/*
    The Macintosh POPmail client Eudora offers a possibility
    to perform the POP and SMTP conversations over a serial
    (dialup) connection. Therefore is needed a 'psuedo-account'
    on a machine where Eudora can login. That account must have
    permission to execute senndmail and popper, not only local
    but also remote (via rsh) on all machines where a popserver
    or smtpserver must be contacted. Eudora is secretive with
    the password while showing its progress (if properly
    configured), but nobody can prevent a curious Macontosh
    owner from looking with ResEdit (or alike's). It can be a
    security leak.
    
    This program srialpop is written to take care of these
    trade off's. It must be used as the pseudo-account's
    loginshell. The commands which are recognized by the
    program are 'logout' and 'exit' (to finish the session
    of course) and 'telnet <host> <port> ...' which performs
    a TCP/IP connection with the indicated host/port. The
    supplied portnumber is checked against a list of valid
    portnumbers (now only POP and SMTP).
    All other commands cause an exit with errormessage.
    
    So the pseudo-account doesn't need permissions to run
    popper and sendmail, neither needed are permissions to
    run rsh to another machine or let another machine rsh
    in. And a diligent user (Macintosh owner) who tries to
    login on the psuedo-account will discover that there is
    no fun.
    
    The program is straightforward and rather simple, and
    it is free. Yet I claim a copyright, with which I mean
    that anybody who feels a need to change (parts of) this
    program is under the obligation to document the changes
    and the need thereof in the program distribution files.
    Neither may this program be selled (as if anybody would
    buy this gadget), or distributed for a fee that extends
    a reasonable retribution for the 8k it occupies on disk
    or other media (I don't ask money, why should you).
    I have tested the program for some time now and found no
    bugs/problems. That doeesn't mean of course there are not.
    I offer this program free for everyone to use because I
    think it can be useful and is less dangerous then the
    shellscript suggested by Steve Dorner. But if you stumble
    over an error I am in no way responsible for the damage
    that can cause, however I don't expect disasters.
    I should welcome (by email) any notification of changes,
    corrections and enhancements in the form of the new program
    source or a diff.

    Rudi van Houten  <rudi@cc.ruu.nl>
    Ac.Comp.Centr.Utrecht
    Budapestlaan 6
    3584 CD Utrecht Netherlands

    Known bugs:
        I found none.

    How to compile:
        On BSD-4.2 (4.3) it can be compiled without any defines.
        On System V (also HP/UX) the symbol SYSV must be defined. 
        It is tested on the following configurations:
        Convex C220 (OS-9.1)
            compilation: 'cc -O -pcc'
        Sun-Sparcstation-330 (OS 4.1)
            compilation: 'cc -O'
        HP9000-832:
            compilation: 'cc -O -DSYSV'
        P9070 (Philips, an M68030 with SysV R3):
            compilation: 'cc -O -DSYSV'
                
    History:
    9 dec 91   original version, only installed at ACCU
               The distribution contains one file 'srialpop.c'
    11 dec 91  some changes in IO-handling after Steve Dorner
               viewed the program and made some sugeestions
*/

#ifdef SYSV
#include <string.h>
#define bcopy(a,b,c) memcpy(b,a,c)
#endif
#include <stdio.h>
#include <signal.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <sgtty.h>

#define iBuflen 512
static char sBuf[iBuflen];

static short iValidPort[]=
        {25     /* SMTP */
        ,109    /* POP2 */
        ,110    /* POP3 */
        };
#define iValidPortsCount sizeof(iValidPort)/sizeof(short)

void errorexit(sFormat,uPar)
char * sFormat;
unsigned int uPar;
{
    close(0);
    fprintf(stderr,sFormat,uPar);
    sleep(1); exit(1);
} /* errorexit */

main()
{
int iSock, iPort, iChild;
register int i, l;
struct in_addr sInAddr;
struct sockaddr_in sServer;
struct hostent *psHost, *gethostbyname(), *gethostbyaddr();
struct sgttyb sTermHold, sTermCurr;
char *psCommand, *psName, *psNumber;

/* get stty structure sTermHold */
ioctl(0,TIOCGETP,&sTermHold);

/* this is the main loop, it reads the telnet or exit commandline */
while (write(1,"%",1), (l= read(0,sBuf,iBuflen)) > 0)
{
    if (sBuf[i= l - 1] == '\n') sBuf[l= i]= '\0';
    if (l == 0) continue;
    if (strcmp(sBuf,"logout") == 0 || strcmp(sBuf,"exit") == 0)
        break; /* finished, logout now */
    i= 0;
    psCommand= psName= psNumber= NULL;
    while (i < l && psNumber == NULL)
    {
        while (sBuf[i] == ' ' || sBuf[i] == '\t') i++;
        if (i >= l) break;
        if (psCommand == NULL) psCommand= &sBuf[i];
        else
        if (psName == NULL) psName= &sBuf[i];
        else psNumber= &sBuf[i];
        do { i++; } while (sBuf[i] != ' ' && sBuf[i] != '\t' && i < l);
        sBuf[i++]= '\0';
    }
    if (strcmp(psCommand,"telnet"))
        errorexit("Sorry, don't know '%s'\n",psCommand);
    if (psName == NULL || psNumber == NULL)
        errorexit("Sorry, hostname or portnumber missing\n",0);
    if (l= strlen(psNumber))
    {
        for (i= 0; i < l; i++)
            if (!isdigit(psNumber[i]))
                errorexit("Portnumber (%s) not numeric\n",psNumber);
        iPort= atoi(psNumber);
    }
    else iPort= 0;
    for (i=0; iPort != iValidPort[i]; i++)
        if (i == iValidPortsCount)
            errorexit("Sorry, %d is not a valid port\n",iPort);

        /*
           (unsigned long)(-1) = 0xffffffff, returnvalue
           from inet_addr() if illegal address passed through.
           I assume then it is a domain name.
           Thanks to Edwin Kremer (edwin@cs.ruu.nl) for the trick
        */
    if ((sInAddr.s_addr= inet_addr(psName)) == 0xffffffff)
        psHost= gethostbyname(psName);
    else
        psHost= gethostbyaddr((char*)&sInAddr,sizeof(struct in_addr),AF_INET);
    if( psHost == 0)
        errorexit("Cannot find server %s (host unknown)\n",psName);
    
        /* create socket */
    if ((iSock= socket(AF_INET,SOCK_STREAM,0)) < 0)
        { perror("Cannot open IP socket"); exit(1); }

        /* fill socket structure .....*/
    sServer.sin_family= AF_INET;
    bcopy(psHost->h_addr,&sServer.sin_addr,psHost->h_length);
    sServer.sin_port= htons(iPort);
    
        /*........and connect */
    if (connect(iSock,&sServer,sizeof(sServer)) < 0)
        { perror("connecting stream socket"); exit(1); }

    bcopy(&sTermHold,&sTermCurr,sizeof(struct sgttyb));
    sTermCurr.sg_flags  &= ~(ECHO | CRMOD);
    /* I don't see why raw mode is needed
    if (iPort == 25) sTermCurr.sg_flags |= RAW; */
    ioctl(0,TIOCSETP,&sTermCurr);

        /* now fork a child to copy stdin to socket */
    iChild= fork();
    if (iChild < 0) { perror("Cannot fork"); exit(1); }
    if (iChild == 0)
    { /* the child copies stdin to the socket */
        while ((l= read(0,sBuf,iBuflen)) > 0) write(iSock,sBuf,l);
        close(0); exit(0);
    }
    else /* if (iChild == 0) */
        /* the parent copies the socket to stdout */
        while ((l= read(iSock,sBuf,iBuflen)) > 0) write(1,sBuf,l);

    close(iSock);
    ioctl(0,TIOCSETP,&sTermHold);
    kill(iChild,SIGTERM);
} /* main loop: while (write(1,"%",1), gets(sBuf) != NULL) */

close(0); close(1); close(2);
exit(0);
} /* main */