/*
     This file is part of GNUnet.
     Copyright (C) 2011, 2012 Christian Grothoff

     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
 */

/**
 * @author Philipp Toelke
 * @author Christian Grothoff
 *
 * @file
 * API for dealing with SUID helper processes
 *
 * @defgroup helper  Helper library
 * Dealing with SUID helper processes.
 *
 * Provides an API for dealing with (SUID) helper processes
 * that communicate via GNUNET_MessageHeaders on STDIN/STDOUT.
 *
 * @{
 */

#ifndef GNUNET_HELPER_LIB_H
#define GNUNET_HELPER_LIB_H

#include "gnunet_scheduler_lib.h"
#include "gnunet_mst_lib.h"


/**
 * The handle to a helper process.
 */
struct GNUNET_HELPER_Handle;


/**
 * Callback that will be called when the helper process dies. This is not called
 * when the helper process is stoped using GNUNET_HELPER_stop()
 *
 * @param cls the closure from GNUNET_HELPER_start()
 */
typedef void
(*GNUNET_HELPER_ExceptionCallback) (void *cls);


/**
 * Starts a helper and begins reading from it. The helper process is
 * restarted when it dies except when it is stopped using GNUNET_HELPER_stop()
 * or when the exp_cb callback is not NULL.
 *
 * @param with_control_pipe does the helper support the use of a control pipe for signalling?
 * @param binary_name name of the binary to run
 * @param binary_argv NULL-terminated list of arguments to give when starting the binary (this
 *                    argument must not be modified by the client for
 *                     the lifetime of the helper handle)
 * @param cb function to call if we get messages from the helper
 * @param exp_cb the exception callback to call. Set this to NULL if the helper
 *          process has to be restarted automatically when it dies/crashes
 * @param cb_cls closure for the above callbacks
 * @return the new Handle, NULL on error
 */
struct GNUNET_HELPER_Handle *
GNUNET_HELPER_start (int with_control_pipe,
                     const char *binary_name,
                     char *const binary_argv[],
                     GNUNET_MessageTokenizerCallback cb,
                     GNUNET_HELPER_ExceptionCallback exp_cb,
                     void *cb_cls);


/**
 * Sends termination signal to the helper process.  The helper process is not
 * reaped; call GNUNET_HELPER_wait() for reaping the dead helper process.
 *
 * @param h the helper handle
 * @param soft_kill if #GNUNET_YES, signals termination by closing the helper's
 *          stdin; #GNUNET_NO to signal termination by sending SIGTERM to helper
 * @return #GNUNET_OK on success; #GNUNET_SYSERR on error
 */
int
GNUNET_HELPER_kill (struct GNUNET_HELPER_Handle *h, int soft_kill);


/**
 * Reap the helper process.  This call is blocking (!).  The helper process
 * should either be sent a termination signal before or should be dead before
 * calling this function
 *
 * @param h the helper handle
 * @return #GNUNET_OK on success; #GNUNET_SYSERR on error
 */
int
GNUNET_HELPER_wait (struct GNUNET_HELPER_Handle *h);


/**
 * Free's the resources occupied by the helper handle
 *
 * @param h the helper handle to free
 */
void
GNUNET_HELPER_destroy (struct GNUNET_HELPER_Handle *h);


/**
 * Kills the helper, closes the pipe, frees the handle and calls wait() on the
 * helper process
 *
 * @param h handle to helper to stop
 * @param soft_kill if #GNUNET_YES, signals termination by closing the helper's
 *          stdin; #GNUNET_NO to signal termination by sending SIGTERM to helper
 */
void
GNUNET_HELPER_stop (struct GNUNET_HELPER_Handle *h, int soft_kill);


/**
 * Continuation function.
 *
 * @param cls closure
 * @param result #GNUNET_OK on success,
 *               #GNUNET_NO if helper process died
 *               #GNUNET_SYSERR during GNUNET_HELPER_destroy
 */
typedef void (*GNUNET_HELPER_Continuation)(void *cls,
                                           int result);


/**
 * Handle to cancel 'send'
 */
struct GNUNET_HELPER_SendHandle;


/**
 * Send an message to the helper.
 *
 * @param h helper to send message to
 * @param msg message to send
 * @param can_drop can the message be dropped if there is already one in the queue?
 * @param cont continuation to run once the message is out (#GNUNET_OK on succees, #GNUNET_NO
 *             if the helper process died, #GNUNET_SYSERR during #GNUNET_HELPER_destroy).
 * @param cont_cls closure for @a cont
 * @return NULL if the message was dropped,
 *         otherwise handle to cancel @a cont (actual transmission may
 *         not be abortable)
 */
struct GNUNET_HELPER_SendHandle *
GNUNET_HELPER_send (struct GNUNET_HELPER_Handle *h,
                    const struct GNUNET_MessageHeader *msg,
                    int can_drop,
                    GNUNET_HELPER_Continuation cont,
                    void *cont_cls);


/**
 * Cancel a #GNUNET_HELPER_send operation.  If possible, transmitting
 * the message is also aborted, but at least 'cont' won't be called.
 *
 * @param sh operation to cancel
 */
void
GNUNET_HELPER_send_cancel (struct GNUNET_HELPER_SendHandle *sh);


#endif
/* end of include guard: GNUNET_HELPER_LIB_H */

/** @} */  /* end of group */