com.ksyun.ks3.service.encryption.internal.AbstractRepeatableCipherInputStream Maven / Gradle / Ivy

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package com.ksyun.ks3.service.encryption.internal;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Common base class used to wrap an InputStream with a cipher input stream to
 * encrypt it, and handles resets by attempting to reset on the original,
 * unencrypted data InputStream, and recreate an identical Cipher and identical
 * CipherInputStream on the original data.
 * 
 * It's repeatable if and only if the underlying unencryptedDataStream is
 * repeatable - if the underlying input stream is not repeatable and you're
 * going to buffer to make it repeatable anyways, it makes more sense to do so
 * after wrapping in this object, so we buffer the encrypted data and don't have
 * to bother re-encrypting on retry.
 * 
 * This stream only supports being marked before the first call to
 * {@code read} or {@code skip}, since it's not possible to rewind the
 * encryption state of a {@code CipherInputStream} to an arbitrary point. If you
 * call {@code mark} after calling {@code read} or {@code skip}, it will throw
 * an {@code UnsupportedOperationException}.
 */
public abstract class AbstractRepeatableCipherInputStream
        extends FilterInputStream {
    private final T cipherFactory;
    private final InputStream unencryptedDataStream;
    private boolean hasBeenAccessed;

    /**
     * Constructs a new repeatable cipher input stream using the specified
     * InputStream as the source data, and the CipherFactory for building
     * Cipher objects.
     * 
     * @param input
     *            The original, unencrypted data stream. This stream should be
     *            markable/resetable in order for this class to work correctly.
     * @param cipherInputStream
     *            The cipher input stream wrapping the original input stream
     * @param cipherFactory
     *            The factory used for creating identical cipher objects when
     *            this stream is reset and a new CipherInputStream is needed.
     */
    protected AbstractRepeatableCipherInputStream(final InputStream input,
            final FilterInputStream cipherInputStream,
            final T cipherFactory) {
        super(cipherInputStream);
        this.unencryptedDataStream = input;
        this.cipherFactory = cipherFactory;
    }

    @Override
    public boolean markSupported() {
    	return unencryptedDataStream.markSupported();
    }
    
    @Override
    public void mark(final int readlimit) {
        if (hasBeenAccessed) {
            throw new UnsupportedOperationException(
                    "Marking is only supported before your first call to "
                    + "read or skip.");
        }

    	unencryptedDataStream.mark(readlimit);
    }

    @Override
    public void reset() throws IOException {
        unencryptedDataStream.reset();
        in = createCipherInputStream(unencryptedDataStream, cipherFactory);
        hasBeenAccessed = false;
    }

    @Override
    public int read() throws IOException {
        hasBeenAccessed = true;
        return super.read();
    }

    @Override
    public int read(final byte[] b) throws IOException {
        hasBeenAccessed = true;
        return super.read(b);
    }

    @Override
    public int read(final byte[] b, final int off, final int len)
            throws IOException {

        hasBeenAccessed = true;
        return super.read(b, off, len);
    }

    @Override
    public long skip(final long n) throws IOException {
        hasBeenAccessed = true;
        return super.skip(n);
    }

    protected abstract FilterInputStream createCipherInputStream(
            InputStream unencryptedDataStream, T cipherFactory);
}