allow empty/NULL context message
[oweals/gnunet.git] / src / peerstore / peerstore_api.c
index 02c8d69df05ad8adc6be6fb72c6e6e66f8debbf2..a288e74d2df162c279929a67aa5807294b4d1194 100644 (file)
@@ -1,6 +1,6 @@
 /*
      This file is part of GNUnet.
-     (C) 
+     Copyright (C) 2013-2016 GNUnet e.V.
 
      GNUnet is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
 
      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
-     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-     Boston, MA 02111-1307, USA.
+     Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+     Boston, MA 02110-1301, USA.
 */
-
 /**
  * @file peerstore/peerstore_api.c
  * @brief API for peerstore
  * @author Omar Tarabai
+ * @author Christian Grothoff
  */
 #include "platform.h"
 #include "gnunet_util_lib.h"
 #include "peerstore.h"
+#include "peerstore_common.h"
 
 #define LOG(kind,...) GNUNET_log_from (kind, "peerstore-api",__VA_ARGS__)
 
 /************************      DATA STRUCTURES     ****************************/
 /******************************************************************************/
 
+/**
+ * Handle to the PEERSTORE service.
+ */
+struct GNUNET_PEERSTORE_Handle
+{
+
+  /**
+   * Our configuration.
+   */
+  const struct GNUNET_CONFIGURATION_Handle *cfg;
+
+  /**
+   * Message queue
+   */
+  struct GNUNET_MQ_Handle *mq;
+
+  /**
+   * Head of active STORE requests.
+   */
+  struct GNUNET_PEERSTORE_StoreContext *store_head;
+
+  /**
+   * Tail of active STORE requests.
+   */
+  struct GNUNET_PEERSTORE_StoreContext *store_tail;
+
+  /**
+   * Head of active ITERATE requests.
+   */
+  struct GNUNET_PEERSTORE_IterateContext *iterate_head;
+
+  /**
+   * Tail of active ITERATE requests.
+   */
+  struct GNUNET_PEERSTORE_IterateContext *iterate_tail;
+
+  /**
+   * Hashmap of watch requests
+   */
+  struct GNUNET_CONTAINER_MultiHashMap *watches;
+
+  /**
+   * Are we in the process of disconnecting but need to sync first?
+   */
+  int disconnecting;
+
+};
+
+/**
+ * Context for a store request
+ */
+struct GNUNET_PEERSTORE_StoreContext
+{
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_StoreContext *next;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_StoreContext *prev;
+
+  /**
+   * Handle to the PEERSTORE service.
+   */
+  struct GNUNET_PEERSTORE_Handle *h;
+
+  /**
+   * Continuation called with service response
+   */
+  GNUNET_PEERSTORE_Continuation cont;
+
+  /**
+   * Closure for @e cont
+   */
+  void *cont_cls;
+
+  /**
+   * Which subsystem does the store?
+   */
+  char *sub_system;
+
+  /**
+   * Key for the store operation.
+   */
+  char *key;
+
+  /**
+   * Contains @e size bytes.
+   */
+  void *value;
+
+  /**
+   * Peer the store is for.
+   */
+  struct GNUNET_PeerIdentity peer;
+
+  /**
+   * Number of bytes in @e value.
+   */
+  size_t size;
+
+  /**
+   * When does the value expire?
+   */
+  struct GNUNET_TIME_Absolute expiry;
+
+  /**
+   * Options for the store operation.
+   */
+  enum GNUNET_PEERSTORE_StoreOption options;
+
+};
+
+/**
+ * Context for a iterate request
+ */
+struct GNUNET_PEERSTORE_IterateContext
+{
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_IterateContext *next;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_IterateContext *prev;
+
+  /**
+   * Handle to the PEERSTORE service.
+   */
+  struct GNUNET_PEERSTORE_Handle *h;
+
+  /**
+   * Which subsystem does the store?
+   */
+  char *sub_system;
+
+  /**
+   * Peer the store is for.
+   */
+  struct GNUNET_PeerIdentity peer;
+
+  /**
+   * Key for the store operation.
+   */
+  char *key;
+
+  /**
+   * Operation timeout
+   */
+  struct GNUNET_TIME_Relative timeout;
+
+  /**
+   * Callback with each matching record
+   */
+  GNUNET_PEERSTORE_Processor callback;
+
+  /**
+   * Closure for @e callback
+   */
+  void *callback_cls;
+
+  /**
+   * #GNUNET_YES if we are currently processing records.
+   */
+  int iterating;
+
+  /**
+   * Task identifier for the function called
+   * on iterate request timeout
+   */
+  struct GNUNET_SCHEDULER_Task *timeout_task;
+
+};
+
+/**
+ * Context for a watch request
+ */
+struct GNUNET_PEERSTORE_WatchContext
+{
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_WatchContext *next;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct GNUNET_PEERSTORE_WatchContext *prev;
+
+  /**
+   * Handle to the PEERSTORE service.
+   */
+  struct GNUNET_PEERSTORE_Handle *h;
+
+  /**
+   * Callback with each record received
+   */
+  GNUNET_PEERSTORE_Processor callback;
+
+  /**
+   * Closure for @e callback
+   */
+  void *callback_cls;
+
+  /**
+   * Hash of the combined key
+   */
+  struct GNUNET_HashCode keyhash;
+
+};
 
 /******************************************************************************/
-/***********************         DECLARATIONS         *************************/
+/*******************             DECLARATIONS             *********************/
 /******************************************************************************/
 
+/**
+ * Close the existing connection to PEERSTORE and reconnect.
+ *
+ * @param h handle to the service
+ */
+static void
+reconnect (struct GNUNET_PEERSTORE_Handle *h);
+
+
+/**
+ * Callback after MQ envelope is sent
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_StoreContext *`
+ */
+static void
+store_request_sent (void *cls)
+{
+  struct GNUNET_PEERSTORE_StoreContext *sc = cls;
+  GNUNET_PEERSTORE_Continuation cont;
+  void *cont_cls;
+
+  cont = sc->cont;
+  cont_cls = sc->cont_cls;
+  GNUNET_PEERSTORE_store_cancel (sc);
+  if (NULL != cont)
+    cont (cont_cls, GNUNET_OK);
+}
+
 
 /******************************************************************************/
 /*******************         CONNECTION FUNCTIONS         *********************/
 /******************************************************************************/
 
+static void
+handle_client_error (void *cls,
+                     enum GNUNET_MQ_Error error)
+{
+  struct GNUNET_PEERSTORE_Handle *h = cls;
+
+  LOG (GNUNET_ERROR_TYPE_ERROR,
+       _("Received an error notification from MQ of type: %d\n"),
+       error);
+  reconnect (h);
+}
+
+
+/**
+ * Iterator over previous watches to resend them
+ *
+ * @param cls the `struct GNUNET_PEERSTORE_Handle`
+ * @param key key for the watch
+ * @param value the `struct GNUNET_PEERSTORE_WatchContext *`
+ * @return #GNUNET_YES (continue to iterate)
+ */
+static int
+rewatch_it (void *cls,
+           const struct GNUNET_HashCode *key,
+           void *value)
+{
+  struct GNUNET_PEERSTORE_Handle *h = cls;
+  struct GNUNET_PEERSTORE_WatchContext *wc = value;
+  struct StoreKeyHashMessage *hm;
+  struct GNUNET_MQ_Envelope *ev;
+
+  ev = GNUNET_MQ_msg (hm, GNUNET_MESSAGE_TYPE_PEERSTORE_WATCH);
+  hm->keyhash = wc->keyhash;
+  GNUNET_MQ_send (h->mq, ev);
+  return GNUNET_YES;
+}
+
+
+/**
+ * Called when the iterate request is timedout
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_IterateContext *`
+ */
+static void
+iterate_timeout (void *cls)
+{
+  struct GNUNET_PEERSTORE_IterateContext *ic = cls;
+  GNUNET_PEERSTORE_Processor callback;
+  void *callback_cls;
+
+  ic->timeout_task = NULL;
+  callback = ic->callback;
+  callback_cls = ic->callback_cls;
+  GNUNET_PEERSTORE_iterate_cancel (ic);
+  if (NULL != callback)
+    callback (callback_cls, NULL, _("timeout"));
+}
+
+
+/**
+ * Iterator over watch requests to cancel them.
+ *
+ * @param cls unsused
+ * @param key key to the watch request
+ * @param value watch context
+ * @return #GNUNET_YES to continue iteration
+ */
+static int
+destroy_watch (void *cls,
+               const struct GNUNET_HashCode *key,
+               void *value)
+{
+  struct GNUNET_PEERSTORE_WatchContext *wc = value;
+
+  GNUNET_PEERSTORE_watch_cancel (wc);
+  return GNUNET_YES;
+}
+
+
+/**
+ * Kill the connection to the service. This can be delayed in case of pending
+ * STORE requests and the user explicitly asked to sync first. Otherwise it is
+ * performed instantly.
+ *
+ * @param h Handle to the service.
+ */
+static void
+do_disconnect (struct GNUNET_PEERSTORE_Handle *h)
+{
+  if (NULL != h->mq)
+  {
+    GNUNET_MQ_destroy (h->mq);
+    h->mq = NULL;
+  }
+  GNUNET_free (h);
+}
+
+
+/**
+ * Connect to the PEERSTORE service.
+ *
+ * @param cfg configuration to use
+ * @return NULL on error
+ */
+struct GNUNET_PEERSTORE_Handle *
+GNUNET_PEERSTORE_connect (const struct GNUNET_CONFIGURATION_Handle *cfg)
+{
+  struct GNUNET_PEERSTORE_Handle *h;
+
+  h = GNUNET_new (struct GNUNET_PEERSTORE_Handle);
+  h->cfg = cfg;
+  h->disconnecting = GNUNET_NO;
+  reconnect (h);
+  if (NULL == h->mq)
+  {
+    GNUNET_free (h);
+    return NULL;
+  }
+  return h;
+}
+
+
+/**
+ * Disconnect from the PEERSTORE service. Any pending ITERATE and WATCH requests
+ * will be canceled.
+ * Any pending STORE requests will depend on @e snyc_first flag.
+ *
+ * @param h handle to disconnect
+ * @param sync_first send any pending STORE requests before disconnecting
+ */
+void
+GNUNET_PEERSTORE_disconnect (struct GNUNET_PEERSTORE_Handle *h,
+                             int sync_first)
+{
+  struct GNUNET_PEERSTORE_IterateContext *ic;
+  struct GNUNET_PEERSTORE_StoreContext *sc;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG, "Disconnecting.\n");
+  if (NULL != h->watches)
+  {
+    GNUNET_CONTAINER_multihashmap_iterate (h->watches, &destroy_watch, NULL);
+    GNUNET_CONTAINER_multihashmap_destroy (h->watches);
+    h->watches = NULL;
+  }
+  while (NULL != (ic = h->iterate_head))
+  {
+    GNUNET_break (0);
+    GNUNET_PEERSTORE_iterate_cancel (ic);
+  }
+  if (NULL != h->store_head)
+  {
+    if (GNUNET_YES == sync_first)
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Delaying disconnection due to pending store requests.\n");
+      h->disconnecting = GNUNET_YES;
+      return;
+    }
+    while (NULL != (sc = h->store_head))
+      GNUNET_PEERSTORE_store_cancel (sc);
+  }
+  do_disconnect (h);
+}
+
+
+/******************************************************************************/
+/*******************            STORE FUNCTIONS           *********************/
+/******************************************************************************/
+
+
+/**
+ * Cancel a store request
+ *
+ * @param sc Store request context
+ */
+void
+GNUNET_PEERSTORE_store_cancel (struct GNUNET_PEERSTORE_StoreContext *sc)
+{
+  struct GNUNET_PEERSTORE_Handle *h = sc->h;
+
+  GNUNET_CONTAINER_DLL_remove (sc->h->store_head, sc->h->store_tail, sc);
+  GNUNET_free (sc->sub_system);
+  GNUNET_free (sc->value);
+  GNUNET_free (sc->key);
+  GNUNET_free (sc);
+  if ((GNUNET_YES == h->disconnecting) && (NULL == h->store_head))
+    do_disconnect (h);
+}
+
+
+/**
+ * Store a new entry in the PEERSTORE.
+ * Note that stored entries can be lost in some cases
+ * such as power failure.
+ *
+ * @param h Handle to the PEERSTORE service
+ * @param sub_system name of the sub system
+ * @param peer Peer Identity
+ * @param key entry key
+ * @param value entry value BLOB
+ * @param size size of @e value
+ * @param expiry absolute time after which the entry is (possibly) deleted
+ * @param options options specific to the storage operation
+ * @param cont Continuation function after the store request is sent
+ * @param cont_cls Closure for @a cont
+ */
+struct GNUNET_PEERSTORE_StoreContext *
+GNUNET_PEERSTORE_store (struct GNUNET_PEERSTORE_Handle *h,
+                        const char *sub_system,
+                        const struct GNUNET_PeerIdentity *peer,
+                        const char *key,
+                        const void *value, size_t size,
+                        struct GNUNET_TIME_Absolute expiry,
+                        enum GNUNET_PEERSTORE_StoreOption options,
+                        GNUNET_PEERSTORE_Continuation cont,
+                        void *cont_cls)
+{
+  struct GNUNET_MQ_Envelope *ev;
+  struct GNUNET_PEERSTORE_StoreContext *sc;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Storing value (size: %lu) for subsytem `%s', peer `%s', key `%s'\n",
+       size, sub_system, GNUNET_i2s (peer), key);
+  ev = PEERSTORE_create_record_mq_envelope (sub_system, peer, key, value, size,
+                                            &expiry, options,
+                                            GNUNET_MESSAGE_TYPE_PEERSTORE_STORE);
+  sc = GNUNET_new (struct GNUNET_PEERSTORE_StoreContext);
+
+  sc->sub_system = GNUNET_strdup (sub_system);
+  sc->peer = *peer;
+  sc->key = GNUNET_strdup (key);
+  sc->value = GNUNET_memdup (value, size);
+  sc->size = size;
+  sc->expiry = expiry;
+  sc->options = options;
+  sc->cont = cont;
+  sc->cont_cls = cont_cls;
+  sc->h = h;
+
+  GNUNET_CONTAINER_DLL_insert_tail (h->store_head, h->store_tail, sc);
+  GNUNET_MQ_notify_sent (ev, &store_request_sent, sc);
+  GNUNET_MQ_send (h->mq, ev);
+  return sc;
+
+}
+
+
+/******************************************************************************/
+/*******************           ITERATE FUNCTIONS          *********************/
+/******************************************************************************/
+
+
+/**
+ * When a response for iterate request is received
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_Handle *`
+ * @param msg message received
+ */
+static void
+handle_iterate_end (void *cls,
+                    const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_PEERSTORE_Handle *h = cls;
+  struct GNUNET_PEERSTORE_IterateContext *ic;
+  GNUNET_PEERSTORE_Processor callback;
+  void *callback_cls;
+
+  ic = h->iterate_head;
+  if (NULL == ic)
+  {
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         _("Unexpected iteration response, this should not happen.\n"));
+    reconnect (h);
+    return;
+  }
+  callback = ic->callback;
+  callback_cls = ic->callback_cls;
+  ic->iterating = GNUNET_NO;
+  GNUNET_PEERSTORE_iterate_cancel (ic);
+  if (NULL != callback)
+    callback (callback_cls, NULL, NULL);
+}
+
+
+/**
+ * When a response for iterate request is received, check the
+ * message is well-formed.
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_Handle *`
+ * @param msg message received
+ */
+static int
+check_iterate_result (void *cls,
+                      const struct GNUNET_MessageHeader *msg)
+{
+  /* we defer validation to #handle_iterate_result */
+  return GNUNET_OK;
+}
+
+
+/**
+ * When a response for iterate request is received
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_Handle *`
+ * @param msg message received
+ */
+static void
+handle_iterate_result (void *cls,
+                       const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_PEERSTORE_Handle *h = cls;
+  struct GNUNET_PEERSTORE_IterateContext *ic;
+  GNUNET_PEERSTORE_Processor callback;
+  void *callback_cls;
+  struct GNUNET_PEERSTORE_Record *record;
+
+  ic = h->iterate_head;
+  if (NULL == ic)
+  {
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         _("Unexpected iteration response, this should not happen.\n"));
+    reconnect (h);
+    return;
+  }
+  ic->iterating = GNUNET_YES;
+  callback = ic->callback;
+  callback_cls = ic->callback_cls;
+  if (NULL == callback)
+    return;
+  record = PEERSTORE_parse_record_message (msg);
+  if (NULL == record)
+  {
+    callback (callback_cls,
+              NULL,
+              _("Received a malformed response from service."));
+  }
+  else
+  {
+    callback (callback_cls,
+              record,
+              NULL);
+    PEERSTORE_destroy_record (record);
+  }
+}
+
+
+/**
+ * Cancel an iterate request
+ * Please do not call after the iterate request is done
+ *
+ * @param ic Iterate request context as returned by GNUNET_PEERSTORE_iterate()
+ */
+void
+GNUNET_PEERSTORE_iterate_cancel (struct GNUNET_PEERSTORE_IterateContext *ic)
+{
+  if (NULL != ic->timeout_task)
+  {
+    GNUNET_SCHEDULER_cancel (ic->timeout_task);
+    ic->timeout_task = NULL;
+  }
+  if (GNUNET_NO == ic->iterating)
+  {
+    GNUNET_CONTAINER_DLL_remove (ic->h->iterate_head,
+                                 ic->h->iterate_tail,
+                                 ic);
+    GNUNET_free (ic->sub_system);
+    GNUNET_free_non_null (ic->key);
+    GNUNET_free (ic);
+  }
+  else
+    ic->callback = NULL;
+}
+
+
+/**
+ * Iterate over records matching supplied key information
+ *
+ * @param h handle to the PEERSTORE service
+ * @param sub_system name of sub system
+ * @param peer Peer identity (can be NULL)
+ * @param key entry key string (can be NULL)
+ * @param timeout time after which the iterate request is canceled
+ * @param callback function called with each matching record, all NULL's on end
+ * @param callback_cls closure for @a callback
+ * @return Handle to iteration request
+ */
+struct GNUNET_PEERSTORE_IterateContext *
+GNUNET_PEERSTORE_iterate (struct GNUNET_PEERSTORE_Handle *h,
+                          const char *sub_system,
+                          const struct GNUNET_PeerIdentity *peer,
+                          const char *key,
+                          struct GNUNET_TIME_Relative timeout,
+                          GNUNET_PEERSTORE_Processor callback,
+                          void *callback_cls)
+{
+  struct GNUNET_MQ_Envelope *ev;
+  struct GNUNET_PEERSTORE_IterateContext *ic;
+
+  ev = PEERSTORE_create_record_mq_envelope (sub_system, peer, key, NULL, 0,
+                                            NULL, 0,
+                                            GNUNET_MESSAGE_TYPE_PEERSTORE_ITERATE);
+  ic = GNUNET_new (struct GNUNET_PEERSTORE_IterateContext);
+
+  ic->callback = callback;
+  ic->callback_cls = callback_cls;
+  ic->h = h;
+  ic->sub_system = GNUNET_strdup (sub_system);
+  if (NULL != peer)
+    ic->peer = *peer;
+  if (NULL != key)
+    ic->key = GNUNET_strdup (key);
+  ic->timeout = timeout;
+  GNUNET_CONTAINER_DLL_insert_tail (h->iterate_head,
+                                    h->iterate_tail,
+                                    ic);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Sending an iterate request for sub system `%s'\n",
+       sub_system);
+  GNUNET_MQ_send (h->mq, ev);
+  ic->timeout_task =
+      GNUNET_SCHEDULER_add_delayed (timeout,
+                                    &iterate_timeout,
+                                    ic);
+  return ic;
+}
+
+
+/******************************************************************************/
+/*******************            WATCH FUNCTIONS           *********************/
+/******************************************************************************/
+
+/**
+ * When a watch record is received, validate it is well-formed.
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_Handle *`
+ * @param msg message received
+ */
+static int
+check_watch_record (void *cls,
+                    const struct GNUNET_MessageHeader *msg)
+{
+  /* we defer validation to #handle_watch_result */
+  return GNUNET_OK;
+}
+
+
+/**
+ * When a watch record is received, process it.
+ *
+ * @param cls a `struct GNUNET_PEERSTORE_Handle *`
+ * @param msg message received
+ */
+static void
+handle_watch_record (void *cls,
+                     const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_PEERSTORE_Handle *h = cls;
+  struct GNUNET_PEERSTORE_Record *record;
+  struct GNUNET_HashCode keyhash;
+  struct GNUNET_PEERSTORE_WatchContext *wc;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Received a watch record from service.\n");
+  record = PEERSTORE_parse_record_message (msg);
+  if (NULL == record)
+  {
+    reconnect (h);
+    return;
+  }
+  PEERSTORE_hash_key (record->sub_system,
+                      record->peer,
+                      record->key,
+                      &keyhash);
+  // FIXME: what if there are multiple watches for the same key?
+  wc = GNUNET_CONTAINER_multihashmap_get (h->watches,
+                                          &keyhash);
+  if (NULL == wc)
+  {
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         _("Received a watch result for a non existing watch.\n"));
+    PEERSTORE_destroy_record (record);
+    reconnect (h);
+    return;
+  }
+  if (NULL != wc->callback)
+    wc->callback (wc->callback_cls,
+                  record,
+                  NULL);
+  PEERSTORE_destroy_record (record);
+}
+
+
+/**
+ * Close the existing connection to PEERSTORE and reconnect.
+ *
+ * @param h handle to the service
+ */
+static void
+reconnect (struct GNUNET_PEERSTORE_Handle *h)
+{
+  GNUNET_MQ_hd_fixed_size (iterate_end,
+                           GNUNET_MESSAGE_TYPE_PEERSTORE_ITERATE_END,
+                           struct GNUNET_MessageHeader);
+  GNUNET_MQ_hd_var_size (iterate_result,
+                         GNUNET_MESSAGE_TYPE_PEERSTORE_ITERATE_RECORD,
+                         struct GNUNET_MessageHeader);
+  GNUNET_MQ_hd_var_size (watch_record,
+                         GNUNET_MESSAGE_TYPE_PEERSTORE_WATCH_RECORD,
+                         struct GNUNET_MessageHeader);
+  struct GNUNET_MQ_MessageHandler mq_handlers[] = {
+    make_iterate_end_handler (h),
+    make_iterate_result_handler (h),
+    make_watch_record_handler (h),
+    GNUNET_MQ_handler_end ()
+  };
+  struct GNUNET_PEERSTORE_IterateContext *ic;
+  struct GNUNET_PEERSTORE_IterateContext *next;
+  GNUNET_PEERSTORE_Processor icb;
+  void *icb_cls;
+  struct GNUNET_PEERSTORE_StoreContext *sc;
+  struct GNUNET_MQ_Envelope *ev;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Reconnecting...\n");
+  for (ic = h->iterate_head; NULL != ic; ic = next)
+  {
+    next = ic->next;
+    if (GNUNET_YES == ic->iterating)
+    {
+      icb = ic->callback;
+      icb_cls = ic->callback_cls;
+      GNUNET_PEERSTORE_iterate_cancel (ic);
+      if (NULL != icb)
+        icb (icb_cls,
+             NULL,
+             "Iteration canceled due to reconnection");
+    }
+  }
+  if (NULL != h->mq)
+  {
+    GNUNET_MQ_destroy (h->mq);
+    h->mq = NULL;
+  }
+  h->mq = GNUNET_CLIENT_connecT (h->cfg,
+                                 "peerstore",
+                                 mq_handlers,
+                                 &handle_client_error,
+                                 h);
+  if (NULL == h->mq)
+    return;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Resending pending requests after reconnect.\n");
+  if (NULL != h->watches)
+    GNUNET_CONTAINER_multihashmap_iterate (h->watches,
+                                           &rewatch_it,
+                                           h);
+  for (ic = h->iterate_head; NULL != ic; ic = ic->next)
+  {
+    ev = PEERSTORE_create_record_mq_envelope (ic->sub_system,
+                                              &ic->peer,
+                                              ic->key,
+                                              NULL, 0,
+                                              NULL, 0,
+                                              GNUNET_MESSAGE_TYPE_PEERSTORE_ITERATE);
+    GNUNET_MQ_send (h->mq, ev);
+    ic->timeout_task
+      = GNUNET_SCHEDULER_add_delayed (ic->timeout,
+                                      &iterate_timeout,
+                                      ic);
+  }
+  for (sc = h->store_head; NULL != sc; sc = sc->next)
+  {
+    ev = PEERSTORE_create_record_mq_envelope (sc->sub_system,
+                                              &sc->peer,
+                                              sc->key,
+                                              sc->value,
+                                              sc->size,
+                                              &sc->expiry,
+                                              sc->options,
+                                              GNUNET_MESSAGE_TYPE_PEERSTORE_STORE);
+    GNUNET_MQ_notify_sent (ev,
+                           &store_request_sent,
+                           sc);
+    GNUNET_MQ_send (h->mq,
+                    ev);
+  }
+}
+
+
+/**
+ * Cancel a watch request
+ *
+ * @param wc handle to the watch request
+ */
+void
+GNUNET_PEERSTORE_watch_cancel (struct GNUNET_PEERSTORE_WatchContext *wc)
+{
+  struct GNUNET_PEERSTORE_Handle *h = wc->h;
+  struct GNUNET_MQ_Envelope *ev;
+  struct StoreKeyHashMessage *hm;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Canceling watch.\n");
+  ev = GNUNET_MQ_msg (hm,
+                      GNUNET_MESSAGE_TYPE_PEERSTORE_WATCH_CANCEL);
+  hm->keyhash = wc->keyhash;
+  GNUNET_MQ_send (h->mq, ev);
+  GNUNET_CONTAINER_multihashmap_remove (h->watches,
+                                        &wc->keyhash,
+                                        wc);
+  GNUNET_free (wc);
+}
+
+
+/**
+ * Request watching a given key
+ * User will be notified with any new values added to key
+ *
+ * @param h handle to the PEERSTORE service
+ * @param sub_system name of sub system
+ * @param peer Peer identity
+ * @param key entry key string
+ * @param callback function called with each new value
+ * @param callback_cls closure for @a callback
+ * @return Handle to watch request
+ */
+struct GNUNET_PEERSTORE_WatchContext *
+GNUNET_PEERSTORE_watch (struct GNUNET_PEERSTORE_Handle *h,
+                        const char *sub_system,
+                        const struct GNUNET_PeerIdentity *peer,
+                        const char *key,
+                        GNUNET_PEERSTORE_Processor callback,
+                        void *callback_cls)
+{
+  struct GNUNET_MQ_Envelope *ev;
+  struct StoreKeyHashMessage *hm;
+  struct GNUNET_PEERSTORE_WatchContext *wc;
+
+  ev = GNUNET_MQ_msg (hm,
+                      GNUNET_MESSAGE_TYPE_PEERSTORE_WATCH);
+  PEERSTORE_hash_key (sub_system,
+                      peer,
+                      key,
+                      &hm->keyhash);
+  wc = GNUNET_new (struct GNUNET_PEERSTORE_WatchContext);
+  wc->callback = callback;
+  wc->callback_cls = callback_cls;
+  wc->h = h;
+  wc->keyhash = hm->keyhash;
+  if (NULL == h->watches)
+    h->watches = GNUNET_CONTAINER_multihashmap_create (5, GNUNET_NO);
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CONTAINER_multihashmap_put (h->watches,
+                                                    &wc->keyhash,
+                                                    wc,
+                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Sending a watch request for ss `%s', peer `%s', key `%s'.\n",
+       sub_system,
+       GNUNET_i2s (peer),
+       key);
+  GNUNET_MQ_send (h->mq, ev);
+  return wc;
+}
 
 /* end of peerstore_api.c */