001/*
002 * ====================================================================
003 * Licensed to the Apache Software Foundation (ASF) under one
004 * or more contributor license agreements.  See the NOTICE file
005 * distributed with this work for additional information
006 * regarding copyright ownership.  The ASF licenses this file
007 * to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance
009 * with the License.  You may obtain a copy of the License at
010 *
011 *   http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing,
014 * software distributed under the License is distributed on an
015 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
016 * KIND, either express or implied.  See the License for the
017 * specific language governing permissions and limitations
018 * under the License.
019 * ====================================================================
020 *
021 * This software consists of voluntary contributions made by many
022 * individuals on behalf of the Apache Software Foundation.  For more
023 * information on the Apache Software Foundation, please see
024 * <http://www.apache.org/>.
025 *
026 */
027
028package org.apache.http.impl;
029
030import org.apache.http.ConnectionReuseStrategy;
031import org.apache.http.Header;
032import org.apache.http.HeaderIterator;
033import org.apache.http.HttpHeaders;
034import org.apache.http.HttpRequest;
035import org.apache.http.HttpResponse;
036import org.apache.http.HttpStatus;
037import org.apache.http.HttpVersion;
038import org.apache.http.ParseException;
039import org.apache.http.ProtocolVersion;
040import org.apache.http.TokenIterator;
041import org.apache.http.annotation.Contract;
042import org.apache.http.annotation.ThreadingBehavior;
043import org.apache.http.message.BasicTokenIterator;
044import org.apache.http.protocol.HTTP;
045import org.apache.http.protocol.HttpContext;
046import org.apache.http.protocol.HttpCoreContext;
047import org.apache.http.util.Args;
048
049/**
050 * Default implementation of a strategy deciding about connection re-use.
051 * The default implementation first checks some basics, for example
052 * whether the connection is still open or whether the end of the
053 * request entity can be determined without closing the connection.
054 * If these checks pass, the tokens in the {@code Connection} header will
055 * be examined. In the absence of a {@code Connection} header, the
056 * non-standard but commonly used {@code Proxy-Connection} header takes
057 * it's role. A token {@code close} indicates that the connection cannot
058 * be reused. If there is no such token, a token {@code keep-alive}
059 * indicates that the connection should be re-used. If neither token is found,
060 * or if there are no {@code Connection} headers, the default policy for
061 * the HTTP version is applied. Since {@code HTTP/1.1}, connections are
062 * re-used by default. Up until {@code HTTP/1.0}, connections are not
063 * re-used by default.
064 *
065 * @since 4.0
066 */
067@Contract(threading = ThreadingBehavior.IMMUTABLE)
068public class DefaultConnectionReuseStrategy implements ConnectionReuseStrategy {
069
070    public static final DefaultConnectionReuseStrategy INSTANCE = new DefaultConnectionReuseStrategy();
071
072    public DefaultConnectionReuseStrategy() {
073        super();
074    }
075
076    // see interface ConnectionReuseStrategy
077    @Override
078    public boolean keepAlive(final HttpResponse response,
079                             final HttpContext context) {
080        Args.notNull(response, "HTTP response");
081        Args.notNull(context, "HTTP context");
082
083        final HttpRequest request = (HttpRequest) context.getAttribute(HttpCoreContext.HTTP_REQUEST);
084        if (request != null) {
085            try {
086                final TokenIterator ti = new BasicTokenIterator(request.headerIterator(HttpHeaders.CONNECTION));
087                while (ti.hasNext()) {
088                    final String token = ti.nextToken();
089                    if (HTTP.CONN_CLOSE.equalsIgnoreCase(token)) {
090                        return false;
091                    }
092                }
093            } catch (final ParseException px) {
094                // invalid connection header. do not re-use
095                return false;
096            }
097        }
098
099        // 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}