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This project contains some of the configurable modules used within the Heritrix application to crawl the web. The modules in this project can be used in applications other than Heritrix, however.

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/*
 *  This file is part of the Heritrix web crawler (crawler.archive.org).
 *
 *  Licensed to the Internet Archive (IA) by one or more individual 
 *  contributors. 
 *
 *  The IA 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.
 */
package org.archive.modules.net;

import java.util.LinkedList;
import java.util.List;

import org.archive.modules.CrawlURI;

/**
 * Follow a most-favored robots policy -- allowing an URL if either the 
 * conventionally-configured User-Agent, or any of a number of alternate 
 * User-Agents (from the candidateUserAgents list) would be allowed. 
 * 
 * Some possible rationales for using this policy could include: 
 * 
 * (1) the current bot is the successor to a previous differently-named bot, 
 * which could reasonably obey the directives for the previous agent if 
 * they are more permissive; 
 * 
 * (2) a project with negotiated or statutory permission to ignore robots still 
 * wishes only to collect material a site has allowed at least some named 
 * robots to collect. (That is, assume that if any of a number of robots is
 * allowed, it will not be disruptive to collect.) 
 * 
 * @author gojomo
 */
public class MostFavoredRobotsPolicy extends RobotsPolicy {
    
    /** list of user-agents to try; if any are allowed, a URI will be crawled */
    protected List candidateUserAgents = new LinkedList();
    public List getCandidateUserAgents() {
        return candidateUserAgents;
    }
    public void setCandidateUserAgents(List candidateUserAgents) {
        this.candidateUserAgents = candidateUserAgents;
    }
    
    /** whether to adopt the user-agent that is allowed for the fetch */
    protected boolean shouldMasquerade = true;
    public boolean getShouldMasquerade() {
        return shouldMasquerade;
    }
    public void setShouldMasquerade(boolean shouldMasquerade) {
        this.shouldMasquerade = shouldMasquerade;
    }
    
    /** whether to obey the 'nofollow' directive in an HTML META ROBOTS element */
    protected boolean obeyMetaRobotsNofollow = true; 
    public boolean isObeyMetaRobotsNofollow() {
        return obeyMetaRobotsNofollow;
    }
    public void setObeyMetaRobotsNofollow(boolean obeyMetaRobotsNofollow) {
        this.obeyMetaRobotsNofollow = obeyMetaRobotsNofollow;
    }
    
    @Override
    public boolean allows(String userAgent, CrawlURI curi, Robotstxt robotstxt) {
        if (robotstxt.getDirectivesFor(userAgent).allows(getPathQuery(curi))) {
            return true;
        }
        for(String candidate : candidateUserAgents) {
            if (robotstxt.getDirectivesFor(candidate).allows(getPathQuery(curi))) {
                if(shouldMasquerade) {
                    curi.setUserAgent(candidate);
                }
                return true;
            }
        }
        // TODO: expand to offer option of following other rules in site's
        // robots.txt, even if they don't match any of candidate set.
        // TBD: which user-agent to use in that case.
        return false;
    }
    
    @Override
    public boolean obeyMetaRobotsNofollow() {
        return obeyMetaRobotsNofollow;
    }
}