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/*
 * 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.sshd.common;

import java.io.IOException;

import org.apache.sshd.common.future.SshFuture;
import org.apache.sshd.common.io.IoSession;
import org.apache.sshd.common.io.IoWriteFuture;
import org.apache.sshd.common.util.Buffer;

/**
 * Represents an SSH session
 *
 * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
 */

public interface Session extends Closeable {

    /**
     * Returns the value of the user-defined attribute of this session.
     *
     * @param key the key of the attribute; must not be null.
     * @return <tt>null</tt> if there is no attribute with the specified key
     */

    <T> T getAttribute(AttributeKey<T> key);

    /**
     * Sets a user-defined attribute.
     *
     * @param key   the key of the attribute; must not be null.
     * @param value the value of the attribute; must not be null.
     * @return The old value of the attribute.  <tt>null</tt> if it is new.
     */

    <T, E extends T> T setAttribute(AttributeKey<T> key, E value);

    /**
     * Retrieve the name of the user authenticated on this session
     * or null if the session has not been authenticated yet.
     *
     * @return the user name.
     */

    String getUsername();

    /**
     * Retrieve the client version for this session.
     *
     * @return the client version.
     */

    String getClientVersion();

    /**
     * Retrieve the server version for this session.
     *
     * @return the server version.
     */

    String getServerVersion();

    /**
     * Retrieve the FactoryManager that has created this session
     *
     * @return the factory manager, can not be <tt>null</tt>.
     */

    FactoryManager getFactoryManager();

    /**
     * Retrieve a configuration property as an integer
     *
     * @param name the name of the property
     * @param defaultValue the default value
     * @return the value of the configuration property or the default value if not found
     */

    int getIntProperty(String name, int defaultValue);

    /**
     * Create a new buffer for the specified SSH packet and reserve the needed space
     * (5 bytes) for the packet header.
     *
     * @param cmd the SSH command
     * @return a new buffer ready for write
     */

    Buffer createBuffer(byte cmd);

    /**
     * Create a new buffer for the specified SSH packet and reserve the needed space
     * (5 bytes) for the packet header.
     *
     * @param cmd the SSH command
     * @param estimatedSize estimated number of bytes the buffer will hold, 0 if unknown.
     * @return a new buffer ready for write
     */

    Buffer createBuffer(byte cmd, int estimatedSize);

    /**
     * Encode and send the given buffer.
     * The buffer has to have 5 bytes free at the beginning to allow the encoding to take place.
     * Also, the write position of the buffer has to be set to the position of the last byte to write.
     *
     * @param buffer the buffer to encode and send
     * @return a future that can be used to check when the packet has actually been sent
     * @throws java.io.IOException if an error occured when encoding sending the packet
     */

    IoWriteFuture writePacket(Buffer buffer) throws IOException;

    /**
     * Send a global request and wait for the response.
     * This must only be used when sending a SSH_MSG_GLOBAL_REQUEST with a result expected,
     * else it will wait forever.
     *
     * @param buffer the buffer containing the global request
     * @return the return buffer if the request was successful, <code>null</code> otherwise.
     * @throws java.io.IOException if an error occurred when encoding sending the packet
     */

    Buffer request(Buffer buffer) throws IOException;

    /**
     * Handle any exceptions that occured on this session.
     * The session will be closed and a disconnect packet will be
     * sent before if the given exception is an
     * {@link org.apache.sshd.common.SshException}.
     *
     * @param t the exception to process
     */

    void exceptionCaught(Throwable t);

    /**
     * Add a session |listener|.
     *
     * @param listener the session listener to add
     */

    void addListener(SessionListener listener);

    /**
     * Remove a session |listener|.
     *
     * @param listener the session listener to remove
     */

    void removeListener(SessionListener listener);

    /**
     * Initiate a new key exchange.
     */

    SshFuture reExchangeKeys() throws IOException;

    /**
     * Get the service of the specified type.
     * If the service is not of the specified class,
     * an IllegalStateException will be thrown.
     *
     * @throws java.lang.IllegalStateException
     */

    <T extends Service> T getService(Class<T> clazz);

    /**
     * Returns the IoSession associated to this ssh session
     */

    IoSession getIoSession();

    /**
     * Type safe key for storage within the user attributes of {@link org.apache.sshd.common.session.AbstractSession}.
     * Typically it is used as a static variable that is shared between the producer
     * and the consumer. To further restrict access the setting or getting it from
     * the Session you can add static get and set methods, e.g:
     *
     * private static final AttributeKey<MyValue> MY_KEY = new AttributeKey<MyValue>();
     *
     * public static MyValue getMyValue(Session s) {
     *   return s.getAttribute(MY_KEY);
     * }
     *
     * private void setMyValue(Session s, MyValue value) {
     *   s.setAttribute(MY_KEY, value);
     * }
     *
     * @param <T> type of value stored in the attribute.
     *
     * @author <a href="mailto:dev@mina.apache.org">Apache MINA SSHD Project</a>
     */

    public class AttributeKey<T> {
    }

}