java.util.zip.CheckedInputStream Maven / Gradle / Ivy
/*
* 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.util.zip;
import libcore.io.Streams;
import java.io.IOException;
import java.io.InputStream;
/**
* The {@code CheckedInputStream} class is used to maintain a checksum at the
* same time as the data, on which the checksum is computed, is read from a
* stream. The purpose of this checksum is to establish data integrity,
* comparing the computed checksum against a published checksum value.
*/
public class CheckedInputStream extends java.io.FilterInputStream {
private final Checksum check;
/**
* Constructs a new {@code CheckedInputStream} on {@code InputStream}
* {@code is}. The checksum will be calculated using the algorithm
* implemented by {@code csum}.
*
* Warning: passing a null source creates an invalid
* {@code CheckedInputStream}. All operations on such a stream will fail.
*
* @param is
* the input stream to calculate checksum from.
* @param csum
* an entity implementing the checksum algorithm.
*/
public CheckedInputStream(InputStream is, Checksum csum) {
super(is);
check = csum;
}
/**
* Reads one byte of data from the underlying input stream and updates the
* checksum with the byte data.
*
* @return {@code -1} at the end of the stream, a single byte value
* otherwise.
* @throws IOException
* if an {@code IOException} occurs.
*/
@Override
public int read() throws IOException {
int x = in.read();
if (x != -1) {
check.update(x);
}
return x;
}
/**
* Reads up to {@code byteCount} bytes of data from the underlying input stream, storing it
* into {@code buffer}, starting at offset {@code byteOffset}. The checksum is
* updated with the bytes read.
* Returns the number of bytes actually read or {@code -1} if arrived at the
* end of the filtered stream while reading the data.
*
* @throws IOException
* if this stream is closed or some I/O error occurs.
*/
@Override
public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {
int bytesRead = in.read(buffer, byteOffset, byteCount);
if (bytesRead != -1) {
check.update(buffer, byteOffset, bytesRead);
}
return bytesRead;
}
/**
* Returns the checksum calculated on the stream read so far.
*/
public Checksum getChecksum() {
return check;
}
/**
* Skip up to {@code byteCount} bytes of data on the underlying input
* stream. Any skipped bytes are added to the running checksum value.
*
* @param byteCount the number of bytes to skip.
* @throws IOException if this stream is closed or another I/O error occurs.
* @return the number of bytes skipped.
*/
@Override
public long skip(long byteCount) throws IOException {
return Streams.skipByReading(this, byteCount);
}
}