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/*
     This file is part of GNUnet
     (C) 2009, 2010 Christian Grothoff (and other contributing authors)

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

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

     You should have received a copy of the GNU General Public License
     along with GNUnet; see the file COPYING.  If not, write to the
     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/

/**
 * @file transport/gnunet_transport_plugin.h
 * @brief API for the transport services.  This header
 *        specifies the struct that is given to the plugin's entry
 *        method and the other struct that must be returned.
 *        Note that the destructors of transport plugins will
 *        be given the value returned by the constructor
 *        and is expected to return a NULL pointer.
 * @author Christian Grothoff
 */
#ifndef PLUGIN_TRANSPORT_H
#define PLUGIN_TRANSPORT_H

#include "gnunet_configuration_lib.h"
#include "gnunet_scheduler_lib.h"
#include "gnunet_statistics_service.h"
#include "gnunet_transport_service.h"


/**
 *  The structs defined here are used by the transport plugin to tell ATS about
 *  the transport's properties like cost and quality and on the other side
 *  the structs are used by highlevel components to communicate the constraints
 *  they have for a transport to ATS
 *
 *                             +---+
 *  +-----------+ Constraints  |   |  Plugin properties +---------+
 *  | Highlevel |------------> |ATS| <------------------|Transport|
 *  | Component | ATS struct   |   |    ATS struct      | Plugin  |
 *  +-----------+              |   |                    +---------+
 *                             +---+
 *
 */

#define GNUNET_TRANSPORT_ATS_ARRAY_TERMINATOR 0

/**
 * Enum defining all known property types for ATS
 * Enum values are used in the GNUNET_TRANSPORT_ATS_Information struct as (key,value)-pair
 *
 * Cost are always stored in uint32_t, so all units used to define costs
 * have to be normalized to fit in uint32_t [0 .. 4.294.967.295]
 *
 * To keep the elements ordered
 *    1..1024 : Values with a relation to cost
 * 1025..2048 : Values with a relation to quality
 * 2049..3072 : Values with a relation to availability
 *
 */
enum GNUNET_TRANSPORT_ATS_Property
{

	/* Cost related values */
	/* =================== */

	/**
	 * Volume based cost in financial units to transmit data
	 *
	 * Note: This value is not bound to a specific currency or unit and only
	 * used locally.
	 * "cent" just refers the smallest amount of money in the respective
	 * currency.
	 *
	 * Unit: [cent/MB]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 * LAN:  0 [cent/MB]
	 * 2G : 10 [cent/MB]
	 */
	GNUNET_TRANSPORT_ATS_COST_FINANCIAL_PER_VOLUME = 1,

	/**
	 * Time based cost in financial units to transmit data
	 *
	 * Note: This value is not bound to a specific currency or unit and only
	 * used locally.
	 * "cent" just refers the smallest amount of money in the respective
	 * currency.
	 *
	 * Unit: [cent/h]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 * LAN   :  0 [cent/h]
	 * Dialup: 10 [cent/h]
	 */
	GNUNET_TRANSPORT_ATS_COST_FINANCIAL_PER_TIME = 2,

	/**
	 * Computational costs
	 *
	 * Effort of preparing data to be sent with this transport
	 * Includes encoding, encryption and conversion of data
	 * Partial values can be summed up: c_sum = c_enc + c_enc + c_conv
	 * Resulting values depend on local system properties, e.g. CPU
	 *
	 * Unit: [ms/GB]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 *
	 * HTTPS with AES CBC-256: 	7,382
	 * HTTPS with AES CBC-128: 	5,279
	 * HTTPS with RC4-1024: 	2,652
	 */
	GNUNET_TRANSPORT_ATS_COST_COMPUTATIONAL = 3,

	/**
	 * Energy consumption
	 *
	 * Energy consumption using this transport when sending with a certain
	 * power at a certain bitrate. This is only an approximation based on:
	 * Energy consumption E = P / D
	 *
	 * with:
	 * Power P in Watt (J/s)
	 * Datarate D in MBit/s
	 *
	 * Conversion between power P and dBm used by WLAN in radiotap's dBm TX power:
	 *
	 * Lp(dbm) = 10 log10 (P/ 1mW)
	 *
	 * => P = 1 mW  * 10^(Lp(dbm)/10)
	 *
	 * Unit: [mJ/MB]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 *
	 * LAN:       0
	 * WLAN:      89 (600 mW @ 802.11g /w 54 MBit/s)
	 * Bluetooth: 267 (100 mW @ BT2.0 EDR /w 3 MBit/s)
	 */
	GNUNET_TRANSPORT_ATS_COST_ENERGY_CONSUMPTION = 4,

	/**
	 * Connect cost
	 * How many bytes are transmitted to initiate a new connection using
	 * this transport?
	 *
	 * Unit: [bytes]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 *
	 * UDP (No connection)      :
	 *     0 bytes
	 * TCP (TCP 3-Way handshake):
	 *   220 bytes Ethernet,  172 bytes TCP/IP,  122 bytes TCP
	 * HTTP (TCP + Header)      :
	 *   477 bytes Ethernet,  429 bytes TCP/IP,  374 bytes TCP,  278 bytes HTTP
	 * HTTPS  HTTP+TLS Handshake:
	 *  2129 bytes Ethernet, 1975 bytes TCP/IP, 1755 bytes TCP, 1403 bytes HTTPS
	 *
	 * */
	GNUNET_TRANSPORT_ATS_COST_CONNECT = 5,

	/**
	 * Bandwidth cost
	 *
	 * How many bandwidth is available to consume?
	 * Used to calculate which impact sending data with this transport has
	 *
	 * Unit: [kB/s]
	 *
	 * Interpretation: more is better
	 *
	 * Examples:
	 * LAN:     12,800  (100 MBit/s)
	 * WLAN:    6,912   (54 MBit/s)
	 * Dial-up: 8       (64 Kbit/s)
	 *
	 */
	GNUNET_TRANSPORT_ATS_COST_BANDWITH_AVAILABLE = 6,

	/**
	 *  Network overhead
	 *
	 * How many bytes are sent over the wire when 1 kilobyte (1024 bytes)
	 * of application data is transmitted?
	 * A factor used with connect cost, bandwidth cost and energy cost
	 * to describe the overhead produced by the transport protocol
	 *
	 * Unit: [bytes/kb]
	 *
	 * Interpretation: less is better
	 *
	 * Examples:
	 *
	 * TCP/IPv4 over Ethernet: 1024 + 38 + 20 + 20 = 1102 [bytes/kb]
	 * TCP/IPv6 over Ethernet: 1024 + 38 + 20 + 40 = 1122 [bytes/kb]
	 * UDP/IPv4 over Ethernet: 1024 + 38 + 20 + 8  = 1090 [bytes/kb]
	 * UDP/IPv6 over Ethernet: 1024 + 38 + 40 + 8  = 1110 [bytes/kb]
	 */
	GNUNET_TRANSPORT_ATS_COST_NETWORK_OVERHEAD = 7,


	/* Quality related values */
	/* ====================== */

    /* Physical layer quality properties */

	/**
	 * Signal strength on physical layer
	 *
	 * Unit: [dBm]
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_PHY_SIGNAL_STRENGTH = 1025,

	/**
	 * Collision rate on physical layer
	 *
	 * Unit: [B/s]
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_PHY_COLLISION_RATE = 1026,

	/**
	 * Error rate on physical layer
	 *
	 * Unit: [B/s]
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_PHY_ERROR_RATE = 1027,

    /* Network layer quality properties */

	/**
	 * Delay
	 * Time between when the time packet is sent and the packet arrives
	 *
	 * Unit: [μs]
	 *
	 * Examples:
	 *
	 * LAN   :  180
	 * Dialup: 4000
	 * WLAN  : 7000
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_DELAY = 1028,

	/**
	 * Jitter
	 * Time variations of the delay
	 * 1st derivative of a delay function
	 *
	 * Unit: [μs]
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_JITTER = 1029,

	/**
	 * Error rate on network layer
	 *
	 * Unit: [B/s]
	 *
	 * Examples:
	 *
	 * LAN       :    0
	 * WLAN      :  400
	 * Bluetooth :  100
	 * Note: This numbers are just assumptions as an example, not
	 * measured or somehow determined
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_ERRORRATE = 1030,

	/**
	 * Drop rate on network layer
     * Bytes actively dismissed by a network component during transmission
     * Reasons for dropped data can be full queues, congestion, quota violations...
	 *
	 * Unit: [B/s]
	 *
	 * Examples:
	 *
	 * LAN       :    0
	 * WLAN      :  400
	 * Bluetooth :  100
	 * Note: This numbers are just assumptions as an example, not
	 * measured or somehow determined
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_DROPRATE = 1031,

	/**
	 * Loss rate on network layer
	 * Bytes lost during transmission
	 * Reasons can be collisions, ...
	 *
	 * Unit: [B/s]
	 *
	 * Examples:
	 *
	 * LAN       :    0
	 * WLAN      :   40
	 * Bluetooth :   10
	 * Note: This numbers are just assumptions as an example, not measured
	 * or somehow determined
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_LOSSRATE = 1032,

	/**
	 * Throughput on network layer
	 *
	 * Unit: [kB/s]
	 *
	 * Examples:
	 *
	 * LAN   : 3400
	 * WLAN  : 1200
	 * Dialup: 	  4
	 *
	 */
	GNUNET_TRANSPORT_ATS_QUALITY_NET_THROUGHPUT = 1033,

	/* Availability related values */
	/* =========================== */

	/**
	 * Is a peer reachable?
	 */
	GNUNET_TRANSPORT_ATS_AVAILABILITY_REACHABLE = 2048,

	/**
	 * Is there a connection established to a peer using this transport
	 */
	GNUNET_TRANSPORT_ATS_AVAILABILITY_CONNECTED = 2049
};

/**
 * This structure will be used by plugins to communicate costs to ATS or by
 * higher level components to tell ATS their constraints.
 * Always a pair of (GNUNET_TRANSPORT_ATS_Property, uint32_t value).
 * Value is always uint32_t, so all units used to define costs have to
 * be normalized to fit uint32_t.
 */
struct GNUNET_TRANSPORT_ATS_Information
{
	/**
	 * ATS property type
	 */
	uint32_t type;

	/**
	 * ATS property value
	 */
	uint32_t value;
};



/**
 * Opaque pointer that plugins can use to distinguish specific
 * connections to a given peer.  Typically used by stateful plugins to
 * allow the service to refer to specific streams instead of a more
 * general notion of "some connection" to the given peer.  This is
 * useful since sometimes (i.e. for inbound TCP connections) a
 * connection may not have an address that can be used for meaningful
 * distinction between sessions to the same peer.
 */
struct Session;

/**
 * Every 'struct Session' must begin with this header.
 */
struct SessionHeader
{

  /**
   * Cached signature for PONG generation for the session.  Do not use
   * in the plugin!
   */
  struct GNUNET_CRYPTO_RsaSignature pong_signature;

  /**
   * Expiration time for signature.  Do not use in the plugin!
   */
  struct GNUNET_TIME_Absolute pong_sig_expires;
  
};

/**
 * Function that will be called whenever the plugin internally
 * cleans up a session pointer and hence the service needs to
 * discard all of those sessions as well.  Plugins that do not
 * use sessions can simply omit calling this function and always
 * use NULL wherever a session pointer is needed.
 * 
 * @param cls closure
 * @param peer which peer was the session for 
 * @param session which session is being destoyed
 */
typedef void (*GNUNET_TRANSPORT_SessionEnd) (void *cls,
					     const struct GNUNET_PeerIdentity *peer,
					     struct Session *session);


/**
 * Function called by the transport for each received message.
 * This function should also be called with "NULL" for the
 * message to signal that the other peer disconnected.
 *
 * @param cls closure
 * @param peer (claimed) identity of the other peer
 * @param message the message, NULL if we only care about
 *                learning about the delay until we should receive again -- FIXME!
 * @param distance in overlay hops; use 1 unless DV (or 0 if message == NULL)
 * @param session identifier used for this session (NULL for plugins
 *                that do not offer bi-directional communication to the sender
 *                using the same "connection")
 * @param sender_address binary address of the sender (if we established the
 *                connection or are otherwise sure of it; should be NULL
 *                for inbound TCP/UDP connections since it it not clear
 *                that we could establish ourselves a connection to that
 *                IP address and get the same system)
 * @param sender_address_len number of bytes in sender_address
 * @return how long the plugin should wait until receiving more data
 *         (plugins that do not support this, can ignore the return value)
 */
typedef struct GNUNET_TIME_Relative (*GNUNET_TRANSPORT_PluginReceiveCallback) (void *cls,
									       const struct
									       GNUNET_PeerIdentity *
									       peer,
									       const struct
									       GNUNET_MessageHeader *
									       message,
									       uint32_t distance,
									       struct Session *session,
									       const char *sender_address,
									       uint16_t sender_address_len);


/**
 * Function that will be called for each address the transport
 * is aware that it might be reachable under.
 *
 * @param cls closure
 * @param name 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 address
 * @param expires when should this address automatically expire?
 */
typedef void (*GNUNET_TRANSPORT_AddressNotification) (void *cls,
                                                      const char *name,
                                                      const void *addr,
                                                      uint16_t addrlen,
                                                      struct
                                                      GNUNET_TIME_Relative
                                                      expires);

/**
 * Function that will be called whenever the plugin receives data over
 * the network and wants to determine how long it should wait until
 * the next time it reads from the given peer.  Note that some plugins
 * (such as UDP) may not be able to wait (for a particular peer), so
 * the waiting part is optional.  Plugins that can wait should call
 * this function, sleep the given amount of time, and call it again
 * (with zero bytes read) UNTIL it returns zero and only then read.
 *
 * @param cls closure
 * @param peer which peer did we read data from
 * @param amount_recved number of bytes read (can be zero)
 * @return how long to wait until reading more from this peer
 *         (to enforce inbound quotas)
 */
typedef struct GNUNET_TIME_Relative (*GNUNET_TRANSPORT_TrafficReport) (void *cls,
                                                                      const struct
                                                                      GNUNET_PeerIdentity *peer,
                                                                      size_t amount_recved);

/**
 * Function called whenever the plugin has to notify ATS about costs for using this transport
 *
 * The cost will be passed as struct GNUNET_TRANSPORT_ATS_Cost_Information[]
 * This array is 0-terminated, so the last element will be a pair:
 * ((cost->cost_type==GNUNET_TRANSPORT_ATS_ARRAY_TERMINATOR) && cost->cost_value==0))
 *
 * @param cls closure
 * @param peer peer
 * @param addr peer address
 * @param addrlen address length
 * @param cost pointer to the first element of struct GNUNET_TRANSPORT_ATS_Cost_Information[]
 */
typedef void (*GNUNET_TRANSPORT_CostReport) (void *cls,
											 const struct GNUNET_PeerIdentity *peer,
                                             const void *addr,
                                             uint16_t addrlen,
											 struct GNUNET_TRANSPORT_ATS_Information * cost);

/**
 * The transport service will pass a pointer to a struct
 * of this type as the first and only argument to the
 * entry point of each transport plugin.
 */
struct GNUNET_TRANSPORT_PluginEnvironment
{
  /**
   * Configuration to use.
   */
  const struct GNUNET_CONFIGURATION_Handle *cfg;

  /**
   * Identity of this peer.
   */
  const struct GNUNET_PeerIdentity *my_identity;

  /**
   * Pointer (!) to our HELLO message.  Note that the address
   * referred to "*our_hello" might change over time.
   */
  struct GNUNET_HELLO_Message *const*our_hello;

  /**
   * Closure for the various callbacks.
   */
  void *cls;

  /**
   * Handle for reporting statistics.
   */
  struct GNUNET_STATISTICS_Handle *stats;

  /**
   * Function that should be called by the transport plugin
   * whenever a message is received.
   */
  GNUNET_TRANSPORT_PluginReceiveCallback receive;

  /**
   * Function that must be called by each plugin to notify the
   * transport service about the addresses under which the transport
   * provided by the plugin can be reached.
   */
  GNUNET_TRANSPORT_AddressNotification notify_address;

  /**
   * Inform service about traffic received, get information
   * about when we might be willing to receive more.
   */
  GNUNET_TRANSPORT_TrafficReport traffic_report;

  /**
   * Function that must be called by the plugin when a non-NULL
   * session handle stops being valid (is destroyed).
   */
  GNUNET_TRANSPORT_SessionEnd session_end;

  /**
   * Inform service about costs for using this transport plugin
   */
  GNUNET_TRANSPORT_CostReport cost_report;

  /**
   * What is the maximum number of connections that this transport
   * should allow?  Transports that do not have sessions (such as
   * UDP) can ignore this value.
   */
  uint32_t max_connections;

};


/**
 * Function called by the GNUNET_TRANSPORT_TransmitFunction
 * upon "completion".
 *
 * @param cls closure
 * @param target who was the recipient of the message?
 * @param result GNUNET_OK on success
 *               GNUNET_SYSERR if the target disconnected;
 *               disconnect will ALSO be signalled using
 *               the ReceiveCallback.
 */
typedef void
  (*GNUNET_TRANSPORT_TransmitContinuation) (void *cls,
                                            const struct GNUNET_PeerIdentity *
                                            target, int result);


/**
 * 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 target who should receive this message
 * @param msgbuf the message to transmit
 * @param msgbuf_size number of bytes in 'msgbuf'
 * @param priority how important is the message (most plugins will
 *                 ignore message priority and just FIFO)
 * @param timeout 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 session which session must be used (or NULL for "any")
 * @param addr the address to use (can be NULL if the plugin
 *                is "on its own" (i.e. re-use existing TCP connection))
 * @param addrlen length of the address in bytes
 * @param force_address GNUNET_YES if the plugin MUST use the given address,
 *                GNUNET_NO means the plugin may use any other address and
 *                GNUNET_SYSERR means that only reliable existing
 *                bi-directional connections should be used (regardless
 *                of address)
 * @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 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)
 */
typedef ssize_t
  (*GNUNET_TRANSPORT_TransmitFunction) (void *cls,
                                        const struct GNUNET_PeerIdentity *
                                        target,
                                        const char *msgbuf,
                                        size_t msgbuf_size,
                                        uint32_t priority,
                                        struct GNUNET_TIME_Relative timeout,
					struct Session *session,
                                        const void *addr,
					size_t addrlen,
					int force_address,
					GNUNET_TRANSPORT_TransmitContinuation
                                        cont, void *cont_cls);


/**
 * 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
 */
typedef void
  (*GNUNET_TRANSPORT_DisconnectFunction) (void *cls,
                                          const struct GNUNET_PeerIdentity *
                                          target);


/**
 * Function called by the pretty printer for the resolved address for
 * each human-readable address obtained.
 *
 * @param cls closure
 * @param hostname one of the names for the host, NULL
 *        on the last call to the callback
 */
typedef void (*GNUNET_TRANSPORT_AddressStringCallback) (void *cls,
                                                        const char *address);


/**
 * Convert the transports address to a nice, human-readable
 * format.
 *
 * @param cls closure
 * @param name 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 address
 * @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 asc
 */
typedef void
  (*GNUNET_TRANSPORT_AddressPrettyPrinter) (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);


/**
 * Another peer has suggested an address for this peer and transport
 * plugin.  Check that this could be a valid address.  This function
 * is not expected to 'validate' the address in the sense of trying to
 * connect to it but simply to see if the binary format is technically
 * legal for establishing a connection to this peer (and make sure that
 * the address really corresponds to our network connection/settings
 * and not some potential man-in-the-middle).
 *
 * @param addr pointer to the address
 * @param addrlen length of addr
 * @return GNUNET_OK if this is a plausible address for this peer
 *         and transport, GNUNET_SYSERR if not
 */
typedef int
(*GNUNET_TRANSPORT_CheckAddress) (void *cls,
				  const void *addr, size_t addrlen);


/**
 * 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
 * @param addr binary address
 * @param addr_len length of the address
 * @return string representing the same address 
 */
typedef const char* (*GNUNET_TRANSPORT_AddressToString) (void *cls,
							 const void *addr,
							 size_t addrlen);


/**
 * Each plugin is required to return a pointer to a struct of this
 * type as the return value from its entry point.
 */
struct GNUNET_TRANSPORT_PluginFunctions
{

  /**
   * Closure for all of the callbacks.
   */
  void *cls;

  /**
   * Function that the transport service will use to transmit data to
   * another peer.  May be NULL for plugins that only support
   * receiving data.  After this call, the plugin call the specified
   * continuation with success or error before notifying us about the
   * target having disconnected.
   */
  GNUNET_TRANSPORT_TransmitFunction send;

  /**
   * Function that can be used to force the plugin to disconnect from
   * the given peer and cancel all previous transmissions (and their
   * continuations).  Note that if the transport does not have
   * sessions / persistent connections (for example, UDP), this
   * function may very well do nothing.
   */
  GNUNET_TRANSPORT_DisconnectFunction disconnect;

  /**
   * Function to pretty-print addresses.  NOTE: this function is not
   * yet used by transport-service, but will be used in the future
   * once the transport-API has been completed.
   */
  GNUNET_TRANSPORT_AddressPrettyPrinter address_pretty_printer;

  /**
   * 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.
   */
  GNUNET_TRANSPORT_CheckAddress check_address;

  /**
   * Function that will be called to convert a binary address
   * to a string (numeric conversion only).
   */
  GNUNET_TRANSPORT_AddressToString address_to_string;

};


#endif