_ERROR_TYPE_DEBUG,
        "Bad address for incoming connection!\n");
    GNUNET_free(vaddr);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    tcp_plugin_disconnect_session (plugin,
                                   session);
    return;
  }
  GNUNET_free(vaddr);
  GNUNET_break(NULL == session->client);
  GNUNET_SERVER_client_keep (client);
  session->client = client;
  GNUNET_STATISTICS_update (plugin->env->stats,
      gettext_noop ("# TCP sessions active"), 1, GNUNET_NO);
  process_pending_messages (session);
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}

/**
 * We've received a welcome from this peer via TCP.  Possibly create a
 * fresh client record and send back our welcome.
 *
 * @param cls closure
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_tcp_welcome (void *cls,
                    struct GNUNET_SERVER_Client *client,
                    const struct GNUNET_MessageHeader *message)
{
  struct Plugin *plugin = cls;
  const struct WelcomeMessage *wm = (const struct WelcomeMessage *) message;
  struct GNUNET_HELLO_Address *address;
  struct Session *session;
  size_t alen;
  void *vaddr;
  struct IPv4TcpAddress t4;
  struct IPv6TcpAddress t6;
  const struct sockaddr_in *s4;
  const struct sockaddr_in6 *s6;
  struct GNUNET_ATS_Information ats;


  if (0 == memcmp (&wm->clientIdentity, plugin->env->my_identity,
          sizeof(struct GNUNET_PeerIdentity)))
  {
    /* refuse connections from ourselves */
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    if (GNUNET_OK == GNUNET_SERVER_client_get_address (client, &vaddr, &alen))
    {
      LOG(GNUNET_ERROR_TYPE_INFO,
          "Received %s message from my own identity `%4s' on address `%s'\n",
          "WELCOME", GNUNET_i2s (&wm->clientIdentity),
          GNUNET_a2s (vaddr, alen));
      GNUNET_free(vaddr);
    }
    return;
  }

  LOG(GNUNET_ERROR_TYPE_DEBUG, "Received %s message from `%4s' %p\n", "WELCOME",
      GNUNET_i2s (&wm->clientIdentity), client);
  GNUNET_STATISTICS_update (plugin->env->stats,
      gettext_noop ("# TCP WELCOME messages received"), 1, GNUNET_NO);
  session = lookup_session_by_client (plugin, client);
  if (NULL != session)
  {
    if (GNUNET_OK == GNUNET_SERVER_client_get_address (client, &vaddr, &alen))
    {
      LOG(GNUNET_ERROR_TYPE_DEBUG, "Found existing session %p for peer `%s'\n",
          session, GNUNET_a2s (vaddr, alen));
      GNUNET_free(vaddr);
    }
  }
  else
  {
    GNUNET_SERVER_client_keep (client);
    if (NULL != plugin->service) /* Otherwise value is incremented in tcp_access_check */
      plugin->cur_connections++;
    if (plugin->cur_connections == plugin->max_connections)
      GNUNET_SERVER_suspend (plugin->server); /* Maximum number of connections rechead */

    if (GNUNET_OK == GNUNET_SERVER_client_get_address (client, &vaddr, &alen))
    {
      if (alen == sizeof(struct sockaddr_in))
      {
        s4 = vaddr;
        memset (&t4, '\0', sizeof (t4));
        t4.options = htonl (0);
        t4.t4_port = s4->sin_port;
        t4.ipv4_addr = s4->sin_addr.s_addr;
        address = GNUNET_HELLO_address_allocate (&wm->clientIdentity,
            PLUGIN_NAME, &t4, sizeof(t4),
            GNUNET_HELLO_ADDRESS_INFO_INBOUND);
      }
      else if (alen == sizeof(struct sockaddr_in6))
      {
        s6 = vaddr;
        memset (&t6, '\0', sizeof (t6));
        t6.options = htonl (0);
        t6.t6_port = s6->sin6_port;
        memcpy (&t6.ipv6_addr, &s6->sin6_addr, sizeof(struct in6_addr));
        address = GNUNET_HELLO_address_allocate (&wm->clientIdentity,
            PLUGIN_NAME, &t6, sizeof (t6),
            GNUNET_HELLO_ADDRESS_INFO_INBOUND);
      }
      else
      {
        GNUNET_break (0);
        GNUNET_free_non_null (vaddr);
        return;
      }
      session = create_session (plugin, address, client, GNUNET_NO);
      GNUNET_HELLO_address_free (address);
      ats = plugin->env->get_address_type (plugin->env->cls, vaddr, alen);
      session->ats_address_network_type = (enum GNUNET_ATS_Network_Type) ntohl (
          ats.value);
      LOG(GNUNET_ERROR_TYPE_DEBUG, "Creating new%s session %p for peer `%s' client %p \n",
          GNUNET_HELLO_address_check_option (session->address,
              GNUNET_HELLO_ADDRESS_INFO_INBOUND) ? " inbound" : "", session,
          tcp_plugin_address_to_string(NULL, (void *) session->address->address,
              session->address->address_length),
          client);
      GNUNET_free(vaddr);
      GNUNET_SERVER_client_set_user_context(session->client, session);
      GNUNET_CONTAINER_multipeermap_put (plugin->sessionmap, &session->target,
          session, GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);

      /* Notify transport and ATS about new session */
      plugin->env->session_start (NULL, session->address, session, &ats, 1);
    }
    else
    {
      LOG(GNUNET_ERROR_TYPE_DEBUG,
          "Did not obtain TCP socket address for incoming connection\n");
      GNUNET_break(0);
      return;
    }
  }

  if (session->expecting_welcome != GNUNET_YES)
  {
    GNUNET_break_op(0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    GNUNET_break(0);
    return;
  }
  session->last_activity = GNUNET_TIME_absolute_get ();
  session->expecting_welcome = GNUNET_NO;

  process_pending_messages (session);
  GNUNET_SERVER_client_set_timeout (client,
      GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * We've received data for this peer via TCP.  Unbox,
 * compute latency and forward.
 *
 * @param cls closure
 * @param client identification of the client
 * @param message the actual message
 */
static void
handle_tcp_data (void *cls,
                 struct GNUNET_SERVER_Client *client,
                 const struct GNUNET_MessageHeader *message)
{
  struct Plugin *plugin = cls;
  struct Session *session;
  struct GNUNET_TIME_Relative delay;
  uint16_t type;

  type = ntohs (message->type);
  if ((GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_WELCOME == type)
      || (GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_NAT_PROBE == type))
  {
    /* We don't want to propagate WELCOME and NAT Probe messages up! */
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
    return;
  }
  session = lookup_session_by_client (plugin, client);
  if (NULL == session)
  {
    /* No inbound session found */
    void *vaddr;
    size_t alen;

    GNUNET_SERVER_client_get_address (client, &vaddr, &alen);
    LOG(GNUNET_ERROR_TYPE_ERROR,
        "Received unexpected %u bytes of type %u from `%s'\n",
        (unsigned int) ntohs (message->size),
        (unsigned int) ntohs (message->type), GNUNET_a2s (vaddr, alen));
    GNUNET_break_op(0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    GNUNET_free_non_null(vaddr);
    return;
  }
  else if (GNUNET_YES == session->expecting_welcome)
  {
    /* Session is expecting WELCOME message */
    void *vaddr;
    size_t alen;

    GNUNET_SERVER_client_get_address (client, &vaddr, &alen);
    LOG(GNUNET_ERROR_TYPE_ERROR,
        "Received unexpected %u bytes of type %u from `%s'\n",
        (unsigned int) ntohs (message->size),
        (unsigned int) ntohs (message->type), GNUNET_a2s (vaddr, alen));
    GNUNET_break_op(0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    GNUNET_free_non_null(vaddr);
    return;
  }

  session->last_activity = GNUNET_TIME_absolute_get ();
  LOG(GNUNET_ERROR_TYPE_DEBUG,
      "Passing %u bytes of type %u from `%4s' to transport service.\n",
      (unsigned int) ntohs (message->size),
      (unsigned int) ntohs (message->type), GNUNET_i2s (&session->target));

  GNUNET_STATISTICS_update (plugin->env->stats,
      gettext_noop ("# bytes received via TCP"), ntohs (message->size),
      GNUNET_NO);
  struct GNUNET_ATS_Information distance;

  distance.type = htonl (GNUNET_ATS_NETWORK_TYPE);
  distance.value = htonl ((uint32_t) session->ats_address_network_type);
  GNUNET_break(session->ats_address_network_type != GNUNET_ATS_NET_UNSPECIFIED);

  GNUNET_assert(GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessionmap,
                                                              &session->target,
                                                              session));

  delay = plugin->env->receive (plugin->env->cls,
                                session->address,
                                session,
                                message);
  plugin->env->update_address_metrics (plugin->env->cls,
                                       session->address,
                                       session,
                                       &distance, 1);
  reschedule_session_timeout (session);
  if (0 == delay.rel_value_us)
  {
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
  }
  else
  {
    LOG(GNUNET_ERROR_TYPE_DEBUG,
        "Throttling receiving from `%s' for %s\n",
        GNUNET_i2s (&session->target),
        GNUNET_STRINGS_relative_time_to_string (delay, GNUNET_YES));
    GNUNET_SERVER_disable_receive_done_warning (client);
    session->receive_delay_task = GNUNET_SCHEDULER_add_delayed (delay,
        &delayed_done, session);
  }
}


/**
 * Functions with this signature are called whenever a peer
 * is disconnected on the network level.
 *
 * @param cls closure
 * @param client identification of the client
 */
static void
disconnect_notify (void *cls,
                   struct GNUNET_SERVER_Client *client)
{
  struct Plugin *plugin = cls;
  struct Session *session;

  if (NULL == client)
    return;
  session = lookup_session_by_client (plugin, client);
  if (NULL == session)
    return; /* unknown, nothing to do */
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Destroying session of `%4s' with %s due to network-level disconnect.\n",
       GNUNET_i2s (&session->target),
       tcp_plugin_address_to_string (session->plugin, session->address->address,
                              session->address->address_length));

  if (plugin->cur_connections == plugin->max_connections)
    GNUNET_SERVER_resume (plugin->server); /* Resume server  */

  if (plugin->cur_connections < 1)
    GNUNET_break(0);
  else
    plugin->cur_connections--;

  GNUNET_STATISTICS_update (session->plugin->env->stats, gettext_noop
                            ("# network-level TCP disconnect events"),
                            1,
                            GNUNET_NO);
  tcp_plugin_disconnect_session (plugin, session);
}


/**
 * We can now send a probe message, copy into buffer to really send.
 *
 * @param cls closure, a struct TCPProbeContext
 * @param size max size to copy
 * @param buf buffer to copy message to
 * @return number of bytes copied into @a buf
 */
static size_t
notify_send_probe (void *cls,
                   size_t size,
                   void *buf)
{
  struct TCPProbeContext *tcp_probe_ctx = cls;
  struct Plugin *plugin = tcp_probe_ctx->plugin;
  size_t ret;

  tcp_probe_ctx->transmit_handle = NULL;
  GNUNET_CONTAINER_DLL_remove (plugin->probe_head,
                               plugin->probe_tail,
                               tcp_probe_ctx);
  if (buf == NULL)
  {
    GNUNET_CONNECTION_destroy (tcp_probe_ctx->sock);
    GNUNET_free(tcp_probe_ctx);
    return 0;
  }
  GNUNET_assert(size >= sizeof(tcp_probe_ctx->message));
  memcpy (buf, &tcp_probe_ctx->message, sizeof(tcp_probe_ctx->message));
  GNUNET_SERVER_connect_socket (tcp_probe_ctx->plugin->server,
                                tcp_probe_ctx->sock);
  ret = sizeof(tcp_probe_ctx->message);
  GNUNET_free(tcp_probe_ctx);
  return ret;
}


/**
 * Function called by the NAT subsystem suggesting another peer wants
 * to connect to us via connection reversal.  Try to connect back to the
 * given IP.
 *
 * @param cls closure
 * @param addr address to try
 * @param addrlen number of bytes in @a addr
 */
static void
try_connection_reversal (void *cls,
                         const struct sockaddr *addr,
                         socklen_t addrlen)
{
  struct Plugin *plugin = cls;
  struct GNUNET_CONNECTION_Handle *sock;
  struct TCPProbeContext *tcp_probe_ctx;

  /**
   * We have received an ICMP response, ostensibly from a peer
   * that wants to connect to us! Send a message to establish a connection.
   */
  sock = GNUNET_CONNECTION_create_from_sockaddr (AF_INET, addr, addrlen);
  if (sock == NULL)
  {
    /* failed for some odd reason (out of sockets?); ignore attempt */
    return;
  }

  tcp_probe_ctx = GNUNET_new (struct TCPProbeContext);
  tcp_probe_ctx->message.header.size
    = htons (sizeof (struct TCP_NAT_ProbeMessage));
  tcp_probe_ctx->message.header.type
    = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_NAT_PROBE);
  tcp_probe_ctx->message.clientIdentity
    = *plugin->env->my_identity;
  tcp_probe_ctx->plugin = plugin;
  tcp_probe_ctx->sock = sock;
  GNUNET_CONTAINER_DLL_insert (plugin->probe_head,
                               plugin->probe_tail,
                               tcp_probe_ctx);
  tcp_probe_ctx->transmit_handle
    = GNUNET_CONNECTION_notify_transmit_ready (sock,
                                               ntohs (tcp_probe_ctx->message.header.size),
                                               GNUNET_TIME_UNIT_FOREVER_REL,
                                               &notify_send_probe,
                                               tcp_probe_ctx);
}


/**
 * Function obtain the network type for a session
 *
 * @param cls closure ('struct Plugin*')
 * @param session the session
 * @return the network type in HBO or #GNUNET_SYSERR
 */
static enum GNUNET_ATS_Network_Type
tcp_plugin_get_network (void *cls,
                        struct Session *session)
{
  return session->ats_address_network_type;
}


/**
 * Return information about the given session to the
 * monitor callback.
 *
 * @param cls the `struct Plugin` with the monitor callback (`sic`)
 * @param peer peer we send information about
 * @param value our `struct Session` to send information about
 * @return #GNUNET_OK (continue to iterate)
 */
static int
send_session_info_iter (void *cls,
                        const struct GNUNET_PeerIdentity *peer,
                        void *value)
{
  struct Plugin *plugin = cls;
  struct Session *session = value;

  notify_session_monitor (plugin,
                          session,
                          GNUNET_TRANSPORT_SS_UP);
  return GNUNET_OK;
}


/**
 * Begin monitoring sessions of a plugin.  There can only
 * be one active monitor per plugin (i.e. if there are
 * multiple monitors, the transport service needs to
 * multiplex the generated events over all of them).
 *
 * @param cls closure of the plugin
 * @param sic callback to invoke, NULL to disable monitor;
 *            plugin will being by iterating over all active
 *            sessions immediately and then enter monitor mode
 * @param sic_cls closure for @a sic
 */
static void
tcp_plugin_setup_monitor (void *cls,
                          GNUNET_TRANSPORT_SessionInfoCallback sic,
                          void *sic_cls)
{
  struct Plugin *plugin = cls;

  plugin->sic = sic;
  plugin->sic_cls = sic_cls;
  if (NULL != sic)
  {
    GNUNET_CONTAINER_multipeermap_iterate (plugin->sessionmap,
                                           &send_session_info_iter,
                                           plugin);
    /* signal end of first iteration */
    sic (sic_cls, NULL, NULL);
  }
}


/**
 * Entry point for the plugin.
 *
 * @param cls closure, the `struct GNUNET_TRANSPORT_PluginEnvironment *`
 * @return the `struct GNUNET_TRANSPORT_PluginFunctions *` or NULL on error
 */
void *
libgnunet_plugin_transport_tcp_init (void *cls)
{
  static const struct GNUNET_SERVER_MessageHandler my_handlers[] = {
    { &handle_tcp_welcome, NULL,
      GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_WELCOME, sizeof(struct WelcomeMessage) },
    { &handle_tcp_nat_probe, NULL,
      GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_NAT_PROBE, sizeof(struct TCP_NAT_ProbeMessage) },
    { &handle_tcp_data, NULL,
      GNUNET_MESSAGE_TYPE_ALL, 0 },
    { NULL, NULL, 0, 0 }
  };
  struct GNUNET_TRANSPORT_PluginEnvironment *env = cls;
  struct GNUNET_TRANSPORT_PluginFunctions *api;
  struct Plugin *plugin;
  struct GNUNET_SERVICE_Context *service;
  unsigned long long aport;
  unsigned long long bport;
  unsigned long long max_connections;
  unsigned int i;
  struct GNUNET_TIME_Relative idle_timeout;
  int ret;
  int ret_s;
  struct sockaddr **addrs;
  socklen_t *addrlens;

  if (NULL == env->receive)
  {
    /* run in 'stub' mode (i.e. as part of gnunet-peerinfo), don't fully
     initialze the plugin or the API */
    api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
    api->cls = NULL;
    api->address_pretty_printer = &tcp_plugin_address_pretty_printer;
    api->address_to_string = &tcp_plugin_address_to_string;
    api->string_to_address = &tcp_plugin_string_to_address;
    return api;
  }

  GNUNET_assert (NULL != env->cfg);
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_number (env->cfg,
                                             "transport-tcp",
                                             "MAX_CONNECTIONS",
                                             &max_connections))
    max_connections = 128;

  aport = 0;
  if ((GNUNET_OK
      != GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-tcp",
          "PORT", &bport)) || (bport > 65535)
      || ((GNUNET_OK
          == GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-tcp",
              "ADVERTISED-PORT", &aport)) && (aport > 65535)))
  {
    LOG(GNUNET_ERROR_TYPE_ERROR,
        _("Require valid port number for service `%s' in configuration!\n"),
        "transport-tcp");
    return NULL ;
  }
  if (aport == 0)
    aport = bport;
  if (bport == 0)
    aport = 0;
  if (bport != 0)
  {
    service = GNUNET_SERVICE_start ("transport-tcp",
                                    env->cfg,
                                    GNUNET_SERVICE_OPTION_NONE);
    if (service == NULL)
    {
      LOG (GNUNET_ERROR_TYPE_WARNING,
           _("Failed to start service.\n"));
      return NULL;
    }
  }
  else
    service = NULL;

  plugin = GNUNET_new (struct Plugin);
  plugin->sessionmap = GNUNET_CONTAINER_multipeermap_create (max_connections,
      GNUNET_YES);
  plugin->max_connections = max_connections;
  plugin->open_port = bport;
  plugin->adv_port = aport;
  plugin->env = env;
  if ( (service != NULL) &&
       (GNUNET_SYSERR !=
        (ret_s =
         GNUNET_SERVICE_get_server_addresses ("transport-tcp",
                                              env->cfg,
                                              &addrs,
                                              &addrlens))))
  {
    for (ret = ret_s-1; ret >= 0; ret--)
      LOG (GNUNET_ERROR_TYPE_INFO,
           "Binding to address `%s'\n",
           GNUNET_a2s (addrs[ret], addrlens[ret]));
    plugin->nat
      = GNUNET_NAT_register (env->cfg,
                             GNUNET_YES,
                             aport,
                             (unsigned int) ret_s,
                             (const struct sockaddr **) addrs, addrlens,
                             &tcp_nat_port_map_callback,
                             &try_connection_reversal,
                             plugin);
    for (ret = ret_s -1; ret >= 0; ret--)
      GNUNET_free (addrs[ret]);
    GNUNET_free_non_null (addrs);
    GNUNET_free_non_null (addrlens);
  }
  else
  {
    plugin->nat = GNUNET_NAT_register (plugin->env->cfg,
                                       GNUNET_YES, 0, 0, NULL, NULL, NULL,
                                       &try_connection_reversal, plugin);
  }
  api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
  api->cls = plugin;
  api->send = &tcp_plugin_send;
  api->get_session = &tcp_plugin_get_session;
  api->disconnect_session = &tcp_plugin_disconnect_session;
  api->query_keepalive_factor = &tcp_plugin_query_keepalive_factor;
  api->disconnect_peer = &tcp_plugin_disconnect;
  api->address_pretty_printer = &tcp_plugin_address_pretty_printer;
  api->check_address = &tcp_plugin_check_address;
  api->address_to_string = &tcp_plugin_address_to_string;
  api->string_to_address = &tcp_plugin_string_to_address;
  api->get_network = &tcp_plugin_get_network;
  api->update_session_timeout = &tcp_plugin_update_session_timeout;
  api->update_inbound_delay = &tcp_plugin_update_inbound_delay;
  api->setup_monitor = &tcp_plugin_setup_monitor;
  plugin->service = service;
  if (NULL != service)
  {
    plugin->server = GNUNET_SERVICE_get_server (service);
  }
  else
  {
    if (GNUNET_OK !=
        GNUNET_CONFIGURATION_get_value_time (env->cfg,
                                             "transport-tcp",
                                             "TIMEOUT",
                                             &idle_timeout))
    {
      GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
                                 "transport-tcp",
                                 "TIMEOUT");
      if (NULL != plugin->nat)
        GNUNET_NAT_unregister (plugin->nat);
      GNUNET_free(plugin);
      GNUNET_free(api);
      return NULL;
    }
    plugin->server
      = GNUNET_SERVER_create_with_sockets (&plugin_tcp_access_check,
                                           plugin, NULL,
                                           idle_timeout, GNUNET_YES);
  }
  plugin->handlers = GNUNET_malloc (sizeof (my_handlers));
  memcpy (plugin->handlers, my_handlers, sizeof(my_handlers));
  for (i = 0;i < sizeof(my_handlers) / sizeof(struct GNUNET_SERVER_MessageHandler);i++)
    plugin->handlers[i].callback_cls = plugin;

  GNUNET_SERVER_add_handlers (plugin->server, plugin->handlers);
  GNUNET_SERVER_disconnect_notify (plugin->server, &disconnect_notify, plugin);
  plugin->nat_wait_conns = GNUNET_CONTAINER_multipeermap_create (16,
                                                                 GNUNET_YES);
  if (0 != bport)
    LOG (GNUNET_ERROR_TYPE_INFO,
         _("TCP transport listening on port %llu\n"),
         bport);
  else
    LOG (GNUNET_ERROR_TYPE_INFO,
         _("TCP transport not listening on any port (client only)\n"));
  if ( (aport != bport) &&
       (0 != bport) )
    LOG (GNUNET_ERROR_TYPE_INFO,
         _("TCP transport advertises itself as being on port %llu\n"),
         aport);
  /* Initially set connections to 0 */
  GNUNET_assert(NULL != plugin->env->stats);
  GNUNET_STATISTICS_set (plugin->env->stats,
                         gettext_noop ("# TCP sessions active"),
                         0,
                         GNUNET_NO);
  return api;
}


/**
 * Exit point from the plugin.
 *
 * @param cls the `struct GNUNET_TRANSPORT_PluginFunctions`
 * @return NULL
 */
void *
libgnunet_plugin_transport_tcp_done (void *cls)
{
  struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
  struct Plugin *plugin = api->cls;
  struct TCPProbeContext *tcp_probe;
  struct PrettyPrinterContext *cur;
  struct PrettyPrinterContext *next;

  if (NULL == plugin)
  {
    GNUNET_free(api);
    return NULL ;
  }
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Shutting down TCP plugin\n");

  /* Removing leftover sessions */
  GNUNET_CONTAINER_multipeermap_iterate (plugin->sessionmap,
                                         &session_disconnect_it,
                                         plugin);
  /* Removing leftover NAT sessions */
  GNUNET_CONTAINER_multipeermap_iterate (plugin->nat_wait_conns,
                                         &session_disconnect_it,
                                         plugin);

  next = ppc_dll_head;
  for (cur = next; NULL != cur; cur = next)
  {
    GNUNET_break (0);
    next = cur->next;
    GNUNET_CONTAINER_DLL_remove (ppc_dll_head,
                                 ppc_dll_tail,
                                 cur);
    GNUNET_RESOLVER_request_cancel (cur->resolver_handle);
    GNUNET_free (cur);
  }

  if (NULL != plugin->service)
    GNUNET_SERVICE_stop (plugin->service);
  else
    GNUNET_SERVER_destroy (plugin->server);
  GNUNET_free(plugin->handlers);
  if (NULL != plugin->nat)
    GNUNET_NAT_unregister (plugin->nat);
  while (NULL != (tcp_probe = plugin->probe_head))
  {
    GNUNET_CONTAINER_DLL_remove (plugin->probe_head,
                                 plugin->probe_tail,
                                 tcp_probe);
    GNUNET_CONNECTION_destroy (tcp_probe->sock);
    GNUNET_free(tcp_probe);
  }
  GNUNET_CONTAINER_multipeermap_destroy (plugin->nat_wait_conns);
  GNUNET_CONTAINER_multipeermap_destroy (plugin->sessionmap);
  GNUNET_free(plugin);
  GNUNET_free(api);
  return NULL;
}

/* end of plugin_transport_tcp.c */