first step to remove plibc

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

/*
  This file is part of GNUnet
  Copyright (C) 2002--2015 GNUnet e.V.

  GNUnet is free software: you can redistribute it and/or modify it
  under the terms of the GNU Affero General Public License as published
  by the Free Software Foundation, either version 3 of the License,
  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
  Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */
/**
 * @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_service.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)

/**
 * Opaque handle that can be used to cancel
 * a transmit-ready notification.
 */
struct GNUNET_CONNECTION_TransmitHandle;

/**
 * @brief handle for a server
 */
struct GNUNET_SERVER_Handle;

/**
 * @brief opaque handle for a client of the server
 */
struct GNUNET_SERVER_Client;

/**
 * @brief opaque handle server returns for aborting transmission to a client.
 */
struct GNUNET_SERVER_TransmitHandle;

/**
 * @brief handle for a network connection
 */
struct GNUNET_CONNECTION_Handle;

/**
 * @brief handle for a network service
 */
struct LEGACY_SERVICE_Context;


/**
 * Stops a service that was started with #GNUNET_SERVICE_start().
 *
 * @param srv service to stop
 */
void
LEGACY_SERVICE_stop (struct LEGACY_SERVICE_Context *srv);


/**
 * Function called to notify a client about the connection begin ready
 * to queue more data.  @a buf will be NULL and @a size zero if the
 * connection 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
 */
typedef size_t (*GNUNET_CONNECTION_TransmitReadyNotify) (void *cls,
                                                         size_t size,
                                                         void *buf);

/**
 * Credentials for UNIX domain sockets.
 */
struct GNUNET_CONNECTION_Credentials
{
  /**
   * UID of the other end of the connection.
   */
  uid_t uid;

  /**
   * GID of the other end of the connection.
   */
  gid_t gid;
};


/**
 * Functions with this signature are called whenever a client
 * is disconnected on the network level.
 *
 * @param cls closure
 * @param client identification of the client; NULL
 *        for the last call when the server is destroyed
 */
typedef void (*GNUNET_SERVER_DisconnectCallback) (
  void *cls,
  struct GNUNET_SERVER_Client *client);


/**
 * Functions with this signature are called whenever a client
 * is connected on the network level.
 *
 * @param cls closure
 * @param client identification of the client
 */
typedef void (*GNUNET_SERVER_ConnectCallback) (
  void *cls,
  struct GNUNET_SERVER_Client *client);


/**
 * Function to call for access control checks.
 *
 * @param cls closure
 * @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).
 */
typedef int (*GNUNET_CONNECTION_AccessCheck) (
  void *cls,
  const struct GNUNET_CONNECTION_Credentials *ucred,
  const struct sockaddr *addr,
  socklen_t addrlen);

/**
 * Callback function for data received from the network.  Note that
 * both "available" and "err" would be 0 if the read simply timed out.
 *
 * @param cls closure
 * @param buf pointer to received data
 * @param available number of bytes availabe in "buf",
 *        possibly 0 (on errors)
 * @param addr address of the sender
 * @param addrlen size of addr
 * @param errCode value of errno (on errors receiving)
 */
typedef void (*GNUNET_CONNECTION_Receiver) (void *cls,
                                            const void *buf,
                                            size_t available,
                                            const struct sockaddr *addr,
                                            socklen_t addrlen,
                                            int errCode);


/**
 * Close the connection and free associated resources.  There must
 * not be any pending requests for reading or writing to the
 * connection at this time.
 *
 * @param connection connection to destroy
 */
void
GNUNET_CONNECTION_destroy (struct GNUNET_CONNECTION_Handle *connection);


/**
 * Signature of a function to create a custom tokenizer.
 *
 * @param cls closure from #GNUNET_SERVER_set_callbacks
 * @param client handle to client the tokenzier will be used for
 * @return handle to custom tokenizer ('mst')
 */
typedef void *(*GNUNET_SERVER_MstCreateCallback) (
  void *cls,
  struct GNUNET_SERVER_Client *client);


/**
 * Signature of a function to destroy a custom tokenizer.
 *
 * @param cls closure from #GNUNET_SERVER_set_callbacks
 * @param mst custom tokenizer handle
 */
typedef void (*GNUNET_SERVER_MstDestroyCallback) (void *cls, void *mst);

/**
 * Signature of a function to receive data for a custom tokenizer.
 *
 * @param cls closure from #GNUNET_SERVER_set_callbacks
 * @param mst custom tokenizer handle
 * @param client_identity ID of client for which this is a buffer,
 *        can be NULL (will be passed back to 'cb')
 * @param buf input data to add
 * @param size number of bytes in @a buf
 * @param purge should any excess bytes in the buffer be discarded
 *       (i.e. for packet-based services like UDP)
 * @param one_shot only call callback once, keep rest of message in buffer
 * @return #GNUNET_OK if we are done processing (need more data)
 *         #GNUNET_NO if one_shot was set and we have another message ready
 *         #GNUNET_SYSERR if the data stream is corrupt
 */
typedef int (*GNUNET_SERVER_MstReceiveCallback) (
  void *cls,
  void *mst,
  struct GNUNET_SERVER_Client *client,
  const char *buf,
  size_t size,
  int purge,
  int one_shot);
/**
 * Functions with this signature are called whenever a message is
 * received.
 *
 * @param cls closure
 * @param client identification of the client
 * @param message the actual message
 */
typedef void (*GNUNET_SERVER_MessageCallback) (
  void *cls,
  struct GNUNET_SERVER_Client *client,
  const struct GNUNET_MessageHeader *message);

/**
 * Message handler.  Each struct specifies how to handle on particular
 * type of message received.
 */
struct GNUNET_SERVER_MessageHandler
{
  /**
   * Function to call for messages of "type".
   */
  GNUNET_SERVER_MessageCallback callback;

  /**
   * Closure argument for @e callback.
   */
  void *callback_cls;

  /**
   * Type of the message this handler covers.
   */
  uint16_t type;

  /**
   * Expected size of messages of this type.  Use 0 for
   * variable-size.  If non-zero, messages of the given
   * type will be discarded (and the connection closed)
   * if they do not have the right size.
   */
  uint16_t expected_size;
};


/**
 * Options for the service (bitmask).
 */
enum LEGACY_SERVICE_Options
{
  /**
   * Use defaults.  Terminates all client connections and the listen
   * sockets immediately upon receiving the shutdown signal.
   */
  LEGACY_SERVICE_OPTION_NONE = 0,

  /**
   * Do not trigger server shutdown on signal at all; instead, allow
   * for the user to terminate the server explicitly when needed
   * by calling #LEGACY_SERVICE_shutdown().
   */
  LEGACY_SERVICE_OPTION_MANUAL_SHUTDOWN = 1,

  /**
   * Trigger a SOFT server shutdown on signals, allowing active
   * non-monitor clients to complete their transactions.
   */
  LEGACY_SERVICE_OPTION_SOFT_SHUTDOWN = 2
};


/**
 * Ask the server to disconnect from the given client.  This is the
 * same as passing #GNUNET_SYSERR to #GNUNET_SERVER_receive_done,
 * except that it allows dropping of a client even when not handling a
 * message from that client.
 *
 * @param client the client to disconnect from
 */
void
GNUNET_SERVER_client_disconnect (struct GNUNET_SERVER_Client *client);

/**
 * Return user context associated with the given client.
 * Note: you should probably use the macro (call without the underscore).
 *
 * @param client client to query
 * @param size number of bytes in user context struct (for verification only)
 * @return pointer to user context
 */
void *
GNUNET_SERVER_client_get_user_context_ (struct GNUNET_SERVER_Client *client,
                                        size_t size);


/**
 * Functions with this signature are called whenever a
 * complete message is received by the tokenizer.
 *
 * Do not call #GNUNET_SERVER_mst_destroy from within
 * the scope of this callback.
 *
 * @param cls closure
 * @param client identification of the client
 * @param message the actual message
 * @return #GNUNET_OK on success, #GNUNET_SYSERR to stop further processing
 */
typedef int (*GNUNET_SERVER_MessageTokenizerCallback) (
  void *cls,
  void *client,
  const struct GNUNET_MessageHeader *message);


/**
 * Create a message stream tokenizer.
 *
 * @param cb function to call on completed messages
 * @param cb_cls closure for @a cb
 * @return handle to tokenizer
 */
struct GNUNET_SERVER_MessageStreamTokenizer *
GNUNET_SERVER_mst_create (GNUNET_SERVER_MessageTokenizerCallback cb,
                          void *cb_cls);

/**
 * Add incoming data to the receive buffer and call the
 * callback for all complete messages.
 *
 * @param mst tokenizer to use
 * @param client_identity ID of client for which this is a buffer,
 *        can be NULL (will be passed back to 'cb')
 * @param buf input data to add
 * @param size number of bytes in @a buf
 * @param purge should any excess bytes in the buffer be discarded
 *       (i.e. for packet-based services like UDP)
 * @param one_shot only call callback once, keep rest of message in buffer
 * @return #GNUNET_OK if we are done processing (need more data)
 *         #GNUNET_NO if one_shot was set and we have another message ready
 *         #GNUNET_SYSERR if the data stream is corrupt
 */
int
GNUNET_SERVER_mst_receive (struct GNUNET_SERVER_MessageStreamTokenizer *mst,
                           void *client_identity,
                           const char *buf,
                           size_t size,
                           int purge,
                           int one_shot);


/**
 * Destroys a tokenizer.
 *
 * @param mst tokenizer to destroy
 */
void
GNUNET_SERVER_mst_destroy (struct GNUNET_SERVER_MessageStreamTokenizer *mst);


/**
 * Set user context to be associated with the given client.
 * Note: you should probably use the macro (call without the underscore).
 *
 * @param client client to query
 * @param ptr pointer to user context
 * @param size number of bytes in user context struct (for verification only)
 */
void
GNUNET_SERVER_client_set_user_context_ (struct GNUNET_SERVER_Client *client,
                                        void *ptr,
                                        size_t size);
/**
 * Return user context associated with the given client.
 *
 * @param client client to query
 * @param type expected return type (i.e. 'struct Foo')
 * @return pointer to user context of type 'type *'.
 */
#define GNUNET_SERVER_client_get_user_context(client, type) \
  (type *) GNUNET_SERVER_client_get_user_context_ (client, sizeof (type))

/**
 * Set user context to be associated with the given client.
 *
 * @param client client to query
 * @param value pointer to user context
 */
#define GNUNET_SERVER_client_set_user_context(client, value) \
  GNUNET_SERVER_client_set_user_context_ (client, value, sizeof (*value))


/**
 * Notify us when the server has enough space to transmit
 * a message of the given size to the given client.
 *
 * @param client client to transmit message to
 * @param size requested amount of buffer space
 * @param timeout after how long should we give up (and call
 *        notify with buf NULL and size 0)?
 * @param callback function to call when space is available
 * @param callback_cls closure for @a callback
 * @return non-NULL if the notify callback was queued; can be used
 *           to cancel the request using
 *           #GNUNET_SERVER_notify_transmit_ready_cancel.
 *         NULL if we are already going to notify someone else (busy)
 */
struct GNUNET_SERVER_TransmitHandle *
GNUNET_SERVER_notify_transmit_ready (
  struct GNUNET_SERVER_Client *client,
  size_t size,
  struct GNUNET_TIME_Relative timeout,
  GNUNET_CONNECTION_TransmitReadyNotify callback,
  void *callback_cls);

/**
 * Abort transmission request.
 *
 * @param th request to abort
 */
void
GNUNET_SERVER_notify_transmit_ready_cancel (
  struct GNUNET_SERVER_TransmitHandle *th);


/**
 * Notify the server that the given client handle should
 * be kept (keeps the connection up if possible, increments
 * the internal reference counter).
 *
 * @param client the client to keep
 */
void
GNUNET_SERVER_client_keep (struct GNUNET_SERVER_Client *client);


/**
 * Notify the server that the given client handle is no
 * longer required.  Decrements the reference counter.  If
 * that counter reaches zero an inactive connection maybe
 * closed.
 *
 * @param client the client to drop
 */
void
GNUNET_SERVER_client_drop (struct GNUNET_SERVER_Client *client);


/**
 * Function called by the service's run
 * method to run service-specific setup code.
 *
 * @param cls closure
 * @param server the initialized server
 * @param cfg configuration to use
 */
typedef void (*LEGACY_SERVICE_Main) (
  void *cls,
  struct GNUNET_SERVER_Handle *server,
  const struct GNUNET_CONFIGURATION_Handle *cfg);


/**
 * Suspend accepting connections from the listen socket temporarily.
 * Resume activity using #GNUNET_SERVER_resume.
 *
 * @param server server to stop accepting connections.
 */
void
GNUNET_SERVER_suspend (struct GNUNET_SERVER_Handle *server);

/**
 * Notify us when the server has enough space to transmit
 * a message of the given size to the given client.
 *
 * @param client client to transmit message to
 * @param size requested amount of buffer space
 * @param timeout after how long should we give up (and call
 *        notify with buf NULL and size 0)?
 * @param callback function to call when space is available
 * @param callback_cls closure for @a callback
 * @return non-NULL if the notify callback was queued; can be used
 *           to cancel the request using
 *           #GNUNET_SERVER_notify_transmit_ready_cancel.
 *         NULL if we are already going to notify someone else (busy)
 */
struct GNUNET_SERVER_TransmitHandle *
GNUNET_SERVER_notify_transmit_ready (
  struct GNUNET_SERVER_Client *client,
  size_t size,
  struct GNUNET_TIME_Relative timeout,
  GNUNET_CONNECTION_TransmitReadyNotify callback,
  void *callback_cls);


/**
 * Add a TCP socket-based connection to the set of handles managed by
 * this server.  Use this function for outgoing (P2P) connections that
 * we initiated (and where this server should process incoming
 * messages).
 *
 * @param server the server to use
 * @param connection the connection to manage (client must
 *        stop using this connection from now on)
 * @return the client handle
 */
struct GNUNET_SERVER_Client *
GNUNET_SERVER_connect_socket (struct GNUNET_SERVER_Handle *server,
                              struct GNUNET_CONNECTION_Handle *connection);


/**
 * Resume accepting connections from the listen socket.
 *
 * @param server server to resume accepting connections.
 */
void
GNUNET_SERVER_resume (struct GNUNET_SERVER_Handle *server);

/**
 * Free resources held by this server.
 *
 * @param server server to destroy
 */
void
GNUNET_SERVER_destroy (struct GNUNET_SERVER_Handle *server);


#include "tcp_connection_legacy.c"
#include "tcp_server_mst_legacy.c"
#include "tcp_server_legacy.c"
#include "tcp_service_legacy.c"

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;
};

/**
 * Bits in the `options` field of TCP addresses.
 */
enum TcpAddressOptions
{

  /**
   * No bits set.
   */
  TCP_OPTIONS_NONE = 0,

  /**
   * See #HTTP_OPTIONS_VERIFY_CERTIFICATE.
   */
  TCP_OPTIONS_RESERVED = 1,

  /**
   * Enable TCP Stealth-style port knocking.
   */
  TCP_OPTIONS_TCP_STEALTH = 2
};

GNUNET_NETWORK_STRUCT_BEGIN

/**
 * Network format for IPv4 addresses.
 */
struct IPv4TcpAddress
{
  /**
   * Optional options and flags for this address,
   * see `enum TcpAddressOptions`
   */
  uint32_t options GNUNET_PACKED;

  /**
   * 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
   * see `enum TcpAddressOptions`
   */
  uint32_t options GNUNET_PACKED;

  /**
   * 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 @e 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 `struct GNUNET_MessageHeader`.
   */
  size_t message_size;
};

/**
 * Session handle for TCP connections.
 */
struct GNUNET_ATS_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;
   */
  struct GNUNET_SCHEDULER_Task *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.
   */
  struct GNUNET_SCHEDULER_Task *receive_delay_task;

  /**
   * Session timeout task
   */
  struct GNUNET_SCHEDULER_Task *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;

  /**
   * Network type of the address.
   */
  enum GNUNET_NetworkType scope;

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

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


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

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

  /**
   * Our plugin.
   */
  struct Plugin *plugin;

  /**
   * Timeout task
   */
  struct GNUNET_SCHEDULER_Task *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;

  /**
   * IPv6 address
   */
  int ipv6;

  /**
   * Options
   */
  uint32_t options;

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


/**
 * 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 LEGACY_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;

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

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

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

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

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

  /**
   * Welcome message used by this peer.
   */
  struct WelcomeMessage my_welcome;

  /**
   * 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;

  /**
   * 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;
};


/**
 * Get the list of addresses that a server for the given service
 * should bind to.
 *
 * @param service_name name of the service
 * @param cfg configuration (which specifies the addresses)
 * @param addrs set (call by reference) to an array of pointers to the
 *              addresses the server should bind to and listen on; the
 *              array will be NULL-terminated (on success)
 * @param addr_lens set (call by reference) to an array of the lengths
 *              of the respective `struct sockaddr` struct in the @a addrs
 *              array (on success)
 * @return number of addresses found on success,
 *              #GNUNET_SYSERR if the configuration
 *              did not specify reasonable finding information or
 *              if it specified a hostname that could not be resolved;
 *              #GNUNET_NO if the number of addresses configured is
 *              zero (in this case, `*addrs` and `*addr_lens` will be
 *              set to NULL).
 */
static int
get_server_addresses (const char *service_name,
                      const struct GNUNET_CONFIGURATION_Handle *cfg,
                      struct sockaddr ***addrs,
                      socklen_t **addr_lens)
{
  int disablev6;
  struct GNUNET_NETWORK_Handle *desc;
  unsigned long long port;
  char *unixpath;
  struct addrinfo hints;
  struct addrinfo *res;
  struct addrinfo *pos;
  struct addrinfo *next;
  unsigned int i;
  int resi;
  int ret;
  int abstract;
  struct sockaddr **saddrs;
  socklen_t *saddrlens;
  char *hostname;

  *addrs = NULL;
  *addr_lens = NULL;
  desc = NULL;
  if (GNUNET_CONFIGURATION_have_value (cfg, service_name, "DISABLEV6"))
  {
    if (GNUNET_SYSERR ==
        (disablev6 = GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                                           service_name,
                                                           "DISABLEV6")))
      return GNUNET_SYSERR;
  }
  else
    disablev6 = GNUNET_NO;

  if (! disablev6)
  {
    /* probe IPv6 support */
    desc = GNUNET_NETWORK_socket_create (PF_INET6, SOCK_STREAM, 0);
    if (NULL == desc)
    {
      if ((ENOBUFS == errno) || (ENOMEM == errno) || (ENFILE == errno) ||
          (EACCES == errno))
      {
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR, "socket");
        return GNUNET_SYSERR;
      }
      LOG (GNUNET_ERROR_TYPE_INFO,
           _ (
             "Disabling IPv6 support for service `%s', failed to create IPv6 socket: %s\n"),
           service_name,
           strerror (errno));
      disablev6 = GNUNET_YES;
    }
    else
    {
      GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (desc));
      desc = NULL;
    }
  }

  port = 0;
  if (GNUNET_CONFIGURATION_have_value (cfg, service_name, "PORT"))
  {
    if (GNUNET_OK != GNUNET_CONFIGURATION_get_value_number (cfg,
                                                            service_name,
                                                            "PORT",
                                                            &port))
    {
      LOG (GNUNET_ERROR_TYPE_ERROR,
           _ ("Require valid port number for service `%s' in configuration!\n"),
           service_name);
    }
    if (port > 65535)
    {
      LOG (GNUNET_ERROR_TYPE_ERROR,
           _ ("Require valid port number for service `%s' in configuration!\n"),
           service_name);
      return GNUNET_SYSERR;
    }
  }

  if (GNUNET_CONFIGURATION_have_value (cfg, service_name, "BINDTO"))
  {
    GNUNET_break (GNUNET_OK ==
                  GNUNET_CONFIGURATION_get_value_string (cfg,
                                                         service_name,
                                                         "BINDTO",
                                                         &hostname));
  }
  else
    hostname = NULL;

  unixpath = NULL;
  abstract = GNUNET_NO;
#ifdef AF_UNIX
  if ((GNUNET_YES ==
       GNUNET_CONFIGURATION_have_value (cfg, service_name, "UNIXPATH")) &&
      (GNUNET_OK == GNUNET_CONFIGURATION_get_value_filename (cfg,
                                                             service_name,
                                                             "UNIXPATH",
                                                             &unixpath)) &&
      (0 < strlen (unixpath)))
  {
    /* probe UNIX support */
    struct sockaddr_un s_un;

    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);
    }
#ifdef LINUX
    abstract = GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                                     "TESTING",
                                                     "USE_ABSTRACT_SOCKETS");
    if (GNUNET_SYSERR == abstract)
      abstract = GNUNET_NO;
#endif
    if ((GNUNET_YES != abstract) &&
        (GNUNET_OK != GNUNET_DISK_directory_create_for_file (unixpath)))
      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR, "mkdir", unixpath);
  }
  if (NULL != unixpath)
  {
    desc = GNUNET_NETWORK_socket_create (AF_UNIX, SOCK_STREAM, 0);
    if (NULL == desc)
    {
      if ((ENOBUFS == errno) || (ENOMEM == errno) || (ENFILE == errno) ||
          (EACCES == errno))
      {
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR, "socket");
        GNUNET_free_non_null (hostname);
        GNUNET_free (unixpath);
        return GNUNET_SYSERR;
      }
      LOG (GNUNET_ERROR_TYPE_INFO,
           _ (
             "Disabling UNIX domain socket support for service `%s', failed to create UNIX domain socket: %s\n"),
           service_name,
           strerror (errno));
      GNUNET_free (unixpath);
      unixpath = NULL;
    }
    else
    {
      GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (desc));
      desc = NULL;
    }
  }
#endif

  if ((0 == port) && (NULL == unixpath))
  {
    LOG (GNUNET_ERROR_TYPE_ERROR,
         _ (
           "Have neither PORT nor UNIXPATH for service `%s', but one is required\n"),
         service_name);
    GNUNET_free_non_null (hostname);
    return GNUNET_SYSERR;
  }
  if (0 == port)
  {
    saddrs = GNUNET_malloc (2 * sizeof (struct sockaddr *));
    saddrlens = GNUNET_malloc (2 * sizeof (socklen_t));
    add_unixpath (saddrs, saddrlens, unixpath, abstract);
    GNUNET_free_non_null (unixpath);
    GNUNET_free_non_null (hostname);
    *addrs = saddrs;
    *addr_lens = saddrlens;
    return 1;
  }

  if (NULL != hostname)
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Resolving `%s' since that is where `%s' will bind to.\n",
         hostname,
         service_name);
    memset (&hints, 0, sizeof (struct addrinfo));
    if (disablev6)
      hints.ai_family = AF_INET;
    hints.ai_protocol = IPPROTO_TCP;
    if ((0 != (ret = getaddrinfo (hostname, NULL, &hints, &res))) ||
        (NULL == res))
    {
      LOG (GNUNET_ERROR_TYPE_ERROR,
           _ ("Failed to resolve `%s': %s\n"),
           hostname,
           gai_strerror (ret));
      GNUNET_free (hostname);
      GNUNET_free_non_null (unixpath);
      return GNUNET_SYSERR;
    }
    next = res;
    i = 0;
    while (NULL != (pos = next))
    {
      next = pos->ai_next;
      if ((disablev6) && (pos->ai_family == AF_INET6))
        continue;
      i++;
    }
    if (0 == i)
    {
      LOG (GNUNET_ERROR_TYPE_ERROR,
           _ ("Failed to find %saddress for `%s'.\n"),
           disablev6 ? "IPv4 " : "",
           hostname);
      freeaddrinfo (res);
      GNUNET_free (hostname);
      GNUNET_free_non_null (unixpath);
      return GNUNET_SYSERR;
    }
    resi = i;
    if (NULL != unixpath)
      resi++;
    saddrs = GNUNET_malloc ((resi + 1) * sizeof (struct sockaddr *));
    saddrlens = GNUNET_malloc ((resi + 1) * sizeof (socklen_t));
    i = 0;
    if (NULL != unixpath)
    {
      add_unixpath (saddrs, saddrlens, unixpath, abstract);
      i++;
    }
    next = res;
    while (NULL != (pos = next))
    {
      next = pos->ai_next;
      if ((disablev6) && (AF_INET6 == pos->ai_family))
        continue;
      if ((IPPROTO_TCP != pos->ai_protocol) && (0 != pos->ai_protocol))
        continue; /* not TCP */
      if ((SOCK_STREAM != pos->ai_socktype) && (0 != pos->ai_socktype))
        continue; /* huh? */
      LOG (GNUNET_ERROR_TYPE_DEBUG,
           "Service `%s' will bind to `%s'\n",
           service_name,
           GNUNET_a2s (pos->ai_addr, pos->ai_addrlen));
      if (AF_INET == pos->ai_family)
      {
        GNUNET_assert (sizeof (struct sockaddr_in) == pos->ai_addrlen);
        saddrlens[i] = pos->ai_addrlen;
        saddrs[i] = GNUNET_malloc (saddrlens[i]);
        GNUNET_memcpy (saddrs[i], pos->ai_addr, saddrlens[i]);
        ((struct sockaddr_in *) saddrs[i])->sin_port = htons (port);
      }
      else
      {
        GNUNET_assert (AF_INET6 == pos->ai_family);
        GNUNET_assert (sizeof (struct sockaddr_in6) == pos->ai_addrlen);
        saddrlens[i] = pos->ai_addrlen;
        saddrs[i] = GNUNET_malloc (saddrlens[i]);
        GNUNET_memcpy (saddrs[i], pos->ai_addr, saddrlens[i]);
        ((struct sockaddr_in6 *) saddrs[i])->sin6_port = htons (port);
      }
      i++;
    }
    GNUNET_free (hostname);
    freeaddrinfo (res);
    resi = i;
  }
  else
  {
    /* will bind against everything, just set port */
    if (disablev6)
    {
      /* V4-only */
      resi = 1;
      if (NULL != unixpath)
        resi++;
      i = 0;
      saddrs = GNUNET_malloc ((resi + 1) * sizeof (struct sockaddr *));
      saddrlens = GNUNET_malloc ((resi + 1) * sizeof (socklen_t));
      if (NULL != unixpath)
      {
        add_unixpath (saddrs, saddrlens, unixpath, abstract);
        i++;
      }
      saddrlens[i] = sizeof (struct sockaddr_in);
      saddrs[i] = GNUNET_malloc (saddrlens[i]);
#if HAVE_SOCKADDR_IN_SIN_LEN
      ((struct sockaddr_in *) saddrs[i])->sin_len = saddrlens[i];
#endif
      ((struct sockaddr_in *) saddrs[i])->sin_family = AF_INET;
      ((struct sockaddr_in *) saddrs[i])->sin_port = htons (port);
    }
    else
    {
      /* dual stack */
      resi = 2;
      if (NULL != unixpath)
        resi++;
      saddrs = GNUNET_malloc ((resi + 1) * sizeof (struct sockaddr *));
      saddrlens = GNUNET_malloc ((resi + 1) * sizeof (socklen_t));
      i = 0;
      if (NULL != unixpath)
      {
        add_unixpath (saddrs, saddrlens, unixpath, abstract);
        i++;
      }
      saddrlens[i] = sizeof (struct sockaddr_in6);
      saddrs[i] = GNUNET_malloc (saddrlens[i]);
#if HAVE_SOCKADDR_IN_SIN_LEN
      ((struct sockaddr_in6 *) saddrs[i])->sin6_len = saddrlens[0];
#endif
      ((struct sockaddr_in6 *) saddrs[i])->sin6_family = AF_INET6;
      ((struct sockaddr_in6 *) saddrs[i])->sin6_port = htons (port);
      i++;
      saddrlens[i] = sizeof (struct sockaddr_in);
      saddrs[i] = GNUNET_malloc (saddrlens[i]);
#if HAVE_SOCKADDR_IN_SIN_LEN
      ((struct sockaddr_in *) saddrs[i])->sin_len = saddrlens[1];
#endif
      ((struct sockaddr_in *) saddrs[i])->sin_family = AF_INET;
      ((struct sockaddr_in *) saddrs[i])->sin_port = htons (port);
    }
  }
  GNUNET_free_non_null (unixpath);
  *addrs = saddrs;
  *addr_lens = saddrlens;
  return resi;
}
/* end ancient copy-and-paste */


/**
 * 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 GNUNET_ATS_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_HELLO_address_check_option (session->address,
                                       GNUNET_HELLO_ADDRESS_INFO_INBOUND);
  info.num_msg_pending = session->msgs_in_queue;
  info.num_bytes_pending = session->bytes_in_queue;
  if (NULL != 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);
}


/**
 * Our external IP address/port mapping has changed.
 *
 * @param cls closure, the `struct Plugin`
 * @param app_ctx[in,out] location where the app can store stuff
 *                  on add and retrieve it on remove
 * @param add_remove #GNUNET_YES to mean the new public IP address, #GNUNET_NO to mean
 *     the previous (now invalid) one
 * @param ac address class the address belongs to
 * @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,
                           void **app_ctx,
                           int add_remove,
                           enum GNUNET_NAT_AddressClass ac,
                           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;

  (void) app_ctx;
  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:
    if (IN6_IS_ADDR_LINKLOCAL (&((struct sockaddr_in6 *) addr)->sin6_addr))
    {
      /* skip link local, we don't allow them in
         #tcp_plugin_check_address() */
      return;
    }
    GNUNET_assert (addrlen == sizeof (struct sockaddr_in6));
    memset (&t6, 0, sizeof (t6));
    GNUNET_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)));
  /* TODO: use 'ac' here in the future... */
  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);
    GNUNET_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);
    GNUNET_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) || (0 == addrlen))
  {
    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 GNUNET_ATS_Session *
lookup_session_by_client (struct Plugin *plugin,
                          struct GNUNET_SERVER_Client *client)
{
  return GNUNET_SERVER_client_get_user_context (client,
                                                struct GNUNET_ATS_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 GNUNET_ATS_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 (session->plugin,
                                     session->address->address,
                                     session->address->address_length));

  if (NULL != session->timeout_task)
  {
    GNUNET_SCHEDULER_cancel (session->timeout_task);
    session->timeout_task = NULL;
    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, NULL);

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

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

  while (NULL != (pm = session->pending_messages_head))
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         (NULL != pm->transmit_cont)
           ? "Could not deliver message to `%s' at %s.\n"
           : "Could not deliver message to `%s' at %s, notifying.\n",
         GNUNET_i2s (&session->target),
         tcp_plugin_address_to_string (session->plugin,
                                       session->address->address,
                                       session->address->address_length));
    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_DONE);

  if (NULL != session->receive_delay_task)
  {
    GNUNET_SCHEDULER_cancel (session->receive_delay_task);
    session->receive_delay_task = NULL;
  }
  if (NULL != session->client)
  {
    GNUNET_SERVER_client_disconnect (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 for too long, so disconnect it
 *
 * @param cls the `struct GNUNET_ATS_Session` of the idle session
 */
static void
session_timeout (void *cls)
{
  struct GNUNET_ATS_Session *s = cls;
  struct GNUNET_TIME_Relative left;

  s->timeout_task = NULL;
  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_UPDATE);
    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 GNUNET_ATS_Session *s)
{
  GNUNET_assert (NULL != 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 scope network scope the address is from
 * @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 GNUNET_ATS_Session *
create_session (struct Plugin *plugin,
                const struct GNUNET_HELLO_Address *address,
                enum GNUNET_NetworkType scope,
                struct GNUNET_SERVER_Client *client,
                int is_nat)
{
  struct GNUNET_ATS_Session *session;
  struct PendingMessage *pm;

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

  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Creating new session for peer `%s' at address %s\n",
       GNUNET_i2s (&address->peer),
       tcp_plugin_address_to_string (plugin,
                                     address->address,
                                     address->address_length));
  session = GNUNET_new (struct GNUNET_ATS_Session);
  session->last_activity = GNUNET_TIME_absolute_get ();
  session->plugin = plugin;
  session->is_nat = is_nat;
  if (NULL != client)
  {
    session->client = client;
    GNUNET_SERVER_client_set_user_context (client, session);
  }
  session->address = GNUNET_HELLO_address_copy (address);
  session->target = address->peer;
  session->expecting_welcome = GNUNET_YES;
  session->scope = scope;
  pm = GNUNET_malloc (sizeof (struct PendingMessage) +
                      sizeof (struct WelcomeMessage));
  pm->msg = (const char *) &pm[1];
  pm->message_size = sizeof (struct WelcomeMessage);
  GNUNET_memcpy (&pm[1], &plugin->my_welcome, sizeof (struct WelcomeMessage));
  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);
  notify_session_monitor (session->plugin, session, GNUNET_TRANSPORT_SS_INIT);
  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);
  }
  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 GNUNET_ATS_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 GNUNET_ATS_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 `%s', 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 `%s'.\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 (NULL != pos->transmit_cont)
        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_UPDATE);
    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 to peer %s at %s\n",
         ntohs (((struct GNUNET_MessageHeader *) pos->msg)->type),
         pos->message_size,
         GNUNET_i2s (&session->target),
         tcp_plugin_address_to_string (session->plugin,
                                       session->address->address,
                                       session->address->address_length));
    /* FIXME: this GNUNET_memcpy can be up to 7% of our total runtime */
    GNUNET_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_UPDATE);
  /* 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 (NULL != pos->transmit_cont)
      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);
  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 GNUNET_ATS_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 @a 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 GNUNET_ATS_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];
  GNUNET_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_UPDATE);
    session->msgs_in_queue++;
    session->bytes_in_queue += pm->message_size;
    process_pending_messages (session);
    return msgbuf_size;
  }
  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;
  }
  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 GNUNET_ATS_SessionItCtx
{
  /**
   * Address we are looking for.
   */
  const struct GNUNET_HELLO_Address *address;

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


/**
 * Look for a session by address.
 *
 * @param cls the `struct GNUNET_ATS_SessionItCtx`
 * @param key unused
 * @param value a `struct GNUNET_ATS_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 GNUNET_ATS_SessionItCtx *si_ctx = cls;
  struct GNUNET_ATS_Session *session = value;

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


/**
 * Task cleaning up a NAT connection attempt after timeout
 *
 * @param cls the `struct GNUNET_ATS_Session`
 */
static void
nat_connect_timeout (void *cls)
{
  struct GNUNET_ATS_Session *session = cls;

  session->nat_connection_timeout = NULL;
  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 (session->plugin,
                                     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 GNUNET_ATS_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 GNUNET_ATS_Session *`
 */
static void
delayed_done (void *cls)
{
  struct GNUNET_ATS_Session *session = cls;

  session->receive_delay_task = NULL;
  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 GNUNET_ATS_Session *session,
                                 struct GNUNET_TIME_Relative delay)
{
  if (NULL == 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 GNUNET_ATS_Session *
tcp_plugin_get_session (void *cls, const struct GNUNET_HELLO_Address *address)
{
  struct Plugin *plugin = cls;
  struct GNUNET_ATS_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;
  unsigned int options;
  enum GNUNET_NetworkType net_type;
  unsigned int is_natd = GNUNET_NO;
  size_t addrlen;
#ifdef TCP_STEALTH
  struct GNUNET_NETWORK_Handle *s;
#endif

  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 (plugin,
                                     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 GNUNET_ATS_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 (NULL != si_ctx.result)
    {
      session = si_ctx.result;
      LOG (GNUNET_ERROR_TYPE_DEBUG,
           "Found existing session for `%s' address `%s'\n",
           GNUNET_i2s (&address->peer),
           tcp_plugin_address_to_string (plugin,
                                         address->address,
                                         address->address_length));
      return session;
    }
    /* This is a bit of a hack, limiting TCP to never allow more than
       one TCP connection to any given peer at the same time.
       Without this, peers sometimes disagree about which of the TCP
       connections they should use, causing one side to believe that
       they transmit successfully, while the other receives nothing. */
    return NULL; /* Refuse to have more than one TCP connection per
                    peer pair at the same time. */
  }

  if (addrlen == sizeof (struct IPv6TcpAddress))
  {
    GNUNET_assert (NULL != address->address); /* make static analysis happy */
    t6 = address->address;
    options = t6->options;
    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;
    GNUNET_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;
    options = t4->options;
    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;
  }

  net_type = plugin->env->get_address_type (plugin->env->cls, sb, sbs);
  GNUNET_break (net_type != GNUNET_NT_UNSPECIFIED);

  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)))
  {
    struct sockaddr_in local_sa;

    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Found valid IPv4 NAT address (creating session)!\n");
    session = create_session (plugin, address, net_type, NULL, GNUNET_YES);
    session->nat_connection_timeout =
      GNUNET_SCHEDULER_add_delayed (NAT_TIMEOUT, &nat_connect_timeout, session);
    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 `%s' at `%s'\n",
         GNUNET_i2s (&session->target),
         GNUNET_a2s (sb, sbs));
    memset (&local_sa, 0, sizeof (local_sa));
    local_sa.sin_family = AF_INET;
    local_sa.sin_port = htons (plugin->open_port);
    /* We leave sin_address at 0, let the kernel figure it out,
       even if our bind() is more specific.  (May want to reconsider
       later.) */
    if (GNUNET_OK == GNUNET_NAT_request_reversal (plugin->nat, &local_sa, &a4))
      return session;
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Running NAT client for `%s' at `%s' failed\n",
         GNUNET_i2s (&session->target),
         GNUNET_a2s (sb, sbs));
    tcp_plugin_disconnect_session (plugin, session);
    return NULL;
  }

  /* create new outbound session */
  if (0 != (options & TCP_OPTIONS_TCP_STEALTH))
  {
#ifdef TCP_STEALTH
    s = GNUNET_NETWORK_socket_create (af, SOCK_STREAM, 0);
    if (NULL == s)
    {
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
                           "socket");
      sa = NULL;
    }
    else
    {
      if ((GNUNET_OK !=
           GNUNET_NETWORK_socket_setsockopt (s,
                                             IPPROTO_TCP,
                                             TCP_STEALTH,
                                             &session->target,
                                             sizeof (
                                               struct GNUNET_PeerIdentity))) ||
          (GNUNET_OK !=
           GNUNET_NETWORK_socket_setsockopt (s,
                                             IPPROTO_TCP,
                                             TCP_STEALTH_INTEGRITY,
                                             &plugin->my_welcome,
                                             sizeof (struct WelcomeMessage))))
      {
        /* TCP STEALTH not supported by kernel */
        GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (s));
        sa = NULL;
      }
      else
      {
        sa = GNUNET_CONNECTION_connect_socket (s, sb, sbs);
      }
    }
#else
    sa = NULL;
#endif
  }
  else
  {
    sa = GNUNET_CONNECTION_create_from_sockaddr (af, sb, sbs);
  }
  if (NULL == sa)
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Failed to create connection to `%s' at `%s'\n",
         GNUNET_i2s (&address->peer),
         GNUNET_a2s (sb, sbs));
    return NULL;
  }
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Asked to transmit to `%s', creating fresh session using address `%s'.\n",
       GNUNET_i2s (&address->peer),
       GNUNET_a2s (sb, sbs));

  session = create_session (plugin,
                            address,
                            net_type,
                            GNUNET_SERVER_connect_socket (plugin->server, sa),
                            GNUNET_NO);
  (void) GNUNET_CONTAINER_multipeermap_put (
    plugin->sessionmap,
    &session->target,
    session,
    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  /* Send TCP Welcome */
  process_pending_messages (session);

  return session;
}


/**
 * We have been asked to destroy all connections to a particular peer.
 * This function is called on each applicable session and must tear it
 * down.
 *
 * @param cls the `struct Plugin *`
 * @param key the peer which the session belongs to (unused)
 * @param value the `struct GNUNET_ATS_Session`
 * @return #GNUNET_YES (continue to iterate)
 */
static int
session_disconnect_it (void *cls,
                       const struct GNUNET_PeerIdentity *key,
                       void *value)
{
  struct Plugin *plugin = cls;
  struct GNUNET_ATS_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 `%s'\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);
}


/**
 * We are processing an address pretty printing request and finished
 * the IP resolution (if applicable).  Append our port and forward the
 * result.  If called with @a hostname NULL, we are done and should
 * clean up the pretty printer (otherwise, there might be multiple
 * hostnames for the IP address and we might receive more).
 *
 * @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;
  struct Plugin *plugin = ppc->plugin;
  char *ret;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "append_port called with hostname `%s'\n",
              hostname);
  if (NULL == hostname)
  {
    /* Final call, done */
    ppc->resolver_handle = NULL;
    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
                                 plugin->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 with the `struct Plugin`
 * @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 Plugin *plugin = 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;
    GNUNET_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 */
    LOG (GNUNET_ERROR_TYPE_WARNING,
         _ ("Unexpected address length: %u bytes\n"),
         (unsigned int) addrlen);
    asc (asc_cls, NULL, GNUNET_SYSERR);
    asc (asc_cls, NULL, GNUNET_OK);
    return;
  }
  ppc = GNUNET_new (struct PrettyPrinterContext);
  ppc->plugin = plugin;
  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;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Starting DNS reverse lookup\n");
  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 (plugin->ppc_dll_head, plugin->ppc_dll_tail, ppc);
}


/**
 * 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 @a 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;
  const struct IPv4TcpAddress *v4;
  const struct IPv6TcpAddress *v6;

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

  if (addrlen == sizeof (struct IPv4TcpAddress))
  {
    struct sockaddr_in s4;

    v4 = (const struct IPv4TcpAddress *) addr;
    if (0 != memcmp (&v4->options, &plugin->myoptions, sizeof (uint32_t)))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    memset (&s4, 0, sizeof (s4));
    s4.sin_family = AF_INET;
#if HAVE_SOCKADDR_IN_SIN_LEN
    s4.sin_len = sizeof (s4);
#endif
    s4.sin_port = v4->t4_port;
    s4.sin_addr.s_addr = v4->ipv4_addr;

    if (GNUNET_OK !=
        GNUNET_NAT_test_address (plugin->nat, &s4, sizeof (struct sockaddr_in)))
      return GNUNET_SYSERR;
  }
  else
  {
    struct sockaddr_in6 s6;

    v6 = (const 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;
    }
    memset (&s6, 0, sizeof (s6));
    s6.sin6_family = AF_INET6;
#if HAVE_SOCKADDR_IN_SIN_LEN
    s6.sin6_len = sizeof (s6);
#endif
    s6.sin6_port = v6->t6_port;
    s6.sin6_addr = v6->ipv6_addr;

    if (GNUNET_OK != GNUNET_NAT_test_address (plugin->nat,
                                              &s6,
                                              sizeof (struct sockaddr_in6)))
      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 GNUNET_ATS_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 (NULL == session)
  {
    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 (NULL != session->nat_connection_timeout)
  {
    GNUNET_SCHEDULER_cancel (session->nat_connection_timeout);
    session->nat_connection_timeout = NULL;
  }

  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_YES ==
    GNUNET_CONTAINER_multipeermap_remove (plugin->nat_wait_conns,
                                          &tcp_nat_probe->clientIdentity,
                                          session));
  GNUNET_SERVER_client_set_user_context (client, session);
  (void) 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 (TCP_OPTIONS_NONE);
    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 (TCP_OPTIONS_NONE);
    t6->t6_port = s6->sin6_port;
    GNUNET_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);
  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 GNUNET_ATS_Session *session;
  size_t alen;
  void *vaddr;
  struct IPv4TcpAddress t4;
  struct IPv6TcpAddress t6;
  const struct sockaddr_in *s4;
  const struct sockaddr_in6 *s6;

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

  if (GNUNET_OK == GNUNET_SERVER_client_get_address (client, &vaddr, &alen))
  {
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Received WELCOME message from `%s' on address `%s'\n",
         GNUNET_i2s (&wm->clientIdentity),
         GNUNET_a2s (vaddr, alen));
    GNUNET_free (vaddr);
  }
  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
  {
    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 (TCP_OPTIONS_NONE);
        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 (TCP_OPTIONS_NONE);
        t6.t6_port = s6->sin6_port;
        GNUNET_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);
        GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
        return;
      }
      session = create_session (plugin,
                                address,
                                plugin->env->get_address_type (plugin->env->cls,
                                                               vaddr,
                                                               alen),
                                client,
                                GNUNET_NO);
      GNUNET_break (GNUNET_NT_UNSPECIFIED != session->scope);
      GNUNET_HELLO_address_free (address);
      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 (plugin,
                                         session->address->address,
                                         session->address->address_length),
           client);
      GNUNET_free (vaddr);
      (void) GNUNET_CONTAINER_multipeermap_put (
        plugin->sessionmap,
        &session->target,
        session,
        GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
      /* Notify transport and ATS about new session */
      plugin->env->session_start (plugin->env->cls,
                                  session->address,
                                  session,
                                  session->scope);
    }
    else
    {
      LOG (GNUNET_ERROR_TYPE_DEBUG,
           "Did not obtain TCP socket address for incoming connection\n");
      GNUNET_break (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  }

  if (GNUNET_YES != session->expecting_welcome)
  {
    GNUNET_break_op (0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    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 GNUNET_ATS_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 = NULL;
    size_t alen;

    GNUNET_assert (GNUNET_OK ==
                   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;
  }
  if (GNUNET_YES == session->expecting_welcome)
  {
    /* Session is expecting WELCOME message */
    void *vaddr = NULL;
    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 ();
  {
    void *vaddr = NULL;
    size_t alen;

    GNUNET_SERVER_client_get_address (client, &vaddr, &alen);
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Passing %u bytes of type %u from `%s' at %s to transport service.\n",
         (unsigned int) ntohs (message->size),
         (unsigned int) ntohs (message->type),
         GNUNET_i2s (&session->target),
         GNUNET_a2s (vaddr, alen));
    GNUNET_free_non_null (vaddr);
  }

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

  GNUNET_assert (
    GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessionmap,
                                                  &session->target,
                                                  session));
  delay =
    plugin->env->receive (plugin->env->cls, session->address, session, message);
  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);
    GNUNET_assert (NULL == session->receive_delay_task);
    session->receive_delay_task =
      GNUNET_SCHEDULER_add_delayed (delay, &delayed_done, session);
  }
}


/**
 * Function called whenever a peer is connected on the "SERVER" level.
 * Increments number of active connections and suspends server if we
 * have reached the limit.
 *
 * @param cls closure
 * @param client identification of the client
 */
static void
connect_notify (void *cls, struct GNUNET_SERVER_Client *client)
{
  struct Plugin *plugin = cls;

  if (NULL == client)
    return;
  plugin->cur_connections++;
  GNUNET_STATISTICS_set (plugin->env->stats,
                         gettext_noop ("# TCP server connections active"),
                         plugin->cur_connections,
                         GNUNET_NO);
  GNUNET_STATISTICS_update (plugin->env->stats,
                            gettext_noop ("# TCP server connect events"),
                            1,
                            GNUNET_NO);
  if (plugin->cur_connections != plugin->max_connections)
    return;
  GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
              _ ("TCP connection limit reached, suspending server\n"));
  GNUNET_STATISTICS_update (plugin->env->stats,
                            gettext_noop ("# TCP service suspended"),
                            1,
                            GNUNET_NO);
  GNUNET_SERVER_suspend (
    plugin->server); /* Maximum number of connections rechead */
}


/**
 * Function called whenever a peer is disconnected on the "SERVER"
 * level.  Cleans up the connection, decrements number of active
 * connections and if applicable resumes listening.
 *
 * @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 GNUNET_ATS_Session *session;

  if (NULL == client)
    return;
  GNUNET_assert (plugin->cur_connections >= 1);
  plugin->cur_connections--;
  session = lookup_session_by_client (plugin, client);
  if (NULL == session)
    return; /* unknown, nothing to do */
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Destroying session of `%s' 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_STATISTICS_update (session->plugin->env->stats,
                              gettext_noop ("# TCP service resumed"),
                              1,
                              GNUNET_NO);
    GNUNET_SERVER_resume (plugin->server); /* Resume server  */
  }
  GNUNET_STATISTICS_set (plugin->env->stats,
                         gettext_noop ("# TCP server connections active"),
                         plugin->cur_connections,
                         GNUNET_NO);
  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 (NULL == buf)
  {
    GNUNET_CONNECTION_destroy (tcp_probe_ctx->sock);
    GNUNET_free (tcp_probe_ctx);
    return 0;
  }
  GNUNET_assert (size >= sizeof (tcp_probe_ctx->message));
  GNUNET_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 (NULL == sock)
  {
    /* 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_NetworkType
tcp_plugin_get_network (void *cls, struct GNUNET_ATS_Session *session)
{
  return session->scope;
}


/**
 * Function obtain the network type for an address.
 *
 * @param cls closure (`struct Plugin *`)
 * @param address the address
 * @return the network type
 */
static enum GNUNET_NetworkType
tcp_plugin_get_network_for_address (void *cls,
                                    const struct GNUNET_HELLO_Address *address)
{
  struct Plugin *plugin = cls;
  size_t addrlen;
  struct sockaddr_in a4;
  struct sockaddr_in6 a6;
  const struct IPv4TcpAddress *t4;
  const struct IPv6TcpAddress *t6;
  const void *sb;
  size_t sbs;

  addrlen = address->address_length;
  if (addrlen == sizeof (struct IPv6TcpAddress))
  {
    GNUNET_assert (NULL != address->address); /* make static analysis happy */
    t6 = address->address;
    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;
    GNUNET_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;
    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;
    a4.sin_addr.s_addr = t4->ipv4_addr;
    sb = &a4;
    sbs = sizeof (a4);
  }
  else
  {
    GNUNET_break (0);
    return GNUNET_NT_UNSPECIFIED;
  }
  return plugin->env->get_address_type (plugin->env->cls, sb, sbs);
}


/**
 * 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 GNUNET_ATS_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 GNUNET_ATS_Session *session = value;

  notify_session_monitor (plugin, session, GNUNET_TRANSPORT_SS_INIT);
  /* FIXME: cannot tell if this is up or not from current
     session state... */
  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 LEGACY_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;
#ifdef TCP_STEALTH
  struct GNUNET_NETWORK_Handle *const *lsocks;
#endif
  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 (0 == aport)
    aport = bport;
  if (0 == bport)
    aport = 0;
  if (0 != bport)
  {
    service = LEGACY_SERVICE_start ("transport-tcp",
                                    env->cfg,
                                    LEGACY_SERVICE_OPTION_NONE);
    if (NULL == service)
    {
      LOG (GNUNET_ERROR_TYPE_WARNING, _ ("Failed to start service.\n"));
      return NULL;
    }
  }
  else
    service = NULL;

  api = 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;
  plugin->my_welcome.header.size = htons (sizeof (struct WelcomeMessage));
  plugin->my_welcome.header.type =
    htons (GNUNET_MESSAGE_TYPE_TRANSPORT_TCP_WELCOME);
  plugin->my_welcome.clientIdentity = *plugin->env->my_identity;

  if ((NULL != service) &&
      (GNUNET_YES == GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
                                                           "transport-tcp",
                                                           "TCP_STEALTH")))
  {
#ifdef TCP_STEALTH
    plugin->myoptions |= TCP_OPTIONS_TCP_STEALTH;
    lsocks = LEGACY_SERVICE_get_listen_sockets (service);
    if (NULL != lsocks)
    {
      uint32_t len = sizeof (struct WelcomeMessage);

      for (i = 0; NULL != lsocks[i]; i++)
      {
        if (
          (GNUNET_OK !=
           GNUNET_NETWORK_socket_setsockopt (lsocks[i],
                                             IPPROTO_TCP,
                                             TCP_STEALTH,
                                             env->my_identity,
                                             sizeof (
                                               struct GNUNET_PeerIdentity))) ||
          (GNUNET_OK !=
           GNUNET_NETWORK_socket_setsockopt (lsocks[i],
                                             IPPROTO_TCP,
                                             TCP_STEALTH_INTEGRITY_LEN,
                                             &len,
                                             sizeof (len))))
        {
          /* TCP STEALTH not supported by kernel */
          GNUNET_assert (0 == i);
          GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                      _ ("TCP_STEALTH not supported on this platform.\n"));
          goto die;
        }
      }
    }
#else
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                _ ("TCP_STEALTH not supported on this platform.\n"));
    goto die;
#endif
  }

  if ((NULL != service) &&
      (GNUNET_SYSERR !=
       (ret_s =
          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,
                                       "transport-tcp",
                                       IPPROTO_TCP,
                                       (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,
                                       "transport-tcp",
                                       IPPROTO_TCP,
                                       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->get_network_for_address = &tcp_plugin_get_network_for_address;
  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 = LEGACY_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");
      goto die;
    }
    plugin->server = GNUNET_SERVER_create_with_sockets (NULL,
                                                        plugin,
                                                        NULL,
                                                        idle_timeout,
                                                        GNUNET_YES);
  }
  plugin->handlers = GNUNET_malloc (sizeof (my_handlers));
  GNUNET_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_connect_notify (plugin->server, &connect_notify, plugin);
  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_STATISTICS_set (plugin->env->stats,
                         gettext_noop ("# TCP sessions active"),
                         0,
                         GNUNET_NO);
  return api;

die:
  if (NULL != plugin->nat)
    GNUNET_NAT_unregister (plugin->nat);
  GNUNET_CONTAINER_multipeermap_destroy (plugin->sessionmap);
  if (NULL != service)
    LEGACY_SERVICE_stop (service);
  GNUNET_free (plugin);
  GNUNET_free_non_null (api);
  return NULL;
}


/**
 * 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);

  for (cur = plugin->ppc_dll_head; NULL != cur; cur = next)
  {
    next = cur->next;
    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
                                 plugin->ppc_dll_tail,
                                 cur);
    GNUNET_RESOLVER_request_cancel (cur->resolver_handle);
    cur->asc (cur->asc_cls, NULL, GNUNET_OK);
    GNUNET_free (cur);
  }

  if (NULL != plugin->service)
    LEGACY_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_break (0 == plugin->cur_connections);
  GNUNET_free (plugin);
  GNUNET_free (api);
  return NULL;
}

/* end of plugin_transport_tcp.c */