/*- * $Id: expn.c,v 1.12 1995/08/11 17:42:50 dupuy Exp $ * * To compile with DNS support, cc -O -o expn expn.c -lresolv * To compile without DNS support, cc -O -o expn -DNO_DOMAINS expn.c * To use, expn user@host * exit codes: 0 = valid address * 1 = system error (address may be valid) * 2 = SMTP server error (address may be valid) * 3 = invalid user * 4 = invalid host * * This started out as mverify, by Jeff Beadles * with a couple of lines of autobounce.c by Pete Shipley * * I decided to enhance it for use in verifying mailing lists, requiring better * support for all the varieties of RFC-821 mailers out there in the swamps. * So I added support for MX records and real handling of RFC-821 result codes. * * If you think there's anything left to add, please send it to me, and I'll * see about adding it. * * Alexander Dupuy * */ #ifdef BSD #include #else #include #include #define index strchr #define bcopy(b1,b2,len) memcpy(b2,b1,len) #endif #include #include #include #include #ifndef NO_DOMAINS #include #include #ifdef NO_HERROR extern void herror (); #endif #endif #include #include #define MAXMXHOSTS 20 #define SYSERR 1 #define SMTPERR 2 #define BADUSER 3 #define BADHOST 4 char *fgets (); char *index (); struct hostent *gethostbyname (); main (argc, argv) int argc; char **argv; { int smtpfd; FILE *fin; /* separate stdio streams to allow */ FILE *fout; /* mixed reads and writes w/o seeks */ char buffer[2048]; /* stdio line buffer */ char *user; /* pieces of argv */ char *orighost; char *host; char *command; /* for expn/vrfy smtp commands */ int exitstatus; struct hostent *hp; /* inet networking */ struct servent *sp; struct sockaddr_in server; char *bp; /* utility infielder */ #ifndef NO_DOMAINS int n; /* utility index */ HEADER *dhp; /* DNS reply header and fields*/ int ancount; int qdcount; union /* DNS reply and pointers */ { HEADER hdr; u_char bytes[PACKETSZ]; } answer; u_char *cp; u_char *eom; char hostbuf[PACKETSZ]; /* hostnames buffer */ int buflen; u_short pref; u_short type; char *hosts[MAXMXHOSTS]; /* arrays for multiple MX hosts */ u_short prefs[MAXMXHOSTS]; u_long bestpref; int besthost; /* indexes into arrays */ int i; #endif if (argc != 2) { (void) fprintf (stderr, "Usage: %s user@host\n", argv[0]); return (SYSERR); } /* * Prevent "Broken Pipe" exit if an SMTP server dies while we are talking * to it. */ signal (SIGPIPE, SIG_IGN); user = argv[1]; if ((orighost = index (user, '@')) == 0) host = "localhost"; else { *orighost = '\0'; orighost++; host = orighost; } server.sin_family = AF_INET; /* * Get the smtp port using tcp. */ sp = getservbyname ("smtp", "tcp"); server.sin_port = sp->s_port; if (!server.sin_port) { (void) fprintf (stderr, "unknown service: smtp/tcp\n"); return (SYSERR); } #ifdef NO_DOMAINS /* * Now get the information for the @host part of the address. */ if ((hp = gethostbyname (host)) == 0) { (void) fprintf (stderr, "%s: unknown host\n", host); return (BADHOST); } #else besthost = -1; /* don't retry MX */ /* * Check MX records for the @host part of the address. */ n = res_search (host, C_IN, T_MX, answer.bytes, sizeof (answer)); if (n < 0) goto punt; /* find first satisfactory answer */ dhp = &answer.hdr; cp = answer.bytes + sizeof (HEADER); eom = answer.bytes + n; for (qdcount = ntohs (dhp->qdcount); qdcount--; cp += n + QFIXEDSZ) if ((n = dn_skipname (cp, eom)) < 0) goto punt; /* copy MX hosts and preferences into arrays */ buflen = sizeof (hostbuf); bp = hostbuf; ancount = ntohs (dhp->ancount); i = 0; while (--ancount >= 0 && cp < eom && i < MAXMXHOSTS) { if ((n = dn_expand (&answer.hdr, eom, cp, bp, buflen)) < 0) break; cp += n; GETSHORT (type, cp); cp += sizeof (u_short) + sizeof (u_long); GETSHORT (n, cp); if (type != T_MX) { cp += n; continue; } GETSHORT (pref, cp); if ((n = dn_expand (&answer.hdr, eom, cp, bp, buflen)) < 0) break; cp += n; prefs[i] = pref; hosts[i] = bp; i++; n = strlen (bp) + 1; bp += n; buflen -= n; } hosts[i] = 0; /* terminate host array */ nextmxhost: i = 0; n = 0; bestpref = 65536; while (hosts[i] && i < MAXMXHOSTS) { if (prefs[i] < 65535) /* count untried MX hosts */ n++; if (prefs[i] < bestpref) { bestpref = prefs[i]; host = hosts[i]; besthost = i; } i++; } if (n <= 1) /* don't retry if this is last host */ besthost = -1; punt: /* * Now get the information for the @host part of the address. */ if ((hp = gethostbyname (host)) == 0) { /* * This is *not* a typo. If gethostbyname fails, it leaves an error * code in h_errno, not in errno, and does not use the error codes * defined in . So if the linker can't find herror() in your * resolver library, use the herror() implementation at the end of this * file. Don't just change this to perror(). */ herror (host); if (besthost >= 0) { prefs[besthost] = 65535; goto nextmxhost; } if (h_errno == TRY_AGAIN) return (SYSERR); return (BADHOST); } #endif reconnect: (void) bcopy (hp->h_addr, (char *) &server.sin_addr, hp->h_length); /* * One socket please... */ if ((smtpfd = socket (AF_INET, SOCK_STREAM, 0)) < 0) { perror ("socket"); return (SYSERR); } /* * Connecting to the socket might make things go a little easier... :-) */ while (connect (smtpfd, (struct sockaddr *) &server, sizeof (server)) < 0) { #ifdef h_addr if (*++hp->h_addr_list) { (void) close (smtpfd); goto reconnect; } #endif perror (host); if (besthost >= 0) { prefs[besthost] = 65535; (void) close (smtpfd); goto nextmxhost; } return (SYSERR); } /* * Change them to streams 'cause I like 'em better. */ fout = fdopen (smtpfd, "w"); fin = fdopen (smtpfd, "r"); /* * The format of SMTP reply codes is a three digit number followed by * either space or '-' minus. The minus code indicates a multi-line * response, so we keep reading lines until we see one with a space. * * Reply codes beginning with 2 are positive, and can be ignored * (although 251 indicates a non-local user). * Reply codes beginning with 4 indicate transient errors. * Reply codes beginning with 5 indicate permanent errors * (although 551 will return a forward-path for a non-local user). * * Note that RFC-1123 defines a new reply code 252 which indicates that * the user cannot be verified, but the server will attempt forwarding. * This is pretty much the same as 251 except there is less assurance that * the address is valid. */ /* * Wait for the smtp mailer to answer. It should greet us with a 220 code */ while (fgets (buffer, sizeof (buffer) - 1, fin) != NULL) { if (buffer[3] == '-') continue; if (!strncmp (buffer, "220 ", 4)) break; else /* some kind of mailer error */ { (void) fputs (buffer, stderr); (void) putc ('\n', stderr); /* fputs doesn't add a newline */ exitstatus = SMTPERR; goto done; } } exitstatus = -1; /* until we get positive response */ if (orighost) command = "EXPN %s@%s\r\n"; /* RFC-821 requires CRLF */ else command = "EXPN %s\r\n"; /* * Now that we have the mailer's attention, tell it to 'verify' the user. * We have four ways of trying this, using EXPN or VRFY, and using @host * or not. We will try all of them (only two if no @host specified). */ (void) fprintf (fout, command, user, orighost); if (fflush (fout) == EOF) { perror (host); #ifdef h_addr if (*++hp->h_addr_list) { (void) fclose (fin); (void) fclose (fout); goto reconnect; } #endif if (besthost >= 0) { prefs[besthost] = 65535; (void) fclose (fin); (void) fclose (fout); goto nextmxhost; } return (SYSERR); } /* * Now just go into a loop reading responses from the mailer. */ while (fgets (buffer, sizeof (buffer) - 1, fin) != NULL) { /* * Zap ^M from the lines. */ if ((bp = index (buffer, '\r')) != 0) *bp = '\0'; if (!strncmp (buffer, "250", 3)) { (void) puts (buffer + 4); /* delete 250- code */ } else if (!strncmp (buffer, "251", 3)) /* only given to VRFY */ { (void) puts (buffer); /* unusual - leave 251 code in */ } else if (!strncmp (buffer, "252", 3)) /* only given to VRFY */ { /* reconstruct the user name we sent */ if (orighost) (void) printf ("<%s@%s>\n", user, orighost); else (void) puts (user); (void) fputs (buffer, stderr); (void) putc ('\n', stderr); /* print warning to stderr */ } else if (!strncmp (buffer, "551", 3)) /* only given to VRFY */ { (void) puts (buffer); /* unusual - leave 551 code in */ (void) fputs (buffer, stderr); (void) putc ('\n', stderr); /* print warning to stderr */ } else if (buffer[0] == '5' && (buffer[1] == '0' || buffer[2] == '0')) { /* 50x syntax err; 550 list vs. user */ /* * We try first with EXPN, then VRFY, since EXPN gives more info. * A server which accepts EXPN but not VRFY can give misleading * results for bad addresses. The only server I have run across * (@lists.psi.com) accepts VRFY but not EXPN, so this is okay. * If some server does accept EXPN but not VRFY, then change this * to retry only for 50x codes. RFC-821 says that a VRFY on a list * or an EXPN on a user is allowed to return 550, but I've never * seen that happen. */ switch (exitstatus) { case -1: /* first failure; try without @host */ if (orighost) /* if we haven't already done so */ { command = "EXPN %s\r\n"; exitstatus = -2; break; } /* fall through if !orighost */ case -2: /* EXPN doesn't work; try VRFY */ if (orighost) { command = "VRFY %s@%s\r\n"; exitstatus = -3; break; } /* fall through if !orighost */ case -3: command = "VRFY %s\r\n"; exitstatus = -4; break; case -4: if (buffer[1] == '5') /* 55x implies bad username */ exitstatus = BADUSER; else exitstatus = SMTPERR; (void) fputs (buffer, stderr); (void) putc ('\n', stderr); goto done; /* we've had enough by now */ } (void) fprintf (fout, command, user, orighost); if (fflush (fout) == EOF) { perror (host); #ifdef h_addr if (*++hp->h_addr_list) { (void) fclose (fin); (void) fclose (fout); goto reconnect; } #endif if (besthost >= 0) { prefs[besthost] = 65535; (void) fclose (fin); (void) fclose (fout); goto nextmxhost; } return (SYSERR); } continue; } else { (void) fputs (buffer, stderr); /* failed bigtime */ (void) putc ('\n', stderr); /* fputs doesn't add a newline */ } if (buffer[3] == ' ') /* no more responses coming */ { if (buffer[0] == '2') exitstatus = 0; /* the last try worked */ else if (buffer[0] == '5' && buffer[1] == '5') exitstatus = BADUSER; /* 55x implies bad username */ else exitstatus = SMTPERR; /* SMTP error */ goto done; } } if (exitstatus < 0) { perror (host); #ifdef h_addr if (*++hp->h_addr_list) { (void) fclose (fin); (void) fclose (fout); goto reconnect; } #endif if (besthost >= 0) { prefs[besthost] = 65535; (void) fclose (fin); (void) fclose (fout); goto nextmxhost; } exitstatus = SYSERR; /* unexpected EOF */ } done: /* * Close the SMTP connection gracefully. */ (void) fputs ("QUIT\r\n", fout); (void) fflush (fout); (void) fclose (fout); (void) fclose (fin); if (fflush (stdout)) /* in case we couldn't write output */ exitstatus = SYSERR; /* * And leave this nice program. */ return (exitstatus); } #ifndef NO_DOMAINS /* * I've been told that some resolver libraries don't provide herror(). If this * is the case, you probably have a very old and broken version of the resolver * libraries, and you should get a current copy of the BIND distribution and * install it. If you really can't be bothered, though, you can use this * version of herror() by defining NO_HERROR. */ #ifdef NO_HERROR char *h_errlist[] = { "Error 0", "Unknown host", /* 1 HOST_NOT_FOUND */ "Host name lookup failure", /* 2 TRY_AGAIN */ "Unknown server error", /* 3 NO_RECOVERY */ "No address associated with name", /* 4 NO_ADDRESS */ }; extern int h_errno; void herror (message) char *message; { if (h_errno < 0 || h_errno > 4) fprintf (stderr, "%s: Unknown error\n", message); else fprintf (stderr, "%s: %s\n", message, h_errlist[h_errno]); } #endif #endif