/*

  * Copyright (c) 1994, 2006, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 package java.io;

 /**

  * This abstract class is the superclass of all classes representing

  * an input stream of bytes.

  *

  * <p> Applications that need to define a subclass of <code>InputStream</code>

  * must always provide a method that returns the next byte of input.

  *

  * @author  Arthur van Hoff

  * @see     java.io.BufferedInputStream

  * @see     java.io.ByteArrayInputStream

  * @see     java.io.DataInputStream

  * @see     java.io.FilterInputStream

  * @see     java.io.InputStream#read()

  * @see     java.io.OutputStream

  * @see     java.io.PushbackInputStream

  * @since   JDK1.0

  */

 public abstract class InputStream implements Closeable {

     // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer

     private static final int SKIP_BUFFER_SIZE = 2048;

     // skipBuffer is initialized in skip(long), if needed.

     private static byte[] skipBuffer;

     /**

      * Reads the next byte of data from the input stream. The value byte is

      * returned as an <code>int</code> in the range <code>0</code> to

      * <code>255</code>. If no byte is available because the end of the stream

      * has been reached, the value <code>-1</code> is returned. This method

      * blocks until input data is available, the end of the stream is detected,

      * or an exception is thrown.

      *

      * <p> A subclass must provide an implementation of this method.

      *

      * @return     the next byte of data, or <code>-1</code> if the end of the

      *             stream is reached.

      * @exception  IOException  if an I/O error occurs.

      */

     public abstract int read() throws IOException;

     /**

      * Reads some number of bytes from the input stream and stores them into

      * the buffer array <code>b</code>. The number of bytes actually read is

      * returned as an integer.  This method blocks until input data is

      * available, end of file is detected, or an exception is thrown.

      *

      * <p> If the length of <code>b</code> is zero, then no bytes are read and

      * <code>0</code> is returned; otherwise, there is an attempt to read at

      * least one byte. If no byte is available because the stream is at the

      * end of the file, the value <code>-1</code> is returned; otherwise, at

      * least one byte is read and stored into <code>b</code>.

      *

      * <p> The first byte read is stored into element <code>b[0]</code>, the

      * next one into <code>b[1]</code>, and so on. The number of bytes read is,

      * at most, equal to the length of <code>b</code>. Let <i>k</i> be the

      * number of bytes actually read; these bytes will be stored in elements

      * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,

      * leaving elements <code>b[</code><i>k</i><code>]</code> through

      * <code>b[b.length-1]</code> unaffected.

      *

      * <p> The <code>read(b)</code> method for class <code>InputStream</code>

      * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>

      *

      * @param      b   the buffer into which the data is read.

      * @return     the total number of bytes read into the buffer, or

      *             <code>-1</code> if there is no more data because the end of

      *             the stream has been reached.

      * @exception  IOException  If the first byte cannot be read for any reason

      * other than the end of the file, if the input stream has been closed, or

      * if some other I/O error occurs.

      * @exception  NullPointerException  if <code>b</code> is <code>null</code>.

      * @see        java.io.InputStream#read(byte[], int, int)

      */

     public int read(byte b[]) throws IOException {

         return read(b, 0, b.length);

     }

     /**

      * Reads up to <code>len</code> bytes of data from the input stream into

      * an array of bytes.  An attempt is made to read as many as

      * <code>len</code> bytes, but a smaller number may be read.

      * The number of bytes actually read is returned as an integer.

      *

      * <p> This method blocks until input data is available, end of file is

      * detected, or an exception is thrown.

      *

      * <p> If <code>len</code> is zero, then no bytes are read and

      * <code>0</code> is returned; otherwise, there is an attempt to read at

      * least one byte. If no byte is available because the stream is at end of

      * file, the value <code>-1</code> is returned; otherwise, at least one

      * byte is read and stored into <code>b</code>.

      *

      * <p> The first byte read is stored into element <code>b[off]</code>, the

      * next one into <code>b[off+1]</code>, and so on. The number of bytes read

      * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of

      * bytes actually read; these bytes will be stored in elements

      * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,

      * leaving elements <code>b[off+</code><i>k</i><code>]</code> through

      * <code>b[off+len-1]</code> unaffected.

      *

      * <p> In every case, elements <code>b[0]</code> through

      * <code>b[off]</code> and elements <code>b[off+len]</code> through

      * <code>b[b.length-1]</code> are unaffected.

      *

      * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method

      * for class <code>InputStream</code> simply calls the method

      * <code>read()</code> repeatedly. If the first such call results in an

      * <code>IOException</code>, that exception is returned from the call to

      * the <code>read(b,</code> <code>off,</code> <code>len)</code> method.  If

      * any subsequent call to <code>read()</code> results in a

      * <code>IOException</code>, the exception is caught and treated as if it

      * were end of file; the bytes read up to that point are stored into

      * <code>b</code> and the number of bytes read before the exception

      * occurred is returned. The default implementation of this method blocks

      * until the requested amount of input data <code>len</code> has been read,

      * end of file is detected, or an exception is thrown. Subclasses are encouraged

      * to provide a more efficient implementation of this method.

      *

      * @param      b     the buffer into which the data is read.

      * @param      off   the start offset in array <code>b</code>

      *                   at which the data is written.

      * @param      len   the maximum number of bytes to read.

      * @return     the total number of bytes read into the buffer, or

      *             <code>-1</code> if there is no more data because the end of

      *             the stream has been reached.

      * @exception  IOException If the first byte cannot be read for any reason

      * other than end of file, or if the input stream has been closed, or if

      * some other I/O error occurs.

      * @exception  NullPointerException If <code>b</code> is <code>null</code>.

      * @exception  IndexOutOfBoundsException If <code>off</code> is negative,

      * <code>len</code> is negative, or <code>len</code> is greater than

      * <code>b.length - off</code>

      * @see        java.io.InputStream#read()

      */

     public int read(byte b[], int off, int len) throws IOException {

         if (b == null) {

             throw new NullPointerException();

         } else if (off < 0 || len < 0 || len > b.length - off) {

             throw new IndexOutOfBoundsException();

         } else if (len == 0) {

             return 0;

         }

         int c = read();

         if (c == -1) {

             return -1;

         }

         b[off] = (byte)c;

         int i = 1;

         try {

             for (; i < len ; i++) {

                 c = read();

                 if (c == -1) {

                     break;

                 }

                 b[off + i] = (byte)c;

             }

         } catch (IOException ee) {

         }

         return i;

     }

     /**

      * Skips over and discards <code>n</code> bytes of data from this input

      * stream. The <code>skip</code> method may, for a variety of reasons, end

      * up skipping over some smaller number of bytes, possibly <code>0</code>.

      * This may result from any of a number of conditions; reaching end of file

      * before <code>n</code> bytes have been skipped is only one possibility.

      * The actual number of bytes skipped is returned.  If <code>n</code> is

      * negative, no bytes are skipped.

      *

      * <p> The <code>skip</code> method of this class creates a

      * byte array and then repeatedly reads into it until <code>n</code> bytes

      * have been read or the end of the stream has been reached. Subclasses are

      * encouraged to provide a more efficient implementation of this method.

      * For instance, the implementation may depend on the ability to seek.

      *

      * @param      n   the number of bytes to be skipped.

      * @return     the actual number of bytes skipped.

      * @exception  IOException  if the stream does not support seek,

      *                          or if some other I/O error occurs.

      */

     public long skip(long n) throws IOException {

         long remaining = n;

         int nr;

         if (skipBuffer == null)

             skipBuffer = new byte[SKIP_BUFFER_SIZE];

         byte[] localSkipBuffer = skipBuffer;

         if (n <= 0) {

             return 0;

         }

         while (remaining > 0) {

             nr = read(localSkipBuffer, 0,

                       (int) Math.min(SKIP_BUFFER_SIZE, remaining));

             if (nr < 0) {

                 break;

             }

             remaining -= nr;

         }

         return n - remaining;

     }

     /**

      * Returns an estimate of the number of bytes that can be read (or

      * skipped over) from this input stream without blocking by the next

      * invocation of a method for this input stream. The next invocation

      * might be the same thread or another thread.  A single read or skip of this

      * many bytes will not block, but may read or skip fewer bytes.

      *

      * <p> Note that while some implementations of {@code InputStream} will return

      * the total number of bytes in the stream, many will not.  It is

      * never correct to use the return value of this method to allocate

      * a buffer intended to hold all data in this stream.

      *

      * <p> A subclass' implementation of this method may choose to throw an

      * {@link IOException} if this input stream has been closed by

      * invoking the {@link #close()} method.

      *

      * <p> The {@code available} method for class {@code InputStream} always

      * returns {@code 0}.

      *

      * <p> This method should be overridden by subclasses.

      *

      * @return     an estimate of the number of bytes that can be read (or skipped

      *             over) from this input stream without blocking or {@code 0} when

      *             it reaches the end of the input stream.

      * @exception  IOException if an I/O error occurs.

      */

     public int available() throws IOException {

         return 0;

     }

     /**

      * Closes this input stream and releases any system resources associated

      * with the stream.

      *

      * <p> The <code>close</code> method of <code>InputStream</code> does

      * nothing.

      *

      * @exception  IOException  if an I/O error occurs.

      */

     public void close() throws IOException {}

     /**

      * Marks the current position in this input stream. A subsequent call to

      * the <code>reset</code> method repositions this stream at the last marked

      * position so that subsequent reads re-read the same bytes.

      *

      * <p> The <code>readlimit</code> arguments tells this input stream to

      * allow that many bytes to be read before the mark position gets

      * invalidated.

      *

      * <p> The general contract of <code>mark</code> is that, if the method

      * <code>markSupported</code> returns <code>true</code>, the stream somehow

      * remembers all the bytes read after the call to <code>mark</code> and

      * stands ready to supply those same bytes again if and whenever the method

      * <code>reset</code> is called.  However, the stream is not required to

      * remember any data at all if more than <code>readlimit</code> bytes are

      * read from the stream before <code>reset</code> is called.

      *

      * <p> Marking a closed stream should not have any effect on the stream.

      *

      * <p> The <code>mark</code> method of <code>InputStream</code> does

      * nothing.

      *

      * @param   readlimit   the maximum limit of bytes that can be read before

      *                      the mark position becomes invalid.

      * @see     java.io.InputStream#reset()

      */

     public synchronized void mark(int readlimit) {}

     /**

      * Repositions this stream to the position at the time the

      * <code>mark</code> method was last called on this input stream.

      *

      * <p> The general contract of <code>reset</code> is:

      *

      * <p><ul>

      *

      * <li> If the method <code>markSupported</code> returns

      * <code>true</code>, then:

      *

      *     <ul><li> If the method <code>mark</code> has not been called since

      *     the stream was created, or the number of bytes read from the stream

      *     since <code>mark</code> was last called is larger than the argument

      *     to <code>mark</code> at that last call, then an

      *     <code>IOException</code> might be thrown.

      *

      *     <li> If such an <code>IOException</code> is not thrown, then the

      *     stream is reset to a state such that all the bytes read since the

      *     most recent call to <code>mark</code> (or since the start of the

      *     file, if <code>mark</code> has not been called) will be resupplied

      *     to subsequent callers of the <code>read</code> method, followed by

      *     any bytes that otherwise would have been the next input data as of

      *     the time of the call to <code>reset</code>. </ul>

      *

      * <li> If the method <code>markSupported</code> returns

      * <code>false</code>, then:

      *

      *     <ul><li> The call to <code>reset</code> may throw an

      *     <code>IOException</code>.

      *

      *     <li> If an <code>IOException</code> is not thrown, then the stream

      *     is reset to a fixed state that depends on the particular type of the

      *     input stream and how it was created. The bytes that will be supplied

      *     to subsequent callers of the <code>read</code> method depend on the

      *     particular type of the input stream. </ul></ul>

      *

      * <p>The method <code>reset</code> for class <code>InputStream</code>

      * does nothing except throw an <code>IOException</code>.

      *

      * @exception  IOException  if this stream has not been marked or if the

      *               mark has been invalidated.

      * @see     java.io.InputStream#mark(int)

      * @see     java.io.IOException

      */

     public synchronized void reset() throws IOException {

         throw new IOException("mark/reset not supported");

     }

     /**

      * Tests if this input stream supports the <code>mark</code> and

      * <code>reset</code> methods. Whether or not <code>mark</code> and

      * <code>reset</code> are supported is an invariant property of a

      * particular input stream instance. The <code>markSupported</code> method

      * of <code>InputStream</code> returns <code>false</code>.

      *

      * @return  <code>true</code> if this stream instance supports the mark

      *          and reset methods; <code>false</code> otherwise.

      * @see     java.io.InputStream#mark(int)

      * @see     java.io.InputStream#reset()

      */

     public boolean markSupported() {

         return false;

     }

 }