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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 okhttp3;
import java.net.Socket;
import 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();
}