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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.extractor;

import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.regex.Matcher;

import org.apache.commons.httpclient.URIException;
import org.archive.io.ReplayCharSequence;
import org.archive.modules.CrawlURI;
import org.archive.net.UURI;
import org.archive.util.DevUtils;
import org.archive.util.TextUtils;

/**
 * This extractor is parsing URIs from CSS type files.
 * The format of a CSS URL value is 'url(' followed by optional white space
 * followed by an optional single quote (') or double quote (") character
 * followed by the URL itself followed by an optional single quote (') or
 * double quote (") character followed by optional white space followed by ')'.
 * Parentheses, commas, white space characters, single quotes (') and double
 * quotes (") appearing in a URL must be escaped with a backslash:
 * '\(', '\)', '\,'. Partial URLs are interpreted relative to the source of
 * the style sheet, not relative to the document. 
 * Source: www.w3.org
 *
 * NOTE: This processor may open a ReplayCharSequence from the 
 * CrawlURI's Recorder, without closing that ReplayCharSequence, to allow
 * reuse by later processors in sequence. In the usual (Heritrix) case, a 
 * call after all processing to the Recorder's endReplays() method ensures
 * timely close of any reused ReplayCharSequences. Reuse of this processor
 * elsewhere should ensure a similar cleanup call to Recorder.endReplays()
 * occurs. 
 * 
 * @author Igor Ranitovic
 *
 **/

public class ExtractorCSS extends ContentExtractor {


    @SuppressWarnings("unused")
    private static final long serialVersionUID = 2L;

    private static Logger logger =
        Logger.getLogger("org.archive.crawler.extractor.ExtractorCSS");

    private static String ESCAPED_AMP = "&";
    // CSS escapes: "Parentheses, commas, whitespace characters, single 
    // quotes (') and double quotes (") appearing in a URL must be 
    // escaped with a backslash"
    protected static final String CSS_BACKSLASH_ESCAPE = "\\\\([,'\"\\(\\)\\s])";
    
    /**
     *  CSS URL extractor pattern.
     *
     *  This pattern extracts URIs for CSS files
     **/
//    static final String CSS_URI_EXTRACTOR =
//        "url[(]\\s*([\"\']?)([^\\\"\\'].*?)\\1\\s*[)]";
    protected static final String CSS_URI_EXTRACTOR =    
    "(?i)(?:@import (?:url[(]|)|url[(])\\s*([\\\"\']?)" + // G1
    "([^\\\"\'].{0,"+UURI.MAX_URL_LENGTH+"}?)\\1\\s*[);]"; // G2
    // GROUPS:
    // (G1) optional ' or "
    // (G2) URI
    

    /**
     */
    public ExtractorCSS() {
    }

    
    @Override
    protected boolean shouldExtract(CrawlURI curi) {
        String mimeType = curi.getContentType();
        if (mimeType == null) {
            return false; // FIXME: This check should be unnecessary
        }
        if ((mimeType.toLowerCase().indexOf("css") < 0) &&
                (!curi.toString().toLowerCase().endsWith(".css"))) {
            return false;
        }
        return true;
    }
    
    /**
     * @param curi Crawl URI to process.
     */
    public boolean innerExtract(CrawlURI curi) {
        try {
            ReplayCharSequence cs = curi.getRecorder().getContentReplayCharSequence();
            numberOfLinksExtracted.addAndGet(
                processStyleCode(this, curi, cs));
            // Set flag to indicate that link extraction is completed.
            return true;
        } catch (IOException e) {
            logger.log(Level.WARNING, "Problem with ReplayCharSequence: " + e.getMessage(), e);
        }
        return false; 
    }

    public static long processStyleCode(Extractor ext, 
            CrawlURI curi, CharSequence cs) {
        long foundLinks = 0;
        Matcher uris = null;
        String cssUri;
        try {
            uris = TextUtils.getMatcher(CSS_URI_EXTRACTOR, cs);
            while (uris.find()) {
                cssUri = uris.group(2);
                // TODO: Escape more HTML Entities.
                cssUri = TextUtils.replaceAll(ESCAPED_AMP, cssUri, "&");
                // Remove backslashes when used as escape character in CSS URL
                cssUri = TextUtils.replaceAll(CSS_BACKSLASH_ESCAPE, cssUri,
                        "$1");
                foundLinks++;
                int max = ext.getExtractorParameters().getMaxOutlinks();
                try {
                	addRelativeToBase(curi, max, cssUri, 
                            LinkContext.EMBED_MISC, Hop.EMBED);
                } catch (URIException e) {
                    ext.logUriError(e, curi.getUURI(), cssUri);
                }
            }
        } catch (StackOverflowError e) {
            DevUtils.warnHandle(e, "ExtractorCSS StackOverflowError");
        } finally {
            TextUtils.recycleMatcher(uris);
        }
        return foundLinks;
    }
}