/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 1983, 1991, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <sys/filio.h>
#include <sys/ioccom.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <sys/ucred.h>
#include <sys/uio.h>
#include <sys/utsname.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pwd.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <syslog.h>
#include <unistd.h>

#include "inetd.h"

static void     chargen_dg(int, struct servtab *);
static void     chargen_stream(int, struct servtab *);
static void     daytime_dg(int, struct servtab *);
static void     daytime_stream(int, struct servtab *);
static void     discard_dg(int, struct servtab *);
static void     discard_stream(int, struct servtab *);
static void     echo_dg(int, struct servtab *);
static void     echo_stream(int, struct servtab *);
static int      get_line(int, char *, int);
static void     iderror(int, int, int, const char *);
static void     ident_stream(int, struct servtab *);
static void     initring(void);
static uint32_t machtime(void);
static void     machtime_dg(int, struct servtab *);
static void     machtime_stream(int, struct servtab *);

static char ring[128];
static char *endring;

struct biltin biltins[] = {
        /* Echo received data */
        { "echo",       SOCK_STREAM,    1, -1,  echo_stream },
        { "echo",       SOCK_DGRAM,     0, 1,   echo_dg },

        /* Internet /dev/null */
        { "discard",    SOCK_STREAM,    1, -1,  discard_stream },
        { "discard",    SOCK_DGRAM,     0, 1,   discard_dg },

        /* Return 32 bit time since 1900 */
        { "time",       SOCK_STREAM,    0, -1,  machtime_stream },
        { "time",       SOCK_DGRAM,     0, 1,   machtime_dg },

        /* Return human-readable time */
        { "daytime",    SOCK_STREAM,    0, -1,  daytime_stream },
        { "daytime",    SOCK_DGRAM,     0, 1,   daytime_dg },

        /* Familiar character generator */
        { "chargen",    SOCK_STREAM,    1, -1,  chargen_stream },
        { "chargen",    SOCK_DGRAM,     0, 1,   chargen_dg },

        { "tcpmux",     SOCK_STREAM,    1, -1,  (bi_fn_t *)tcpmux },

        { "auth",       SOCK_STREAM,    1, -1,  ident_stream },

        { NULL,         0,              0, 0,   NULL }
};

/*
 * RFC864 Character Generator Protocol. Generates character data without
 * any regard for input.
 */

static void
initring(void)
{
        int i;

        endring = ring;

        for (i = 0; i <= 128; ++i)
                if (isprint(i))
                        *endring++ = i;
}

/* Character generator
 * The RFC says that we should send back a random number of
 * characters chosen from the range 0 to 512. We send LINESIZ+2.
 */
/* ARGSUSED */
static void
chargen_dg(int s, struct servtab *sep)
{
        struct sockaddr_storage ss;
        static char *rs;
        int len;
        socklen_t size;
        char text[LINESIZ+2];

        if (endring == NULL)
                initring();
        if (rs == NULL)
                rs = ring;

        size = sizeof(ss);
        if (recvfrom(s, text, sizeof(text), 0,
                     (struct sockaddr *)&ss, &size) < 0)
                return;

        if (check_loop((struct sockaddr *)&ss, sep))
                return;

        if ((len = endring - rs) >= LINESIZ)
                memmove(text, rs, LINESIZ);
        else {
                memmove(text, rs, len);
                memmove(text + len, ring, LINESIZ - len);
        }
        if (++rs == endring)
                rs = ring;
        text[LINESIZ] = '\r';
        text[LINESIZ + 1] = '\n';
        (void) sendto(s, text, sizeof(text), 0, (struct sockaddr *)&ss, size);
}

/* Character generator */
/* ARGSUSED */
static void
chargen_stream(int s, struct servtab *sep)
{
        int len;
        char *rs, text[LINESIZ+2];

        inetd_setproctitle(sep->se_service, s);

        if (!endring)
                initring();

        text[LINESIZ] = '\r';
        text[LINESIZ + 1] = '\n';
        for (rs = ring;;) {
                if ((len = endring - rs) >= LINESIZ)
                        memmove(text, rs, LINESIZ);
                else {
                        memmove(text, rs, len);
                        memmove(text + len, ring, LINESIZ - len);
                }
                if (++rs == endring)
                        rs = ring;
                if (write(s, text, sizeof(text)) != sizeof(text))
                        break;
        }
        exit(0);
}

/*
 * RFC867 Daytime Protocol. Sends the current date and time as an ascii
 * character string without any regard for input.
 */

/* Return human-readable time of day */
/* ARGSUSED */
static void
daytime_dg(int s, struct servtab *sep)
{
        char buffer[256];
        time_t now;
        struct sockaddr_storage ss;
        socklen_t size;

        now = time((time_t *) 0);

        size = sizeof(ss);
        if (recvfrom(s, buffer, sizeof(buffer), 0,
                     (struct sockaddr *)&ss, &size) < 0)
                return;

        if (check_loop((struct sockaddr *)&ss, sep))
                return;

        (void) sprintf(buffer, "%.24s\r\n", ctime(&now));
        (void) sendto(s, buffer, strlen(buffer), 0,
                      (struct sockaddr *)&ss, size);
}

/* Return human-readable time of day */
/* ARGSUSED */
static void
daytime_stream(int s, struct servtab *sep __unused)
{
        char buffer[256];
        time_t now;

        now = time((time_t *) 0);

        (void) sprintf(buffer, "%.24s\r\n", ctime(&now));
        (void) send(s, buffer, strlen(buffer), MSG_EOF);
}

/*
 * RFC863 Discard Protocol. Any data received is thrown away and no response
 * is sent.
 */

/* Discard service -- ignore data */
/* ARGSUSED */
static void
discard_dg(int s, struct servtab *sep __unused)
{
        char buffer[BUFSIZE];

        (void) read(s, buffer, sizeof(buffer));
}

/* Discard service -- ignore data */
/* ARGSUSED */
static void
discard_stream(int s, struct servtab *sep)
{
        int ret;
        char buffer[BUFSIZE];

        inetd_setproctitle(sep->se_service, s);
        while (1) {
                while ((ret = read(s, buffer, sizeof(buffer))) > 0)
                        ;
                if (ret == 0 || errno != EINTR)
                        break;
        }
        exit(0);
}

/*
 * RFC862 Echo Protocol. Any data received is sent back to the sender as
 * received.
 */

/* Echo service -- echo data back */
/* ARGSUSED */
static void
echo_dg(int s, struct servtab *sep)
{
        char buffer[65536]; /* Should be sizeof(max datagram). */
        int i;
        socklen_t size;
        struct sockaddr_storage ss;

        size = sizeof(ss);
        if ((i = recvfrom(s, buffer, sizeof(buffer), 0,
                          (struct sockaddr *)&ss, &size)) < 0)
                return;

        if (check_loop((struct sockaddr *)&ss, sep))
                return;

        (void) sendto(s, buffer, i, 0, (struct sockaddr *)&ss, size);
}

/* Echo service -- echo data back */
/* ARGSUSED */
static void
echo_stream(int s, struct servtab *sep)
{
        char buffer[BUFSIZE];
        int i;

        inetd_setproctitle(sep->se_service, s);
        while ((i = read(s, buffer, sizeof(buffer))) > 0 &&
            write(s, buffer, i) > 0)
                ;
        exit(0);
}

/*
 * RFC1413 Identification Protocol. Given a TCP port number pair, return a
 * character string which identifies the owner of that connection on the
 * server's system. Extended to allow for ~/.fakeid support and ~/.noident
 * support.
 */

/* RFC 1413 says the following are the only errors you can return. */
#define ID_INVALID      "INVALID-PORT"  /* Port number improperly specified. */
#define ID_NOUSER       "NO-USER"       /* Port not in use/not identifiable. */
#define ID_HIDDEN       "HIDDEN-USER"   /* Hidden at user's request. */
#define ID_UNKNOWN      "UNKNOWN-ERROR" /* Everything else. */

/* Generic ident_stream error-sending func */
/* ARGSUSED */
static void
iderror(int lport, int fport, int s, const char *er)
{
        char *p;

        asprintf(&p, "%d , %d : ERROR : %s\r\n", lport, fport, er);
        if (p == NULL) {
                syslog(LOG_ERR, "asprintf: %m");
                exit(EX_OSERR);
        }
        send(s, p, strlen(p), MSG_EOF);
        free(p);

        exit(0);
}

/* Ident service (AKA "auth") */
/* ARGSUSED */
static void
ident_stream(int s, struct servtab *sep)
{
        struct utsname un;
        struct stat sb;
        struct sockaddr_in sin4[2];
#ifdef INET6
        struct sockaddr_in6 sin6[2];
#endif
        struct sockaddr_storage ss[2];
        struct xucred uc;
        struct timeval tv = {
                10,
                0
        }, to;
        struct passwd *pw = NULL;
        fd_set fdset;
        char buf[BUFSIZE], *p, **av, *osname = NULL, e;
        char idbuf[MAXLOGNAME] = ""; /* Big enough to hold uid in decimal. */
        socklen_t socklen;
        ssize_t ssize;
        size_t size, bufsiz;
        int c, fflag = 0, nflag = 0, rflag = 0, argc = 0;
        int gflag = 0, iflag = 0, Fflag = 0, getcredfail = 0, onreadlen;
        u_short lport, fport;

        inetd_setproctitle(sep->se_service, s);
        /*
         * Reset getopt() since we are a fork() but not an exec() from
         * a parent which used getopt() already.
         */
        optind = 1;
        optreset = 1;
        /*
         * Take the internal argument vector and count it out to make an
         * argument count for getopt. This can be used for any internal
         * service to read arguments and use getopt() easily.
         */
        for (av = sep->se_argv; *av; av++)
                argc++;
        if (argc) {
                int sec, usec;
                size_t i;
                u_int32_t rnd32;

                while ((c = getopt(argc, sep->se_argv, "d:fFgino:rt:")) != -1)
                        switch (c) {
                        case 'd':
                                if (!gflag)
                                        strlcpy(idbuf, optarg, sizeof(idbuf));
                                break;
                        case 'f':
                                fflag = 1;
                                break;
                        case 'F':
                                fflag = 1;
                                Fflag=1;
                                break;
                        case 'g':
                                gflag = 1;
                                rnd32 = 0;      /* Shush, compiler. */
                                /*
                                 * The number of bits in "rnd32" divided
                                 * by the number of bits needed per iteration
                                 * gives a more optimal way to reload the
                                 * random number only when necessary.
                                 *
                                 * 32 bits from arc4random corresponds to
                                 * about 6 base-36 digits, so we reseed every 6.
                                 */
                                for (i = 0; i < sizeof(idbuf) - 1; i++) {
                                        static const char *const base36 =
                                            "0123456789"
                                            "abcdefghijklmnopqrstuvwxyz";
                                        if (i % 6 == 0)
                                                rnd32 = arc4random();
                                        idbuf[i] = base36[rnd32 % 36];
                                        rnd32 /= 36;
                                }
                                idbuf[i] = '\0';
                                break;
                        case 'i':
                                iflag = 1;
                                break;
                        case 'n':
                                nflag = 1;
                                break;
                        case 'o':
                                osname = optarg;
                                break;
                        case 'r':
                                rflag = 1;
                                break;
                        case 't':
                                switch (sscanf(optarg, "%d.%d", &sec, &usec)) {
                                case 2:
                                        tv.tv_usec = usec;
                                        /* FALLTHROUGH */
                                case 1:
                                        tv.tv_sec = sec;
                                        break;
                                default:
                                        if (debug)
                                                warnx("bad -t argument");
                                        break;
                                }
                                break;
                        default:
                                break;
                        }
        }
        if (osname == NULL) {
                if (uname(&un) == -1)
                        iderror(0, 0, s, ID_UNKNOWN);
                osname = un.sysname;
        }

        /*
         * We're going to prepare for and execute reception of a
         * packet of data from the user. The data is in the format
         * "local_port , foreign_port\r\n" (with local being the
         * server's port and foreign being the client's.)
         */
        gettimeofday(&to, NULL);
        to.tv_sec += tv.tv_sec;
        to.tv_usec += tv.tv_usec;
        if (to.tv_usec >= 1000000) {
                to.tv_usec -= 1000000;
                to.tv_sec++;
        }

        size = 0;
        bufsiz = sizeof(buf) - 1;
        FD_ZERO(&fdset);
        while (bufsiz > 0) {
                gettimeofday(&tv, NULL);
                tv.tv_sec = to.tv_sec - tv.tv_sec;
                tv.tv_usec = to.tv_usec - tv.tv_usec;
                if (tv.tv_usec < 0) {
                        tv.tv_usec += 1000000;
                        tv.tv_sec--;
                }
                if (tv.tv_sec < 0)
                        break;
                FD_SET(s, &fdset);
                if (select(s + 1, &fdset, NULL, NULL, &tv) == -1)
                        iderror(0, 0, s, ID_UNKNOWN);
                if (ioctl(s, FIONREAD, &onreadlen) == -1)
                        iderror(0, 0, s, ID_UNKNOWN);
                if ((size_t)onreadlen > bufsiz)
                        onreadlen = bufsiz;
                ssize = read(s, &buf[size], (size_t)onreadlen);
                if (ssize == -1)
                        iderror(0, 0, s, ID_UNKNOWN);
                else if (ssize == 0)
                        break;
                bufsiz -= ssize;
                size += ssize;
                if (memchr(&buf[size - ssize], '\n', ssize) != NULL)
                        break;
        }
        buf[size] = '\0';
        /* Read two characters, and check for a delimiting character */
        if (sscanf(buf, "%hu , %hu%c", &lport, &fport, &e) != 3 || isdigit(e))
                iderror(0, 0, s, ID_INVALID);

        /* Send garbage? */
        if (gflag)
                goto printit;

        /*
         * If not "real" (-r), send a HIDDEN-USER error for everything.
         * If -d is used to set a fallback username, this is used to
         * override it, and the fallback is returned instead.
         */
        if (!rflag) {
                if (*idbuf == '\0')
                        iderror(lport, fport, s, ID_HIDDEN);
                goto printit;
        }

        /*
         * We take the input and construct an array of two sockaddr_ins
         * which contain the local address information and foreign
         * address information, respectively, used to look up the
         * credentials for the socket (which are returned by the
         * sysctl "net.inet.tcp.getcred" when we call it.)
         */
        socklen = sizeof(ss[0]);
        if (getsockname(s, (struct sockaddr *)&ss[0], &socklen) == -1)
                iderror(lport, fport, s, ID_UNKNOWN);
        socklen = sizeof(ss[1]);
        if (getpeername(s, (struct sockaddr *)&ss[1], &socklen) == -1)
                iderror(lport, fport, s, ID_UNKNOWN);
        if (ss[0].ss_family != ss[1].ss_family)
                iderror(lport, fport, s, ID_UNKNOWN);
        size = sizeof(uc);
        switch (ss[0].ss_family) {
        case AF_INET:
                sin4[0] = *(struct sockaddr_in *)&ss[0];
                sin4[0].sin_port = htons(lport);
                sin4[1] = *(struct sockaddr_in *)&ss[1];
                sin4[1].sin_port = htons(fport);
                if (sysctlbyname("net.inet.tcp.getcred", &uc, &size, sin4,
                                 sizeof(sin4)) == -1)
                        getcredfail = errno;
                break;
#ifdef INET6
        case AF_INET6:
                sin6[0] = *(struct sockaddr_in6 *)&ss[0];
                sin6[0].sin6_port = htons(lport);
                sin6[1] = *(struct sockaddr_in6 *)&ss[1];
                sin6[1].sin6_port = htons(fport);
                if (sysctlbyname("net.inet6.tcp6.getcred", &uc, &size, sin6,
                                 sizeof(sin6)) == -1)
                        getcredfail = errno;
                break;
#endif
        default: /* should not reach here */
                getcredfail = EAFNOSUPPORT;
                break;
        }
        if (getcredfail != 0 || uc.cr_version != XUCRED_VERSION) {
                if (*idbuf == '\0')
                        iderror(lport, fport, s,
                            getcredfail == ENOENT ? ID_NOUSER : ID_UNKNOWN);
                goto printit;
        }

        /* Look up the pw to get the username and home directory*/
        errno = 0;
        pw = getpwuid(uc.cr_uid);
        if (pw == NULL)
                iderror(lport, fport, s, errno == 0 ? ID_NOUSER : ID_UNKNOWN);

        if (iflag)
                snprintf(idbuf, sizeof(idbuf), "%u", (unsigned)pw->pw_uid);
        else
                strlcpy(idbuf, pw->pw_name, sizeof(idbuf));

        /*
         * If enabled, we check for a file named ".noident" in the user's
         * home directory. If found, we return HIDDEN-USER.
         */
        if (nflag) {
                if (asprintf(&p, "%s/.noident", pw->pw_dir) == -1)
                        iderror(lport, fport, s, ID_UNKNOWN);
                if (lstat(p, &sb) == 0) {
                        free(p);
                        iderror(lport, fport, s, ID_HIDDEN);
                }
                free(p);
        }

        /*
         * Here, if enabled, we read a user's ".fakeid" file in their
         * home directory. It consists of a line containing the name
         * they want.
         */
        if (fflag) {
                int fakeid_fd;

                /*
                 * Here we set ourself to effectively be the user, so we don't
                 * open any files we have no permission to open, especially
                 * symbolic links to sensitive root-owned files or devices.
                 */
                if (initgroups(pw->pw_name, pw->pw_gid) == -1)
                        iderror(lport, fport, s, ID_UNKNOWN);
                if (setegid(pw->pw_gid) == -1)
                        iderror(lport, fport, s, ID_UNKNOWN);
                if (seteuid(pw->pw_uid) == -1)
                        iderror(lport, fport, s, ID_UNKNOWN);
                /*
                 * We can't stat() here since that would be a race
                 * condition.
                 * Therefore, we open the file we have permissions to open
                 * and if it's not a regular file, we close it and end up
                 * returning the user's real username.
                 */
                if (asprintf(&p, "%s/.fakeid", pw->pw_dir) == -1)
                        iderror(lport, fport, s, ID_UNKNOWN);
                fakeid_fd = open(p, O_RDONLY | O_NONBLOCK);
                free(p);
                if (fakeid_fd == -1 || fstat(fakeid_fd, &sb) == -1 ||
                    !S_ISREG(sb.st_mode))
                        goto fakeid_fail;

                if ((ssize = read(fakeid_fd, buf, sizeof(buf) - 1)) < 0)
                        goto fakeid_fail;
                buf[ssize] = '\0';

                /*
                 * Usually, the file will have the desired identity
                 * in the form "identity\n". Allow for leading white
                 * space and trailing white space/end of line.
                 */
                p = buf;
                p += strspn(p, " \t");
                p[strcspn(p, " \t\r\n")] = '\0';
                if (strlen(p) > MAXLOGNAME - 1) /* Too long (including nul)? */
                        p[MAXLOGNAME - 1] = '\0';

                /*
                 * If the name is a zero-length string or matches it
                 * the id or name of another user (unless permitted by -F)
                 * then it is invalid.
                 */
                if (*p == '\0')
                        goto fakeid_fail;
                if (!Fflag) {
                        if (iflag) {
                                const char *errstr;
                                uid_t uid;

                                uid = strtonum(p, 0, UID_MAX, &errstr);
                                if (errstr != NULL)
                                        goto fakeid_fail;

                                if (getpwuid(uid) != NULL)
                                        goto fakeid_fail;
                        } else {
                                if (getpwnam(p) != NULL)
                                        goto fakeid_fail;
                        }
                }

                strlcpy(idbuf, p, sizeof(idbuf));

fakeid_fail:
                if (fakeid_fd != -1)
                        close(fakeid_fd);
        }

printit:
        /* Finally, we make and send the reply. */
        if (asprintf(&p, "%d , %d : USERID : %s : %s\r\n", lport, fport, osname,
            idbuf) == -1) {
                syslog(LOG_ERR, "asprintf: %m");
                exit(EX_OSERR);
        }
        send(s, p, strlen(p), MSG_EOF);
        free(p);
        
        exit(0);
}

/*
 * RFC738/868 Time Server.
 * Return a machine readable date and time, in the form of the
 * number of seconds since midnight, Jan 1, 1900.  Since gettimeofday
 * returns the number of seconds since midnight, Jan 1, 1970,
 * we must add 2208988800 seconds to this figure to make up for
 * some seventy years Bell Labs was asleep.
 */

static uint32_t
machtime(void)
{

#define OFFSET ((uint32_t)25567 * 24*60*60)
        return (htonl((uint32_t)(time(NULL) + OFFSET)));
#undef OFFSET
}

/* ARGSUSED */
static void
machtime_dg(int s, struct servtab *sep)
{
        uint32_t result;
        struct sockaddr_storage ss;
        socklen_t size;

        size = sizeof(ss);
        if (recvfrom(s, (char *)&result, sizeof(result), 0,
                     (struct sockaddr *)&ss, &size) < 0)
                return;

        if (check_loop((struct sockaddr *)&ss, sep))
                return;

        result = machtime();
        (void) sendto(s, (char *) &result, sizeof(result), 0,
                      (struct sockaddr *)&ss, size);
}

/* ARGSUSED */
static void
machtime_stream(int s, struct servtab *sep __unused)
{
        uint32_t result;

        result = machtime();
        (void) send(s, (char *) &result, sizeof(result), MSG_EOF);
}

/*
 * RFC1078 TCP Port Service Multiplexer (TCPMUX). Service connections to
 * services based on the service name sent.
 *
 *  Based on TCPMUX.C by Mark K. Lottor November 1988
 *  sri-nic::ps:<mkl>tcpmux.c
 */

#define MAX_SERV_LEN    (256+2)         /* 2 bytes for \r\n */
#define strwrite(fd, buf)       (void) write(fd, buf, sizeof(buf)-1)

static int              /* # of characters up to \r,\n or \0 */
get_line(int fd, char *buf, int len)
{
        int count = 0, n;
        struct sigaction sa;

        sa.sa_flags = 0;
        sigemptyset(&sa.sa_mask);
        sa.sa_handler = SIG_DFL;
        sigaction(SIGALRM, &sa, (struct sigaction *)0);
        do {
                alarm(10);
                n = read(fd, buf, len-count);
                alarm(0);
                if (n == 0)
                        return (count);
                if (n < 0)
                        return (-1);
                while (--n >= 0) {
                        if (*buf == '\r' || *buf == '\n' || *buf == '\0')
                                return (count);
                        count++;
                        buf++;
                }
        } while (count < len);
        return (count);
}

struct servtab *
tcpmux(int s)
{
        struct servtab *sep;
        char service[MAX_SERV_LEN+1];
        int len;

        /* Get requested service name */
        if ((len = get_line(s, service, MAX_SERV_LEN)) < 0) {
                strwrite(s, "-Error reading service name\r\n");
                return (NULL);
        }
        service[len] = '\0';

        if (debug)
                warnx("tcpmux: someone wants %s", service);

        /*
         * Help is a required command, and lists available services,
         * one per line.
         */
        if (!strcasecmp(service, "help")) {
                for (sep = servtab; sep; sep = sep->se_next) {
                        if (!ISMUX(sep))
                                continue;
                        (void)write(s,sep->se_service,strlen(sep->se_service));
                        strwrite(s, "\r\n");
                }
                return (NULL);
        }

        /* Try matching a service in inetd.conf with the request */
        for (sep = servtab; sep; sep = sep->se_next) {
                if (!ISMUX(sep))
                        continue;
                if (!strcasecmp(service, sep->se_service)) {
                        if (ISMUXPLUS(sep)) {
                                strwrite(s, "+Go\r\n");
                        }
                        return (sep);
                }
        }
        strwrite(s, "-Service not available\r\n");
        return (NULL);
}