[chise/xemacs-chise.git.1] / lib-src / pop.c

/* pop.c: client routines for talking to a POP3-protocol post-office server
   Copyright (c) 1991, 1993, 1996 Free Software Foundation, Inc.
   Written by Jonathan Kamens, jik@security.ov.com.

This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Emacs 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 GNU Emacs; see the file COPYING.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#ifdef HAVE_CONFIG_H
#define NO_SHORTNAMES   /* Tell config not to load remap.h */
#include <../src/config.h>
#else
#define MAIL_USE_POP
#endif

#ifdef MAIL_USE_POP

#ifdef HAVE_CONFIG_H
/* Cancel these substitutions made in config.h */
#undef open
#undef read
#undef write
#undef close
#endif

#include <sys/types.h>
#ifdef WINDOWSNT
#include "ntlib.h"
#include <winsock.h>
#undef SOCKET_ERROR
#define RECV(s,buf,len,flags) recv(s,buf,len,flags)
#define SEND(s,buf,len,flags) send(s,buf,len,flags)
#define CLOSESOCKET(s) closesocket(s)
#else
#include <netinet/in.h>
#include <sys/socket.h>
#define RECV(s,buf,len,flags) read(s,buf,len)
#define SEND(s,buf,len,flags) write(s,buf,len)
#define CLOSESOCKET(s) close(s)
#endif
#include "pop.h"

#ifdef sun
#include <malloc.h>
#endif /* sun */

#ifdef HESIOD
#include <hesiod.h>
/*
 * It really shouldn't be necessary to put this declaration here, but
 * the version of hesiod.h that Athena has installed in release 7.2
 * doesn't declare this function; I don't know if the 7.3 version of
 * hesiod.h does.
 */
extern struct servent *hes_getservbyname (/* char *, char * */);
#endif

#include <pwd.h>
#include <netdb.h>
#include <errno.h>
#include <stdio.h>

#include <unistd.h>
#include <sys/stat.h>
#include <sys/file.h>
#include "../src/syswait.h"
#include "../src/systime.h"
#include <stdlib.h>
#include <string.h>

#ifdef KERBEROS
#ifndef KRB5
#include <des.h>
#include <krb.h>
#else /* KRB5 */
#include <krb5/krb5.h>
#include <krb5/ext-proto.h>
#include <ctype.h>
#endif /* KRB5 */
#endif /* KERBEROS */

#ifdef KERBEROS
#ifndef KRB5
extern int krb_sendauth (/* long, int, KTEXT, char *, char *, char *,
                            u_long, MSG_DAT *, CREDENTIALS *, Key_schedule,
                            struct sockaddr_in *, struct sockaddr_in *,
                            char * */);
extern char *krb_realmofhost (/* char * */);
#endif /* ! KRB5 */
#endif /* KERBEROS */

#ifndef WINDOWSNT
#if !defined(HAVE_H_ERRNO) || !defined(HAVE_CONFIG_H)
extern int h_errno;
#endif
#endif

static int socket_connection (char *, int);
static char *pop_getline (popserver);
static int sendline (popserver, char *);
static int fullwrite (int, char *, int);
static int getok (popserver);
#if 0
static int gettermination (popserver);
#endif
static void pop_trash (popserver);
static char *find_crlf (char *);

#define ERROR_MAX 80            /* a pretty arbitrary size */
#define POP_PORT 110
#define KPOP_PORT 1109
#if defined(WINDOWSNT) || defined(__CYGWIN32__)
#define POP_SERVICE "pop3"      /* we don't want the POP2 port! */
#else
#define POP_SERVICE "pop"
#endif
#ifdef KERBEROS
#ifdef KRB5
#define KPOP_SERVICE "k5pop";
#else
#define KPOP_SERVICE "kpop"
#endif
#endif

char pop_error[ERROR_MAX];
int pop_debug = 0;

#ifndef min
#define min(a,b) (((a) < (b)) ? (a) : (b))
#endif

/*
 * Function: pop_open (char *host, char *username, char *password,
 *                     int flags)
 *
 * Purpose: Establishes a connection with a post-office server, and
 *      completes the authorization portion of the session.
 *
 * Arguments:
 *      host    The server host with which the connection should be
 *              established.  Optional.  If omitted, internal
 *              heuristics will be used to determine the server host,
 *              if possible.
 *      username
 *              The username of the mail-drop to access.  Optional.
 *              If omitted, internal heuristics will be used to
 *              determine the username, if possible.
 *      password
 *              The password to use for authorization.  If omitted,
 *              internal heuristics will be used to determine the
 *              password, if possible.
 *      flags   A bit mask containing flags controlling certain
 *              functions of the routine.  Valid flags are defined in
 *              the file pop.h
 *
 * Return value: Upon successful establishment of a connection, a
 *      non-null popserver will be returned.  Otherwise, null will be
 *      returned, and the string variable pop_error will contain an
 *      explanation of the error.
 */
popserver
pop_open (char *host, char *username, char *password, int flags)
{
  int sock;
  popserver server;

  /* Determine the user name */
  if (! username)
    {
      username = getenv ("USER");
      if (! (username && *username))
        {
          username = getlogin ();
          if (! (username && *username))
            {
              struct passwd *passwd;
              passwd = getpwuid (getuid ());
              if (passwd && passwd->pw_name && *passwd->pw_name)
                {
                  username = passwd->pw_name;
                }
              else
                {
                  strcpy (pop_error, "Could not determine username");
                  return (0);
                }
            }
        }
    }

  /*
   *  Determine the mail host.
   */

  if (! host)
    {
      host = getenv ("MAILHOST");
    }

#ifdef HESIOD
  if ((! host) && (! (flags & POP_NO_HESIOD)))
    {
      struct hes_postoffice *office;
      office = hes_getmailhost (username);
      if (office && office->po_type && (! strcmp (office->po_type, "POP"))
          && office->po_name && *office->po_name && office->po_host
          && *office->po_host)
        {
          host = office->po_host;
          username = office->po_name;
        }
    }
#endif

#ifdef MAILHOST
  if (! host)
    {
      host = MAILHOST;
    }
#endif

  if (! host)
    {
      strcpy (pop_error, "Could not determine POP server");
      return (0);
    }

  /* Determine the password */
#ifdef KERBEROS
#define DONT_NEED_PASSWORD (! (flags & POP_NO_KERBEROS))
#else
#define DONT_NEED_PASSWORD 0
#endif
 
  if ((! password) && (! DONT_NEED_PASSWORD))
    {
      if (! (flags & POP_NO_GETPASS))
        {
          password = getpass ("Enter POP password:");
        }
      if (! password)
        {
          strcpy (pop_error, "Could not determine POP password");
          return (0);
        }
    }
  if (password)
    flags |= POP_NO_KERBEROS;
  else
    password = username;

  sock = socket_connection (host, flags);
  if (sock == -1)
    return (0);

  server = (popserver) malloc (sizeof (struct _popserver));
  if (! server)
    {
      strcpy (pop_error, "Out of memory in pop_open");
      return (0);
    }
  server->buffer = (char *) malloc (GETLINE_MIN);
  if (! server->buffer)
    {
      strcpy (pop_error, "Out of memory in pop_open");
      free ((char *) server);
      return (0);
    }
          
  server->file = sock;
  server->data = 0;
  server->buffer_index = 0;
  server->buffer_size = GETLINE_MIN;
  server->in_multi = 0;
  server->trash_started = 0;

  if (getok (server))
    return (0);

  /*
   * I really shouldn't use the pop_error variable like this, but....
   */
  if (strlen (username) > ERROR_MAX - 6)
    {
      pop_close (server);
      strcpy (pop_error,
              "Username too long; recompile pop.c with larger ERROR_MAX");
      return (0);
    }
  sprintf (pop_error, "USER %s", username);

  if (sendline (server, pop_error) || getok (server))
    {
      return (0);
    }

  if (strlen (password) > ERROR_MAX - 6)
    {
      pop_close (server);
      strcpy (pop_error,
              "Password too long; recompile pop.c with larger ERROR_MAX");
      return (0);
    }
  sprintf (pop_error, "PASS %s", password);

  if (sendline (server, pop_error) || getok (server))
    {
      return (0);
    }

  return (server);
}

/*
 * Function: pop_stat
 *
 * Purpose: Issue the STAT command to the server and return (in the
 *      value parameters) the number of messages in the maildrop and
 *      the total size of the maildrop.
 *
 * Return value: 0 on success, or non-zero with an error in pop_error
 *      in failure.
 *
 * Side effects: On failure, may make further operations on the
 *      connection impossible.
 */
int
pop_stat (popserver server, int *count, int *size)
{
  char *fromserver;

  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_stat");
      return (-1);
    }
     
  if (sendline (server, "STAT") || (! (fromserver = pop_getline (server))))
    return (-1);

  if (strncmp (fromserver, "+OK ", 4))
    {
      if (0 == strncmp (fromserver, "-ERR", 4))
        {
          strncpy (pop_error, fromserver, ERROR_MAX);
        }
      else
        {
          strcpy (pop_error,
                  "Unexpected response from POP server in pop_stat");
          pop_trash (server);
        }
      return (-1);
    }

  *count = atoi (&fromserver[4]);
     
  fromserver = strchr (&fromserver[4], ' ');
  if (! fromserver)
    {
      strcpy (pop_error,
              "Badly formatted response from server in pop_stat");
      pop_trash (server);
      return (-1);
    }

  *size = atoi (fromserver + 1);

  return (0);
}

/*
 * Function: pop_list
 *
 * Purpose: Performs the POP "list" command and returns (in value
 *      parameters) two malloc'd zero-terminated arrays -- one of
 *      message IDs, and a parallel one of sizes.
 *
 * Arguments:
 *      server  The pop connection to talk to.
 *      message The number of the one message about which to get
 *              information, or 0 to get information about all
 *              messages.
 *
 * Return value: 0 on success, non-zero with error in pop_error on
 *      failure.
 *
 * Side effects: On failure, may make further operations on the
 *      connection impossible.
 */
int
pop_list (popserver server, int message, int **IDs, int **sizes)
{
  int how_many, i;
  char *fromserver;

  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_list");
      return (-1);
    }

  if (message)
    how_many = 1;
  else
    {
      int count, size;
      if (pop_stat (server, &count, &size))
        return (-1);
      how_many = count;
    }

  *IDs = (int *) malloc ((how_many + 1) * sizeof (int));
  *sizes = (int *) malloc ((how_many + 1) * sizeof (int));
  if (! (*IDs && *sizes))
    {
      strcpy (pop_error, "Out of memory in pop_list");
      return (-1);
    }

  if (message)
    {
      sprintf (pop_error, "LIST %d", message);
      if (sendline (server, pop_error))
        {
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      if (! (fromserver = pop_getline (server)))
        {
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      if (strncmp (fromserver, "+OK ", 4))
        {
          if (! strncmp (fromserver, "-ERR", 4))
            strncpy (pop_error, fromserver, ERROR_MAX);
          else
            {
              strcpy (pop_error,
                      "Unexpected response from server in pop_list");
              pop_trash (server);
            }
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      (*IDs)[0] = atoi (&fromserver[4]);
      fromserver = strchr (&fromserver[4], ' ');
      if (! fromserver)
        {
          strcpy (pop_error,
                  "Badly formatted response from server in pop_list");
          pop_trash (server);
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      (*sizes)[0] = atoi (fromserver);
      (*IDs)[1] = (*sizes)[1] = 0;
      return (0);
    }
  else
    {
      if (pop_multi_first (server, "LIST", &fromserver))
        {
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      for (i = 0; i < how_many; i++)
        {
          if (pop_multi_next (server, &fromserver))
            {
              free ((char *) *IDs);
              free ((char *) *sizes);
              return (-1);
            }
          (*IDs)[i] = atoi (fromserver);
          fromserver = strchr (fromserver, ' ');
          if (! fromserver)
            {
              strcpy (pop_error,
                      "Badly formatted response from server in pop_list");
              free ((char *) *IDs);
              free ((char *) *sizes);
              pop_trash (server);
              return (-1);
            }
          (*sizes)[i] = atoi (fromserver);
        }
      if (pop_multi_next (server, &fromserver))
        {
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      else if (fromserver)
        {
          strcpy (pop_error,
                  "Too many response lines from server in pop_list");
          free ((char *) *IDs);
          free ((char *) *sizes);
          return (-1);
        }
      (*IDs)[i] = (*sizes)[i] = 0;
      return (0);
    }
}

/*
 * Function: pop_retrieve
 *
 * Purpose: Retrieve a specified message from the maildrop.
 *
 * Arguments:
 *      server  The server to retrieve from.
 *      message The message number to retrieve.
 *      markfrom
 *              If true, then mark the string "From " at the beginning
 *              of lines with '>'.
 * 
 * Return value: A string pointing to the message, if successful, or
 *      null with pop_error set if not.
 *
 * Side effects: May kill connection on error.
 */
char *
pop_retrieve (popserver server, int message, int markfrom)
{
  int *IDs, *sizes, bufsize, fromcount = 0, cp = 0;
  char *ptr, *fromserver;
  int ret;

  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_retrieve");
      return (0);
    }

  if (pop_list (server, message, &IDs, &sizes))
    return (0);

  if (pop_retrieve_first (server, message, &fromserver))
    {
      return (0);
    }

  /*
   * The "5" below is an arbitrary constant -- I assume that if
   * there are "From" lines in the text to be marked, there
   * probably won't be more than 5 of them.  If there are, I
   * allocate more space for them below.
   */
  bufsize = sizes[0] + (markfrom ? 5 : 0);
  ptr = (char *)malloc (bufsize);
  free ((char *) IDs);
  free ((char *) sizes);

  if (! ptr)
    {
      strcpy (pop_error, "Out of memory in pop_retrieve");
      pop_retrieve_flush (server);
      return (0);
    }

  while (! (ret = pop_retrieve_next (server, &fromserver)))
    {
      int linesize;

      if (! fromserver)
        {
          ptr[cp] = '\0';
          return (ptr);
        }
      if (markfrom && fromserver[0] == 'F' && fromserver[1] == 'r' &&
          fromserver[2] == 'o' && fromserver[3] == 'm' &&
          fromserver[4] == ' ')
        {
          if (++fromcount == 5)
            {
              bufsize += 5;
              ptr = (char *)realloc (ptr, bufsize);
              if (! ptr)
                {
                  strcpy (pop_error, "Out of memory in pop_retrieve");
                  pop_retrieve_flush (server);
                  return (0);
                }
              fromcount = 0;
            }
          ptr[cp++] = '>';
        }
      linesize = strlen (fromserver);
      memcpy (&ptr[cp], fromserver, linesize);
      cp += linesize;
      ptr[cp++] = '\n';
    }

  if (ret)
    {
      free (ptr);
      /* return (0); */
    }
  /* This function used to fall off the end, but that doesn't make any sense */
  return (0);
}     

int
pop_retrieve_first (popserver server, int message, char **response)
{
  sprintf (pop_error, "RETR %d", message);
  return (pop_multi_first (server, pop_error, response));
}

int
pop_retrieve_next (popserver server, char **line)
{
  return (pop_multi_next (server, line));
}

int
pop_retrieve_flush (popserver server)
{
  return (pop_multi_flush (server));
}

int
pop_top_first (popserver server, int message, int lines, char **response)
{
  sprintf (pop_error, "TOP %d %d", message, lines);
  return (pop_multi_first (server, pop_error, response));
}

int
pop_top_next (popserver server, char **line)
{
  return (pop_multi_next (server, line));
}

int
pop_top_flush (popserver server)
{
  return (pop_multi_flush (server));
}

int
pop_multi_first (popserver server, char *command, char **response)
{
  if (server->in_multi)
    {
      strcpy (pop_error,
              "Already in multi-line query in pop_multi_first");
      return (-1);
    }

  if (sendline (server, command) || (! (*response = pop_getline (server))))
    {
      return (-1);
    }

  if (0 == strncmp (*response, "-ERR", 4))
    {
      strncpy (pop_error, *response, ERROR_MAX);
      return (-1);
    }
  else if (0 == strncmp (*response, "+OK", 3))
    {
      for (*response += 3; **response == ' '; (*response)++) /* empty */;
      server->in_multi = 1;
      return (0);
    }
  else
    {
      strcpy (pop_error,
              "Unexpected response from server in pop_multi_first");
      return (-1);
    }
}

int
pop_multi_next (popserver server, char **line)
{
  char *fromserver;

  if (! server->in_multi)
    {
      strcpy (pop_error, "Not in multi-line query in pop_multi_next");
      return (-1);
    }

  fromserver = pop_getline (server);
  if (! fromserver)
    {
      return (-1);
    }

  if (fromserver[0] == '.')
    {
      if (! fromserver[1])
        {
          *line = 0;
          server->in_multi = 0;
          return (0);
        }
      else
        {
          *line = fromserver + 1;
          return (0);
        }
    }
  else
    {
      *line = fromserver;
      return (0);
    }
}

int
pop_multi_flush (popserver server)
{
  char *line;

  if (! server->in_multi)
    {
      return (0);
    }

  while (! pop_multi_next (server, &line))
    {
      if (! line)
        {
          return (0);
        }
    }

  return (-1);
}

/* Function: pop_delete
 *
 * Purpose: Delete a specified message.
 *
 * Arguments:
 *      server  Server from which to delete the message.
 *      message Message to delete.
 *
 * Return value: 0 on success, non-zero with error in pop_error
 *      otherwise.
 */
int
pop_delete (popserver server, int message)
{
  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_delete");
      return (-1);
    }

  sprintf (pop_error, "DELE %d", message);

  if (sendline (server, pop_error) || getok (server))
    return (-1);

  return (0);
}

/*
 * Function: pop_noop
 *
 * Purpose: Send a noop command to the server.
 *
 * Argument:
 *      server  The server to send to.
 *
 * Return value: 0 on success, non-zero with error in pop_error
 *      otherwise.
 *
 * Side effects: Closes connection on error.
 */
int
pop_noop (popserver server)
{
  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_noop");
      return (-1);
    }

  if (sendline (server, "NOOP") || getok (server))
    return (-1);

  return (0);
}

/*
 * Function: pop_last
 *
 * Purpose: Find out the highest seen message from the server.
 *
 * Arguments:
 *      server  The server.
 *
 * Return value: If successful, the highest seen message, which is
 *      greater than or equal to 0.  Otherwise, a negative number with
 *      the error explained in pop_error.
 *
 * Side effects: Closes the connection on error.
 */
int
pop_last (popserver server)
{
  char *fromserver;
     
  if (server->in_multi)
    {
      strcpy (pop_error, "In multi-line query in pop_last");
      return (-1);
    }

  if (sendline (server, "LAST"))
    return (-1);

  if (! (fromserver = pop_getline (server)))
    return (-1);

  if (! strncmp (fromserver, "-ERR", 4))
    {
      strncpy (pop_error, fromserver, ERROR_MAX);
      return (-1);
    }
  else if (strncmp (fromserver, "+OK ", 4))
    {
      strcpy (pop_error, "Unexpected response from server in pop_last");
      pop_trash (server);
      return (-1);
    }
  else
    {
      return (atoi (&fromserver[4]));
    }
}

/*
 * Function: pop_reset
 *
 * Purpose: Reset the server to its initial connect state
 *
 * Arguments:
 *      server  The server.
 *
 * Return value: 0 for success, non-0 with error in pop_error
 *      otherwise.
 *
 * Side effects: Closes the connection on error.
 */
int
pop_reset (popserver server)
{
  if (pop_retrieve_flush (server))
    {
      return (-1);
    }

  if (sendline (server, "RSET") || getok (server))
    return (-1);

  return (0);
}

/*
 * Function: pop_quit
 *
 * Purpose: Quit the connection to the server,
 *
 * Arguments:
 *      server  The server to quit.
 *
 * Return value: 0 for success, non-zero otherwise with error in
 *      pop_error.
 *
 * Side Effects: The popserver passed in is unusable after this
 *      function is called, even if an error occurs.
 */
int
pop_quit (popserver server)
{
  int ret = 0;

  if (server->file >= 0)
    {
      if (pop_retrieve_flush (server))
        {
          ret = -1;
        }

      if (sendline (server, "QUIT") || getok (server))
        {
          ret = -1;
        }

      close (server->file);
    }

  if (server->buffer)
    free (server->buffer);
  free ((char *) server);

  return (ret);
}

#ifdef WINDOWSNT
static int have_winsock = 0;
#endif

/*
 * Function: socket_connection
 *
 * Purpose: Opens the network connection with the mail host, without
 *      doing any sort of I/O with it or anything.
 *
 * Arguments:
 *      host    The host to which to connect.
 *      flags   Option flags.
 *      
 * Return value: A file descriptor indicating the connection, or -1
 *      indicating failure, in which case an error has been copied
 *      into pop_error.
 */
static int
socket_connection (char *host, int flags)
{
  struct hostent *hostent;
  struct servent *servent;
  struct sockaddr_in addr;
  char found_port = 0;
  char *service;
  int sock;
#ifdef KERBEROS
#ifdef KRB5
  krb5_error_code rem;
  krb5_ccache ccdef;
  krb5_principal client, server;
  krb5_error *err_ret;
  register char *cp;
#else
  KTEXT ticket;
  MSG_DAT msg_data;
  CREDENTIALS cred;
  Key_schedule schedule;
  int rem;
#endif /* KRB5 */
#endif /* KERBEROS */

  int try_count = 0;

#ifdef WINDOWSNT
  {
    WSADATA winsockData;
    if (WSAStartup (0x101, &winsockData) == 0)
      have_winsock = 1;
  }
#endif

  do
    {
      hostent = gethostbyname (host);
      try_count++;
      if ((! hostent) 
#ifndef BROKEN_CYGWIN     
          && ((h_errno != TRY_AGAIN) || (try_count == 5))
#endif
          )
        {
          strcpy (pop_error, "Could not determine POP server's address");
          return (-1);
        }
    } while (! hostent);

  memset (&addr, 0, sizeof (addr));
  addr.sin_family = AF_INET;

#ifdef KERBEROS
  service = (flags & POP_NO_KERBEROS) ? POP_SERVICE : KPOP_SERVICE;
#else
  service = POP_SERVICE;
#endif

#ifdef HESIOD
  if (! (flags & POP_NO_HESIOD))
    {
      servent = hes_getservbyname (service, "tcp");
      if (servent)
        {
          addr.sin_port = servent->s_port;
          found_port = 1;
        }
    }
#endif
  if (! found_port)
    {
      servent = getservbyname (service, "tcp");
      if (servent)
        {
          addr.sin_port = servent->s_port;
        }
      else
        {
#ifdef KERBEROS
          addr.sin_port = htons ((flags & POP_NO_KERBEROS) ?
                                POP_PORT : KPOP_PORT);
#else
          addr.sin_port = htons (POP_PORT);
#endif
        }
    }

#define SOCKET_ERROR "Could not create socket for POP connection: "

  sock = socket (PF_INET, SOCK_STREAM, 0);
  if (sock < 0)
    {
      strcpy (pop_error, SOCKET_ERROR);
      strncat (pop_error, strerror (errno),
               ERROR_MAX - sizeof (SOCKET_ERROR));
      return (-1);
          
    }

  while (*hostent->h_addr_list)
    {
      memcpy (&addr.sin_addr, *hostent->h_addr_list, hostent->h_length);
      if (! connect (sock, (struct sockaddr *) &addr, sizeof (addr)))
        break;
      hostent->h_addr_list++;
    }

#define CONNECT_ERROR "Could not connect to POP server: "
     
  if (! *hostent->h_addr_list)
    {
      CLOSESOCKET (sock);
      strcpy (pop_error, CONNECT_ERROR);
      strncat (pop_error, strerror (errno),
               ERROR_MAX - sizeof (CONNECT_ERROR));
      return (-1);
          
    }

#ifdef KERBEROS
#define KRB_ERROR "Kerberos error connecting to POP server: "
  if (! (flags & POP_NO_KERBEROS))
    {
#ifdef KRB5
      krb5_init_ets ();

      if (rem = krb5_cc_default (&ccdef))
        {
        krb5error:
          strcpy (pop_error, KRB_ERROR);
          strncat (pop_error, error_message (rem),
                   ERROR_MAX - sizeof(KRB_ERROR));
          CLOSESOCKET (sock);
          return (-1);
        }

      if (rem = krb5_cc_get_principal (ccdef, &client))
        {
          goto krb5error;
        }

      for (cp = hostent->h_name; *cp; cp++)
        {
          if (isupper (*cp))
            {
              *cp = tolower (*cp);
            }
        }

      if (rem = krb5_sname_to_principal (hostent->h_name, POP_SERVICE,
                                         FALSE, &server))
        {
          goto krb5error;
        }

      rem = krb5_sendauth ((krb5_pointer) &sock, "KPOPV1.0", client, server,
                          AP_OPTS_MUTUAL_REQUIRED,
                          0,    /* no checksum */
                          0,    /* no creds, use ccache instead */
                          ccdef,
                          0,    /* don't need seq # */
                          0,    /* don't need subsession key */
                          &err_ret,
                          0);   /* don't need reply */
      krb5_free_principal (server);
      if (rem)
        {
          if (err_ret && err_ret->text.length)
            {
              strcpy (pop_error, KRB_ERROR);
              strncat (pop_error, error_message (rem),
                       ERROR_MAX - sizeof (KRB_ERROR));
              strncat (pop_error, " [server says '",
                       ERROR_MAX - strlen (pop_error) - 1);
              strncat (pop_error, err_ret->text.data,
                       min (ERROR_MAX - strlen (pop_error) - 1,
                            err_ret->text.length));
              strncat (pop_error, "']",
                       ERROR_MAX - strlen (pop_error) - 1);
            }
          else
            {
              strcpy (pop_error, KRB_ERROR);
              strncat (pop_error, error_message (rem),
                       ERROR_MAX - sizeof (KRB_ERROR));
            }
          if (err_ret)
            krb5_free_error (err_ret);

          CLOSESOCKET (sock);
          return (-1);
        }
#else  /* ! KRB5 */       
      ticket = (KTEXT) malloc (sizeof (KTEXT_ST));
      rem = krb_sendauth (0L, sock, ticket, "pop", hostent->h_name,
                          (char *) krb_realmofhost (hostent->h_name),
                          (unsigned long) 0, &msg_data, &cred, schedule,
                          (struct sockaddr_in *) 0,
                          (struct sockaddr_in *) 0,
                          "KPOPV0.1");
      free ((char *) ticket);
      if (rem != KSUCCESS)
        {
          strcpy (pop_error, KRB_ERROR);
          strncat (pop_error, krb_err_txt[rem],
                   ERROR_MAX - sizeof (KRB_ERROR));
          CLOSESOCKET (sock);
          return (-1);
        }
#endif /* KRB5 */
    }
#endif /* KERBEROS */

  return (sock);
} /* socket_connection */

/*
 * Function: pop_getline
 *
 * Purpose: Get a line of text from the connection and return a
 *      pointer to it.  The carriage return and linefeed at the end of
 *      the line are stripped, but periods at the beginnings of lines
 *      are NOT dealt with in any special way.
 *
 * Arguments:
 *      server  The server from which to get the line of text.
 *
 * Returns: A non-null pointer if successful, or a null pointer on any
 *      error, with an error message copied into pop_error.
 *
 * Notes: The line returned is overwritten with each call to pop_getline.
 *
 * Side effects: Closes the connection on error.
 */
static char *
pop_getline (popserver server)
{
#define GETLINE_ERROR "Error reading from server: "

  int ret;
  int search_offset = 0;

  if (server->data)
    {
      char *cp = find_crlf (server->buffer + server->buffer_index);
      if (cp)
        {
          int found;
          int data_used;

          found = server->buffer_index;
          data_used = (cp + 2) - server->buffer - found;
               
          *cp = '\0';           /* terminate the string to be returned */
          server->data -= data_used;
          server->buffer_index += data_used;

          if (pop_debug)
            fprintf (stderr, "<<< %s\n", server->buffer + found);
          return (server->buffer + found);
        }
      else
        {
          memcpy (server->buffer,
                  server->buffer + server->buffer_index,
                  server->data);
          /* Record the fact that we've searched the data already in
             the buffer for a CRLF, so that when we search below, we
             don't have to search the same data twice.  There's a "-
             1" here to account for the fact that the last character
             of the data we have may be the CR of a CRLF pair, of
             which we haven't read the second half yet, so we may have
             to search it again when we read more data. */
          search_offset = server->data - 1;
          server->buffer_index = 0;
        }
    }
  else
    {
      server->buffer_index = 0;
    }

  while (1)
    {
      /* There's a "- 1" here to leave room for the null that we put
         at the end of the read data below.  We put the null there so
         that find_crlf knows where to stop when we call it. */
      if (server->data == server->buffer_size - 1)
        {
          server->buffer_size += GETLINE_INCR;
          server->buffer = (char *)realloc (server->buffer, server->buffer_size);
          if (! server->buffer)
            {
              strcpy (pop_error, "Out of memory in pop_getline");
              pop_trash (server);
              return (0);
            }
        }
      ret = RECV (server->file, server->buffer + server->data,
                  server->buffer_size - server->data - 1, 0);
      if (ret < 0)
        {
          strcpy (pop_error, GETLINE_ERROR);
          strncat (pop_error, strerror (errno),
                   ERROR_MAX - sizeof (GETLINE_ERROR));
          pop_trash (server);
          return (0);
        }
      else if (ret == 0)
        {
          strcpy (pop_error, "Unexpected EOF from server in pop_getline");
          pop_trash (server);
          return (0);
        }
      else
        {
          char *cp;
          server->data += ret;
          server->buffer[server->data] = '\0';
               
          cp = find_crlf (server->buffer + search_offset);
          if (cp)
            {
              int data_used = (cp + 2) - server->buffer;
              *cp = '\0';
              server->data -= data_used;
              server->buffer_index = data_used;

              if (pop_debug)
                fprintf (stderr, "<<< %s\n", server->buffer);
              return (server->buffer);
            }
          search_offset += ret;
        }
    }

  /* NOTREACHED */
}

/*
 * Function: sendline
 *
 * Purpose: Sends a line of text to the POP server.  The line of text
 *      passed into this function should NOT have the carriage return
 *      and linefeed on the end of it.  Periods at beginnings of lines
 *      will NOT be treated specially by this function.
 *
 * Arguments:
 *      server  The server to which to send the text.
 *      line    The line of text to send.
 *
 * Return value: Upon successful completion, a value of 0 will be
 *      returned.  Otherwise, a non-zero value will be returned, and
 *      an error will be copied into pop_error.
 *
 * Side effects: Closes the connection on error.
 */
static int
sendline (popserver server, char *line)
{
#define SENDLINE_ERROR "Error writing to POP server: "
  int ret;

  ret = fullwrite (server->file, line, strlen (line));
  if (ret >= 0)
    {                           /* 0 indicates that a blank line was written */
      ret = fullwrite (server->file, "\r\n", 2);
    }

  if (ret < 0)
    {
      pop_trash (server);
      strcpy (pop_error, SENDLINE_ERROR);
      strncat (pop_error, strerror (errno),
               ERROR_MAX - sizeof (SENDLINE_ERROR));
      return (ret);
    }

  if (pop_debug)
    fprintf (stderr, ">>> %s\n", line);

  return (0);
}

/*
 * Procedure: fullwrite
 *
 * Purpose: Just like write, but keeps trying until the entire string
 *      has been written.
 *
 * Return value: Same as write.  Pop_error is not set.
 */
static int
fullwrite (int fd, char *buf, int nbytes)
{
  char *cp;
  int ret;

  cp = buf;
  while ((ret = SEND (fd, cp, nbytes, 0)) > 0)
    {
      cp += ret;
      nbytes -= ret;
    }

  return (ret);
}

/*
 * Procedure getok
 *
 * Purpose: Reads a line from the server.  If the return indicator is
 *      positive, return with a zero exit status.  If not, return with
 *      a negative exit status.
 *
 * Arguments:
 *      server  The server to read from.
 * 
 * Returns: 0 for success, else for failure and puts error in pop_error.
 *
 * Side effects: On failure, may make the connection unusable.
 */
static int
getok (popserver server)
{
  char *fromline;

  if (! (fromline = pop_getline (server)))
    {
      return (-1);
    }

  if (! strncmp (fromline, "+OK", 3))
    return (0);
  else if (! strncmp (fromline, "-ERR", 4))
    {
      strncpy (pop_error, fromline, ERROR_MAX);
      pop_error[ERROR_MAX-1] = '\0';
      return (-1);
    }
  else
    {
      strcpy (pop_error,
              "Unexpected response from server; expecting +OK or -ERR");
      pop_trash (server);
      return (-1);
    }
}         

#if 0
/*
 * Function: gettermination
 *
 * Purpose: Gets the next line and verifies that it is a termination
 *      line (nothing but a dot).
 *
 * Return value: 0 on success, non-zero with pop_error set on error.
 *
 * Side effects: Closes the connection on error.
 */
static int
gettermination (popserver server)
{
  char *fromserver;

  fromserver = pop_getline (server);
  if (! fromserver)
    return (-1);

  if (strcmp (fromserver, "."))
    {
      strcpy (pop_error,
              "Unexpected response from server in gettermination");
      pop_trash (server);
      return (-1);
    }

  return (0);
}
#endif

/*
 * Function pop_close
 *
 * Purpose: Close a pop connection, sending a "RSET" command to try to
 *      preserve any changes that were made and a "QUIT" command to
 *      try to get the server to quit, but ignoring any responses that
 *      are received.
 *
 * Side effects: The server is unusable after this function returns.
 *      Changes made to the maildrop since the session was started (or
 *      since the last pop_reset) may be lost.
 */
void 
pop_close (popserver server)
{
  pop_trash (server);
  free ((char *) server);

  return;
}

/*
 * Function: pop_trash
 *
 * Purpose: Like pop_close or pop_quit, but doesn't deallocate the
 *      memory associated with the server.  It is legal to call
 *      pop_close or pop_quit after this function has been called.
 */
static void
pop_trash (popserver server)
{
  if (server->file >= 0)
    {
      /* avoid recursion; sendline can call pop_trash */
      if (server->trash_started)
        return;
      server->trash_started = 1;

      sendline (server, "RSET");
      sendline (server, "QUIT");

      CLOSESOCKET (server->file);
      server->file = -1;
      if (server->buffer)
        {
          free (server->buffer);
          server->buffer = 0;
        }
    }

#ifdef WINDOWSNT
  if (have_winsock)
    WSACleanup ();
#endif
}

/* Return a pointer to the first CRLF in IN_STRING,
   or 0 if it does not contain one.  */

static char *
find_crlf (char *in_string)
{
  while (1)
    {
      if (! *in_string)
        return (0);
      else if (*in_string == '\r')
        {
          if (*++in_string == '\n')
            return (in_string - 1);
        }
      else
        in_string++;
    }
  /* NOTREACHED */
}

#endif /* MAIL_USE_POP */