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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.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.protocol.HTTP;
39  import org.apache.http.protocol.HttpContext;
40  import org.apache.http.TokenIterator;
41  import org.apache.http.annotation.Immutable;
42  import org.apache.http.message.BasicTokenIterator;
43  
44  /**
45   * Default implementation of a strategy deciding about connection re-use.
46   * The default implementation first checks some basics, for example
47   * whether the connection is still open or whether the end of the
48   * request entity can be determined without closing the connection.
49   * If these checks pass, the tokens in the <code>Connection</code> header will
50   * be examined. In the absence of a <code>Connection</code> header, the
51   * non-standard but commonly used <code>Proxy-Connection</code> header takes
52   * it's role. A token <code>close</code> indicates that the connection cannot
53   * be reused. If there is no such token, a token <code>keep-alive</code>
54   * indicates that the connection should be re-used. If neither token is found,
55   * or if there are no <code>Connection</code> headers, the default policy for
56   * the HTTP version is applied. Since <code>HTTP/1.1</code>, connections are
57   * re-used by default. Up until <code>HTTP/1.0</code>, connections are not
58   * re-used by default.
59   *
60   * @since 4.0
61   */
62  @Immutable
63  public class DefaultConnectionReuseStrategy implements ConnectionReuseStrategy {
64  
65      public DefaultConnectionReuseStrategy() {
66          super();
67      }
68  
69      // see interface ConnectionReuseStrategy
70      public boolean keepAlive(final HttpResponse response,
71                               final HttpContext context) {
72          if (response == null) {
73              throw new IllegalArgumentException
74                  ("HTTP response may not be null.");
75          }
76          if (context == null) {
77              throw new IllegalArgumentException
78                  ("HTTP context may not be null.");
79          }
80  
81          // Check for a self-terminating entity. If the end of the entity will
82          // be indicated by closing the connection, there is no keep-alive.
83          ProtocolVersion ver = response.getStatusLine().getProtocolVersion();
84          Header teh = response.getFirstHeader(HTTP.TRANSFER_ENCODING);
85          if (teh != null) {
86              if (!HTTP.CHUNK_CODING.equalsIgnoreCase(teh.getValue())) {
87                  return false;
88              }
89          } else {
90              if (canResponseHaveBody(response)) {
91                  Header[] clhs = response.getHeaders(HTTP.CONTENT_LEN);
92                  // Do not reuse if not properly content-length delimited
93                  if (clhs.length == 1) {
94                      Header clh = clhs[0];
95                      try {
96                          int contentLen = Integer.parseInt(clh.getValue());
97                          if (contentLen < 0) {
98                              return false;
99                          }
100                     } catch (NumberFormatException ex) {
101                         return false;
102                     }
103                 } else {
104                     return false;
105                 }
106             }
107         }
108 
109         // Check for the "Connection" header. If that is absent, check for
110         // the "Proxy-Connection" header. The latter is an unspecified and
111         // broken but unfortunately common extension of HTTP.
112         HeaderIterator hit = response.headerIterator(HTTP.CONN_DIRECTIVE);
113         if (!hit.hasNext())
114             hit = response.headerIterator("Proxy-Connection");
115 
116         // Experimental usage of the "Connection" header in HTTP/1.0 is
117         // documented in RFC 2068, section 19.7.1. A token "keep-alive" is
118         // used to indicate that the connection should be persistent.
119         // Note that the final specification of HTTP/1.1 in RFC 2616 does not
120         // include this information. Neither is the "Connection" header
121         // mentioned in RFC 1945, which informally describes HTTP/1.0.
122         //
123         // RFC 2616 specifies "close" as the only connection token with a
124         // specific meaning: it disables persistent connections.
125         //
126         // The "Proxy-Connection" header is not formally specified anywhere,
127         // but is commonly used to carry one token, "close" or "keep-alive".
128         // The "Connection" header, on the other hand, is defined as a
129         // sequence of tokens, where each token is a header name, and the
130         // token "close" has the above-mentioned additional meaning.
131         //
132         // To get through this mess, we treat the "Proxy-Connection" header
133         // in exactly the same way as the "Connection" header, but only if
134         // the latter is missing. We scan the sequence of tokens for both
135         // "close" and "keep-alive". As "close" is specified by RFC 2068,
136         // it takes precedence and indicates a non-persistent connection.
137         // If there is no "close" but a "keep-alive", we take the hint.
138 
139         if (hit.hasNext()) {
140             try {
141                 TokenIterator ti = createTokenIterator(hit);
142                 boolean keepalive = false;
143                 while (ti.hasNext()) {
144                     final String token = ti.nextToken();
145                     if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
146                         return false;
147                     } else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) {
148                         // continue the loop, there may be a "close" afterwards
149                         keepalive = true;
150                     }
151                 }
152                 if (keepalive)
153                     return true;
154                 // neither "close" nor "keep-alive", use default policy
155 
156             } catch (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(HeaderIterator hit) {
178         return new BasicTokenIterator(hit);
179     }
180 
181     private boolean canResponseHaveBody(final HttpResponse response) {
182         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 }