org.ttzero.excel.hash.AbstractStreamingHasher Maven / Gradle / Ivy
/*
* 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 org.ttzero.excel.hash;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
/**
* A convenience base class for implementors of {@code Hasher}; handles accumulating data until an
* entire "chunk" (of implementation-dependent length) is ready to be hashed.
*
* @author Kevin Bourrillion
* @author Dimitris Andreou
*/
abstract class AbstractStreamingHasher {
/**
* Buffer via which we pass data to the hash algorithm (the implementor)
*/
private final ByteBuffer buffer;
/**
* Number of bytes to be filled before process() invocation(s).
*/
private final int bufferSize;
/**
* Number of bytes processed per process() invocation.
*/
private final int chunkSize;
/**
* Temporary use
*/
private ByteBuffer tmpBuffer = ByteBuffer.allocate(512).order(ByteOrder.LITTLE_ENDIAN);
/**
* Constructor for use by subclasses. This hasher instance will process chunks of the specified
* size.
*
* @param chunkSize the number of bytes available per {@link #process(ByteBuffer)} invocation;
* must be at least 4
*/
protected AbstractStreamingHasher(int chunkSize) {
this(chunkSize, chunkSize);
}
/**
* Constructor for use by subclasses. This hasher instance will process chunks of the specified
* size, using an internal buffer of {@code bufferSize} size, which must be a multiple of {@code
* chunkSize}.
*
* @param chunkSize the number of bytes available per {@link #process(ByteBuffer)} invocation;
* must be at least 4
* @param bufferSize the size of the internal buffer. Must be a multiple of chunkSize
*/
protected AbstractStreamingHasher(int chunkSize, int bufferSize) {
int mod = bufferSize % chunkSize;
if (mod != 0) bufferSize += (chunkSize - mod);
// always space for a single primitive
this.buffer = ByteBuffer.allocate(bufferSize + 7).order(ByteOrder.LITTLE_ENDIAN);
this.bufferSize = bufferSize;
this.chunkSize = chunkSize;
}
/**
* Processes the available bytes of the buffer (at most {@code chunk} bytes).
*/
protected abstract void process(ByteBuffer bb);
/**
* This is invoked for the last bytes of the input, which are not enough to fill a whole chunk.
* The passed {@code ByteBuffer} is guaranteed to be non-empty.
*
* This implementation simply pads with zeros and delegates to {@link #process(ByteBuffer)}.
*/
protected void processRemaining(ByteBuffer bb) {
bb.position(bb.limit()); // move at the end
bb.limit(chunkSize + 7); // get ready to pad with longs
while (bb.position() < chunkSize) {
bb.putLong(0);
}
bb.limit(chunkSize);
bb.flip();
process(bb);
}
public final AbstractStreamingHasher putBytes(byte[] bytes) {
return putBytes(bytes, 0, bytes.length);
}
public final AbstractStreamingHasher putBytes(byte[] bytes, int off, int len) {
if (tmpBuffer.capacity() >= len) {
tmpBuffer.clear();
tmpBuffer.put(bytes, off, len);
tmpBuffer.flip();
} else {
tmpBuffer = ByteBuffer.wrap(bytes, off, len).order(ByteOrder.LITTLE_ENDIAN);
}
return putBytesInternal(tmpBuffer);
}
private AbstractStreamingHasher putBytesInternal(ByteBuffer readBuffer) {
// If we have room for all of it, this is easy
if (readBuffer.remaining() <= buffer.remaining()) {
buffer.put(readBuffer);
munchIfFull();
return this;
}
// First add just enough to fill buffer size, and munch that
int bytesToCopy = bufferSize - buffer.position();
for (int i = 0; i < bytesToCopy; i++) {
buffer.put(readBuffer.get());
}
munch(); // buffer becomes empty here, since chunkSize divides bufferSize
// Now process directly from the rest of the input buffer
while (readBuffer.remaining() >= chunkSize) {
process(readBuffer);
}
// Finally stick the remainder back in our usual buffer
buffer.put(readBuffer);
return this;
}
public final byte[] hash() {
munch();
buffer.flip();
if (buffer.remaining() > 0) {
processRemaining(buffer);
buffer.position(buffer.limit());
}
return makeHash();
}
/**
* Computes a hash code based on the data that have been provided to this hasher. This is called
* after all chunks are handled with {@link #process} and any leftover bytes that did not make a
* complete chunk are handled with {@link #processRemaining}.
*/
protected abstract byte[] makeHash();
// Process pent-up data in chunks
private void munchIfFull() {
if (buffer.remaining() < 8) {
// buffer is full; not enough room for a primitive. We have at least one full chunk.
munch();
}
}
private void munch() {
buffer.flip();
while (buffer.remaining() >= chunkSize) {
// we could limit the buffer to ensure process() does not read more than
// chunkSize number of bytes, but we trust the implementations
process(buffer);
}
buffer.compact(); // preserve any remaining data that do not make a full chunk
}
// Clear Buffer
protected AbstractStreamingHasher clear() {
buffer.clear();
return this;
}
}