/* tinyproxy - A fast light-weight HTTP proxy
 * Copyright (C) 2000 Robert James Kaes <rjkaes@users.sourceforge.net>
 *
 * 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.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

/* Handles the creation/destruction of the various children required for
 * processing incoming connections.
 */

#include "main.h"

#include "child.h"
#include "daemon.h"
#include "filter.h"
#include "heap.h"
#include "log.h"
#include "reqs.h"
#include "sock.h"
#include "utils.h"

static int listenfd;
static socklen_t addrlen;

/*
 * Stores the internal data needed for each child (connection)
 */
enum child_status_t { T_EMPTY, T_WAITING, T_CONNECTED };
struct child_s {
        pid_t tid;
        unsigned int connects;
        enum child_status_t status;
};

/*
 * A pointer to an array of children. A certain number of children are
 * created when the program is started.
 */
static struct child_s *child_ptr;

static struct child_config_s {
        unsigned int maxclients, maxrequestsperchild;
        unsigned int maxspareservers, minspareservers, startservers;
} child_config;

static unsigned int *servers_waiting;   /* servers waiting for a connection */

/*
 * Lock/Unlock the "servers_waiting" variable so that two children cannot
 * modify it at the same time.
 */
#define SERVER_COUNT_LOCK()   _child_lock_wait()
#define SERVER_COUNT_UNLOCK() _child_lock_release()

/* START OF LOCKING SECTION */

/*
 * These variables are required for the locking mechanism.  Also included
 * are the "private" functions for locking/unlocking.
 */
static struct flock lock_it, unlock_it;
static int lock_fd = -1;

static void _child_lock_init (void)
{
        char lock_file[] = "/tmp/tinyproxy.servers.lock.XXXXXX";

        /* Only allow u+rw bits. This may be required for some versions
         * of glibc so that mkstemp() doesn't make us vulnerable.
         */
        umask (0177);

        lock_fd = mkstemp (lock_file);
        unlink (lock_file);

        lock_it.l_type = F_WRLCK;
        lock_it.l_whence = SEEK_SET;
        lock_it.l_start = 0;
        lock_it.l_len = 0;

        unlock_it.l_type = F_UNLCK;
        unlock_it.l_whence = SEEK_SET;
        unlock_it.l_start = 0;
        unlock_it.l_len = 0;
}

static void _child_lock_wait (void)
{
        int rc;

        while ((rc = fcntl (lock_fd, F_SETLKW, &lock_it)) < 0) {
                if (errno == EINTR)
                        continue;
                else
                        return;
        }
}

static void _child_lock_release (void)
{
        if (fcntl (lock_fd, F_SETLKW, &unlock_it) < 0)
                return;
}

/* END OF LOCKING SECTION */

#define SERVER_INC() do { \
    SERVER_COUNT_LOCK(); \
    ++(*servers_waiting); \
    DEBUG2("INC: servers_waiting: %d", *servers_waiting); \
    SERVER_COUNT_UNLOCK(); \
} while (0)

#define SERVER_DEC() do { \
    SERVER_COUNT_LOCK(); \
    assert(*servers_waiting > 0); \
    --(*servers_waiting); \
    DEBUG2("DEC: servers_waiting: %d", *servers_waiting); \
    SERVER_COUNT_UNLOCK(); \
} while (0)

/*
 * Set the configuration values for the various child related settings.
 */
short int child_configure (child_config_t type, unsigned int val)
{
        switch (type) {
        case CHILD_MAXCLIENTS:
                child_config.maxclients = val;
                break;
        case CHILD_MAXSPARESERVERS:
                child_config.maxspareservers = val;
                break;
        case CHILD_MINSPARESERVERS:
                child_config.minspareservers = val;
                break;
        case CHILD_STARTSERVERS:
                child_config.startservers = val;
                break;
        case CHILD_MAXREQUESTSPERCHILD:
                child_config.maxrequestsperchild = val;
                break;
        default:
                DEBUG2 ("Invalid type (%d)", type);
                return -1;
        }

        return 0;
}

/**
 * child signal handler for sighup
 */
static void child_sighup_handler (int sig)
{
        if (sig == SIGHUP) {
#ifdef FILTER_ENABLE
                filter_reload ();
#endif /* FILTER_ENABLE */
        }
}

/*
 * This is the main (per child) loop.
 */
static void child_main (struct child_s *ptr)
{
        int connfd;
        struct sockaddr *cliaddr;
        socklen_t clilen;

        cliaddr = (struct sockaddr *) safemalloc (addrlen);
        if (!cliaddr) {
                log_message (LOG_CRIT,
                             "Could not allocate memory for child address.");
                exit (0);
        }

        ptr->connects = 0;

        while (!config.quit) {
                ptr->status = T_WAITING;

                clilen = addrlen;

                connfd = accept (listenfd, cliaddr, &clilen);

#ifndef NDEBUG
                /*
                 * Enable the TINYPROXY_DEBUG environment variable if you
                 * want to use the GDB debugger.
                 */
                if (getenv ("TINYPROXY_DEBUG")) {
                        /* Pause for 10 seconds to allow us to connect debugger */
                        fprintf (stderr,
                                 "Process has accepted connection: %ld\n",
                                 (long int) ptr->tid);
                        sleep (10);
                        fprintf (stderr, "Continuing process: %ld\n",
                                 (long int) ptr->tid);
                }
#endif

                /*
                 * Make sure no error occurred...
                 */
                if (connfd < 0) {
                        log_message (LOG_ERR,
                                     "Accept returned an error (%s) ... retrying.",
                                     strerror (errno));
                        continue;
                }

                ptr->status = T_CONNECTED;

                SERVER_DEC ();

                handle_connection (connfd);
                ptr->connects++;

                if (child_config.maxrequestsperchild != 0) {
                        DEBUG2 ("%u connections so far...", ptr->connects);

                        if (ptr->connects == child_config.maxrequestsperchild) {
                                log_message (LOG_NOTICE,
                                             "Child has reached MaxRequestsPerChild (%u). "
                                             "Killing child.", ptr->connects);
                                break;
                        }
                }

                SERVER_COUNT_LOCK ();
                if (*servers_waiting > child_config.maxspareservers) {
                        /*
                         * There are too many spare children, kill ourself
                         * off.
                         */
                        log_message (LOG_NOTICE,
                                     "Waiting servers (%d) exceeds MaxSpareServers (%d). "
                                     "Killing child.",
                                     *servers_waiting,
                                     child_config.maxspareservers);
                        SERVER_COUNT_UNLOCK ();

                        break;
                } else {
                        SERVER_COUNT_UNLOCK ();
                }

                SERVER_INC ();
        }

        ptr->status = T_EMPTY;

        safefree (cliaddr);
        exit (0);
}

/*
 * Fork a child "child" (or in our case a process) and then start up the
 * child_main() function.
 */
static pid_t child_make (struct child_s *ptr)
{
        pid_t pid;

        if ((pid = fork ()) > 0)
                return pid;     /* parent */

        /*
         * Reset the SIGNALS so that the child can be reaped.
         */
        set_signal_handler (SIGCHLD, SIG_DFL);
        set_signal_handler (SIGTERM, SIG_DFL);
        set_signal_handler (SIGHUP, child_sighup_handler);

        child_main (ptr);       /* never returns */
        return -1;
}

/*
 * Create a pool of children to handle incoming connections
 */
short int child_pool_create (void)
{
        unsigned int i;

        /*
         * Make sure the number of MaxClients is not zero, since this
         * variable determines the size of the array created for children
         * later on.
         */
        if (child_config.maxclients == 0) {
                log_message (LOG_ERR,
                             "child_pool_create: \"MaxClients\" must be "
                             "greater than zero.");
                return -1;
        }
        if (child_config.startservers == 0) {
                log_message (LOG_ERR,
                             "child_pool_create: \"StartServers\" must be "
                             "greater than zero.");
                return -1;
        }

        child_ptr =
            (struct child_s *) calloc_shared_memory (child_config.maxclients,
                                                     sizeof (struct child_s));
        if (!child_ptr) {
                log_message (LOG_ERR,
                             "Could not allocate memory for children.");
                return -1;
        }

        servers_waiting =
            (unsigned int *) malloc_shared_memory (sizeof (unsigned int));
        if (servers_waiting == MAP_FAILED) {
                log_message (LOG_ERR,
                             "Could not allocate memory for child counting.");
                return -1;
        }
        *servers_waiting = 0;

        /*
         * Create a "locking" file for use around the servers_waiting
         * variable.
         */
        _child_lock_init ();

        if (child_config.startservers > child_config.maxclients) {
                log_message (LOG_WARNING,
                             "Can not start more than \"MaxClients\" servers. "
                             "Starting %u servers instead.",
                             child_config.maxclients);
                child_config.startservers = child_config.maxclients;
        }

        for (i = 0; i != child_config.maxclients; i++) {
                child_ptr[i].status = T_EMPTY;
                child_ptr[i].connects = 0;
        }

        for (i = 0; i != child_config.startservers; i++) {
                DEBUG2 ("Trying to create child %d of %d", i + 1,
                        child_config.startservers);
                child_ptr[i].status = T_WAITING;
                child_ptr[i].tid = child_make (&child_ptr[i]);

                if (child_ptr[i].tid < 0) {
                        log_message (LOG_WARNING,
                                     "Could not create child number %d of %d",
                                     i, child_config.startservers);
                        return -1;
                } else {
                        log_message (LOG_INFO,
                                     "Creating child number %d of %d ...",
                                     i + 1, child_config.startservers);

                        SERVER_INC ();
                }
        }

        log_message (LOG_INFO, "Finished creating all children.");

        return 0;
}

/*
 * Keep the proper number of servers running. This is the birth of the
 * servers. It monitors this at least once a second.
 */
void child_main_loop (void)
{
        unsigned int i;

        while (1) {
                if (config.quit)
                        return;

                /* If there are not enough spare servers, create more */
                SERVER_COUNT_LOCK ();
                if (*servers_waiting < child_config.minspareservers) {
                        log_message (LOG_NOTICE,
                                     "Waiting servers (%d) is less than MinSpareServers (%d). "
                                     "Creating new child.",
                                     *servers_waiting,
                                     child_config.minspareservers);

                        SERVER_COUNT_UNLOCK ();

                        for (i = 0; i != child_config.maxclients; i++) {
                                if (child_ptr[i].status == T_EMPTY) {
                                        child_ptr[i].status = T_WAITING;
                                        child_ptr[i].tid =
                                            child_make (&child_ptr[i]);
                                        if (child_ptr[i].tid < 0) {
                                                log_message (LOG_NOTICE,
                                                             "Could not create child");

                                                child_ptr[i].status = T_EMPTY;
                                                break;
                                        }

                                        SERVER_INC ();

                                        break;
                                }
                        }
                } else {
                        SERVER_COUNT_UNLOCK ();
                }

                sleep (5);

                /* Handle log rotation if it was requested */
                if (received_sighup) {
                        truncate_log_file ();

#ifdef FILTER_ENABLE
                        filter_reload ();
#endif /* FILTER_ENABLE */

                        received_sighup = FALSE;
                }
        }
}

/*
 * Go through all the non-empty children and cancel them.
 */
void child_kill_children (int sig)
{
        unsigned int i;

        for (i = 0; i != child_config.maxclients; i++) {
                if (child_ptr[i].status != T_EMPTY)
                        kill (child_ptr[i].tid, sig);
        }
}

int child_listening_sock (uint16_t port)
{
        listenfd = listen_sock (port, &addrlen);
        return listenfd;
}

void child_close_sock (void)
{
        close (listenfd);
}