/*
This file is part of GNUnet.
- (C) 2013 Christian Grothoff (and other contributing authors)
+ Copyright (C) 2013 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
/**
* @file include/gnunet_social_service.h
- * @brief Social service; implements social functionality using the PSYC service
- * @author tg
+ * @brief Social service; implements social interactions using the PSYC service.
+ * @author Gabor X Toth
+ * @author Christian Grothoff
*/
#ifndef GNUNET_SOCIAL_SERVICE_H
#define GNUNET_SOCIAL_SERVICE_H
#endif
#include "gnunet_util_lib.h"
+#include "gnunet_env_lib.h"
+#include "gnunet_identity_service.h"
#include "gnunet_psyc_service.h"
+
/**
* Version number of GNUnet Social API.
*/
#define GNUNET_SOCIAL_VERSION 0x00000000
+
+/**
+ * Handle for a pseudonym of another user in the network.
+ */
+struct GNUNET_SOCIAL_Nym;
+
+/**
+ * Handle for a place where social interactions happen.
+ */
+struct GNUNET_SOCIAL_Place;
+
+/**
+ * Host handle for a place that we entered.
+ */
+struct GNUNET_SOCIAL_Host;
+
+/**
+ * Guest handle for place that we entered.
+ */
+struct GNUNET_SOCIAL_Guest;
+
+/**
+ * Handle to an implementation of try-and-slice.
+ */
+struct GNUNET_SOCIAL_Slicer;
+
+
+/**
+ * Function called upon receiving a message indicating a call to a @e method.
+ *
+ * This function is called one or more times for each message until all data
+ * fragments arrive from the network.
+ *
+ * @param cls
+ * Closure.
+ * @param msg
+ * Message part, as it arrived from the network.
+ * @param message_id
+ * Message counter, monotonically increasing from 1.
+ * @param nym
+ * The sender of the message.
+ * Can be NULL if the message is not connected to a pseudonym.
+ * @param flags
+ * OR'ed GNUNET_PSYC_MessageFlags
+ * @param method_name
+ * Original method name from PSYC.
+ * May be more specific than the registered method name due to
+ * try-and-slice matching.
+ */
+typedef void
+(*GNUNET_SOCIAL_MethodCallback) (void *cls,
+ const struct GNUNET_PSYC_MessageMethod *msg,
+ uint64_t message_id,
+ uint32_t flags,
+ const struct GNUNET_SOCIAL_Nym *nym,
+ const char *method_name);
+
+
+/**
+ * Function called upon receiving a data fragment of a message.
+ *
+ * @param cls
+ * Closure.
+ * @param message_id
+ * Message ID this data fragment belongs to.
+ * @param msg
+ * Message part, as it arrived from the network.
+ * @param oper
+ * Operation to perform.
+ * @param name
+ * Name of the modifier.
+ * @param value
+ * Value of the modifier.
+ * @param value_size
+ * Size of @value.
+ */
+typedef void
+(*GNUNET_SOCIAL_ModifierCallback) (void *cls,
+ const struct GNUNET_PSYC_MessageModifier *msg,
+ uint64_t message_id,
+ enum GNUNET_ENV_Operator oper,
+ const char *name,
+ const void *value,
+ uint16_t value_size);
+
+
+/**
+ * Function called upon receiving a data fragment of a message.
+ *
+ * @param cls
+ * Closure.
+ * @param message_id
+ * Message ID this data fragment belongs to.
+ * @param msg
+ * Message part, as it arrived from the network.
+ * @param data_offset
+ * Byte offset of @a data in the overall data of the method.
+ * @param data_size
+ * Number of bytes in @a data.
+ * @param data
+ * Data stream given to the method.
+ * @param end
+ * End of message?
+ * #GNUNET_NO if there are further fragments,
+ * #GNUNET_YES if this is the last fragment,
+ * #GNUNET_SYSERR indicates the message was cancelled by the sender.
+ */
+typedef void
+(*GNUNET_SOCIAL_DataCallback) (void *cls,
+ const struct GNUNET_MessageHeader *msg,
+ uint64_t message_id,
+ uint64_t data_offset,
+ const void *data,
+ uint16_t data_size);
+
+
+/**
+ * End of message.
+ *
+ * @param cls
+ * Closure.
+ * @param msg
+ * Message part, as it arrived from the network.
+ * @param message_id
+ * Message ID this data fragment belongs to.
+ * @param cancelled.
+ * #GNUNET_YES if the message was cancelled,
+ * #GNUNET_NO if the message is complete.
+ */
+typedef void
+(*GNUNET_SOCIAL_EndOfMessageCallback) (void *cls,
+ const struct GNUNET_MessageHeader *msg,
+ uint64_t message_id,
+ uint8_t cancelled);
+
+
+/**
+ * Create a try-and-slice instance.
+ *
+ * @return A new try-and-slice construct.
+ */
+struct GNUNET_SOCIAL_Slicer *
+GNUNET_SOCIAL_slicer_create (void);
+
+
+/**
+ * Add a method to the try-and-slice instance.
+ *
+ * A slicer processes messages and calls methods that match a message. A match
+ * happens whenever the method name of a message starts with the method_name
+ * parameter given here.
+ *
+ * @param slicer The try-and-slice instance to extend.
+ * @param method_name Name of the given method, use empty string for default.
+ * @param method Method to invoke.
+ * @param method_cls Closure for method.
+ */
+void
+GNUNET_SOCIAL_slicer_add (struct GNUNET_SOCIAL_Slicer *slicer,
+ const char *method_name,
+ GNUNET_SOCIAL_MethodCallback method_cb,
+ GNUNET_SOCIAL_ModifierCallback modifier_cb,
+ GNUNET_SOCIAL_DataCallback data_cb,
+ GNUNET_SOCIAL_EndOfMessageCallback eom_cb,
+ void *cls);
+
+
/**
- * Handle for a social channel
+ * Remove a registered method handler from the try-and-slice instance.
+ *
+ * @param slicer The try-and-slice instance.
+ * @param method_name Name of the method to remove.
+ * @param method Method handler.
*/
-struct GNUNET_SOCIAL_Channel;
+int
+GNUNET_SOCIAL_slicer_remove (struct GNUNET_SOCIAL_Slicer *slicer,
+ const char *method_name,
+ GNUNET_SOCIAL_MethodCallback method_cb,
+ GNUNET_SOCIAL_ModifierCallback modifier_cb,
+ GNUNET_SOCIAL_DataCallback data_cb,
+ GNUNET_SOCIAL_EndOfMessageCallback eom_cb);
+
+
+/**
+ * Destroy a given try-and-slice instance.
+ *
+ * @param slicer slicer to destroy
+ */
+void
+GNUNET_SOCIAL_slicer_destroy (struct GNUNET_SOCIAL_Slicer *slicer);
+
+
+/**
+ * Function called asking for nym to be admitted to the place.
+ *
+ * Should call either GNUNET_SOCIAL_host_admit() or
+ * GNUNET_SOCIAL_host_reject_entry() (possibly asynchronously). If this host
+ * cannot decide, it is fine to call neither function, in which case hopefully
+ * some other host of the place exists that will make the decision. The @a nym
+ * reference remains valid until the #GNUNET_SOCIAL_FarewellCallback is invoked
+ * for it.
+ *
+ * @param cls Closure.
+ * @param nym Handle for the user who wants to enter.
+ * @param method_name Method name in the entry request.
+ * @param variable_count Number of elements in the @a variables array.
+ * @param variables Variables present in the message.
+ * @param data_size Number of bytes in @a data.
+ * @param data Payload given on enter (e.g. a password).
+ */
+typedef void
+(*GNUNET_SOCIAL_AnswerDoorCallback) (void *cls,
+ struct GNUNET_SOCIAL_Nym *nym,
+ const char *method_name,
+ struct GNUNET_ENV_Environment *env,
+ size_t data_size,
+ const void *data);
+
+
+/**
+ * Function called when a @a nym leaves the place.
+ *
+ * This is also called if the @a nym was never given permission to enter
+ * (i.e. the @a nym stopped asking to get in).
+ *
+ * @param cls Closure.
+ * @param nym Handle for the user who left.
+ * @param variable_count Number of elements in the @a variables array.
+ * @param variables Variables present in the message.
+ */
+typedef void
+(*GNUNET_SOCIAL_FarewellCallback) (void *cls,
+ struct GNUNET_SOCIAL_Nym *nym,
+ struct GNUNET_ENV_Environment *env,
+ size_t variable_count,
+ struct GNUNET_ENV_Modifier *variables);
+
+
+/**
+ * Function called after the host entered the place.
+ *
+ * @param cls
+ * Closure.
+ * @param result
+ * #GNUNET_OK on success, or
+ * #GNUNET_SYSERR on error.
+ * @param max_message_id
+ * Last message ID sent to the channel.
+ * Or 0 if no messages have been sent to the place yet.
+ */
+typedef void
+(*GNUNET_SOCIAL_HostEnterCallback) (void *cls, int result,
+ uint64_t max_message_id);
+
+
+/**
+ * Enter a place as host.
+ *
+ * A place is created upon first entering, and it is active until permanently
+ * left using GNUNET_SOCIAL_host_leave().
+ *
+ * @param cfg
+ * Configuration to contact the social service.
+ * @param ego
+ * Identity of the host.
+ * @param place_key
+ * Private-public key pair of the place.
+ * NULL for ephemeral places.
+ * @param policy
+ * Policy specifying entry and history restrictions for the place.
+ * @param slicer
+ * Slicer to handle incoming messages.
+ * @param answer_door_cb
+ * Function to handle new nyms that want to enter.
+ * @param farewell_cb
+ * Function to handle departing nyms.
+ * @param cls
+ * Closure for the callbacks.
+ *
+ * @return Handle for the host.
+ */
+struct GNUNET_SOCIAL_Host *
+GNUNET_SOCIAL_host_enter (const struct GNUNET_CONFIGURATION_Handle *cfg,
+ const struct GNUNET_IDENTITY_Ego *ego,
+ const struct GNUNET_CRYPTO_EddsaPrivateKey *place_key,
+ enum GNUNET_PSYC_Policy policy,
+ struct GNUNET_SOCIAL_Slicer *slicer,
+ GNUNET_SOCIAL_HostEnterCallback enter_cb,
+ GNUNET_SOCIAL_AnswerDoorCallback answer_door_cb,
+ GNUNET_SOCIAL_FarewellCallback farewell_cb,
+ void *cls);
+
+
+/**
+ * Decision whether to admit @a nym into the place or refuse entry.
+ *
+ * @param hst
+ * Host of the place.
+ * @param nym
+ * Handle for the entity that wanted to enter.
+ * @param is_admitted
+ * #GNUNET_YES if @a nym is admitted,
+ * #GNUNET_NO if @a nym is refused entry,
+ * #GNUNET_SYSERR if we cannot answer the request.
+ * @param method_name
+ * Method name for the rejection message.
+ * @param env
+ * Environment containing variables for the message, or NULL.
+ * @param data
+ * Data for the rejection message to send back.
+ * @param data_size
+ * Number of bytes in @a data for method.
+ * @return #GNUNET_OK on success,
+ * #GNUNET_SYSERR if the message is too large.
+ */
+int
+GNUNET_SOCIAL_host_entry_decision (struct GNUNET_SOCIAL_Host *hst,
+ struct GNUNET_SOCIAL_Nym *nym,
+ int is_admitted,
+ const struct GNUNET_PSYC_Message *entry_resp);
+
+
+/**
+ * Throw @a nym out of the place.
+ *
+ * The @a nym reference will remain valid until the
+ * #GNUNET_SOCIAL_FarewellCallback is invoked,
+ * which should be very soon after this call.
+ *
+ * @param host Host of the place.
+ * @param nym Handle for the entity to be ejected.
+ */
+void
+GNUNET_SOCIAL_host_eject (struct GNUNET_SOCIAL_Host *host,
+ struct GNUNET_SOCIAL_Nym *nym);
+
+
+/**
+ * Get the public key of a @a nym.
+ *
+ * Suitable, for example, to be used with GNUNET_NAMESTORE_zone_to_name().
+ *
+ * @param nym
+ * Pseudonym to map to a cryptographic identifier.
+ *
+ * @return Public key of nym;
+ */
+struct GNUNET_CRYPTO_EcdsaPublicKey *
+GNUNET_SOCIAL_nym_get_key (struct GNUNET_SOCIAL_Nym *nym);
+
+
+/**
+ * Obtain the private-public key pair of the host.
+ *
+ * @param host Host to get the key of.
+ * @param[out] host_key Set to the private-public key pair of the host. The
+ * public part is suitable for storing in GNS within a "PLACE"
+ * record, along with peer IDs to join at.
+ */
+void
+GNUNET_SOCIAL_host_get_key (struct GNUNET_SOCIAL_Host *host,
+ struct GNUNET_CRYPTO_EddsaPrivateKey *host_key);
+
+
+/**
+ * Advertise the place in the GNS zone of the @e ego of the @a host.
+ *
+ * @param host Host of the place.
+ * @param name The name for the PLACE record to put in the zone.
+ * @param peer_count Number of elements in the @a peers array.
+ * @param peers List of peers in the PLACE record that can be used to send join
+ * requests to.
+ * @param expiration_time Expiration time of the record, use 0 to remove the record.
+ * @param password Password used to encrypt the record.
+ */
+void
+GNUNET_SOCIAL_host_advertise (struct GNUNET_SOCIAL_Host *host,
+ const char *name,
+ size_t peer_count,
+ const struct GNUNET_PeerIdentity *peers,
+ struct GNUNET_TIME_Relative expiration_time,
+ const char *password);
+
+
+/**
+ * Flags for announcements by a host.
+ */
+enum GNUNET_SOCIAL_AnnounceFlags
+{
+ GNUNET_SOCIAL_ANNOUNCE_NONE = 0,
+
+ /**
+ * Whether this announcement removes all objects from the place.
+ *
+ * New objects can be still added to the now empty place using the @e env
+ * parameter of the same announcement.
+ */
+ GNUNET_SOCIAL_ANNOUNCE_CLEAR_OBJECTS = 1 << 0
+};
+
+
+/**
+ * Handle for an announcement request.
+ */
+struct GNUNET_SOCIAL_Announcement;
+
+
+/**
+ * Send a message to all nyms that are present in the place.
+ *
+ * This function is restricted to the host. Nyms can only send requests
+ * to the host who can decide to relay it to everyone in the place.
+ *
+ * @param host
+ * Host of the place.
+ * @param method_name
+ * Method to use for the announcement.
+ * @param env
+ * Environment containing variables for the message and operations
+ * on objects of the place.
+ * Has to remain available until the first call to @a notify_data.
+ * Can be NULL.
+ * @param notify_data
+ * Function to call to get the payload of the announcement.
+ * @param notify_data_cls
+ * Closure for @a notify.
+ * @param flags
+ * Flags for this announcement.
+ *
+ * @return NULL on error (another announcement already in progress?).
+ */
+struct GNUNET_SOCIAL_Announcement *
+GNUNET_SOCIAL_host_announce (struct GNUNET_SOCIAL_Host *host,
+ const char *method_name,
+ const struct GNUNET_ENV_Environment *env,
+ GNUNET_PSYC_TransmitNotifyData notify_data,
+ void *notify_data_cls,
+ enum GNUNET_SOCIAL_AnnounceFlags flags);
+
+
+/**
+ * Resume transmitting announcement.
+ *
+ * @param a
+ * The announcement to resume.
+ */
+void
+GNUNET_SOCIAL_host_announce_resume (struct GNUNET_SOCIAL_Announcement *a);
+
+
+/**
+ * Cancel announcement.
+ *
+ * @param a
+ * The announcement to cancel.
+ */
+void
+GNUNET_SOCIAL_host_announce_cancel (struct GNUNET_SOCIAL_Announcement *a);
+
+
+/**
+ * Obtain handle for a hosted place.
+ *
+ * The returned handle can be used to access the place API.
+ *
+ * @param host
+ * Handle for the host.
+ *
+ * @return Handle for the hosted place, valid as long as @a host is valid.
+ */
+struct GNUNET_SOCIAL_Place *
+GNUNET_SOCIAL_host_get_place (struct GNUNET_SOCIAL_Host *host);
+
+
+/**
+ * Stop hosting a place.
+ *
+ * Invalidates host handle.
+ *
+ * @param host
+ * Host leaving the place.
+ * @param keep_active
+ * Keep the place active after last host disconnected.
+ * @param leave_cb
+ * Function called after the host left the place
+ * and disconnected from the social service.
+ * @param leave_cls
+ * Closure for @a leave_cb.
+ */
+void
+GNUNET_SOCIAL_host_leave (struct GNUNET_SOCIAL_Host *host,
+ int keep_active,
+ GNUNET_ContinuationCallback leave_cb,
+ void *leave_cls);
+
+
+/**
+ * Function called after the guest entered the local copy of the place.
+ *
+ * History and object query functions can be used after this call,
+ * but new messages can't be sent or received.
+ *
+ * @param cls
+ * Closure.
+ * @param result
+ * #GNUNET_OK on success, or
+ * #GNUNET_SYSERR on error, e.g. could not connect to the service, or
+ * could not resolve GNS name.
+ * @param max_message_id
+ * Last message ID sent to the place.
+ * Or 0 if no messages have been sent to the place yet.
+ */
+typedef void
+(*GNUNET_SOCIAL_GuestEnterCallback) (void *cls, int result,
+ uint64_t max_message_id);
+
+
+/**
+ * Function called upon a guest receives a decision about entry to the place.
+ *
+ * @param is_admitted
+ * Is the guest admitted to the place?
+ * #GNUNET_YES if admitted,
+ * #GNUNET_NO if refused entry
+ * #GNUNET_SYSERR if the request could not be answered.
+ * @param method_name
+ * Method for the message sent along with the decision.
+ * NULL if no message was sent.
+ * @param env
+ * Environment with variables for the message.
+ * NULL if there are no variables.
+ * It has to be freed using GNUNET_ENV_environment_destroy()
+ * when it is not needed anymore.
+ * @param data_size
+ * Size of @data.
+ * @param data
+ * Payload of the message.
+ */
+typedef void
+(*GNUNET_SOCIAL_EntryDecisionCallback) (void *cls,
+ int is_admitted,
+ const struct GNUNET_PSYC_Message *entry_resp);
+
+
+/**
+ * Request entry to a place as a guest.
+ *
+ * @param cfg Configuration to contact the social service.
+ * @param ego Identity of the guest.
+ * @param crypto_address Public key of the place to enter.
+ * @param origin Peer identity of the origin of the underlying multicast group.
+ * @param relay_count Number of elements in the @a relays array.
+ * @param relays Relays for the underlying multicast group.
+ * @param method_name Method name for the message.
+ * @param env Environment containing variables for the message, or NULL.
+ * @param data Payload for the message to give to the enter callback.
+ * @param data_size Number of bytes in @a data.
+ * @param slicer Slicer to use for processing incoming requests from guests.
+ *
+ * @return NULL on errors, otherwise handle for the guest.
+ */
+struct GNUNET_SOCIAL_Guest *
+GNUNET_SOCIAL_guest_enter (const struct GNUNET_CONFIGURATION_Handle *cfg,
+ const struct GNUNET_IDENTITY_Ego *ego,
+ const struct GNUNET_CRYPTO_EddsaPublicKey *place_key,
+ const struct GNUNET_PeerIdentity *origin,
+ uint32_t relay_count,
+ const struct GNUNET_PeerIdentity *relays,
+ const struct GNUNET_PSYC_Message *entry_msg,
+ struct GNUNET_SOCIAL_Slicer *slicer,
+ GNUNET_SOCIAL_GuestEnterCallback local_enter_cb,
+ GNUNET_SOCIAL_EntryDecisionCallback entry_decision_cb,
+ void *cls);
+
+
+/**
+ * Request entry to a place as a guest using a GNS name.
+ *
+ * @param cfg Configuration to contact the social service.
+ * @param ego Identity of the guest.
+ * @param address GNS name of the place to enter. Either in the form of
+ * 'room.friend.gnu', or 'NYMPUBKEY.zkey'. This latter case refers to
+ * the 'PLACE' record of the empty label ("+") in the GNS zone with the
+ * nym's public key 'NYMPUBKEY', and can be used to request entry to a
+ * pseudonym's place directly.
+ * @param method_name Method name for the message.
+ * @param env Environment containing variables for the message, or NULL.
+ * @param data Payload for the message to give to the enter callback.
+ * @param data_size Number of bytes in @a data.
+ * @param slicer Slicer to use for processing incoming requests from guests.
+ *
+ * @return NULL on errors, otherwise handle for the guest.
+ */
+struct GNUNET_SOCIAL_Guest *
+GNUNET_SOCIAL_guest_enter_by_name (const struct GNUNET_CONFIGURATION_Handle *cfg,
+ struct GNUNET_IDENTITY_Ego *ego,
+ char *gns_name,
+ const struct GNUNET_PSYC_Message *join_msg,
+ struct GNUNET_SOCIAL_Slicer *slicer,
+ GNUNET_SOCIAL_GuestEnterCallback local_enter_cb,
+ GNUNET_SOCIAL_EntryDecisionCallback entry_decision_cb,
+ void *cls);
+
+
+/**
+ * Flags for talking to the host of a place.
+ */
+enum GNUNET_SOCIAL_TalkFlags
+{
+ GNUNET_SOCIAL_TALK_NONE = 0
+};
+
+
+/**
+ * A talk request.
+ */
+struct GNUNET_SOCIAL_TalkRequest;
+
+
+/**
+ * Talk to the host of the place.
+ *
+ * @param place
+ * Place where we want to talk to the host.
+ * @param method_name
+ * Method to invoke on the host.
+ * @param env
+ * Environment containing variables for the message, or NULL.
+ * @param notify_data
+ * Function to use to get the payload for the method.
+ * @param notify_data_cls
+ * Closure for @a notify_data.
+ * @param flags
+ * Flags for the message being sent.
+ *
+ * @return NULL if we are already trying to talk to the host,
+ * otherwise handle to cancel the request.
+ */
+struct GNUNET_SOCIAL_TalkRequest *
+GNUNET_SOCIAL_guest_talk (struct GNUNET_SOCIAL_Guest *guest,
+ const char *method_name,
+ const struct GNUNET_ENV_Environment *env,
+ GNUNET_PSYC_TransmitNotifyData notify_data,
+ void *notify_data_cls,
+ enum GNUNET_SOCIAL_TalkFlags flags);
+
+
+/**
+ * Resume talking to the host of the place.
+ *
+ * @param tr
+ * Talk request to resume.
+ */
+void
+GNUNET_SOCIAL_guest_talk_resume (struct GNUNET_SOCIAL_TalkRequest *tr);
+
+
+/**
+ * Cancel talking to the host of the place.
+ *
+ * @param tr
+ * Talk request to cancel.
+ */
+void
+GNUNET_SOCIAL_guest_talk_cancel (struct GNUNET_SOCIAL_TalkRequest *tr);
+
+
+/**
+ * Leave a place permanently.
+ *
+ * Notifies the owner of the place about leaving, and destroys the place handle.
+ *
+ * @param place
+ * Place to leave permanently.
+ * @param keep_active
+ * Keep place active after last application disconnected.
+ * @param leave_cb
+ * Function called after the guest left the place
+ * and disconnected from the social service.
+ * @param leave_cls
+ * Closure for @a leave_cb.
+ */
+void
+GNUNET_SOCIAL_guest_leave (struct GNUNET_SOCIAL_Guest *guest,
+ int keep_active,
+ GNUNET_ContinuationCallback leave_cb,
+ void *leave_cls);
+
+
+/**
+ * Obtain handle for a place entered as guest.
+ *
+ * The returned handle can be used to access the place API.
+ *
+ * @param guest Handle for the guest.
+ *
+ * @return Handle for the place, valid as long as @a guest is valid.
+ */
+struct GNUNET_SOCIAL_Place *
+GNUNET_SOCIAL_guest_get_place (struct GNUNET_SOCIAL_Guest *guest);
+
+
+/**
+ * A history lesson.
+ */
+struct GNUNET_SOCIAL_HistoryLesson;
+
+/**
+ * Learn about the history of a place.
+ *
+ * Sends messages through the slicer function of the place where
+ * start_message_id <= message_id <= end_message_id.
+ * The messages will have the #GNUNET_PSYC_MESSAGE_HISTORIC flag set.
+ *
+ * To get the latest message, use 0 for both the start and end message ID.
+ *
+ * @param place Place we want to learn more about.
+ * @param start_message_id First historic message we are interested in.
+ * @param end_message_id Last historic message we are interested in (inclusive).
+ * @param slicer Slicer to use to process history. Can be the same as the
+ * slicer of the place, as the HISTORIC flag allows distinguishing
+ * old messages from fresh ones.
+ * @param finish_cb Function called after the last message in the history lesson
+ * is passed through the @a slicer. NULL if not needed.
+ * @param finish_cb_cls Closure for @a finish_cb.
+ * @return Handle to abort history lesson, never NULL (multiple lessons
+ * at the same time are allowed).
+ */
+struct GNUNET_SOCIAL_HistoryLesson *
+GNUNET_SOCIAL_place_get_history (struct GNUNET_SOCIAL_Place *place,
+ uint64_t start_message_id,
+ uint64_t end_message_id,
+ const struct GNUNET_SOCIAL_Slicer *slicer,
+ void (*finish_cb)(void *),
+ void *finish_cb_cls);
+
+
+/**
+ * Stop processing messages from the history lesson.
+ *
+ * Must not be called after the finish callback of the history lesson is called.
+ *
+ * @param hist History lesson to cancel.
+ */
+void
+GNUNET_SOCIAL_place_get_history_cancel (struct GNUNET_SOCIAL_HistoryLesson *hist);
+
+
+struct GNUNET_SOCIAL_WatchHandle;
+
+/**
+ * Watch a place for changed objects.
+ *
+ * @param place
+ * Place to watch.
+ * @param object_filter
+ * Object prefix to match.
+ * @param state_var_cb
+ * Function to call when an object/state var changes.
+ * @param cls
+ * Closure for callback.
+ *
+ * @return Handle that can be used to cancel watching.
+ */
+struct GNUNET_SOCIAL_WatchHandle *
+GNUNET_SOCIAL_place_watch (struct GNUNET_SOCIAL_Place *place,
+ const char *object_filter,
+ GNUNET_PSYC_StateVarCallback state_var_cb,
+ void *cls);
+
+
+/**
+ * Cancel watching a place for changed objects.
+ *
+ * @param wh Watch handle to cancel.
+ */
+void
+GNUNET_SOCIAL_place_watch_cancel (struct GNUNET_SOCIAL_WatchHandle *wh);
+
+
+struct GNUNET_SOCIAL_LookHandle;
+
+
+/**
+ * Look at objects in the place with a matching name prefix.
+ *
+ * @param place
+ * The place to look its objects at.
+ * @param name_prefix
+ * Look at objects with names beginning with this value.
+ * @param state_var_cb
+ * Function to call for each object found.
+ * @param cls
+ * Closure for callback function.
+ *
+ * @return Handle that can be used to stop looking at objects.
+ */
+struct GNUNET_SOCIAL_LookHandle *
+GNUNET_SOCIAL_place_look (struct GNUNET_SOCIAL_Place *place,
+ const char *name_prefix,
+ GNUNET_PSYC_StateVarCallback state_var_cb,
+ void *cls);
+
+
+/**
+ * Stop looking at objects.
+ *
+ * @param lh Look handle to stop.
+ */
+void
+GNUNET_SOCIAL_place_look_cancel (struct GNUNET_SOCIAL_LookHandle *lh);
+
+
/**
- * Handle for a social client
+ * Look at a particular object in the place.
+ *
+ * The best matching object is returned (its name might be less specific than
+ * what was requested).
+ *
+ * @param place The place to look the object at.
+ * @param full_name Full name of the object.
+ * @param value_size Set to the size of the returned value.
+ * @return NULL if there is no such object at this place.
*/
-struct GNUNET_SOCIAL_Client;
+const void *
+GNUNET_SOCIAL_place_look_at (struct GNUNET_SOCIAL_Place *place,
+ const char *full_name,
+ size_t *value_size);
#if 0 /* keep Emacsens' auto-indent happy */