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/*
* Copyright (C) 2011 The Guava Authors
*
* Licensed 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 com.google.common.hash;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import java.io.Serializable;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
/**
* {@link HashFunction} adapter for {@link MessageDigest} instances.
*
* @author Kevin Bourrillion
* @author Dimitris Andreou
*/
final class MessageDigestHashFunction extends AbstractStreamingHashFunction
implements Serializable {
private final MessageDigest prototype;
private final int bytes;
private final boolean supportsClone;
private final String toString;
MessageDigestHashFunction(String algorithmName, String toString) {
this.prototype = getMessageDigest(algorithmName);
this.bytes = prototype.getDigestLength();
this.toString = checkNotNull(toString);
this.supportsClone = supportsClone();
}
MessageDigestHashFunction(String algorithmName, int bytes, String toString) {
this.toString = checkNotNull(toString);
this.prototype = getMessageDigest(algorithmName);
int maxLength = prototype.getDigestLength();
checkArgument(bytes >= 4 && bytes <= maxLength,
"bytes (%s) must be >= 4 and < %s", bytes, maxLength);
this.bytes = bytes;
this.supportsClone = supportsClone();
}
private boolean supportsClone() {
try {
prototype.clone();
return true;
} catch (CloneNotSupportedException e) {
return false;
}
}
@Override public int bits() {
return bytes * Byte.SIZE;
}
@Override public String toString() {
return toString;
}
private static MessageDigest getMessageDigest(String algorithmName) {
try {
return MessageDigest.getInstance(algorithmName);
} catch (NoSuchAlgorithmException e) {
throw new AssertionError(e);
}
}
@Override public Hasher newHasher() {
if (supportsClone) {
try {
return new MessageDigestHasher((MessageDigest) prototype.clone(), bytes);
} catch (CloneNotSupportedException e) {
// falls through
}
}
return new MessageDigestHasher(getMessageDigest(prototype.getAlgorithm()), bytes);
}
private static final class SerializedForm implements Serializable {
private final String algorithmName;
private final int bytes;
private final String toString;
private SerializedForm(String algorithmName, int bytes, String toString) {
this.algorithmName = algorithmName;
this.bytes = bytes;
this.toString = toString;
}
private Object readResolve() {
return new MessageDigestHashFunction(algorithmName, bytes, toString);
}
private static final long serialVersionUID = 0;
}
Object writeReplace() {
return new SerializedForm(prototype.getAlgorithm(), bytes, toString);
}
/**
* Hasher that updates a message digest.
*/
private static final class MessageDigestHasher extends AbstractByteHasher {
private final MessageDigest digest;
private final int bytes;
private boolean done;
private MessageDigestHasher(MessageDigest digest, int bytes) {
this.digest = digest;
this.bytes = bytes;
}
@Override
protected void update(byte b) {
checkNotDone();
digest.update(b);
}
@Override
protected void update(byte[] b) {
checkNotDone();
digest.update(b);
}
@Override
protected void update(byte[] b, int off, int len) {
checkNotDone();
digest.update(b, off, len);
}
private void checkNotDone() {
checkState(!done, "Cannot use Hasher after calling #hash() on it");
}
@Override
public HashCode hash() {
done = true;
return (bytes == digest.getDigestLength())
? HashCodes.fromBytesNoCopy(digest.digest())
: HashCodes.fromBytesNoCopy(Arrays.copyOf(digest.digest(), bytes));
}
}
}
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