/*
 * $Id: POP3Connection.java,v 1.14 2004/08/07 14:39:46 dog Exp $
 * Copyright (C) 2003 The Free Software Foundation
 * 
 * This file is part of GNU inetlib, a library.
 * 
 * GNU inetlib 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 of the License, or
 * (at your option) any later version.
 * 
 * GNU inetlib 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 this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * As a special exception, if you link this library with other files to
 * produce an executable, this library does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * This exception does not however invalidate any other reasons why the
 * executable file might be covered by the GNU General Public License.
 */

package gnu.inet.pop3;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.ProtocolException;
import java.net.Socket;
import java.net.UnknownHostException;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;

import javax.security.auth.callback.CallbackHandler;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslClient;
import javax.security.sasl.SaslException;

import gnu.inet.util.BASE64;
import gnu.inet.util.CRLFInputStream;
import gnu.inet.util.CRLFOutputStream;
import gnu.inet.util.EmptyX509TrustManager;
import gnu.inet.util.LineInputStream;
import gnu.inet.util.Logger;
import gnu.inet.util.MessageInputStream;
import gnu.inet.util.SaslCallbackHandler;
import gnu.inet.util.SaslInputStream;
import gnu.inet.util.SaslOutputStream;

/**
 * A POP3 client connection.
 * This implements the entire POP3 specification as detailed in RFC 1939,
 * with the exception of the no-arg LIST and UIDL commands (use STAT
 * followed by multiple LIST and/or UIDL instead) and TOP with a specified
 * number of content lines. It also implements the POP3 extension mechanism
 * CAPA, documented in RFC 2449, as well as the STLS command to initiate TLS
 * over POP3 documented in RFC 2595 and the AUTH command in RFC 1734.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 * @version $Revision: 1.14 $ $Date: 2004/08/07 14:39:46 $
 */
public class POP3Connection
{

  /**
   * The default POP3 port.
   */
  public static final int DEFAULT_PORT = 110;

  // -- POP3 vocabulary --
  private static final String _OK = "+OK";
  private static final String _ERR = "-ERR";
  private static final String _READY = "+ ";

  protected static final String STAT = "STAT";
  protected static final String LIST = "LIST";
  protected static final String RETR = "RETR";
  protected static final String DELE = "DELE";
  protected static final String NOOP = "NOOP";
  protected static final String RSET = "RSET";
  protected static final String QUIT = "QUIT";
  protected static final String TOP = "TOP";
  protected static final String UIDL = "UIDL";
  protected static final String USER = "USER";
  protected static final String PASS = "PASS";
  protected static final String APOP = "APOP";
  protected static final String CAPA = "CAPA";
  protected static final String STLS = "STLS";
  protected static final String AUTH = "AUTH";

  protected static final int OK = 0;
  protected static final int ERR = 1;
  protected static final int READY = 2;

  /**
   * The socket used to communicate with the server.
   */
  protected Socket socket;

  /**
   * The socket input stream.
   */
  protected LineInputStream in;

  /**
   * The socket output stream.
   */
  protected CRLFOutputStream out;

  /**
   * The last response received from the server.
   * The status code (+OK or -ERR) is stripped from the line.
   */
  protected String response;

  /**
   * If true, print debugging information.
   */
  protected boolean debug;

  /**
   * The APOP timestamp, if sent by the server on connection.
   * Otherwise null.
   */
  protected byte[] timestamp;

  /**
   * Creates a new connection to the server.
   * @param hostname the hostname of the server to connect to
   */
  public POP3Connection (String hostname)
    throws UnknownHostException, IOException
  {
    this (hostname, -1, 0, 0, false);
  }

  /**
   * Creates a new connection to the server.
   * @param hostname the hostname of the server to connect to
   * @param port the port to connect to (if &lt;=0, use default POP3 port)
   */
  public POP3Connection (String hostname, int port)
    throws UnknownHostException, IOException
  {
    this (hostname, port, 0, 0, false);
  }

  /**
   * Creates a new connection to the server.
   * @param hostname the hostname of the server to connect to
   * @param port the port to connect to (if &lt;=0, use default POP3 port)
   * @param connectionTimeout the connection timeout, in milliseconds
   * @param timeout the I/O timeout, in milliseconds
   * @param debug print debugging information
   */
  public POP3Connection (String hostname, int port,
                         int connectionTimeout, int timeout, boolean debug)
    throws UnknownHostException, IOException
  {
    this.debug = debug;
    if (port <= 0)
      {
        port = DEFAULT_PORT;
      }
    
    // Set up socket
    socket = new Socket ();
    InetSocketAddress address = new InetSocketAddress (hostname, port);
    if (connectionTimeout > 0)
      {
        socket.connect (address, connectionTimeout);
      }
    else
      {
        socket.connect (address);
      }
    if (timeout > 0)
      {
        socket.setSoTimeout (timeout);
      }
    
    InputStream in = socket.getInputStream ();
    in = new BufferedInputStream (in);
    in = new CRLFInputStream (in);
    this.in = new LineInputStream (in);
    OutputStream out = socket.getOutputStream ();
    out = new BufferedOutputStream (out);
    this.out = new CRLFOutputStream (out);
    
    if (getResponse() != OK)
      {
        throw new ProtocolException ("Connect failed: " + response);
      }
    // APOP timestamp
    timestamp = parseTimestamp (response);
  }

  /**
   * Authenticates the connection using the specified SASL mechanism,
   * username, and password.
   * @param mechanism a SASL authentication mechanism, e.g. LOGIN, PLAIN,
   * CRAM-MD5, GSSAPI
   * @param username the authentication principal
   * @param password the authentication credentials
   * @return true if authentication was successful, false otherwise
   */
  public boolean auth (String mechanism, String username, String password)
    throws IOException
  {
    try
      {
        String[] m = new String[] { mechanism };
        CallbackHandler ch = new SaslCallbackHandler (username, password);
        // Avoid lengthy callback procedure for GNU Crypto
        Properties p = new Properties ();
        p.put ("gnu.crypto.sasl.username", username);
        p.put ("gnu.crypto.sasl.password", password);
        SaslClient sasl =
          Sasl.createSaslClient (m, null, "smtp",
                                 socket.getInetAddress ().getHostName (),
                                 p, ch);
        if (sasl == null)
          {
            return false;
          }
        
        StringBuffer cmd = new StringBuffer (AUTH);
        cmd.append (' ');
        cmd.append (mechanism);
        if (sasl.hasInitialResponse ())
          {
            cmd.append (' ');
            byte[] init = sasl.evaluateChallenge (new byte[0]);
            cmd.append (new String (init, "US-ASCII"));
          }
        send (cmd.toString ());
        while (true)
          {
            switch (getResponse ())
              {
              case OK:
                String qop = (String) sasl.getNegotiatedProperty (Sasl.QOP);
                if ("auth-int".equalsIgnoreCase (qop)
                    || "auth-conf".equalsIgnoreCase (qop))
                  {
                    InputStream in = socket.getInputStream ();
                    in = new BufferedInputStream (in);
                    in = new SaslInputStream (sasl, in);
                    in = new CRLFInputStream (in);
                    this.in = new LineInputStream (in);
                    OutputStream out = socket.getOutputStream ();
                    out = new BufferedOutputStream (out);
                    out = new SaslOutputStream (sasl, out);
                    this.out = new CRLFOutputStream (out);
                  }
                return true;
              case READY:
                try
                  {
                    byte[] c0 = response.getBytes ("US-ASCII");
                    byte[] c1 = BASE64.decode (c0);       // challenge
                    byte[] r0 = sasl.evaluateChallenge (c1);
                    byte[] r1 = BASE64.encode (r0);       // response
                    out.write (r1);
                    out.write (0x0d);
                    out.flush ();
                  }
                catch (SaslException e)
                  {
                    // Error in SASL challenge evaluation - cancel exchange
                    out.write (0x2a);
                    out.write (0x0d);
                    out.flush ();
                  }
              default:
                return false;
              }
          }
      }
    catch (SaslException e)
      {
        return false;             // No provider for mechanism
      }
    catch (RuntimeException e)
      {
        return false;             // No javax.security.sasl classes
      }
  }
  
  /**
   * Authenticate the specified user using the APOP MD5-based method.
   * This does not transmit the password in the clear, but doesn't provide
   * any transport-level privacy features either.
   * @param username the user to authenticate
   * @param password the user's password
   */
  public boolean apop (String username, String password)
    throws IOException
  {
    if (username == null || password == null || timestamp == null)
      {
        return false;
      }
    // APOP <username> <digest>
    try
      {
        byte[] secret = password.getBytes ("US-ASCII");
        // compute digest
        byte[] target = new byte[timestamp.length + secret.length];
        System.arraycopy (timestamp, 0, target, 0, timestamp.length);
        System.arraycopy (secret, 0, target, timestamp.length, secret.length);
        MessageDigest md5 = MessageDigest.getInstance ("MD5");
        byte[] db = md5.digest (target);
        // create hexadecimal representation
        StringBuffer digest = new StringBuffer ();
        for (int i = 0; i < db.length; i++)
          {
            int c = (int) db[i];
            if (c < 0)
              {
                c += 256;
              }
            digest.append (Integer.toHexString ((c & 0xf0) >> 4));
            digest.append (Integer.toHexString (c & 0x0f));
          }
        // send command
        String cmd = new StringBuffer (APOP)
          .append (' ')
          .append (username)
          .append (' ')
          .append (digest.toString ())
          .toString ();
        send (cmd);
        return getResponse () == OK;
      }
    catch (NoSuchAlgorithmException e)
      {
        Logger logger = Logger.getInstance ();
        logger.log ("pop3", "MD5 algorithm not found");
        return false;
      }
  }
  
  /**
   * Authenticate the user using the basic USER and PASS handshake.
   * It is recommended to use a more secure authentication method such as
   * the <code>auth</code> or <code>apop</code> method if the server
   * understands them.
   * @param username the user to authenticate
   * @param password the user's password
   */
  public boolean login (String username, String password)
    throws IOException
  {
    if (username == null || password == null)
      {
        return false;
      }
    // USER <username>
    String cmd = USER + ' ' + username;
    send (cmd);
    if (getResponse () != OK)
      {
        return false;
      }
    // PASS <password>
    cmd = PASS + ' ' + password;
    send (cmd);
    return getResponse () == OK;
  }
  
  /**
   * Attempts to start TLS on the specified connection.
   * See RFC 2595 for details
   * @return true if successful, false otherwise
   */
  public boolean stls ()
    throws IOException
  {
    return stls (new EmptyX509TrustManager ());
  }
  
  /**
   * Attempts to start TLS on the specified connection.
   * See RFC 2595 for details
   * @param tm the custom trust manager to use
   * @return true if successful, false otherwise
   */
  public boolean stls (TrustManager tm)
    throws IOException
  {
    try
      {
        // Use SSLSocketFactory to negotiate a TLS session and wrap the
        // current socket.
        SSLContext context = SSLContext.getInstance ("TLS");
        // We don't require strong validation of the server certificate
        TrustManager[] trust = new TrustManager[] { tm };
        context.init (null, trust, null);
        SSLSocketFactory factory = context.getSocketFactory ();
        
        send (STLS);
        if (getResponse () != OK)
          {
            return false;
          }
        
        String hostname = socket.getInetAddress ().getHostName ();
        int port = socket.getPort ();
        SSLSocket ss =
          (SSLSocket) factory.createSocket (socket, hostname, port, true);
        String[] protocols = { "TLSv1", "SSLv3" };
        ss.setEnabledProtocols (protocols);
        ss.setUseClientMode (true);
        ss.startHandshake ();
        
        // set up streams
        InputStream in = ss.getInputStream ();
        in = new BufferedInputStream (in);
        in = new CRLFInputStream (in);
        this.in = new LineInputStream (in);
        OutputStream out = ss.getOutputStream ();
        out = new BufferedOutputStream (out);
        this.out = new CRLFOutputStream (out);
        
        return true;
      }
    catch (GeneralSecurityException e)
      {
        return false;
      }
  }
  
  /**
   * Returns the number of messages in the maildrop.
   */
  public int stat ()
    throws IOException
  {
    send (STAT);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("STAT failed: " + response);
      }
    try
      {
        return
          Integer.parseInt (response.substring (0, response.indexOf (' ')));
      }
    catch (NumberFormatException e)
      {
        throw new ProtocolException ("Not a number: " + response);
      }
    catch (ArrayIndexOutOfBoundsException e)
      {
        throw new ProtocolException ("Not a STAT response: " + response);
      }
  }
  
  /**
   * Returns the size of the specified message.
   * @param msgnum the message number
   */
  public int list (int msgnum)
    throws IOException
  {
    String cmd = LIST + ' ' + msgnum;
    send (cmd);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("LIST failed: " + response);
      }
    try
      {
        return
          Integer.parseInt (response.substring (response.indexOf (' ') + 1));
      }
    catch (NumberFormatException e)
      {
        throw new ProtocolException ("Not a number: " + response);
      }
  }
  
  /**
   * Returns an input stream containing the entire message.
   * This input stream must be read in its entirety before further commands
   * can be issued on this connection.
   * @param msgnum the message number
   */
  public InputStream retr (int msgnum)
    throws IOException
  {
    String cmd = RETR + ' ' + msgnum;
    send (cmd);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("RETR failed: " + response);
      }
    return new MessageInputStream (in);
  }
  
  /**
   * Marks the specified message as deleted.
   * @param msgnum the message number
   */
  public void dele (int msgnum)
    throws IOException
  {
    String cmd = DELE + ' ' + msgnum;
    send (cmd);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("DELE failed: " + response);
      }
  }
  
  /**
   * Does nothing.
   * This can be used to keep the connection alive.
   */
  public void noop ()
    throws IOException
  {
    send (NOOP);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("NOOP failed: " + response);
      }
  }

  /**
   * If any messages have been marked as deleted, they are unmarked.
   */
  public void rset ()
    throws IOException
  {
    send (RSET);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("RSET failed: " + response);
      }
  }
  
  /**
   * Closes the connection.
   * No further commands may be issued on this connection after this method
   * has been called.
   * @return true if all deleted messages were successfully removed, false
   * otherwise
   */
  public boolean quit ()
    throws IOException
  {
    send (QUIT);
    int ret = getResponse ();
    socket.close ();
    return ret == OK;
  }

  /**
   * Returns just the headers of the specified message as an input stream.
   * The stream must be read in its entirety before further commands can be
   * issued.
   * @param msgnum the message number
   */
  public InputStream top (int msgnum)
    throws IOException
  {
    String cmd = TOP + ' ' + msgnum + ' ' + '0';
    send (cmd);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("TOP failed: " + response);
      }
    return new MessageInputStream (in);
  }
  
  /**
   * Returns a unique identifier for the specified message.
   * @param msgnum the message number
   */
  public String uidl (int msgnum)
    throws IOException
  {
    String cmd = UIDL + ' ' + msgnum;
    send (cmd);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("UIDL failed: " + response);
      }
    return response.substring (response.indexOf (' ') + 1);
  }

  /**
   * Returns a map of message number to UID pairs.
   * Message numbers are Integers, UIDs are Strings.
   */
  public Map uidl ()
    throws IOException
  {
    send (UIDL);
    if (getResponse () != OK)
      {
        throw new ProtocolException ("UIDL failed: " + response);
      }
    Map uids = new LinkedHashMap ();
    String line = in.readLine ();
    while (line != null && !(".".equals (line)))
      {
        int si = line.indexOf (' ');
        if (si < 1)
          {
            throw new ProtocolException ("Invalid UIDL response: " + line);
          }
        try
          {
            uids.put (new Integer (line.substring (0, si)),
                      line.substring (si + 1));
          }
        catch (NumberFormatException e)
          {
            throw new ProtocolException ("Invalid message number: " + line);
          }
      }
    return Collections.unmodifiableMap (uids);
  }

  /**
   * Returns a list of capabilities supported by the POP3 server.
   * If the server does not support POP3 extensions, returns
   * <code>null</code>.
   */
  public List capa ()
    throws IOException
  {
    send (CAPA);
    if (getResponse () == OK)
      {
        final String DOT = ".";
        List list = new ArrayList ();
        for (String line = in.readLine ();
             !DOT.equals (line);
             line = in.readLine ())
          {
            list.add (line);
          }
        return Collections.unmodifiableList (list);
      }
    return null;
  }
  
  /** 
   * Send the command to the server.
   * If <code>debug</code> is <code>true</code>,
   * the command is logged.
   */
  protected void send (String command)
    throws IOException
  {
    if (debug)
      {
        Logger logger = Logger.getInstance ();
        logger.log ("pop3", "> " + command);
      }
    out.write (command);
    out.writeln ();
    out.flush ();
  }
  
  /**
   * Parse the response from the server.
   * If <code>debug</code> is <code>true</code>,
   * the response is logged.
   */
  protected int getResponse ()
    throws IOException
  {
    response = in.readLine ();
    if (debug)
      {
        Logger logger = Logger.getInstance ();
        logger.log ("pop3", "< " + response);
      }
    if (response.indexOf (_OK) == 0)
      {
        response = response.substring (3).trim ();
        return OK;
      }
    else if (response.indexOf (_ERR) == 0)
      {
        response = response.substring (4).trim ();
        return ERR;
      }
    else if (response.indexOf (_READY) == 0)
      {
        response = response.substring (2).trim ();
        return READY;
      }
    else
      {
        throw new ProtocolException ("Unexpected response: " + response);
      }
  }
  
  /*
   * Parse the APOP timestamp from the server's banner greeting.
   */
  byte[] parseTimestamp (String greeting)
    throws IOException
  {
    int bra = greeting.indexOf ('<');
    if (bra != -1)
      {
        int ket = greeting.indexOf ('>', bra);
        if (ket != -1)
          {
            String mid = greeting.substring (bra, ket + 1);
            int at = mid.indexOf ('@');
            if (at != -1)           // This is a valid RFC822 msg-id
              {
                return mid.getBytes ("US-ASCII");
              }
          }
      }
    return null;
  }
  
}