org.apache.tika.parser.html.HtmlEncodingDetector Maven / Gradle / Ivy
/*
* 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.tika.parser.html;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.apache.tika.detect.EncodingDetector;
import org.apache.tika.metadata.Metadata;
import org.apache.tika.utils.CharsetUtils;
/**
* Character encoding detector for determining the character encoding of a
* HTML document based on the potential charset parameter found in a
* Content-Type http-equiv meta tag somewhere near the beginning. Especially
* useful for determining the type among multiple closely related encodings
* (ISO-8859-*) for which other types of encoding detection are unreliable.
*
* @since Apache Tika 1.2
*/
public class HtmlEncodingDetector implements EncodingDetector {
// TIKA-357 - use bigger buffer for meta tag sniffing (was 4K)
private static final int META_TAG_BUFFER_SIZE = 8192;
private static final Pattern HTTP_META_PATTERN = Pattern.compile(
"(?is)<\\s*meta\\s+([^<>]+)"
);
//this should match both the older:
//
//and
//html5
//See http://webdesign.about.com/od/metatags/qt/meta-charset.htm
//for the noisiness that one might encounter in charset attrs.
//Chose to go with strict ([-_:\\.a-z0-9]+) to match encodings
//following http://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html
//For a more general "not" matcher, try:
//("(?is)charset\\s*=\\s*['\\\"]?\\s*([^<>\\s'\\\";]+)")
private static final Pattern FLEXIBLE_CHARSET_ATTR_PATTERN = Pattern.compile(
("(?is)charset\\s*=\\s*(?:['\\\"]\\s*)?([-_:\\.a-z0-9]+)")
);
private static final Charset ASCII = Charset.forName("US-ASCII");
public Charset detect(InputStream input, Metadata metadata)
throws IOException {
if (input == null) {
return null;
}
// Read enough of the text stream to capture possible meta tags
input.mark(META_TAG_BUFFER_SIZE);
byte[] buffer = new byte[META_TAG_BUFFER_SIZE];
int n = 0;
int m = input.read(buffer);
while (m != -1 && n < buffer.length) {
n += m;
m = input.read(buffer, n, buffer.length - n);
}
input.reset();
// Interpret the head as ASCII and try to spot a meta tag with
// a possible character encoding hint
String head = ASCII.decode(ByteBuffer.wrap(buffer, 0, n)).toString();
Matcher equiv = HTTP_META_PATTERN.matcher(head);
Matcher charsetMatcher = FLEXIBLE_CHARSET_ATTR_PATTERN.matcher("");
//iterate through meta tags
while (equiv.find()) {
String attrs = equiv.group(1);
charsetMatcher.reset(attrs);
//iterate through charset= and return the first match
//that is valid
while (charsetMatcher.find()){
String candCharset = charsetMatcher.group(1);
if (CharsetUtils.isSupported(candCharset)){
try{
return CharsetUtils.forName(candCharset);
} catch (Exception e){
//ignore
}
}
}
}
return null;
}
}