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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 com.facebook.presto.jdbc.internal.okhttp3;

import java.net.Socket;
import com.facebook.presto.jdbc.internal.javax.annotation.Nullable;

/**
 * The sockets and streams of an HTTP, HTTPS, or HTTPS+HTTP/2 connection. May be used for multiple
 * HTTP request/response exchanges. Connections may be direct to the origin server or via a proxy.
 *
 * 

Typically instances of this class are created, connected and exercised automatically by the * HTTP client. Applications may use this class to monitor HTTP connections as members of a * {@linkplain ConnectionPool connection pool}. * *

Do not confuse this class with the misnamed {@code HttpURLConnection}, which isn't so much a * connection as a single request/response exchange. * *

Modern TLS

* *

There are tradeoffs when selecting which options to include when negotiating a secure * connection to a remote host. Newer TLS options are quite useful: * *

    *
  • Server Name Indication (SNI) enables one IP address to negotiate secure connections for * multiple domain names. *
  • Application Layer Protocol Negotiation (ALPN) enables the HTTPS port (443) to be used to * negotiate HTTP/2. *
* *

Unfortunately, older HTTPS servers refuse to connect when such options are presented. Rather * than avoiding these options entirely, this class allows a connection to be attempted with modern * options and then retried without them should the attempt fail. * *

Connection Reuse

* *

Each connection can carry a varying number of streams, depending on the underlying protocol * being used. HTTP/1.x connections can carry either zero or one streams. HTTP/2 connections can * carry any number of streams, dynamically configured with {@code SETTINGS_MAX_CONCURRENT_STREAMS}. * A connection currently carrying zero streams is an idle stream. We keep it alive because reusing * an existing connection is typically faster than establishing a new one. * *

When a single logical call requires multiple streams due to redirects or authorization * challenges, we prefer to use the same physical connection for all streams in the sequence. There * are potential performance and behavior consequences to this preference. To support this feature, * this class separates allocations from streams. An allocation is created by a call, * used for one or more streams, and then released. An allocated connection won't be stolen by other * calls while a redirect or authorization challenge is being handled. * *

When the maximum concurrent streams limit is reduced, some allocations will be rescinded. * Attempting to create new streams on these allocations will fail. * *

Note that an allocation may be released before its stream is completed. This is intended to * make bookkeeping easier for the caller: releasing the allocation as soon as the terminal stream * has been found. But only complete the stream once its data stream has been exhausted. */ public interface Connection { /** Returns the route used by this connection. */ Route route(); /** * Returns the socket that this connection is using. Returns an {@linkplain * javax.net.ssl.SSLSocket SSL socket} if this connection is HTTPS. If this is an HTTP/2 * connection the socket may be shared by multiple concurrent calls. */ Socket socket(); /** * Returns the TLS handshake used to establish this connection, or null if the connection is not * HTTPS. */ @Nullable Handshake handshake(); /** * Returns the protocol negotiated by this connection, or {@link Protocol#HTTP_1_1} if no protocol * has been negotiated. This method returns {@link Protocol#HTTP_1_1} even if the remote peer is * using {@link Protocol#HTTP_1_0}. */ Protocol protocol(); }





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