1 files changed, 1199 insertions, 0 deletions

diff --git a/src/contrib/service/set/set_api.c b/src/contrib/service/set/set_api.c
new file mode 100644
index 000000000..4f73ff06c
--- /dev/null
+++ b/src/contrib/service/set/set_api.c
@@ -0,0 +1,1199 @@
+/*
+     This file is part of GNUnet.
+     Copyright (C) 2012-2016 GNUnet e.V.
+
+     GNUnet is free software: you can redistribute it and/or modify it
+     under the terms of the GNU Affero General Public License as published
+     by the Free Software Foundation, either version 3 of the License,
+     or (at your option) any later version.
+
+     GNUnet is distributed in the hope that it will be useful, but
+     WITHOUT ANY WARRANTY; without even the implied warranty of
+     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+     Affero General Public License for more details.
+
+     You should have received a copy of the GNU Affero General Public License
+     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+     SPDX-License-Identifier: AGPL3.0-or-later
+ */
+/**
+ * @file set/set_api.c
+ * @brief api for the set service
+ * @author Florian Dold
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include "gnunet_util_lib.h"
+#include "gnunet_protocols.h"
+#include "gnunet_set_service.h"
+#include "set.h"
+
+
+#define LOG(kind, ...) GNUNET_log_from (kind, "set-api", __VA_ARGS__)
+
+struct SetCopyRequest
+{
+  struct SetCopyRequest *next;
+
+  struct SetCopyRequest *prev;
+
+  void *cls;
+
+  GNUNET_SET_CopyReadyCallback cb;
+};
+
+/**
+ * Opaque handle to a set.
+ */
+struct GNUNET_SET_Handle
+{
+  /**
+   * Message queue for @e client.
+   */
+  struct GNUNET_MQ_Handle *mq;
+
+  /**
+   * Linked list of operations on the set.
+   */
+  struct GNUNET_SET_OperationHandle *ops_head;
+
+  /**
+   * Linked list of operations on the set.
+   */
+  struct GNUNET_SET_OperationHandle *ops_tail;
+
+  /**
+   * Callback for the current iteration over the set,
+   * NULL if no iterator is active.
+   */
+  GNUNET_SET_ElementIterator iterator;
+
+  /**
+   * Closure for @e iterator
+   */
+  void *iterator_cls;
+
+  /**
+   * Should the set be destroyed once all operations are gone?
+   * #GNUNET_SYSERR if #GNUNET_SET_destroy() must raise this flag,
+   * #GNUNET_YES if #GNUNET_SET_destroy() did raise this flag.
+   */
+  int destroy_requested;
+
+  /**
+   * Has the set become invalid (e.g. service died)?
+   */
+  int invalid;
+
+  /**
+   * Both client and service count the number of iterators
+   * created so far to match replies with iterators.
+   */
+  uint16_t iteration_id;
+
+  /**
+   * Configuration, needed when creating (lazy) copies.
+   */
+  const struct GNUNET_CONFIGURATION_Handle *cfg;
+
+  /**
+   * Doubly linked list of copy requests.
+   */
+  struct SetCopyRequest *copy_req_head;
+
+  /**
+   * Doubly linked list of copy requests.
+   */
+  struct SetCopyRequest *copy_req_tail;
+};
+
+
+/**
+ * Handle for a set operation request from another peer.
+ */
+struct GNUNET_SET_Request
+{
+  /**
+   * Id of the request, used to identify the request when
+   * accepting/rejecting it.
+   */
+  uint32_t accept_id;
+
+  /**
+   * Has the request been accepted already?
+   * #GNUNET_YES/#GNUNET_NO
+   */
+  int accepted;
+};
+
+
+/**
+ * Handle to an operation.  Only known to the service after committing
+ * the handle with a set.
+ */
+struct GNUNET_SET_OperationHandle
+{
+  /**
+   * Function to be called when we have a result,
+   * or an error.
+   */
+  GNUNET_SET_ResultIterator result_cb;
+
+  /**
+   * Closure for @e result_cb.
+   */
+  void *result_cls;
+
+  /**
+   * Local set used for the operation,
+   * NULL if no set has been provided by conclude yet.
+   */
+  struct GNUNET_SET_Handle *set;
+
+  /**
+   * Message sent to the server on calling conclude,
+   * NULL if conclude has been called.
+   */
+  struct GNUNET_MQ_Envelope *conclude_mqm;
+
+  /**
+   * Address of the request if in the conclude message,
+   * used to patch the request id into the message when the set is known.
+   */
+  uint32_t *request_id_addr;
+
+  /**
+   * Handles are kept in a linked list.
+   */
+  struct GNUNET_SET_OperationHandle *prev;
+
+  /**
+   * Handles are kept in a linked list.
+   */
+  struct GNUNET_SET_OperationHandle *next;
+
+  /**
+   * Request ID to identify the operation within the set.
+   */
+  uint32_t request_id;
+};
+
+
+/**
+ * Opaque handle to a listen operation.
+ */
+struct GNUNET_SET_ListenHandle
+{
+  /**
+   * Message queue for the client.
+   */
+  struct GNUNET_MQ_Handle*mq;
+
+  /**
+   * Configuration handle for the listener, stored
+   * here to be able to reconnect transparently on
+   * connection failure.
+   */
+  const struct GNUNET_CONFIGURATION_Handle *cfg;
+
+  /**
+   * Function to call on a new incoming request,
+   * or on error.
+   */
+  GNUNET_SET_ListenCallback listen_cb;
+
+  /**
+   * Closure for @e listen_cb.
+   */
+  void *listen_cls;
+
+  /**
+   * Application ID we listen for.
+   */
+  struct GNUNET_HashCode app_id;
+
+  /**
+   * Time to wait until we try to reconnect on failure.
+   */
+  struct GNUNET_TIME_Relative reconnect_backoff;
+
+  /**
+   * Task for reconnecting when the listener fails.
+   */
+  struct GNUNET_SCHEDULER_Task *reconnect_task;
+
+  /**
+   * Operation we listen for.
+   */
+  enum GNUNET_SET_OperationType operation;
+};
+
+
+/* mutual recursion with handle_copy_lazy */
+static struct GNUNET_SET_Handle *
+create_internal (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                 enum GNUNET_SET_OperationType op,
+                 const uint32_t *cookie);
+
+
+/**
+ * Handle element for iteration over the set.  Notifies the
+ * iterator and sends an acknowledgement to the service.
+ *
+ * @param cls the `struct GNUNET_SET_Handle *`
+ * @param msg the message
+ */
+static void
+handle_copy_lazy (void *cls,
+                  const struct GNUNET_SET_CopyLazyResponseMessage *msg)
+{
+  struct GNUNET_SET_Handle *set = cls;
+  struct SetCopyRequest *req;
+  struct GNUNET_SET_Handle *new_set;
+
+  req = set->copy_req_head;
+  if (NULL == req)
+  {
+    /* Service sent us unsolicited lazy copy response */
+    GNUNET_break (0);
+    return;
+  }
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Handling response to lazy copy\n");
+  GNUNET_CONTAINER_DLL_remove (set->copy_req_head,
+                               set->copy_req_tail,
+                               req);
+  // We pass none as operation here, since it doesn't matter when
+  // cloning.
+  new_set = create_internal (set->cfg,
+                             GNUNET_SET_OPERATION_NONE,
+                             &msg->cookie);
+  req->cb (req->cls, new_set);
+  GNUNET_free (req);
+}
+
+
+/**
+ * Check that the given @a msg is well-formed.
+ *
+ * @param cls closure
+ * @param msg message to check
+ * @return #GNUNET_OK if message is well-formed
+ */
+static int
+check_iter_element (void *cls,
+                    const struct GNUNET_SET_IterResponseMessage *msg)
+{
+  /* minimum size was already checked, everything else is OK! */
+  return GNUNET_OK;
+}
+
+
+/**
+ * Handle element for iteration over the set.  Notifies the
+ * iterator and sends an acknowledgement to the service.
+ *
+ * @param cls the `struct GNUNET_SET_Handle *`
+ * @param msg the message
+ */
+static void
+handle_iter_element (void *cls,
+                     const struct GNUNET_SET_IterResponseMessage *msg)
+{
+  struct GNUNET_SET_Handle *set = cls;
+  GNUNET_SET_ElementIterator iter = set->iterator;
+  struct GNUNET_SET_Element element;
+  struct GNUNET_SET_IterAckMessage *ack_msg;
+  struct GNUNET_MQ_Envelope *ev;
+  uint16_t msize;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Received element in set iteration\n");
+  msize = ntohs (msg->header.size);
+  if (set->iteration_id != ntohs (msg->iteration_id))
+  {
+    /* element from a previous iteration, skip! */
+    iter = NULL;
+  }
+  if (NULL != iter)
+  {
+    element.size = msize - sizeof(struct GNUNET_SET_IterResponseMessage);
+    element.element_type = ntohs (msg->element_type);
+    element.data = &msg[1];
+    iter (set->iterator_cls,
+          &element);
+  }
+  ev = GNUNET_MQ_msg (ack_msg,
+                      GNUNET_MESSAGE_TYPE_SET_ITER_ACK);
+  ack_msg->send_more = htonl ((NULL != iter));
+  GNUNET_MQ_send (set->mq, ev);
+}
+
+
+/**
+ * Handle message signalling conclusion of iteration over the set.
+ * Notifies the iterator that we are done.
+ *
+ * @param cls the set
+ * @param mh the message
+ */
+static void
+handle_iter_done (void *cls,
+                  const struct GNUNET_MessageHeader *mh)
+{
+  struct GNUNET_SET_Handle *set = cls;
+  GNUNET_SET_ElementIterator iter = set->iterator;
+
+  if (NULL == iter)
+  {
+    /* FIXME: if this is true, could cancel+start a fresh one
+       cause elements to go to the wrong iteration? */
+    LOG (GNUNET_ERROR_TYPE_INFO,
+         "Service completed set iteration that was already cancelled\n");
+    return;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Set iteration completed\n");
+  set->destroy_requested = GNUNET_SYSERR;
+  set->iterator = NULL;
+  set->iteration_id++;
+  iter (set->iterator_cls,
+        NULL);
+  if (GNUNET_SYSERR == set->destroy_requested)
+    set->destroy_requested = GNUNET_NO;
+  if (GNUNET_YES == set->destroy_requested)
+    GNUNET_SET_destroy (set);
+}
+
+
+/**
+ * Check that the given @a msg is well-formed.
+ *
+ * @param cls closure
+ * @param msg message to check
+ * @return #GNUNET_OK if message is well-formed
+ */
+static int
+check_result (void *cls,
+              const struct GNUNET_SET_ResultMessage *msg)
+{
+  /* minimum size was already checked, everything else is OK! */
+  return GNUNET_OK;
+}
+
+
+/**
+ * Handle result message for a set operation.
+ *
+ * @param cls the set
+ * @param mh the message
+ */
+static void
+handle_result (void *cls,
+               const struct GNUNET_SET_ResultMessage *msg)
+{
+  struct GNUNET_SET_Handle *set = cls;
+  struct GNUNET_SET_OperationHandle *oh;
+  struct GNUNET_SET_Element e;
+  enum GNUNET_SET_Status result_status;
+  int destroy_set;
+
+  GNUNET_assert (NULL != set->mq);
+  result_status = (enum GNUNET_SET_Status) ntohs (msg->result_status);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Got result message with status %d\n",
+       result_status);
+
+  oh = GNUNET_MQ_assoc_get (set->mq,
+                            ntohl (msg->request_id));
+  if (NULL == oh)
+  {
+    /* 'oh' can be NULL if we canceled the operation, but the service
+       did not get the cancel message yet. */
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Ignoring result from canceled operation\n");
+    return;
+  }
+
+  switch (result_status)
+  {
+  case GNUNET_SET_STATUS_OK:
+  case GNUNET_SET_STATUS_ADD_LOCAL:
+  case GNUNET_SET_STATUS_ADD_REMOTE:
+    goto do_element;
+
+  case GNUNET_SET_STATUS_FAILURE:
+  case GNUNET_SET_STATUS_DONE:
+    goto do_final;
+
+  case GNUNET_SET_STATUS_HALF_DONE:
+    /* not used anymore */
+    GNUNET_assert (0);
+  }
+
+do_final:
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Treating result as final status\n");
+  GNUNET_MQ_assoc_remove (set->mq,
+                          ntohl (msg->request_id));
+  GNUNET_CONTAINER_DLL_remove (set->ops_head,
+                               set->ops_tail,
+                               oh);
+  /* Need to do this calculation _before_ the result callback,
+     as IF the application still has a valid set handle, it
+     may trigger destruction of the set during the callback. */
+  destroy_set = (GNUNET_YES == set->destroy_requested) &&
+                (NULL == set->ops_head);
+  if (NULL != oh->result_cb)
+  {
+    oh->result_cb (oh->result_cls,
+                   NULL,
+                   GNUNET_ntohll (msg->current_size),
+                   result_status);
+  }
+  else
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "No callback for final status\n");
+  }
+  if (destroy_set)
+    GNUNET_SET_destroy (set);
+  GNUNET_free (oh);
+  return;
+
+do_element:
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Treating result as element\n");
+  e.data = &msg[1];
+  e.size = ntohs (msg->header.size) - sizeof(struct GNUNET_SET_ResultMessage);
+  e.element_type = ntohs (msg->element_type);
+  if (NULL != oh->result_cb)
+    oh->result_cb (oh->result_cls,
+                   &e,
+                   GNUNET_ntohll (msg->current_size),
+                   result_status);
+}
+
+
+/**
+ * Destroy the given set operation.
+ *
+ * @param oh set operation to destroy
+ */
+static void
+set_operation_destroy (struct GNUNET_SET_OperationHandle *oh)
+{
+  struct GNUNET_SET_Handle *set = oh->set;
+  struct GNUNET_SET_OperationHandle *h_assoc;
+
+  if (NULL != oh->conclude_mqm)
+    GNUNET_MQ_discard (oh->conclude_mqm);
+  /* is the operation already committed? */
+  if (NULL != set)
+  {
+    GNUNET_CONTAINER_DLL_remove (set->ops_head,
+                                 set->ops_tail,
+                                 oh);
+    h_assoc = GNUNET_MQ_assoc_remove (set->mq,
+                                      oh->request_id);
+    GNUNET_assert ((NULL == h_assoc) ||
+                   (h_assoc == oh));
+  }
+  GNUNET_free (oh);
+}
+
+
+/**
+ * Cancel the given set operation.  We need to send an explicit cancel
+ * message, as all operations one one set communicate using one
+ * handle.
+ *
+ * @param oh set operation to cancel
+ */
+void
+GNUNET_SET_operation_cancel (struct GNUNET_SET_OperationHandle *oh)
+{
+  struct GNUNET_SET_Handle *set = oh->set;
+  struct GNUNET_SET_CancelMessage *m;
+  struct GNUNET_MQ_Envelope *mqm;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Cancelling SET operation\n");
+  if (NULL != set)
+  {
+    mqm = GNUNET_MQ_msg (m, GNUNET_MESSAGE_TYPE_SET_CANCEL);
+    m->request_id = htonl (oh->request_id);
+    GNUNET_MQ_send (set->mq, mqm);
+  }
+  set_operation_destroy (oh);
+  if ((NULL != set) &&
+      (GNUNET_YES == set->destroy_requested) &&
+      (NULL == set->ops_head))
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Destroying set after operation cancel\n");
+    GNUNET_SET_destroy (set);
+  }
+}
+
+
+/**
+ * We encountered an error communicating with the set service while
+ * performing a set operation. Report to the application.
+ *
+ * @param cls the `struct GNUNET_SET_Handle`
+ * @param error error code
+ */
+static void
+handle_client_set_error (void *cls,
+                         enum GNUNET_MQ_Error error)
+{
+  struct GNUNET_SET_Handle *set = cls;
+  GNUNET_SET_ElementIterator iter = set->iterator;
+
+  LOG (GNUNET_ERROR_TYPE_ERROR,
+       "Handling client set error %d\n",
+       error);
+  while (NULL != set->ops_head)
+  {
+    if ((NULL != set->ops_head->result_cb) &&
+        (GNUNET_NO == set->destroy_requested))
+      set->ops_head->result_cb (set->ops_head->result_cls,
+                                NULL,
+                                0,
+                                GNUNET_SET_STATUS_FAILURE);
+    set_operation_destroy (set->ops_head);
+  }
+  set->iterator = NULL;
+  set->iteration_id++;
+  set->invalid = GNUNET_YES;
+  if (NULL != iter)
+    iter (set->iterator_cls,
+          NULL);
+}
+
+
+/**
+ * FIXME.
+ */
+static struct GNUNET_SET_Handle *
+create_internal (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                 enum GNUNET_SET_OperationType op,
+                 const uint32_t *cookie)
+{
+  struct GNUNET_SET_Handle *set = GNUNET_new (struct GNUNET_SET_Handle);
+  struct GNUNET_MQ_MessageHandler mq_handlers[] = {
+    GNUNET_MQ_hd_var_size (result,
+                           GNUNET_MESSAGE_TYPE_SET_RESULT,
+                           struct GNUNET_SET_ResultMessage,
+                           set),
+    GNUNET_MQ_hd_var_size (iter_element,
+                           GNUNET_MESSAGE_TYPE_SET_ITER_ELEMENT,
+                           struct GNUNET_SET_IterResponseMessage,
+                           set),
+    GNUNET_MQ_hd_fixed_size (iter_done,
+                             GNUNET_MESSAGE_TYPE_SET_ITER_DONE,
+                             struct GNUNET_MessageHeader,
+                             set),
+    GNUNET_MQ_hd_fixed_size (copy_lazy,
+                             GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_RESPONSE,
+                             struct GNUNET_SET_CopyLazyResponseMessage,
+                             set),
+    GNUNET_MQ_handler_end ()
+  };
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_CreateMessage *create_msg;
+  struct GNUNET_SET_CopyLazyConnectMessage *copy_msg;
+
+  set->cfg = cfg;
+  set->mq = GNUNET_CLIENT_connect (cfg,
+                                   "set",
+                                   mq_handlers,
+                                   &handle_client_set_error,
+                                   set);
+  if (NULL == set->mq)
+  {
+    GNUNET_free (set);
+    return NULL;
+  }
+  if (NULL == cookie)
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Creating new set (operation %u)\n",
+         op);
+    mqm = GNUNET_MQ_msg (create_msg,
+                         GNUNET_MESSAGE_TYPE_SET_CREATE);
+    create_msg->operation = htonl (op);
+  }
+  else
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Creating new set (lazy copy)\n");
+    mqm = GNUNET_MQ_msg (copy_msg,
+                         GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_CONNECT);
+    copy_msg->cookie = *cookie;
+  }
+  GNUNET_MQ_send (set->mq,
+                  mqm);
+  return set;
+}
+
+
+/**
+ * Create an empty set, supporting the specified operation.
+ *
+ * @param cfg configuration to use for connecting to the
+ *        set service
+ * @param op operation supported by the set
+ *        Note that the operation has to be specified
+ *        beforehand, as certain set operations need to maintain
+ *        data structures specific to the operation
+ * @return a handle to the set
+ */
+struct GNUNET_SET_Handle *
+GNUNET_SET_create (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                   enum GNUNET_SET_OperationType op)
+{
+  struct GNUNET_SET_Handle *set;
+
+  set = create_internal (cfg,
+                         op,
+                         NULL);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Creating set %p for operation %d\n",
+       set,
+       op);
+  return set;
+}
+
+
+int
+GNUNET_SET_add_element (struct GNUNET_SET_Handle *set,
+                        const struct GNUNET_SET_Element *element,
+                        GNUNET_SET_Continuation cont,
+                        void *cont_cls)
+{
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_ElementMessage *msg;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "adding element of type %u to set %p\n",
+       (unsigned int) element->element_type,
+       set);
+  GNUNET_assert (NULL != set);
+  if (GNUNET_YES == set->invalid)
+  {
+    if (NULL != cont)
+      cont (cont_cls);
+    return GNUNET_SYSERR;
+  }
+  mqm = GNUNET_MQ_msg_extra (msg,
+                             element->size,
+                             GNUNET_MESSAGE_TYPE_SET_ADD);
+  msg->element_type = htons (element->element_type);
+  GNUNET_memcpy (&msg[1],
+                 element->data,
+                 element->size);
+  GNUNET_MQ_notify_sent (mqm,
+                         cont, cont_cls);
+  GNUNET_MQ_send (set->mq, mqm);
+  return GNUNET_OK;
+}
+
+
+int
+GNUNET_SET_remove_element (struct GNUNET_SET_Handle *set,
+                           const struct GNUNET_SET_Element *element,
+                           GNUNET_SET_Continuation cont,
+                           void *cont_cls)
+{
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_ElementMessage *msg;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Removing element from set %p\n",
+       set);
+  if (GNUNET_YES == set->invalid)
+  {
+    if (NULL != cont)
+      cont (cont_cls);
+    return GNUNET_SYSERR;
+  }
+  mqm = GNUNET_MQ_msg_extra (msg,
+                             element->size,
+                             GNUNET_MESSAGE_TYPE_SET_REMOVE);
+  msg->element_type = htons (element->element_type);
+  GNUNET_memcpy (&msg[1],
+                 element->data,
+                 element->size);
+  GNUNET_MQ_notify_sent (mqm,
+                         cont, cont_cls);
+  GNUNET_MQ_send (set->mq, mqm);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Destroy the set handle if no operations are left, mark the set
+ * for destruction otherwise.
+ *
+ * @param set set handle to destroy
+ */
+void
+GNUNET_SET_destroy (struct GNUNET_SET_Handle *set)
+{
+  /* destroying set while iterator is active is currently
+     not supported; we should expand the API to allow
+     clients to explicitly cancel the iteration! */
+  GNUNET_assert (NULL != set);
+  if ((NULL != set->ops_head) ||
+      (NULL != set->iterator) ||
+      (GNUNET_SYSERR == set->destroy_requested))
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Set operations are pending, delaying set destruction\n");
+    set->destroy_requested = GNUNET_YES;
+    return;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Really destroying set\n");
+  if (NULL != set->mq)
+  {
+    GNUNET_MQ_destroy (set->mq);
+    set->mq = NULL;
+  }
+  GNUNET_free (set);
+}
+
+
+struct GNUNET_SET_OperationHandle *
+GNUNET_SET_prepare (const struct GNUNET_PeerIdentity *other_peer,
+                    const struct GNUNET_HashCode *app_id,
+                    const struct GNUNET_MessageHeader *context_msg,
+                    enum GNUNET_SET_ResultMode result_mode,
+                    struct GNUNET_SET_Option options[],
+                    GNUNET_SET_ResultIterator result_cb,
+                    void *result_cls)
+{
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_OperationHandle *oh;
+  struct GNUNET_SET_EvaluateMessage *msg;
+  struct GNUNET_SET_Option *opt;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Client prepares set operation (%d)\n",
+       result_mode);
+  oh = GNUNET_new (struct GNUNET_SET_OperationHandle);
+  oh->result_cb = result_cb;
+  oh->result_cls = result_cls;
+  mqm = GNUNET_MQ_msg_nested_mh (msg,
+                                 GNUNET_MESSAGE_TYPE_SET_EVALUATE,
+                                 context_msg);
+  msg->app_id = *app_id;
+  msg->result_mode = htonl (result_mode);
+  msg->target_peer = *other_peer;
+  for (opt = options; opt->type != 0; opt++)
+  {
+    switch (opt->type)
+    {
+    case GNUNET_SET_OPTION_BYZANTINE:
+      msg->byzantine = GNUNET_YES;
+      msg->byzantine_lower_bound = opt->v.num;
+      break;
+
+    case GNUNET_SET_OPTION_FORCE_FULL:
+      msg->force_full = GNUNET_YES;
+      break;
+
+    case GNUNET_SET_OPTION_FORCE_DELTA:
+      msg->force_delta = GNUNET_YES;
+      break;
+
+    default:
+      LOG (GNUNET_ERROR_TYPE_ERROR,
+           "Option with type %d not recognized\n", (int) opt->type);
+    }
+  }
+  oh->conclude_mqm = mqm;
+  oh->request_id_addr = &msg->request_id;
+
+  return oh;
+}
+
+
+/**
+ * Connect to the set service in order to listen for requests.
+ *
+ * @param cls the `struct GNUNET_SET_ListenHandle *` to connect
+ */
+static void
+listen_connect (void *cls);
+
+
+/**
+ * Check validity of request message for a listen operation
+ *
+ * @param cls the listen handle
+ * @param msg the message
+ * @return #GNUNET_OK if the message is well-formed
+ */
+static int
+check_request (void *cls,
+               const struct GNUNET_SET_RequestMessage *msg)
+{
+  const struct GNUNET_MessageHeader *context_msg;
+
+  if (ntohs (msg->header.size) == sizeof(*msg))
+    return GNUNET_OK; /* no context message is OK */
+  context_msg = GNUNET_MQ_extract_nested_mh (msg);
+  if (NULL == context_msg)
+  {
+    /* malformed context message is NOT ok */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Handle request message for a listen operation
+ *
+ * @param cls the listen handle
+ * @param msg the message
+ */
+static void
+handle_request (void *cls,
+                const struct GNUNET_SET_RequestMessage *msg)
+{
+  struct GNUNET_SET_ListenHandle *lh = cls;
+  struct GNUNET_SET_Request req;
+  const struct GNUNET_MessageHeader *context_msg;
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_RejectMessage *rmsg;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Processing incoming operation request with id %u\n",
+       ntohl (msg->accept_id));
+  /* we got another valid request => reset the backoff */
+  lh->reconnect_backoff = GNUNET_TIME_UNIT_MILLISECONDS;
+  req.accept_id = ntohl (msg->accept_id);
+  req.accepted = GNUNET_NO;
+  context_msg = GNUNET_MQ_extract_nested_mh (msg);
+  /* calling #GNUNET_SET_accept() in the listen cb will set req->accepted */
+  lh->listen_cb (lh->listen_cls,
+                 &msg->peer_id,
+                 context_msg,
+                 &req);
+  if (GNUNET_YES == req.accepted)
+    return; /* the accept-case is handled in #GNUNET_SET_accept() */
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Rejected request %u\n",
+       ntohl (msg->accept_id));
+  mqm = GNUNET_MQ_msg (rmsg,
+                       GNUNET_MESSAGE_TYPE_SET_REJECT);
+  rmsg->accept_reject_id = msg->accept_id;
+  GNUNET_MQ_send (lh->mq, mqm);
+}
+
+
+/**
+ * Our connection with the set service encountered an error,
+ * re-initialize with exponential back-off.
+ *
+ * @param cls the `struct GNUNET_SET_ListenHandle *`
+ * @param error reason for the disconnect
+ */
+static void
+handle_client_listener_error (void *cls,
+                              enum GNUNET_MQ_Error error)
+{
+  struct GNUNET_SET_ListenHandle *lh = cls;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Listener broke down (%d), re-connecting\n",
+       (int) error);
+  GNUNET_MQ_destroy (lh->mq);
+  lh->mq = NULL;
+  lh->reconnect_task = GNUNET_SCHEDULER_add_delayed (lh->reconnect_backoff,
+                                                     &listen_connect,
+                                                     lh);
+  lh->reconnect_backoff = GNUNET_TIME_STD_BACKOFF (lh->reconnect_backoff);
+}
+
+
+/**
+ * Connect to the set service in order to listen for requests.
+ *
+ * @param cls the `struct GNUNET_SET_ListenHandle *` to connect
+ */
+static void
+listen_connect (void *cls)
+{
+  struct GNUNET_SET_ListenHandle *lh = cls;
+  struct GNUNET_MQ_MessageHandler mq_handlers[] = {
+    GNUNET_MQ_hd_var_size (request,
+                           GNUNET_MESSAGE_TYPE_SET_REQUEST,
+                           struct GNUNET_SET_RequestMessage,
+                           lh),
+    GNUNET_MQ_handler_end ()
+  };
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_ListenMessage *msg;
+
+  lh->reconnect_task = NULL;
+  GNUNET_assert (NULL == lh->mq);
+  lh->mq = GNUNET_CLIENT_connect (lh->cfg,
+                                  "set",
+                                  mq_handlers,
+                                  &handle_client_listener_error,
+                                  lh);
+  if (NULL == lh->mq)
+    return;
+  mqm = GNUNET_MQ_msg (msg, GNUNET_MESSAGE_TYPE_SET_LISTEN);
+  msg->operation = htonl (lh->operation);
+  msg->app_id = lh->app_id;
+  GNUNET_MQ_send (lh->mq,
+                  mqm);
+}
+
+
+/**
+ * Wait for set operation requests for the given application id
+ *
+ * @param cfg configuration to use for connecting to
+ *            the set service, needs to be valid for the lifetime of the listen handle
+ * @param operation operation we want to listen for
+ * @param app_id id of the application that handles set operation requests
+ * @param listen_cb called for each incoming request matching the operation
+ *                  and application id
+ * @param listen_cls handle for @a listen_cb
+ * @return a handle that can be used to cancel the listen operation
+ */
+struct GNUNET_SET_ListenHandle *
+GNUNET_SET_listen (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                   enum GNUNET_SET_OperationType operation,
+                   const struct GNUNET_HashCode *app_id,
+                   GNUNET_SET_ListenCallback listen_cb,
+                   void *listen_cls)
+{
+  struct GNUNET_SET_ListenHandle *lh;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Starting listener for app %s\n",
+       GNUNET_h2s (app_id));
+  lh = GNUNET_new (struct GNUNET_SET_ListenHandle);
+  lh->listen_cb = listen_cb;
+  lh->listen_cls = listen_cls;
+  lh->cfg = cfg;
+  lh->operation = operation;
+  lh->app_id = *app_id;
+  lh->reconnect_backoff = GNUNET_TIME_UNIT_MILLISECONDS;
+  listen_connect (lh);
+  if (NULL == lh->mq)
+  {
+    GNUNET_free (lh);
+    return NULL;
+  }
+  return lh;
+}
+
+
+/**
+ * Cancel the given listen operation.
+ *
+ * @param lh handle for the listen operation
+ */
+void
+GNUNET_SET_listen_cancel (struct GNUNET_SET_ListenHandle *lh)
+{
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Canceling listener %s\n",
+       GNUNET_h2s (&lh->app_id));
+  if (NULL != lh->mq)
+  {
+    GNUNET_MQ_destroy (lh->mq);
+    lh->mq = NULL;
+  }
+  if (NULL != lh->reconnect_task)
+  {
+    GNUNET_SCHEDULER_cancel (lh->reconnect_task);
+    lh->reconnect_task = NULL;
+  }
+  GNUNET_free (lh);
+}
+
+
+struct GNUNET_SET_OperationHandle *
+GNUNET_SET_accept (struct GNUNET_SET_Request *request,
+                   enum GNUNET_SET_ResultMode result_mode,
+                   struct GNUNET_SET_Option options[],
+                   GNUNET_SET_ResultIterator result_cb,
+                   void *result_cls)
+{
+  struct GNUNET_MQ_Envelope *mqm;
+  struct GNUNET_SET_OperationHandle *oh;
+  struct GNUNET_SET_AcceptMessage *msg;
+
+  GNUNET_assert (GNUNET_NO == request->accepted);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Client accepts set operation (%d) with id %u\n",
+       result_mode,
+       request->accept_id);
+  request->accepted = GNUNET_YES;
+  mqm = GNUNET_MQ_msg (msg,
+                       GNUNET_MESSAGE_TYPE_SET_ACCEPT);
+  msg->accept_reject_id = htonl (request->accept_id);
+  msg->result_mode = htonl (result_mode);
+  oh = GNUNET_new (struct GNUNET_SET_OperationHandle);
+  oh->result_cb = result_cb;
+  oh->result_cls = result_cls;
+  oh->conclude_mqm = mqm;
+  oh->request_id_addr = &msg->request_id;
+  return oh;
+}
+
+
+/**
+ * Commit a set to be used with a set operation.
+ * This function is called once we have fully constructed
+ * the set that we want to use for the operation.  At this
+ * time, the P2P protocol can then begin to exchange the
+ * set information and call the result callback with the
+ * result information.
+ *
+ * @param oh handle to the set operation
+ * @param set the set to use for the operation
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR if the
+ *         set is invalid (e.g. the set service crashed)
+ */
+int
+GNUNET_SET_commit (struct GNUNET_SET_OperationHandle *oh,
+                   struct GNUNET_SET_Handle *set)
+{
+  if (NULL != oh->set)
+  {
+    /* Some other set was already committed for this
+     * operation, there is a logic bug in the client of this API */
+    GNUNET_break (0);
+    return GNUNET_OK;
+  }
+  GNUNET_assert (NULL != set);
+  if (GNUNET_YES == set->invalid)
+    return GNUNET_SYSERR;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Client commits to SET\n");
+  GNUNET_assert (NULL != oh->conclude_mqm);
+  oh->set = set;
+  GNUNET_CONTAINER_DLL_insert (set->ops_head,
+                               set->ops_tail,
+                               oh);
+  oh->request_id = GNUNET_MQ_assoc_add (set->mq,
+                                        oh);
+  *oh->request_id_addr = htonl (oh->request_id);
+  GNUNET_MQ_send (set->mq,
+                  oh->conclude_mqm);
+  oh->conclude_mqm = NULL;
+  oh->request_id_addr = NULL;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Iterate over all elements in the given set.  Note that this
+ * operation involves transferring every element of the set from the
+ * service to the client, and is thus costly.
+ *
+ * @param set the set to iterate over
+ * @param iter the iterator to call for each element
+ * @param iter_cls closure for @a iter
+ * @return #GNUNET_YES if the iteration started successfully,
+ *         #GNUNET_NO if another iteration is active
+ *         #GNUNET_SYSERR if the set is invalid (e.g. the server crashed, disconnected)
+ */
+int
+GNUNET_SET_iterate (struct GNUNET_SET_Handle *set,
+                    GNUNET_SET_ElementIterator iter,
+                    void *iter_cls)
+{
+  struct GNUNET_MQ_Envelope *ev;
+
+  GNUNET_assert (NULL != iter);
+  if (GNUNET_YES == set->invalid)
+    return GNUNET_SYSERR;
+  if (NULL != set->iterator)
+    return GNUNET_NO;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Iterating over set\n");
+  set->iterator = iter;
+  set->iterator_cls = iter_cls;
+  ev = GNUNET_MQ_msg_header (GNUNET_MESSAGE_TYPE_SET_ITER_REQUEST);
+  GNUNET_MQ_send (set->mq, ev);
+  return GNUNET_YES;
+}
+
+
+void
+GNUNET_SET_copy_lazy (struct GNUNET_SET_Handle *set,
+                      GNUNET_SET_CopyReadyCallback cb,
+                      void *cls)
+{
+  struct GNUNET_MQ_Envelope *ev;
+  struct SetCopyRequest *req;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Creating lazy copy of set\n");
+  ev = GNUNET_MQ_msg_header (GNUNET_MESSAGE_TYPE_SET_COPY_LAZY_PREPARE);
+  GNUNET_MQ_send (set->mq, ev);
+
+  req = GNUNET_new (struct SetCopyRequest);
+  req->cb = cb;
+  req->cls = cls;
+  GNUNET_CONTAINER_DLL_insert (set->copy_req_head,
+                               set->copy_req_tail,
+                               req);
+}
+
+
+/**
+ * Create a copy of an element.  The copy
+ * must be GNUNET_free-d by the caller.
+ *
+ * @param element the element to copy
+ * @return the copied element
+ */
+struct GNUNET_SET_Element *
+GNUNET_SET_element_dup (const struct GNUNET_SET_Element *element)
+{
+  struct GNUNET_SET_Element *copy;
+
+  copy = GNUNET_malloc (element->size + sizeof(struct GNUNET_SET_Element));
+  copy->size = element->size;
+  copy->element_type = element->element_type;
+  copy->data = &copy[1];
+  GNUNET_memcpy (&copy[1],
+                 element->data,
+                 copy->size);
+  return copy;
+}
+
+
+void
+GNUNET_SET_element_hash (const struct GNUNET_SET_Element *element,
+                         struct GNUNET_HashCode *ret_hash)
+{
+  struct GNUNET_HashContext *ctx = GNUNET_CRYPTO_hash_context_start ();
+
+  /* It's not guaranteed that the element data is always after the element header,
+     so we need to hash the chunks separately. */
+  GNUNET_CRYPTO_hash_context_read (ctx, &element->size, sizeof(uint16_t));
+  GNUNET_CRYPTO_hash_context_read (ctx, &element->element_type,
+                                   sizeof(uint16_t));
+  GNUNET_CRYPTO_hash_context_read (ctx, element->data, element->size);
+  GNUNET_CRYPTO_hash_context_finish (ctx, ret_hash);
+}
+
+
+/* end of set_api.c */