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package com.qcloud.cos.utils;

import java.io.ByteArrayInputStream;
import java.nio.ByteBuffer;
import java.util.Arrays;

import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.binary.Hex;

/**
 * Utilities for encoding and decoding binary data to and from different forms.
 */
public class BinaryUtils {
    /**
     * Converts byte data to a Hex-encoded string in lower case.
     *
     * @param data data to hex encode.
     *
     * @return hex-encoded string.
     */
    public static String toHex(byte[] data) {
        return Hex.encodeHexString(data);
    }

    /**
     * Converts a Hex-encoded data string to the original byte data.
     *
     * @param hexData hex-encoded data to decode.
     * @return decoded data from the hex string.
     * @throws DecoderException
     */
    public static byte[] fromHex(String hexData) throws DecoderException {
        return Hex.decodeHex(hexData.toCharArray());
    }

    /**
     * Converts byte data to a Base64-encoded string.
     *
     * @param data data to Base64 encode.
     * @return encoded Base64 string.
     */
    public static String toBase64(byte[] data) {
        return Base64.encodeAsString(data);
    }

    /**
     * Converts a Base64-encoded string to the original byte data.
     *
     * @param b64Data a Base64-encoded string to decode.
     *
     * @return bytes decoded from a Base64 string.
     */
    public static byte[] fromBase64(String b64Data) {
        return b64Data == null ? null : Base64.decode(b64Data);
    }

    /**
     * Wraps a ByteBuffer in an InputStream. If the input {@code byteBuffer} is null, returns an
     * empty stream.
     *
     * @param byteBuffer The ByteBuffer to wrap.
     *
     * @return An InputStream wrapping the ByteBuffer content.
     */
    public static ByteArrayInputStream toStream(ByteBuffer byteBuffer) {
        if (byteBuffer == null) {
            return new ByteArrayInputStream(new byte[0]);
        }
        return new ByteArrayInputStream(copyBytesFrom(byteBuffer));
    }

    /**
     * Returns a copy of all the bytes from the given ByteBuffer, from the beginning to
     * the buffer's limit; or null if the input is null.
     * 
     * The internal states of the given byte buffer will be restored when this method completes
     * execution.
     * 

     * When handling ByteBuffer from user's input, it's typical to call the
     * {@link #copyBytesFrom(ByteBuffer)} instead of {@link #copyAllBytesFrom(ByteBuffer)} so as to
     * account for the position of the input ByteBuffer. The opposite is typically
     * true, however, when handling ByteBuffer from withint the unmarshallers of the
     * low-level clients.
     */
    public static byte[] copyAllBytesFrom(ByteBuffer bb) {
        if (bb == null) {
            return null;
        }

        if (bb.hasArray()) {
            return Arrays.copyOfRange(bb.array(), bb.arrayOffset(), bb.arrayOffset() + bb.limit());
        }

        ByteBuffer copy = bb.asReadOnlyBuffer();
        copy.rewind();

        byte[] dst = new byte[copy.remaining()];
        copy.get(dst);
        return dst;
    }

    /**
     * Returns a copy of the bytes from the given ByteBuffer, ranging from the the
     * buffer's current position to the buffer's limit; or null if the input is null.
     * 

     * The internal states of the given byte buffer will be restored when this method completes
     * execution.
     * 
     * When handling ByteBuffer from user's input, it's typical to call the
     * {@link #copyBytesFrom(ByteBuffer)} instead of {@link #copyAllBytesFrom(ByteBuffer)} so as to
     * account for the position of the input ByteBuffer. The opposite is typically
     * true, however, when handling ByteBuffer from withint the unmarshallers of the
     * low-level clients.
     */
    public static byte[] copyBytesFrom(ByteBuffer bb) {
        if (bb == null) {
            return null;
        }

        if (bb.hasArray()) {
            return Arrays.copyOfRange(bb.array(), bb.arrayOffset() + bb.position(),
                    bb.arrayOffset() + bb.limit());
        }

        byte[] dst = new byte[bb.remaining()];
        bb.asReadOnlyBuffer().get(dst);
        return dst;
    }
}