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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.impl.client;

import java.net.URI;
import java.net.URISyntaxException;
import java.util.Locale;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.Header;
import org.apache.http.HttpHost;
import org.apache.http.HttpRequest;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.ProtocolException;
import org.apache.http.annotation.Contract;
import org.apache.http.annotation.ThreadingBehavior;
import org.apache.http.client.CircularRedirectException;
import org.apache.http.client.RedirectStrategy;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpHead;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.methods.RequestBuilder;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.client.utils.URIUtils;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.Args;
import org.apache.http.util.Asserts;
import org.apache.http.util.TextUtils;

Default implementation of RedirectStrategy. This strategy honors the restrictions on automatic redirection of entity enclosing methods such as POST and PUT imposed by the HTTP specification. 302 Moved Temporarily, 301 Moved Permanently and 307 Temporary Redirect status codes will result in an automatic redirect of HEAD and GET methods only. POST and PUT methods will not be automatically redirected as requiring user confirmation. 
 The restriction on automatic redirection of POST methods can be relaxed by using LaxRedirectStrategy instead of DefaultRedirectStrategy. 
See Also:
LaxRedirectStrategy
Since:
4.1/**
 * Default implementation of {@link RedirectStrategy}. This strategy honors the restrictions
 * on automatic redirection of entity enclosing methods such as POST and PUT imposed by the
 * HTTP specification. {@code 302 Moved Temporarily}, {@code 301 Moved Permanently} and
 * {@code 307 Temporary Redirect} status codes will result in an automatic redirect of
 * HEAD and GET methods only. POST and PUT methods will not be automatically redirected
 * as requiring user confirmation.
 * <p>
 * The restriction on automatic redirection of POST methods can be relaxed by using
 * {@link LaxRedirectStrategy} instead of {@link DefaultRedirectStrategy}.
 * </p>
 *
 * @see LaxRedirectStrategy
 * @since 4.1
 */
@Contract(threading = ThreadingBehavior.IMMUTABLE)
public class DefaultRedirectStrategy implements RedirectStrategy {

    private final Log log = LogFactory.getLog(getClass());

    
Deprecated:
(4.3) use HttpClientContext.REDIRECT_LOCATIONS./**
     * @deprecated (4.3) use {@link org.apache.http.client.protocol.HttpClientContext#REDIRECT_LOCATIONS}.
     */
    @Deprecated
    public static final String REDIRECT_LOCATIONS = "http.protocol.redirect-locations";

    public static final DefaultRedirectStrategy INSTANCE = new DefaultRedirectStrategy();

    
Redirectable methods.
/**
     * Redirectable methods.
     */
    private static final String[] REDIRECT_METHODS = new String[] {
        HttpGet.METHOD_NAME,
        HttpHead.METHOD_NAME
    };

    public DefaultRedirectStrategy() {
        super();
    }

    @Override
    public boolean isRedirected(
            final HttpRequest request,
            final HttpResponse response,
            final HttpContext context) throws ProtocolException {
        Args.notNull(request, "HTTP request");
        Args.notNull(response, "HTTP response");

        final int statusCode = response.getStatusLine().getStatusCode();
        final String method = request.getRequestLine().getMethod();
        final Header locationHeader = response.getFirstHeader("location");
        switch (statusCode) {
        case HttpStatus.SC_MOVED_TEMPORARILY:
            return isRedirectable(method) && locationHeader != null;
        case HttpStatus.SC_MOVED_PERMANENTLY:
        case HttpStatus.SC_TEMPORARY_REDIRECT:
            return isRedirectable(method);
        case HttpStatus.SC_SEE_OTHER:
            return true;
        default:
            return false;
        } //end of switch
    }

    public URI getLocationURI(
            final HttpRequest request,
            final HttpResponse response,
            final HttpContext context) throws ProtocolException {
        Args.notNull(request, "HTTP request");
        Args.notNull(response, "HTTP response");
        Args.notNull(context, "HTTP context");

        final HttpClientContext clientContext = HttpClientContext.adapt(context);

        //get the location header to find out where to redirect to
        final Header locationHeader = response.getFirstHeader("location");
        if (locationHeader == null) {
            // got a redirect response, but no location header
            throw new ProtocolException(
                    "Received redirect response " + response.getStatusLine()
                    + " but no location header");
        }
        final String location = locationHeader.getValue();
        if (this.log.isDebugEnabled()) {
            this.log.debug("Redirect requested to location '" + location + "'");
        }

        final RequestConfig config = clientContext.getRequestConfig();

        URI uri = createLocationURI(location);

        // rfc2616 demands the location value be a complete URI
        // Location       = "Location" ":" absoluteURI
        try {
            if (!uri.isAbsolute()) {
                if (!config.isRelativeRedirectsAllowed()) {
                    throw new ProtocolException("Relative redirect location '"
                            + uri + "' not allowed");
                }
                // Adjust location URI
                final HttpHost target = clientContext.getTargetHost();
                Asserts.notNull(target, "Target host");
                final URI requestURI = new URI(request.getRequestLine().getUri());
                final URI absoluteRequestURI = URIUtils.rewriteURI(requestURI, target, false);
                uri = URIUtils.resolve(absoluteRequestURI, uri);
            }
        } catch (final URISyntaxException ex) {
            throw new ProtocolException(ex.getMessage(), ex);
        }

        RedirectLocations redirectLocations = (RedirectLocations) clientContext.getAttribute(
                HttpClientContext.REDIRECT_LOCATIONS);
        if (redirectLocations == null) {
            redirectLocations = new RedirectLocations();
            context.setAttribute(HttpClientContext.REDIRECT_LOCATIONS, redirectLocations);
        }
        if (!config.isCircularRedirectsAllowed()) {
            if (redirectLocations.contains(uri)) {
                throw new CircularRedirectException("Circular redirect to '" + uri + "'");
            }
        }
        redirectLocations.add(uri);
        return uri;
    }

    
Since:
4.1/**
     * @since 4.1
     */
    protected URI createLocationURI(final String location) throws ProtocolException {
        try {
            final URIBuilder b = new URIBuilder(new URI(location).normalize());
            final String host = b.getHost();
            if (host != null) {
                b.setHost(host.toLowerCase(Locale.ROOT));
            }
            final String path = b.getPath();
            if (TextUtils.isEmpty(path)) {
                b.setPath("/");
            }
            return b.build();
        } catch (final URISyntaxException ex) {
            throw new ProtocolException("Invalid redirect URI: " + location, ex);
        }
    }

    
Since:
4.2/**
     * @since 4.2
     */
    protected boolean isRedirectable(final String method) {
        for (final String m: REDIRECT_METHODS) {
            if (m.equalsIgnoreCase(method)) {
                return true;
            }
        }
        return false;
    }

    @Override
    public HttpUriRequest getRedirect(
            final HttpRequest request,
            final HttpResponse response,
            final HttpContext context) throws ProtocolException {
        final URI uri = getLocationURI(request, response, context);
        final String method = request.getRequestLine().getMethod();
        if (method.equalsIgnoreCase(HttpHead.METHOD_NAME)) {
            return new HttpHead(uri);
        } else if (method.equalsIgnoreCase(HttpGet.METHOD_NAME)) {
            return new HttpGet(uri);
        } else {
            final int status = response.getStatusLine().getStatusCode();
            return status == HttpStatus.SC_TEMPORARY_REDIRECT
                            ? RequestBuilder.copy(request).setUri(uri).build()
                            : new HttpGet(uri);
        }
    }

}