src/plugin/protocol-ftp/src/java/org/apache/nutch/protocol/ftp/FtpRobotRulesParser.java

/*
 * 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.
 */
package org.apache.nutch.protocol.ftp;

import java.lang.invoke.MethodHandles;
import java.net.URL;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.nutch.crawl.CrawlDatum;
import org.apache.nutch.protocol.Content;
import org.apache.nutch.protocol.Protocol;
import org.apache.nutch.protocol.ProtocolOutput;
import org.apache.nutch.protocol.ProtocolStatus;
import org.apache.nutch.protocol.RobotRulesParser;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import crawlercommons.robots.BaseRobotRules;

/**
 * This class is used for parsing robots for urls belonging to FTP protocol. It
 * extends the generic {@link RobotRulesParser} class and contains Ftp protocol
 * specific implementation for obtaining the robots file.
 */
public class FtpRobotRulesParser extends RobotRulesParser {

  private static final String CONTENT_TYPE = "text/plain";
  private static final Logger LOG = LoggerFactory
      .getLogger(MethodHandles.lookup().lookupClass());

  FtpRobotRulesParser() {
  }

  public FtpRobotRulesParser(Configuration conf) {
    super(conf);
  }

  /**
   * The hosts for which the caching of robots rules is yet to be done, it sends
   * a Ftp request to the host corresponding to the {@link URL} passed, gets
   * robots file, parses the rules and caches the rules object to avoid re-work
   * in future.
   * 
   * @param ftp
   *          The {@link Protocol} object
   * @param url
   *          URL
   * @param robotsTxtContent
   *          container to store responses when fetching the robots.txt file for
   *          debugging or archival purposes. Instead of a robots.txt file, it
   *          may include redirects or an error page (404, etc.). Response
   *          {@link Content} is appended to the passed list. If null is passed
   *          nothing is stored.
   * 
   * @return robotRules A {@link BaseRobotRules} object for the rules
   */
  @Override
  public BaseRobotRules getRobotRulesSet(Protocol ftp, URL url,
      List<Content> robotsTxtContent) {

    String protocol = url.getProtocol().toLowerCase(); // normalize to lower
                                                       // case
    String host = url.getHost().toLowerCase(); // normalize to lower case

    if (LOG.isTraceEnabled() && isWhiteListed(url)) {
      LOG.trace("Ignoring robots.txt (host is whitelisted) for URL: {}", url);
    }

    BaseRobotRules robotRules = CACHE.get(protocol + ":" + host);

    if (robotRules != null) {
      return robotRules; // cached rule
    } else if (LOG.isTraceEnabled()) {
      LOG.trace("cache miss " + url);
    }

    boolean cacheRule = true;

    if (isWhiteListed(url)) {
      // check in advance whether a host is whitelisted
      // (we do not need to fetch robots.txt)
      robotRules = EMPTY_RULES;
      LOG.info("Whitelisted host found for: {}", url);
      LOG.info("Ignoring robots.txt for all URLs from whitelisted host: {}", host);

    } else {
      try {
        Text robotsUrl = new Text(new URL(url, "/robots.txt").toString());
        ProtocolOutput output = ((Ftp) ftp).getProtocolOutput(robotsUrl,
            new CrawlDatum());
        ProtocolStatus status = output.getStatus();

        if (robotsTxtContent != null) {
          robotsTxtContent.add(output.getContent());
        }

        if (status.getCode() == ProtocolStatus.SUCCESS) {
          robotRules = parseRules(url.toString(), output.getContent()
              .getContent(), CONTENT_TYPE, agentNames);
        } else {
          robotRules = EMPTY_RULES; // use default rules
        }
      } catch (Throwable t) {
        if (LOG.isInfoEnabled()) {
          LOG.info("Couldn't get robots.txt for " + url + ": " + t.toString());
        }
        cacheRule = false; // try again later to fetch robots.txt
        robotRules = EMPTY_RULES;
      }

    }

    if (cacheRule)
      CACHE.put(protocol + ":" + host, robotRules); // cache rules for host

    return robotRules;
  }

}