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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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.android.server.wifi.util;
import java.util.ArrayList;
/**
* A ring buffer where each element of the ring is itself a byte array.
*/
public class ByteArrayRingBuffer {
private ArrayList<byte[]> mArrayList;
private int mMaxBytes;
private int mBytesUsed;
/**
* Creates a ring buffer that holds at most |maxBytes| of data. The overhead for each element
* is not included in this limit.
* @param maxBytes upper bound on the amount of data to hold
*/
public ByteArrayRingBuffer(int maxBytes) {
if (maxBytes < 1) {
throw new IllegalArgumentException();
}
mArrayList = new ArrayList<byte[]>();
mMaxBytes = maxBytes;
mBytesUsed = 0;
}
/**
* Adds |newData| to the ring buffer. Removes existing entries to make room, if necessary.
* Existing entries are removed in FIFO order.
* <p><b>Note:</b> will fail if |newData| itself exceeds the size limit for this buffer.
* Will first remove all existing entries in this case. (This guarantees that the ring buffer
* always represents a contiguous sequence of data.)
* @param newData data to be added to the ring
* @return true if the data was added
*/
public boolean appendBuffer(byte[] newData) {
pruneToSize(mMaxBytes - newData.length);
if (mBytesUsed + newData.length > mMaxBytes) {
return false;
}
mArrayList.add(newData);
mBytesUsed += newData.length;
return true;
}
/**
* Returns the |i|-th element of the ring. The element retains its position in the ring.
* @param i
* @return the requested element
*/
public byte[] getBuffer(int i) {
return mArrayList.get(i);
}
/**
* Returns the number of elements present in the ring.
* @return the number of elements present
*/
public int getNumBuffers() {
return mArrayList.size();
}
/**
* Resize the buffer, removing existing data if necessary.
* @param maxBytes upper bound on the amount of data to hold
*/
public void resize(int maxBytes) {
pruneToSize(maxBytes);
mMaxBytes = maxBytes;
}
private void pruneToSize(int sizeBytes) {
int newBytesUsed = mBytesUsed;
int i = 0;
while (i < mArrayList.size() && newBytesUsed > sizeBytes) {
newBytesUsed -= mArrayList.get(i).length;
i++;
}
mArrayList.subList(0, i).clear();
mBytesUsed = newBytesUsed;
}
}
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