/*
 * $Id: SMTPConnection.java,v 1.15 2004/08/07 14:39:46 dog Exp $
 * Copyright (C) 2003 Chris Burdess <dog@gnu.org>
 * 
 * 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.smtp;

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.security.GeneralSecurityException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
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.MessageOutputStream;
import gnu.inet.util.SaslCallbackHandler;
import gnu.inet.util.SaslInputStream;
import gnu.inet.util.SaslOutputStream;

/**
 * An SMTP client.
 * This implements RFC 2821.
 *
 * @author <a href="mailto:dog@gnu.org">Chris Burdess</a>
 * @version $Revision: 1.15 $ $Date: 2004/08/07 14:39:46 $
 */
public class SMTPConnection
{

  /**
   * The default SMTP port.
   */
  public static final int DEFAULT_PORT = 25;

  protected static final String MAIL_FROM = "MAIL FROM:";
  protected static final String RCPT_TO = "RCPT TO:";
  protected static final String SP = " SP ";
  protected static final String DATA = "DATA";
  protected static final String FINISH_DATA = "\n.";
  protected static final String RSET = "RSET";
  protected static final String VRFY = "VRFY";
  protected static final String EXPN = "EXPN";
  protected static final String HELP = "HELP";
  protected static final String NOOP = "NOOP";
  protected static final String QUIT = "QUIT";
  protected static final String HELO = "HELO";
  protected static final String EHLO = "EHLO";
  protected static final String AUTH = "AUTH";
  protected static final String STARTTLS = "STARTTLS";

  protected static final int INFO = 214;
  protected static final int READY = 220;
  protected static final int OK = 250;
  protected static final int OK_NOT_LOCAL = 251;
  protected static final int OK_UNVERIFIED = 252;
  protected static final int SEND_DATA = 354;
  protected static final int AMBIGUOUS = 553;

  /**
   * The underlying socket used for communicating with the server.
   */
  protected Socket socket;

  /**
   * The input stream used to read responses from the server.
   */
  protected LineInputStream in;

  /**
   * The output stream used to send commands to the server.
   */
  protected CRLFOutputStream out;

  /**
   * If true, log events.
   */
  protected boolean debug;

  /**
   * The last response message received from the server.
   */
  protected String response;

  /**
   * If true, there are more responses to read.
   */
  protected boolean continuation;

  /**
   * The greeting message given by the server.
   */
  protected final String greeting;

  /**
   * Creates a new connection to the specified host, using the default SMTP
   * port.
   * @param host the server hostname
   */
  public SMTPConnection (String host) throws IOException
  {
    this (host, DEFAULT_PORT);
  }

  /**
   * Creates a new connection to the specified host, using the specified
   * port.
   * @param host the server hostname
   * @param port the port to connect to
   */
  public SMTPConnection (String host, int port) throws IOException
  {
    this (host, port, 0, 0, false);
  }

  /**
   * Creates a new connection to the specified host, using the specified
   * port.
   * @param host the server hostname
   * @param port the port to connect to
   * @param connectionTimeout the connection timeout in milliseconds
   * @param timeout the I/O timeout in milliseconds
   * @param debug whether to log progress
   */
  public SMTPConnection (String host, int port,
                         int connectionTimeout, int timeout, boolean debug)
    throws IOException
  {
    if (port <= 0)
      {
        port = DEFAULT_PORT;
      }
    response = null;
    continuation = false;
    this.debug = debug;
    
    // Initialise socket
    socket = new Socket ();
    InetSocketAddress address = new InetSocketAddress (host, port);
    if (connectionTimeout > 0)
      {
        socket.connect (address, connectionTimeout);
      }
    else
      {
        socket.connect (address);
      }
    if (timeout > 0)
      {
        socket.setSoTimeout (timeout);
      }
    
    // Initialise streams
    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);
    
    // Greeting
    StringBuffer greetingBuffer = new StringBuffer ();
    boolean notFirst = false;
    do
      {
        if (getResponse () != READY)
          {
            throw new ProtocolException (response);
          }
        if (notFirst)
          {
            greetingBuffer.append ('\n');
          }
        else
          {
            notFirst = true;
          }
        greetingBuffer.append (response);
        
      }
    while (continuation);
    greeting = greetingBuffer.toString ();
  }
  
  /**
   * Returns the server greeting message.
   */
  public String getGreeting ()
  {
    return greeting;
  }

  /**
   * Returns the text of the last response received from the server.
   */
  public String getLastResponse ()
  {
    return response;
  }

  // -- 3.3 Mail transactions --

  /**
   * Execute a MAIL command.
   * @param reversePath the source mailbox (from address)
   * @param parameters optional ESMTP parameters
   * @return true if accepted, false otherwise
   */
  public boolean mailFrom (String reversePath, ParameterList parameters)
    throws IOException
  {
    StringBuffer command = new StringBuffer (MAIL_FROM);
    command.append ('<');
    command.append (reversePath);
    command.append ('>');
    if (parameters != null)
      {
        command.append (SP);
        command.append (parameters);
      }
    send (command.toString ());
    switch (getAllResponses ())
      {
      case OK:
      case OK_NOT_LOCAL:
      case OK_UNVERIFIED:
        return true;
      default:
        return false;
      }
  }

  /**
   * Execute a RCPT command.
   * @param forwardPath the forward-path (recipient address)
   * @param parameters optional ESMTP parameters
   * @return true if successful, false otherwise
   */
  public boolean rcptTo (String forwardPath, ParameterList parameters)
    throws IOException
  {
    StringBuffer command = new StringBuffer (RCPT_TO);
    command.append ('<');
    command.append (forwardPath);
    command.append ('>');
    if (parameters != null)
      {
        command.append (SP);
        command.append (parameters);
      }
    send (command.toString ());
    switch (getAllResponses ())
      {
      case OK:
      case OK_NOT_LOCAL:
      case OK_UNVERIFIED:
        return true;
      default:
        return false;
      }
  }

  /**
   * Requests an output stream to write message data to.
   * When the entire message has been written to the stream, the
   * <code>flush</code> method must be called on the stream. Until then no
   * further methods should be called on the connection.
   * Immediately after this procedure is complete, <code>finishData</code>
   * must be called to complete the transfer and determine its success.
   * @return a stream for writing messages to
   */
  public OutputStream data () throws IOException
  {
    send (DATA);
    switch (getAllResponses ())
      {
      case SEND_DATA:
        return new MessageOutputStream (out);
      default:
        throw new ProtocolException (response);
      }
  }

  /**
   * Completes the DATA procedure.
   * @see #data
   * @return true id transfer was successful, false otherwise
   */
  public boolean finishData () throws IOException
  {
    send (FINISH_DATA);
    switch (getAllResponses ())
      {
      case OK:
        return true;
      default:
        return false;
      }
  }

  /**
   * Aborts the current mail transaction.
   */
  public void rset () throws IOException
  {
    send (RSET);
    if (getAllResponses () != OK)
      {
        throw new ProtocolException (response);
      }
  }

  // -- 3.5 Commands for Debugging Addresses --

  /**
   * Returns a list of valid possibilities for the specified address, or
   * null on failure.
   * @param address a mailbox, or real name and mailbox
   */
  public List vrfy (String address) throws IOException
  {
    String command = VRFY + ' ' + address;
    send (command);
    List list = new ArrayList ();
    do
      {
        switch (getResponse ())
          {
          case OK:
          case AMBIGUOUS:
            response = response.trim ();
            if (response.indexOf ('@') != -1)
              {
                list.add (response);
              }
            else if (response.indexOf ('<') != -1)
              {
                list.add (response);
              }
            else if (response.indexOf (' ') == -1)
              {
                list.add (response);
              }
            break;
          default:
            return null;
          }
      }
    while (continuation);
    return Collections.unmodifiableList (list);
  }

  /**
   * Returns a list of valid possibilities for the specified mailing list,
   * or null on failure.
   * @param address a mailing list name
   */
  public List expn (String address) throws IOException
  {
    String command = EXPN + ' ' + address;
    send (command);
    List list = new ArrayList ();
    do
      {
        switch (getResponse ())
          {
          case OK:
            response = response.trim ();
            list.add (response);
            break;
          default:
            return null;
          }
      }
    while (continuation);
    return Collections.unmodifiableList (list);
  }

  /**
   * Returns some useful information about the specified parameter.
   * Typically this is a command.
   * @param arg the context of the query, or null for general information
   * @return a list of possibly useful information, or null if the command
   * failed.
   */
  public List help (String arg) throws IOException
  {
    String command = (arg == null) ? HELP :
      HELP + ' ' + arg;
    send (command);
    List list = new ArrayList ();
    do
      {
        switch (getResponse ())
          {
          case INFO:
            list.add (response);
            break;
          default:
            return null;
          }
      }
    while (continuation);
    return Collections.unmodifiableList (list);
  }

  /**
   * Issues a NOOP command.
   * This does nothing, but can be used to keep the connection alive.
   */
  public void noop () throws IOException
  {
    send (NOOP);
    getAllResponses ();
  }

  /**
   * Close the connection to the server.
   */
  public void quit () throws IOException
  {
    try
      {
        send (QUIT);
        getAllResponses ();
        /* RFC 2821 states that the server MUST send an OK reply here, but
         * many don't: postfix, for instance, sends 221.
         * In any case we have done our best. */
      }
    catch (IOException e)
      {
      }
    finally
      {
        // Close the socket anyway.
        socket.close ();
      }
  }

  /**
   * Issues a HELO command.
   * @param hostname the local host name
   */
  public boolean helo (String hostname) throws IOException
  {
    String command = HELO + ' ' + hostname;
    send (command);
    return (getAllResponses () == OK);
  }

  /**
   * Issues an EHLO command.
   * If successful, returns a list of the SMTP extensions supported by the
   * server.
   * Otherwise returns null, and HELO should be called.
   * @param hostname the local host name
   */
  public List ehlo (String hostname) throws IOException
  {
    String command = EHLO + ' ' + hostname;
    send (command);
    List extensions = new ArrayList ();
    do
      {
        switch (getResponse ())
          {
          case OK:
            extensions.add (response);
            break;
          default:
            return null;
          }
      }
    while (continuation);
    return Collections.unmodifiableList (extensions);
  }

  /**
   * Negotiate TLS over the current connection.
   * This depends on many features, such as the JSSE classes being in the
   * classpath. Returns true if successful, false otherwise.
   */
  public boolean starttls () throws IOException
  {
    return starttls (new EmptyX509TrustManager ());
  }
  
  /**
   * Negotiate TLS over the current connection.
   * This depends on many features, such as the JSSE classes being in the
   * classpath. Returns true if successful, false otherwise.
   * @param tm the custom trust manager to use
   */
  public boolean starttls (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 (STARTTLS);
        if (getAllResponses () != READY)
          {
            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;
      }
  }

  // -- Authentication --

  /**
   * 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 authenticate (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 (getAllResponses ())
              {
              case 334:
                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 ();
                  }
                break;
              case 235:
                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;
              default:
                return false;
              }
          }
      }
    catch (SaslException e)
      {
        return false;             // No provider for mechanism
      }
    catch (RuntimeException e)
      {
        return false;             // No javax.security.sasl classes
      }
  }

  // -- Utility methods --

  /**
   * Send the specified command string to the server.
   * @param command the command to send
   */
  protected void send (String command) throws IOException
  {
    if (debug)
      {
        Logger logger = Logger.getInstance ();
        logger.log ("smtp", "> " + command);
      }
    out.write (command.getBytes ("US-ASCII"));
    out.write (0x0d);
    out.flush ();
  }
  
  /**
   * Returns the next response from the server.
   */
  protected int getResponse () throws IOException
  {
    String line = null;
    try
      {
        line = in.readLine ();
        // Handle special case eg 334 where CRLF occurs after code.
        if (line.length () < 4)
          {
            line = line + '\n' + in.readLine();
          }
        if (debug)
          {
            Logger logger = Logger.getInstance ();
            logger.log ("smtp", "< " + line);
          }
        int code = Integer.parseInt (line.substring (0, 3));
        continuation = (line.charAt (3) == '-');
        response = line.substring (4);
        return code;
      }
    catch (NumberFormatException e)
      {
        throw new ProtocolException ("Unexpected response: " + line);
      }
  }

  /**
   * Returns the next response from the server.
   * If the response is a continuation, continues to read responses until
   * continuation ceases. If a different response code from the first is
   * encountered, this causes a protocol exception.
   */
  protected int getAllResponses () throws IOException
  {
    int code1, code;
    boolean err = false;
    code1 = code = getResponse ();
    while (continuation)
      {
        code = getResponse();
        if (code != code1)
          {
            err = true;
          }
      }
    if (err)
      {
        throw new ProtocolException ("Conflicting response codes");
      }
    return code;
  }

}