connections.c 28.8 KB
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/*
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 * $Id: connections.c,v 0.121 2003/08/14 17:08:34 ceder Exp $
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 * Copyright (C) 1991-2002  Lysator Academic Computer Association.
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 *
 * This file is part of the LysKOM server.
 * 
 * LysKOM 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 1, or (at your option) 
 * any later version.
 * 
 * LysKOM 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 LysKOM; see the file COPYING.  If not, write to
 * Lysator, c/o ISY, Linkoping University, S-581 83 Linkoping, SWEDEN,
 * or the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
 * MA 02139, USA.
 *
 * Please mail bug reports to bug-lyskom@lysator.liu.se. 
 */
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/*
 * connections.c
 *
 * Denna fil inneh}ller niv}n ovanf|r isc.
 *
 * Created by Willf|r 31/3-90. Mostly written by ceder.
 */

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#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

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#include <errno.h>
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#include <stdio.h>
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#include <setjmp.h>
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#ifdef HAVE_STRING_H
#  include <string.h>
#endif
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#include <sys/types.h>
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#include <sys/stat.h>
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#include "timewrap.h"
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#include <sys/socket.h>
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#include <signal.h>
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#include <assert.h>
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#include <netdb.h>
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#include <stdlib.h>
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#include "adns.h"
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#include "oop.h"

#include "unused.h"
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#include "ldifftime.h"
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#include "misc-types.h"
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#include "s-string.h"
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#include "kom-types.h"
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#include "kom-memory.h"
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#include "debug.h"
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#include "isc-interface.h"
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#include "com.h"
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#include "async.h"
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#include "connections.h"
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#include "internal-connections.h"
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#include "prot-a-parse-arg.h"
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#include "log.h"
#include "lyskomd.h"
#include "services.h"
#include "isc-parse.h"
#include "prot-a.h"
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#include "prot-a-parse.h"
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#include "server/smalloc.h"
#include "end-of-atomic.h"
#include "send-async.h"
#include "cache.h"
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#include "rfc931.h"
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#include "param.h"
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#include "kom-config.h"
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#include "kom-errno.h"
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#include "sigflags.h"
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#include "server-time.h"
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#include "aux-items.h"
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#include "eintr.h"
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#include "text-garb.h"
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#include "timeval-util.h"
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#include "stats.h"
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#include "string-malloc.h"
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#include "manipulate.h"
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oop_source_sys * kom_server_oop_src = NULL;
struct isc_mcb * kom_server_mcb    = NULL;
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Connection     * active_connection = NULL;

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/*
 * This is set TRUE when the server should be closed. It is checked
 * each time around the main loop. It is set if someone with enough
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 * privileges issues a `shutdown', or of lyskomd receives a SIGTERM.
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 * This not an abort: all data is saved before we exit.
 */
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Bool go_and_die = FALSE;
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/*
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 * The number of times that the session penalties has been averaged.
 * Beware: this number will wrap around.
 */
static unsigned int penalty_generation = 0;

/*
 * These state variables are used to find out if we are busy or not.
 * When a packet arrives, data_available_callback() will set work_done
 * to TRUE and is_idle to FALSE.
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 */
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static Bool work_done = FALSE;
static Bool is_idle = FALSE;
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jmp_buf 	 parse_env;


const Fnc_descriptor fnc_defs[]={
#include "fnc-def-init.incl"
};

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const int num_fnc_defs = sizeof (fnc_defs) / sizeof (Fnc_descriptor);
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unsigned long service_statistics[sizeof (fnc_defs) / sizeof (Fnc_descriptor)];
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BUGDECL;

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static oop_call_fd data_available_callback;
static oop_call_time check_kill_flg;
static oop_call_time check_idle_callback;
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static isc_write_error_cb write_err_cb;
static isc_stale_output_cb stale_cb;
static isc_stale_output_cb idle_cb;
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static Connection *queue_first = NULL;
static Connection *queue_last = NULL;

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static void busy(void);


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static void
queue_add(Connection *c)
{
    assert(c->on_queue == FALSE);
    c->on_queue = TRUE;

    c->queue_prev = queue_last;
    c->queue_next = NULL;

    if (queue_first == NULL)
	queue_first = c;
    else
	queue_last->queue_next = c;

    queue_last = c;
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    update_stat(STAT_RUN_QUEUE, 1);
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}

static void
queue_remove(Connection *c)
{
    assert(c->on_queue == TRUE);
    c->on_queue = FALSE;

    if (c->queue_next != NULL)
	c->queue_next->queue_prev = c->queue_prev;
    else
	queue_last = c->queue_prev;
    
    if (c->queue_prev != NULL)
	c->queue_prev->queue_next = c->queue_next;
    else
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	queue_first = c->queue_next;
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    c->queue_prev = NULL;
    c->queue_next = NULL;
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    update_stat(STAT_RUN_QUEUE, -1);
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}

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void
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set_time(void)
{
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    struct timeval last_time;
    static int limiter = 0;
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    last_time = current_time;
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    if (gettimeofday(&current_time, NULL) < 0)
    {
	if (limiter < 50)
	{
	    kom_log("WARNING: gettimeofday failed: %s\n", strerror(errno));
	    if (++limiter == 50)
		kom_log("WARNING: will not log the above message again.\n");
	}
    }

    if (timeval_less(current_time, last_time))
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    {
	kom_log("WARNING: Time is moving in the wrong direction.\n");
	/* FIXME (bug 62): Should we take more decisive action here? */
    }
}
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static void
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logout_client(Connection *cp)
{
    Connection *real_active_connection;
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    int ret;
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    if ( active_connection != NULL )
    {
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	kom_log("BUGCHK: logout_client(%ld): connection %ld is active.\n",
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	    cp->session_no, active_connection->session_no);
    }
    
    if ( cp->pers_no != 0 )
    {
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	int ctr = 0;

	if (active_connection != NULL)
	{
	    kom_log("WNG: logout_client(): active_connection != NULL\n");
	    if (ctr < 100)
		ctr++;
	    else
		kom_log("WNG: won't log the above message more\n");
	}

	real_active_connection = active_connection;
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	active_connection = cp;
	logout();
	active_connection = real_active_connection;
    }
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    else
    {
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#if 0
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	/* FIXME (bug 908): send a new async here instead.  This causes the
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	   elisp client to say that a secret (or unknown) person has
	   left the system.  */
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        async_logout( 0, cp->session_no );
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#endif
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    }
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    switch(cp->protocol)
    {
    case 0:			/* Hasn't yet allocated any protocol. */
	break;
	
    case 'A':
	prot_a_destruct(cp);
	break;
	
    default:
	restart_kom("logout_client(): Bad protocol.\n");
    }

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    ret = isc_destroy(kom_server_mcb, cp->isc_session);
    if (ret < 0)
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	kom_log("logout_client(): isc_destroyed returned %d\n", ret);
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    cp->isc_session = NULL;
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    if (cp->on_queue)
	queue_remove(cp);
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    kill_client(cp);		/* Free the Connection */
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    update_stat(STAT_CLIENTS, -1);
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}

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/*
 * This function is part of the shutdown tidy-up sequence.
 */
void
logout_all_clients(void)
{
    Session_no sess = 0;
    Connection *conn;
    
    while ( (sess = traverse_connections (sess)) != 0)
    {
	conn = get_conn_by_number (sess);

	if ( conn == NULL )
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	    restart_kom("logout_all_clients(): cant get session %ld.\n",
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			sess);
	else
	    logout_client (conn);
    }

    if ( traverse_connections (0) != 0)
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	restart_kom("logout_all_clients(): traverse_connections(0) == %ld.\n",
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		    traverse_connections(0));
}

    
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/*
 * Call a function in services.c. A pointer to the result is returned.
 * The pointer points to static data which is overwritten on each call.
 */
static Success
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call_function(Connection *client,
	      union result_holder *res)
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{
    Success	status=FAILURE;	/* OK if the call was successful. */

    if ( active_connection != NULL )
    {
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	kom_log("call_function(%ld): active_connection = %ld\n",
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	    client->session_no, active_connection->session_no);
    }
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    if (client->function == illegal_fnc) 
    {
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        err_stat = 0;
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	kom_errno = KOM_NOT_IMPL;
	return FAILURE;
    }

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    active_connection = client;

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    service_statistics[client->function_index]++;
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#include "call-switch.incl"

    active_connection = NULL;

    return status;
}


static void
parse_packet(Connection *client)
{
    if ( client->protocol == '\0' ) /* Not known yet. */
    {
	client->protocol = parse_char(client);
	switch(client->protocol)
	{
	case 'A':
	    prot_a_init(client);
	    break;

	default:
	    client->protocol = '\0';
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	    isc_puts("%%LysKOM unsupported protocol.\n", client->isc_session);
	    isc_flush(client->isc_session);
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	    BUG(("%%%%Unsupported protocol.\n"));
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	    longjmp(parse_env, KOM_LOGOUT);
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	}
    }

    switch(client->protocol)
    {
    case 'A':
	prot_a_parse_packet(client);
	break;

    default:
	restart_kom("parse_packet(): Bad protocol.\n");
	break;
    }
}

/*
 * Free all parsed areas which are no longer needed. Re-initialize all
 * parse_pos fields so that the parse will expect a new function.
 *
 * This function is called
 *	when a parse error occurs
 *	when a parse is complete and the function has executed.
 */
static void
free_parsed(Connection *client)
{
    s_clear(&client->c_string0);
    s_clear(&client->c_string1);
    client->string0 = EMPTY_STRING; /* So that no one frees it. */
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    sfree(client->misc_info_list.misc);
    client->misc_info_list.misc = 0;
    client->misc_info_list.no_of_misc = 0;
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    s_clear(&client->aux_item.data);
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    s_clear(&client->dummy_aux_item.data);
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    sfree( client->c_local_text_no_p);
    client->c_local_text_no_p = NULL;
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    sfree(client->read_range_list.ranges);
    client->read_range_list.ranges = NULL;
    client->read_range_list.length = 0;
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    client->parse_pos = 0;
    client->fnc_parse_pos = 0;
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    client->array_parse_index = 0;
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    client->array_parse_parsed_length = 0;
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    client->array_parse_pos = 0;
    client->struct_parse_pos = 0;
    client->string_parse_pos = 0;
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    client->hunt_parse_pos = 0;
    client->array_hunt_num = 0;
    client->array_hunt_depth = 0;
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    sfree(client->num_list.data);
    client->num_list.data = NULL;
    client->num_list.length = 0;
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    free_aux_item_list(&client->aux_item_list);
    client->info.highest_aux_no = 0;
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}

/*
 * Send a reply to a call.
 */
static void
reply(Connection *client,
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      Success status,
      union result_holder *result)
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{
    switch(client->protocol)
    {
    case 'A':
	prot_a_reply(client, status, result);
	break;

    default:
	restart_kom("reply(): Bad protocol.\n");
	break;
    }
}


/*
 * Try to parse enough data from client->unparsed to call a function.
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 * If more data is needed set client->more_to_parse to FALSE.  Returns
 * TRUE if anything was (or might have been) written to the client.
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 */
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static Bool
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parse_unparsed(Connection *client)
{
    Success       status;
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    union result_holder result;
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    switch ( setjmp(parse_env) )
    {
    case 0 :
	/* Parse message. If message is complete call function and reply. */
	parse_packet(client);
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	if (client->blocked_by_dns)
	    return TRUE;
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	update_stat(STAT_REQUESTS, 1);
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	status = call_function(client, &result);
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	update_stat(STAT_REQUESTS, -1);
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	reply(client, status, &result);
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	client->penalty += param.penalty_per_call;
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	free_parsed(client);
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	end_of_atomic();
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	return TRUE;
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    case KOM_PROTOCOL_ERR:
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	s_clear(&client->string0);
	free_parsed(client);
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	isc_puts("%% LysKOM protocol error.\n", client->isc_session);
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	BUG(("%%%% Protocol error.\n"));
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	client->penalty += param.max_penalty;
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	s_clear(&client->unparsed);
	client->first_to_parse = 0;
	client->more_to_parse = FALSE;
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	end_of_atomic();
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	return TRUE;
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    case KOM_MSG_INCOMPLETE:
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	client->more_to_parse = FALSE;
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	return FALSE;
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    case KOM_LOGOUT:
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	add_to_kill_list(client);
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	client->more_to_parse = FALSE;
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	return TRUE;
    default:
	restart_kom("Bad longjmp return value.\n");
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    }
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    /*NOTREACHED*/
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}


/* Return 1 if the named file exists, 0 otherwise */
static int
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fexists(const char *filename)
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{
    struct stat buf;
    int code;
  
    code = !stat(filename, &buf);
    errno = 0;

    return code;
}


void
dump_statistics(void)
{
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    static struct timeval last_dump = {0, 0};
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    int i;
    FILE *fp;

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    if ((fp = i_fopen(param.statistic_name, "a")) == NULL)
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    {
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	kom_log("dump_statistics(): can't open file %s\n",
		param.statistic_name);
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	return;
    }

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    if (timeval_zero(last_dump))
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    {
	fprintf(fp, "RESTART\n");
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	last_dump = current_time;
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    }
    
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    fprintf(fp, "TIME: %s", ctime(&current_time.tv_sec));
    fprintf(fp, "SECONDS: %ld\n", timeval_diff_sec(current_time, last_dump));
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    fprintf(fp, "STATISTICS:");
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    /* The last entry corresponds to the dummy entry that is used to
       skip arguments to unimplemented requests.  Skip that, since it
       contains no useful statistics.  */
    for (i = 0; i < num_fnc_defs - 1; i++)
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    {
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	fprintf(fp, " %d:%lu", fnc_defs[i].function, service_statistics[i]);
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	service_statistics[i]=0;
    }

    fprintf(fp, "\n");
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    i_fclose(fp);
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    last_dump = current_time;
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}

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/* List of connections to kill. */

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static Session_no *kill_list = NULL;
static int kill_list_size = 0;
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static int kill_pending = 0;
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/* Schedule this client for termination. */
void
add_to_kill_list(Connection *conn)
{
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    oop_source *source;
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    int i;

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    if (conn->kill_pending)
    {
	for (i = 0; i < kill_list_size; i++)
	    if (kill_list[i] == conn->session_no)
		return;
	restart_kom("add_to_kill_list(): kill_pending set but not on list.\n");
    }

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    for (i = 0; i < kill_list_size; i++)
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	if (kill_list[i] == conn->session_no)
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	    restart_kom("add_to_kill_list(): on list but not kill_pending.\n");
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    if (kill_list == NULL)
    {
	if (kill_list_size != 0)
	    restart_kom("add_to_kill_list(): size = %d\n", kill_list_size);

	kill_list_size = 1;
	kill_list = smalloc(sizeof(Session_no));
    }
    else
    {
	kill_list_size++;
	kill_list = srealloc(kill_list, kill_list_size * sizeof(Session_no));
    }

    kill_list[kill_list_size-1] = conn->session_no;
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    conn->kill_pending = TRUE;
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    if (!kill_pending)
    {
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	source = isc_getoopsource(conn->isc_session);
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	source->on_time(source, OOP_TIME_NOW, check_kill_flg, NULL);
	kill_pending = 1;
    }
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}
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void
dump_connections(void)
{
    Session_no s;
    Connection *conn;
    FILE *fp;

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    if ((fp = i_fopen(param.connection_status_file_tmp, "w")) == NULL)
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    {
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	kom_log("dump_connections(): can't open file %s: %s\n",
		param.connection_status_file_tmp, strerror(errno));
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	return;
    }

    for (s = 0; (s = traverse_connections(s)) != 0;)
    {
	conn = get_conn_by_number(s);
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	fprintf(fp, "%d %lu %d %s\n", conn->isc_session->fd, conn->session_no,
		handshake_ok(conn, 0),
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		conn->peer);
    }

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    if (fflush(fp) != 0)
	kom_log("dump_connections(): fflush() says an error has occured.\n");
	
    if (ferror(fp))
	kom_log("dump_connections(): ferror() says an error has occured.\n");

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    if (i_fclose(fp) < 0)
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    {
	kom_log("dump_connections(): fclose failed: %s (ignored)\n",
		strerror(errno));
    }

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    errno = 0;
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    if (i_rename(param.connection_status_file_tmp,
		 param.connection_status_file) < 0)
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    {
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	kom_log("dump_connections(): can't rename %s to %s: %s\n",
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		param.connection_status_file_tmp,
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		param.connection_status_file,
		strerror(errno));
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    }
}


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/*
 * check_kill_flg must NEVER be called inside an atomic call!
 */
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static void *
check_kill_flg(oop_source *UNUSED(source),
	       struct timeval UNUSED(tv),
	       void *UNUSED(user))
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{
    Connection *conn;
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    Bool changed = FALSE;
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    kill_pending = 0;

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    if ( active_connection != NULL )
    {
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	restart_kom("check_kill_flg: active_connection == %ld",
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		    active_connection->session_no);
    }

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    while (kill_list_size > 0)
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    {
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	--kill_list_size;
	conn = get_conn_by_number (kill_list[kill_list_size]);
	if (conn == NULL)
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	{
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	    kom_log("check_kill_flg(): Connection %ld doesn't exist.\n",
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		kill_list[kill_list_size]);
	}
	else
	{
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	    assert(conn->kill_pending);
	    conn->kill_pending = FALSE;
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	    logout_client(conn);
	    end_of_atomic();
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	    changed = TRUE;
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	}
    }
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    if (kill_list != NULL)
    {
	sfree (kill_list);
	kill_list = NULL;
    }
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    if (changed == TRUE)
	dump_connections();
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    return OOP_CONTINUE;
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}

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static void *
dns_resolution(struct isc_scb *scb,
	       enum isc_resolve_status res,
	       long errcode)
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{
    struct timeval after;
    double diff = -1.0;
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    Connection *conn;
    char *hostname = NULL;
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    update_stat(STAT_DNS_QUEUE, -1);
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    conn = scb->udg;
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    conn->dns_done = TRUE;
    if (conn->blocked_by_dns)
    {
	conn->blocked_by_dns = FALSE;
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	if (!conn->on_queue)
	    queue_add(conn);
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    }

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    if (res == isc_resolve_aborted)
	return OOP_CONTINUE;

    if (gettimeofday(&after, NULL) < 0)
	kom_log("gettimeofday failed: %s\n", strerror(errno));

    diff = timeval_diff_d(after, conn->connect_time);
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    busy();

    switch (res)
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    {
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    case isc_resolve_h_errno:
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	if (hostname == NULL)
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	    hostname = s_crea_c_str(scb->remote);

	if (errcode == HOST_NOT_FOUND)
	    kom_log("No hostname found for %s.\n", hostname);
	else if (errcode == TRY_AGAIN)
	    kom_log("Lookup of %s timed out.\n", hostname);
	else if (errcode == NO_RECOVERY)
	    kom_log("Non-recoverable error looking up %s.\n", hostname);
	else if (errcode == NO_ADDRESS)
	    kom_log("Got NO_ADDRESS error looking up %s.\n", hostname);
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	else
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	    kom_log("Unknown resolver error %ld looking up %s.\n",
		    errcode, hostname);
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	break;
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    case isc_resolve_adns_error:
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	if (hostname == NULL)
	    hostname = s_crea_c_str(scb->remote);

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	/* Misconfigurations of localhost are common and harmless.
	   Don't bother logging them, since that makes the test cases fail. */
	if ((errcode != adns_s_inconsistent && errcode != adns_s_nxdomain)
	    || strcmp(hostname, "127.0.0.1") != 0)
	    kom_log("Error looking up %s: %s\n",
		    hostname, adns_strerror(errcode));
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	break;

    case isc_resolve_aborted:
	abort();

    case isc_resolve_ok:
	break;
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    }

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    if (diff > param.dns_log_threshold)
    {
	if (hostname == NULL)
	    hostname = s_crea_c_str(scb->remote);

	if (res == isc_resolve_ok)
	    kom_log("Slow DNS: got %s after %f seconds\n", hostname, diff);
	else
	    kom_log("Slow bad DNS: %s failed after %f seconds\n",
		    hostname, diff);
   }

    if (hostname != NULL)
	string_free(hostname); 

    return OOP_CONTINUE;
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}

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static void
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write_err_cb(struct isc_scb *cb_session,
	     int saved_errno)
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{
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    Connection  * cp = cb_session->udg;
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    if (saved_errno != ECONNRESET && saved_errno != EPIPE)
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	kom_log("Failed to write to client %lu from %s: %s\n",
		cp->session_no, cp->peer, strerror(saved_errno));
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    cp->penalty += param.max_penalty;
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    add_to_kill_list(cp);
}


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static void
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stale_cb(struct isc_scb *cb_session)
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{
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    Connection *cp = cb_session->udg;
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    kom_log("Client %lu from %s has stalled.  Killing it.\n",
	    cp->session_no, cp->peer);
    cp->penalty += param.max_penalty;
    add_to_kill_list(cp);
}
    
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static void
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idle_cb(struct isc_scb *cb_session)
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{
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    Connection *cp = cb_session->udg;
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    kom_log("Client %lu from %s has been idle too long.  Killing it.\n",
	    cp->session_no, cp->peer);
    cp->penalty += param.max_penalty;
    add_to_kill_list(cp);
}


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static void
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login_request(struct isc_scb *session)
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{
    Connection  * cp;
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    const char *realuser;
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    char portbuf[1+2+3*sizeof(long)];
    size_t portlen;
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    char *remote_ip = NULL;
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    /* Supress logins if /etc/nologin exists */
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    if (fexists(param.nologin_file))
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    {
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	isc_puts("%% No logins allowed.\n", session);
	isc_flush(session);
 	isc_destroy(kom_server_mcb, session);
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	return;
    }

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    /* Create a Connection, and link the Connection and the
       isc_session together. */
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    cp = new_client();
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    cp->isc_session = session;
    session->udg = cp;
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    update_stat(STAT_CLIENTS, 1);
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    /* Store the IP address in readable form. */
    s_crea_str(&cp->remote_ip, isc_getipnum(session->raddr, NULL, 0));
    remote_ip = s_crea_c_str(cp->remote_ip);
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    /* Initiate DNS lookup. */
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    if (param.use_dns && isc_resolve_remote(session, dns_resolution) == 0)
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	update_stat(STAT_DNS_QUEUE, 1);
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    else
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	s_strcpy(&session->remote, cp->remote_ip);
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    /* Update the status file that contains all connection. */
    sprintf(portbuf, " %d", isc_getportnum(session->raddr));
    portlen = strlen(portbuf);
    cp->peer = smalloc(s_strlen(cp->remote_ip) + portlen + 1);
    strcpy(cp->peer, remote_ip);
    strcpy(cp->peer + s_strlen(cp->remote_ip), portbuf);
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    dump_connections();
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    /* Start with max penalty, so that it doesn't pay to make a lot of
       new connections.  */
    cp->penalty = param.max_penalty;
    cp->penalty_generation = penalty_generation;
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    /* Get the real user name, as returned by the Ident protocol (rfc 931). */
    realuser = get_real_username(session, remote_ip);
    if (realuser == NULL && param.authentication_level == 2)
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    {
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	kom_log("Connection from %s rejected - no IDENT available.\n", 
		remote_ip);

	isc_puts("%% No IDENT server reachable at your site.\n",
		 session);
	isc_flush(session);
	logout_client(cp);
	string_free(remote_ip);
	return;
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    }

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    if (realuser != NULL)
	s_crea_str(&cp->ident_user, realuser);

    BUG(("\n[Client %lu from %s is connecting]\n", cp->session_no, remote_ip));
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    isc_set_read_callback(session, data_available_callback, write_err_cb,
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			  stale_cb, idle_cb);
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    string_free(remote_ip);
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}

static void
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adjust_penalty(Connection *conn)
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{
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    while (penalty_generation - conn->penalty_generation > 0)
    {
	conn->penalty /= 2;
	if (conn->penalty == 0)
	    conn->penalty_generation = penalty_generation;
	else
	    conn->penalty_generation++;
    }
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}


static void
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read_from_connection(Connection *conn)
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{
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    Bool would_block = FALSE;
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    Bool need_flush = FALSE;
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    String_size pre;
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    adjust_penalty(conn);

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    while (!would_block && !go_and_die && conn->penalty < param.max_penalty
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	   && !conn->kill_pending && !conn->blocked_by_dns)
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    {
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	pre = s_strlen(conn->unparsed) - conn->first_to_parse;
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	while (conn->more_to_parse
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	       && !go_and_die && conn->penalty < param.max_penalty
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	       && !conn->kill_pending && !conn->blocked_by_dns)
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	    need_flush |= parse_unparsed(conn);
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	update_stat(STAT_RECV_QUEUE,
		    s_strlen(conn->unparsed) - conn->first_to_parse - pre);
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	if (go_and_die || conn->penalty >= param.max_penalty
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	    || conn->kill_pending || conn->blocked_by_dns)
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	    break;

	if (!conn->more_to_parse)
	{
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	    pre = s_strlen(conn->unparsed) - conn->first_to_parse;
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	    switch (isc_read_data(conn->isc_session,
				  &conn->unparsed,
				  &conn->first_to_parse))
	    {
	    case ISC_READ_DATA:
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		update_stat(STAT_RECV_QUEUE,
			    s_strlen(conn->unparsed) - conn->first_to_parse
			    - pre);