text: /*
       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 General Public License as published
       by the Free Software Foundation; either version 3, 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
       General Public License for more details.
  
       You should have received a copy of the GNU General Public License
       along with GNUnet; see the file COPYING.  If not, write to the
       Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
       Boston, MA 02110-1301, USA.
  */
  
  /**
   * @file util/helper.c
   * @brief API for dealing with (SUID) helper processes that communicate via
   *          GNUNET_MessageHeaders on stdin/stdout
   * @author Philipp Toelke
   * @author Christian Grothoff
   */
  #include "platform.h"
  #include "gnunet_util_lib.h"
  
  
  /**
   * Entry in the queue of messages we need to transmit to the helper.
   */
  struct GNUNET_HELPER_SendHandle
  {
  
    /**
     * This is an entry in a DLL.
     */
    struct GNUNET_HELPER_SendHandle *next;
  
    /**
     * This is an entry in a DLL.
     */
    struct GNUNET_HELPER_SendHandle *prev;
  
    /**
     * Message to transmit (allocated at the end of this struct)
     */
    const struct GNUNET_MessageHeader *msg;
  
    /**
     * The handle to a helper process.
     */
    struct GNUNET_HELPER_Handle *h;
  
    /**
     * Function to call upon completion.
     */
    GNUNET_HELPER_Continuation cont;
  
    /**
     * Closure to 'cont'.
     */
    void *cont_cls;
  
    /**
     * Current write position.
     */
    unsigned int wpos;
  
  };
  
  
  /**
   * The handle to a helper process.
   */
  struct GNUNET_HELPER_Handle
  {
  
    /**
     * PipeHandle to receive data from the helper
     */
    struct GNUNET_DISK_PipeHandle *helper_in;
  
    /**
     * PipeHandle to send data to the helper
     */
    struct GNUNET_DISK_PipeHandle *helper_out;
  
    /**
     * FileHandle to receive data from the helper
     */
    const struct GNUNET_DISK_FileHandle *fh_from_helper;
  
    /**
     * FileHandle to send data to the helper
     */
    const struct GNUNET_DISK_FileHandle *fh_to_helper;
  
    /**
     * The process id of the helper
     */
    struct GNUNET_OS_Process *helper_proc;
  
    /**
     * The Message-Tokenizer that tokenizes the messages comming from the helper
     */
    struct GNUNET_SERVER_MessageStreamTokenizer *mst;
  
    /**
     * The exception callback
     */
    GNUNET_HELPER_ExceptionCallback exp_cb;
  
    /**
     * The closure for callbacks
     */
    void *cb_cls;
  
    /**
     * First message queued for transmission to helper.
     */
    struct GNUNET_HELPER_SendHandle *sh_head;
  
    /**
     * Last message queued for transmission to helper.
     */
    struct GNUNET_HELPER_SendHandle *sh_tail;
  
    /**
     * Binary to run.
     */
    char *binary_name;
  
    /**
     * NULL-terminated list of command-line arguments.
     */
    char **binary_argv;
  
    /**
     * Task to read from the helper.
     */
    struct GNUNET_SCHEDULER_Task *read_task;
  
    /**
     * Task to read from the helper.
     */
    struct GNUNET_SCHEDULER_Task *write_task;
  
    /**
     * Restart task.
     */
    struct GNUNET_SCHEDULER_Task *restart_task;
  
    /**
     * Does the helper support the use of a control pipe for signalling?
     */
    int with_control_pipe;
  
    /**
     * Count start attempts to increase linear back off
     */
    unsigned int retry_back_off;
  };
  
  
  /**
   * 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)
  {
    struct GNUNET_HELPER_SendHandle *sh;
    int ret;
  
    while (NULL != (sh = h->sh_head))
    {
      GNUNET_CONTAINER_DLL_remove (h->sh_head,
  				 h->sh_tail,
  				 sh);
      if (NULL != sh->cont)
        sh->cont (sh->cont_cls, GNUNET_NO);
      GNUNET_free (sh);
    }
    if (NULL != h->restart_task)
    {
      GNUNET_SCHEDULER_cancel (h->restart_task);
      h->restart_task = NULL;
    }
    if (NULL != h->read_task)
    {
      GNUNET_SCHEDULER_cancel (h->read_task);
      h->read_task = NULL;
    }
    if (NULL == h->helper_proc)
      return GNUNET_SYSERR;
    if (GNUNET_YES == soft_kill)
    {
      /* soft-kill only possible with pipes */
      GNUNET_assert (NULL != h->helper_in);
      ret = GNUNET_DISK_pipe_close (h->helper_in);
      h->helper_in = NULL;
      h->fh_to_helper = NULL;
      return ret;
    }
    if (0 != GNUNET_OS_process_kill (h->helper_proc, GNUNET_TERM_SIG))
      return GNUNET_SYSERR;
    return GNUNET_OK;
  }
  
  
  /**
   * 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)
  {
    struct GNUNET_HELPER_SendHandle *sh;
    int ret;
  
    ret = GNUNET_SYSERR;
    if (NULL != h->helper_proc)
    {
      ret = GNUNET_OS_process_wait (h->helper_proc);
      GNUNET_OS_process_destroy (h->helper_proc);
      h->helper_proc = NULL;
    }
    if (NULL != h->read_task)
    {
      GNUNET_SCHEDULER_cancel (h->read_task);
      h->read_task = NULL;
    }
    if (NULL != h->write_task)
    {
      GNUNET_SCHEDULER_cancel (h->write_task);
      h->write_task = NULL;
    }
    if (NULL != h->helper_in)
    {
      GNUNET_DISK_pipe_close (h->helper_in);
      h->helper_in = NULL;
      h->fh_to_helper = NULL;
    }
    if (NULL != h->helper_out)
    {
      GNUNET_DISK_pipe_close (h->helper_out);
      h->helper_out = NULL;
      h->fh_from_helper = NULL;
    }
    while (NULL != (sh = h->sh_head))
    {
      GNUNET_CONTAINER_DLL_remove (h->sh_head,
  				 h->sh_tail,
  				 sh);
      if (NULL != sh->cont)
        sh->cont (sh->cont_cls, GNUNET_NO);
      GNUNET_free (sh);
    }
    /* purge MST buffer */
    if (NULL != h->mst)
      (void) GNUNET_SERVER_mst_receive (h->mst, NULL, NULL, 0, GNUNET_YES, GNUNET_NO);
    return ret;
  }
  
  
  /**
   * Stop the helper process, we're closing down or had an error.
   *
   * @param h handle to the helper process
   * @param soft_kill if #GNUNET_YES, signals termination by closing the helper's
   *          stdin; #GNUNET_NO to signal termination by sending SIGTERM to helper
   */
  static void
  stop_helper (struct GNUNET_HELPER_Handle *h,
  	     int soft_kill)
  {
    if (NULL != h->restart_task)
    {
      GNUNET_SCHEDULER_cancel (h->restart_task);
      h->restart_task = NULL;
    }
    else
    {
      GNUNET_break (GNUNET_OK == GNUNET_HELPER_kill (h, soft_kill));
      GNUNET_break (GNUNET_OK == GNUNET_HELPER_wait (h));
    }
  }
  
  
  /**
   * Restart the helper process.
   *
   * @param cls handle to the helper process
   */
  static void
  restart_task (void *cls);
  
  
  /**
   * Read from the helper-process
   *
   * @param cls handle to the helper process
   */
  static void
  helper_read (void *cls)
  {
    struct GNUNET_HELPER_Handle *h = cls;
    char buf[GNUNET_SERVER_MAX_MESSAGE_SIZE] GNUNET_ALIGN;
    ssize_t t;
  
    h->read_task = NULL;
    t = GNUNET_DISK_file_read (h->fh_from_helper, &buf, sizeof (buf));
    if (t < 0)
    {
      /* On read-error, restart the helper */
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  _("Error reading from `%s': %s\n"),
  		h->binary_name,
  		STRERROR (errno));
      if (NULL != h->exp_cb)
      {
        h->exp_cb (h->cb_cls);
        GNUNET_HELPER_stop (h, GNUNET_NO);
        return;
      }
      stop_helper (h, GNUNET_NO);
      /* Restart the helper */
      h->restart_task = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
  										   h->retry_back_off),
  						    &restart_task, h);
      return;
    }
    if (0 == t)
    {
      /* this happens if the helper is shut down via a
         signal, so it is not a "hard" error */
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  		"Got 0 bytes from helper `%s' (EOF)\n",
  		h->binary_name);
      if (NULL != h->exp_cb)
      {
        h->exp_cb (h->cb_cls);
        GNUNET_HELPER_stop (h, GNUNET_NO);
        return;
      }
      stop_helper (h, GNUNET_NO);
      /* Restart the helper */
      h->restart_task
        = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
  								   h->retry_back_off),
  				     &restart_task, h);
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  	      "Got %u bytes from helper `%s'\n",
  	      (unsigned int) t,
  	      h->binary_name);
    h->read_task = GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
  						 h->fh_from_helper,
  						 &helper_read, h);
    if (GNUNET_SYSERR ==
        GNUNET_SERVER_mst_receive (h->mst,
  				 NULL,
  				 buf, t,
  				 GNUNET_NO, GNUNET_NO))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
  		_("Failed to parse inbound message from helper `%s'\n"),
  		h->binary_name);
      if (NULL != h->exp_cb)
      {
        h->exp_cb (h->cb_cls);
        GNUNET_HELPER_stop (h, GNUNET_NO);
        return;
      }
      stop_helper (h, GNUNET_NO);
      /* Restart the helper */
      h->restart_task = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_SECONDS,
  										  h->retry_back_off),
  						    &restart_task, h);
      return;
    }
  }
  
  
  /**
   * Start the helper process.
   *
   * @param h handle to the helper process
   */
  static void
  start_helper (struct GNUNET_HELPER_Handle *h)
  {
    h->helper_in = GNUNET_DISK_pipe (GNUNET_YES, GNUNET_YES, GNUNET_YES, GNUNET_NO);
    h->helper_out = GNUNET_DISK_pipe (GNUNET_YES, GNUNET_YES, GNUNET_NO, GNUNET_YES);
    if ( (h->helper_in == NULL) || (h->helper_out == NULL))
    {
      /* out of file descriptors? try again later... */
      stop_helper (h, GNUNET_NO);
      h->restart_task =
        GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_SECONDS,
  								  h->retry_back_off),
  				    &restart_task, h);
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  	      "Starting HELPER process `%s'\n",
  	      h->binary_name);
    h->fh_from_helper =
        GNUNET_DISK_pipe_handle (h->helper_out, GNUNET_DISK_PIPE_END_READ);
    h->fh_to_helper =
        GNUNET_DISK_pipe_handle (h->helper_in, GNUNET_DISK_PIPE_END_WRITE);
    h->helper_proc =
      GNUNET_OS_start_process_vap (h->with_control_pipe, GNUNET_OS_INHERIT_STD_ERR,
  				 h->helper_in, h->helper_out, NULL,
  				 h->binary_name,
  				 h->binary_argv);
    if (NULL == h->helper_proc)
    {
      /* failed to start process? try again later... */
      stop_helper (h, GNUNET_NO);
      h->restart_task = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_SECONDS,
  										  h->retry_back_off),
  						    &restart_task, h);
      return;
    }
    GNUNET_DISK_pipe_close_end (h->helper_out, GNUNET_DISK_PIPE_END_WRITE);
    GNUNET_DISK_pipe_close_end (h->helper_in, GNUNET_DISK_PIPE_END_READ);
    if (NULL != h->mst)
      h->read_task = GNUNET_SCHEDULER_add_read_file (GNUNET_TIME_UNIT_FOREVER_REL,
  						   h->fh_from_helper,
  						   &helper_read,
  						   h);
  }
  
  
  /**
   * Restart the helper process.
   *
   * @param cls handle to the helper process
   */
  static void
  restart_task (void *cls)
  {
    struct GNUNET_HELPER_Handle*h = cls;
  
    h->restart_task = NULL;
    h->retry_back_off++;
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Restarting helper with back-off %u\n",
                h->retry_back_off);
    start_helper (h);
  }
  
  
  /**
   * 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 callback
   * @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_SERVER_MessageTokenizerCallback cb,
  		     GNUNET_HELPER_ExceptionCallback exp_cb,
  		     void *cb_cls)
  {
    struct GNUNET_HELPER_Handle *h;
    unsigned int c;
  
    h = GNUNET_new (struct GNUNET_HELPER_Handle);
    h->with_control_pipe = with_control_pipe;
    /* Lookup in libexec path only if we are starting gnunet helpers */
    if (NULL != strstr (binary_name, "gnunet"))
      h->binary_name = GNUNET_OS_get_libexec_binary_path (binary_name);
    else
      h->binary_name = GNUNET_strdup (binary_name);
    for (c = 0; NULL != binary_argv[c]; c++);
    h->binary_argv = GNUNET_malloc (sizeof (char *) * (c + 1));
    for (c = 0; NULL != binary_argv[c]; c++)
      h->binary_argv[c] = GNUNET_strdup (binary_argv[c]);
    h->binary_argv[c] = NULL;
    h->cb_cls = cb_cls;
    if (NULL != cb)
      h->mst = GNUNET_SERVER_mst_create (cb, h->cb_cls);
    h->exp_cb = exp_cb;
    h->retry_back_off = 0;
    start_helper (h);
    return 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)
  {
    unsigned int c;
    struct GNUNET_HELPER_SendHandle *sh;
  
    if (NULL != h->write_task)
    {
      GNUNET_SCHEDULER_cancel (h->write_task);
      h->write_task = NULL;
    }
    GNUNET_assert (NULL == h->read_task);
    GNUNET_assert (NULL == h->restart_task);
    while (NULL != (sh = h->sh_head))
    {
      GNUNET_CONTAINER_DLL_remove (h->sh_head,
  				 h->sh_tail,
  				 sh);
      if (NULL != sh->cont)
        sh->cont (sh->cont_cls, GNUNET_SYSERR);
      GNUNET_free (sh);
    }
    if (NULL != h->mst)
      GNUNET_SERVER_mst_destroy (h->mst);
    GNUNET_free (h->binary_name);
    for (c = 0; h->binary_argv[c] != NULL; c++)
      GNUNET_free (h->binary_argv[c]);
    GNUNET_free (h->binary_argv);
    GNUNET_free (h);
  }
  
  
  /**
   * Kills the helper, closes the pipe and frees the handle
   *
   * @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)
  {
    h->exp_cb = NULL;
    stop_helper (h, soft_kill);
    GNUNET_HELPER_destroy (h);
  }
  
  
  /**
   * Write to the helper-process
   *
   * @param cls handle to the helper process
   */
  static void
  helper_write (void *cls)
  {
    struct GNUNET_HELPER_Handle *h = cls;
    struct GNUNET_HELPER_SendHandle *sh;
    const char *buf;
    ssize_t t;
  
    h->write_task = NULL;
    if (NULL == (sh = h->sh_head))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  		"Helper write had no work!\n");
      return; /* how did this happen? */
    }
    buf = (const char*) sh->msg;
    t = GNUNET_DISK_file_write (h->fh_to_helper,
  			      &buf[sh->wpos],
  			      ntohs (sh->msg->size) - sh->wpos);
    if (-1 == t)
    {
      /* On write-error, restart the helper */
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
  		_("Error writing to `%s': %s\n"),
  		h->binary_name,
  		STRERROR (errno));
      if (NULL != h->exp_cb)
      {
        h->exp_cb (h->cb_cls);
        GNUNET_HELPER_stop (h, GNUNET_NO);
        return;
      }
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  		"Stopping and restarting helper task!\n");
      stop_helper (h, GNUNET_NO);
      /* Restart the helper */
      h->restart_task = GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_SECONDS,
  										  h->retry_back_off),
  						    &restart_task, h);
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
  	      "Transmitted %u bytes to %s\n",
  	      (unsigned int) t,
  	      h->binary_name);
    sh->wpos += t;
    if (sh->wpos == ntohs (sh->msg->size))
    {
      GNUNET_CONTAINER_DLL_remove (h->sh_head,
  				 h->sh_tail,
  				 sh);
      if (NULL != sh->cont)
        sh->cont (sh->cont_cls, GNUNET_YES);
      GNUNET_free (sh);
    }
    if (NULL != h->sh_head)
      h->write_task = GNUNET_SCHEDULER_add_write_file (GNUNET_TIME_UNIT_FOREVER_REL,
  						     h->fh_to_helper,
  						     &helper_write,
  						     h);
  }
  
  
  /**
   * 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 *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)
  {
    struct GNUNET_HELPER_SendHandle *sh;
    uint16_t mlen;
  
    if (NULL == h->fh_to_helper)
      return NULL;
    if ( (GNUNET_YES == can_drop) &&
         (NULL != h->sh_head) )
      return NULL;
    mlen = ntohs (msg->size);
    sh = GNUNET_malloc (sizeof (struct GNUNET_HELPER_SendHandle) + mlen);
    sh->msg = (const struct GNUNET_MessageHeader*) &sh[1];
    GNUNET_memcpy (&sh[1], msg, mlen);
    sh->h = h;
    sh->cont = cont;
    sh->cont_cls = cont_cls;
    GNUNET_CONTAINER_DLL_insert_tail (h->sh_head,
  				    h->sh_tail,
  				    sh);
    if (NULL == h->write_task)
      h->write_task = GNUNET_SCHEDULER_add_write_file (GNUNET_TIME_UNIT_FOREVER_REL,
  						     h->fh_to_helper,
  						     &helper_write,
  						     h);
  
    return sh;
  }
  
  /**
   * 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)
  {
    struct GNUNET_HELPER_Handle *h = sh->h;
  
    sh->cont = NULL;
    sh->cont_cls = NULL;
    if (0 == sh->wpos)
    {
      GNUNET_CONTAINER_DLL_remove (h->sh_head, h->sh_tail, sh);
      GNUNET_free (sh);
      if (NULL == h->sh_head)
      {
        GNUNET_SCHEDULER_cancel (h->write_task);
        h->write_task = NULL;
      }
    }
  }
  
  
  /* end of helper.c */
  