package org.warp.commonutils.stream; /** * A {@code PushbackInputStream} adds * functionality to another input stream, namely * the ability to "push back" or "unread" bytes, * by storing pushed-back bytes in an internal buffer. * This is useful in situations where * it is convenient for a fragment of code * to read an indefinite number of data bytes * that are delimited by a particular byte * value; after reading the terminating byte, * the code fragment can "unread" it, so that * the next read operation on the input stream * will reread the byte that was pushed back. * For example, bytes representing the characters * constituting an identifier might be terminated * by a byte representing an operator character; * a method whose job is to read just an identifier * can read until it sees the operator and * then push the operator back to be re-read. * * @author David Connelly * @author Jonathan Payne * @since 1.0 */ public class SafePushbackInputStream extends SafeFilterInputStream { /** * The pushback buffer. * @since 1.1 */ protected byte[] buf; /** * The position within the pushback buffer from which the next byte will * be read. When the buffer is empty, {@code pos} is equal to * {@code buf.length}; when the buffer is full, {@code pos} is * equal to zero. * * @since 1.1 */ protected int pos; /** * Check to make sure that this stream has not been closed */ private void ensureOpen() { if (in == null) throw new IllegalStateException("Stream closed"); } /** * Creates a {@code PushbackInputStream} * with a pushback buffer of the specified {@code size}, * and saves its argument, the input stream * {@code in}, for later use. Initially, * the pushback buffer is empty. * * @param in the input stream from which bytes will be read. * @param size the size of the pushback buffer. * @throws IllegalArgumentException if {@code size <= 0} * @since 1.1 */ public SafePushbackInputStream(SafeInputStream in, int size) { super(in); if (size <= 0) { throw new IllegalArgumentException("size <= 0"); } this.buf = new byte[size]; this.pos = size; } /** * Creates a {@code PushbackInputStream} * with a 1-byte pushback buffer, and saves its argument, the input stream * {@code in}, for later use. Initially, * the pushback buffer is empty. * * @param in the input stream from which bytes will be read. */ public SafePushbackInputStream(SafeInputStream in) { this(in, 1); } /** * Reads the next byte of data from this 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. * *

This method returns the most recently pushed-back byte, if there is * one, and otherwise calls the {@code read} method of its underlying * input stream and returns whatever value that method returns. * * @return the next byte of data, or {@code -1} if the end of the * stream has been reached. * or an I/O error occurs. * @see java.io.InputStream#read() */ public int read() { ensureOpen(); if (pos < buf.length) { return buf[pos++] & 0xff; } return super.read(); } /** * Reads up to {@code len} bytes of data from this input stream into * an array of bytes. This method first reads any pushed-back bytes; after * that, if fewer than {@code len} bytes have been read then it * reads from the underlying input stream. If {@code len} is not zero, the method * blocks until at least 1 byte of input is available; otherwise, no * bytes are read and {@code 0} is returned. * * @param b the buffer into which the data is read. * @param off the start offset in the destination array {@code b} * @param len the maximum number of bytes 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 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} * or an I/O error occurs. * @see java.io.InputStream#read(byte[], int, int) */ public int read(byte[] b, int off, int len) { ensureOpen(); 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 avail = buf.length - pos; if (avail > 0) { if (len < avail) { avail = len; } System.arraycopy(buf, pos, b, off, avail); pos += avail; off += avail; len -= avail; } if (len > 0) { len = super.read(b, off, len); if (len == -1) { return avail == 0 ? -1 : avail; } return avail + len; } return avail; } /** * Pushes back a byte by copying it to the front of the pushback buffer. * After this method returns, the next byte to be read will have the value * {@code (byte)b}. * * @param b the {@code int} value whose low-order * byte is to be pushed back. */ public void unread(int b) { ensureOpen(); if (pos == 0) { throw new IllegalStateException("Push back buffer is full"); } buf[--pos] = (byte)b; } /** * Pushes back a portion of an array of bytes by copying it to the front * of the pushback buffer. After this method returns, the next byte to be * read will have the value {@code b[off]}, the byte after that will * have the value {@code b[off+1]}, and so forth. * * @param b the byte array to push back. * @param off the start offset of the data. * @param len the number of bytes to push back. * @throws NullPointerException If {@code b} is {@code null}. * @since 1.1 */ public void unread(byte[] b, int off, int len) { ensureOpen(); if (len > pos) { throw new IllegalStateException("Push back buffer is full"); } pos -= len; System.arraycopy(b, off, buf, pos, len); } /** * Pushes back an array of bytes by copying it to the front of the * pushback buffer. After this method returns, the next byte to be read * will have the value {@code b[0]}, the byte after that will have the * value {@code b[1]}, and so forth. * * @param b the byte array to push back * @throws NullPointerException If {@code b} is {@code null}. * @since 1.1 */ public void unread(byte[] b) { unread(b, 0, b.length); } /** * 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. * *

The method returns the sum of the number of bytes that have been * pushed back and the value returned by {@link * SafeFilterInputStream#available available}. * * @return the number of bytes that can be read (or skipped over) from * the input stream without blocking. * @see SafeFilterInputStream#in * @see java.io.InputStream#available() */ public int available() { ensureOpen(); int n = buf.length - pos; int avail = super.available(); return n > (Integer.MAX_VALUE - avail) ? Integer.MAX_VALUE : n + avail; } /** * Skips over and discards {@code n} bytes of data from this * input stream. The {@code skip} method may, for a variety of * reasons, end up skipping over some smaller number of bytes, * possibly zero. If {@code n} is negative, no bytes are skipped. * *

The {@code skip} method of {@code PushbackInputStream} * first skips over the bytes in the pushback buffer, if any. It then * calls the {@code skip} method of the underlying input stream if * more bytes need to be skipped. The actual number of bytes skipped * is returned. * * @param n {@inheritDoc} * @return {@inheritDoc} * @see SafeFilterInputStream#in * @see java.io.InputStream#skip(long n) * @since 1.2 */ public long skip(long n) { ensureOpen(); if (n <= 0) { return 0; } long pskip = buf.length - pos; if (pskip > 0) { if (n < pskip) { pskip = n; } pos += pskip; n -= pskip; } if (n > 0) { pskip += super.skip(n); } return pskip; } /** * Tests if this input stream supports the {@code mark} and * {@code reset} methods, which it does not. * * @return {@code false}, since this class does not support the * {@code mark} and {@code reset} methods. * @see java.io.InputStream#mark(int) * @see java.io.InputStream#reset() */ public boolean markSupported() { return false; } /** * Marks the current position in this input stream. * *

The {@code mark} method of {@code PushbackInputStream} * 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 void mark(int readlimit) { } /** * Repositions this stream to the position at the time the * {@code mark} method was last called on this input stream. * *

The method {@code reset} for class * {@code PushbackInputStream} does nothing except throw an * {@code IOException}. * * @see java.io.InputStream#mark(int) * @see java.io.IOException */ public void reset() { throw new UnsupportedOperationException("mark/reset not supported"); } /** * Closes this input stream and releases any system resources * associated with the stream. * Once the stream has been closed, further read(), unread(), * available(), reset(), or skip() invocations will throw an IOException. * Closing a previously closed stream has no effect. * */ public void close() { if (in == null) return; in.close(); in = null; buf = null; } }