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Smack is an Open Source XMPP (Jabber) client library for instant messaging and presence. This library provides the client side functionality as specified in the extensions to the XMPP specifications as related to the client side of said specifications.
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/**
 * $RCSfile$
 * $Revision: $
 * $Date: $
 *
 * Copyright 2003-2007 Jive Software.
 *
 * All rights reserved. Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.jivesoftware.smack.sasl;

import org.jivesoftware.smack.XMPPException;
import org.jivesoftware.smack.SASLAuthentication;
import org.jivesoftware.smack.packet.Packet;
import org.jivesoftware.smack.util.Base64;

import java.io.IOException;
import java.util.Map;
import java.util.HashMap;
import javax.security.auth.callback.CallbackHandler;
import javax.security.auth.callback.UnsupportedCallbackException;
import javax.security.auth.callback.Callback;
import javax.security.auth.callback.NameCallback;
import javax.security.auth.callback.PasswordCallback;
import javax.security.sasl.RealmCallback;
import javax.security.sasl.RealmChoiceCallback;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslClient;
import javax.security.sasl.SaslException;

/**
 * Base class for SASL mechanisms. Subclasses must implement these methods:
 * 
 *  {@link #getName()} -- returns the common name of the SASL mechanism.
 * 
 * Subclasses will likely want to implement their own versions of these mthods:
 *  {@link #authenticate(String, String, String)} -- Initiate authentication stanza using the
 *  deprecated method.
 *  {@link #authenticate(String, String, CallbackHandler)} -- Initiate authentication stanza
 *  using the CallbackHandler method.
 *  {@link #challengeReceived(String)} -- Handle a challenge from the server.
 * 
 *
 * @author Jay Kline
 */
public abstract class SASLMechanism implements CallbackHandler {

    private SASLAuthentication saslAuthentication;
    protected SaslClient sc;
    protected String authenticationId;
    protected String password;
    protected String hostname;


    public SASLMechanism(SASLAuthentication saslAuthentication) {
        this.saslAuthentication = saslAuthentication;
    }

    /**
     * Builds and sends the auth stanza to the server. Note that this method of
     * authentication is not recommended, since it is very inflexable.  Use
     * {@link #authenticate(String, String, CallbackHandler)} whenever possible.
     *
     * @param username the username of the user being authenticated.
     * @param host     the hostname where the user account resides.
     * @param password the password for this account.
     * @throws IOException If a network error occurs while authenticating.
     * @throws XMPPException If a protocol error occurs or the user is not authenticated.
     */
    public void authenticate(String username, String host, String password) throws IOException, XMPPException {
        //Since we were not provided with a CallbackHandler, we will use our own with the given
        //information

        //Set the authenticationID as the username, since they must be the same in this case.
        this.authenticationId = username;
        this.password = password;
        this.hostname = host;

        String[] mechanisms = { getName() };
        Map props = new HashMap();
        sc = Sasl.createSaslClient(mechanisms, username, "xmpp", host, props, this);
        authenticate();
    }

    /**
     * Builds and sends the auth stanza to the server. The callback handler will handle
     * any additional information, such as the authentication ID or realm, if it is needed.
     *
     * @param username the username of the user being authenticated.
     * @param host     the hostname where the user account resides.
     * @param cbh      the CallbackHandler to obtain user information.
     * @throws IOException If a network error occures while authenticating.
     * @throws XMPPException If a protocol error occurs or the user is not authenticated.
     */
    public void authenticate(String username, String host, CallbackHandler cbh) throws IOException, XMPPException {
        String[] mechanisms = { getName() };
        Map props = new HashMap();
        sc = Sasl.createSaslClient(mechanisms, username, "xmpp", host, props, cbh);
        authenticate();
    }

    protected void authenticate() throws IOException, XMPPException {
        String authenticationText = null;
        try {
            if(sc.hasInitialResponse()) {
                byte[] response = sc.evaluateChallenge(new byte[0]);
                authenticationText = Base64.encodeBytes(response,Base64.DONT_BREAK_LINES);
            }
        } catch (SaslException e) {
            throw new XMPPException("SASL authentication failed", e);
        }

        // Send the authentication to the server
        getSASLAuthentication().send(new AuthMechanism(getName(), authenticationText));
    }


    /**
     * The server is challenging the SASL mechanism for the stanza he just sent. Send a
     * response to the server's challenge.
     *
     * @param challenge a base64 encoded string representing the challenge.
     * @throws IOException if an exception sending the response occurs.
     */
    public void challengeReceived(String challenge) throws IOException {
        byte response[];
        if(challenge != null) {
            response = sc.evaluateChallenge(Base64.decode(challenge));
        } else {
            response = sc.evaluateChallenge(new byte[0]);
        }

        Packet responseStanza;
        if (response == null) {
            responseStanza = new Response();
        }
        else {
            responseStanza = new Response(Base64.encodeBytes(response,Base64.DONT_BREAK_LINES));
        }

        // Send the authentication to the server
        getSASLAuthentication().send(responseStanza);
    }

    /**
     * Returns the common name of the SASL mechanism. E.g.: PLAIN, DIGEST-MD5 or GSSAPI.
     *
     * @return the common name of the SASL mechanism.
     */
    protected abstract String getName();


    protected SASLAuthentication getSASLAuthentication() {
        return saslAuthentication;
    }

    /**
     * 
     */
    public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
        for (int i = 0; i < callbacks.length; i++) {
            if (callbacks[i] instanceof NameCallback) {
                NameCallback ncb = (NameCallback)callbacks[i];
                ncb.setName(authenticationId);
            } else if(callbacks[i] instanceof PasswordCallback) {
                PasswordCallback pcb = (PasswordCallback)callbacks[i];
                pcb.setPassword(password.toCharArray());
            } else if(callbacks[i] instanceof RealmCallback) {
                RealmCallback rcb = (RealmCallback)callbacks[i];
                rcb.setText(hostname);
            } else if(callbacks[i] instanceof RealmChoiceCallback){
                //unused
                //RealmChoiceCallback rccb = (RealmChoiceCallback)callbacks[i];
            } else {
               throw new UnsupportedCallbackException(callbacks[i]);
            }
         }
    }

    /**
     * Initiating SASL authentication by select a mechanism.
     */
    public class AuthMechanism extends Packet {
        final private String name;
        final private String authenticationText;

        public AuthMechanism(String name, String authenticationText) {
            if (name == null) {
                throw new NullPointerException("SASL mechanism name shouldn't be null.");
            }
            this.name = name;
            this.authenticationText = authenticationText;
        }

        public String toXML() {
            StringBuilder stanza = new StringBuilder();
            stanza.append("");
            if (authenticationText != null &&
                    authenticationText.trim().length() > 0) {
                stanza.append(authenticationText);
            }
            stanza.append("");
            return stanza.toString();
        }
    }

    /**
     * A SASL challenge stanza.
     */
    public static class Challenge extends Packet {
        final private String data;

        public Challenge(String data) {
            this.data = data;
        }

        public String toXML() {
            StringBuilder stanza = new StringBuilder();
            stanza.append("");
            if (data != null &&
                    data.trim().length() > 0) {
                stanza.append(data);
            }
            stanza.append("");
            return stanza.toString();
        }
    }

    /**
     * A SASL response stanza.
     */
    public class Response extends Packet {
        final private String authenticationText;

        public Response() {
            authenticationText = null;
        }

        public Response(String authenticationText) {
            if (authenticationText == null || authenticationText.trim().length() == 0) {
                this.authenticationText = null;
            }
            else {
                this.authenticationText = authenticationText;
            }
        }

        public String toXML() {
            StringBuilder stanza = new StringBuilder();
            stanza.append("");
            if (authenticationText != null) {
                stanza.append(authenticationText);
            }
            else {
                stanza.append("=");
            }
            stanza.append("");
            return stanza.toString();
        }
    }

    /**
     * A SASL success stanza.
     */
    public static class Success extends Packet {
        final private String data;

        public Success(String data) {
            this.data = data;
        }

        public String toXML() {
            StringBuilder stanza = new StringBuilder();
            stanza.append("");
            if (data != null &&
                    data.trim().length() > 0) {
                stanza.append(data);
            }
            stanza.append("");
            return stanza.toString();
        }
    }

    /**
     * A SASL failure stanza.
     */
    public static class Failure extends Packet {
        final private String condition;

        public Failure(String condition) {
            this.condition = condition;
        }

        /**
         * Get the SASL related error condition.
         * 
         * @return the SASL related error condition.
         */
        public String getCondition() {
            return condition;
        }

        public String toXML() {
            StringBuilder stanza = new StringBuilder();
            stanza.append("");
            if (condition != null &&
                    condition.trim().length() > 0) {
                stanza.append("<").append(condition).append("/>");
            }
            stanza.append("");
            return stanza.toString();
        }
    }
}