LexicalAnalyzerSelector.java
/* Copyright 2002-2021 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS 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.orekit.files.ccsds.utils.lexical;
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import org.orekit.data.DataSource;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
/** Utility class for selecting either {@link XmlLexicalAnalyzer} or {@link KvnLexicalAnalyzer} depending on
* data first bytes.
* @author Luc Maisonobe
* @since 11.0
*/
public class LexicalAnalyzerSelector {
/** Buffer size. */
private static final int BUFFER = 4096;
/** First bytes in XML document, UCS-4, big-endian, with Byte Order Mark. */
private static final byte[] UCS_4_BE_BOM = {
0x00, 0x00, -0x02, -0X01, 0x00, 0x00, 0x00, 0x3c, 0x00, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x00, 0x78, 0x00, 0x00, 0x00, 0x6d, 0x00, 0x00, 0x00, 0x6c
};
/** First bytes in XML document, UCS-4, little-endian, with Byte Order Mark. */
private static final byte[] UCS_4_LE_BOM = {
-0x01, -0X02, 0x00, 0x00, 0x3c, 0x00, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x00, 0x78, 0x00, 0x00, 0x00, 0x6d, 0x00, 0x00, 0x00, 0x6c, 0x00, 0x00, 0x00
};
/** First bytes in XML document, UTF-16, big-endian, with Byte Order Mark. */
private static final byte[] UTF_16_BE_BOM = {
-0x02, -0X01, 0x00, 0x3c, 0x00, 0x3f, 0x00, 0x78, 0x00, 0x6d, 0x00, 0x6c
};
/** First bytes in XML document, UTF-16, little-endian, with Byte Order Mark. */
private static final byte[] UTF_16_LE_BOM = {
-0x01, -0X02, 0x3c, 0x00, 0x3f, 0x00, 0x78, 0x00, 0x6d, 0x00, 0x6c, 0x00
};
/** First bytes in XML document, UTF-8, endianness irrelevant, with Byte Order Mark. */
private static final byte[] UTF_8_BOM = {
-0x11, -0x45, -0x41, 0x3c, 0x3f, 0x78, 0x6d, 0x6c
};
/** First bytes in XML document, UCS-4, big-endian, without Byte Order Mark. */
private static final byte[] UCS_4_BE = {
0x00, 0x00, 0x00, 0x3c, 0x00, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x00, 0x78, 0x00, 0x00, 0x00, 0x6d, 0x00, 0x00, 0x00, 0x6c
};
/** First bytes in XML document, UCS-4, little-endian, without Byte Order Mark. */
private static final byte[] UCS_4_LE = {
0x3c, 0x00, 0x00, 0x00, 0x3f, 0x00, 0x00, 0x00, 0x78, 0x00, 0x00, 0x00, 0x6d, 0x00, 0x00, 0x00, 0x6c, 0x00, 0x00, 0x00
};
/** First bytes in XML document, UTF-16, big-endian, without Byte Order Mark. */
private static final byte[] UTF_16_BE = {
0x00, 0x3c, 0x00, 0x3f, 0x00, 0x78, 0x00, 0x6d, 0x00, 0x6c
};
/** First bytes in XML document, UTF-16, little-endian, without Byte Order Mark. */
private static final byte[] UTF_16_LE = {
0x3c, 0x00, 0x3f, 0x00, 0x78, 0x00, 0x6d, 0x00, 0x6c, 0x00
};
/** First bytes in XML document, UTF-8, endianness irrelevant, without Byte Order Mark. */
private static final byte[] UTF_8 = {
0x3c, 0x3f, 0x78, 0x6d, 0x6c
};
/** First characters in XML document, with Byte Order Mark. */
private static final String CHARS_BOM = "\ufeff<?xml";
/** First characters in XML document, without Byte Order Mark. */
private static final String CHARS = "<?xml";
/** Private constructor for a utility class.
*/
private LexicalAnalyzerSelector() {
// never called
}
/** Select a {@link LexicalAnalyzer} for a {@link DataSource} based on content.
* @param source data source to analyze
* @return lexical analyzer suited for the data source format
* @throws IOException if first bytes of source cannot be read
*/
public static LexicalAnalyzer select(final DataSource source) throws IOException {
final DataSource.Opener opener = source.getOpener();
if (opener.rawDataIsBinary()) {
return select(source.getName(), opener.openStreamOnce());
} else {
return select(source.getName(), opener.openReaderOnce());
}
}
/** Select a {@link LexicalAnalyzer} based on content.
* @param name message name
* @param stream binary stream with message content
* @return lexical analyzer suited for the data source format
* @throws IOException if first bytes of source cannot be read
*/
private static LexicalAnalyzer select(final String name, final InputStream stream) throws IOException {
if (stream == null) {
throw new OrekitException(OrekitMessages.UNABLE_TO_FIND_FILE, name);
}
final BufferedInputStream bis = new BufferedInputStream(stream, BUFFER);
// read the first bytes
final int size = UCS_4_BE_BOM.length; // UCS-4 with BOM is the longest reference sequence
bis.mark(size);
final byte[] first = new byte[size];
int read = 0;
while (read < first.length) {
final int n = bis.read(first, read, size - read);
if (n < 0) {
// the file is too short for a proper CCSDS message,
// we return arbitrarily a KVN lexical analyzer,
// anyway, it will fail shortly during parsing
bis.reset();
return new KvnLexicalAnalyzer(new DataSource(name, () -> bis));
}
read += n;
}
// attempt to recognize an XML prolog, taking care of Byte Order Mark and encoding
// we use the tables from section F of Extensible Markup Language (XML) 1.0 (Fifth Edition)
// W3C Recommendation 26 November 2008 (https://www.w3.org/TR/2008/REC-xml-20081126/#sec-guessing),
// ignoring the unusual octet orders 2143 and 3412
if (checkSequence(first, UTF_8) || checkSequence(first, UTF_8_BOM) ||
checkSequence(first, UTF_16_LE) || checkSequence(first, UTF_16_LE_BOM) ||
checkSequence(first, UTF_16_BE) || checkSequence(first, UTF_16_BE_BOM) ||
checkSequence(first, UCS_4_LE) || checkSequence(first, UCS_4_LE_BOM) ||
checkSequence(first, UCS_4_BE) || checkSequence(first, UCS_4_BE_BOM)) {
// we recognized the "<?xml" sequence at start of an XML file
bis.reset();
return new XmlLexicalAnalyzer(new DataSource(name, () -> bis));
} else {
// it was not XML, the only other option is KVN
bis.reset();
return new KvnLexicalAnalyzer(new DataSource(name, () -> bis));
}
}
/** Select a {@link LexicalAnalyzer} based on content.
* @param name message name
* @param reader character stream with message content
* @return lexical analyzer suited for the data source format
* @throws IOException if first bytes of source cannot be read
*/
private static LexicalAnalyzer select(final String name, final Reader reader) throws IOException {
if (reader == null) {
throw new OrekitException(OrekitMessages.UNABLE_TO_FIND_FILE, name);
}
final BufferedReader br = new BufferedReader(reader, BUFFER);
// read the first characters
final int size = CHARS_BOM.length();
br.mark(size);
final char[] first = new char[size];
int read = 0;
while (read < first.length) {
final int n = br.read(first, read, size - read);
if (n < 0) {
// the file is too short for a proper CCSDS message,
// we return arbitrarily a KVN lexical analyzer,
// anyway, it will fail shortly during parsing
br.reset();
return new KvnLexicalAnalyzer(new DataSource(name, () -> br));
}
read += n;
}
final String firstString = new String(first);
// attempt to recognize an XML prolog
if (firstString.startsWith(CHARS) || CHARS_BOM.equals(firstString)) {
// we recognized the "<?xml" sequence at start of an XML file
br.reset();
return new XmlLexicalAnalyzer(new DataSource(name, () -> br));
} else {
// it was not XML, the only other option is KVN
br.reset();
return new KvnLexicalAnalyzer(new DataSource(name, () -> br));
}
}
/** Check if first bytes match reference sequence.
* @param first first bytes read
* @param reference reference sequence
* @return true if first bytes match reference sequence
*/
private static boolean checkSequence(final byte[] first, final byte[] reference) {
for (int i = 0; i < reference.length; ++i) {
if (first[i] != reference[i]) {
return false;
}
}
return true;
}
}