/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
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 *
 */

package java.security;

import java.io.IOException;
import java.io.EOFException;
import java.io.InputStream;
import java.io.FilterInputStream;
import java.io.PrintStream;
import java.io.ByteArrayInputStream;

/**
 * A transparent stream that updates the associated message digest using
 * the bits going through the stream.
 *
 * <p>To complete the message digest computation, call one of the
 * {@code digest} methods on the associated message
 * digest after your calls to one of this digest input stream's
 * {@link #read() read} methods.
 *
 * <p>It is possible to turn this stream on or off (see
 * {@link #on(boolean) on}). When it is on, a call to one of the
 * {@code read} methods
 * results in an update on the message digest. But when it is off,
 * the message digest is not updated. The default is for the stream
 * to be on.
 *
 * <p>Note that digest objects can compute only one digest (see
 * {@link MessageDigest}),
 * so that in order to compute intermediate digests, a caller should
 * retain a handle onto the digest object, and clone it for each
 * digest to be computed, leaving the original digest untouched.
 *
 * @see MessageDigest
 *
 * @see DigestOutputStream
 *
 * @author Benjamin Renaud
 * @since 1.2
 */

public class DigestInputStream extends FilterInputStream {

 /* NOTE: This should be made a generic UpdaterInputStream */

 /* Are we on or off? */
 private boolean on = true;

 /**
 * The message digest associated with this stream.
 */
 protected MessageDigest digest;

 /**
 * Creates a digest input stream, using the specified input stream
 * and message digest.
 *
 * @param stream the input stream.
 *
 * @param digest the message digest to associate with this stream.
 */
 public DigestInputStream(InputStream stream, MessageDigest digest) {
 super(stream);
 setMessageDigest(digest);
 }

 /**
 * Returns the message digest associated with this stream.
 *
 * @return the message digest associated with this stream.
 * @see #setMessageDigest(java.security.MessageDigest)
 */
 public MessageDigest getMessageDigest() {
 return digest;
 }

 /**
 * Associates the specified message digest with this stream.
 *
 * @param digest the message digest to be associated with this stream.
 * @see #getMessageDigest()
 */
 public void setMessageDigest(MessageDigest digest) {
 this.digest = digest;
 }

 /**
 * Reads a byte, and updates the message digest (if the digest
 * function is on). That is, this method reads a byte from the
 * input stream, blocking until the byte is actually read. If the
 * digest function is on (see {@link #on(boolean) on}), this method
 * will then call {@code update} on the message digest associated
 * with this stream, passing it the byte read.
 *
 * @return the byte read.
 *
 * @exception IOException if an I/O error occurs.
 *
 * @see MessageDigest#update(byte)
 */
 public int read() throws IOException {
 int ch = in.read();
 if (on && ch != -1) {
 digest.update((byte)ch);
 }
 return ch;
 }

 /**
 * Reads into a byte array, and updates the message digest (if the
 * digest function is on). That is, this method reads up to
 * {@code len} bytes from the input stream into the array
 * {@code b}, starting at offset {@code off}. This method
 * blocks until the data is actually
 * read. If the digest function is on (see
 * {@link #on(boolean) on}), this method will then call {@code update}
 * on the message digest associated with this stream, passing it
 * the data.
 *
 * @param b the array into which the data is read.
 *
 * @param off the starting offset into {@code b} of where the
 * data should be placed.
 *
 * @param len the maximum number of bytes to be read from the input
 * stream into b, starting at offset {@code off}.
 *
 * @return the actual number of bytes read. This is less than
 * {@code len} if the end of the stream is reached prior to
 * reading {@code len} bytes. -1 is returned if no bytes were
 * read because the end of the stream had already been reached when
 * the call was made.
 *
 * @exception IOException if an I/O error occurs.
 *
 * @see MessageDigest#update(byte[], int, int)
 */
 public int read(byte[] b, int off, int len) throws IOException {
 int result = in.read(b, off, len);
 if (on && result != -1) {
 digest.update(b, off, result);
 }
 return result;
 }

 /**
 * Turns the digest function on or off. The default is on. When
 * it is on, a call to one of the {@code read} methods results in an
 * update on the message digest. But when it is off, the message
 * digest is not updated.
 *
 * @param on true to turn the digest function on, false to turn
 * it off.
 */
 public void on(boolean on) {
 this.on = on;
 }

 /**
 * Prints a string representation of this digest input stream and
 * its associated message digest object.
 */
 public String toString() {
 return "[Digest Input Stream] " + digest.toString();
 }
}