com.microsoft.azure.storage.blob.SubStream Maven / Gradle / Ivy
/**
* Copyright Microsoft Corporation
*
* Licensed 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.microsoft.azure.storage.blob;
import com.microsoft.azure.storage.Constants;
import com.microsoft.azure.storage.core.SR;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
public class SubStream extends InputStream {
// A mutal exclusion lock shared between other related substream instances.
private final Object lock;
// Stream to be wrapped.
private InputStream wrappedStream;
// The current, relative position in the substream.
private long substreamCurrentIndex;
// The position in the wrapped stream (relative to the last mark) where the substream should logically begin.
private long streamBeginIndex;
// The length of the substream.
private long streamLength;
// Tracks the marked position in the substream.
private long markIndex;
// Buffer for read requests.
private byte[] readBuffer;
private ByteArrayInputStream readBufferStream;
// Keeps track of the remaining valid bytes available in the read buffer.
private int readBufferLength;
/**
* Creates a new substream instance that partitions the wrapped stream source from
* startIndex up to streamLength. Each substream instance that wraps the same
* underlying InputStream must share the same mutual exclusion lock to avoid race
* conditions from concurrent operations.
*
* @param source The markable InputStream to be wrapped.
* @param startIndex A valid index in the wrapped stream where the substream should logically begin.
* @param streamLength The length of the substream.
* @param lock An intrinsic lock to ensure thread-safe, concurrent operations
* on substream instances wrapping the same InputStream.
*/
public SubStream(InputStream source, long startIndex, long streamLength, Object lock) {
if (startIndex < 0 || streamLength < 1) {
throw new IndexOutOfBoundsException();
}
else if (source == null) {
throw new NullPointerException("Source stream is null.");
}
else if (!source.markSupported()) {
throw new IllegalArgumentException("The source stream to be wrapped must be markable.");
}
this.wrappedStream = source;
this.streamBeginIndex = startIndex;
this.substreamCurrentIndex = 0;
this.streamLength = streamLength;
this.lock = lock;
this.readBuffer = new byte[Constants.SUBSTREAM_BUFFER_SIZE];
this.readBufferStream = new ByteArrayInputStream(this.readBuffer);
// Set empty read buffer to force refresh upon first read.
this.readBufferLength = 0;
// By default, mark the beginning of the stream.
this.markIndex = 0;
this.readBufferStream.mark(Integer.MAX_VALUE);
}
public InputStream getInputStream() {
return this.wrappedStream;
}
public long getLength() {
return this.streamLength;
}
/**
* Reads the next byte of data from the wrapped stream. The value byte is
* returned as an int in the range 0 to
* 255. If no byte is available because the end of the substream
* has been reached, the value -1 is returned. This method
* blocks until input data is available, the end of the stream is detected,
* or an exception is thrown.
*
* @return the next byte of data, or -1 if the end of the
* substream is reached.
* @throws IOException if an I/O error occurs.
*/
@Override
public int read() throws IOException {
throw new IOException();
}
/**
* Reads some number of bytes from the wrapped stream and stores them into
* the buffer array 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.
*
*
If the length of b is zero, then no bytes are read and
* 0 is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the substream is at the
* end of the file, the value -1 is returned; otherwise, at
* least one byte is read and stored into b.
*
*
The first byte read is stored into element b[0], the
* next one into b[1], and so on. The number of bytes read is,
* at most, equal to the length of b. Let k be the
* number of bytes actually read; these bytes will be stored in elements
* b[0] through b[k-1],
* leaving elements b[k] through
* b[b.length-1] unaffected.
*
*
The read(b) method for class SubStream
* has the same effect as:
read(b, 0, b.length)
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* -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 wrapped stream has been closed, or
* if some other I/O error occurs.
* @throws NullPointerException if b is null.
* @see SubStream#read(byte[], int, int)
*/
@Override
public synchronized int read(byte[] b) throws IOException {
return this.read(b, 0, b.length);
}
/**
* Reads up to len bytes of data from the substream. Buffers data from the wrapped stream
* in order to minimize skip and read overhead. The wrappedstream will only be invoked if the readBuffer
* cannot fulfil the the read request.
* In order to ensure valid results, the wrapped stream must be marked prior to reading from the substream.
* This allows us to reset to the relative substream position in the wrapped stream.
* The number of bytes actually read is returned as an integer. All these operations are done
* synchronously within an intrinsic lock to ensure other concurrent requests by substream instances
* do not result in race conditions.
*
*
The underlying call to the read of the wrapped stream will blocks until input data
* is available, end of file is detected, or an exception is thrown.
*
*
If len is zero, then no bytes are read and
* 0 is returned; otherwise, there is an attempt to read at
* least one byte. If no byte is available because the substream is at end of
* file, the value -1 is returned; otherwise, at least one
* byte is read and stored into b.
*
* @param b the buffer into which the data is read.
* @param off the start offset in array 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
* -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 wrapped stream has been closed, or if
* some other I/O error occurs.
* @throws NullPointerException If b is null.
* @throws IndexOutOfBoundsException If off is negative,
* len is negative, or len is greater than
* b.length - off
* @see SubStream#read()
*/
@Override
public synchronized int read(byte[] b, int off, int len) throws IOException {
if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
}
else if (len == 0) {
return 0;
}
int bytesRead = -1;
int readLength = len;
// Ensure we read within the substream bounds.
if (this.substreamCurrentIndex + len > this.streamLength) {
readLength = (int) (this.streamLength - this.substreamCurrentIndex);
}
// Read from previously buffered data and only up until the valid bytes available in the buffer.
int bytesFromBuffer = readBufferStream.read(b, off, Math.min(this.readBufferLength, readLength));
bytesRead = Math.max(0, bytesFromBuffer);
this.readBufferLength -= bytesRead;
// Read request was fully satisfied.
if (bytesFromBuffer == readLength) {
this.substreamCurrentIndex += bytesRead;
return bytesRead;
}
else if (bytesFromBuffer < readLength) {
// Refresh the buffer to fulfil request.
this.readBufferStream.reset();
this.readBufferLength = this.readHelper(this.readBuffer, 0, readBuffer.length);
if (this.readBufferLength == -1) {
this.readBufferLength = 0;
}
}
// Read the remaining bytes from the read buffer.
bytesFromBuffer = readBufferStream.read(b, bytesRead + off, Math.min(this.readBufferLength, readLength - bytesRead));
if (bytesFromBuffer != -1) {
bytesRead += bytesFromBuffer;
this.readBufferLength -= bytesFromBuffer;
}
this.substreamCurrentIndex += bytesRead;
return bytesRead;
}
private int readHelper(byte[] b, int off, int len) throws IOException {
synchronized (this.lock) {
wrappedStream.reset();
long bytesSkipped = 0;
byte failSkipCount = 0;
long streamCurrentIndex = this.streamBeginIndex + this.substreamCurrentIndex;
// Must be done in a loop as skip may return less than the requested number of bytes.
do {
if (failSkipCount > 7) {
throw new IOException(SR.STREAM_SKIP_FAILED);
}
long skipped = wrappedStream.skip(streamCurrentIndex - bytesSkipped);
if (skipped == 0) {
failSkipCount++;
}
else {
failSkipCount = 0;
bytesSkipped += skipped;
}
}
while (bytesSkipped != streamCurrentIndex);
return wrappedStream.read(b, off, len);
}
}
/**
* Advances the current position of the substream by n.
* The skip method does not invoke the underlying skip method
* of the wrapped stream class. The actual skipping of bytes will be accounted for
* during subsequent substream read operations.
*
* @param n the number of bytes to be effectively skipped.
* @return the actual number of bytes skipped.
*/
@Override
public long skip(long n) {
if (this.substreamCurrentIndex + n > this.streamLength) {
n = this.streamLength - this.substreamCurrentIndex;
}
this.substreamCurrentIndex += n;
this.readBufferLength = (int) Math.max(0, this.readBufferLength - n);
return n;
}
/**
* Marks the current position in the substream. A subsequent call to
* the reset method will reposition the stream to this stored position.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see SubStream#reset()
*/
@Override
public synchronized void mark(int readlimit) {
this.markIndex = this.substreamCurrentIndex;
}
/**
* Repositions the substream position to the index where the mark method
* was last called.
*
* The new reset position on substream does not take effect until subsequent reads.
*
* @see SubStream#mark(int)
*/
@Override
public synchronized void reset() {
this.substreamCurrentIndex = this.markIndex;
}
/**
* The substream wrapper class is only compatible with markable input streams and hence
* will always return true. This requirement is enforced in the class constructor.
*
* @return true
* @see SubStream#mark(int)
* @see SubStream#reset()
*/
@Override
public boolean markSupported() {
return true;
}
/**
* Closes the substream.
*/
@Override
public void close() throws IOException {
this.wrappedStream = null;
this.readBuffer = null;
this.readBufferStream.close();
this.readBufferStream = null;
}
}