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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.HttpHeaders;
34  import org.apache.http.HttpRequest;
35  import org.apache.http.HttpResponse;
36  import org.apache.http.HttpStatus;
37  import org.apache.http.HttpVersion;
38  import org.apache.http.ParseException;
39  import org.apache.http.ProtocolVersion;
40  import org.apache.http.TokenIterator;
41  import org.apache.http.annotation.Contract;
42  import org.apache.http.annotation.ThreadingBehavior;
43  import org.apache.http.message.BasicTokenIterator;
44  import org.apache.http.protocol.HTTP;
45  import org.apache.http.protocol.HttpContext;
46  import org.apache.http.protocol.HttpCoreContext;
47  import org.apache.http.util.Args;
48  
49  /**
50   * Default implementation of a strategy deciding about connection re-use.
51   * The default implementation first checks some basics, for example
52   * whether the connection is still open or whether the end of the
53   * request entity can be determined without closing the connection.
54   * If these checks pass, the tokens in the {@code Connection} header will
55   * be examined. In the absence of a {@code Connection} header, the
56   * non-standard but commonly used {@code Proxy-Connection} header takes
57   * it's role. A token {@code close} indicates that the connection cannot
58   * be reused. If there is no such token, a token {@code keep-alive}
59   * indicates that the connection should be re-used. If neither token is found,
60   * or if there are no {@code Connection} headers, the default policy for
61   * the HTTP version is applied. Since {@code HTTP/1.1}, connections are
62   * re-used by default. Up until {@code HTTP/1.0}, connections are not
63   * re-used by default.
64   *
65   * @since 4.0
66   */
67  @Contract(threading = ThreadingBehavior.IMMUTABLE)
68  public class DefaultConnectionReuseStrategy implements ConnectionReuseStrategy {
69  
70      public static final DefaultConnectionReuseStrategy INSTANCE = new DefaultConnectionReuseStrategy();
71  
72      public DefaultConnectionReuseStrategy() {
73          super();
74      }
75  
76      // see interface ConnectionReuseStrategy
77      @Override
78      public boolean keepAlive(final HttpResponse response,
79                               final HttpContext context) {
80          Args.notNull(response, "HTTP response");
81          Args.notNull(context, "HTTP context");
82  
83          final HttpRequest request = (HttpRequest) context.getAttribute(HttpCoreContext.HTTP_REQUEST);
84          if (request != null) {
85              try {
86                  final TokenIterator ti = new BasicTokenIterator(request.headerIterator(HttpHeaders.CONNECTION));
87                  while (ti.hasNext()) {
88                      final String token = ti.nextToken();
89                      if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
90                          return false;
91                      }
92                  }
93              } catch (final ParseException px) {
94                  // invalid connection header. do not re-use
95                  return false;
96              }
97          }
98  
99          // Check for a self-terminating entity. If the end of the entity will
100         // be indicated by closing the connection, there is no keep-alive.
101         final ProtocolVersion ver = response.getStatusLine().getProtocolVersion();
102         final Header teh = response.getFirstHeader(HTTP.TRANSFER_ENCODING);
103         if (teh != null) {
104             if (!HTTP.CHUNK_CODING.equalsIgnoreCase(teh.getValue())) {
105                 return false;
106             }
107         } else {
108             if (canResponseHaveBody(request, response)) {
109                 final Header[] clhs = response.getHeaders(HTTP.CONTENT_LEN);
110                 // Do not reuse if not properly content-length delimited
111                 if (clhs.length == 1) {
112                     final Header clh = clhs[0];
113                     try {
114                         final int contentLen = Integer.parseInt(clh.getValue());
115                         if (contentLen < 0) {
116                             return false;
117                         }
118                     } catch (final NumberFormatException ex) {
119                         return false;
120                     }
121                 } else {
122                     return false;
123                 }
124             }
125         }
126 
127         // Check for the "Connection" header. If that is absent, check for
128         // the "Proxy-Connection" header. The latter is an unspecified and
129         // broken but unfortunately common extension of HTTP.
130         HeaderIterator headerIterator = response.headerIterator(HTTP.CONN_DIRECTIVE);
131         if (!headerIterator.hasNext()) {
132             headerIterator = response.headerIterator("Proxy-Connection");
133         }
134 
135         // Experimental usage of the "Connection" header in HTTP/1.0 is
136         // documented in RFC 2068, section 19.7.1. A token "keep-alive" is
137         // used to indicate that the connection should be persistent.
138         // Note that the final specification of HTTP/1.1 in RFC 2616 does not
139         // include this information. Neither is the "Connection" header
140         // mentioned in RFC 1945, which informally describes HTTP/1.0.
141         //
142         // RFC 2616 specifies "close" as the only connection token with a
143         // specific meaning: it disables persistent connections.
144         //
145         // The "Proxy-Connection" header is not formally specified anywhere,
146         // but is commonly used to carry one token, "close" or "keep-alive".
147         // The "Connection" header, on the other hand, is defined as a
148         // sequence of tokens, where each token is a header name, and the
149         // token "close" has the above-mentioned additional meaning.
150         //
151         // To get through this mess, we treat the "Proxy-Connection" header
152         // in exactly the same way as the "Connection" header, but only if
153         // the latter is missing. We scan the sequence of tokens for both
154         // "close" and "keep-alive". As "close" is specified by RFC 2068,
155         // it takes precedence and indicates a non-persistent connection.
156         // If there is no "close" but a "keep-alive", we take the hint.
157 
158         if (headerIterator.hasNext()) {
159             try {
160                 final TokenIterator ti = new BasicTokenIterator(headerIterator);
161                 boolean keepalive = false;
162                 while (ti.hasNext()) {
163                     final String token = ti.nextToken();
164                     if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
165                         return false;
166                     } else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) {
167                         // continue the loop, there may be a "close" afterwards
168                         keepalive = true;
169                     }
170                 }
171                 if (keepalive) {
172                     return true;
173                 // neither "close" nor "keep-alive", use default policy
174                 }
175 
176             } catch (final ParseException px) {
177                 // invalid connection header. do not re-use
178                 return false;
179             }
180         }
181 
182         // default since HTTP/1.1 is persistent, before it was non-persistent
183         return !ver.lessEquals(HttpVersion.HTTP_1_0);
184     }
185 
186 
187     /**
188      * Creates a token iterator from a header iterator.
189      * This method can be overridden to replace the implementation of
190      * the token iterator.
191      *
192      * @param hit       the header iterator
193      *
194      * @return  the token iterator
195      */
196     protected TokenIterator createTokenIterator(final HeaderIterator hit) {
197         return new BasicTokenIterator(hit);
198     }
199 
200     private boolean canResponseHaveBody(final HttpRequest request, final HttpResponse response) {
201         if (request != null && request.getRequestLine().getMethod().equalsIgnoreCase("HEAD")) {
202             return false;
203         }
204         final int status = response.getStatusLine().getStatusCode();
205         return status >= HttpStatus.SC_OK
206             && status != HttpStatus.SC_NO_CONTENT
207             && status != HttpStatus.SC_NOT_MODIFIED
208             && status != HttpStatus.SC_RESET_CONTENT;
209     }
210 
211 }