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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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.http.conn;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

import org.apache.http.HttpClientConnection;
import org.apache.http.conn.routing.HttpRoute;
import org.apache.http.protocol.HttpContext;

/**
 * Represents a manager of persistent client connections.
 * <p>
 * The purpose of an HTTP connection manager is to serve as a factory for new
 * HTTP connections, manage persistent connections and synchronize access to
 * persistent connections making sure that only one thread of execution can
 * have access to a connection at a time.
 * </p>
 * <p>
 * Implementations of this interface must be thread-safe. Access to shared
 * data must be synchronized as methods of this interface may be executed
 * from multiple threads.
 * </p>
 *
 * @since 4.3
 */
public interface HttpClientConnectionManager {

    /**
     * Returns a new {@link ConnectionRequest}, from which a
     * {@link HttpClientConnection} can be obtained or the request can be
     * aborted.
     * <p>
     * Please note that newly allocated connections can be returned
     * in the closed state. The consumer of that connection is responsible
     * for fully establishing the route the to the connection target
     * by calling {@link #connect(org.apache.http.HttpClientConnection,
     *   org.apache.http.conn.routing.HttpRoute, int,
     *   org.apache.http.protocol.HttpContext) connect} in order to connect
     * directly to the target or to the first proxy hop, optionally calling
     * {@link #upgrade(org.apache.http.HttpClientConnection,
     *   org.apache.http.conn.routing.HttpRoute,
     *   org.apache.http.protocol.HttpContext) upgrade} method to upgrade
     * the connection after having executed {@code CONNECT} method to
     * all intermediate proxy hops and and finally calling {@link #routeComplete(
     *  org.apache.http.HttpClientConnection,
     *  org.apache.http.conn.routing.HttpRoute,
     *  org.apache.http.protocol.HttpContext) routeComplete} to mark the route
     *  as fully completed.
     * </p>
     *
     * @param route HTTP route of the requested connection.
     * @param state expected state of the connection or {@code null}
     *              if the connection is not expected to carry any state.
     */
    ConnectionRequest requestConnection(HttpRoute route, Object state);

    /**
     * Releases the connection back to the manager making it potentially
     * re-usable by other consumers. Optionally, the maximum period
     * of how long the manager should keep the connection alive can be
     * defined using {@code validDuration} and {@code timeUnit}
     * parameters.
     *
     * @param conn      the managed connection to release.
     * @param validDuration the duration of time this connection is valid for reuse.
     * @param timeUnit the time unit.
     *
     * @see #closeExpiredConnections()
     */
    void releaseConnection(
            HttpClientConnection conn, Object newState, long validDuration, TimeUnit timeUnit);

    /**
     * Connects the underlying connection socket to the connection target in case
     * of a direct route or to the first proxy hop in case of a route via a proxy
     * (or multiple proxies).
     *
     * @param conn the managed connection.
     * @param route the route of the connection.
     * @param connectTimeout connect timeout in milliseconds.
     * @param context the actual HTTP context.
     * @throws IOException
     */
    void connect(
            HttpClientConnection conn,
            HttpRoute route,
            int connectTimeout,
            HttpContext context) throws IOException;

    /**
     * Upgrades the underlying connection socket to TLS/SSL (or another layering
     * protocol) after having executed {@code CONNECT} method to all
     * intermediate proxy hops
     *
     * @param conn the managed connection.
     * @param route the route of the connection.
     * @param context the actual HTTP context.
     * @throws IOException
     */
    void upgrade(
            HttpClientConnection conn,
            HttpRoute route,
            HttpContext context) throws IOException;

    /**
     * Marks the connection as fully established with all its intermediate
     * hops completed.
     *
     * @param conn the managed connection.
     * @param route the route of the connection.
     * @param context the actual HTTP context.
     * @throws IOException
     */
    void routeComplete(
            HttpClientConnection conn,
            HttpRoute route,
            HttpContext context) throws IOException;

    /**
     * Closes idle connections in the pool.
     * <p>
     * Open connections in the pool that have not been used for the
     * timespan given by the argument will be closed.
     * Currently allocated connections are not subject to this method.
     * Times will be checked with milliseconds precision
     * </p>
     * <p>
     * All expired connections will also be closed.
     * </p>
     *
     * @param idletime  the idle time of connections to be closed
     * @param tunit     the unit for the {@code idletime}
     *
     * @see #closeExpiredConnections()
     */
    void closeIdleConnections(long idletime, TimeUnit tunit);

    /**
     * Closes all expired connections in the pool.
     * <p>
     * Open connections in the pool that have not been used for
     * the timespan defined when the connection was released will be closed.
     * Currently allocated connections are not subject to this method.
     * Times will be checked with milliseconds precision.
     * </p>
     */
    void closeExpiredConnections();

    /**
     * Shuts down this connection manager and releases allocated resources.
     * This includes closing all connections, whether they are currently
     * used or not.
     */
    void shutdown();

}