/**
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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.apache.hadoop.hbase.security;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.ipc.RemoteException;
  import org.apache.hadoop.security.UserGroupInformation;
  import org.apache.hadoop.security.token.Token;
  import org.apache.hadoop.security.token.TokenIdentifier;
  
  import javax.security.auth.callback.CallbackHandler;
  import javax.security.sasl.Sasl;
  import javax.security.sasl.SaslClient;
  import javax.security.sasl.SaslException;
  
  import java.io.IOException;
  import java.nio.charset.Charset;
  import java.security.PrivilegedExceptionAction;
  import java.util.Map;
  import java.util.Random;
  
  /**
   * Handles Sasl connections
   */
  @InterfaceAudience.Private
  public class SaslClientHandler extends ChannelDuplexHandler {
    private static final Log LOG = LogFactory.getLog(SaslClientHandler.class);
  
    private final boolean fallbackAllowed;
  
    private final UserGroupInformation ticket;
  
    /**
     * Used for client or server's token to send or receive from each other.
     */
    private final SaslClient saslClient;
    private final Map<String, String> saslProps;
    private final SaslExceptionHandler exceptionHandler;
    private final SaslSuccessfulConnectHandler successfulConnectHandler;
    private byte[] saslToken;
    private boolean firstRead = true;
  
    private int retryCount = 0;
    private Random random;
  
    /**
     * @param ticket                   the ugi
     * @param method                   auth method
     * @param token                    for Sasl
     * @param serverPrincipal          Server's Kerberos principal name
     * @param fallbackAllowed          True if server may also fall back to less secure connection
     * @param rpcProtection            Quality of protection. Can be 'authentication', 'integrity' or
     *                                 'privacy'.
     * @throws java.io.IOException if handler could not be created
     */
    public SaslClientHandler(UserGroupInformation ticket, AuthMethod method,
        Token<? extends TokenIdentifier> token, String serverPrincipal, boolean fallbackAllowed,
        String rpcProtection, SaslExceptionHandler exceptionHandler,
        SaslSuccessfulConnectHandler successfulConnectHandler) throws IOException {
      this.ticket = ticket;
      this.fallbackAllowed = fallbackAllowed;
  
      this.exceptionHandler = exceptionHandler;
      this.successfulConnectHandler = successfulConnectHandler;
  
      saslProps = SaslUtil.initSaslProperties(rpcProtection);
      switch (method) {
      case DIGEST:
        if (LOG.isDebugEnabled())
          LOG.debug("Creating SASL " + AuthMethod.DIGEST.getMechanismName()
              + " client to authenticate to service at " + token.getService());
        saslClient = createDigestSaslClient(new String[] { AuthMethod.DIGEST.getMechanismName() },
            SaslUtil.SASL_DEFAULT_REALM, new HBaseSaslRpcClient.SaslClientCallbackHandler(token));
        break;
     case KERBEROS:
       if (LOG.isDebugEnabled()) {
         LOG.debug("Creating SASL " + AuthMethod.KERBEROS.getMechanismName()
             + " client. Server's Kerberos principal name is " + serverPrincipal);
       }
       if (serverPrincipal == null || serverPrincipal.isEmpty()) {
         throw new IOException("Failed to specify server's Kerberos principal name");
       }
       String[] names = SaslUtil.splitKerberosName(serverPrincipal);
       if (names.length != 3) {
         throw new IOException(
             "Kerberos principal does not have the expected format: " + serverPrincipal);
       }
       saslClient = createKerberosSaslClient(new String[] { AuthMethod.KERBEROS.getMechanismName() },
           names[0], names[1]);
       break;
     default:
       throw new IOException("Unknown authentication method " + method);
     }
     if (saslClient == null) {
       throw new IOException("Unable to find SASL client implementation");
     }
   }
 
   /**
    * Create a Digest Sasl client
    */
   protected SaslClient createDigestSaslClient(String[] mechanismNames, String saslDefaultRealm,
       CallbackHandler saslClientCallbackHandler) throws IOException {
     return Sasl.createSaslClient(mechanismNames, null, null, saslDefaultRealm, saslProps,
         saslClientCallbackHandler);
   }
 
   /**
    * Create Kerberos client
    *
    * @param userFirstPart  first part of username
    * @param userSecondPart second part of username
    */
   protected SaslClient createKerberosSaslClient(String[] mechanismNames, String userFirstPart,
       String userSecondPart) throws IOException {
     return Sasl
         .createSaslClient(mechanismNames, null, userFirstPart, userSecondPart, saslProps,
             null);
   }
 
   @Override
   public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
     saslClient.dispose();
   }
 
   private byte[] evaluateChallenge(final byte[] challenge) throws Exception {
     return ticket.doAs(new PrivilegedExceptionAction<byte[]>() {
 
       @Override
       public byte[] run() throws Exception {
         return saslClient.evaluateChallenge(challenge);
       }
     });
   }
 
   @Override
   public void handlerAdded(final ChannelHandlerContext ctx) throws Exception {
     saslToken = new byte[0];
     if (saslClient.hasInitialResponse()) {
       saslToken = evaluateChallenge(saslToken);
     }
     if (saslToken != null) {
       writeSaslToken(ctx, saslToken);
       if (LOG.isDebugEnabled()) {
         LOG.debug("Have sent token of size " + saslToken.length + " from initSASLContext.");
       }
     }
   }
 
   @Override
   public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
     ByteBuf in = (ByteBuf) msg;
 
     // If not complete, try to negotiate
     if (!saslClient.isComplete()) {
       while (!saslClient.isComplete() && in.isReadable()) {
         readStatus(in);
         int len = in.readInt();
         if (firstRead) {
           firstRead = false;
           if (len == SaslUtil.SWITCH_TO_SIMPLE_AUTH) {
             if (!fallbackAllowed) {
               throw new IOException("Server asks us to fall back to SIMPLE auth, " + "but this "
                   + "client is configured to only allow secure connections.");
             }
             if (LOG.isDebugEnabled()) {
               LOG.debug("Server asks us to fall back to simple auth.");
             }
             saslClient.dispose();
 
             ctx.pipeline().remove(this);
             successfulConnectHandler.onSuccess(ctx.channel());
             return;
           }
         }
         saslToken = new byte[len];
         if (LOG.isDebugEnabled()) {
           LOG.debug("Will read input token of size " + saslToken.length
               + " for processing by initSASLContext");
         }
         in.readBytes(saslToken);
 
         saslToken = evaluateChallenge(saslToken);
         if (saslToken != null) {
           if (LOG.isDebugEnabled()) {
             LOG.debug("Will send token of size " + saslToken.length + " from initSASLContext.");
           }
           writeSaslToken(ctx, saslToken);
         }
       }
 
       if (saslClient.isComplete()) {
         String qop = (String) saslClient.getNegotiatedProperty(Sasl.QOP);
 
         if (LOG.isDebugEnabled()) {
           LOG.debug("SASL client context established. Negotiated QoP: " + qop);
         }
 
         boolean useWrap = qop != null && !"auth".equalsIgnoreCase(qop);
 
         if (!useWrap) {
           ctx.pipeline().remove(this);
         }
         successfulConnectHandler.onSuccess(ctx.channel());
       }
     }
     // Normal wrapped reading
     else {
       try {
         int length = in.readInt();
         if (LOG.isDebugEnabled()) {
           LOG.debug("Actual length is " + length);
         }
         saslToken = new byte[length];
         in.readBytes(saslToken);
       } catch (IndexOutOfBoundsException e) {
         return;
       }
       try {
         ByteBuf b = ctx.channel().alloc().buffer(saslToken.length);
 
         b.writeBytes(saslClient.unwrap(saslToken, 0, saslToken.length));
         ctx.fireChannelRead(b);
 
       } catch (SaslException se) {
         try {
           saslClient.dispose();
         } catch (SaslException ignored) {
           LOG.debug("Ignoring SASL exception", ignored);
         }
         throw se;
       }
     }
   }
 
   private void writeSaslToken(final ChannelHandlerContext ctx, byte[] saslToken) {
     ByteBuf b = ctx.alloc().buffer(4 + saslToken.length);
     b.writeInt(saslToken.length);
     b.writeBytes(saslToken, 0, saslToken.length);
     ctx.writeAndFlush(b).addListener(new ChannelFutureListener() {
       @Override
       public void operationComplete(ChannelFuture future) throws Exception {
         if (!future.isSuccess()) {
           exceptionCaught(ctx, future.cause());
         }
       }
     });
   }
 
   /**
    * Get the read status
    */
   private static void readStatus(ByteBuf inStream) throws RemoteException {
     int status = inStream.readInt(); // read status
     if (status != SaslStatus.SUCCESS.state) {
       throw new RemoteException(inStream.toString(Charset.forName("UTF-8")),
           inStream.toString(Charset.forName("UTF-8")));
     }
   }
 
   @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
       throws Exception {
     saslClient.dispose();
 
     ctx.close();
 
     if (this.random == null) {
       this.random = new Random();
     }
     exceptionHandler.handle(this.retryCount++, this.random, cause);
   }
 
   @Override
   public void write(final ChannelHandlerContext ctx, Object msg, ChannelPromise promise)
       throws Exception {
     // If not complete, try to negotiate
     if (!saslClient.isComplete()) {
       super.write(ctx, msg, promise);
     } else {
       ByteBuf in = (ByteBuf) msg;
 
       try {
         saslToken = saslClient.wrap(in.array(), in.readerIndex(), in.readableBytes());
       } catch (SaslException se) {
         try {
           saslClient.dispose();
         } catch (SaslException ignored) {
           LOG.debug("Ignoring SASL exception", ignored);
         }
         promise.setFailure(se);
       }
       if (saslToken != null) {
         ByteBuf out = ctx.channel().alloc().buffer(4 + saslToken.length);
         out.writeInt(saslToken.length);
         out.writeBytes(saslToken, 0, saslToken.length);
 
         ctx.write(out).addListener(new ChannelFutureListener() {
           @Override public void operationComplete(ChannelFuture future) throws Exception {
             if (!future.isSuccess()) {
               exceptionCaught(ctx, future.cause());
             }
           }
         });
 
         saslToken = null;
       }
     }
   }
 
   /**
    * Handler for exceptions during Sasl connection
    */
   public interface SaslExceptionHandler {
     /**
      * Handle the exception
      *
      * @param retryCount current retry count
      * @param random     to create new backoff with
      */
     public void handle(int retryCount, Random random, Throwable cause);
   }
 
   /**
    * Handler for successful connects
    */
   public interface SaslSuccessfulConnectHandler {
     /**
      * Runs on success
      *
      * @param channel which is successfully authenticated
      */
     public void onSuccess(Channel channel);
   }
 }