1/*
2 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk/module-main/src/main/java/org/apache/http/impl/DefaultConnectionReuseStrategy.java $
3 * $Revision: 602537 $
4 * $Date: 2007-12-08 11:42:06 -0800 (Sat, 08 Dec 2007) $
5 *
6 * ====================================================================
7 * Licensed to the Apache Software Foundation (ASF) under one
8 * or more contributor license agreements.  See the NOTICE file
9 * distributed with this work for additional information
10 * regarding copyright ownership.  The ASF licenses this file
11 * to you under the Apache License, Version 2.0 (the
12 * "License"); you may not use this file except in compliance
13 * with the License.  You may obtain a copy of the License at
14 *
15 *   http://www.apache.org/licenses/LICENSE-2.0
16 *
17 * Unless required by applicable law or agreed to in writing,
18 * software distributed under the License is distributed on an
19 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
20 * KIND, either express or implied.  See the License for the
21 * specific language governing permissions and limitations
22 * under the License.
23 * ====================================================================
24 *
25 * This software consists of voluntary contributions made by many
26 * individuals on behalf of the Apache Software Foundation.  For more
27 * information on the Apache Software Foundation, please see
28 * <http://www.apache.org/>.
29 *
30 */
31
32package org.apache.http.impl;
33
34import org.apache.http.ConnectionReuseStrategy;
35import org.apache.http.HttpConnection;
36import org.apache.http.HeaderIterator;
37import org.apache.http.HttpEntity;
38import org.apache.http.HttpResponse;
39import org.apache.http.HttpVersion;
40import org.apache.http.ParseException;
41import org.apache.http.ProtocolVersion;
42import org.apache.http.protocol.HTTP;
43import org.apache.http.protocol.HttpContext;
44import org.apache.http.protocol.ExecutionContext;
45import org.apache.http.TokenIterator;
46import org.apache.http.message.BasicTokenIterator;
47
48/**
49 * Default implementation of a strategy deciding about connection re-use.
50 * The default implementation first checks some basics, for example
51 * whether the connection is still open or whether the end of the
52 * request entity can be determined without closing the connection.
53 * If these checks pass, the tokens in the "Connection" header will
54 * be examined. In the absence of a "Connection" header, the
55 * non-standard but commonly used "Proxy-Connection" header takes
56 * it's role. A token "close" indicates that the connection cannot
57 * be reused. If there is no such token, a token "keep-alive" indicates
58 * that the connection should be re-used. If neither token is found,
59 * or if there are no "Connection" headers, the default policy for
60 * the HTTP version is applied. Since HTTP/1.1, connections are re-used
61 * by default. Up until HTTP/1.0, connections are not re-used by default.
62 *
63 * @author <a href="mailto:oleg at ural.ru">Oleg Kalnichevski</a>
64 * @author <a href="mailto:rolandw at apache.org">Roland Weber</a>
65 *
66 * @version $Revision: 602537 $
67 *
68 * @since 4.0
69 *
70 * @deprecated Please use {@link java.net.URL#openConnection} instead.
71 *     Please visit <a href="http://android-developers.blogspot.com/2011/09/androids-http-clients.html">this webpage</a>
72 *     for further details.
73 */
74@Deprecated
75public class DefaultConnectionReuseStrategy
76    implements ConnectionReuseStrategy {
77
78    public DefaultConnectionReuseStrategy() {
79        super();
80    }
81
82    // see interface ConnectionReuseStrategy
83    public boolean keepAlive(final HttpResponse response,
84                             final HttpContext context) {
85        if (response == null) {
86            throw new IllegalArgumentException
87                ("HTTP response may not be null.");
88        }
89        if (context == null) {
90            throw new IllegalArgumentException
91                ("HTTP context may not be null.");
92        }
93
94        HttpConnection conn = (HttpConnection)
95            context.getAttribute(ExecutionContext.HTTP_CONNECTION);
96
97        if (conn != null && !conn.isOpen())
98            return false;
99        // do NOT check for stale connection, that is an expensive operation
100
101        // Check for a self-terminating entity. If the end of the entity will
102        // be indicated by closing the connection, there is no keep-alive.
103        HttpEntity entity = response.getEntity();
104        ProtocolVersion ver = response.getStatusLine().getProtocolVersion();
105        if (entity != null) {
106            if (entity.getContentLength() < 0) {
107                if (!entity.isChunked() ||
108                    ver.lessEquals(HttpVersion.HTTP_1_0)) {
109                    // if the content length is not known and is not chunk
110                    // encoded, the connection cannot be reused
111                    return false;
112                }
113            }
114        }
115
116        // Check for the "Connection" header. If that is absent, check for
117        // the "Proxy-Connection" header. The latter is an unspecified and
118        // broken but unfortunately common extension of HTTP.
119        HeaderIterator hit = response.headerIterator(HTTP.CONN_DIRECTIVE);
120        if (!hit.hasNext())
121            hit = response.headerIterator("Proxy-Connection");
122
123        // Experimental usage of the "Connection" header in HTTP/1.0 is
124        // documented in RFC 2068, section 19.7.1. A token "keep-alive" is
125        // used to indicate that the connection should be persistent.
126        // Note that the final specification of HTTP/1.1 in RFC 2616 does not
127        // include this information. Neither is the "Connection" header
128        // mentioned in RFC 1945, which informally describes HTTP/1.0.
129        //
130        // RFC 2616 specifies "close" as the only connection token with a
131        // specific meaning: it disables persistent connections.
132        //
133        // The "Proxy-Connection" header is not formally specified anywhere,
134        // but is commonly used to carry one token, "close" or "keep-alive".
135        // The "Connection" header, on the other hand, is defined as a
136        // sequence of tokens, where each token is a header name, and the
137        // token "close" has the above-mentioned additional meaning.
138        //
139        // To get through this mess, we treat the "Proxy-Connection" header
140        // in exactly the same way as the "Connection" header, but only if
141        // the latter is missing. We scan the sequence of tokens for both
142        // "close" and "keep-alive". As "close" is specified by RFC 2068,
143        // it takes precedence and indicates a non-persistent connection.
144        // If there is no "close" but a "keep-alive", we take the hint.
145
146        if (hit.hasNext()) {
147            try {
148                TokenIterator ti = createTokenIterator(hit);
149                boolean keepalive = false;
150                while (ti.hasNext()) {
151                    final String token = ti.nextToken();
152                    if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
153                        return false;
154                    } else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) {
155                        // continue the loop, there may be a "close" afterwards
156                        keepalive = true;
157                    }
158                }
159                if (keepalive)
160                    return true;
161                // neither "close" nor "keep-alive", use default policy
162
163            } catch (ParseException px) {
164                // invalid connection header means no persistent connection
165                // we don't have logging in HttpCore, so the exception is lost
166                return false;
167            }
168        }
169
170        // default since HTTP/1.1 is persistent, before it was non-persistent
171        return !ver.lessEquals(HttpVersion.HTTP_1_0);
172    }
173
174
175    /**
176     * Creates a token iterator from a header iterator.
177     * This method can be overridden to replace the implementation of
178     * the token iterator.
179     *
180     * @param hit       the header iterator
181     *
182     * @return  the token iterator
183     */
184    protected TokenIterator createTokenIterator(HeaderIterator hit) {
185        return new BasicTokenIterator(hit);
186    }
187}
188