PEERSTORE — Extensible local persistent data storage
GNUnet’s PEERSTORE subsystem offers persistent per-peer storage for other GNUnet subsystems. GNUnet subsystems can use PEERSTORE to persistently store and retrieve arbitrary data. Each data record stored with PEERSTORE contains the following fields:
subsystem: Name of the subsystem responsible for the record.
peerid: Identity of the peer this record is related to.
key: a key string identifying the record.
value: binary record value.
expiry: record expiry date.
Subsystems can store any type of value under a (subsystem, peerid, key) combination. A "replace" flag set during store operations forces the PEERSTORE to replace any old values stored under the same (subsystem, peerid, key) combination with the new value. Additionally, an expiry date is set after which the record is *possibly* deleted by PEERSTORE.
Subsystems can iterate over all values stored under any of the following combination of fields:
(subsystem, peerid, key)
Subsystems can also request to be notified about any new values stored under a (subsystem, peerid, key) combination by sending a "watch" request to PEERSTORE.
PEERSTORE implements the following components:
PEERSTORE service: Handles store, iterate and watch operations.
PEERSTORE API: API to be used by other subsystems to communicate and issue commands to the PEERSTORE service.
PEERSTORE plugins: Handles the persistent storage. At the moment, only an "sqlite" plugin is implemented.
libgnunetpeerstore is the library containing the PEERSTORE API.
Subsystems wishing to communicate with the PEERSTORE service use this
API to open a connection to PEERSTORE. This is done by calling
GNUNET_PEERSTORE_connect which returns a handle to the newly created
connection. This handle has to be used with any further calls to the
To store a new record, the function
GNUNET_PEERSTORE_store is to be
used which requires the record fields and a continuation function that
will be called by the API after the STORE request is sent to the
PEERSTORE service. Note that calling the continuation function does not
mean that the record is successfully stored, only that the STORE request
has been successfully sent to the PEERSTORE service.
GNUNET_PEERSTORE_store_cancel can be called to cancel the STORE
request only before the continuation function has been called.
To iterate over stored records, the function
GNUNET_PEERSTORE_iterate is to be used. peerid and key can be
set to NULL. An iterator callback function will be called with each
matching record found and a NULL record at the end to signal the end of
GNUNET_PEERSTORE_iterate_cancel can be used to cancel
the ITERATE request before the iterator callback is called with a NULL
To be notified with new values stored under a (subsystem, peerid, key)
combination, the function
GNUNET_PEERSTORE_watch is to be used. This
will register the watcher with the PEERSTORE service, any new records
matching the given combination will trigger the callback function passed
GNUNET_PEERSTORE_watch. This continues until
GNUNET_PEERSTORE_watch_cancel is called or the connection to the
service is destroyed.
After the connection is no longer needed, the function
GNUNET_PEERSTORE_disconnect can be called to disconnect from the
PEERSTORE service. Any pending ITERATE or WATCH requests will be
destroyed. If the
sync_first flag is set to
GNUNET_YES, the API
will delay the disconnection until all pending STORE requests are sent
to the PEERSTORE service, otherwise, the pending STORE requests will be
destroyed as well.