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 32 package org.apache.http.impl; 33 34 import org.apache.http.ConnectionReuseStrategy; 35 import org.apache.http.HttpConnection; 36 import org.apache.http.HeaderIterator; 37 import org.apache.http.HttpEntity; 38 import org.apache.http.HttpResponse; 39 import org.apache.http.HttpVersion; 40 import org.apache.http.ParseException; 41 import org.apache.http.ProtocolVersion; 42 import org.apache.http.protocol.HTTP; 43 import org.apache.http.protocol.HttpContext; 44 import org.apache.http.protocol.ExecutionContext; 45 import org.apache.http.TokenIterator; 46 import 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 public class DefaultConnectionReuseStrategy 71 implements ConnectionReuseStrategy { 72 73 public DefaultConnectionReuseStrategy() { 74 super(); 75 } 76 77 // see interface ConnectionReuseStrategy 78 public boolean keepAlive(final HttpResponse response, 79 final HttpContext context) { 80 if (response == null) { 81 throw new IllegalArgumentException 82 ("HTTP response may not be null."); 83 } 84 if (context == null) { 85 throw new IllegalArgumentException 86 ("HTTP context may not be null."); 87 } 88 89 HttpConnection conn = (HttpConnection) 90 context.getAttribute(ExecutionContext.HTTP_CONNECTION); 91 92 if (conn != null && !conn.isOpen()) 93 return false; 94 // do NOT check for stale connection, that is an expensive operation 95 96 // Check for a self-terminating entity. If the end of the entity will 97 // be indicated by closing the connection, there is no keep-alive. 98 HttpEntity entity = response.getEntity(); 99 ProtocolVersion ver = response.getStatusLine().getProtocolVersion(); 100 if (entity != null) { 101 if (entity.getContentLength() < 0) { 102 if (!entity.isChunked() || 103 ver.lessEquals(HttpVersion.HTTP_1_0)) { 104 // if the content length is not known and is not chunk 105 // encoded, the connection cannot be reused 106 return false; 107 } 108 } 109 } 110 111 // Check for the "Connection" header. If that is absent, check for 112 // the "Proxy-Connection" header. The latter is an unspecified and 113 // broken but unfortunately common extension of HTTP. 114 HeaderIterator hit = response.headerIterator(HTTP.CONN_DIRECTIVE); 115 if (!hit.hasNext()) 116 hit = response.headerIterator("Proxy-Connection"); 117 118 // Experimental usage of the "Connection" header in HTTP/1.0 is 119 // documented in RFC 2068, section 19.7.1. A token "keep-alive" is 120 // used to indicate that the connection should be persistent. 121 // Note that the final specification of HTTP/1.1 in RFC 2616 does not 122 // include this information. Neither is the "Connection" header 123 // mentioned in RFC 1945, which informally describes HTTP/1.0. 124 // 125 // RFC 2616 specifies "close" as the only connection token with a 126 // specific meaning: it disables persistent connections. 127 // 128 // The "Proxy-Connection" header is not formally specified anywhere, 129 // but is commonly used to carry one token, "close" or "keep-alive". 130 // The "Connection" header, on the other hand, is defined as a 131 // sequence of tokens, where each token is a header name, and the 132 // token "close" has the above-mentioned additional meaning. 133 // 134 // To get through this mess, we treat the "Proxy-Connection" header 135 // in exactly the same way as the "Connection" header, but only if 136 // the latter is missing. We scan the sequence of tokens for both 137 // "close" and "keep-alive". As "close" is specified by RFC 2068, 138 // it takes precedence and indicates a non-persistent connection. 139 // If there is no "close" but a "keep-alive", we take the hint. 140 141 if (hit.hasNext()) { 142 try { 143 TokenIterator ti = createTokenIterator(hit); 144 boolean keepalive = false; 145 while (ti.hasNext()) { 146 final String token = ti.nextToken(); 147 if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) { 148 return false; 149 } else if (HTTP.CONN_KEEP_ALIVE.equalsIgnoreCase(token)) { 150 // continue the loop, there may be a "close" afterwards 151 keepalive = true; 152 } 153 } 154 if (keepalive) 155 return true; 156 // neither "close" nor "keep-alive", use default policy 157 158 } catch (ParseException px) { 159 // invalid connection header means no persistent connection 160 // we don't have logging in HttpCore, so the exception is lost 161 return false; 162 } 163 } 164 165 // default since HTTP/1.1 is persistent, before it was non-persistent 166 return !ver.lessEquals(HttpVersion.HTTP_1_0); 167 } 168 169 170 /** 171 * Creates a token iterator from a header iterator. 172 * This method can be overridden to replace the implementation of 173 * the token iterator. 174 * 175 * @param hit the header iterator 176 * 177 * @return the token iterator 178 */ 179 protected TokenIterator createTokenIterator(HeaderIterator hit) { 180 return new BasicTokenIterator(hit); 181 } 182 } 183
