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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.
/*
* 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.recrawl;
import static org.archive.modules.CoreAttributeConstants.A_FETCH_BEGAN_TIME;
import static org.archive.modules.recrawl.RecrawlAttributeConstants.A_CONTENT_DIGEST;
import static org.archive.modules.recrawl.RecrawlAttributeConstants.A_ETAG_HEADER;
import static org.archive.modules.recrawl.RecrawlAttributeConstants.A_LAST_MODIFIED_HEADER;
import static org.archive.modules.recrawl.RecrawlAttributeConstants.A_REFERENCE_LENGTH;
import static org.archive.modules.recrawl.RecrawlAttributeConstants.A_STATUS;
import java.util.HashMap;
import java.util.Map;
import org.archive.modules.CrawlURI;
import org.archive.modules.Processor;
import org.archive.modules.revisit.IdenticalPayloadDigestRevisit;
import org.archive.modules.revisit.ServerNotModifiedRevisit;
/**
* Maintain a history of fetch information inside the CrawlURI's attributes.
*
* @author gojomo
* @version $Date: 2006-09-25 20:19:54 +0000 (Mon, 25 Sep 2006) $, $Revision: 4654 $
*/
public class FetchHistoryProcessor extends Processor {
@SuppressWarnings("unused")
private static final long serialVersionUID = 1L;
/** Desired history array length. */
protected int historyLength = 2;
public int getHistoryLength() {
return this.historyLength;
}
public void setHistoryLength(int length) {
this.historyLength = length;
}
// key description: "Number of previous fetch entries to retain in the URI " +
// "history. The current fetch becomes a history entry at " +
// "this Processor step, so the smallest useful value is " +
// "'2' (including the current fetch). Default is '2'."
// class description: "FetchHistoryProcessor. Maintain a history of fetch " +
// "information inside the CrawlURI's attributes.."
public FetchHistoryProcessor() {
}
@Override
protected void innerProcess(CrawlURI puri) throws InterruptedException {
CrawlURI curi = (CrawlURI) puri;
HashMap latestFetch = new HashMap();
// save status
latestFetch.put(A_STATUS, curi.getFetchStatus());
// save fetch start time
latestFetch.put(A_FETCH_BEGAN_TIME, curi.getFetchBeginTime());
// save digest
String digest = curi.getContentDigestSchemeString();
if (digest != null) {
latestFetch.put(A_CONTENT_DIGEST, digest);
}
// save relevant HTTP headers, if available
if (curi.isHttpTransaction()) {
saveHeader(curi, latestFetch, A_ETAG_HEADER);
saveHeader(curi, latestFetch, A_LAST_MODIFIED_HEADER);
// save reference length (real or virtual)
long referenceLength;
if (curi.containsDataKey(A_REFERENCE_LENGTH)) {
// reuse previous length if available (see FetchHTTP#setSizes).
referenceLength = (Long) curi.getData().get(A_REFERENCE_LENGTH);
} else {
// normally, use content-length
referenceLength = curi.getContentLength();
}
latestFetch.put(A_REFERENCE_LENGTH, referenceLength);
}
HashMap[] history = historyRealloc(curi);
// rotate all history entries up one slot, insert new at [0]
for (int i = history.length - 1; i > 0; i--) {
history[i] = history[i - 1];
}
history[0] = latestFetch;
curi.setFetchHistory(history);
if (curi.getFetchStatus() == 304) {
if( history.length >= 2 && history[1] != null && history[1].containsKey(A_CONTENT_DIGEST)) {
// Copy forward the content digest as the current digest is simply of an empty response
latestFetch.put(A_CONTENT_DIGEST, history[1].get(A_CONTENT_DIGEST));
// Create revisit profile
curi.getAnnotations().add("duplicate:server-not-modified");
ServerNotModifiedRevisit revisit = new ServerNotModifiedRevisit();
revisit.setETag((String) latestFetch.get(A_ETAG_HEADER));
revisit.setLastModified((String) latestFetch.get(A_LAST_MODIFIED_HEADER));
revisit.setPayloadDigest((String)latestFetch.get(A_CONTENT_DIGEST));
curi.setRevisitProfile(revisit);
}
} else if (hasIdenticalDigest(curi)) {
curi.getAnnotations().add("duplicate:digest");
IdenticalPayloadDigestRevisit revisit =
new IdenticalPayloadDigestRevisit((String)history[1].get(A_CONTENT_DIGEST));
revisit.setRefersToTargetURI(curi.getURI()); // Matches are always on the same URI
revisit.setRefersToDate((Long)history[1].get(A_FETCH_BEGAN_TIME));
curi.setRevisitProfile(revisit);
}
}
/**
* Utility method for testing if a CrawlURI's last two history
* entries (one being the most recent fetch) have identical
* content-digest information.
*
* @param curi CrawlURI to test
* @return true if last two history entries have identical digests,
* otherwise false
*/
public static boolean hasIdenticalDigest(CrawlURI curi) {
Map[] history = curi.getFetchHistory();
return history != null
&& history[0] != null
&& history[0].containsKey(A_CONTENT_DIGEST)
&& history[1] != null
&& history[1].containsKey(A_CONTENT_DIGEST)
&& history[0].get(A_CONTENT_DIGEST).equals(history[1].get(A_CONTENT_DIGEST));
}
/** Get or create proper-sized history array */
@SuppressWarnings("unchecked")
protected HashMap[] historyRealloc(CrawlURI curi) {
int targetHistoryLength = getHistoryLength();
HashMap[] history = curi.getFetchHistory();
if (history == null) {
history = new HashMap[targetHistoryLength];
}
if (history.length != targetHistoryLength) {
HashMap[] newHistory = new HashMap[targetHistoryLength];
System.arraycopy(history, 0, newHistory, 0,
Math.min(history.length, newHistory.length));
history = newHistory;
}
return history;
}
/** Save a header from the given HTTP operation into the Map. */
protected void saveHeader(CrawlURI curi, Map map,
String key) {
String value = curi.getHttpResponseHeader(key);
if (value != null) {
map.put(key, value);
}
}
@Override
protected boolean shouldProcess(CrawlURI curi) {
// only process if curi contains evidence of fetch attempt
return curi.containsDataKey(A_FETCH_BEGAN_TIME);
}
}