/*
* Copyright 2010-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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.amazonaws.services.s3.internal.crypto;
import com.amazonaws.internal.SdkInputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* Reads only a specific range of bytes from the underlying input stream.
*/
public class AdjustedRangeInputStream extends SdkInputStream {
private InputStream decryptedContents;
private long virtualAvailable;
private boolean closed;
/**
* Creates a new DecryptedContentsInputStream object.
*
* @param objectContents The input stream containing the object contents
* retrieved from S3
* @param rangeBeginning The position of the left-most byte desired by the
* user
* @param rangeEnd The position of the right-most byte desired by the user
* @throws IOException If there are errors skipping to the left-most byte
* desired by the user.
*/
public AdjustedRangeInputStream(InputStream objectContents, long rangeBeginning, long rangeEnd)
throws IOException {
this.decryptedContents = objectContents;
this.closed = false;
initializeForRead(rangeBeginning, rangeEnd);
}
/**
* Skip to the start location of the range of bytes desired by the user.
*/
private void initializeForRead(long rangeBeginning, long rangeEnd) throws IOException {
// To get to the left-most byte desired by a user, we must skip over the
// 16 bytes of the
// preliminary cipher block, and then possibly skip a few more bytes
// into the next block
// to where the the left-most byte is located.
int numBytesToSkip;
if (rangeBeginning < JceEncryptionConstants.SYMMETRIC_CIPHER_BLOCK_SIZE) {
numBytesToSkip = (int) rangeBeginning;
} else {
int offsetIntoBlock = (int) (rangeBeginning % JceEncryptionConstants.SYMMETRIC_CIPHER_BLOCK_SIZE);
numBytesToSkip = JceEncryptionConstants.SYMMETRIC_CIPHER_BLOCK_SIZE + offsetIntoBlock;
}
if (numBytesToSkip != 0) {
// Skip to the left-most desired byte. The read() method is used
// instead of the skip() method
// since the skip() method will not block if the underlying input
// stream is waiting for more input.
while (numBytesToSkip > 0) {
this.decryptedContents.read();
numBytesToSkip--;
}
}
// The number of bytes the user may read is equal to the number of the
// bytes in the range.
// Note that the range includes the endpoints.
this.virtualAvailable = (rangeEnd - rangeBeginning) + 1;
}
/*
* (non-Javadoc)
* @see java.io.InputStream#read()
*/
@Override
public int read() throws IOException {
abortIfNeeded();
int result = 0;
// If there are no more available bytes, mark that we are at the end of
// the stream.
if (this.virtualAvailable <= 0) {
result = -1;
} else {
// Otherwise, read a byte.
result = this.decryptedContents.read();
}
// If we have not reached the end of the stream, decrement the number of
// available bytes.
if (result != -1) {
this.virtualAvailable--;
} else {
// If we are at the end of the stream, close it.
close();
this.virtualAvailable = 0;
}
return result;
}
/*
* (non-Javadoc)
* @see java.io.InputStream#read(byte[], int, int)
*/
@Override
public int read(byte[] buffer, int offset, int length) throws IOException {
abortIfNeeded();
int numBytesRead;
// If no more bytes are available, do not read any bytes into the buffer
if (this.virtualAvailable <= 0) {
numBytesRead = -1;
} else {
// If the desired read length is greater than the number of
// available bytes,
// shorten the read length to the number of available bytes.
if (length > this.virtualAvailable) {
// If the number of available bytes is greater than the maximum
// value of a 32 bit int, then
// read as many bytes as an int can.
length = (this.virtualAvailable < Integer.MAX_VALUE) ? (int) this.virtualAvailable
: Integer.MAX_VALUE;
}
// Read bytes into the buffer.
numBytesRead = this.decryptedContents.read(buffer, offset, length);
}
// If we were able to read bytes, decrement the number of bytes
// available to be read.
if (numBytesRead != -1) {
this.virtualAvailable -= numBytesRead;
} else {
// If we've reached the end of the stream, close it
close();
this.virtualAvailable = 0;
}
return numBytesRead;
}
/*
* (non-Javadoc)
* @see java.io.InputStream#available()
*/
@Override
public int available() throws IOException {
abortIfNeeded();
int available = this.decryptedContents.available();
if (available < this.virtualAvailable) {
return available;
} else {
// Limit the number of bytes available to the number
// of bytes remaining in the range.
return (int) this.virtualAvailable;
}
}
/*
* (non-Javadoc)
* @see java.io.InputStream#close()
*/
@Override
public void close() throws IOException {
// If not already closed, then close the input stream.
if (!this.closed) {
this.closed = true;
this.decryptedContents.close();
}
abortIfNeeded();
}
@Override
protected InputStream getWrappedInputStream() {
return decryptedContents;
}
}