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The Async Http Client (AHC) classes.
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/*
 * Copyright (c) 2015 AsyncHttpClient Project. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at
 *     http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */
package org.asynchttpclient.util;

import io.netty.buffer.ByteBuf;

import java.io.UTFDataFormatException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.StandardCharsets;
import java.util.List;

public final class ByteBufUtils {

    public static final byte[] EMPTY_BYTE_ARRAY = new byte[0];

    private ByteBufUtils() {
    }

    public static String byteBuf2String(ByteBuf buf, Charset charset) throws UTFDataFormatException, IndexOutOfBoundsException, CharacterCodingException {

        int byteLen = buf.readableBytes();

        if (charset.equals(StandardCharsets.US_ASCII)) {
            return Utf8Reader.readUtf8(buf, byteLen);
        } else if (charset.equals(StandardCharsets.UTF_8)) {
            try {
                return Utf8Reader.readUtf8(buf.duplicate(), (int) (byteLen * 1.4));
            } catch (IndexOutOfBoundsException e) {
                // try again with 3 bytes per char
                return Utf8Reader.readUtf8(buf, byteLen * 3);
            }
        } else {
            return byteBuffersToString(buf.nioBuffers(), charset);
        }
    }

    private static String byteBuffersToString(ByteBuffer[] bufs, Charset cs) throws CharacterCodingException {

        CharsetDecoder cd = cs.newDecoder();
        int len = 0;
        for (ByteBuffer buf : bufs) {
            len += buf.remaining();
        }
        int en = (int) (len * (double) cd.maxCharsPerByte());
        char[] ca = new char[en];
        cd.reset();
        CharBuffer cb = CharBuffer.wrap(ca);

        CoderResult cr = null;

        for (int i = 0; i < bufs.length; i++) {

            ByteBuffer buf = bufs[i];
            cr = cd.decode(buf, cb, i < bufs.length - 1);
            if (!cr.isUnderflow())
                cr.throwException();
        }

        cr = cd.flush(cb);
        if (!cr.isUnderflow())
            cr.throwException();

        return new String(ca, 0, cb.position());
    }

    public static byte[] byteBuf2Bytes(ByteBuf buf) {
        int readable = buf.readableBytes();
        int readerIndex = buf.readerIndex();
        if (buf.hasArray()) {
            byte[] array = buf.array();
            if (buf.arrayOffset() == 0 && readerIndex == 0 && array.length == readable) {
                return array;
            }
        }
        byte[] array = new byte[readable];
        buf.getBytes(readerIndex, array);
        return array;
    }

    public static byte[] byteBufs2Bytes(List bufs) {

        if (bufs.isEmpty()) {
            return EMPTY_BYTE_ARRAY;

        } else if (bufs.size() == 1) {
            return byteBuf2Bytes(bufs.get(0));

        } else {
            int totalSize = 0;
            for (ByteBuf buf : bufs) {
                totalSize += buf.readableBytes();
            }

            byte[] bytes = new byte[totalSize];
            int offset = 0;
            for (ByteBuf buf : bufs) {
                int readable = buf.readableBytes();
                buf.getBytes(buf.readerIndex(), bytes, offset, readable);
                offset += readable;
            }
            return bytes;
        }
    }
}