/*
* 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 java.io;
import org.apache.harmony.luni.util.Msg;
/**
* The base class for all input streams. An input stream is a means of reading
* data from a source in a byte-wise manner.
* <p>
* Some input streams also support marking a position in the input stream and
* returning to this position later. This abstract class does not provide a
* fully working implementation, so it needs to be subclassed, and at least the
* {@link #read()} method needs to be overridden. Overriding some of the
* non-abstract methods is also often advised, since it might result in higher
* efficiency.
* <p>
* Many specialized input streams for purposes like reading from a file already
* exist in this package.
*
* @see OutputStream
*/
public abstract class InputStream extends Object implements Closeable {
private static byte[] skipBuf;
/**
* This constructor does nothing. It is provided for signature
* compatibility.
*/
public InputStream() {
/* empty */
}
/**
* Returns an estimated number of bytes that can be read or skipped without blocking for more
* input.
*
* <p>Note that this method provides such a weak guarantee that it is not very useful in
* practice.
*
* <p>Firstly, the guarantee is "without blocking for more input" rather than "without
* blocking": a read may still block waiting for I/O to complete — the guarantee is
* merely that it won't have to wait indefinitely for data to be written. The result of this
* method should not be used as a license to do I/O on a thread that shouldn't be blocked.
*
* <p>Secondly, the result is a
* conservative estimate and may be significantly smaller than the actual number of bytes
* available. In particular, an implementation that always returns 0 would be correct.
* In general, callers should only use this method if they'd be satisfied with
* treating the result as a boolean yes or no answer to the question "is there definitely
* data ready?".
*
* <p>Thirdly, the fact that a given number of bytes is "available" does not guarantee that a
* read or skip will actually read or skip that many bytes: they may read or skip fewer.
*
* <p>It is particularly important to realize that you <i>must not</i> use this method to
* size a container and assume that you can read the entirety of the stream without needing
* to resize the container. Such callers should probably write everything they read to a
* {@link ByteArrayOutputStream} and convert that to a byte array. Alternatively, if you're
* reading from a file, {@link File#length} returns the current length of the file (though
* assuming the file's length can't change may be incorrect, reading a file is inherently
* racy).
*
* <p>The default implementation of this method in {@code InputStream} always returns 0.
* Subclasses should override this method if they are able to indicate the number of bytes
* available.
*
* @return the estimated number of bytes available
* @throws IOException if this stream is closed or an error occurs
*/
public int available() throws IOException {
return 0;
}
/**
* Closes this stream. Concrete implementations of this class should free
* any resources during close. This implementation does nothing.
*
* @throws IOException
* if an error occurs while closing this stream.
*/
public void close() throws IOException {
/* empty */
}
/**
* Sets a mark position in this InputStream. The parameter {@code readlimit}
* indicates how many bytes can be read before the mark is invalidated.
* Sending {@code reset()} will reposition the stream back to the marked
* position provided {@code readLimit} has not been surpassed.
* <p>
* This default implementation does nothing and concrete subclasses must
* provide their own implementation.
*
* @param readlimit
* the number of bytes that can be read from this stream before
* the mark is invalidated.
* @see #markSupported()
* @see #reset()
*/
public void mark(int readlimit) {
/* empty */
}
/**
* Indicates whether this stream supports the {@code mark()} and
* {@code reset()} methods. The default implementation returns {@code false}.
*
* @return always {@code false}.
* @see #mark(int)
* @see #reset()
*/
public boolean markSupported() {
return false;
}
/**
* Reads a single byte from this stream and returns it as an integer in the
* range from 0 to 255. Returns -1 if the end of the stream has been
* reached. Blocks until one byte has been read, the end of the source
* stream is detected or an exception is thrown.
*
* @return the byte read or -1 if the end of stream has been reached.
* @throws IOException
* if the stream is closed or another IOException occurs.
*/
public abstract int read() throws IOException;
/**
* Reads bytes from this stream and stores them in the byte array {@code b}.
*
* @param b
* the byte array in which to store the bytes read.
* @return the number of bytes actually read or -1 if the end of the stream
* has been reached.
* @throws IOException
* if this stream is closed or another IOException occurs.
*/
public int read(byte[] b) throws IOException {
// BEGIN android-note
// changed array notation to be consistent with the rest of harmony
// END android-note
return read(b, 0, b.length);
}
/**
* Reads at most {@code length} bytes from this stream and stores them in
* the byte array {@code b} starting at {@code offset}.
*
* @param b
* the byte array in which to store the bytes read.
* @param offset
* the initial position in {@code buffer} to store the bytes read
* from this stream.
* @param length
* the maximum number of bytes to store in {@code b}.
* @return the number of bytes actually read or -1 if the end of the stream
* has been reached.
* @throws IndexOutOfBoundsException
* if {@code offset < 0} or {@code length < 0}, or if
* {@code offset + length} is greater than the length of
* {@code b}.
* @throws IOException
* if the stream is closed or another IOException occurs.
*/
public int read(byte[] b, int offset, int length) throws IOException {
// BEGIN android-note
// changed array notation to be consistent with the rest of harmony
// END android-note
// Force null check for b first!
if (offset > b.length || offset < 0) {
// K002e=Offset out of bounds \: {0}
throw new ArrayIndexOutOfBoundsException(Msg.getString("K002e", offset)); //$NON-NLS-1$
}
if (length < 0 || length > b.length - offset) {
// K0031=Length out of bounds \: {0}
throw new ArrayIndexOutOfBoundsException(Msg.getString("K0031", length)); //$NON-NLS-1$
}
for (int i = 0; i < length; i++) {
int c;
try {
if ((c = read()) == -1) {
return i == 0 ? -1 : i;
}
} catch (IOException e) {
if (i != 0) {
return i;
}
throw e;
}
b[offset + i] = (byte) c;
}
return length;
}
/**
* Resets this stream to the last marked location. Throws an
* {@code IOException} if the number of bytes read since the mark has been
* set is greater than the limit provided to {@code mark}, or if no mark
* has been set.
* <p>
* This implementation always throws an {@code IOException} and concrete
* subclasses should provide the proper implementation.
*
* @throws IOException
* if this stream is closed or another IOException occurs.
*/
public synchronized void reset() throws IOException {
throw new IOException();
}
/**
* Skips at most {@code n} bytes in this stream. This method does nothing and returns
* 0 if {@code n} is negative.
*
* <p>Note the "at most" in the description of this method: this method may choose to skip
* fewer bytes than requested. Callers should <i>always</i> check the return value.
*
* <p>This default implementation reads bytes into a temporary
* buffer. Concrete subclasses should provide their own implementation.
*
* @param n the number of bytes to skip.
* @return the number of bytes actually skipped.
* @throws IOException
* if this stream is closed or another IOException occurs.
*/
public long skip(long n) throws IOException {
if (n <= 0) {
return 0;
}
long skipped = 0;
int toRead = n < 4096 ? (int) n : 4096;
// We are unsynchronized, so take a local copy of the skipBuf at some
// point in time.
byte[] localBuf = skipBuf;
if (localBuf == null || localBuf.length < toRead) {
// May be lazily written back to the static. No matter if it
// overwrites somebody else's store.
skipBuf = localBuf = new byte[toRead];
}
while (skipped < n) {
int read = read(localBuf, 0, toRead);
if (read == -1) {
return skipped;
}
skipped += read;
if (read < toRead) {
return skipped;
}
if (n - skipped < toRead) {
toRead = (int) (n - skipped);
}
}
return skipped;
}
}