Added a notice about a (not yet fixed) dcache bug.

[betaftpd] / ftpd.c

/*  ftpd.c: BetaFTPD main
    Copyright (C) 1999-2000 Steinar H. Gunderson

    This program is is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 2 if the
    License as published by the Free Software Foundation.

    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.
*/

/*
 * Special note: this file has been overwritten by another (0-byte) file, been
 * through the dead, and restored (with the help of dd, grep, gpm, vi and less)
 * with a sucess rate of 99.9%. Show it a little respect -- don't add junk
 * to it. :-)
 */

#define _GNU_SOURCE

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

#if HAVE_ERRNO_H
#include <errno.h>
#endif

#if HAVE_STROPTS_H
#include <stropts.h>
#endif

#if HAVE_SYS_CONF_H
#include <sys/conf.h>
#endif

#if HAVE_FCNTL_H
#include <fcntl.h>
#endif

#if HAVE_STDIO_H
#include <stdio.h>
#endif

#if HAVE_ASSERT_H
#include <assert.h>
#endif

#if HAVE_STRING_H
#include <string.h>
#endif

#if HAVE_STRINGS_H
#include <strings.h>
#endif

#if HAVE_STDARG_H
#include <stdarg.h>
#endif

#if HAVE_STDLIB_H
#include <stdlib.h>
#endif

#if HAVE_UNISTD_H
#include <unistd.h>
#endif

#if HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif

#if HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

#if HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif

#if HAVE_NETINET_IN_SYSTM_H
#include <netinet/in_systm.h>
#endif

#if HAVE_NETINET_IP_H
#include <netinet/ip.h>
#endif

#if HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif

#if HAVE_LINUX_SOCKET_H
#include <linux/socket.h>
#endif

#if HAVE_LINUX_TCP_H
#include <linux/tcp.h>
#endif

#if HAVE_MMAP
#include <sys/mman.h>
#endif

#if HAVE_TIME_H
#include <time.h>
#endif

#if HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#if HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#if HAVE_SYS_FILIO_H
#include <sys/filio.h>
#endif

#if HAVE_NETDB_H
#include <netdb.h>
#endif

#if HAVE_SIGNAL_H
#include <signal.h>
#endif

#if HAVE_GLOB_H
#include <glob.h>
#endif

#if HAVE_SYS_SIGNAL_H
#include <sys/signal.h>
#endif

#if HAVE_SYS_POLL_H
#include <sys/poll.h>
#endif

#if HAVE_SYS_SENDFILE_H
#include <sys/sendfile.h>
#endif

/*
 * <linux/socket.h> does not export this to glibc2 systems, and it isn't
 * always defined anywhere else.
 */
#if !defined(TCP_CORK) && defined(__linux__)
#define TCP_CORK 3
#endif

#include <ftpd.h>
#include <cmds.h>

#if WANT_ASCII
#include <ascii.h>
#endif

#if WANT_DCACHE
#include <dcache.h>
#endif

#ifndef MAP_FAILED
#define MAP_FAILED -1
#endif

struct conn *first_conn = NULL;
struct ftran *first_ftran = NULL;
#if WANT_DCACHE
struct dcache *first_dcache = NULL;
#endif

#if HAVE_POLL
unsigned int highest_fds = 0;

#define FD_MAX 1024
#define fds_send fds
struct pollfd fds[FD_MAX];

#define MAXCLIENTS FD_MAX
#else
fd_set master_fds, master_send_fds;
#define MAXCLIENTS FD_SETSIZE
#endif

#if WANT_XFERLOG
FILE *xferlog = NULL;
#endif

#if HAVE_LINUX_SENDFILE
int sendfile_supported = 1;
#endif

/*
 * This variable specifies if it's soon time to check for timed out
 * clients, and timed out directory listing cache entries. It is
 * set to 1 by a signal handler every minute, and set to 0 when the
 * checking has been performed.
 */
int time_to_check = 1;

#ifndef HAVE_SPRINTF
/*
 * snprintf():  snprintf() replacement for systems that miss it. Note
 *              that this implementation does _not_ necessarily protect
 *              against all buffer overflows. Get a real snprintf() in
 *              your C library. That being said, the 8k limit is
 *              substantially larger than any other string in BetaFTPD,
 *              which should make such an attack harder.
 */
int snprintf(char *str, size_t n, const char *format, ...)
{
        char buf[8192];
        va_list args;
        int err;

        va_start(args, format);
        err = vsprintf(buf, format, args);
        va_end(args);

        buf[(int)n] = 0;
        strcpy(str, buf);

        return err;
}
#endif

#ifndef HAVE_VSNPRINTF
/*
 * vsnprintf:   vsnprintf() replacement for systems that miss it. Please
 *              see snprintf (above) for more information.
 */
int vsnprintf(char *str, size_t n, const char *format, va_list ap)
{
        char buf[8192];
        int err;

        err = vsprintf(buf, format, ap);
        buf[(int)n] = 0;
        strcpy(str, buf);
        return err;
}
#endif

/*
 * add_fd():    Add an fd to the set we monitor. Return 0 on success.
 *              This code is shared between poll() and select() versions.
 */
int add_fd(const int fd, const int events)
{
#if HAVE_POLL
        if (fd >= FD_MAX) {
                printf("add_fd(%d, %x): failed\n", fd, events);
                return E2BIG;
        }

        fds[fd].fd = fd;
        fds[fd].events = events;
        if (highest_fds < fd) 
                highest_fds = fd;
#else 
        if (fd >= FD_SETSIZE)
                return E2BIG;
        if (events & POLLIN)
                FD_SET(fd, &master_fds);
        if (events & POLLOUT)
                FD_SET(fd, &master_send_fds);
#endif
        return 0;
}

/*
 * del_fd():    Close and remove an fd from the set(s) we monitor. (See also add_fd().)
 */
void del_fd(const int fd)
{
#if HAVE_POLL
        if (fd >= FD_MAX)
                return;

        fds[fd].fd = -1;
        fds[fd].events = 0;

        /* Reduce poll()'s workload by not making it watch past end of array */
        while ((highest_fds > 0) && (fds[highest_fds].fd == -1))
                highest_fds--;
#else 
        if (fd >= FD_SETSIZE)
                return;
        FD_CLR(fd, &master_fds);
        FD_CLR(fd, &master_send_fds);
#endif

        close(fd);
}

#if 0
void list_clients()
{
        struct conn *c = first_conn;
        printf("list_clients:\n");
        while (c && c->next_conn) {
                c = c->next_conn;
                printf("list_clients: fd %d\n", c->sock);
        }
}
#endif

/*
 * add_to_linked_list():
 *              Inserts an element (conn, ftran or dcache) into its linked list.
 *              The list is placed at the beginning, right after the (bogus)
 *              first element of the list.
 */
void add_to_linked_list(struct list_element * const first,
                        struct list_element * const elem)
{
        elem->prev = first;

        if (first) {
                elem->next = first->next;
                if (elem->next) elem->next->prev = elem;
                first->next = elem;
        } else {
                /* this is the bogus head of the list */
                elem->next = NULL;
        }
}

/*
 * remove_from_linked_list():
 *              Removes an element (conn, ftran or dcache) from its linked list,
 *              then frees it.
 */
void remove_from_linked_list(struct list_element * const elem)
{
        if (elem->prev != NULL) elem->prev->next = elem->next;
        if (elem->next != NULL) elem->next->prev = elem->prev;
        free(elem);
}

/*
 * alloc_new_conn():
 *              Allocates a new control connection (type `struct conn'),
 *              initializes it, and adds it to the linked list. The connection
 *              operates on the socket SOCK.
 */
struct conn *alloc_new_conn(const int sock)
{
        const unsigned int one = 1;
        struct conn *c = (struct conn *)(malloc(sizeof(struct conn)));

        if (c == NULL) return c;

        if (sock != -1) {
                ioctl(sock, FIONBIO, &one);
                if (add_fd(sock, POLLIN) != 0) {
                        /* temp unavail */
                        send(sock, "230 Server too busy, please try again later.\r\n", 46, 0);
                        close(sock);
                        return NULL;
                }

                add_to_linked_list((struct list_element *)first_conn,
                                   (struct list_element *)c);
        } else {
                /* this is the bogus head of the list */
                c->next_conn = NULL;
                c->prev_conn = NULL;
        }

        c->transfer = NULL;
        c->sock = sock;
        c->buf_len = c->auth = c->rest_pos = 0;
#if WANT_ASCII
        c->ascii_mode = 0;
#endif

        /*
         * equals:
         * strcpy(c->curr_dir, "/");
         * strcpy(c->last_cmd, "");
         * strcpy(c->rename_from, "")
         */
        c->curr_dir[0] = '/';
#if WANT_FULLSCREEN
        c->curr_dir[1] = c->last_cmd[0] = c->rename_from[0] = '\0';
#else
        c->curr_dir[1] = c->rename_from[0] = '\0';
#endif

        time(&(c->last_transfer));

        /*list_clients();*/

        return c;
}

/*
 * alloc_new_ftran():
 *              Allocates a new data connection (type `struct ftran'), and
 *              adds it to the linked list. The connection operates on the
 *              socket SOCK, and has the control connection C as its parent.
 */
struct ftran *alloc_new_ftran(const int sock, const struct conn * const c)
{
        struct ftran *f = (struct ftran *)(malloc(sizeof(struct ftran)));

        if (f == NULL) return f;
        if (c == NULL) {
                /* this is the bogus head of the list */
                f->next_ftran = NULL;
                f->prev_ftran = NULL;
        } else {
                add_to_linked_list((struct list_element *)first_ftran,
                                   (struct list_element *)f);
        }

#if HAVE_MMAP
        f->file_data = NULL;
#endif
        f->owner = (struct conn * const)c;
        f->sock = sock;
        f->state = 0;
        f->local_file = -1;

#if WANT_DCACHE
        f->dir_cache = NULL;
#endif

        f->dir_listing = 0;
        return f;
}

/*
 * destroy_conn():
 *              Destroy a control connection, remove it from the linked
 *              list, and clean up after it.
 */
void destroy_conn(struct conn * const c)
{
        if (c == NULL) return;
        del_fd(c->sock);

        destroy_ftran(c->transfer);
        remove_from_linked_list((struct list_element *)c);
}

/*
 * destroy_ftran():
 *              Destroy a data connection, remove it from the linked list,
 *              and clean up after it.
 *
 *              For some reason, TCP_CORK (Linux 2.2.x-only) doesn't flush
 *              even _after_ the socket is closed, so we zero it just before
 *              closing. We also zero just before sending the last packet,
 *              as it seems to be needed on some systems.
 *
 *              If you wonder why I check for `defined(SOL_TCP)' and don't
 *              provide an alternative, see the comments on init_file_transfer().
 */
void destroy_ftran(struct ftran * const f)
{
        const unsigned int zero = 0;

        if (f == NULL) return;
#if defined(TCP_CORK) && defined(SOL_TCP)
        setsockopt(f->sock, SOL_TCP, TCP_CORK, (void *)&zero, sizeof(zero));
#endif
        del_fd(f->sock);

#if WANT_DCACHE
        if (f->dir_cache) {
                time(&(f->dir_cache->last_used));
                f->dir_cache->use_count--;
                f->dir_cache = NULL;
        } else
#endif
#if HAVE_MMAP
                if (f->file_data) {
                        if (f->dir_listing) {
                                free(f->file_data);
                                f->file_data = NULL;
                        } else {
                                munmap(f->file_data, f->size);
                        }
                }

        if (!f->dir_listing)
#endif
                if (f->local_file != -1) close(f->local_file);

#if !HAVE_MMAP
        if (f->dir_listing) unlink(f->filename);
#endif

        f->owner->transfer = NULL;

#if WANT_DCACHE
        if (f->dir_cache != NULL) f->dir_cache->use_count--;
#endif

        remove_from_linked_list((struct list_element *)f);
}

/*
 * process_all_clients():
 *              Processes all the _control_ connections in active_clients
 *              (normally returned from a select(), there are at max
 *              NUM_AC active connections in the set), sending them
 *              through to the command parser if a command has been
 *              entered.
 */
#if HAVE_POLL
int process_all_clients(const int num_ac)
#else
int process_all_clients(const fd_set * const active_clients, const int num_ac)
#endif
{
        struct conn *c = NULL, *next = first_conn->next_conn;
        int checked_through = 0;

        /* run through the linked list */
        while (next != NULL && checked_through < num_ac) {
                int bytes_avail;

                c = next;
                next = c->next_conn;
#if HAVE_POLL
                if ((fds[c->sock].revents & (POLLIN|POLLERR|POLLHUP|POLLNVAL)) == 0) {
                        continue;
                }
#else
                if (!FD_ISSET(c->sock, active_clients)) {
                        continue;
                }
#endif

                checked_through++;

                bytes_avail = recv(c->sock, c->recv_buf + c->buf_len,
                                   255 - c->buf_len, 0);
                if (bytes_avail <= 0) {
                        /*
                         * select() has already told us there's something about
                         * this socket, so if we get a return value of zero, the
                         * client has closed the socket. If we get a return value
                         * of -1 (error), we close the socket ourselves.
                         *
                         * We do the same for poll(), even though we actually have
                         * bits that tell us what is happening (in case of new 
                         * input AND error/hangup at the same time, we do an
                         * explicit check at the bottom of the loop as well).
                         */
                        destroy_conn(c);
                        continue;
                }

                /* overrun = disconnect */
                if (c->buf_len + bytes_avail > 254) {
                        numeric(c, 503, "Buffer overrun; disconnecting.");
                        destroy_conn(c);
                        continue;
                }

                c->buf_len += bytes_avail;
                parse_command(c);

                if (fds[c->sock].revents & (POLLERR|POLLHUP|POLLNVAL)) {
                        destroy_conn(c);
                }
        }
        return checked_through;
}

/*
 * process_all_sendfiles():
 *              Sends data to all clients that are ready to receive it.
 *              Also checks for data connections that are newly-connected,
 *              and handler xferlog entries for the files that are finished.
 */
#if HAVE_POLL
int process_all_sendfiles(const int num_ac)
#else
int process_all_sendfiles(fd_set * const active_clients, const int num_ac)
#endif
{
        struct ftran *f = NULL, *next = first_ftran->next_ftran;
        int checked_through = 0;
        struct sockaddr tempaddr;
        int tempaddr_len = sizeof(tempaddr);
 
        while (next != NULL && checked_through < num_ac) {
                f = next;
                next = f->next_ftran;

#if HAVE_POLL
                if (fds[f->sock].revents & (POLLHUP|POLLERR|POLLNVAL)) {
                        destroy_ftran(f);
                        continue;
                }
#endif

                /* state = 2: incoming PASV, state >3: send file */
#if HAVE_POLL
                if ((f->state < 2) || (f->state == 3) ||  (fds[f->sock].revents & (POLLIN|POLLOUT)) == 0) {
#else
                if ((f->state < 2) || (f->state == 3) || !FD_ISSET(f->sock, active_clients)) {
#endif
                        continue;
                }

                checked_through++;

#if HAVE_POLL
                /* Nothing is needed for the poll() version? */
#else
                FD_CLR(f->sock, active_clients);
#endif

                if (f->state == 2) {            /* incoming PASV */
                        const unsigned int one = 1;
                        const int tempsock = accept(f->sock, (struct sockaddr *)&tempaddr,
                                                        &tempaddr_len);

                        del_fd(f->sock);

                        if (tempsock == -1) {
                                destroy_ftran(f);
                                continue;
                        }

                        f->sock = tempsock;
                        ioctl(f->sock, FIONBIO, &one);
                        init_file_transfer(f);
#if WANT_UPLOAD
                        if (f->upload) continue;
#endif
                }
                if (f->state < 5) {
                        init_file_transfer(f);
#if WANT_UPLOAD
                        if (f->upload) continue;
#endif
                }

                /* for download, we send the first packets right away */
#if WANT_UPLOAD
                if (f->upload) {
                        if (do_upload(f)) continue;
                } else
#endif
                        if (do_download(f)) continue;

                /* do_{upload,download} returned 0, the transfer is complete */
                numeric(f->owner, 226, "Transfer complete.");
                time(&(f->owner->last_transfer));

#if WANT_XFERLOG
                if (!f->dir_listing) {
                        write_xferlog(f);
                }
#endif

                destroy_ftran(f);
#if WANT_FULLSCREEN
                update_display(first_conn);
#endif
        }

        return checked_through;
}

#if WANT_UPLOAD
int do_upload(struct ftran *f)
{
        char upload_buf[16384];
        int size;
#if WANT_ASCII
        /* keep buffer size small in ascii transfers 
           to prevent process stalling while filtering
           data on slower computers */

        /* 
         * This isn't a big problem, since we won't get
         * packets this big anyway, the biggest I've seen
         * was 12kB on 100mbit (but that was from a Windows
         * machine), so I've reduced the buffer from 64 kB
         * to 16 kB :-) --Steinar
         */
        const int maxlen = (f->ascii_mode == 1) ? 4096 : 16384;
#else
        const int maxlen = 16384;
#endif

        errno = 0;
        size = recv(f->sock, upload_buf, maxlen, 0);
        if (size >= 0) {
                f->pos += size;
        }
#if WANT_ASCII
        if (size > 0 && f->ascii_mode == 1) {
                size = ascii_uploadfilter(upload_buf, size);
        }
#endif
        if (size > 0 && (write(f->local_file, upload_buf, size) == size)) {
                return 1;
        } else if (size == -1) {
                /* don't write xferlog... or? */
                numeric(f->owner, 426, strerror(errno));
                destroy_ftran(f);
                return 1;
        }
        return 0;
} 
#endif

int do_download(struct ftran *f)
{
#if defined(TCP_CORK) && defined(SOL_TCP)
        unsigned int zero = 0;
#endif
        char *sendfrom_buf;
        int bytes_to_send;
        int more_to_send = 0;

#if !HAVE_MMAP
        char buf[MAX_BLOCK_SIZE];
#endif
#if WANT_ASCII
        char buf2[MAX_BLOCK_SIZE * 2];
#endif
        int size;

#if HAVE_LINUX_SENDFILE
        /*
         * We handle the optimal case first, which is sendfile().
         * Here we use a rather simplified sending `algorithm',
         * leaving most of the quirks to the system calls.
         */
        if (sendfile_supported == 1 && f->dir_listing == 0) {
                int err;
                size = f->size - f->pos;

                if (size > f->block_size) size = f->block_size;
                if (size < 0) size = 0;

#ifdef TCP_CORK
                if (size != f->block_size) {
                        setsockopt(f->sock, SOL_TCP, TCP_CORK, (void *)&zero, sizeof(zero));
                }       
#endif

                err = sendfile(f->sock, f->local_file, &f->pos, size);
                return (f->pos < f->size) && (err > -1);
        }
#endif

#if HAVE_MMAP
        size = f->size - f->pos;

        if (size > f->block_size) size = f->block_size;
        if (size < 0) size = 0;

        bytes_to_send = size;
        sendfrom_buf = f->file_data + f->pos;
#else
        bytes_to_send = read(f->local_file, buf, f->block_size);
        sendfrom_buf = buf;
#endif

        if (bytes_to_send == f->block_size) more_to_send = 1;

#if WANT_ASCII
        if (f->ascii_mode == 1) {
                bytes_to_send = ascii_downloadfilter(sendfrom_buf,
                                                     buf2, bytes_to_send);
                sendfrom_buf = buf2;
        }
#endif /* WANT_ASCII */

#if defined(TCP_CORK) && defined(SOL_TCP)
        /* if we believe this is the last packet, unset TCP_CORK */
        if (more_to_send == 0) {
                setsockopt(f->sock, SOL_TCP, TCP_CORK, (void *)&zero, sizeof(zero));
        }
#endif

        size = send(f->sock, sendfrom_buf, bytes_to_send, 0);
        if (size < bytes_to_send) more_to_send = 1;

#if WANT_ASCII
        if (f->ascii_mode == 1 && size < bytes_to_send && size > 0) {
                size = ascii_findlength(sendfrom_buf, size);
        }
#endif

#if HAVE_MMAP
        if (size > 0) f->pos += size;
#endif

        return more_to_send;
}

#if WANT_XFERLOG
void write_xferlog(struct ftran *f)
{
        char temp[256];
        time_t now = time(NULL);
        struct tm *t = localtime(&now);

        if (xferlog == NULL) return;

        strftime(temp, 256, "%a %b %d %H:%M:%S %Y", t);
#if WANT_UPLOAD
        fprintf(xferlog, "%s %u %s %lu %s b _ %c a %s ftp 0 * \n",
#else
        fprintf(xferlog, "%s %u %s %lu %s b _ o a %s ftp 0 *\n",
#endif
                temp, (int)(difftime(now, f->tran_start)),
                inet_ntoa(f->sin.sin_addr), f->size,
                f->filename,
#if WANT_UPLOAD
                (f->upload) ? 'i' : 'o',
#endif
                f->owner->username);
        fflush(xferlog);

#if 0
        /* vim needs this to work properly :-( */
        )
#endif
}
#endif

#if 0
/* Reallocate the buggers constantly */
void screw_clients()
{
        struct conn *c = first_conn;
        int maxloops = MAXCLIENTS;

        while (c && c->next_conn) {
                struct conn *temp = malloc(sizeof(*temp));
                if (!temp) break;
                *temp = *(c->next_conn);
                if (temp->transfer) temp->transfer->owner = temp;
                memset(c->next_conn, 0, sizeof(struct conn));
                free(c->next_conn);
                temp->prev_conn = c;
                c->next_conn = temp;
                c = c->next_conn;
                maxloops--;
                assert(maxloops > 0);
        }
}
#endif

/*
 * main():      Main function. Does the initialization, and contains
 *              the main server loop. Takes no command-line arguments
 *              (see README for justification).
 */
int main(void)
{
        int server_sock;

#if HAVE_POLL
        /* the sets are declared globally if we use poll() */
#else
        fd_set fds, fds_send;
#endif

        /*setlinebuf(stdout);*/
        setvbuf(stdout, (char *)NULL, _IOLBF, 0); 

        signal(SIGPIPE, SIG_IGN);

        printf("BetaFTPD version %s, Copyright (C) 1999-2000 Steinar H. Gunderson\n", VERSION);
        puts("BetaFTPD comes with ABSOLUTELY NO WARRANTY; for details see the file");
        puts("COPYING. This is free software, and you are welcome to redistribute it");
        puts("under certain conditions; again see the file COPYING for details.");
        puts("");

        /* we don't need stdin */
        close(0);

#if HAVE_POLL
        {
                int i;
                for (i = 0; i < FD_MAX; i++) {
                        fds[i].fd = -1;
                        fds[i].events = 0;
                }
        }
#else
        FD_ZERO(&master_fds);
        FD_ZERO(&master_send_fds);
#endif

        server_sock = create_server_socket();

#if WANT_FULLSCREEN
        printf("%cc", (char)27);        /* reset and clear the screen */
#endif

        /* init dummy first connection */
        first_conn = alloc_new_conn(-1);
        first_ftran = alloc_new_ftran(0, NULL);
#if WANT_DCACHE
        first_dcache = alloc_new_dcache();
#endif

#if WANT_XFERLOG
#if WANT_NONROOT
#warning No xferlog support for nonroot yet
#else
        /* open xferlog */
        xferlog = fopen("/var/log/xferlog", "r+");
        if (xferlog == NULL) xferlog = fopen("/usr/adm/xferlog", "r+");

        if (xferlog != NULL) {
                 fseek(xferlog, 0L, SEEK_END);
        }
#endif
#endif

#if WANT_FORK
        switch (fork()) {
        case -1:
                perror("fork()");
                puts("fork() failed, exiting");
                exit(0);
        case 0:
                break;
        default:
                puts("BetaFTPD forked into the background");
                exit(0);
        }
#else
        puts("BetaFTPD active");
#endif

        /* set timeout alarm here (after the fork) */
        alarm(60);
        signal(SIGALRM, handle_alarm);

#if HAVE_LINUX_SENDFILE
        /* check that sendfile() is really implemented (same check as configure does) */
        {
                int out_fd = 1, in_fd = 0;
                off_t offset = 0;
                size_t size = 1024;

                errno = 0;
                sendfile(out_fd, in_fd, &offset, size);
                if (errno == ENOSYS) sendfile_supported = 0;
        }
#endif

        for ( ;; ) {
                int i;
#ifndef HAVE_POLL
                struct timeval timeout;
#endif

                /*screw_clients();       //look for memory errors */

#if WANT_FULLSCREEN
                update_display(first_conn);
#endif

#if HAVE_POLL
                i = poll(fds, highest_fds + 1, 60000);
#if 0
                {
                        int j;
                        for (j=0; j<=highest_fds; j++) {
                                if (fds[j].revents) printf("fds[%d].fd %d, .revents %x\n", j, fds[j].fd, fds[j].revents);
                        }
                }
#endif
#else
                /* reset fds (gets changed by select()) */
                fds = master_fds;
                fds_send = master_send_fds;

                /*
                 * wait up to 60 secs for any activity 
                 */
                timeout.tv_sec = 60;
                timeout.tv_usec = 0;

                i = select(FD_SETSIZE, &fds, &fds_send, NULL, &timeout);
#endif

                if (i == -1) {
                        if (errno == EBADF) {
#if !HAVE_POLL
                                /* don't like this, but we have to */
                                clear_bad_fds(&server_sock);
#endif
                        } else if (errno != EINTR) {
#if HAVE_POLL
                                perror("poll()");
#else
                                perror("select()");
#endif
                                continue;
                        }
                }

#if HAVE_POLL
                /* fix an invalid server socket */
                if (fds[server_sock].revents & POLLERR) {
                        del_fd(server_sock);
                        server_sock = create_server_socket();
                }
#endif

                /* remove any timed out sockets */
                if (time_to_check) {
                        time_out_sockets();
#if WANT_DCACHE
                        time_out_dcache();
#endif
                        time_to_check = 0;
                }

                if (i <= 0) continue;

#if HAVE_POLL
                i -= process_all_sendfiles(i);
                process_all_clients(i);
#else
                /* sends are given highest `priority' */
                i -= process_all_sendfiles(&fds_send, i);

                /* incoming PASV connections and uploads */
                i -= process_all_sendfiles(&fds, i);

                /*
                 * check the incoming PASV connections first, so
                 * process_all_clients() won't be confused.
                 */ 
                process_all_clients(&fds, i);
#endif

#if HAVE_POLL
                if (fds[server_sock].revents & POLLIN) {
#else
                if (FD_ISSET(server_sock, &fds)) {
#endif
                        accept_new_client(&server_sock);
                        i--;
                }
        }
}

/*
 * accept_new_client():
 *              Open a socket for the new client, say hello and put it in
 *              among the others.
 */
void accept_new_client(int * const server_sock)
{
        struct sockaddr_in tempaddr;
        int tempaddr_len = sizeof(tempaddr);
        const int tempsock = accept(*server_sock, (struct sockaddr *)&tempaddr, &tempaddr_len);

        static int num_err = 0;

        if (tempsock < 0) {
#ifndef WANT_FORK
                perror("accept()");
#endif
                close(tempsock);
                if ((errno == EBADF || errno == EPIPE) && ++num_err >= 3) {
                        del_fd(*server_sock);
                        *server_sock = create_server_socket();
                }
        } else {
                struct conn * const c = alloc_new_conn(tempsock);
                num_err = 0;
                if (c != NULL) {
                        numeric(c, 220, "BetaFTPD " VERSION " ready.");
#if WANT_STAT
                        memcpy(&(c->addr), &tempaddr, sizeof(struct sockaddr));
#endif
                }
        }
}

/*
 * time_out_sockets():
 *              Times out any socket that has not had any transfer
 *              in the last 15 minutes (delay not customizable by FTP
 *              user -- you must change it in ftpd.h).
 *
 *              Note that RFC959 explicitly states that there are no
 *              `spontaneous' error replies, yet we have to do it to
 *              get the message through at all.
 *
 *              If we check this list for every accept() call, it's
 *              actually eating a lot of CPU time, so we only check
 *              it every minute. We used to do a time() call here,
 *              but we've changed to do use an alarm() call and set
 *              the time_to_check_flag in the SIGALRM handler.
 */
RETSIGTYPE handle_alarm(int signum)
{
        time_to_check = 1;
        alarm(60);

        /* for libc5 */
        signal(SIGALRM, handle_alarm);
}

void time_out_sockets()
{
        struct conn *c = NULL, *next = first_conn->next_conn;
        time_t now = time(NULL);  

        /* run through the linked list */
        while (next != NULL) {
                c = next;
                next = c->next_conn;

                if ((c->transfer == NULL || c->transfer->state != 5) &&
                    (now - c->last_transfer > TIMEOUT_SECS)) {
                        /* RFC violation? */
                        numeric(c, 421, "Timeout (%u minutes): Closing control connection.", TIMEOUT_SECS/60);
                        destroy_conn(c);
                }
        }
}

/*
 * remove_bytes():
 *              Remove some bytes from the incoming buffer. This gives
 *              room for new data on the control connection, and should
 *              be called when the code has finished using the data.
 *              (This is done automatically for all commands, so you
 *              normally need not worry about it.)
 */
void remove_bytes(struct conn * const c, const int num)
{
        if (c->buf_len <= num) {
                c->buf_len = 0;
        } else {
                c->buf_len -= num;
                memmove(c->recv_buf, c->recv_buf + num, c->buf_len);
        }
}

/*
 * numeric():   Sends a numeric FTP reply to the client. Note that
 *              you can use this command much the same way as you
 *              would use a printf() (with all the normal %s, %d,
 *              etc.), since it actually uses printf() internally.
 */
void numeric(struct conn * const c, const int numeric, const char * const format, ...)
{
        char buf[256], fmt[256];
        va_list args;
        int i, err;

        snprintf(fmt, 256, "%03u %s\r\n", numeric, format);

        va_start(args, format);
        i = vsnprintf(buf, 256, fmt, args);
        va_end(args);

        err = send(c->sock, buf, i, 0);
        if (err == -1 && errno == EPIPE) {
                destroy_conn(c);
        }
}

/*
 * init_file_transfer():
 *              Initiate a data connection for sending. This does not open
 *              any files etc., just does whatever is needed for the socket,
 *              if needed. It does, however, send the 150 reply to the client,
 *              and mmap()s if needed.
 *
 *              Linux systems (others?) define SOL_TCP right away, which saves us
 *              some grief and code size. Perhaps using getprotoent() is the `right'
 *              way, but it's bigger :-) (Optionally, we could figure it out at
 *              configure time, of course...)
 *
 *              For optimal speed, we use the Linux 2.2.x-only TCP_CORK flag if
 *              possible. Note that this is only defined in the first `arm' --
 *              we silently assume that Linux is the only OS supporting this
 *              flag. This might be an over-generalization, but I it looks like
 *              we'll have to depend on it other places as well, so we might
 *              just as well be evil here.
 */
void init_file_transfer(struct ftran * const f)
{
        struct linger ling;
        struct conn * const c = f->owner;
        const int mode = IPTOS_THROUGHPUT, zero = 0, one = 1;
        struct stat buf;
        int events;

#ifdef SOL_TCP
        /* we want max throughput */
        setsockopt(f->sock, SOL_IP, IP_TOS, (void *)&mode, sizeof(mode));
        setsockopt(f->sock, SOL_TCP, TCP_NODELAY, (void *)&zero, sizeof(zero));
#ifdef TCP_CORK
        setsockopt(f->sock, SOL_TCP, TCP_CORK, (void *)&one, sizeof(one));
#endif
#else
        /* should these pointers be freed afterwards? */
        {
                getprotoent();  /* legal? */
                {
                        const struct protoent * const pe_ip  = getprotobyname("ip");
                        const struct protoent * const pe_tcp = getprotobyname("tcp");
                        setsockopt(f->sock, pe_ip->p_proto, IP_TOS, (void *)&mode, sizeof(mode));
                        setsockopt(f->sock, pe_tcp->p_proto, TCP_NODELAY, (void *)&zero, sizeof(zero));
                }
                endprotoent();
        }
#endif

        if (f->dir_listing) {
                f->block_size = MAX_BLOCK_SIZE;
        } else {
#if WANT_ASCII
                f->ascii_mode = f->owner->ascii_mode;
#endif

                /* find the preferred block size */
                f->block_size = MAX_BLOCK_SIZE;
                if (fstat(f->local_file, &buf) != -1 &&
                    buf.st_blksize < MAX_BLOCK_SIZE) {
                        f->block_size = buf.st_blksize;
                }
        }

        f->state = 5;

        events = POLLOUT;
#if WANT_UPLOAD
        if (f->upload) {
                events = POLLIN;
        }
#endif /* WANT_UPLOAD */

        TRAP_ERROR(add_fd(f->sock, events), 500, return);

        ling.l_onoff = 0;
        ling.l_linger = 0;
        setsockopt(f->sock, SOL_SOCKET, SO_LINGER, &ling, sizeof(ling));

#if !HAVE_POLL && WANT_UPLOAD
        /*
         * if we let an upload socket stay in master_send_fds, we would
         * get data that would fool us into closing the socket... (sigh)
         */
        if (f->upload) {
                FD_CLR(f->sock, &master_send_fds);
                FD_SET(f->sock, &master_fds);
        }
#endif

        time(&(f->owner->last_transfer));
        
        if (f->dir_listing) {
                /* include size? */
                numeric(f->owner, 150, "Opening ASCII mode data connection for directory listing.");
        } else {
                /*
                 * slightly kludged -- perhaps we should kill the second arm,
                 * at the expense of code size? Or perhaps we could collapse
                 * the two possible replies into one?
                 */
#if WANT_ASCII
                if (f->ascii_mode
#if WANT_UPLOAD
                        || f->upload
#endif /* WANT_UPLOAD */
                ) {
                        numeric(f->owner, 150, "Opening %s mode data connection for '%s'",
                                (f->ascii_mode) ? "ASCII" : "BINARY", f->filename);
                } else {
                        numeric(f->owner, 150, "Opening %s mode data connection for '%s' (%u bytes)",
                                (f->ascii_mode) ? "ASCII" : "BINARY", f->filename,
                                f->size); 
                }
#else /* !WANT_ASCII */
#if WANT_UPLOAD
                if (f->upload) {
                        numeric(f->owner, 150, "Opening BINARY mode data connection for '%s'", f->filename);
                } else
#endif /* WANT_UPLOAD */
                        numeric(f->owner, 150, "Opening BINARY mode data connection for '%s' (%u bytes)", f->filename, f->size);
#endif /* !WANT_ASCII */
        }

        /*
         * This section _could_ in theory be more optimized, but it's
         * much easier this way, and hopefully, the compiler will be
         * intelligent enough to optimize most of this away. The idea
         * is, some modes _require_ use of mmap (or not). The preferred
         * thing is using mmap() when we don't have sendfile(), and not
         * using mmap() when we have sendfile().
         */
#if HAVE_MMAP
        if (f->dir_listing == 0) {
#if HAVE_LINUX_SENDFILE
                int do_mmap = (sendfile_supported) ? 0 : 1;
#else
                int do_mmap = 1;
#endif
#if WANT_ASCII
                if (f->ascii_mode == 1) do_mmap = 1;
#endif
#if WANT_UPLOAD
                if (f->upload == 1) do_mmap = 0;
#endif
 
                if (do_mmap == 1) {
                        f->file_data = mmap(NULL, f->size, PROT_READ, MAP_SHARED, f->local_file, 0);
                        if (f->file_data == MAP_FAILED) f->file_data = NULL;
                } else {
                        f->file_data = NULL;
                }
                f->pos = f->owner->rest_pos;
        }
#else /* !HAVE_MMAP */
        lseek(f->local_file, f->owner->rest_pos, SEEK_SET);
#endif
}

/*
 * create_server_socket():
 *              Create and bind a server socket, that we can use to
 *              listen to new clients on.
 */
int create_server_socket()
{
        int server_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        const unsigned int one = 1;
        struct sockaddr_in addr;
        int err;
        
        /*
         * In the `perfect' world, if an address was in use, we could
         * just wait for the kernel to clear everything up, and everybody
         * would be happy. But when you just found out your server socket
         * was invalid, it has to be `re-made', and 3000 users are trying
         * to access your fileserver, I think it's nice that it comes
         * up right away... hence this option.
         */
        setsockopt(server_sock, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
        ioctl(server_sock, FIONBIO, &one);      /* just in case */

        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = INADDR_ANY;
        addr.sin_port = htons(FTP_PORT);

        do {
                err = bind(server_sock, (struct sockaddr *)&addr, sizeof(struct sockaddr));

                if (err == -1) {
                        perror("bind()");
                
                        /* try to recover from recoverable errors... */
                        if (errno == ENOMEM || errno == EADDRINUSE) {
                                puts("Waiting 1 sec before trying again...");
                                sleep(1);
                        } else {
                                puts("Giving up.");
                                exit(1); 
                        }
                }
        } while (err == -1);

        listen(server_sock, 20);

        err = add_fd(server_sock, POLLIN);
        if (err) {
                perror("add_fd");
                return -1;
        }

        return server_sock;
}

#if !HAVE_POLL
/*
 * clear_bad_fds():
 *              Try to find invalid socket descriptors, and clean them.
 *              The methods used are rather UGLY, but I can't think of
 *              any good way of checking e.g. server_sock without
 *              doing anything to it :-(
 *
 *              poll() is able to do this in a much cleaner way, which 
 *              we use if we use poll(). That checking isn't done here,
 *              though.
 */
void clear_bad_fds(int * const server_sock)
{
        {
                fd_set fds;
                struct timeval tv = { 0, 0 };

                FD_ZERO(&fds);
                FD_SET(*server_sock, &fds); 
                if (select(*server_sock, &fds, NULL, NULL, &tv) == -1) {
                        FD_CLR(*server_sock, &master_fds);
                        close(*server_sock);
                        *server_sock = create_server_socket();
                }
        }

        /* could do this (conn, ftran) in any order */
        {
                struct conn *c = NULL, *next = first_conn->next_conn;
        
                /* run through the linked list */
                while (next != NULL) {
                        char buf[1];

                        c = next;
                        next = c->next_conn;

                        if (read(c->sock, &buf, 0) == -1 &&
                            errno == EBADF) {
                                destroy_conn(c);
                        }
                }
        }

        {
                struct ftran *f = NULL, *next = first_ftran->next_ftran;
        
                while (next != NULL) {
                        char buf[1];

                        f = next;
                        next = f->next_ftran;

                        if (read(f->sock, &buf, 0) == -1 &&
                            errno == EBADF) {
                                destroy_ftran(f);
                        }
                }
        }       
}
#endif

#if WANT_MESSAGE
/*
 * dump_file(): Dumps a file on the control connection. Used for
 *              welcome messages and the likes. Note that outbuf
 *              is so big, to prevent any crashing from users creating
 *              weird .message files (like 1024 LFs)... The size of
 *              the file is limited to 1024 bytes (by truncation).
 */
void dump_file(struct conn * const c, const int num, const char * const filename)
{
        char buf[1024], outbuf[5121];
        char *ptr = outbuf + 4;
        int i, j = -1;

        const int dumpfile = open(filename, O_RDONLY);
        if (dumpfile == -1) return;

        i = read(dumpfile, buf, 1024);
        if (i <= 0) {
                close(dumpfile);
                return;
        }

        sprintf(outbuf, "%03u-", num);
        while (++j < i) {
                *ptr++ = buf[j];
                if (buf[j] == '\n') {
                        sprintf(ptr, "%03u-", num);
                        ptr += 4;
                }
        }
        *ptr++ = '\n';

        send(c->sock, outbuf, ptr - outbuf, 0);
        close(dumpfile);
}


/*
 * list_readme():
 *              Lists all README file in the current (ie. OS current)
 *              directory, in a 250- message.
 */
void list_readmes(struct conn * const c)
{
        glob_t pglob;
        const time_t now = time(NULL);
        int i;

        if (glob("README*", 0, NULL, &pglob) != 0) return;

        for (i = 0; i < pglob.gl_pathc; i++) {
                struct stat buf;
                char str[256];
                char *tm;

                if (stat(pglob.gl_pathv[i], &buf) == -1) continue;

                /* remove trailing LF */
                tm = ctime(&buf.st_mtime);
                tm[strlen(tm) - 1] = 0;

                snprintf(str, 256, "250-Please read the file %s\r\n"
                                   "250-\tIt was last modified %s - %ld days ago\r\n",
                        pglob.gl_pathv[i], tm,
                        (now - buf.st_mtime) / 86400);
                send(c->sock, str, strlen(str), 0);
        }
        globfree(&pglob);
}
#endif