1 /*
2 * ====================================================================
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing,
14 * software distributed under the License is distributed on an
15 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16 * KIND, either express or implied. See the License for the
17 * specific language governing permissions and limitations
18 * under the License.
19 * ====================================================================
20 *
21 * This software consists of voluntary contributions made by many
22 * individuals on behalf of the Apache Software Foundation. For more
23 * information on the Apache Software Foundation, please see
24 * <http://www.apache.org/>.
25 *
26 */
27
28 package org.apache.http.impl;
29
30 import org.apache.http.ConnectionReuseStrategy;
31 import org.apache.http.Header;
32 import org.apache.http.HeaderIterator;
33 import org.apache.http.HttpResponse;
34 import org.apache.http.HttpStatus;
35 import org.apache.http.HttpVersion;
36 import org.apache.http.ParseException;
37 import org.apache.http.ProtocolVersion;
38 import org.apache.http.TokenIterator;
39 import org.apache.http.annotation.Immutable;
40 import org.apache.http.message.BasicTokenIterator;
41 import org.apache.http.protocol.HTTP;
42 import org.apache.http.protocol.HttpContext;
43 import org.apache.http.util.Args;
44
45 /**
46 * Default implementation of a strategy deciding about connection re-use.
47 * The default implementation first checks some basics, for example
48 * whether the connection is still open or whether the end of the
49 * request entity can be determined without closing the connection.
50 * If these checks pass, the tokens in the <code>Connection</code> header will
51 * be examined. In the absence of a <code>Connection</code> header, the
52 * non-standard but commonly used <code>Proxy-Connection</code> header takes
53 * it's role. A token <code>close</code> indicates that the connection cannot
54 * be reused. If there is no such token, a token <code>keep-alive</code>
55 * indicates that the connection should be re-used. If neither token is found,
56 * or if there are no <code>Connection</code> headers, the default policy for
57 * the HTTP version is applied. Since <code>HTTP/1.1</code>, connections are
58 * re-used by default. Up until <code>HTTP/1.0</code>, connections are not
59 * re-used by default.
60 *
61 * @since 4.0
62 */
63 @Immutable
64 public class DefaultConnectionReuseStrategy implements ConnectionReuseStrategy {
65
66 public static final DefaultConnectionReuseStrategy INSTANCE = new DefaultConnectionReuseStrategy();
67
68 public DefaultConnectionReuseStrategy() {
69 super();
70 }
71
72 // see interface ConnectionReuseStrategy
73 public boolean keepAlive(final HttpResponse response,
74 final HttpContext context) {
75 Args.notNull(response, "HTTP response");
76 Args.notNull(context, "HTTP context");
77
78 // Check for a self-terminating entity. If the end of the entity will
79 // be indicated by closing the connection, there is no keep-alive.
80 final ProtocolVersion ver = response.getStatusLine().getProtocolVersion();
81 final Header teh = response.getFirstHeader(HTTP.TRANSFER_ENCODING);
82 if (teh != null) {
83 if (!HTTP.CHUNK_CODING.equalsIgnoreCase(teh.getValue())) {
84 return false;
85 }
86 } else {
87 if (canResponseHaveBody(response)) {
88 final Header[] clhs = response.getHeaders(HTTP.CONTENT_LEN);
89 // Do not reuse if not properly content-length delimited
90 if (clhs.length == 1) {
91 final Header clh = clhs[0];
92 try {
93 final int contentLen = Integer.parseInt(clh.getValue());
94 if (contentLen < 0) {
95 return false;
96 }
97 } catch (final NumberFormatException ex) {
98 return false;
99 }
100 } else {
101 return false;
102 }
103 }
104 }
105
106 // Check for the "Connection" header. If that is absent, check for
107 // the "Proxy-Connection" header. The latter is an unspecified and
108 // broken but unfortunately common extension of HTTP.
109 HeaderIterator hit = response.headerIterator(HTTP.CONN_DIRECTIVE);
110 if (!hit.hasNext()) {
111 hit = response.headerIterator("Proxy-Connection");
112 }
113
114 // Experimental usage of the "Connection" header in HTTP/1.0 is
115 // documented in RFC 2068, section 19.7.1. A token "keep-alive" is
116 // used to indicate that the connection should be persistent.
117 // Note that the final specification of HTTP/1.1 in RFC 2616 does not
118 // include this information. Neither is the "Connection" header
119 // mentioned in RFC 1945, which informally describes HTTP/1.0.
120 //
121 // RFC 2616 specifies "close" as the only connection token with a
122 // specific meaning: it disables persistent connections.
123 //
124 // The "Proxy-Connection" header is not formally specified anywhere,
125 // but is commonly used to carry one token, "close" or "keep-alive".
126 // The "Connection" header, on the other hand, is defined as a
127 // sequence of tokens, where each token is a header name, and the
128 // token "close" has the above-mentioned additional meaning.
129 //
130 // To get through this mess, we treat the "Proxy-Connection" header
131 // in exactly the same way as the "Connection" header, but only if
132 // the latter is missing. We scan the sequence of tokens for both
133 // "close" and "keep-alive". As "close" is specified by RFC 2068,
134 // it takes precedence and indicates a non-persistent connection.
135 // If there is no "close" but a "keep-alive", we take the hint.
136
137 if (hit.hasNext()) {
138 try {
139 final TokenIterator ti = createTokenIterator(hit);
140 boolean keepalive = false;
141 while (ti.hasNext()) {
142 final String token = ti.nextToken();
143 if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
144 return false;
145 } else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) {
146 // continue the loop, there may be a "close" afterwards
147 keepalive = true;
148 }
149 }
150 if (keepalive)
151 {
152 return true;
153 // neither "close" nor "keep-alive", use default policy
154 }
155
156 } catch (final ParseException px) {
157 // invalid connection header means no persistent connection
158 // we don't have logging in HttpCore, so the exception is lost
159 return false;
160 }
161 }
162
163 // default since HTTP/1.1 is persistent, before it was non-persistent
164 return !ver.lessEquals(HttpVersion.HTTP_1_0);
165 }
166
167
168 /**
169 * Creates a token iterator from a header iterator.
170 * This method can be overridden to replace the implementation of
171 * the token iterator.
172 *
173 * @param hit the header iterator
174 *
175 * @return the token iterator
176 */
177 protected TokenIterator createTokenIterator(final HeaderIterator hit) {
178 return new BasicTokenIterator(hit);
179 }
180
181 private boolean canResponseHaveBody(final HttpResponse response) {
182 final int status = response.getStatusLine().getStatusCode();
183 return status >= HttpStatus.SC_OK
184 && status != HttpStatus.SC_NO_CONTENT
185 && status != HttpStatus.SC_NOT_MODIFIED
186 && status != HttpStatus.SC_RESET_CONTENT;
187 }
188
189 }