org.apache.tika.parser.html.HtmlEncodingDetector Maven / Gradle / Ivy
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* 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.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.HashSet;
import java.util.Locale;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.apache.tika.config.Field;
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 {
/**
* HTML can include non-iana supported charsets that Java
* recognizes, e.g. "unicode". This can lead to incorrect detection/mojibake.
* Ignore charsets in html meta-headers that are not supported by IANA.
* See: TIKA-2592
*/
private static Set CHARSETS_UNSUPPORTED_BY_IANA;
static {
Set unsupported = new HashSet<>();
try (BufferedReader reader =
new BufferedReader(
new InputStreamReader(
HtmlEncodingDetector.class
.getResourceAsStream("StandardCharsets_unsupported_by_IANA.txt"),
StandardCharsets.UTF_8))) {
String line = reader.readLine();
while (line != null) {
if (line.startsWith("#")) {
line = reader.readLine();
continue;
}
line = line.trim();
if (line.length() > 0) {
unsupported.add(line.toLowerCase(Locale.US));
}
line = reader.readLine();
}
} catch (IOException e) {
throw new IllegalArgumentException("couldn't find StandardCharsets_unsupported_by_IANA.txt on the class path");
}
CHARSETS_UNSUPPORTED_BY_IANA = Collections.unmodifiableSet(unsupported);
}
// TIKA-357 - use bigger buffer for meta tag sniffing (was 4K)
private static final int DEFAULT_MARK_LIMIT = 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)\\bcharset\\s*=\\s*(?:['\\\"]\\s*)?([-_:\\.a-z0-9]+)")
);
private static final Charset ASCII = Charset.forName("US-ASCII");
@Field
private int markLimit = DEFAULT_MARK_LIMIT;
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(markLimit);
byte[] buffer = new byte[markLimit];
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();
//strip out comments
String headNoComments = head.replaceAll("|$)", " ");
//try to find the encoding in head without comments
Charset charset = findCharset(headNoComments);
//if nothing is found, back off to find any encoding
if (charset == null) {
return findCharset(head);
}
return charset;
}
//returns null if no charset was found
private Charset findCharset(String s) {
Matcher equiv = HTTP_META_PATTERN.matcher(s);
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 (CHARSETS_UNSUPPORTED_BY_IANA.contains(candCharset.toLowerCase(Locale.US))) {
continue;
}
if ("x-user-defined".equalsIgnoreCase(candCharset)) {
candCharset = "windows-1252";
}
if (CharsetUtils.isSupported(candCharset)) {
try {
return CharsetUtils.forName(candCharset);
} catch (Exception e) {
//ignore
}
}
}
}
return null;
}
/**
* How far into the stream to read for charset detection.
* Default is 8192.
*
* @param markLimit
*/
@Field
public void setMarkLimit(int markLimit) {
this.markLimit = markLimit;
}
public int getMarkLimit() {
return markLimit;
}
}