libio/misc/hook.c

/*
 *  ircd-hybrid: an advanced Internet Relay Chat Daemon(ircd).
 *  hook.c: Provides a generic event hooking interface.
 *
 *  Copyright (C) 2003 Piotr Nizynski, Advanced IRC Services Project Team
 *  Copyright (C) 2005 Hybrid Development Team
 *
 *  This program 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 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
 *  USA
 *
 *  $Id$
 */

#include "stdinc.h"

dlink_list callback_list = {NULL, NULL, 0};

/*
 * register_callback()
 *
 * Creates a new callback.
 *
 * inputs:
 *   name  -  name used to identify the callback
 *            (can be NULL for anonymous callbacks)
 *   func  -  initial function attached to the chain
 *            (can be NULL to create an empty chain)
 * output: pointer to Callback structure or NULL if already exists
 *
 * NOTE: Once registered, a callback should never be freed!
 * That's because there may be modules which depend on it
 * (even if no functions are attached). That's also why
 * we dynamically allocate the struct here -- we don't want
 * to allow anyone to place it in module data, which can be
 * unloaded at any time.
 */
struct Callback *
register_callback(const char *name, CBFUNC *func)
{
  struct Callback *cb;

  if (name != NULL)
    if ((cb = find_callback(name)) != NULL)
    {
      dlinkAddTail(func, MyMalloc(sizeof(dlink_node)), &cb->chain);
      return (cb);
    }

  cb = MyMalloc(sizeof(struct Callback));
  if (func != NULL)
    dlinkAdd(func, MyMalloc(sizeof(dlink_node)), &cb->chain);
  if (name != NULL)
  {
    DupString(cb->name, name);
    dlinkAdd(cb, &cb->node, &callback_list);
  }
  return (cb);
}

/*
 * execute_callback()
 *
 * Passes control down the callback hook chain.
 *
 * inputs:
 *   callback  -  pointer to Callback structure
 *   param     -  argument to pass
 * output: function return value
 */
void *
execute_callback(struct Callback *cb, ...)
{
  void *res;
  va_list args;

  cb->called++;
  cb->last = CurrentTime;

  if (!is_callback_present(cb))
    return (NULL);

  va_start(args, cb);
  res = ((CBFUNC *) cb->chain.head->data)(args);
  va_end(args);
  return (res);
}

/*
 * pass_callback()
 *
 * Called by a hook function to pass code flow further
 * in the hook chain.
 *
 * inputs:
 *   this_hook  -  pointer to dlink_node of the current hook function
 *   ...        -  (original or modified) arguments to be passed
 * output: callback return value
 */
void *
pass_callback(dlink_node *this_hook, ...)
{
  void *res;
  va_list args;

  if (this_hook->next == NULL)
    return (NULL);  /* reached the last one */

  va_start(args, this_hook);
  res = ((CBFUNC *) this_hook->next->data)(args);
  va_end(args);
  return (res);
}

/*
 * find_callback()
 *
 * Finds a named callback.
 *
 * inputs:
 *   name  -  name of the callback
 * output: pointer to Callback structure or NULL if not found
 */
struct Callback *
find_callback(const char *name)
{
  struct Callback *cb;
  dlink_node *ptr;

  DLINK_FOREACH(ptr, callback_list.head)
  {
    cb = ptr->data;
    if (!irccmp(cb->name, name))
      return (cb);
  }

  return (NULL);
}

/*
 * install_hook()
 *
 * Installs a hook for the given callback.
 *
 * inputs:
 *   cb      -  pointer to Callback structure
 *   hook    -  address of hook function
 * output: pointer to dlink_node of the hook (used when
 *         passing control to the next hook in the chain);
 *         valid till uninstall_hook() is called
 *
 * NOTE: The new hook is installed at the beginning of the chain,
 * so it has full control over functions installed earlier.
 */
dlink_node *
install_hook(struct Callback *cb, CBFUNC *hook)
{
  dlink_node *node = MyMalloc(sizeof(dlink_node));

  dlinkAdd(hook, node, &cb->chain);
  return (node);
}

/*
 * uninstall_hook()
 *
 * Removes a specific hook for the given callback.
 *
 * inputs:
 *   cb      -  pointer to Callback structure
 *   hook    -  address of hook function
 * output: none
 */
void
uninstall_hook(struct Callback *cb, CBFUNC *hook)
{
  /* let it core if not found */
  dlink_node *ptr = dlinkFind(&cb->chain, hook);

  dlinkDelete(ptr, &cb->chain);
  MyFree(ptr);
}
Revision:	85
Committed:	Wed Oct 5 14:29:35 2005 UTC (20 years, 10 months ago) by adx
Content type:	text/x-csrc
File size:	4715 byte(s)
Log Message:	- register_callback: always restore the original handler at the end of the chain, not only when the chain is empty
#	User	Rev	Content
1	adx	61	/*
2			* ircd-hybrid: an advanced Internet Relay Chat Daemon(ircd).
3			* hook.c: Provides a generic event hooking interface.
4			*
5			* Copyright (C) 2003 Piotr Nizynski, Advanced IRC Services Project Team
6			* Copyright (C) 2005 Hybrid Development Team
7			*
8			* This program is free software; you can redistribute it and/or modify
9			* it under the terms of the GNU General Public License as published by
10			* the Free Software Foundation; either version 2 of the License, or
11			* (at your option) any later version.
12			*
13			* This program is distributed in the hope that it will be useful,
14			* but WITHOUT ANY WARRANTY; without even the implied warranty of
15			* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16			* GNU General Public License for more details.
17			*
18			* You should have received a copy of the GNU General Public License
19			* along with this program; if not, write to the Free Software
20			* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
21			* USA
22			*
23	knight	71	* $Id$
24	adx	61	*/
25
26			#include "stdinc.h"
27
28			dlink_list callback_list = {NULL, NULL, 0};
29
30			/*
31			* register_callback()
32			*
33			* Creates a new callback.
34			*
35			* inputs:
36			* name - name used to identify the callback
37			* (can be NULL for anonymous callbacks)
38			* func - initial function attached to the chain
39			* (can be NULL to create an empty chain)
40			* output: pointer to Callback structure or NULL if already exists
41			*
42			* NOTE: Once registered, a callback should never be freed!
43			* That's because there may be modules which depend on it
44			* (even if no functions are attached). That's also why
45			* we dynamically allocate the struct here -- we don't want
46			* to allow anyone to place it in module data, which can be
47			* unloaded at any time.
48			*/
49			struct Callback *
50			register_callback(const char name, CBFUNC func)
51			{
52			struct Callback *cb;
53
54			if (name != NULL)
55			if ((cb = find_callback(name)) != NULL)
56			{
57	adx	85	dlinkAddTail(func, MyMalloc(sizeof(dlink_node)), &cb->chain);
58			return (cb);
59	adx	61	}
60
61			cb = MyMalloc(sizeof(struct Callback));
62			if (func != NULL)
63			dlinkAdd(func, MyMalloc(sizeof(dlink_node)), &cb->chain);
64			if (name != NULL)
65			{
66			DupString(cb->name, name);
67			dlinkAdd(cb, &cb->node, &callback_list);
68			}
69			return (cb);
70			}
71
72			/*
73			* execute_callback()
74			*
75			* Passes control down the callback hook chain.
76			*
77			* inputs:
78			* callback - pointer to Callback structure
79			* param - argument to pass
80			* output: function return value
81			*/
82			void *
83			execute_callback(struct Callback *cb, ...)
84			{
85			void *res;
86			va_list args;
87
88			cb->called++;
89			cb->last = CurrentTime;
90
91			if (!is_callback_present(cb))
92			return (NULL);
93
94			va_start(args, cb);
95			res = ((CBFUNC *) cb->chain.head->data)(args);
96			va_end(args);
97			return (res);
98			}
99
100			/*
101			* pass_callback()
102			*
103			* Called by a hook function to pass code flow further
104			* in the hook chain.
105			*
106			* inputs:
107			* this_hook - pointer to dlink_node of the current hook function
108			* ... - (original or modified) arguments to be passed
109			* output: callback return value
110			*/
111			void *
112			pass_callback(dlink_node *this_hook, ...)
113			{
114			void *res;
115			va_list args;
116
117			if (this_hook->next == NULL)
118			return (NULL); /* reached the last one */
119
120			va_start(args, this_hook);
121			res = ((CBFUNC *) this_hook->next->data)(args);
122			va_end(args);
123			return (res);
124			}
125
126			/*
127			* find_callback()
128			*
129			* Finds a named callback.
130			*
131			* inputs:
132			* name - name of the callback
133			* output: pointer to Callback structure or NULL if not found
134			*/
135			struct Callback *
136			find_callback(const char *name)
137			{
138			struct Callback *cb;
139			dlink_node *ptr;
140
141			DLINK_FOREACH(ptr, callback_list.head)
142			{
143			cb = ptr->data;
144			if (!irccmp(cb->name, name))
145			return (cb);
146			}
147
148			return (NULL);
149			}
150
151			/*
152			* install_hook()
153			*
154			* Installs a hook for the given callback.
155			*
156			* inputs:
157			* cb - pointer to Callback structure
158			* hook - address of hook function
159			* output: pointer to dlink_node of the hook (used when
160			* passing control to the next hook in the chain);
161			* valid till uninstall_hook() is called
162			*
163			* NOTE: The new hook is installed at the beginning of the chain,
164			* so it has full control over functions installed earlier.
165			*/
166			dlink_node *
167			install_hook(struct Callback cb, CBFUNC hook)
168			{
169			dlink_node *node = MyMalloc(sizeof(dlink_node));
170
171			dlinkAdd(hook, node, &cb->chain);
172			return (node);
173			}
174
175			/*
176			* uninstall_hook()
177			*
178			* Removes a specific hook for the given callback.
179			*
180			* inputs:
181			* cb - pointer to Callback structure
182			* hook - address of hook function
183			* output: none
184			*/
185			void
186			uninstall_hook(struct Callback cb, CBFUNC hook)
187			{
188			/* let it core if not found */
189			dlink_node *ptr = dlinkFind(&cb->chain, hook);
190
191			dlinkDelete(ptr, &cb->chain);
192			MyFree(ptr);
193			}