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[oweals/gnunet.git] / src / core / gnunet-service-core.c

/*
     This file is part of GNUnet.
     (C) 2009 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 2, 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 core/gnunet-service-core.c
 * @brief high-level P2P messaging
 * @author Christian Grothoff
 *
 * TODO:
 * TESTING:
 * - write test for basic core functions:
 *   + connect to peer
 *   + transmit (encrypted) message [with handshake]
 *   + receive (encrypted) message, forward plaintext to clients
 * POST-TESTING:
 * - revisit API (which arguments are used, needed)?
 * - add code to bound queue size when handling client's SEND message
 * - add code to bound message queue size when passing messages to clients
 * - add code to discard_expired_messages
 * - add code to re-transmit key if first attempt failed
 *   + timeout on connect / key exchange, etc.
 *   + timeout for automatic re-try, etc.
 * - add code to give up re-transmission of key if many attempts fail
 * - add code to send PINGs if we are about to time-out otherwise
 * ? add heuristic to do another send_key in "handle_set_key"
 *   in case previous attempt failed / didn't work / persist
 *   (but don't do it always to avoid storm of SET_KEY's going
 *   back and forth!) --- alternatively, add "status" field
 *   of the other peer to the set key message, that way we'd
 *   know for sure!
 * - check that hostkey used by transport (for HELLOs) is the
 *   same as the hostkey that we are using!
 * - free list of clients on exit
 * - topology management:
 *   + bootstrapping (transport offer hello, plugins)
 *   + internal neighbour selection
 *   + update bandwidth usage statistics
 *   + bandwidth allocation (transport set quota)
 * - optimize lookup (many O(n) list traversals
 *   could ideally be changed to O(1) hash map lookups)
 */
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_hello_lib.h"
#include "gnunet_peerinfo_service.h"
#include "gnunet_protocols.h"
#include "gnunet_signatures.h"
#include "gnunet_transport_service.h"
#include "core.h"


/**
 * Receive and send buffer windows grow over time.  For
 * how long can 'unused' bandwidth accumulate before we
 * need to cap it?  (specified in ms).
 */
#define MAX_WINDOW_TIME (5 * 60 * 1000)


/**
 * Amount of bytes per minute (in/out) to assume initially
 * (before either peer has communicated any particular
 * preference).  Should be rather low.
 */
#define DEFAULT_BPM_IN_OUT 2048


/**
 * What is the maximum delay for a SET_KEY message?
 */
#define MAX_SET_KEY_DELAY GNUNET_TIME_UNIT_SECONDS


/**
 * What how long do we wait for SET_KEY confirmation initially?
 */
#define INITIAL_SET_KEY_RETRY_FREQUENCY GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 3)


/**
 * What is the maximum delay for a PING message?
 */
#define MAX_PING_DELAY GNUNET_TIME_UNIT_SECONDS


/**
 * What is the maximum delay for a PONG message?
 */
#define MAX_PONG_DELAY GNUNET_TIME_UNIT_SECONDS


/**
 * What is the priority for a SET_KEY message?
 */
#define SET_KEY_PRIORITY 0xFFFFFF


/**
 * What is the priority for a PING message?
 */
#define PING_PRIORITY 0xFFFFFF


/**
 * What is the priority for a PONG message?
 */
#define PONG_PRIORITY 0xFFFFFF


/**
 * What is the maximum age of a message for us to consider
 * processing it?  Note that this looks at the timestamp used
 * by the other peer, so clock skew between machines does
 * come into play here.  So this should be picked high enough
 * so that a little bit of clock skew does not prevent peers
 * from connecting to us.
 */
#define MAX_MESSAGE_AGE GNUNET_TIME_UNIT_DAYS


/**
 * What is the maximum size for encrypted messages?  Note that this
 * number imposes a clear limit on the maximum size of any message.
 * Set to a value close to 64k but not so close that transports will
 * have trouble with their headers.
 */
#define MAX_ENCRYPTED_MESSAGE_SIZE (63 * 1024)


/**
 * State machine for our P2P encryption handshake.  Everyone starts in
 * "DOWN", if we receive the other peer's key (other peer initiated)
 * we start in state RECEIVED (since we will immediately send our
 * own); otherwise we start in SENT.  If we get back a PONG from
 * within either state, we move up to CONFIRMED (the PONG will always
 * be sent back encrypted with the key we sent to the other peer).
 */
enum PeerStateMachine
{
  PEER_STATE_DOWN,
  PEER_STATE_KEY_SENT,
  PEER_STATE_KEY_RECEIVED,
  PEER_STATE_KEY_CONFIRMED
};


/**
 * Number of bytes (at the beginning) of "struct EncryptedMessage"
 * that are NOT encrypted.
 */
#define ENCRYPTED_HEADER_SIZE (sizeof(struct GNUNET_MessageHeader) + sizeof(uint32_t) + sizeof(GNUNET_HashCode))

/**
 * Encapsulation for encrypted messages exchanged between
 * peers.  Followed by the actual encrypted data.
 */
struct EncryptedMessage
{
  /**
   * Message type is either CORE_ENCRYPTED_MESSAGE.
   */
  struct GNUNET_MessageHeader header;

  /**
   * Always zero.
   */
  uint32_t reserved GNUNET_PACKED;

  /**
   * Hash of the plaintext, used to verify message integrity;
   * ALSO used as the IV for the symmetric cipher!  Everything
   * after this hash will be encrypted.  ENCRYPTED_HEADER_SIZE
   * must be set to the offset of the next field.
   */
  GNUNET_HashCode plaintext_hash;

  /**
   * Sequence number, in network byte order.  This field
   * must be the first encrypted/decrypted field and the
   * first byte that is hashed for the plaintext hash.
   */
  uint32_t sequence_number GNUNET_PACKED;

  /**
   * Desired bandwidth (how much we should send to this
   * peer / how much is the sender willing to receive),
   * in bytes per minute.
   */
  uint32_t inbound_bpm_limit GNUNET_PACKED;

  /**
   * Timestamp.  Used to prevent reply of ancient messages
   * (recent messages are caught with the sequence number).
   */
  struct GNUNET_TIME_AbsoluteNBO timestamp;

};

/**
 * We're sending an (encrypted) PING to the other peer to check if he
 * can decrypt.  The other peer should respond with a PONG with the
 * same content, except this time encrypted with the receiver's key.
 */
struct PingMessage
{
  /**
   * Message type is either CORE_PING or CORE_PONG.
   */
  struct GNUNET_MessageHeader header;

  /**
   * Random number chosen to make reply harder.
   */
  uint32_t challenge GNUNET_PACKED;

  /**
   * Intended target of the PING, used primarily to check
   * that decryption actually worked.
   */
  struct GNUNET_PeerIdentity target;
};


/**
 * Message transmitted to set (or update) a session key.
 */
struct SetKeyMessage
{

  /**
   * Message type is either CORE_SET_KEY.
   */
  struct GNUNET_MessageHeader header;

  /**
   * Status of the sender (should be in "enum PeerStateMachine"), nbo.
   */
  int32_t sender_status GNUNET_PACKED;

  /**
   * Purpose of the signature, will be
   * GNUNET_SIGNATURE_PURPOSE_SET_KEY.
   */
  struct GNUNET_CRYPTO_RsaSignaturePurpose purpose;

  /**
   * At what time was this key created?
   */
  struct GNUNET_TIME_AbsoluteNBO creation_time;

  /**
   * The encrypted session key.
   */
  struct GNUNET_CRYPTO_RsaEncryptedData encrypted_key;

  /**
   * Who is the intended recipient?
   */
  struct GNUNET_PeerIdentity target;

  /**
   * Signature of the stuff above (starting at purpose).
   */
  struct GNUNET_CRYPTO_RsaSignature signature;

};


/**
 * Message waiting for transmission. This struct
 * is followed by the actual content of the message.
 */
struct MessageEntry
{

  /**
   * We keep messages in a linked list (for now).
   */
  struct MessageEntry *next;

  /**
   * By when are we supposed to transmit this message?
   */
  struct GNUNET_TIME_Absolute deadline;

  /**
   * How important is this message to us?
   */
  unsigned int priority;

  /**
   * How long is the message? (number of bytes following
   * the "struct MessageEntry", but not including the
   * size of "struct MessageEntry" itself!)
   */
  uint16_t size;

  /**
   * Was this message selected for transmission in the
   * current round? GNUNET_YES or GNUNET_NO.
   */
  int16_t do_transmit;

};


struct Neighbour
{
  /**
   * We keep neighbours in a linked list (for now).
   */
  struct Neighbour *next;

  /**
   * Unencrypted messages destined for this peer.
   */
  struct MessageEntry *messages;

  /**
   * Head of the batched, encrypted message queue (already ordered,
   * transmit starting with the head).
   */
  struct MessageEntry *encrypted_head;

  /**
   * Tail of the batched, encrypted message queue (already ordered,
   * append new messages to tail)
   */
  struct MessageEntry *encrypted_tail;

  /**
   * Handle for pending requests for transmission to this peer
   * with the transport service.  NULL if no request is pending.
   */
  struct GNUNET_TRANSPORT_TransmitHandle *th;

  /**
   * Public key of the neighbour, NULL if we don't have it yet.
   */
  struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded *public_key;

  /**
   * We received a PING message before we got the "public_key"
   * (or the SET_KEY).  We keep it here until we have a key
   * to decrypt it.  NULL if no PING is pending.
   */
  struct PingMessage *pending_ping;

  /**
   * Identity of the neighbour.
   */
  struct GNUNET_PeerIdentity peer;

  /**
   * Key we use to encrypt our messages for the other peer
   * (initialized by us when we do the handshake).
   */
  struct GNUNET_CRYPTO_AesSessionKey encrypt_key;

  /**
   * Key we use to decrypt messages from the other peer
   * (given to us by the other peer during the handshake).
   */
  struct GNUNET_CRYPTO_AesSessionKey decrypt_key;

  /**
   * ID of task used for re-trying plaintext scheduling.
   */
  GNUNET_SCHEDULER_TaskIdentifier retry_plaintext_task;

  /**
   * ID of task used for re-trying SET_KEY and PING message.
   */
  GNUNET_SCHEDULER_TaskIdentifier retry_set_key_task;

  /**
   * At what time did we generate our encryption key?
   */
  struct GNUNET_TIME_Absolute encrypt_key_created;

  /**
   * At what time did the other peer generate the decryption key?
   */
  struct GNUNET_TIME_Absolute decrypt_key_created;

  /**
   * At what time did we initially establish (as in, complete session
   * key handshake) this connection?  Should be zero if status != KEY_CONFIRMED.
   */
  struct GNUNET_TIME_Absolute time_established;

  /**
   * At what time did we last receive an encrypted message from the
   * other peer?  Should be zero if status != KEY_CONFIRMED.
   */
  struct GNUNET_TIME_Absolute last_activity;

  /**
   * Last latency observed from this peer.
   */
  struct GNUNET_TIME_Relative last_latency;

  /**
   * At what frequency are we currently re-trying SET KEY messages?
   */
  struct GNUNET_TIME_Relative set_key_retry_frequency;

  /**
   * Time of our last update to the "available_send_window".
   */
  struct GNUNET_TIME_Absolute last_asw_update;

  /**
   * Time of our last update to the "available_recv_window".
   */
  struct GNUNET_TIME_Absolute last_arw_update;

  /**
   * Number of bytes that we are eligible to transmit to this
   * peer at this point.  Incremented every minute by max_out_bpm,
   * bounded by max_bpm (no back-log larger than MAX_BUF_FACT minutes,
   * bandwidth-hogs are sampled at a frequency of about 78s!);
   * may get negative if we have VERY high priority content.
   */
  long long available_send_window;

  /**
   * How much downstream capacity of this peer has been reserved for
   * our traffic?  (Our clients can request that a certain amount of
   * bandwidth is available for replies to them; this value is used to
   * make sure that this reserved amount of bandwidth is actually
   * available).
   */
  long long available_recv_window;

  /**
   * How valueable were the messages of this peer recently?
   */
  double current_preference;

  /**
   * Bit map indicating which of the 32 sequence numbers before the last
   * were received (good for accepting out-of-order packets and
   * estimating reliability of the connection)
   */
  unsigned int last_packets_bitmap;

  /**
   * Number of messages in the message queue for this peer.
   */
  unsigned int message_queue_size;

  /**
   * last sequence number received on this connection (highest)
   */
  uint32_t last_sequence_number_received;

  /**
   * last sequence number transmitted
   */
  uint32_t last_sequence_number_sent;

  /**
   * Available bandwidth in for this peer (current target).
   */
  uint32_t bpm_in;

  /**
   * Available bandwidth out for this peer (current target).
   */
  uint32_t bpm_out;

  /**
   * Internal bandwidth limit set for this peer (initially
   * typcially set to "-1").  "bpm_out" is MAX of
   * "bpm_out_internal_limit" and "bpm_out_external_limit".
   */
  uint32_t bpm_out_internal_limit;

  /**
   * External bandwidth limit set for this peer by the
   * peer that we are communicating with.  "bpm_out" is MAX of
   * "bpm_out_internal_limit" and "bpm_out_external_limit".
   */
  uint32_t bpm_out_external_limit;

  /**
   * What was our PING challenge number?
   */
  uint32_t ping_challenge;

  /**
   * What is our connection status?
   */
  enum PeerStateMachine status;

};


/**
 * Events are messages for clients.  The struct
 * itself is followed by the actual message.
 */
struct Event
{
  /**
   * This is a linked list.
   */
  struct Event *next;

  /**
   * Size of the message.
   */
  size_t size;

  /**
   * Could this event be dropped if this queue
   * is getting too large? (NOT YET USED!)
   */
  int can_drop;

};


/**
 * Data structure for each client connected to the core service.
 */
struct Client
{
  /**
   * Clients are kept in a linked list.
   */
  struct Client *next;

  /**
   * Handle for the client with the server API.
   */
  struct GNUNET_SERVER_Client *client_handle;

  /**
   * Linked list of messages we still need to deliver to
   * this client.
   */
  struct Event *event_head;

  /**
   * Tail of the linked list of events.
   */
  struct Event *event_tail;

  /**
   * Current transmit handle, NULL if no transmission request
   * is pending.
   */
  struct GNUNET_NETWORK_TransmitHandle *th;

  /**
   * Array of the types of messages this peer cares
   * about (with "tcnt" entries).  Allocated as part
   * of this client struct, do not free!
   */
  uint16_t *types;

  /**
   * Options for messages this client cares about,
   * see GNUNET_CORE_OPTION_ values.
   */
  uint32_t options;

  /**
   * Number of types of incoming messages this client
   * specifically cares about.  Size of the "types" array.
   */
  unsigned int tcnt;

};


/**
 * Our public key.
 */
static struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded my_public_key;

/**
 * Our identity.
 */
static struct GNUNET_PeerIdentity my_identity;

/**
 * Our private key.
 */
static struct GNUNET_CRYPTO_RsaPrivateKey *my_private_key;

/**
 * Our scheduler.
 */
struct GNUNET_SCHEDULER_Handle *sched;

/**
 * Our configuration.
 */
struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Our server.
 */
static struct GNUNET_SERVER_Handle *server;

/**
 * Transport service.
 */
static struct GNUNET_TRANSPORT_Handle *transport;

/**
 * We keep neighbours in a linked list (for now).
 */
static struct Neighbour *neighbours;

/**
 * Linked list of our clients.
 */
static struct Client *clients;


/**
 * Recalculate the number of bytes we expect to
 * receive or transmit in a given window.
 *
 * @param window pointer to the byte counter (updated)
 * @param ts pointer to the timestamp (updated)
 * @param bpm number of bytes per minute that should
 *        be added to the window.
 */
static void
update_window (long long *window,
               struct GNUNET_TIME_Absolute *ts, unsigned int bpm)
{
  struct GNUNET_TIME_Relative since;

  since = GNUNET_TIME_absolute_get_duration (*ts);
  if (since.value < 60 * 1000)
    return;                     /* not even a minute has passed */
  *ts = GNUNET_TIME_absolute_get ();
  *window += (bpm * since.value) / 60 / 1000;
  if (*window > MAX_WINDOW_TIME * bpm)
    *window = MAX_WINDOW_TIME * bpm;
}


/**
 * Find the entry for the given neighbour.
 *
 * @param peer identity of the neighbour
 * @return NULL if we are not connected, otherwise the
 *         neighbour's entry.
 */
static struct Neighbour *
find_neighbour (const struct GNUNET_PeerIdentity *peer)
{
  struct Neighbour *ret;

  ret = neighbours;
  while ((ret != NULL) &&
         (0 != memcmp (&ret->peer,
                       peer, sizeof (struct GNUNET_PeerIdentity))))
    ret = ret->next;
  return ret;
}


/**
 * Find the entry for the given client.
 *
 * @param client handle for the client
 * @return NULL if we are not connected, otherwise the
 *         client's struct.
 */
static struct Client *
find_client (const struct GNUNET_SERVER_Client *client)
{
  struct Client *ret;

  ret = clients;
  while ((ret != NULL) && (client != ret->client_handle))
    ret = ret->next;
  return ret;
}


/**
 * If necessary, initiate a request with the server to
 * transmit messages from the queue of the given client.
 * @param client who to transfer messages to
 */
static void request_transmit (struct Client *client);


/**
 * Client is ready to receive data, provide it.
 * @param cls closure
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
do_client_transmit (void *cls, size_t size, void *buf)
{
  struct Client *client = cls;
  struct Event *e;
  char *tgt;
  size_t ret;

  client->th = NULL;
#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client ready to receive %u bytes.\n", size);
#endif
  if (buf == NULL)
    {
#if DEBUG_CORE
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "Failed to transmit data to client (disconnect)?\n");
#endif
      return 0;                 /* we'll surely get a disconnect soon... */
    }
  tgt = buf;
  ret = 0;
  while ((NULL != (e = client->event_head)) && (e->size <= size))
    {
      memcpy (&tgt[ret], &e[1], e->size);
      size -= e->size;
      ret += e->size;
      client->event_head = e->next;
      GNUNET_free (e);
    }
  GNUNET_assert (ret > 0);
  if (client->event_head == NULL)
    client->event_tail = NULL;
#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Transmitting %u bytes to client\n", ret);
#endif
  request_transmit (client);
  return ret;
}


/**
 * If necessary, initiate a request with the server to
 * transmit messages from the queue of the given client.
 * @param client who to transfer messages to
 */
static void
request_transmit (struct Client *client)
{

  if (NULL != client->th)
    return;                     /* already pending */
  if (NULL == client->event_head)
    return;                     /* no more events pending */
#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asking server to transmit %u bytes to client\n",
              client->event_head->size);
#endif
  client->th
    = GNUNET_SERVER_notify_transmit_ready (client->client_handle,
                                           client->event_head->size,
                                           GNUNET_TIME_UNIT_FOREVER_REL,
                                           &do_client_transmit, client);
}


/**
 * Send a message to one of our clients.
 * @param client target for the message
 * @param msg message to transmit
 * @param can_drop could this message be dropped if the
 *        client's queue is getting too large?
 */
static void
send_to_client (struct Client *client,
                const struct GNUNET_MessageHeader *msg, int can_drop)
{
  struct Event *e;
  uint16_t msize;

#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Preparing to send message of type %u to client.\n",
              ntohs (msg->type));
#endif
  msize = ntohs (msg->size);
  e = GNUNET_malloc (sizeof (struct Event) + msize);
  /* append */
  if (client->event_tail != NULL)
    client->event_tail->next = e;
  else
    client->event_head = e;
  client->event_tail = e;
  e->can_drop = can_drop;
  e->size = msize;
  memcpy (&e[1], msg, msize);
  request_transmit (client);
}


/**
 * Send a message to all of our current clients.
 */
static void
send_to_all_clients (const struct GNUNET_MessageHeader *msg, int can_drop)
{
  struct Client *c;

  c = clients;
  while (c != NULL)
    {
      send_to_client (c, msg, can_drop);
      c = c->next;
    }
}


/**
 * Handle CORE_INIT request.
 */
static void
handle_client_init (void *cls,
                    struct GNUNET_SERVER_Client *client,
                    const struct GNUNET_MessageHeader *message)
{
  const struct InitMessage *im;
  struct InitReplyMessage irm;
  struct Client *c;
  uint16_t msize;
  const uint16_t *types;
  struct Neighbour *n;
  struct ConnectNotifyMessage cnm;

#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client connecting to core service with `%s' message\n",
              "INIT");
#endif
  /* check that we don't have an entry already */
  c = clients;
  while (c != NULL)
    {
      if (client == c->client_handle)
        {
          GNUNET_break (0);
          GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
          return;
        }
      c = c->next;
    }
  msize = ntohs (message->size);
  if (msize < sizeof (struct InitMessage))
    {
      GNUNET_break (0);
      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  im = (const struct InitMessage *) message;
  types = (const uint16_t *) &im[1];
  msize -= sizeof (struct InitMessage);
  c = GNUNET_malloc (sizeof (struct Client) + msize);
  c->client_handle = client;
  c->next = clients;
  clients = c;
  memcpy (&c[1], types, msize);
  c->types = (uint16_t *) & c[1];
  c->options = ntohl (im->options);
  c->tcnt = msize / sizeof (uint16_t);
  /* send init reply message */
  irm.header.size = htons (sizeof (struct InitReplyMessage));
  irm.header.type = htons (GNUNET_MESSAGE_TYPE_CORE_INIT_REPLY);
  irm.reserved = htonl (0);
  memcpy (&irm.publicKey,
          &my_public_key,
          sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded));
#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending `%s' message to client.\n", "INIT_REPLY");
#endif
  send_to_client (c, &irm.header, GNUNET_NO);
  /* notify new client about existing neighbours */
  cnm.header.size = htons (sizeof (struct ConnectNotifyMessage));
  cnm.header.type = htons (GNUNET_MESSAGE_TYPE_CORE_NOTIFY_CONNECT);
  n = neighbours;
  while (n != NULL)
    {
#if DEBUG_CORE_CLIENT
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending `%s' message to client.\n", "NOTIFY_CONNECT");
#endif
      cnm.bpm_available = htonl (n->bpm_out);
      cnm.last_activity = GNUNET_TIME_absolute_hton (n->last_activity);
      cnm.peer = n->peer;
      send_to_client (c, &cnm.header, GNUNET_NO);
      n = n->next;
    }
  GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * A client disconnected, clean up.
 *
 * @param cls closure
 * @param client identification of the client
 */
static void
handle_client_disconnect (void *cls, struct GNUNET_SERVER_Client *client)
{
  struct Client *pos;
  struct Client *prev;

#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client has disconnected from core service.\n");
#endif
  prev = NULL;
  pos = clients;
  while (pos != NULL)
    {
      if (client == pos->client_handle)
        {
          if (prev == NULL)
            clients = pos->next;
          else
            prev->next = pos->next;
          if (pos->th != NULL)
            GNUNET_NETWORK_notify_transmit_ready_cancel (pos->th);
          GNUNET_free (pos);
          return;
        }
      prev = pos;
      pos = pos->next;
    }
  /* client never sent INIT */
}


/**
 * Handle REQUEST_CONFIGURE request.
 */
static void
handle_client_request_configure (void *cls,
                                 struct GNUNET_SERVER_Client *client,
                                 const struct GNUNET_MessageHeader *message)
{
  const struct RequestConfigureMessage *rcm;
  struct Neighbour *n;
  struct ConfigurationInfoMessage cim;
  struct Client *c;
  int reserv;

#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service receives `%s' request.\n", "CONFIGURE");
#endif
  rcm = (const struct RequestConfigureMessage *) message;
  n = find_neighbour (&rcm->peer);
  memset (&cim, 0, sizeof (cim));
  if ((n != NULL) && (n->status == PEER_STATE_KEY_CONFIRMED))
    {
      n->bpm_out_internal_limit = ntohl (rcm->limit_outbound_bpm);
      n->bpm_out = GNUNET_MAX (n->bpm_out_internal_limit,
                               n->bpm_out_external_limit);
      reserv = ntohl (rcm->reserve_inbound);
      if (reserv < 0)
        {
          n->available_recv_window += reserv;
        }
      else if (reserv > 0)
        {
          update_window (&n->available_recv_window,
                         &n->last_arw_update, n->bpm_in);
          if (n->available_recv_window < reserv)
            reserv = n->available_recv_window;
          n->available_recv_window -= reserv;
        }
      n->current_preference += rcm->preference_change;
      if (n->current_preference < 0)
        n->current_preference = 0;
      cim.reserved_amount = htonl (reserv);
      cim.bpm_in = htonl (n->bpm_in);
      cim.bpm_out = htonl (n->bpm_out);
      cim.latency = GNUNET_TIME_relative_hton (n->last_latency);
      cim.preference = n->current_preference;
    }
  cim.header.size = htons (sizeof (struct ConfigurationInfoMessage));
  cim.header.type = htons (GNUNET_MESSAGE_TYPE_CORE_CONFIGURATION_INFO);
  cim.peer = rcm->peer;
  c = find_client (client);
  if (c == NULL)
    {
      GNUNET_break (0);
      return;
    }
#if DEBUG_CORE_CLIENT
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending `%s' message to client.\n", "CONFIGURATION_INFO");
#endif
  send_to_client (c, &cim.header, GNUNET_NO);
}


/**
 * Check if we have encrypted messages for the specified neighbour
 * pending, and if so, check with the transport about sending them
 * out.
 *
 * @param n neighbour to check.
 */
static void process_encrypted_neighbour_queue (struct Neighbour *n);


/**
 * Function called when the transport service is ready to
 * receive an encrypted message for the respective peer
 *
 * @param cls neighbour to use message from
 * @param size number of bytes we can transmit
 * @param buf where to copy the message
 * @return number of bytes transmitted
 */
static size_t
notify_encrypted_transmit_ready (void *cls, size_t size, void *buf)
{
  struct Neighbour *n = cls;
  struct MessageEntry *m;
  size_t ret;
  char *cbuf;

  n->th = NULL;
  GNUNET_assert (NULL != (m = n->encrypted_head));
  n->encrypted_head = m->next;
  if (m->next == NULL)
    n->encrypted_tail = NULL;
  ret = 0;
  cbuf = buf;
  if (buf != NULL)
    {
      GNUNET_assert (size >= m->size);
      memcpy (cbuf, &m[1], m->size);
      ret = m->size;
      process_encrypted_neighbour_queue (n);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Copied message of type %u and size %u into transport buffer for `%4s'\n",
                  ntohs (((struct GNUNET_MessageHeader *) &m[1])->type),
                  ret, GNUNET_i2s (&n->peer));
    }
  else
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "Transmission for message of type %u and size %u failed\n",
                  ntohs (((struct GNUNET_MessageHeader *) &m[1])->type),
                  m->size);
    }
  GNUNET_free (m);
  return ret;
}


/**
 * Check if we have plaintext messages for the specified neighbour
 * pending, and if so, consider batching and encrypting them (and
 * then trigger processing of the encrypted queue if needed).
 *
 * @param n neighbour to check.
 */
static void process_plaintext_neighbour_queue (struct Neighbour *n);


/**
 * Check if we have encrypted messages for the specified neighbour
 * pending, and if so, check with the transport about sending them
 * out.
 *
 * @param n neighbour to check.
 */
static void
process_encrypted_neighbour_queue (struct Neighbour *n)
{
  if (n->th != NULL)
    return;  /* request already pending */
  if (n->encrypted_head == NULL)
    {
      /* encrypted queue empty, try plaintext instead */
      process_plaintext_neighbour_queue (n);
      return;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asking transport for transmission of %u bytes to `%4s' in next %llu ms\n",
              n->encrypted_head->size,
              GNUNET_i2s (&n->peer),
              GNUNET_TIME_absolute_get_remaining (n->
                                                  encrypted_head->deadline).
              value);
  n->th =
    GNUNET_TRANSPORT_notify_transmit_ready (transport, &n->peer,
                                            n->encrypted_head->size,
                                            GNUNET_TIME_absolute_get_remaining
                                            (n->encrypted_head->deadline),
                                            &notify_encrypted_transmit_ready,
                                            n);
  if (n->th == NULL)
    {
      /* message request too large (oops) */
      GNUNET_break (0);
      /* FIXME: handle error somehow! */
    }
}


/**
 * Decrypt size bytes from in and write the result to out.  Use the
 * key for inbound traffic of the given neighbour.  This function does
 * NOT do any integrity-checks on the result.
 *
 * @param n neighbour we are receiving from
 * @param iv initialization vector to use
 * @param in ciphertext
 * @param out plaintext
 * @param size size of in/out
 * @return GNUNET_OK on success
 */
static int
do_decrypt (struct Neighbour *n,
            const GNUNET_HashCode * iv,
            const void *in, void *out, size_t size)
{
  if (size != (uint16_t) size)
    {
      GNUNET_break (0);
      return GNUNET_NO;
    }
  if ((n->status != PEER_STATE_KEY_RECEIVED) &&
      (n->status != PEER_STATE_KEY_CONFIRMED))
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
  if (size !=
      GNUNET_CRYPTO_aes_decrypt (&n->decrypt_key,
                                 in,
                                 (uint16_t) size,
                                 (const struct
                                  GNUNET_CRYPTO_AesInitializationVector *) iv,
                                 out))
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Decrypted %u bytes from `%4s' using key %u\n",
              size, GNUNET_i2s (&n->peer), n->decrypt_key.crc32);
  return GNUNET_OK;
}


/**
 * Encrypt size bytes from in and write the result to out.  Use the
 * key for outbound traffic of the given neighbour.
 *
 * @param n neighbour we are sending to
 * @param iv initialization vector to use
 * @param in ciphertext
 * @param out plaintext
 * @param size size of in/out
 * @return GNUNET_OK on success
 */
static int
do_encrypt (struct Neighbour *n,
            const GNUNET_HashCode * iv,
            const void *in, void *out, size_t size)
{
  if (size != (uint16_t) size)
    {
      GNUNET_break (0);
      return GNUNET_NO;
    }
  GNUNET_assert (size ==
                 GNUNET_CRYPTO_aes_encrypt (in,
                                            (uint16_t) size,
                                            &n->encrypt_key,
                                            (const struct
                                             GNUNET_CRYPTO_AesInitializationVector
                                             *) iv, out));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Encrypted %u bytes for `%4s' using key %u\n", size,
              GNUNET_i2s (&n->peer), n->encrypt_key.crc32);
  return GNUNET_OK;
}


/**
 * Select messages for transmission.  This heuristic uses a combination
 * of earliest deadline first (EDF) scheduling (with bounded horizon)
 * and priority-based discard (in case no feasible schedule exist) and
 * speculative optimization (defer any kind of transmission until
 * we either create a batch of significant size, 25% of max, or until
 * we are close to a deadline).  Furthermore, when scheduling the
 * heuristic also packs as many messages into the batch as possible,
 * starting with those with the earliest deadline.  Yes, this is fun.
 *
 * @param n neighbour to select messages from
 * @param size number of bytes to select for transmission
 * @param retry_time set to the time when we should try again
 *        (only valid if this function returns zero)
 * @return number of bytes selected, or 0 if we decided to
 *         defer scheduling overall; in that case, retry_time is set.
 */
static size_t
select_messages (struct Neighbour *n,
                 size_t size, struct GNUNET_TIME_Relative *retry_time)
{
  struct MessageEntry *pos;
  struct MessageEntry *min;
  struct MessageEntry *last;
  unsigned int min_prio;
  struct GNUNET_TIME_Absolute t;
  struct GNUNET_TIME_Absolute now;
  uint64_t delta;
  uint64_t avail;
  unsigned long long slack;     /* how long could we wait before missing deadlines? */
  size_t off;
  int discard_low_prio;

  GNUNET_assert (NULL != n->messages);
  now = GNUNET_TIME_absolute_get ();
  /* last entry in linked list of messages processed */
  last = NULL;
  /* should we remove the entry with the lowest
     priority from consideration for scheduling at the
     end of the loop? */
  discard_low_prio = GNUNET_YES;
  while (GNUNET_YES == discard_low_prio)
    {
      min = NULL;
      min_prio = -1;
      discard_low_prio = GNUNET_NO;
      /* number of bytes available for transmission at time "t" */
      avail = n->available_send_window;
      t = n->last_asw_update;
      /* how many bytes have we (hyptothetically) scheduled so far */
      off = 0;
      /* maximum time we can wait before transmitting anything
         and still make all of our deadlines */
      slack = -1;

      pos = n->messages;
      /* note that we use "*2" here because we want to look
         a bit further into the future; much more makes no
         sense since new message might be scheduled in the
         meantime... */
      while ((pos != NULL) && (off < size * 2))
        {
          if (pos->do_transmit == GNUNET_YES)
            {
              /* already removed from consideration */
              pos = pos->next;
              continue;
            }
          if (discard_low_prio == GNUNET_NO)
            {
              delta = pos->deadline.value;
              if (delta < t.value)
                delta = 0;
              else
                delta = t.value - delta;
              avail += delta * n->bpm_out / 1000 / 60;
              if (avail < pos->size)
                {
                  discard_low_prio = GNUNET_YES;        /* we could not schedule this one! */
                }
              else
                {
                  avail -= pos->size;
                  /* update slack, considering both its absolute deadline
                     and relative deadlines caused by other messages
                     with their respective load */
                  slack = GNUNET_MIN (slack, avail / n->bpm_out);
                  if (pos->deadline.value < now.value)
                    slack = 0;
                  else
                    slack =
                      GNUNET_MIN (slack, pos->deadline.value - now.value);
                }
            }
          off += pos->size;
          t.value = GNUNET_MAX (pos->deadline.value, t.value);
          if (pos->priority <= min_prio)
            {
              /* update min for discard */
              min_prio = pos->priority;
              min = pos;
            }
          pos = pos->next;
        }
      if (discard_low_prio)
        {
          GNUNET_assert (min != NULL);
          /* remove lowest-priority entry from consideration */
          min->do_transmit = GNUNET_YES;        /* means: discard (for now) */
        }
      last = pos;
    }
  /* guard against sending "tiny" messages with large headers without
     urgent deadlines */
  if ((slack > 1000) && (size > 4 * off))
    {
      /* less than 25% of message would be filled with
         deadlines still being met if we delay by one
         second or more; so just wait for more data */
      retry_time->value = slack / 2;
      /* reset do_transmit values for next time */
      while (pos != last)
        {
          pos->do_transmit = GNUNET_NO;
          pos = pos->next;
        }
      return 0;
    }
  /* select marked messages (up to size) for transmission */
  off = 0;
  pos = n->messages;
  while (pos != last)
    {
      if ((pos->size <= size) && (pos->do_transmit == GNUNET_NO))
        {
          pos->do_transmit = GNUNET_YES;        /* mark for transmission */
          off += pos->size;
          size -= pos->size;
        }
      else
        pos->do_transmit = GNUNET_NO;   /* mark for not transmitting! */
      pos = pos->next;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Selected %u bytes of plaintext messages for transmission to `%4s'.\n",
              off, GNUNET_i2s (&n->peer));
  return off;
}


/**
 * Batch multiple messages into a larger buffer.
 *
 * @param n neighbour to take messages from
 * @param buf target buffer
 * @param size size of buf
 * @param deadline set to transmission deadline for the result
 * @param retry_time set to the time when we should try again
 *        (only valid if this function returns zero)
 * @param priority set to the priority of the batch
 * @return number of bytes written to buf (can be zero)
 */
static size_t
batch_message (struct Neighbour *n,
               char *buf,
               size_t size,
               struct GNUNET_TIME_Absolute *deadline,
               struct GNUNET_TIME_Relative *retry_time,
               unsigned int *priority)
{
  struct MessageEntry *pos;
  struct MessageEntry *prev;
  struct MessageEntry *next;
  size_t ret;

  ret = 0;
  *priority = 0;
  *deadline = GNUNET_TIME_UNIT_FOREVER_ABS;
  *retry_time = GNUNET_TIME_UNIT_FOREVER_REL;
  if (0 == select_messages (n, size, retry_time))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "No messages selected, will try again in %llu ms\n",
                  retry_time->value);
      return 0;
    }
  pos = n->messages;
  prev = NULL;
  while ((pos != NULL) && (size >= sizeof (struct GNUNET_MessageHeader)))
    {
      next = pos->next;
      if (GNUNET_YES == pos->do_transmit)
        {
          GNUNET_assert (pos->size <= size);
          memcpy (&buf[ret], &pos[1], pos->size);
          ret += pos->size;
          size -= pos->size;
          *priority += pos->priority;
          deadline->value = GNUNET_MIN (deadline->value, pos->deadline.value);
          GNUNET_free (pos);
          if (prev == NULL)
            n->messages = next;
          else
            prev->next = next;
        }
      else
        {
          prev = pos;
        }
      pos = next;
    }
  return ret;
}


/**
 * Remove messages with deadlines that have long expired from
 * the queue.
 *
 * @param n neighbour to inspect
 */
static void
discard_expired_messages (struct Neighbour *n)
{
  /* FIXME */
}


/**
 * Signature of the main function of a task.
 *
 * @param cls closure
 * @param tc context information (why was this task triggered now)
 */
static void
retry_plaintext_processing (void *cls,
                            const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Neighbour *n = cls;

  n->retry_plaintext_task = GNUNET_SCHEDULER_NO_PREREQUISITE_TASK;
  process_plaintext_neighbour_queue (n);
}


/**
 * Send our key (and encrypted PING) to the other peer.
 *
 * @param n the other peer
 */
static void send_key (struct Neighbour *n);


/**
 * Check if we have plaintext messages for the specified neighbour
 * pending, and if so, consider batching and encrypting them (and
 * then trigger processing of the encrypted queue if needed).
 *
 * @param n neighbour to check.
 */
static void
process_plaintext_neighbour_queue (struct Neighbour *n)
{
  char pbuf[MAX_ENCRYPTED_MESSAGE_SIZE];        /* plaintext */
  size_t used;
  size_t esize;
  struct EncryptedMessage *em;  /* encrypted message */
  struct EncryptedMessage *ph;  /* plaintext header */
  struct MessageEntry *me;
  unsigned int priority;
  struct GNUNET_TIME_Absolute deadline;
  struct GNUNET_TIME_Relative retry_time;

  if (n->retry_plaintext_task != GNUNET_SCHEDULER_NO_PREREQUISITE_TASK)
    {
      GNUNET_SCHEDULER_cancel (sched, n->retry_plaintext_task);
      n->retry_plaintext_task = GNUNET_SCHEDULER_NO_PREREQUISITE_TASK;
    }
  switch (n->status)
    {
    case PEER_STATE_DOWN:
      send_key (n);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Not yet connected to `%4s', deferring processing of plaintext messages.\n",
                  GNUNET_i2s(&n->peer));
      return;
    case PEER_STATE_KEY_SENT:
      GNUNET_assert (n->retry_set_key_task !=
                     GNUNET_SCHEDULER_NO_PREREQUISITE_TASK);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Not yet connected to `%4s', deferring processing of plaintext messages.\n",
                  GNUNET_i2s(&n->peer));
      return;
    case PEER_STATE_KEY_RECEIVED:
      GNUNET_assert (n->retry_set_key_task !=
                     GNUNET_SCHEDULER_NO_PREREQUISITE_TASK);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Not yet connected to `%4s', deferring processing of plaintext messages.\n",
                  GNUNET_i2s(&n->peer));
      return;
    case PEER_STATE_KEY_CONFIRMED:
      /* ready to continue */
      break;
    }
  if (n->messages == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Plaintext message queue for `%4s' is empty.\n",
                  GNUNET_i2s(&n->peer));
      return;                   /* no pending messages */
    }
  discard_expired_messages (n);
  if (n->encrypted_head != NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Encrypted message queue for `%4s' is still full, delaying plaintext processing.\n",
                  GNUNET_i2s(&n->peer));
      return;                   /* wait for messages already encrypted to be
                                   processed first! */
    }
  ph = (struct EncryptedMessage *) pbuf;
  deadline = GNUNET_TIME_UNIT_FOREVER_ABS;
  priority = 0;
  used = sizeof (struct EncryptedMessage);

  used += batch_message (n,
                         &pbuf[used],
                         MAX_ENCRYPTED_MESSAGE_SIZE - used,
                         &deadline, &retry_time, &priority);
  if (used == sizeof (struct EncryptedMessage))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "No messages selected for transmission to `%4s' at this time, will try again later.\n",
                  GNUNET_i2s(&n->peer));
      /* no messages selected for sending, try again later... */
      n->retry_plaintext_task =
        GNUNET_SCHEDULER_add_delayed (sched,
                                      GNUNET_NO,
                                      GNUNET_SCHEDULER_PRIORITY_IDLE,
                                      GNUNET_SCHEDULER_NO_PREREQUISITE_TASK,
                                      retry_time,
                                      &retry_plaintext_processing, n);
      return;
    }

  ph->sequence_number = htonl (++n->last_sequence_number_sent);
  ph->inbound_bpm_limit = htonl (n->bpm_in);
  ph->timestamp = GNUNET_TIME_absolute_hton (GNUNET_TIME_absolute_get ());

  /* setup encryption message header */
  me = GNUNET_malloc (sizeof (struct MessageEntry) + used);
  me->deadline = deadline;
  me->priority = priority;
  me->size = used;
  em = (struct EncryptedMessage *) &me[1];
  em->header.size = htons (used);
  em->header.type = htons (GNUNET_MESSAGE_TYPE_CORE_ENCRYPTED_MESSAGE);
  em->reserved = htonl (0);
  esize = used - ENCRYPTED_HEADER_SIZE;
  GNUNET_CRYPTO_hash (&ph->sequence_number, esize, &em->plaintext_hash);
  /* encrypt */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Encrypting %u bytes of plaintext messages for `%4s' for transmission.\n",
              esize,
              GNUNET_i2s(&n->peer));
  GNUNET_assert (GNUNET_OK ==
                 do_encrypt (n,
                             &em->plaintext_hash,
                             &ph->sequence_number,
                             &em->sequence_number, esize));
  /* append to transmission list */
  if (n->encrypted_tail == NULL)
    n->encrypted_head = me;
  else
    n->encrypted_tail->next = me;
  n->encrypted_tail = me;
  process_encrypted_neighbour_queue (n);
}


/**
 * Handle CORE_SEND request.
 */
static void
handle_client_send (void *cls,
                    struct GNUNET_SERVER_Client *client,
                    const struct GNUNET_MessageHeader *message);


/**
 * Function called to notify us that we either succeeded
 * or failed to connect (at the transport level) to another
 * peer.  We should either free the message we were asked
 * to transmit or re-try adding it to the queue.
 *
 * @param cls closure
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
send_connect_continuation (void *cls, size_t size, void *buf)
{
  struct SendMessage *sm = cls;

  if (buf == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Asked to send message to disconnected peer `%4s' and connection failed.  Discarding message.\n",
                  GNUNET_i2s (&sm->peer));
      GNUNET_free (sm);
      /* FIXME: do we need to do something here to let the
         client know about the failure!? */
      return 0;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Connection to peer `%4s' succeeded, retrying original transmission request\n",
              GNUNET_i2s (&sm->peer));
  handle_client_send (NULL, NULL, &sm->header);
  GNUNET_free (sm);
  return 0;
}


/**
 * Handle CORE_SEND request.
 */
static void
handle_client_send (void *cls,
                    struct GNUNET_SERVER_Client *client,
                    const struct GNUNET_MessageHeader *message)
{
  const struct SendMessage *sm;
  struct SendMessage *smc;
  const struct GNUNET_MessageHeader *mh;
  struct Neighbour *n;
  struct MessageEntry *pred;
  struct MessageEntry *pos;
  struct MessageEntry *e;
  uint16_t msize;

  msize = ntohs (message->size);
  if (msize <
      sizeof (struct SendMessage) + sizeof (struct GNUNET_MessageHeader))
    {
      GNUNET_break (0);
      if (client != NULL)
        GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  sm = (const struct SendMessage *) message;
  msize -= sizeof (struct SendMessage);
  mh = (const struct GNUNET_MessageHeader *) &sm[1];
  if (msize != ntohs (mh->size))
    {
      GNUNET_break (0);
      if (client != NULL)
        GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
      return;
    }
  n = find_neighbour (&sm->peer);
  if (n == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Core received `%s' request for `%4s', will try to establish connection within %llu ms\n",
                  "SEND",
                  GNUNET_i2s (&sm->peer),
                  sm->deadline.value);
      msize += sizeof (struct SendMessage);
      /* ask transport to connect to the peer */
      /* FIXME: this code does not handle the
         case where we get multiple SendMessages before
         transport responds to this request;
         => need to track pending requests! */
      smc = GNUNET_malloc (msize);
      memcpy (smc, sm, msize);
      GNUNET_TRANSPORT_notify_transmit_ready (transport,
                                              &sm->peer,
                                              0,
                                              GNUNET_TIME_absolute_get_remaining
                                              (GNUNET_TIME_absolute_ntoh
                                               (sm->deadline)),
                                              &send_connect_continuation,
                                              smc);
      if (client != NULL)
        GNUNET_SERVER_receive_done (client, GNUNET_OK);
      return;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core received `%s' request, queueing %u bytes of plaintext data for transmission to `%4s'.\n",
              "SEND",
              msize, 
              GNUNET_i2s (&sm->peer));
  /* FIXME: consider bounding queue size */
  e = GNUNET_malloc (sizeof (struct MessageEntry) + msize);
  e->deadline = GNUNET_TIME_absolute_ntoh (sm->deadline);
  e->priority = ntohl (sm->priority);
  e->size = msize;
  memcpy (&e[1], mh, msize);

  /* insert, keep list sorted by deadline */
  pred = NULL;
  pos = n->messages;
  while ((pos != NULL) && (pos->deadline.value < e->deadline.value))
    {
      pred = pos;
      pos = pos->next;
    }
  if (pred == NULL)
    n->messages = e;
  else
    pred->next = e;
  e->next = pos;

  /* consider scheduling now */
  process_plaintext_neighbour_queue (n);
  if (client != NULL)
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
}


/**
 * List of handlers for the messages understood by this
 * service.
 */
static struct GNUNET_SERVER_MessageHandler handlers[] = {
  {&handle_client_init, NULL,
   GNUNET_MESSAGE_TYPE_CORE_INIT, 0},
  {&handle_client_request_configure, NULL,
   GNUNET_MESSAGE_TYPE_CORE_REQUEST_CONFIGURE,
   sizeof (struct RequestConfigureMessage)},
  {&handle_client_send, NULL,
   GNUNET_MESSAGE_TYPE_CORE_SEND, 0},
  {NULL, NULL, 0, 0}
};


/**
 * PEERINFO is giving us a HELLO for a peer.  Add the
 * public key to the neighbour's struct and retry
 * send_key.  Or, if we did not get a HELLO, just do
 * nothing.
 *
 * @param cls NULL
 * @param peer the peer for which this is the HELLO
 * @param hello HELLO message of that peer
 * @param trust amount of trust we currently have in that peer
 */
static void
process_hello_retry_send_key (void *cls,
                              const struct GNUNET_PeerIdentity *peer,
                              const struct GNUNET_HELLO_Message *hello,
                              uint32_t trust)
{
  struct Neighbour *n;

  if (peer == NULL)
    return;
  n = find_neighbour (peer);
  if (n == NULL)
    return;
  if (n->public_key != NULL)
    return;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received new `%s' message for `%4s', initiating key exchange.\n",
              "HELLO",
              GNUNET_i2s (peer));
  n->public_key =
    GNUNET_malloc (sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded));
  if (GNUNET_OK != GNUNET_HELLO_get_key (hello, n->public_key))
    {
      GNUNET_free (n->public_key);
      n->public_key = NULL;
      return;
    }
  send_key (n);
}


/**
 * Task that will retry "send_key" if our previous attempt failed
 * to yield a PONG.
 */
static void
set_key_retry_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct Neighbour *n = cls;

  GNUNET_assert (n->status != PEER_STATE_KEY_CONFIRMED);
  n->retry_set_key_task = GNUNET_SCHEDULER_NO_PREREQUISITE_TASK;
  n->set_key_retry_frequency =
    GNUNET_TIME_relative_multiply (n->set_key_retry_frequency, 2);
  send_key (n);
}


/**
 * Send our key (and encrypted PING) to the other peer.
 *
 * @param n the other peer
 */
static void
send_key (struct Neighbour *n)
{
  struct SetKeyMessage *sm;
  struct MessageEntry *me;
  struct PingMessage pp;
  struct PingMessage *pm;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asked to perform key exchange with `%4s'.\n",
              GNUNET_i2s (&n->peer));
  if (n->public_key == NULL)
    {
      /* lookup n's public key, then try again */
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Lacking public key for `%4s', trying to obtain one.\n",
                  GNUNET_i2s (&n->peer));
      GNUNET_PEERINFO_for_all (cfg,
                               sched,
                               &n->peer,
                               0,
                               GNUNET_TIME_UNIT_MINUTES,
                               &process_hello_retry_send_key, NULL);
      return;
    }
  /* first, set key message */
  me = GNUNET_malloc (sizeof (struct MessageEntry) +
                      sizeof (struct SetKeyMessage));
  me->deadline = GNUNET_TIME_relative_to_absolute (MAX_SET_KEY_DELAY);
  me->priority = SET_KEY_PRIORITY;
  me->size = sizeof (struct SetKeyMessage);
  if (n->encrypted_head == NULL)
    n->encrypted_head = me;
  else
    n->encrypted_tail->next = me;
  n->encrypted_tail = me;
  sm = (struct SetKeyMessage *) &me[1];
  sm->header.size = htons (sizeof (struct SetKeyMessage));
  sm->header.type = htons (GNUNET_MESSAGE_TYPE_CORE_SET_KEY);
  sm->sender_status = htonl ((int32_t) ((n->status == PEER_STATE_DOWN) ?
                                        PEER_STATE_KEY_SENT : n->status));
  sm->purpose.size =
    htonl (sizeof (struct GNUNET_CRYPTO_RsaSignaturePurpose) +
           sizeof (struct GNUNET_TIME_AbsoluteNBO) +
           sizeof (struct GNUNET_CRYPTO_RsaEncryptedData) +
           sizeof (struct GNUNET_PeerIdentity));
  sm->purpose.purpose = htonl (GNUNET_SIGNATURE_PURPOSE_SET_KEY);
  sm->creation_time = GNUNET_TIME_absolute_hton (n->encrypt_key_created);
  sm->target = n->peer;
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CRYPTO_rsa_encrypt (&n->encrypt_key,
                                            sizeof (struct
                                                    GNUNET_CRYPTO_AesSessionKey),
                                            n->public_key,
                                            &sm->encrypted_key));
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CRYPTO_rsa_sign (my_private_key, &sm->purpose,
                                         &sm->signature));

  /* second, encrypted PING message */
  me = GNUNET_malloc (sizeof (struct MessageEntry) +
                      sizeof (struct PingMessage));
  me->deadline = GNUNET_TIME_relative_to_absolute (MAX_PING_DELAY);
  me->priority = PING_PRIORITY;
  me->size = sizeof (struct PingMessage);
  n->encrypted_tail->next = me;
  n->encrypted_tail = me;
  pm = (struct PingMessage *) &me[1];
  pm->header.size = htons (sizeof (struct PingMessage));
  pm->header.type = htons (GNUNET_MESSAGE_TYPE_CORE_PING);
  pp.challenge = htonl (n->ping_challenge);
  pp.target = n->peer;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Encrypting `%s' and `%s' messages for `%4s'.\n",
              "SET_KEY", "PING", GNUNET_i2s (&n->peer));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending `%s' to `%4s' with challenge %u encrypted using key %u\n",
              "PING",
              GNUNET_i2s (&n->peer), n->ping_challenge, n->encrypt_key.crc32);
  do_encrypt (n,
              &n->peer.hashPubKey,
              &pp.challenge,
              &pm->challenge,
              sizeof (struct PingMessage) -
              sizeof (struct GNUNET_MessageHeader));
  /* update status */
  switch (n->status)
    {
    case PEER_STATE_DOWN:
      n->status = PEER_STATE_KEY_SENT;
      break;
    case PEER_STATE_KEY_SENT:
      break;
    case PEER_STATE_KEY_RECEIVED:
      break;
    case PEER_STATE_KEY_CONFIRMED:
      GNUNET_break (0);
      break;
    default:
      GNUNET_break (0);
      break;
    }
  /* trigger queue processing */
  process_encrypted_neighbour_queue (n);
  if (n->status != PEER_STATE_KEY_CONFIRMED)
    n->retry_set_key_task
      = GNUNET_SCHEDULER_add_delayed (sched,
                                      GNUNET_NO,
                                      GNUNET_SCHEDULER_PRIORITY_KEEP,
                                      GNUNET_SCHEDULER_NO_PREREQUISITE_TASK,
                                      n->set_key_retry_frequency,
                                      &set_key_retry_task, n);
}


/**
 * We received a SET_KEY message.  Validate and update
 * our key material and status.
 *
 * @param n the neighbour from which we received message m
 * @param m the set key message we received
 */
static void
handle_set_key (struct Neighbour *n, const struct SetKeyMessage *m);


/**
 * PEERINFO is giving us a HELLO for a peer.  Add the public key to
 * the neighbour's struct and retry handling the set_key message.  Or,
 * if we did not get a HELLO, just free the set key message.
 *
 * @param cls pointer to the set key message
 * @param peer the peer for which this is the HELLO
 * @param hello HELLO message of that peer
 * @param trust amount of trust we currently have in that peer
 */
static void
process_hello_retry_handle_set_key (void *cls,
                                    const struct GNUNET_PeerIdentity *peer,
                                    const struct GNUNET_HELLO_Message *hello,
                                    uint32_t trust)
{
  struct SetKeyMessage *sm = cls;
  struct Neighbour *n;

  if (peer == NULL)
    {
      GNUNET_free (sm);
      return;
    }
  n = find_neighbour (peer);
  if (n == NULL)
    {
      GNUNET_break (0);
      return;
    }
  if (n->public_key != NULL)
    return;                     /* multiple HELLOs match!? */
  n->public_key =
    GNUNET_malloc (sizeof (struct GNUNET_CRYPTO_RsaPublicKeyBinaryEncoded));
  if (GNUNET_OK != GNUNET_HELLO_get_key (hello, n->public_key))
    {
      GNUNET_break_op (0);
      GNUNET_free (n->public_key);
      n->public_key = NULL;
      return;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received `%s' for `%4s', continuing processing of `%s' message.\n",
              "HELLO", GNUNET_i2s (peer), "SET_KEY");
  handle_set_key (n, sm);
}


/**
 * We received a PING message.  Validate and transmit
 * PONG.
 *
 * @param n sender of the PING
 * @param m the encrypted PING message itself
 */
static void
handle_ping (struct Neighbour *n, const struct PingMessage *m)
{
  struct PingMessage t;
  struct PingMessage *tp;
  struct MessageEntry *me;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service receives `%s' request from `%4s'.\n",
              "PING", GNUNET_i2s (&n->peer));
  if (GNUNET_OK !=
      do_decrypt (n,
                  &my_identity.hashPubKey,
                  &m->challenge,
                  &t.challenge,
                  sizeof (struct PingMessage) -
                  sizeof (struct GNUNET_MessageHeader)))
    return;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Decrypted `%s' to `%4s' with challenge %u decrypted using key %u\n",
              "PING",
              GNUNET_i2s (&t.target),
              ntohl (t.challenge), n->decrypt_key.crc32);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Target of `%s' request is `%4s'.\n",
              "PING", GNUNET_i2s (&t.target));
  if (0 != memcmp (&t.target,
                   &my_identity, sizeof (struct GNUNET_PeerIdentity)))
    {
      GNUNET_break_op (0);
      return;
    }
  me = GNUNET_malloc (sizeof (struct MessageEntry) +
                      sizeof (struct PingMessage));
  if (n->encrypted_tail != NULL)
    n->encrypted_tail->next = me;
  else
    {
      n->encrypted_tail = me;
      n->encrypted_head = me;
    }
  me->deadline = GNUNET_TIME_relative_to_absolute (MAX_PONG_DELAY);
  me->priority = PONG_PRIORITY;
  me->size = sizeof (struct PingMessage);
  tp = (struct PingMessage *) &me[1];
  tp->header.type = htons (GNUNET_MESSAGE_TYPE_CORE_PONG);
  tp->header.size = htons (sizeof (struct PingMessage));
  do_encrypt (n,
              &my_identity.hashPubKey,
              &t.challenge,
              &tp->challenge,
              sizeof (struct PingMessage) -
              sizeof (struct GNUNET_MessageHeader));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Encrypting `%s' with challenge %u using key %u\n", "PONG",
              ntohl (t.challenge), n->encrypt_key.crc32);
  /* trigger queue processing */
  process_encrypted_neighbour_queue (n);
}


/**
 * We received a SET_KEY message.  Validate and update
 * our key material and status.
 *
 * @param n the neighbour from which we received message m
 * @param m the set key message we received
 */
static void
handle_set_key (struct Neighbour *n, const struct SetKeyMessage *m)
{
  struct SetKeyMessage *m_cpy;
  struct GNUNET_TIME_Absolute t;
  struct GNUNET_CRYPTO_AesSessionKey k;
  struct PingMessage *ping;
  enum PeerStateMachine sender_status;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service receives `%s' request from `%4s'.\n",
              "SET_KEY", GNUNET_i2s (&n->peer));
  if (n->public_key == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Lacking public key for peer, trying to obtain one.\n");
      m_cpy = GNUNET_malloc (sizeof (struct SetKeyMessage));
      memcpy (m_cpy, m, sizeof (struct SetKeyMessage));
      /* lookup n's public key, then try again */
      GNUNET_PEERINFO_for_all (cfg,
                               sched,
                               &n->peer,
                               0,
                               GNUNET_TIME_UNIT_MINUTES,
                               &process_hello_retry_handle_set_key, m_cpy);
      return;
    }
  if ((ntohl (m->purpose.size) !=
       sizeof (struct GNUNET_CRYPTO_RsaSignaturePurpose) +
       sizeof (struct GNUNET_TIME_AbsoluteNBO) +
       sizeof (struct GNUNET_CRYPTO_RsaEncryptedData) +
       sizeof (struct GNUNET_PeerIdentity)) ||
      (GNUNET_OK !=
       GNUNET_CRYPTO_rsa_verify (GNUNET_SIGNATURE_PURPOSE_SET_KEY,
                                 &m->purpose, &m->signature, n->public_key)))
    {
      /* invalid signature */
      GNUNET_break_op (0);
      return;
    }
  t = GNUNET_TIME_absolute_ntoh (m->creation_time);
  if (((n->status == PEER_STATE_KEY_RECEIVED) ||
       (n->status == PEER_STATE_KEY_CONFIRMED)) &&
      (t.value < n->decrypt_key_created.value))
    {
      /* this could rarely happen due to massive re-ordering of
         messages on the network level, but is most likely either
         a bug or some adversary messing with us.  Report. */
      GNUNET_break_op (0);
      return;
    }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Decrypting key material.\n");
  if ((GNUNET_CRYPTO_rsa_decrypt (my_private_key,
                                  &m->encrypted_key,
                                  &k,
                                  sizeof (struct GNUNET_CRYPTO_AesSessionKey))
       != sizeof (struct GNUNET_CRYPTO_AesSessionKey)) ||
      (GNUNET_OK != GNUNET_CRYPTO_aes_check_session_key (&k)))
    {
      /* failed to decrypt !? */
      GNUNET_break_op (0);
      return;
    }

  n->decrypt_key = k;
  if (n->decrypt_key_created.value != t.value)
    {
      /* fresh key, reset sequence numbers */
      n->last_sequence_number_received = 0;
      n->last_packets_bitmap = 0;
      n->decrypt_key_created = t;
    }
  sender_status = (enum PeerStateMachine) ntohl (m->sender_status);
  switch (n->status)
    {
    case PEER_STATE_DOWN:
      n->status = PEER_STATE_KEY_RECEIVED;
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Responding to `%s' with my own key.\n", "SET_KEY");
      send_key (n);
      break;
    case PEER_STATE_KEY_SENT:
    case PEER_STATE_KEY_RECEIVED:
      n->status = PEER_STATE_KEY_RECEIVED;
      if ((sender_status != PEER_STATE_KEY_RECEIVED) &&
          (sender_status != PEER_STATE_KEY_CONFIRMED))
        {
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Responding to `%s' with my own key (other peer has status %u).\n",
                      "SET_KEY", sender_status);
          send_key (n);
        }
      break;
    case PEER_STATE_KEY_CONFIRMED:
      if ((sender_status != PEER_STATE_KEY_RECEIVED) &&
          (sender_status != PEER_STATE_KEY_CONFIRMED))
        {
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Responding to `%s' with my own key (other peer has status %u), I was already fully up.\n",
                      "SET_KEY", sender_status);
          send_key (n);
        }
      break;
    default:
      GNUNET_break (0);
      break;
    }
  if (n->pending_ping != NULL)
    {
      ping = n->pending_ping;
      n->pending_ping = NULL;
      handle_ping (n, ping);
      GNUNET_free (ping);
    }
}


/**
 * We received a PONG message.  Validate and update
 * our status.
 *
 * @param n sender of the PONG
 * @param m the encrypted PONG message itself
 */
static void
handle_pong (struct Neighbour *n, const struct PingMessage *m)
{
  struct PingMessage t;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service receives `%s' request from `%4s'.\n",
              "PONG", GNUNET_i2s (&n->peer));
  if (GNUNET_OK !=
      do_decrypt (n,
                  &n->peer.hashPubKey,
                  &m->challenge,
                  &t.challenge,
                  sizeof (struct PingMessage) -
                  sizeof (struct GNUNET_MessageHeader)))
    return;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Decrypted `%s' from `%4s' with challenge %u using key %u\n",
              "PONG",
              GNUNET_i2s (&t.target),
              ntohl (t.challenge), n->decrypt_key.crc32);
  if ((0 != memcmp (&t.target,
                    &n->peer,
                    sizeof (struct GNUNET_PeerIdentity))) ||
      (n->ping_challenge != ntohl (t.challenge)))
    {
      /* PONG malformed */
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Received malfromed `%s' wanted sender `%4s' with challenge %u\n",
                  "PONG", GNUNET_i2s (&n->peer), n->ping_challenge);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Received malfromed `%s' received from `%4s' with challenge %u\n",
                  "PONG", GNUNET_i2s (&t.target), ntohl (t.challenge));
      GNUNET_break_op (0);
      return;
    }
  switch (n->status)
    {
    case PEER_STATE_DOWN:
      GNUNET_break (0);         /* should be impossible */
      return;
    case PEER_STATE_KEY_SENT:
      GNUNET_break (0);         /* should be impossible, how did we decrypt? */
      return;
    case PEER_STATE_KEY_RECEIVED:
      n->status = PEER_STATE_KEY_CONFIRMED;
      if (n->retry_set_key_task != GNUNET_SCHEDULER_NO_PREREQUISITE_TASK)
        {
          GNUNET_SCHEDULER_cancel (sched, n->retry_set_key_task);
          n->retry_set_key_task = GNUNET_SCHEDULER_NO_PREREQUISITE_TASK;
        }
      process_encrypted_neighbour_queue (n);
      break;
    case PEER_STATE_KEY_CONFIRMED:
      /* duplicate PONG? */
      break;
    default:
      GNUNET_break (0);
      break;
    }
}


/**
 * Send a P2P message to a client.
 *
 * @param sender who sent us the message?
 * @param client who should we give the message to?
 * @param m contains the message to transmit
 * @param msize number of bytes in buf to transmit
 */
static void
send_p2p_message_to_client (struct Neighbour *sender,
                            struct Client *client,
                            const void *m, size_t msize)
{
  char buf[msize + sizeof (struct NotifyTrafficMessage)];
  struct NotifyTrafficMessage *ntm;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service passes message from `%4s' of type %u to client.\n",
              GNUNET_i2s(&sender->peer),
              ntohs (((const struct GNUNET_MessageHeader *) m)->type));
  ntm = (struct NotifyTrafficMessage *) buf;
  ntm->header.size = htons (msize + sizeof (struct NotifyTrafficMessage));
  ntm->header.type = htons (GNUNET_MESSAGE_TYPE_CORE_NOTIFY_INBOUND);
  ntm->reserved = htonl (0);
  ntm->peer = sender->peer;
  memcpy (&ntm[1], m, msize);
  send_to_client (client, &ntm->header, GNUNET_YES);
}


/**
 * Deliver P2P message to interested clients.
 *
 * @param sender who sent us the message?
 * @param m the message
 * @param msize size of the message (including header)
 */
static void
deliver_message (struct Neighbour *sender,
                 const struct GNUNET_MessageHeader *m, size_t msize)
{
  struct Client *cpos;
  uint16_t type;
  unsigned int tpos;
  int deliver_full;

  type = ntohs (m->type);
  cpos = clients;
  while (cpos != NULL)
    {
      deliver_full = GNUNET_NO;
      if (cpos->options & GNUNET_CORE_OPTION_SEND_FULL_INBOUND)
        deliver_full = GNUNET_YES;
      else
        {
          for (tpos = 0; tpos < cpos->tcnt; tpos++)
            {
              if (type != cpos->types[tpos])
                continue;
              deliver_full = GNUNET_YES;
              break;
            }
        }
      if (GNUNET_YES == deliver_full)
        send_p2p_message_to_client (sender, cpos, m, msize);
      else if (cpos->options & GNUNET_CORE_OPTION_SEND_HDR_INBOUND)
        send_p2p_message_to_client (sender, cpos, m,
                                    sizeof (struct GNUNET_MessageHeader));
      cpos = cpos->next;
    }
}


/**
 * Align P2P message and then deliver to interested clients.
 *
 * @param sender who sent us the message?
 * @param buffer unaligned (!) buffer containing message
 * @param msize size of the message (including header)
 */
static void
align_and_deliver (struct Neighbour *sender, const char *buffer, size_t msize)
{
  char abuf[msize];

  /* TODO: call to statistics? */
  memcpy (abuf, buffer, msize);
  deliver_message (sender, (const struct GNUNET_MessageHeader *) abuf, msize);
}


/**
 * Deliver P2P messages to interested clients.
 *
 * @param sender who sent us the message?
 * @param buffer buffer containing messages, can be modified
 * @param buffer_size size of the buffer (overall)
 * @param offset offset where messages in the buffer start
 */
static void
deliver_messages (struct Neighbour *sender,
                  const char *buffer, size_t buffer_size, size_t offset)
{
  struct GNUNET_MessageHeader *mhp;
  struct GNUNET_MessageHeader mh;
  uint16_t msize;
  int need_align;

  while (offset + sizeof (struct GNUNET_MessageHeader) <= buffer_size)
    {
      if (0 != offset % sizeof (uint16_t))
        {
          /* outch, need to copy to access header */
          memcpy (&mh, &buffer[offset], sizeof (struct GNUNET_MessageHeader));
          mhp = &mh;
        }
      else
        {
          /* can access header directly */
          mhp = (struct GNUNET_MessageHeader *) &buffer[offset];
        }
      msize = ntohs (mhp->size);
      if (msize + offset > buffer_size)
        {
          /* malformed message, header says it is larger than what
             would fit into the overall buffer */
          GNUNET_break_op (0);
          break;
        }
#if HAVE_UNALIGNED_64_ACCESS
      need_align = (0 != offset % 4) ? GNUNET_YES : GNUNET_NO;
#else
      need_align = (0 != offset % 8) ? GNUNET_YES : GNUNET_NO;
#endif
      if (GNUNET_YES == need_align)
        align_and_deliver (sender, &buffer[offset], msize);
      else
        deliver_message (sender,
                         (const struct GNUNET_MessageHeader *)
                         &buffer[offset], msize);
      offset += msize;
    }
}


/**
 * We received an encrypted message.  Decrypt, validate and
 * pass on to the appropriate clients.
 */
static void
handle_encrypted_message (struct Neighbour *n,
                          const struct EncryptedMessage *m)
{
  size_t size = ntohs (m->header.size);
  char buf[size];
  struct EncryptedMessage *pt;  /* plaintext */
  GNUNET_HashCode ph;
  size_t off;
  uint32_t snum;
  struct GNUNET_TIME_Absolute t;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service receives `%s' request from `%4s'.\n",
              "ENCRYPTED_MESSAGE", GNUNET_i2s (&n->peer));
  /* decrypt */
  if (GNUNET_OK !=
      do_decrypt (n,
                  &m->plaintext_hash,
                  &m->sequence_number,
                  &buf[ENCRYPTED_HEADER_SIZE], size - ENCRYPTED_HEADER_SIZE))
    return;
  pt = (struct EncryptedMessage *) buf;

  /* validate hash */
  GNUNET_CRYPTO_hash (&pt->sequence_number,
                      size - ENCRYPTED_HEADER_SIZE, &ph);
  if (0 != memcmp (&ph, &m->plaintext_hash, sizeof (GNUNET_HashCode)))
    {
      /* checksum failed */
      GNUNET_break_op (0);
      return;
    }

  /* validate sequence number */
  snum = ntohl (pt->sequence_number);
  if (n->last_sequence_number_received == snum)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Received duplicate message, ignoring.\n");
      /* duplicate, ignore */
      return;
    }
  if ((n->last_sequence_number_received > snum) &&
      (n->last_sequence_number_received - snum > 32))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Received ancient out of sequence message, ignoring.\n");
      /* ancient out of sequence, ignore */
      return;
    }
  if (n->last_sequence_number_received > snum)
    {
      unsigned int rotbit =
        1 << (n->last_sequence_number_received - snum - 1);
      if ((n->last_packets_bitmap & rotbit) != 0)
        {
          GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                      "Received duplicate message, ignoring.\n");
          /* duplicate, ignore */
          return;
        }
      n->last_packets_bitmap |= rotbit;
    }
  if (n->last_sequence_number_received < snum)
    {
      n->last_packets_bitmap <<= (snum - n->last_sequence_number_received);
      n->last_sequence_number_received = snum;
    }

  /* check timestamp */
  t = GNUNET_TIME_absolute_ntoh (pt->timestamp);
  if (GNUNET_TIME_absolute_get_duration (t).value > MAX_MESSAGE_AGE.value)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  _
                  ("Message received far too old (%llu ms). Content ignored.\n"),
                  GNUNET_TIME_absolute_get_duration (t).value);
      return;
    }

  /* process decrypted message(s) */
  n->bpm_out_external_limit = ntohl (pt->inbound_bpm_limit);
  n->bpm_out = GNUNET_MAX (n->bpm_out_external_limit,
                           n->bpm_out_internal_limit);
  n->last_activity = GNUNET_TIME_absolute_get ();
  off = sizeof (struct EncryptedMessage);
  deliver_messages (n, buf, size, off);
}


/**
 * Function called by the transport for each received message.
 *
 * @param cls closure
 * @param latency estimated latency for communicating with the
 *             given peer
 * @param peer (claimed) identity of the other peer
 * @param message the message
 */
static void
handle_transport_receive (void *cls,
                          struct GNUNET_TIME_Relative latency,
                          const struct GNUNET_PeerIdentity *peer,
                          const struct GNUNET_MessageHeader *message)
{
  struct Neighbour *n;
  struct GNUNET_TIME_Absolute now;
  int up;
  uint16_t type;
  uint16_t size;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received message of type %u from `%4s', demultiplexing.\n",
              ntohs (message->type), GNUNET_i2s (peer));
  n = find_neighbour (peer);
  if (n == NULL)
    {
      GNUNET_break (0);
      return;
    }
  n->last_latency = latency;
  up = n->status == PEER_STATE_KEY_CONFIRMED;
  type = ntohs (message->type);
  size = ntohs (message->size);
  switch (type)
    {
    case GNUNET_MESSAGE_TYPE_CORE_SET_KEY:
      if (size != sizeof (struct SetKeyMessage))
        {
          GNUNET_break_op (0);
          return;
        }
      handle_set_key (n, (const struct SetKeyMessage *) message);
      break;
    case GNUNET_MESSAGE_TYPE_CORE_ENCRYPTED_MESSAGE:
      if (size < sizeof (struct EncryptedMessage) +
          sizeof (struct GNUNET_MessageHeader))
        {
          GNUNET_break_op (0);
          return;
        }
      if ((n->status != PEER_STATE_KEY_RECEIVED) &&
          (n->status != PEER_STATE_KEY_CONFIRMED))
        {
          GNUNET_break_op (0);
          return;
        }
      handle_encrypted_message (n, (const struct EncryptedMessage *) message);
      break;
    case GNUNET_MESSAGE_TYPE_CORE_PING:
      if (size != sizeof (struct PingMessage))
        {
          GNUNET_break_op (0);
          return;
        }
      if ((n->status != PEER_STATE_KEY_RECEIVED) &&
          (n->status != PEER_STATE_KEY_CONFIRMED))
        {
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "Core service receives `%s' request from `%4s' but have not processed key; marking as pending.\n",
                      "PING", GNUNET_i2s (&n->peer));
          GNUNET_free_non_null (n->pending_ping);
          n->pending_ping = GNUNET_malloc (sizeof (struct PingMessage));
          memcpy (n->pending_ping, message, sizeof (struct PingMessage));
          return;
        }
      handle_ping (n, (const struct PingMessage *) message);
      break;
    case GNUNET_MESSAGE_TYPE_CORE_PONG:
      if (size != sizeof (struct PingMessage))
        {
          GNUNET_break_op (0);
          return;
        }
      if ((n->status != PEER_STATE_KEY_SENT) &&
          (n->status != PEER_STATE_KEY_RECEIVED) &&
          (n->status != PEER_STATE_KEY_CONFIRMED))
        {
          /* could not decrypt pong, oops! */
          GNUNET_break_op (0);
          return;
        }
      handle_pong (n, (const struct PingMessage *) message);
      break;
    default:
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _("Unsupported message of type %u received.\n"), type);
      return;
    }
  if (n->status == PEER_STATE_KEY_CONFIRMED)
    {
      now = GNUNET_TIME_absolute_get ();
      n->last_activity = now;
      if (!up)
        n->time_established = now;
    }
}


/**
 * Function called by transport to notify us that
 * a peer connected to us (on the network level).
 *
 * @param cls closure
 * @param peer the peer that connected
 * @param latency current latency of the connection
 */
static void
handle_transport_notify_connect (void *cls,
                                 const struct GNUNET_PeerIdentity *peer,
                                 struct GNUNET_TIME_Relative latency)
{
  struct Neighbour *n;
  struct GNUNET_TIME_Absolute now;
  struct ConnectNotifyMessage cnm;

  n = find_neighbour (peer);
  if (n != NULL)
    {
      /* duplicate connect notification!? */
      GNUNET_break (0);
      return;
    }
  now = GNUNET_TIME_absolute_get ();
  n = GNUNET_malloc (sizeof (struct Neighbour));
  n->next = neighbours;
  neighbours = n;
  n->peer = *peer;
  n->last_latency = latency;
  GNUNET_CRYPTO_aes_create_session_key (&n->encrypt_key);
  n->encrypt_key_created = now;
  n->set_key_retry_frequency = INITIAL_SET_KEY_RETRY_FREQUENCY;
  n->last_asw_update = now;
  n->last_arw_update = now;
  n->bpm_in = DEFAULT_BPM_IN_OUT;
  n->bpm_out = DEFAULT_BPM_IN_OUT;
  n->bpm_out_internal_limit = (uint32_t) - 1;
  n->bpm_out_external_limit = DEFAULT_BPM_IN_OUT;
  n->ping_challenge = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
                                                (uint32_t) - 1);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received connection from `%4s'.\n",
              GNUNET_i2s (&n->peer));
  cnm.header.size = htons (sizeof (struct ConnectNotifyMessage));
  cnm.header.type = htons (GNUNET_MESSAGE_TYPE_CORE_NOTIFY_CONNECT);
  cnm.bpm_available = htonl (DEFAULT_BPM_IN_OUT);
  cnm.peer = *peer;
  cnm.last_activity = GNUNET_TIME_absolute_hton (now);
  send_to_all_clients (&cnm.header, GNUNET_YES);
}


/**
 * Free the given entry for the neighbour (it has
 * already been removed from the list at this point).
 * @param n neighbour to free
 */
static void
free_neighbour (struct Neighbour *n)
{
  struct MessageEntry *m;

  while (NULL != (m = n->messages))
    {
      n->messages = m->next;
      GNUNET_free (m);
    }
  while (NULL != (m = n->encrypted_head))
    {
      n->encrypted_head = m->next;
      GNUNET_free (m);
    }
  if (NULL != n->th)
    GNUNET_TRANSPORT_notify_transmit_ready_cancel (n->th);
  if (n->retry_plaintext_task != GNUNET_SCHEDULER_NO_PREREQUISITE_TASK)
    GNUNET_SCHEDULER_cancel (sched, n->retry_plaintext_task);
  if (n->retry_set_key_task != GNUNET_SCHEDULER_NO_PREREQUISITE_TASK)
    GNUNET_SCHEDULER_cancel (sched, n->retry_set_key_task);
  GNUNET_free_non_null (n->public_key);
  GNUNET_free_non_null (n->pending_ping);
  GNUNET_free (n);
}


/**
 * Function called by transport telling us that a peer
 * disconnected.
 *
 * @param cls closure
 * @param peer the peer that disconnected
 */
static void
handle_transport_notify_disconnect (void *cls,
                                    const struct GNUNET_PeerIdentity *peer)
{
  struct ConnectNotifyMessage cnm;
  struct Neighbour *n;
  struct Neighbour *p;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer `%4s' disconnected from us.\n", GNUNET_i2s (peer));
  p = NULL;
  n = neighbours;
  while ((n != NULL) &&
         (0 != memcmp (&n->peer, peer, sizeof (struct GNUNET_PeerIdentity))))
    {
      p = n;
      n = n->next;
    }
  if (n == NULL)
    {
      GNUNET_break (0);
      return;
    }
  if (p == NULL)
    neighbours = n->next;
  else
    p->next = n->next;
  cnm.header.size = htons (sizeof (struct ConnectNotifyMessage));
  cnm.header.type = htons (GNUNET_MESSAGE_TYPE_CORE_NOTIFY_DISCONNECT);
  cnm.bpm_available = htonl (0);
  cnm.peer = *peer;
  cnm.last_activity = GNUNET_TIME_absolute_hton (n->last_activity);
  send_to_all_clients (&cnm.header, GNUNET_YES);
  free_neighbour (n);
}


/**
 * Last task run during shutdown.  Disconnects us from
 * the transport.
 */
static void
cleaning_task (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Core service shutting down.\n");
  GNUNET_assert (transport != NULL);
  GNUNET_TRANSPORT_disconnect (transport);
  transport = NULL;
}


/**
 * Initiate core service.
 *
 * @param cls closure
 * @param s scheduler to use
 * @param serv the initialized server
 * @param c configuration to use
 */
static void
run (void *cls,
     struct GNUNET_SCHEDULER_Handle *s,
     struct GNUNET_SERVER_Handle *serv, struct GNUNET_CONFIGURATION_Handle *c)
{
#if 0
  unsigned long long qin;
  unsigned long long qout;
  unsigned long long tneigh;
#endif
  char *keyfile;

  sched = s;
  cfg = c;
  /* parse configuration */
  if (
#if 0
       (GNUNET_OK !=
        GNUNET_CONFIGURATION_get_value_number (c,
                                               "CORE",
                                               "XX",
                                               &qin)) ||
       (GNUNET_OK !=
        GNUNET_CONFIGURATION_get_value_number (c,
                                               "CORE",
                                               "YY",
                                               &qout)) ||
       (GNUNET_OK !=
        GNUNET_CONFIGURATION_get_value_number (c,
                                               "CORE",
                                               "ZZ_LIMIT", &tneigh)) ||
#endif
       (GNUNET_OK !=
        GNUNET_CONFIGURATION_get_value_filename (c,
                                                 "GNUNETD",
                                                 "HOSTKEY", &keyfile)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _
                  ("Core service is lacking key configuration settings.  Exiting.\n"));
      GNUNET_SCHEDULER_shutdown (s);
      return;
    }
  my_private_key = GNUNET_CRYPTO_rsa_key_create_from_file (keyfile);
  GNUNET_free (keyfile);
  if (my_private_key == NULL)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  _("Core service could not access hostkey.  Exiting.\n"));
      GNUNET_SCHEDULER_shutdown (s);
      return;
    }
  GNUNET_CRYPTO_rsa_key_get_public (my_private_key, &my_public_key);
  GNUNET_CRYPTO_hash (&my_public_key,
                      sizeof (my_public_key), &my_identity.hashPubKey);
  /* setup notification */
  server = serv;
  GNUNET_SERVER_disconnect_notify (server, &handle_client_disconnect, NULL);
  /* setup transport connection */
  transport = GNUNET_TRANSPORT_connect (sched,
                                        cfg,
                                        NULL,
                                        &handle_transport_receive,
                                        &handle_transport_notify_connect,
                                        &handle_transport_notify_disconnect);
  GNUNET_assert (NULL != transport);
  GNUNET_SCHEDULER_add_delayed (sched,
                                GNUNET_YES,
                                GNUNET_SCHEDULER_PRIORITY_IDLE,
                                GNUNET_SCHEDULER_NO_PREREQUISITE_TASK,
                                GNUNET_TIME_UNIT_FOREVER_REL,
                                &cleaning_task, NULL);
  /* process client requests */
  GNUNET_SERVER_add_handlers (server, handlers);
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              _("Core service of `%4s' ready.\n"), GNUNET_i2s (&my_identity));
}


/**
 * Function called during shutdown.  Clean up our state.
 */
static void
cleanup (void *cls, struct GNUNET_CONFIGURATION_Handle *cfg)
{
  struct Neighbour *n;

  if (my_private_key != NULL)
    GNUNET_CRYPTO_rsa_key_free (my_private_key);
  while (NULL != (n = neighbours))
    {
      neighbours = n->next;
      free_neighbour (n);
    }
  /*
     FIXME:
     - free clients
   */
}


/**
 * The main function for the transport service.
 *
 * @param argc number of arguments from the command line
 * @param argv command line arguments
 * @return 0 ok, 1 on error
 */
int
main (int argc, char *const *argv)
{
  return (GNUNET_OK ==
          GNUNET_SERVICE_run (argc,
                              argv,
                              "core", &run, NULL, &cleanup, NULL)) ? 0 : 1;
}

/* end of gnunet-service-core.c */