BOMInputStream.java

/*
 * 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 com.ctrip.framework.foundation.internals.io;


import static com.ctrip.framework.foundation.internals.io.IOUtils.EOF;

import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

/**
 * This class is used to wrap a stream that includes an encoded {@link ByteOrderMark} as its first bytes.
 *
 * This class detects these bytes and, if required, can automatically skip them and return the subsequent byte as the
 * first byte in the stream.
 *
 * The {@link ByteOrderMark} implementation has the following pre-defined BOMs:
 * <ul>
 * <li>UTF-8 - {@link ByteOrderMark#UTF_8}</li>
 * <li>UTF-16BE - {@link ByteOrderMark#UTF_16LE}</li>
 * <li>UTF-16LE - {@link ByteOrderMark#UTF_16BE}</li>
 * <li>UTF-32BE - {@link ByteOrderMark#UTF_32LE}</li>
 * <li>UTF-32LE - {@link ByteOrderMark#UTF_32BE}</li>
 * </ul>
 *
 *
 * <h3>Example 1 - Detect and exclude a UTF-8 BOM</h3>
 *
 * <pre>
 * BOMInputStream bomIn = new BOMInputStream(in);
 * if (bomIn.hasBOM()) {
 *   // has a UTF-8 BOM
 * }
 * </pre>
 *
 * <h3>Example 2 - Detect a UTF-8 BOM (but don't exclude it)</h3>
 *
 * <pre>
 * boolean include = true;
 * BOMInputStream bomIn = new BOMInputStream(in, include);
 * if (bomIn.hasBOM()) {
 *   // has a UTF-8 BOM
 * }
 * </pre>
 *
 * <h3>Example 3 - Detect Multiple BOMs</h3>
 *
 * <pre>
 * BOMInputStream bomIn = new BOMInputStream(in, ByteOrderMark.UTF_16LE, ByteOrderMark.UTF_16BE, ByteOrderMark.UTF_32LE,
 *     ByteOrderMark.UTF_32BE);
 * if (bomIn.hasBOM() == false) {
 *   // No BOM found
 * } else if (bomIn.hasBOM(ByteOrderMark.UTF_16LE)) {
 *   // has a UTF-16LE BOM
 * } else if (bomIn.hasBOM(ByteOrderMark.UTF_16BE)) {
 *   // has a UTF-16BE BOM
 * } else if (bomIn.hasBOM(ByteOrderMark.UTF_32LE)) {
 *   // has a UTF-32LE BOM
 * } else if (bomIn.hasBOM(ByteOrderMark.UTF_32BE)) {
 *   // has a UTF-32BE BOM
 * }
 * </pre>
 *
 * @see ByteOrderMark
 * @see <a href="http://en.wikipedia.org/wiki/Byte_order_mark">Wikipedia - Byte Order Mark</a>
 * @version $Id: BOMInputStream.java 1686527 2015-06-20 06:31:39Z krosenvold $
 * @since 2.0
 */
public class BOMInputStream extends ProxyInputStream {
  private final boolean include;
  /**
   * BOMs are sorted from longest to shortest.
   */
  private final List<ByteOrderMark> boms;
  private ByteOrderMark byteOrderMark;
  private int[] firstBytes;
  private int fbLength;
  private int fbIndex;
  private int markFbIndex;
  private boolean markedAtStart;

  /**
   * Constructs a new BOM InputStream that excludes a {@link ByteOrderMark#UTF_8} BOM.
   *
   * @param delegate the InputStream to delegate to
   */
  public BOMInputStream(final InputStream delegate) {
    this(delegate, false, ByteOrderMark.UTF_8);
  }

  /**
   * Constructs a new BOM InputStream that detects a a {@link ByteOrderMark#UTF_8} and optionally includes it.
   *
   * @param delegate the InputStream to delegate to
   * @param include true to include the UTF-8 BOM or false to exclude it
   */
  public BOMInputStream(final InputStream delegate, final boolean include) {
    this(delegate, include, ByteOrderMark.UTF_8);
  }

  /**
   * Constructs a new BOM InputStream that excludes the specified BOMs.
   *
   * @param delegate the InputStream to delegate to
   * @param boms The BOMs to detect and exclude
   */
  public BOMInputStream(final InputStream delegate, final ByteOrderMark... boms) {
    this(delegate, false, boms);
  }

  /**
   * Compares ByteOrderMark objects in descending length order.
   */
  private static final Comparator<ByteOrderMark> ByteOrderMarkLengthComparator = new Comparator<ByteOrderMark>() {

    public int compare(final ByteOrderMark bom1, final ByteOrderMark bom2) {
      final int len1 = bom1.length();
      final int len2 = bom2.length();
      if (len1 > len2) {
        return EOF;
      }
      if (len2 > len1) {
        return 1;
      }
      return 0;
    }
  };

  /**
   * Constructs a new BOM InputStream that detects the specified BOMs and optionally includes them.
   *
   * @param delegate the InputStream to delegate to
   * @param include true to include the specified BOMs or false to exclude them
   * @param boms The BOMs to detect and optionally exclude
   */
  public BOMInputStream(final InputStream delegate, final boolean include, final ByteOrderMark... boms) {
    super(delegate);
    if (boms == null || boms.length == 0) {
      throw new IllegalArgumentException("No BOMs specified");
    }
    this.include = include;
    // Sort the BOMs to match the longest BOM first because some BOMs have the same starting two bytes.
    Arrays.sort(boms, ByteOrderMarkLengthComparator);
    this.boms = Arrays.asList(boms);

  }

  /**
   * Indicates whether the stream contains one of the specified BOMs.
   *
   * @return true if the stream has one of the specified BOMs, otherwise false if it does not
   * @throws IOException if an error reading the first bytes of the stream occurs
   */
  public boolean hasBOM() throws IOException {
    return getBOM() != null;
  }

  /**
   * Indicates whether the stream contains the specified BOM.
   *
   * @param bom The BOM to check for
   * @return true if the stream has the specified BOM, otherwise false if it does not
   * @throws IllegalArgumentException if the BOM is not one the stream is configured to detect
   * @throws IOException if an error reading the first bytes of the stream occurs
   */
  public boolean hasBOM(final ByteOrderMark bom) throws IOException {
    if (!boms.contains(bom)) {
      throw new IllegalArgumentException("Stream not configure to detect " + bom);
    }
    return byteOrderMark != null && getBOM().equals(bom);
  }

  /**
   * Return the BOM (Byte Order Mark).
   *
   * @return The BOM or null if none
   * @throws IOException if an error reading the first bytes of the stream occurs
   */
  public ByteOrderMark getBOM() throws IOException {
    if (firstBytes == null) {
      fbLength = 0;
      // BOMs are sorted from longest to shortest
      final int maxBomSize = boms.get(0).length();
      firstBytes = new int[maxBomSize];
      // Read first maxBomSize bytes
      for (int i = 0; i < firstBytes.length; i++) {
        firstBytes[i] = in.read();
        fbLength++;
        if (firstBytes[i] < 0) {
          break;
        }
      }
      // match BOM in firstBytes
      byteOrderMark = find();
      if (byteOrderMark != null) {
        if (!include) {
          if (byteOrderMark.length() < firstBytes.length) {
            fbIndex = byteOrderMark.length();
          } else {
            fbLength = 0;
          }
        }
      }
    }
    return byteOrderMark;
  }

  /**
   * Return the BOM charset Name - {@link ByteOrderMark#getCharsetName()}.
   *
   * @return The BOM charset Name or null if no BOM found
   * @throws IOException if an error reading the first bytes of the stream occurs
   *
   */
  public String getBOMCharsetName() throws IOException {
    getBOM();
    return byteOrderMark == null ? null : byteOrderMark.getCharsetName();
  }

  /**
   * This method reads and either preserves or skips the first bytes in the stream. It behaves like the single-byte
   * <code>read()</code> method, either returning a valid byte or -1 to indicate that the initial bytes have been
   * processed already.
   *
   * @return the byte read (excluding BOM) or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  private int readFirstBytes() throws IOException {
    getBOM();
    return fbIndex < fbLength ? firstBytes[fbIndex++] : EOF;
  }

  /**
   * Find a BOM with the specified bytes.
   *
   * @return The matched BOM or null if none matched
   */
  private ByteOrderMark find() {
    for (final ByteOrderMark bom : boms) {
      if (matches(bom)) {
        return bom;
      }
    }
    return null;
  }

  /**
   * Check if the bytes match a BOM.
   *
   * @param bom The BOM
   * @return true if the bytes match the bom, otherwise false
   */
  private boolean matches(final ByteOrderMark bom) {
    // if (bom.length() != fbLength) {
    // return false;
    // }
    // firstBytes may be bigger than the BOM bytes
    for (int i = 0; i < bom.length(); i++) {
      if (bom.get(i) != firstBytes[i]) {
        return false;
      }
    }
    return true;
  }

  // ----------------------------------------------------------------------------
  // Implementation of InputStream
  // ----------------------------------------------------------------------------

  /**
   * Invokes the delegate's <code>read()</code> method, detecting and optionally skipping BOM.
   *
   * @return the byte read (excluding BOM) or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read() throws IOException {
    final int b = readFirstBytes();
    return b >= 0 ? b : in.read();
  }

  /**
   * Invokes the delegate's <code>read(byte[], int, int)</code> method, detecting and optionally skipping BOM.
   *
   * @param buf the buffer to read the bytes into
   * @param off The start offset
   * @param len The number of bytes to read (excluding BOM)
   * @return the number of bytes read or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read(final byte[] buf, int off, int len) throws IOException {
    int firstCount = 0;
    int b = 0;
    while (len > 0 && b >= 0) {
      b = readFirstBytes();
      if (b >= 0) {
        buf[off++] = (byte) (b & 0xFF);
        len--;
        firstCount++;
      }
    }
    final int secondCount = in.read(buf, off, len);
    return secondCount < 0 ? firstCount > 0 ? firstCount : EOF : firstCount + secondCount;
  }

  /**
   * Invokes the delegate's <code>read(byte[])</code> method, detecting and optionally skipping BOM.
   *
   * @param buf the buffer to read the bytes into
   * @return the number of bytes read (excluding BOM) or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public int read(final byte[] buf) throws IOException {
    return read(buf, 0, buf.length);
  }

  /**
   * Invokes the delegate's <code>mark(int)</code> method.
   *
   * @param readlimit read ahead limit
   */
  @Override
  public synchronized void mark(final int readlimit) {
    markFbIndex = fbIndex;
    markedAtStart = firstBytes == null;
    in.mark(readlimit);
  }

  /**
   * Invokes the delegate's <code>reset()</code> method.
   *
   * @throws IOException if an I/O error occurs
   */
  @Override
  public synchronized void reset() throws IOException {
    fbIndex = markFbIndex;
    if (markedAtStart) {
      firstBytes = null;
    }

    in.reset();
  }

  /**
   * Invokes the delegate's <code>skip(long)</code> method, detecting and optionallyskipping BOM.
   *
   * @param n the number of bytes to skip
   * @return the number of bytes to skipped or -1 if the end of stream
   * @throws IOException if an I/O error occurs
   */
  @Override
  public long skip(long n) throws IOException {
    int skipped = 0;
    while ((n > skipped) && (readFirstBytes() >= 0)) {
      skipped++;
    }
    return in.skip(n - skipped) + skipped;
  }
}