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/*
* Copyright 2013-2014 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.internal;
import java.io.IOException;
import java.io.InputStream;
import java.security.DigestInputStream;
import java.security.MessageDigest;
/**
* Base class for AWS Java SDK specific {@link DigestInputStream}.
*/
public class SdkDigestInputStream extends DigestInputStream implements MetricAware {
private static final int SKIP_BUF_SIZE = 2*1024;
public SdkDigestInputStream(InputStream stream, MessageDigest digest) {
super(stream, digest);
}
@Override
public final boolean isMetricActivated() {
if (in instanceof MetricAware) {
MetricAware metricAware = (MetricAware)in;
return metricAware.isMetricActivated();
}
return false;
}
// https://github.com/aws/aws-sdk-java/issues/232
/**
* Skips over and discards n bytes of data from this input
* stream, while taking the skipped bytes into account for digest
* calculation. The skip method may, for a variety of reasons,
* end up skipping over some smaller number of bytes, possibly
* 0. This may result from any of a number of conditions;
* reaching end of file before n bytes have been skipped is
* only one possibility. The actual number of bytes skipped is returned. If
* n is negative, no bytes are skipped.
*
*
* The skip method of this class creates a byte array and then
* repeatedly reads into it until n bytes have been read or the
* end of the stream has been reached. Subclasses are encouraged to provide
* a more efficient implementation of this method. For instance, the
* implementation may depend on the ability to seek.
*
* @param n
* the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException
* if the stream does not support seek, or if some other I/O
* error occurs.
*/
@Override
public final long skip(final long n) throws IOException {
if (n <= 0)
return n;
byte[] b = new byte[(int)Math.min(SKIP_BUF_SIZE, n)];
long m = n; // remaining number of bytes to read
while (m > 0) {
int len = read(b, 0, (int)Math.min(m, b.length));
if (len == -1)
return (m == n) ? -1 : (n - m);
m -= len;
}
assert (m == 0);
return n;
}
}