@subsection Starting a Service}
The key API definition for creating a service is the {\tt GNUNET\_SERVICE\_MAIN} macro:
-\lstset{language=C}
-\begin{lstlisting}
-GNUNET_SERVICE_MAIN
-("service-name",
- GNUNET_SERVICE_OPTION_NONE,
- &run,
- &client_connect_cb,
- &client_disconnect_cb,
- NULL,
- GNUNET_MQ_hd_fixed_size (...),
- GNUNET_MQ_hd_var_size (...),
- GNUNET_MQ_handler_end ());
+@example
+@verbatiminclude tutorial-examples/007.c
@end example
In addition to the service name and flags, the macro takes three
A minimal version of the three central service funtions would look
like this:
-
-\lstset{language=c}
-\begin{lstlisting}
-static void
-run (void *cls,
- const struct GNUNET_CONFIGURATION_Handle *c,
- struct GNUNET_SERVICE_Handle *service)
-{
-}
-
-static void *
-client_connect_cb (void *cls,
- struct GNUNET_SERVICE_Client *c,
- struct GNUNET_MQ_Handle *mq)
-{
- return c;
-}
-
-static void
-client_disconnect_cb (void *cls,
- struct GNUNET_SERVICE_Client *c,
- void *internal_cls)
-{
- GNUNET_assert (c == internal_cls);
-}
+@example
+@verbatiminclude tutorial-examples/008.c
@end example
Exercise: Write a stub service that processes no messages at all
One of the first things any service that extends the P2P protocol typically does
is connect to the @code{CORE} service using:
-
-\lstset{language=C}
-\begin{lstlisting}
-#include <gnunet/gnunet_core_service.h>
-
-struct GNUNET_CORE_Handle *
-GNUNET_CORE_connect (const struct GNUNET_CONFIGURATION_Handle *cfg,
- void *cls,
- GNUNET_CORE_StartupCallback init,
- GNUNET_CORE_ConnectEventHandler connects,
- GNUNET_CORE_DisconnectEventHandler disconnects,
- const struct GNUNET_MQ_MessageHandler *handlers);
+@example
+@verbatiminclude tutorial-examples/009.c
@end example
@subsection New P2P connections}
Before any traffic with a different peer can be exchanged, the peer must be
known to the service. This is notified by the @code{CORE} {\tt connects} callback,
which communicates the identity of the new peer to the service:
-
-\lstset{language=C}
-\begin{lstlisting}
-void *
-connects (void *cls,
- const struct GNUNET_PeerIdentity *peer,
- struct GNUNET_MQ_Handle *mq)
-{
- return mq;
-}
+@example
+@verbatiminclude tutorial-examples/010.c
@end example
Note that whatever you return from {\tt connects} is given as the
the peer disconnected. After this notification no more messages will be received
from the peer and the service is no longer allowed to send messages to the peer.
The disconnect callback looks like the following:
-
-\lstset{language=C}
-\begin{lstlisting}
-void
-disconnects (void *cls,
- const struct GNUNET_PeerIdentity * peer)
-{
- /* Remove peer's identity from known peers */
- /* Make sure no messages are sent to peer from now on */
-}
+@example
+@verbatiminclude tutorial-examples/011.c
@end example
Exercise: Fix your service to handle peer disconnects.}
\end{itemize}
The first step is to start a connection to the PEERSTORE service:
-\begin{lstlisting}
-#include "gnunet_peerstore_service.h"
-
-peerstore_handle = GNUNET_PEERSTORE_connect (cfg);
+@example
+@verbatiminclude tutorial-examples/012.c
@end example
+
The service handle \lstinline|peerstore_handle| will be needed for all subsequent
PEERSTORE operations.
@subsection Storing records}
To store a new record, use the following function:
-\begin{lstlisting}
-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);
+@example
+@verbatiminclude tutorial-examples/013.c
@end example
The \lstinline|options| parameter can either be \lstinline|GNUNET_PEERSTORE_STOREOPTION_MULTIPLE|
The \lstinline|GNUNET_PEERSTORE_store| function returns a handle to the store operation. This handle
can be used to cancel the store operation only before the continuation function is called:
-\begin{lstlisting}
+@example
void
GNUNET_PEERSTORE_store_cancel (struct GNUNET_PEERSTORE_StoreContext *sc);
@end example
@subsection Retrieving records
To retrieve stored records, use the following function:
-\begin{lstlisting}
-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);
+@example
+@verbatiminclude tutorial-examples/014.c
@end example
+
The values of \lstinline|peer| and \lstinline|key| can be \lstinline|NULL|. This allows the
iteration over values stored under any of the following key combinations:
\begin{itemize}
PEERSTORE offers the functionality of monitoring for new records stored under a specific key
combination (subsystem, peerid, key). To start the monitoring, use the following function:
-\begin{lstlisting}
-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);
+@example
+@verbatiminclude tutorial-examples/015.c
@end example
Whenever a new record is stored under the given key combination, the \lstinline|callback| function
will be called with this new record. This will continue until the connection to the PEERSTORE service
is broken or the watch operation is canceled:
-\begin{lstlisting}
-void
-GNUNET_PEERSTORE_watch_cancel (struct GNUNET_PEERSTORE_WatchContext *wc);
+@example
+@verbatiminclude tutorial-examples/016.c
@end example
@subsection Disconnecting from PEERSTORE
When the connection to the PEERSTORE service is no longer needed, disconnect using the following
function:
-\begin{lstlisting}
-void
-GNUNET_PEERSTORE_disconnect (struct GNUNET_PEERSTORE_Handle *h, int sync_first);
+@example
+@verbatiminclude tutorial-examples/017.c
@end example
If the \lstinline|sync_first| flag is set to \lstinline|GNUNET_YES|, the API will delay the
access it and retrieve data stored by any peers in the network.
This section will explain how to use the DHT. Of course, the first
thing to do is to connect to the DHT service:
-\lstset{language=C}
-\begin{lstlisting}
-dht_handle = GNUNET_DHT_connect (cfg, parallel_requests);
+@example
+@verbatiminclude tutorial-examples/018.c
@end example
+
The second parameter indicates how many requests in parallel to expect.
It is not a hard limit, but a good approximation will make the DHT more
efficient.
has been sucessfully stored or where it has been stored. In order to improve
the availablilty of the data and to compensate for possible errors, peers leaving
and other unfavorable events, just make several PUT requests!
-
-\lstset{language=C}
-\begin{lstlisting}
-static void
-message_sent_cont (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
-{
- // Request has left local node
-}
-
-struct GNUNET_DHT_PutHandle *
-GNUNET_DHT_put (struct GNUNET_DHT_Handle *handle,
- const struct GNUNET_HashCode *key,
- uint32_t desired_replication_level,
- enum GNUNET_DHT_RouteOption options,
- enum GNUNET_BLOCK_Type type, size_t size, const void *data,
- struct GNUNET_TIME_Absolute exp,
- struct GNUNET_TIME_Relative timeout,
- GNUNET_DHT_PutContinuation cont, void *cont_cls)
+@example
+@verbatiminclude tutorial-examples/019.c
@end example
Exercise: Store a value in the DHT periodically to make sure it is available
If we give a route option {\tt GNUNET\_DHT\_RO\_RECORD\_ROUTE} the callback
will get a list of all the peers the data has travelled, both on the PUT
path and on the GET path.
-\lstset{language=C}
-\begin{lstlisting}
-static void
-get_result_iterator (void *cls, struct GNUNET_TIME_Absolute expiration,
- const struct GNUNET_HashCode *key,
- const struct GNUNET_PeerIdentity *get_path,
- unsigned int get_path_length,
- const struct GNUNET_PeerIdentity *put_path,
- unsigned int put_path_length,
- enum GNUNET_BLOCK_Type type, size_t size, const void *data)
-{
- // Optionally:
- GNUNET_DHT_get_stop (get_handle);
-}
-
-get_handle =
- GNUNET_DHT_get_start (dht_handle,
- block_type,
- &key,
- replication,
- GNUNET_DHT_RO_NONE,
- NULL,
- 0,
- &get_result_iterator,
- cls)
+@example
+@verbatiminclude tutorial-examples/020.c
@end example
Exercise: Store a value in the DHT and after a while retrieve it. Show the IDs of all
do not use an extended query should check that the {\tt xquery\_size}
is zero. The block group is typically used to filter duplicate
replies.
-
-\lstset{language=C}
-\begin{lstlisting}
-static enum GNUNET_BLOCK_EvaluationResult
-block_plugin_SERVICE_evaluate (void *cls,
- enum GNUNET_BLOCK_Type type,
- struct GNUNET_BlockGroup *bg,
- const GNUNET_HashCode *query,
- const void *xquery,
- size_t xquery_size,
- const void *reply_block,
- size_t reply_block_size)
-{
- // Verify type, block and bg
-}
+@example
+@verbatiminclude tutorial-examples/021.c
@end example
Note that it is mandatory to detect duplicate replies in this function
means of hashing. If deriving the key is not possible, the function
should simply return {\tt GNUNET\_SYSERR} (the DHT will still work
just fine with such blocks).
-
@example
-static int
-block_plugin_SERVICE_get_key (void *cls, enum GNUNET_BLOCK_Type type,
- const void *block, size_t block_size,
- struct GNUNET_HashCode *key)
-{
- // Store the key in the key argument, return GNUNET_OK on success.
-}
+@verbatiminclude tutorial-examples/022.c
@end example
@subsubsection Initialization of the plugin
initialization function specifies what block types the plugin cares
about and returns a struct with the functions that are to be used for
validation and obtaining keys (the ones just defined above).
-
@example
-void *
-libgnunet_plugin_block_SERVICE_init (void *cls)
-{
- static enum GNUNET_BLOCK_Type types[] =
- {
- GNUNET_BLOCK_TYPE_SERVICE_BLOCKYPE,
- GNUNET_BLOCK_TYPE_ANY
- };
- struct GNUNET_BLOCK_PluginFunctions *api;
-
- api = GNUNET_new (struct GNUNET_BLOCK_PluginFunctions);
- api->evaluate = &block_plugin_SERICE_evaluate;
- api->get_key = &block_plugin_SERVICE_get_key;
- api->types = types;
- return api;
-}
+@verbatiminclude tutorial-examples/023.c
@end example
@subsubsection Shutdown of the plugin
Following GNUnet's general plugin API concept, the plugin must
export a second function for cleaning up. It usually does very
little.
-
@example
-void *
-libgnunet_plugin_block_SERVICE_done (void *cls)
-{
- struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
-
- GNUNET_free (api);
- return NULL;
-}
+@verbatiminclude tutorial-examples/024.c
@end example
-
@subsubsection Integration of the plugin with the build system
In order to compile the plugin, the Makefile.am file for the
service SERVICE should contain a rule similar to this:
-
+@c* Actually this is a Makefile not c. But the whole structure of examples
+@c* must be improved.
@example
- plugindir = $(libdir)/gnunet
-
- plugin_LTLIBRARIES = \
- libgnunet_plugin_block_ext.la
- libgnunet_plugin_block_ext_la_SOURCES = \
- plugin_block_ext.c
- libgnunet_plugin_block_ext_la_LIBADD = \
- $(prefix)/lib/libgnunethello.la \
- $(prefix)/lib/libgnunetblock.la \
- $(prefix)/lib/libgnunetutil.la
- libgnunet_plugin_block_ext_la_LDFLAGS = \
- $(GN_PLUGIN_LDFLAGS)
- libgnunet_plugin_block_ext_la_DEPENDENCIES = \
- $(prefix)/lib/libgnunetblock.la
+@verbatiminclude tutorial-examples/025.c
@end example
-
Exercise: Write a block plugin that accepts all queries
and all replies but prints information about queries and replies
when the respective validation hooks are called.
to allow for filtering of messages. When an event happens, the appropiate callback
is called with all the information about the event.
@example
-static void
-get_callback (void *cls,
- enum GNUNET_DHT_RouteOption options,
- enum GNUNET_BLOCK_Type type,
- uint32_t hop_count,
- uint32_t desired_replication_level,
- unsigned int path_length,
- const struct GNUNET_PeerIdentity *path,
- const struct GNUNET_HashCode * key)
-{
-}
-
-
-static void
-get_resp_callback (void *cls,
- enum GNUNET_BLOCK_Type type,
- const struct GNUNET_PeerIdentity *get_path,
- unsigned int get_path_length,
- const struct GNUNET_PeerIdentity *put_path,
- unsigned int put_path_length,
- struct GNUNET_TIME_Absolute exp,
- const struct GNUNET_HashCode * key,
- const void *data,
- size_t size)
-{
-}
-
-
-static void
-put_callback (void *cls,
- enum GNUNET_DHT_RouteOption options,
- enum GNUNET_BLOCK_Type type,
- uint32_t hop_count,
- uint32_t desired_replication_level,
- unsigned int path_length,
- const struct GNUNET_PeerIdentity *path,
- struct GNUNET_TIME_Absolute exp,
- const struct GNUNET_HashCode * key,
- const void *data,
- size_t size)
-{
-}
-
-
-monitor_handle = GNUNET_DHT_monitor_start (dht_handle,
- block_type,
- key,
- &get_callback,
- &get_resp_callback,
- &put_callback,
- cls);
+@verbatiminclude tutorial-examples/026.c
@end example
-
@section Debugging with gnunet-arm
Even if services are managed by @command{gnunet-arm}, you can start them with
projects / oweals / gnunet.git / commitdiff