/*

 * Copyright (c) 1994, 2019, 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.io;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.Objects;

/**

 * 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}

 * 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   1.0

 */

public abstract class InputStream implements Closeable {

    // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to

    // use when skipping.

    private static final int MAX_SKIP_BUFFER_SIZE = 2048;

    private static final int DEFAULT_BUFFER_SIZE = 8192;

    /**

     * Constructor for subclasses to call.

     */

    public InputStream() {}

    /**

     * Returns a new {@code InputStream} that reads no bytes. The returned

     * stream is initially open.  The stream is closed by calling the

     * {@code close()} method.  Subsequent calls to {@code close()} have no

     * effect.

     *

     * <p> While the stream is open, the {@code available()}, {@code read()},

     * {@code read(byte[])}, {@code read(byte[], int, int)},

     * {@code readAllBytes()}, {@code readNBytes(byte[], int, int)},

     * {@code readNBytes(int)}, {@code skip(long)}, {@code skipNBytes(long)},

     * and {@code transferTo()} methods all behave as if end of stream has been

     * reached.  After the stream has been closed, these methods all throw

     * {@code IOException}.

     *

     * <p> The {@code markSupported()} method returns {@code false}.  The

     * {@code mark()} method does nothing, and the {@code reset()} method

     * throws {@code IOException}.

     *

     * @return an {@code InputStream} which contains no bytes

     *

     * @since 11

     */

    public static InputStream nullInputStream() {

        return new InputStream() {

            private volatile boolean closed;

            private void ensureOpen() throws IOException {

                if (closed) {

                    throw new IOException("Stream closed");

                }

            }

            @Override

            public int available () throws IOException {

                ensureOpen();

                return 0;

            }

            @Override

            public int read() throws IOException {

                ensureOpen();

                return -1;

            }

            @Override

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

                Objects.checkFromIndexSize(off, len, b.length);

                if (len == 0) {

                    return 0;

                }

                ensureOpen();

                return -1;

            }

            @Override

            public byte[] readAllBytes() throws IOException {

                ensureOpen();

                return new byte[0];

            }

            @Override

            public int readNBytes(byte[] b, int off, int len)

                throws IOException {

                Objects.checkFromIndexSize(off, len, b.length);

                ensureOpen();

                return 0;

            }

            @Override

            public byte[] readNBytes(int len) throws IOException {

                if (len < 0) {

                    throw new IllegalArgumentException("len < 0");

                }

                ensureOpen();

                return new byte[0];

            }

            @Override

            public long skip(long n) throws IOException {

                ensureOpen();

                return 0L;

            }

            @Override

            public void skipNBytes(long n) throws IOException {

                ensureOpen();

                if (n > 0) {

                    throw new EOFException();

                }

            }

            @Override

            public long transferTo(OutputStream out) throws IOException {

                Objects.requireNonNull(out);

                ensureOpen();

                return 0L;

            }

            @Override

            public void close() throws IOException {

                closed = true;

            }

        };

    }

    /**

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

     * returned as an {@code int} in the range {@code 0} to

     * {@code 255}. If no byte is available because the end of the stream

     * has been reached, the value {@code -1} 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} if the end of the

     *             stream is reached.

     * @throws     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}. 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} is zero, then no bytes are read and

     * {@code 0} 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} is returned; otherwise, at

     * least one byte is read and stored into {@code b}.

     *

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

     * next one into {@code b[1]}, and so on. The number of bytes read is,

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

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

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

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

     * {@code b[b.length-1]} unaffected.

     *

     * <p> The {@code read(b)} method for class {@code InputStream}

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

     *

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

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

     *             {@code -1} if there is no more data because the end of

     *             the stream has been reached.

     * @throws     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.

     * @throws     NullPointerException  if {@code b} is {@code null}.

     * @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} bytes of data from the input stream into

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

     * {@code len} 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} is zero, then no bytes are read and

     * {@code 0} 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} is returned; otherwise, at least one

     * byte is read and stored into {@code b}.

     *

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

     * next one into {@code b[off+1]}, and so on. The number of bytes read

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

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

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

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

     * {@code b[off+len-1]} unaffected.

     *

     * <p> In every case, elements {@code b[0]} through

     * {@code b[off-1]} and elements {@code b[off+len]} through

     * {@code b[b.length-1]} are unaffected.

     *

     * <p> The {@code read(b, off, len)} method

     * for class {@code InputStream} simply calls the method

     * {@code read()} repeatedly. If the first such call results in an

     * {@code IOException}, that exception is returned from the call to

     * the {@code read(b,} {@code off,} {@code len)} method.  If

     * any subsequent call to {@code read()} results in a

     * {@code IOException}, 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} 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} 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}

     *                   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} if there is no more data because the end of

     *             the stream has been reached.

     * @throws     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.

     * @throws     NullPointerException If {@code b} is {@code null}.

     * @throws     IndexOutOfBoundsException If {@code off} is negative,

     *             {@code len} is negative, or {@code len} is greater than

     *             {@code b.length - off}

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

     */

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

        Objects.checkFromIndexSize(off, len, b.length);

        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;

    }

    /**

     * The maximum size of array to allocate.

     * Some VMs reserve some header words in an array.

     * Attempts to allocate larger arrays may result in

     * OutOfMemoryError: Requested array size exceeds VM limit

     */

    private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;

    /**

     * Reads all remaining bytes from the input stream. This method blocks until

     * all remaining bytes have been read and end of stream is detected, or an

     * exception is thrown. This method does not close the input stream.

     *

     * <p> When this stream reaches end of stream, further invocations of this

     * method will return an empty byte array.

     *

     * <p> Note that this method is intended for simple cases where it is

     * convenient to read all bytes into a byte array. It is not intended for

     * reading input streams with large amounts of data.

     *

     * <p> The behavior for the case where the input stream is <i>asynchronously

     * closed</i>, or the thread interrupted during the read, is highly input

     * stream specific, and therefore not specified.

     *

     * <p> If an I/O error occurs reading from the input stream, then it may do

     * so after some, but not all, bytes have been read. Consequently the input

     * stream may not be at end of stream and may be in an inconsistent state.

     * It is strongly recommended that the stream be promptly closed if an I/O

     * error occurs.

     *

     * @implSpec

     * This method invokes {@link #readNBytes(int)} with a length of

     * {@link Integer#MAX_VALUE}.

     *

     * @return a byte array containing the bytes read from this input stream

     * @throws IOException if an I/O error occurs

     * @throws OutOfMemoryError if an array of the required size cannot be

     *         allocated.

     *

     * @since 9

     */

    public byte[] readAllBytes() throws IOException {

        return readNBytes(Integer.MAX_VALUE);

    }

    /**

     * Reads up to a specified number of bytes from the input stream. This

     * method blocks until the requested number of bytes have been read, end

     * of stream is detected, or an exception is thrown. This method does not

     * close the input stream.

     *

     * <p> The length of the returned array equals the number of bytes read

     * from the stream. If {@code len} is zero, then no bytes are read and

     * an empty byte array is returned. Otherwise, up to {@code len} bytes

     * are read from the stream. Fewer than {@code len} bytes may be read if

     * end of stream is encountered.

     *

     * <p> When this stream reaches end of stream, further invocations of this

     * method will return an empty byte array.

     *

     * <p> Note that this method is intended for simple cases where it is

     * convenient to read the specified number of bytes into a byte array. The

     * total amount of memory allocated by this method is proportional to the

     * number of bytes read from the stream which is bounded by {@code len}.

     * Therefore, the method may be safely called with very large values of

     * {@code len} provided sufficient memory is available.

     *

     * <p> The behavior for the case where the input stream is <i>asynchronously

     * closed</i>, or the thread interrupted during the read, is highly input

     * stream specific, and therefore not specified.

     *

     * <p> If an I/O error occurs reading from the input stream, then it may do

     * so after some, but not all, bytes have been read. Consequently the input

     * stream may not be at end of stream and may be in an inconsistent state.

     * It is strongly recommended that the stream be promptly closed if an I/O

     * error occurs.

     *

     * @implNote

     * The number of bytes allocated to read data from this stream and return

     * the result is bounded by {@code 2*(long)len}, inclusive.

     *

     * @param len the maximum number of bytes to read

     * @return a byte array containing the bytes read from this input stream

     * @throws IllegalArgumentException if {@code length} is negative

     * @throws IOException if an I/O error occurs

     * @throws OutOfMemoryError if an array of the required size cannot be

     *         allocated.

     *

     * @since 11

     */

    public byte[] readNBytes(int len) throws IOException {

        if (len < 0) {

            throw new IllegalArgumentException("len < 0");

        }

        List<byte[]> bufs = null;

        byte[] result = null;

        int total = 0;

        int remaining = len;

        int n;

        do {

            byte[] buf = new byte[Math.min(remaining, DEFAULT_BUFFER_SIZE)];

            int nread = 0;

            // read to EOF which may read more or less than buffer size

            while ((n = read(buf, nread,

                    Math.min(buf.length - nread, remaining))) > 0) {

                nread += n;

                remaining -= n;

            }

            if (nread > 0) {

                if (MAX_BUFFER_SIZE - total < nread) {

                    throw new OutOfMemoryError("Required array size too large");

                }

                total += nread;

                if (result == null) {

                    result = buf;

                } else {

                    if (bufs == null) {

                        bufs = new ArrayList<>();

                        bufs.add(result);

                    }

                    bufs.add(buf);

                }

            }

            // if the last call to read returned -1 or the number of bytes

            // requested have been read then break

        } while (n >= 0 && remaining > 0);

        if (bufs == null) {

            if (result == null) {

                return new byte[0];

            }

            return result.length == total ?

                result : Arrays.copyOf(result, total);

        }

        result = new byte[total];

        int offset = 0;

        remaining = total;

        for (byte[] b : bufs) {

            int count = Math.min(b.length, remaining);

            System.arraycopy(b, 0, result, offset, count);

            offset += count;

            remaining -= count;

        }

        return result;

    }

    /**

     * Reads the requested number of bytes from the input stream into the given

     * byte array. This method blocks until {@code len} bytes of input data have

     * been read, end of stream is detected, or an exception is thrown. The

     * number of bytes actually read, possibly zero, is returned. This method

     * does not close the input stream.

     *

     * <p> In the case where end of stream is reached before {@code len} bytes

     * have been read, then the actual number of bytes read will be returned.

     * When this stream reaches end of stream, further invocations of this

     * method will return zero.

     *

     * <p> If {@code len} is zero, then no bytes are read and {@code 0} is

     * returned; otherwise, there is an attempt to read up to {@code len} bytes.

     *

     * <p> The first byte read is stored into element {@code b[off]}, the next

     * one in to {@code b[off+1]}, and so on. The number of bytes read is, at

     * most, equal to {@code len}. Let <i>k</i> be the number of bytes actually

     * read; these bytes will be stored in elements {@code b[off]} through

     * {@code b[off+}<i>k</i>{@code -1]}, leaving elements {@code b[off+}<i>k</i>

     * {@code ]} through {@code b[off+len-1]} unaffected.

     *

     * <p> The behavior for the case where the input stream is <i>asynchronously

     * closed</i>, or the thread interrupted during the read, is highly input

     * stream specific, and therefore not specified.

     *

     * <p> If an I/O error occurs reading from the input stream, then it may do

     * so after some, but not all, bytes of {@code b} have been updated with

     * data from the input stream. Consequently the input stream and {@code b}

     * may be in an inconsistent state. It is strongly recommended that the

     * stream be promptly closed if an I/O error occurs.

     *

     * @param  b the byte array into which the data is read

     * @param  off the start offset in {@code b} at which the data is written

     * @param  len the maximum number of bytes to read

     * @return the actual number of bytes read into the buffer

     * @throws IOException if an I/O error occurs

     * @throws NullPointerException if {@code b} is {@code null}

     * @throws IndexOutOfBoundsException If {@code off} is negative, {@code len}

     *         is negative, or {@code len} is greater than {@code b.length - off}

     *