/* 
   Unix SMB/Netbios implementation.
   Version 3.0
   Samba internal messaging functions
   Copyright (C) Andrew Tridgell 2000
   
   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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/* this module is used for internal messaging between Samba daemons. 

   The idea is that if a part of Samba wants to do communication with
   another Samba process then it will do a message_register() of a
   dispatch function, and use message_send_pid() to send messages to
   that process.

   This system doesn't have any inherent size limitations but is not
   very efficient for large messages or when messages are sent in very
   quick succession.

*/

#include "includes.h"

/* the locking database handle */
static TDB_CONTEXT *tdb;
static int received_signal;

/* change the message version with any incompatible changes in the protocol */
#define MESSAGE_VERSION 1

struct message_rec {
	int msg_version;
	int msg_type;
	pid_t dest;
	pid_t src;
	size_t len;
};

/* we have a linked list of dispatch handlers */
static struct dispatch_fns {
	struct dispatch_fns *next, *prev;
	int msg_type;
	void (*fn)(int msg_type, pid_t pid, void *buf, size_t len);
} *dispatch_fns;

/****************************************************************************
notifications come in as signals
****************************************************************************/
static void sig_usr1(void)
{
	received_signal = 1;
	sys_select_signal();
}

/****************************************************************************
a useful function for testing the message system
****************************************************************************/
void ping_message(int msg_type, pid_t src, void *buf, size_t len)
{
	message_send_pid(src, MSG_PONG, buf, len);
}

/****************************************************************************
 Initialise the messaging functions. 
****************************************************************************/
BOOL message_init(void)
{
	if (tdb) return True;

	tdb = tdb_open(lock_path("messages.tdb"), 
		       0, TDB_CLEAR_IF_FIRST, 
		       O_RDWR|O_CREAT,0600);

	if (!tdb) {
		DEBUG(0,("ERROR: Failed to initialise messages database\n"));
		return False;
	}

	CatchSignal(SIGUSR1, sig_usr1);

	message_register(MSG_PING, ping_message);

	return True;
}


/*******************************************************************
 form a static tdb key from a pid
******************************************************************/
static TDB_DATA message_key_pid(pid_t pid)
{
	static char key[20];
	TDB_DATA kbuf;

	slprintf(key, sizeof(key), "PID/%d", (int)pid);

	kbuf.dptr = (char *)key;
	kbuf.dsize = sizeof(key);
	return kbuf;
}


/****************************************************************************
notify a process that it has a message. If the process doesn't exist 
then delete its record in the database
****************************************************************************/
static BOOL message_notify(pid_t pid)
{
	if (kill(pid, SIGUSR1) == -1) {
		if (errno == ESRCH) {
			DEBUG(2,("pid %d doesn't exist - deleting messages record\n", (int)pid));
			tdb_delete(tdb, message_key_pid(pid));
		} else {
			DEBUG(2,("message to process %d failed - %s\n", (int)pid, strerror(errno)));
		}
		return False;
	}
	return True;
}

/****************************************************************************
send a message to a particular pid
****************************************************************************/
BOOL message_send_pid(pid_t pid, int msg_type, void *buf, size_t len)
{
	TDB_DATA kbuf;
	TDB_DATA dbuf;
	struct message_rec rec;
	void *p;

	rec.msg_version = MESSAGE_VERSION;
	rec.msg_type = msg_type;
	rec.dest = pid;
	rec.src = sys_getpid();
	rec.len = len;

	kbuf = message_key_pid(pid);

	/* lock the record for the destination */
	tdb_lockchain(tdb, kbuf);

	dbuf = tdb_fetch(tdb, kbuf);

	if (!dbuf.dptr) {
		/* its a new record */
		p = (void *)malloc(len + sizeof(rec));
		if (!p) goto failed;

		memcpy(p, &rec, sizeof(rec));
		if (len > 0) memcpy(p+sizeof(rec), buf, len);

		dbuf.dptr = p;
		dbuf.dsize = len + sizeof(rec);
		tdb_store(tdb, kbuf, dbuf, TDB_REPLACE);
		free(p);
		goto ok;
	}

	/* we're adding to an existing entry */
	p = (void *)malloc(dbuf.dsize + len + sizeof(rec));
	if (!p) goto failed;

	memcpy(p, dbuf.dptr, dbuf.dsize);
	memcpy(p+dbuf.dsize, &rec, sizeof(rec));
	if (len > 0) memcpy(p+dbuf.dsize+sizeof(rec), buf, len);

	free(dbuf.dptr);
	dbuf.dptr = p;
	dbuf.dsize += len + sizeof(rec);
	tdb_store(tdb, kbuf, dbuf, TDB_REPLACE);
	free(dbuf.dptr);

 ok:
	tdb_unlockchain(tdb, kbuf);
	return message_notify(pid);

 failed:
	tdb_unlockchain(tdb, kbuf);
	return False;
}



/****************************************************************************
retrieve the next message for the current process
****************************************************************************/
static BOOL message_recv(int *msg_type, pid_t *src, void **buf, size_t *len)
{
	TDB_DATA kbuf;
	TDB_DATA dbuf;
	struct message_rec rec;

	kbuf = message_key_pid(sys_getpid());

	tdb_lockchain(tdb, kbuf);
	
	dbuf = tdb_fetch(tdb, kbuf);
	if (dbuf.dptr == NULL || dbuf.dsize == 0) goto failed;

	memcpy(&rec, dbuf.dptr, sizeof(rec));

	if (rec.msg_version != MESSAGE_VERSION) {
		DEBUG(0,("message version %d received (expected %d)\n", rec.msg_version, MESSAGE_VERSION));
		goto failed;
	}

	if (rec.len > 0) {
		(*buf) = (void *)malloc(rec.len);
		if (!(*buf)) goto failed;

		memcpy(*buf, dbuf.dptr+sizeof(rec), rec.len);
	} else {
		*buf = NULL;
	}

	*len = rec.len;
	*msg_type = rec.msg_type;
	*src = rec.src;

	memmove(dbuf.dptr, dbuf.dptr+sizeof(rec)+rec.len, dbuf.dsize - (sizeof(rec)+rec.len));
	dbuf.dsize -= sizeof(rec)+rec.len;
	tdb_store(tdb, kbuf, dbuf, TDB_REPLACE);

	free(dbuf.dptr);
	tdb_unlockchain(tdb, kbuf);
	return True;

 failed:
	tdb_unlockchain(tdb, kbuf);
	return False;
}


/****************************************************************************
receive and dispatch any messages pending for this process
notice that all dispatch handlers for a particular msg_type get called,
so you can register multiple handlers for a message
****************************************************************************/
void message_dispatch(void)
{
	int msg_type;
	pid_t src;
	void *buf;
	size_t len;
	struct dispatch_fns *dfn;

	if (!received_signal) return;
	received_signal = 0;

	while (message_recv(&msg_type, &src, &buf, &len)) {
		for (dfn = dispatch_fns; dfn; dfn = dfn->next) {
			if (dfn->msg_type == msg_type) {
				dfn->fn(msg_type, src, buf, len);
			}
		}
		if (buf) free(buf);
	}
}


/****************************************************************************
register a dispatch function for a particular message type
****************************************************************************/
void message_register(int msg_type, 
		      void (*fn)(int msg_type, pid_t pid, void *buf, size_t len))
{
	struct dispatch_fns *dfn;

	dfn = (struct dispatch_fns *)malloc(sizeof(*dfn));

	ZERO_STRUCTP(dfn);

	dfn->msg_type = msg_type;
	dfn->fn = fn;

	DLIST_ADD(dispatch_fns, dfn);
}

/****************************************************************************
de-register the function for a particular message type
****************************************************************************/
void message_deregister(int msg_type)
{
	struct dispatch_fns *dfn, *next;

	for (dfn = dispatch_fns; dfn; dfn = next) {
		next = dfn->next;
		if (dfn->msg_type == msg_type) {
			DLIST_REMOVE(dispatch_fns, dfn);
			free(dfn);
		}
	}	
}