Drop LAST support, force UIDL.

[~andy/fetchmail] / pop3.c

/*
 * pop3.c -- POP3 protocol methods
 *
 * Copyright 1998 by Eric S. Raymond.
 * For license terms, see the file COPYING in this directory.
 */

#include  "config.h"
#ifdef POP3_ENABLE
#include  <stdio.h>
#include  <string.h>
#include  <ctype.h>
#include <unistd.h>
#include  <stdlib.h>
#include  <errno.h>

#include  "fetchmail.h"
#include  "socket.h"
#include  "gettext.h"
#include  "uid_db.h"

#ifdef OPIE_ENABLE
#ifdef __cplusplus
extern "C" {
#endif
#include <opie.h>
#ifdef __cplusplus
}
#endif
#endif /* OPIE_ENABLE */

/* global variables: please reinitialize them explicitly for proper
 * working in daemon mode */

/* TODO: session variables to be initialized before server greeting */
#ifdef OPIE_ENABLE
static char lastok[POPBUFSIZE+1];
#endif /* OPIE_ENABLE */

/* session variables initialized in capa_probe() or pop3_getauth() */
flag done_capa = FALSE;
#if defined(GSSAPI)
flag has_gssapi = FALSE;
#endif /* defined(GSSAPI) */
#if defined(KERBEROS_V5)
flag has_kerberos = FALSE;
#endif /* defined(KERBEROS_V5) */
static flag has_cram = FALSE;
#ifdef OPIE_ENABLE
flag has_otp = FALSE;
#endif /* OPIE_ENABLE */
#ifdef NTLM_ENABLE
flag has_ntlm = FALSE;
#endif /* NTLM_ENABLE */
#ifdef SSL_ENABLE
static flag has_stls = FALSE;
#endif /* SSL_ENABLE */

/* mailbox variables initialized in pop3_getrange() */
static int last;

/* mail variables initialized in pop3_fetch() */
#ifdef SDPS_ENABLE
char *sdps_envfrom;
char *sdps_envto;
#endif /* SDPS_ENABLE */

#ifdef NTLM_ENABLE
#include "ntlm.h"

/*
 * NTLM support by Grant Edwards.
 *
 * Handle MS-Exchange NTLM authentication method.  This is the same
 * as the NTLM auth used by Samba for SMB related services. We just
 * encode the packets in base64 instead of sending them out via a
 * network interface.
 * 
 * Much source (ntlm.h, smb*.c smb*.h) was borrowed from Samba.
 */

static int do_pop3_ntlm(int sock, struct query *ctl,
        int msn_instead /** if true, send AUTH MSN, else send AUTH NTLM */)
{
    char msgbuf[POPBUFSIZE+1];
    int result;

    gen_send(sock, msn_instead ? "AUTH MSN" : "AUTH NTLM");

    if ((result = ntlm_helper(sock, ctl, "POP3")))
        return result;

    if ((result = gen_recv (sock, msgbuf, sizeof msgbuf)))
        return result;

    if (strstr (msgbuf, "OK"))
        return PS_SUCCESS;
    else
        return PS_AUTHFAIL;
}
#endif /* NTLM */


#define DOTLINE(s)      (s[0] == '.' && (s[1]=='\r'||s[1]=='\n'||s[1]=='\0'))

static int pop3_ok (int sock, char *argbuf)
/* parse command response */
{
    int ok;
    char buf [POPBUFSIZE+1];
    char *bufp;

    if ((ok = gen_recv(sock, buf, sizeof(buf))) == 0)
    {   bufp = buf;
        if (*bufp == '+' || *bufp == '-')
            bufp++;
        else
            return(PS_PROTOCOL);

        while (isalpha((unsigned char)*bufp))
            bufp++;

        if (*bufp)
          *(bufp++) = '\0';

        if (strcmp(buf,"+OK") == 0)
        {
#ifdef OPIE_ENABLE
            strcpy(lastok, bufp);
#endif /* OPIE_ENABLE */
            ok = 0;
        }
        else if (strncmp(buf,"-ERR", 4) == 0)
        {
            if (stage == STAGE_FETCH)
                ok = PS_TRANSIENT;
            else if (stage > STAGE_GETAUTH)
                ok = PS_PROTOCOL;
            /*
             * We're checking for "lock busy", "unable to lock", 
             * "already locked", "wait a few minutes" etc. here. 
             * This indicates that we have to wait for the server to
             * unwedge itself before we can poll again.
             *
             * PS_LOCKBUSY check empirically verified with two recent
             * versions of the Berkeley popper; QPOP (version 2.2)  and
             * QUALCOMM Pop server derived from UCB (version 2.1.4-R3)
             * These are caught by the case-indifferent "lock" check.
             * The "wait" catches "mail storage services unavailable,
             * wait a few minutes and try again" on the InterMail server.
             *
             * If these aren't picked up on correctly, fetchmail will 
             * think there is an authentication failure and wedge the
             * connection in order to prevent futile polls.
             *
             * Gad, what a kluge.
             */
            else if (strstr(bufp,"lock")
                     || strstr(bufp,"Lock")
                     || strstr(bufp,"LOCK")
                     || strstr(bufp,"wait")
                     /* these are blessed by RFC 2449 */
                     || strstr(bufp,"[IN-USE]")||strstr(bufp,"[LOGIN-DELAY]"))
                ok = PS_LOCKBUSY;
            else if ((strstr(bufp,"Service")
                     || strstr(bufp,"service"))
                         && (strstr(bufp,"unavailable")))
                ok = PS_SERVBUSY;
            else
                ok = PS_AUTHFAIL;
            /*
             * We always want to pass the user lock-busy messages, because
             * they're red flags.  Other stuff (like AUTH failures on non-
             * RFC1734 servers) only if we're debugging.
             */
            if (*bufp && (ok == PS_LOCKBUSY || outlevel >= O_MONITOR))
              report(stderr, "%s\n", bufp);
        }
        else
            ok = PS_PROTOCOL;

#if POPBUFSIZE > MSGBUFSIZE
#error "POPBUFSIZE must not be larger than MSGBUFSIZE"
#endif
        if (argbuf != NULL)
            strcpy(argbuf,bufp);
    }

    return(ok);
}



static int capa_probe(int sock)
/* probe the capabilities of the remote server */
{
    int ok;

    if (done_capa) {
        return PS_SUCCESS;
    }
#if defined(GSSAPI)
    has_gssapi = FALSE;
#endif /* defined(GSSAPI) */
#if defined(KERBEROS_V5)
    has_kerberos = FALSE;
#endif /* defined(KERBEROS_V5) */
    has_cram = FALSE;
#ifdef OPIE_ENABLE
    has_otp = FALSE;
#endif /* OPIE_ENABLE */
#ifdef NTLM_ENABLE
    has_ntlm = FALSE;
#endif /* NTLM_ENABLE */

    ok = gen_transact(sock, "CAPA");
    if (ok == PS_SUCCESS)
    {
        char buffer[64];

        /* determine what authentication methods we have available */
        while ((ok = gen_recv(sock, buffer, sizeof(buffer))) == 0)
        {
            if (DOTLINE(buffer))
                break;

#ifdef SSL_ENABLE
            if (strstr(buffer, "STLS"))
                has_stls = TRUE;
#endif /* SSL_ENABLE */

#if defined(GSSAPI)
            if (strstr(buffer, "GSSAPI"))
                has_gssapi = TRUE;
#endif /* defined(GSSAPI) */

#ifdef OPIE_ENABLE
            if (strstr(buffer, "X-OTP"))
                has_otp = TRUE;
#endif /* OPIE_ENABLE */

#ifdef NTLM_ENABLE
            if (strstr(buffer, "NTLM"))
                has_ntlm = TRUE;
#endif /* NTLM_ENABLE */

            if (strstr(buffer, "CRAM-MD5"))
                has_cram = TRUE;
        }
    }
    done_capa = TRUE;
    return(ok);
}

static void set_peek_capable(struct query *ctl)
{
    /* we're peek-capable means that the use of TOP is enabled,
     * see pop3_fetch for details - short story, we can use TOP if
     * we have a means of reliably tracking which mail we need to
     * refetch should the connection abort in the middle.
     * fetchall forces RETR, as does keep without UIDL */
    peek_capable = !ctl->fetchall;
}

static int pop3_getauth(int sock, struct query *ctl, char *greeting)
/* apply for connection authorization */
{
    int ok;
    char *start,*end;
    char *msg;
#ifdef OPIE_ENABLE
    char *challenge;
#endif /* OPIE_ENABLE */
#ifdef SSL_ENABLE
    flag connection_may_have_tls_errors = FALSE;
#endif /* SSL_ENABLE */

    done_capa = FALSE;
#if defined(GSSAPI)
    has_gssapi = FALSE;
#endif /* defined(GSSAPI) */
#if defined(KERBEROS_V5)
    has_kerberos = FALSE;
#endif /* defined(KERBEROS_V5) */
    has_cram = FALSE;
#ifdef OPIE_ENABLE
    has_otp = FALSE;
#endif /* OPIE_ENABLE */
#ifdef SSL_ENABLE
    has_stls = FALSE;
#endif /* SSL_ENABLE */

    /* Set this up before authentication quits early. */
    set_peek_capable(ctl);

    /* Hack: allow user to force RETR. */
    if (peek_capable && getenv("FETCHMAIL_POP3_FORCE_RETR")) {
        peek_capable = 0;
    }

    /*
     * The "Maillennium POP3/PROXY server" deliberately truncates
     * TOP replies after c. 64 or 80 kByte (we have varying reports), so
     * disable TOP. Comcast once spewed marketing babble to the extent
     * of protecting Outlook -- pretty overzealous to break a protocol
     * for that that Microsoft could have read, too. Comcast aren't
     * alone in using this software though.
     * <http://lists.ccil.org/pipermail/fetchmail-friends/2004-April/008523.html>
     * (Thanks to Ed Wilts for reminding me of that.)
     *
     * The warning is printed once per server, until fetchmail exits.
     * It will be suppressed when --fetchall or other circumstances make
     * us use RETR anyhow.
     *
     * Matthias Andree
     */
    if (peek_capable && strstr(greeting, "Maillennium POP3/PROXY server")) {
        if ((ctl->server.workarounds & WKA_TOP) == 0) {
            report(stdout, GT_("Warning: \"Maillennium POP3/PROXY server\" found, using RETR command instead of TOP.\n"));
            ctl->server.workarounds |= WKA_TOP;
        }
        peek_capable = 0;
    }
    if (ctl->server.authenticate == A_SSH) {
        return PS_SUCCESS;
    }

#ifdef SDPS_ENABLE
    /*
     * This needs to catch both demon.co.uk and demon.net.
     * If we see either, and we're in multidrop mode, try to use
     * the SDPS *ENV extension.
     */
    if (!(ctl->server.sdps) && MULTIDROP(ctl) && strstr(greeting, "demon."))
        ctl->server.sdps = TRUE;
#endif /* SDPS_ENABLE */

   switch (ctl->server.protocol) {
    case P_POP3:
#ifdef RPA_ENABLE
        /* XXX FIXME: AUTH probing (RFC1734) should become global */
        /* CompuServe POP3 Servers as of 990730 want AUTH first for RPA */
        if (strstr(ctl->remotename, "@compuserve.com"))
        {
            /* AUTH command should return a list of available mechanisms */
            if (gen_transact(sock, "AUTH") == 0)
            {
                char buffer[10];
                flag has_rpa = FALSE;

                while ((ok = gen_recv(sock, buffer, sizeof(buffer))) == 0)
                {
                    if (DOTLINE(buffer))
                        break;
                    if (strncasecmp(buffer, "rpa", 3) == 0)
                        has_rpa = TRUE;
                }
                if (has_rpa && !POP3_auth_rpa(ctl->remotename, 
                                              ctl->password, sock))
                    return(PS_SUCCESS);
            }

            return(PS_AUTHFAIL);
        }
#endif /* RPA_ENABLE */

        /*
         * CAPA command may return a list including available
         * authentication mechanisms and STLS capability.
         *
         * If it doesn't, no harm done, we just fall back to a plain
         * login -- if the user allows it.
         *
         * Note that this code latches the server's authentication type,
         * so that in daemon mode the CAPA check only needs to be done
         * once at start of run.
         *
         * If CAPA fails, then force the authentication method to
         * PASSWORD, switch off opportunistic and repoll immediately.
         * If TLS is mandatory, fail up front.
         */
        if ((ctl->server.authenticate == A_ANY) ||
                (ctl->server.authenticate == A_GSSAPI) ||
                (ctl->server.authenticate == A_KERBEROS_V5) ||
                (ctl->server.authenticate == A_OTP) ||
                (ctl->server.authenticate == A_CRAM_MD5) ||
                maybe_tls(ctl))
        {
            if ((ok = capa_probe(sock)) != PS_SUCCESS)
                /* we are in STAGE_GETAUTH => failure is PS_AUTHFAIL! */
                if (ok == PS_AUTHFAIL ||
                    /* Some servers directly close the socket. However, if we
                     * have already authenticated before, then a previous CAPA
                     * must have succeeded. In that case, treat this as a
                     * genuine socket error and do not change the auth method.
                     */
                    (ok == PS_SOCKET && !ctl->wehaveauthed))
                {
#ifdef SSL_ENABLE
                    if (must_tls(ctl)) {
                        /* fail with mandatory STLS without repoll */
                        report(stderr, GT_("TLS is mandatory for this session, but server refused CAPA command.\n"));
                        report(stderr, GT_("The CAPA command is however necessary for TLS.\n"));
                        return ok;
                    } else if (maybe_tls(ctl)) {
                        /* defeat opportunistic STLS */
                        xfree(ctl->sslproto);
                        ctl->sslproto = xstrdup("");
                    }
#endif
                    /* If strong authentication was opportunistic, retry without, else fail. */
                    switch (ctl->server.authenticate) {
                        case A_ANY:
                            ctl->server.authenticate = A_PASSWORD;
                            /* FALLTHROUGH */
                        case A_PASSWORD: /* this should only happen with TLS enabled */
                            return PS_REPOLL;
                        default:
                            return PS_AUTHFAIL;
                    }
                }
        }

#ifdef SSL_ENABLE
        if (maybe_tls(ctl)) {
            char *commonname;

            commonname = ctl->server.pollname;
            if (ctl->server.via)
                commonname = ctl->server.via;
            if (ctl->sslcommonname)
                commonname = ctl->sslcommonname;

           if (has_stls
                   || must_tls(ctl)) /* if TLS is mandatory, ignore capabilities */
           {
               /* Use "tls1" rather than ctl->sslproto because tls1 is the only
                * protocol that will work with STARTTLS.  Don't need to worry
                * whether TLS is mandatory or opportunistic unless SSLOpen() fails
                * (see below). */
               if (gen_transact(sock, "STLS") == PS_SUCCESS
                       && SSLOpen(sock, ctl->sslcert, ctl->sslkey, "tls1", ctl->sslcertck,
                           ctl->sslcertfile, ctl->sslcertpath, ctl->sslfingerprint, commonname,
                           ctl->server.pollname, &ctl->remotename) != -1)
               {
                   /*
                    * RFC 2595 says this:
                    *
                    * "Once TLS has been started, the client MUST discard cached
                    * information about server capabilities and SHOULD re-issue the
                    * CAPABILITY command.  This is necessary to protect against
                    * man-in-the-middle attacks which alter the capabilities list prior
                    * to STARTTLS.  The server MAY advertise different capabilities
                    * after STARTTLS."
                    *
                    * Now that we're confident in our TLS connection we can
                    * guarantee a secure capability re-probe.
                    */
                   done_capa = FALSE;
                   ok = capa_probe(sock);
                   if (ok != PS_SUCCESS) {
                       return ok;
                   }
                   if (outlevel >= O_VERBOSE)
                   {
                       report(stdout, GT_("%s: upgrade to TLS succeeded.\n"), commonname);
                   }
               } else if (must_tls(ctl)) {
                   /* Config required TLS but we couldn't guarantee it, so we must
                    * stop. */
                   report(stderr, GT_("%s: upgrade to TLS failed.\n"), commonname);
                   return PS_SOCKET;
               } else {
                   /* We don't know whether the connection is usable, and there's
                    * no command we can reasonably issue to test it (NOOP isn't
                    * allowed til post-authentication), so leave it in an unknown
                    * state, mark it as such, and check more carefully if things
                    * go wrong when we try to authenticate. */
                   connection_may_have_tls_errors = TRUE;
                   if (outlevel >= O_VERBOSE)
                   {
                       report(stdout, GT_("%s: opportunistic upgrade to TLS failed, trying to continue.\n"), commonname);
                   }
               }
           }
        } /* maybe_tls() */
#endif /* SSL_ENABLE */

        /*
         * OK, we have an authentication type now.
         */

#if defined(GSSAPI)
        if (has_gssapi &&
            (ctl->server.authenticate == A_GSSAPI ||
            (ctl->server.authenticate == A_ANY
             && check_gss_creds("pop", ctl->server.truename) == PS_SUCCESS)))
        {
            ok = do_gssauth(sock,"AUTH","pop",ctl->server.truename,ctl->remotename);
            if (ok == PS_SUCCESS || ctl->server.authenticate != A_ANY)
                break;
        }
#endif /* defined(GSSAPI) */

#ifdef OPIE_ENABLE
        if (has_otp &&
            (ctl->server.authenticate == A_OTP ||
             ctl->server.authenticate == A_ANY))
        {
            ok = do_otp(sock, "AUTH", ctl);
            if (ok == PS_SUCCESS || ctl->server.authenticate != A_ANY)
                break;
        }
#endif /* OPIE_ENABLE */

#ifdef NTLM_ENABLE
    /* MSN servers require the use of NTLM (MSN) authentication */
    if (!strcasecmp(ctl->server.pollname, "pop3.email.msn.com") ||
            ctl->server.authenticate == A_MSN)
        return (do_pop3_ntlm(sock, ctl, 1) == 0) ? PS_SUCCESS : PS_AUTHFAIL;
    if (ctl->server.authenticate == A_NTLM || (has_ntlm && ctl->server.authenticate == A_ANY)) {
        ok = do_pop3_ntlm(sock, ctl, 0);
        if (ok == 0 || ctl->server.authenticate != A_ANY)
            break;
    }
#else
    if (ctl->server.authenticate == A_NTLM || ctl->server.authenticate == A_MSN)
    {
        report(stderr,
           GT_("Required NTLM capability not compiled into fetchmail\n"));
    }
#endif

        if (ctl->server.authenticate == A_CRAM_MD5 || 
            (has_cram && ctl->server.authenticate == A_ANY))
        {
            ok = do_cram_md5(sock, "AUTH", ctl, NULL);
            if (ok == PS_SUCCESS || ctl->server.authenticate != A_ANY)
                break;
        }

        /* ordinary validation, no one-time password or RPA */ 
        if ((ok = gen_transact(sock, "USER %s", ctl->remotename)))
            break;

#ifdef OPIE_ENABLE
        /* see RFC1938: A One-Time Password System */
        if ((challenge = strstr(lastok, "otp-"))) {
          char response[OPIE_RESPONSE_MAX+1];
          int i;
          char *n = xstrdup("");

          i = opiegenerator(challenge, !strcmp(ctl->password, "opie") ? n : ctl->password, response);
          free(n);
          if ((i == -2) && !run.poll_interval) {
            char secret[OPIE_SECRET_MAX+1];
            fprintf(stderr, GT_("Secret pass phrase: "));
            if (opiereadpass(secret, sizeof(secret), 0))
              i = opiegenerator(challenge,  secret, response);
            memset(secret, 0, sizeof(secret));
          };

          if (i) {
            ok = PS_ERROR;
            break;
          };

          ok = gen_transact(sock, "PASS %s", response);
          break;
        }
#endif /* OPIE_ENABLE */

        /* KPOP uses out-of-band authentication and does not check what
         * we send here, so send some random fixed string, to avoid
         * users switching *to* KPOP accidentally revealing their
         * password */
        if ((ctl->server.authenticate == A_ANY
                    || ctl->server.authenticate == A_KERBEROS_V5)
                && (ctl->server.service != NULL
                    && strcmp(ctl->server.service, KPOP_PORT) == 0))
        {
            ok = gen_transact(sock, "PASS krb_ticket");
            break;
        }

        /* check if we are actually allowed to send the password */
        if (ctl->server.authenticate == A_ANY
                || ctl->server.authenticate == A_PASSWORD) {
            strlcpy(shroud, ctl->password, sizeof(shroud));
            ok = gen_transact(sock, "PASS %s", ctl->password);
        } else {
            report(stderr, GT_("We've run out of allowed authenticators and cannot continue.\n"));
            ok = PS_AUTHFAIL;
        }
        memset(shroud, 0x55, sizeof(shroud));
        shroud[0] = '\0';
        break;

    case P_APOP:
        /* build MD5 digest from greeting timestamp + password */
        /* find start of timestamp */
        for (start = greeting;  *start != 0 && *start != '<';  start++)
            continue;
        if (*start == 0) {
            report(stderr,
                   GT_("Required APOP timestamp not found in greeting\n"));
            return(PS_AUTHFAIL);
        }

        /* find end of timestamp */
        for (end = start;  *end != 0  && *end != '>';  end++)
            continue;
        if (*end == 0 || end == start + 1) {
            report(stderr, 
                   GT_("Timestamp syntax error in greeting\n"));
            return(PS_AUTHFAIL);
        }
        else
            *++end = '\0';

        /* SECURITY: 2007-03-17
         * Strictly validating the presented challenge for RFC-822
         * conformity (it must be a msg-id in terms of that standard) is
         * supposed to make attacks against the MD5 implementation
         * harder[1]
         *
         * [1] "Security vulnerability in APOP authentication",
         *     Gaëtan Leurent, fetchmail-devel, 2007-03-17 */
        if (!rfc822_valid_msgid((unsigned char *)start)) {
            report(stderr,
                    GT_("Invalid APOP timestamp.\n"));
            return PS_AUTHFAIL;
        }

        /* copy timestamp and password into digestion buffer */
        msg = (char *)xmalloc((end-start+1) + strlen(ctl->password) + 1);
        strcpy(msg,start);
        strcat(msg,ctl->password);
        strcpy((char *)ctl->digest, MD5Digest((unsigned char *)msg));
        free(msg);

        ok = gen_transact(sock, "APOP %s %s", ctl->remotename, (char *)ctl->digest);
        break;

    default:
        report(stderr, GT_("Undefined protocol request in POP3_auth\n"));
        ok = PS_ERROR;
    }

#ifdef SSL_ENABLE
    /* this is for servers which claim to support TLS, but actually
     * don't! */
    if (connection_may_have_tls_errors
                    && (ok == PS_SOCKET || ok == PS_PROTOCOL))
    {
        xfree(ctl->sslproto);
        ctl->sslproto = xstrdup("");
        /* repoll immediately without TLS */
        ok = PS_REPOLL;
    }
#endif

    if (ok != 0)
    {
        /* maybe we detected a lock-busy condition? */
        if (ok == PS_LOCKBUSY)
            report(stderr, GT_("lock busy!  Is another session active?\n")); 

        return(ok);
    }

/* Disable the sleep. Based on patch by Brian Candler 2004-04-19/2004-11-08,
 * accepted by Matthias Andree.
 *
 * Rationale: the server must have locked the spool before returning +OK;
 * this sleep just wastes time and hence, for modem and GSM CSD users, money. */
#ifdef WANT_BOGUS
    /*
     * Empirical experience shows some server/OS combinations
     * may need a brief pause even after any lockfiles on the
     * server are released, to give the server time to finish
     * copying back very large mailfolders from the temp-file...
     * this is only ever an issue with extremely large mailboxes.
     */
    sleep(3); /* to be _really_ safe, probably need sleep(5)! */
#endif

    /* we're approved */
    return(PS_SUCCESS);
}

/* cut off C string at first POSIX space */
static void trim(char *s) {
    s += strcspn(s, POSIX_space);
    s[0] = '\0';
}

/** Parse the UID response (leading +OK must have been
 * stripped off) in buf, store the number in gotnum, and store the ID
 * into the caller-provided buffer "id" of size "idsize".
 * Returns PS_SUCCESS or PS_PROTOCOL for failure. */
static int parseuid(const char *buf, unsigned long *gotnum, char *id, size_t idsize)
{
    const char *i;
    char *j;

    /* skip leading blanks ourselves */
    i = buf;
    i += strspn(i, POSIX_space);
    errno = 0;
    *gotnum = strtoul(i, &j, 10);
    if (j == i || !*j || errno || NULL == strchr(POSIX_space, *j)) {
        report(stderr, GT_("Cannot handle UIDL response from upstream server.\n"));
        return PS_PROTOCOL;
    }
    j += strspn(j, POSIX_space);
    strlcpy(id, j, idsize);
    trim(id);
    return PS_SUCCESS;
}

/** request UIDL for single message \a num and stuff the result into the
 * buffer \a id which can hold \a idsize bytes */
static int pop3_getuidl(int sock, int num, char *id /** output */, size_t idsize)
{
    int ok;
    char buf [POPBUFSIZE+1];
    unsigned long gotnum;

    gen_send(sock, "UIDL %d", num);
    if ((ok = pop3_ok(sock, buf)) != 0)
        return(ok);
    if ((ok = parseuid(buf, &gotnum, id, idsize)))
        return ok;
    if (gotnum != (unsigned long)num) {
        report(stderr, GT_("Server responded with UID for wrong message.\n"));
        return PS_PROTOCOL;
    }
    return(PS_SUCCESS);
}

static int pop3_fastuidl( int sock,  struct query *ctl, unsigned int count, int *newp)
{
    int ok;
    unsigned int first_nr, last_nr, try_nr;
    char id [IDLEN+1];

    first_nr = 0;
    last_nr = count + 1;
    while (first_nr < last_nr - 1)
    {
        struct uid_db_record *rec;

        try_nr = (first_nr + last_nr) / 2;
        if ((ok = pop3_getuidl(sock, try_nr, id, sizeof(id))) != 0)
            return ok;
        if ((rec = find_uid_by_id(&ctl->oldsaved, id)))
        {
            flag mark = rec->status;
            if (mark == UID_DELETED || mark == UID_EXPUNGED)
            {
                if (outlevel >= O_VERBOSE)
                    report(stderr, GT_("id=%s (num=%u) was deleted, but is still present!\n"), id, try_nr);
                /* just mark it as seen now! */
                rec->status = mark = UID_SEEN;
            }

            /* narrow the search region! */
            if (mark == UID_UNSEEN)
            {
                if (outlevel >= O_DEBUG)
                    report(stdout, GT_("%u is unseen\n"), try_nr);
                last_nr = try_nr;
            }
            else
                first_nr = try_nr;

            /* save the number */
            set_uid_db_num(&ctl->oldsaved, rec, try_nr);
        }
        else
        {
            if (outlevel >= O_DEBUG)
                report(stdout, GT_("%u is unseen\n"), try_nr);
            last_nr = try_nr;

            /* save it */
            rec = uid_db_insert(&ctl->oldsaved, id, UID_UNSEEN);
            set_uid_db_num(&ctl->oldsaved, rec, try_nr);
        }
    }
    if (outlevel >= O_DEBUG && last_nr <= count)
        report(stdout, GT_("%u is first unseen\n"), last_nr);

    /* update last! */
    *newp = count - first_nr;
    last = first_nr;
    return 0;
}

static int pop3_getrange(int sock, 
                         struct query *ctl,
                         const char *folder,
                         int *countp, int *newp, int *bytes)
/* get range of messages to be fetched */
{
    int ok;
    char buf [POPBUFSIZE+1];

    (void)folder;
    /* Ensure that the new list is properly empty */
    clear_uid_db(&ctl->newsaved);

#ifdef MBOX
    /* Alain Knaff suggests this, but it's not RFC standard */
    if (folder)
        if ((ok = gen_transact(sock, "MBOX %s", folder)))
            return ok;
#endif /* MBOX */

    /* get the total message count */
    gen_send(sock, "STAT");
    ok = pop3_ok(sock, buf);
    if (ok == 0) {
        int asgn;

        asgn = sscanf(buf,"%d %d", countp, bytes);
        if (asgn != 2)
                return PS_PROTOCOL;
    } else
        return(ok);

    /* unless fetching all mail, get UID list (UIDL) */
    last = 0;
    *newp = -1;
    if (*countp > 0)
    {
        int fastuidl;
        char id [IDLEN+1];

        set_uid_db_num_pos_0(&ctl->oldsaved, *countp);
        set_uid_db_num_pos_0(&ctl->newsaved, *countp);

        /* should we do fast uidl this time? */
        fastuidl = ctl->fastuidl;
        if (*countp > 7 &&              /* linear search is better if there are few mails! */
            !ctl->fetchall &&           /* with fetchall, all uids are required */
            !ctl->flush &&              /* with flush, it is safer to disable fastuidl */
            NUM_NONZERO (fastuidl))
        {
            if (fastuidl == 1)
                dofastuidl = 1;
            else
                dofastuidl = ctl->fastuidlcount != 0;
        }
        else
            dofastuidl = 0;

        {
            /* do UIDL */
            if (dofastuidl)
                return(pop3_fastuidl( sock, ctl, *countp, newp));
            /* grab the mailbox's UID list */
            if (gen_transact(sock, "UIDL") != 0)
            {
                    report(stderr, GT_("protocol error while fetching UIDLs\n"));
                    return(PS_ERROR);
            }
            else
            {
                /* UIDL worked - parse reply */
                unsigned long unum;

                *newp = 0;
                while (gen_recv(sock, buf, sizeof(buf)) == PS_SUCCESS)
                {
                    if (DOTLINE(buf))
                        break;

                    if (parseuid(buf, &unum, id, sizeof(id)) == PS_SUCCESS)
                    {
                        struct uid_db_record    *old_rec, *new_rec;

                        new_rec = uid_db_insert(&ctl->newsaved, id, UID_UNSEEN);

                        if ((old_rec = find_uid_by_id(&ctl->oldsaved, id)))
                        {
                            flag mark = old_rec->status;
                            if (mark == UID_DELETED || mark == UID_EXPUNGED)
                            {
                                /* XXX FIXME: switch 3 occurrences from
                                 * (int)unum or (unsigned int)unum to
                                 * remove the cast and use %lu - not now
                                 * though, time for new release */
                                if (outlevel >= O_VERBOSE)
                                    report(stderr, GT_("id=%s (num=%d) was deleted, but is still present!\n"), id, (int)unum);
                                /* just mark it as seen now! */
                                old_rec->status = mark = UID_SEEN;
                            }
                            new_rec->status = mark;
                            if (mark == UID_UNSEEN)
                            {
                                (*newp)++;
                                if (outlevel >= O_DEBUG)
                                    report(stdout, GT_("%u is unseen\n"), (unsigned int)unum);
                            }
                        }
                        else
                        {
                            (*newp)++;
                            if (outlevel >= O_DEBUG)
                                report(stdout, GT_("%u is unseen\n"), (unsigned int)unum);
                            /* add it to oldsaved also! In case, we do not
                             * swap the lists (say, due to socket error),
                             * the same mail will not be downloaded again.
                             */
                            old_rec = uid_db_insert(&ctl->oldsaved, id, UID_UNSEEN);

                        }
                        /* save the number */
                        if (new_rec->status == UID_UNSEEN || !ctl->keep) {
                            set_uid_db_num(&ctl->oldsaved, old_rec, unum);
                            set_uid_db_num(&ctl->newsaved, new_rec, unum);
                        }
                    } else
                        return PS_ERROR;
                } /* multi-line loop for UIDL reply */
            } /* UIDL parser */
        } /* do UIDL */
    }

    return(PS_SUCCESS);
}

static int pop3_getpartialsizes(int sock, int first, int last, int *sizes)
/* capture the size of message #first */
{
    int ok = 0, i, num;
    char buf [POPBUFSIZE+1];
    unsigned int size;

    for (i = first; i <= last; i++) {
        gen_send(sock, "LIST %d", i);
        if ((ok = pop3_ok(sock, buf)) != 0)
            return(ok);
        if (sscanf(buf, "%d %u", &num, &size) == 2) {
            if (num == i)
                sizes[i - first] = size;
            else
                /* warn about possible attempt to induce buffer overrun
                 *
                 * we expect server reply message number and requested
                 * message number to match */
                report(stderr, "Warning: ignoring bogus data for message sizes returned by server.\n");
        }
    }
    return(ok);
}

static int pop3_getsizes(int sock, int count, int *sizes)
/* capture the sizes of all messages */
{
    int ok;

    if ((ok = gen_transact(sock, "LIST")) != 0)
        return(ok);
    else
    {
        char buf [POPBUFSIZE+1];

        while ((ok = gen_recv(sock, buf, sizeof(buf))) == 0)
        {
            unsigned int num, size;

            if (DOTLINE(buf))
                break;
            else if (sscanf(buf, "%u %u", &num, &size) == 2) {
                if (num > 0 && num <= (unsigned)count)
                    sizes[num - 1] = size;
                else
                    /* warn about possible attempt to induce buffer overrun */
                    report(stderr, "Warning: ignoring bogus data for message sizes returned by server.\n");
            }
        }

        return(ok);
    }
}

static int pop3_is_old(int sock, struct query *ctl, int num)
/* is the given message old? */
{
    struct uid_db_record *rec;

    if (!uid_db_n_records(&ctl->oldsaved))
        return (num <= last);
    else if (dofastuidl)
    {
        char id [IDLEN+1];

        if (num <= last)
            return(TRUE);

        /* in fast uidl, we manipulate the old list only! */
        if ((rec = find_uid_by_num(&ctl->oldsaved, num)))
        {
            /* we already have the id! */
            return(rec->status != UID_UNSEEN);
        }

        /* get the uidl first! */
        if (pop3_getuidl(sock, num, id, sizeof(id)) != PS_SUCCESS)
            return(TRUE);

        if ((rec = find_uid_by_id(&ctl->oldsaved, id))) {
            /* we already have the id! */
            set_uid_db_num(&ctl->oldsaved, rec, num);
            return(rec->status != UID_UNSEEN);
        }

        /* save it */
        rec = uid_db_insert(&ctl->oldsaved, id, UID_UNSEEN);
        set_uid_db_num(&ctl->oldsaved, rec, num);

        return(FALSE);
    } else {
        rec = find_uid_by_num(&ctl->newsaved, num);
        return !rec || rec->status != UID_UNSEEN;
    }
}

static int pop3_fetch(int sock, struct query *ctl, int number, int *lenp)
/* request nth message */
{
    int ok;
    char buf[POPBUFSIZE+1];

#ifdef SDPS_ENABLE
    /*
     * See http://www.demon.net/helpdesk/producthelp/mail/sdps-tech.html/
     * for a description of what we're parsing here.
     * -- updated 2006-02-22
     */
    if (ctl->server.sdps)
    {
        int     linecount = 0;

        sdps_envfrom = (char *)NULL;
        sdps_envto = (char *)NULL;
        gen_send(sock, "*ENV %d", number);
        do {
            if (gen_recv(sock, buf, sizeof(buf)))
            {
                break;
            }
            linecount++;
            switch (linecount) {
            case 4:
                /* No need to wrap envelope from address */
                /* FIXME: some parts of fetchmail don't handle null
                 * envelope senders, so use <> to mark null sender
                 * as a workaround. */
                if (strspn(buf, " \t") == strlen(buf))
                    strcpy(buf, "<>");
                sdps_envfrom = (char *)xmalloc(strlen(buf)+1);
                strcpy(sdps_envfrom,buf);
                break;
            case 5:
                /* Wrap address with To: <> so nxtaddr() likes it */
                sdps_envto = (char *)xmalloc(strlen(buf)+7);
                sprintf(sdps_envto,"To: <%s>",buf);
                break;
            }
        } while
            (!(buf[0] == '.' && (buf[1] == '\r' || buf[1] == '\n' || buf[1] == '\0')));
    }
#else
    (void)ctl;
#endif /* SDPS_ENABLE */

    /*
     * Though the POP RFCs don't document this fact, on almost every
     * POP3 server I know of messages are marked "seen" only at the
     * time the OK response to a RETR is issued.
     *
     * This means we can use TOP to fetch the message without setting its
     * seen flag.  This is good!  It means that if the protocol exchange
     * craps out during the message, it will still be marked `unseen' on
     * the server.  (Exception: in early 1999 SpryNet's POP3 servers were
     * reported to mark messages seen on a TOP fetch.)
     *
     * However...*don't* do this if we're using keep to suppress deletion!
     * In that case, marking the seen flag is the only way to prevent the
     * message from being re-fetched on subsequent runs.
     *
     * Also use RETR (that means no TOP, no peek) if fetchall is on.
     * This gives us a workaround for servers like usa.net's that bungle
     * TOP.  It's pretty harmless because fetchall guarantees that any
     * message dropped by an interrupted RETR will be picked up on the
     * next poll of the site.
     *
     * We take advantage here of the fact that, according to all the
     * POP RFCs, "if the number of lines requested by the POP3 client
     * is greater than than the number of lines in the body, then the
     * POP3 server sends the entire message.").
     *
     * The line count passed (99999999) is the maximum value CompuServe will
     * accept; it's much lower than the natural value 2147483646 (the maximum
     * twos-complement signed 32-bit integer minus 1) */
    if (!peek_capable)
        gen_send(sock, "RETR %d", number);
    else
        gen_send(sock, "TOP %d 99999999", number);
    if ((ok = pop3_ok(sock, buf)) != 0)
        return(ok);

    *lenp = -1;         /* we got sizes from the LIST response */

    return(PS_SUCCESS);
}

static void mark_uid_seen(struct query *ctl, int number)
/* Tell the UID code we've seen this. */
{
    struct uid_db_record *rec;

    if ((rec = find_uid_by_num(&ctl->newsaved, number)))
        rec->status = UID_SEEN;
    /* mark it as seen in oldsaved also! In case, we do not swap the lists
     * (say, due to socket error), the same mail will not be downloaded
     * again.
     */
    if ((rec = find_uid_by_num(&ctl->oldsaved, number)))
        rec->status = UID_SEEN;
}

static int pop3_delete(int sock, struct query *ctl, int number)
/* delete a given message */
{
    struct uid_db_record *rec;
    int ok;
    mark_uid_seen(ctl, number);
    /* actually, mark for deletion -- doesn't happen until QUIT time */
    ok = gen_transact(sock, "DELE %d", number);
    if (ok != PS_SUCCESS)
        return(ok);

    rec = find_uid_by_num(dofastuidl ? &ctl->oldsaved : &ctl->newsaved, number);
    rec->status = UID_DELETED;
    return(PS_SUCCESS);
}

static int pop3_mark_seen(int sock, struct query *ctl, int number)
/* mark a given message as seen */
{
    (void)sock;
    mark_uid_seen(ctl, number);
    return(PS_SUCCESS);
}

static int pop3_logout(int sock, struct query *ctl)
/* send logout command */
{
    int ok;

    ok = gen_transact(sock, "QUIT");
    if (!ok)
        expunge_uids(ctl);

    return(ok);
}

static const struct method pop3 =
{
    "POP3",             /* Post Office Protocol v3 */
    "pop3",             /* port for plain and TLS POP3 */
    "pop3s",            /* port for SSL POP3 */
    FALSE,              /* this is not a tagged protocol */
    TRUE,               /* this uses a message delimiter */
    pop3_ok,            /* parse command response */
    pop3_getauth,       /* get authorization */
    pop3_getrange,      /* query range of messages */
    pop3_getsizes,      /* we can get a list of sizes */
    pop3_getpartialsizes,       /* we can get the size of 1 mail */
    pop3_is_old,        /* how do we tell a message is old? */
    pop3_fetch,         /* request given message */
    NULL,               /* no way to fetch body alone */
    NULL,               /* no message trailer */
    pop3_delete,        /* how to delete a message */
    pop3_mark_seen,     /* how to mark a message as seen */
    NULL,               /* no action at end of mailbox */
    pop3_logout,        /* log out, we're done */
    FALSE,              /* no, we can't re-poll */
};

int doPOP3 (struct query *ctl)
/* retrieve messages using POP3 */
{
#ifndef MBOX
    if (ctl->mailboxes->id) {
        fprintf(stderr,GT_("Option --folder is not supported with POP3\n"));
        return(PS_SYNTAX);
    }
#endif /* MBOX */

    return(do_protocol(ctl, &pop3));
}
#endif /* POP3_ENABLE */

/* pop3.c ends here */