netty5/buffer/src/main/java/io/net5/buffer/api/Buffer.java

/*
 * Copyright 2021 The Netty Project
 *
 * The Netty Project licenses this file to you 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:
 *
 *   https://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 io.net5.buffer.api;

import java.nio.ByteBuffer;

/**
 * A life cycled buffer of memory, with separate reader and writer offsets.
 * <p>
 * A buffer is a logically sequential stretch of memory with a certain capacity, an offset for writing,
 * and an offset for reading.
 * Buffers may be {@linkplain CompositeBuffer composed} of multiple {@linkplain #countComponents() components},
 * where each component is a guaranteed contiguous chunk of memory.
 *
 * <h3>Creating a buffer</h3>
 *
 * Buffers are created by {@linkplain BufferAllocator allocators}, and their {@code allocate} family of methods.
 * A number of standard allocators exist, and are available through static methods on the {@code BufferAllocator}
 * interface.
 *
 * <h3>Buffer life cycle</h3>
 *
 * The buffer has a life cycle, where it is allocated, used, and deallocated.
 * When the buffer is initially allocated, a pairing {@link #close()} call will deallocate it.
 * If a buffer is {@linkplain #send() sent} elsewhere, the {@linkplain #close() close} method on the given instance
 * will become a no-op.
 * The buffer can be thought of as a view onto memory, and calling {@link #send()} on the buffer will effectively close
 * that view, and recreate it upon reception at its destination.
 *
 * <h3>Thread-safety</h3>
 *
 * Buffers are <strong>not</strong> thread-safe.
 *
 * <h3>Accessing data</h3>
 *
 * Data access methods fall into two classes:
 * <ol>
 *     <li>Access that are based on, and updates, the read or write offset positions.</li>
 *     <ul><li>These accessor methods are typically called {@code readX} or {@code writeX}.</li></ul>
 *     <li>Access that take offsets as arguments, and do not update read or write offset positions.</li>
 *     <ul><li>These accessor methods are typically called {@code getX} or {@code setX}.</li></ul>
 * </ol>
 *
 * A buffer contains two mutable offset positions: one for reading and one for writing.
 * These positions use <a href="https://en.wikipedia.org/wiki/Zero-based_numbering">zero-based indexing</a>,
 * such that the first byte of data in the buffer is placed at offset {@code 0},
 * and the last byte in the buffer is at offset {@link #capacity() capacity - 1}.
 * The {@link #readerOffset()} is the offset into the buffer from which the next read will take place,
 * and is initially zero.
 * The reader offset must always be less than or equal to the {@link #writerOffset()}.
 * The {@link #writerOffset()} is likewise the offset into the buffer where the next write will take place.
 * The writer offset is also initially zero, and must be less than or equal to the {@linkplain #capacity() capacity}.
 * <p>
 * This carves the buffer into three regions, as demonstrated by this diagram:
 * <pre>
 *      +-------------------+------------------+------------------+
 *      | discardable bytes |  readable bytes  |  writable bytes  |
 *      |                   |     (CONTENT)    |                  |
 *      +-------------------+------------------+------------------+
 *      |                   |                  |                  |
 *      0      <=     readerOffset  <=   writerOffset    <=    capacity
 * </pre>
 *
 * <h3>Byte Order</h3>
 *
 * Buffers are always big endian, and this cannot be changed.
 * Usages that need to get, set, read, or write, little-endian values will have to flip the byte order of the values
 * they read and write.
 *
 * <h3 name="split">Splitting buffers</h3>
 *
 * The {@link #split()} method breaks a buffer into two.
 * The two buffers will share the underlying memory, but their regions will not overlap, ensuring that the memory is
 * safely shared between the two.
 * <p>
 * Splitting a buffer is useful for when you want to hand over a region of a buffer to some other,
 * perhaps unknown, piece of code, and relinquish your ownership of that buffer region in the process.
 * Examples include aggregating messages into an accumulator buffer, and sending messages down the pipeline for
 * further processing, as split buffer regions, once their data has been received in its entirety.
 *
 * If you instead wish to temporarily share a region of a buffer, you will have to pass offset and length along with the
 * buffer, or you will have to make a copy of the region.
 *
 * <h3>Buffers as constants</h3>
 *
 * Sometimes, the same bit of data will be processed or transmitted over and over again. In such cases, it can be
 * tempting to allocate and fill a buffer once, and then reuse it.
 * Such reuse must be done carefully, however, to avoid a number of bugs.
 * The {@link BufferAllocator} has a {@link BufferAllocator#constBufferSupplier(byte[])} method that solves this, and
 * prevents these bugs from occurring.
 */
public interface Buffer extends Resource<Buffer>, BufferAccessor {
    /**
     * The capacity of this buffer, that is, the maximum number of bytes it can contain.
     *
     * @return The capacity in bytes.
     */
    int capacity();

    /**
     * Get the current reader offset. The next read will happen from this byte offset into the buffer.
     *
     * @return The current reader offset.
     */
    int readerOffset();

    /**
     * Set the reader offset. Make the next read happen from the given offset into the buffer.
     *
     * @param offset The reader offset to set.
     * @return This Buffer.
     * @throws IndexOutOfBoundsException if the specified {@code offset} is less than zero or greater than the current
     *                                   {@link #writerOffset()}.
     * @throws BufferClosedException if this buffer is closed.
     */
    Buffer readerOffset(int offset);

    /**
     * Get the current writer offset. The next write will happen at this byte offset into the buffer.
     *
     * @return The current writer offset.
     */
    int writerOffset();

    /**
     * Set the writer offset. Make the next write happen at the given offset.
     *
     * @param offset The writer offset to set.
     * @return This Buffer.
     * @throws IndexOutOfBoundsException if the specified {@code offset} is less than the current
     * {@link #readerOffset()} or greater than {@link #capacity()}.
     * @throws BufferClosedException if this buffer is closed.
     * @throws BufferReadOnlyException if this buffer is {@linkplain #readOnly() read-only}.
     */
    Buffer writerOffset(int offset);

    /**
     * Returns the number of readable bytes which is equal to {@code (writerOffset() - readerOffset())}.
     */
    default int readableBytes() {
        return writerOffset() - readerOffset();
    }

    /**
     * Returns the number of writable bytes which is equal to {@code (capacity() - writerOffset())}.
     */
    default int writableBytes() {
        return capacity() - writerOffset();
    }

    /**
     * Fills the buffer with the given byte value. This method does not respect the {@link #readerOffset()} or {@link
     * #writerOffset()}, but copies the full capacity of the buffer. The {@link #readerOffset()} and {@link
     * #writerOffset()} are not modified.
     *
     * @param value The byte value to write at every offset in the buffer.
     * @return This Buffer.
     * @throws BufferReadOnlyException if this buffer is {@linkplain #readOnly() read-only}.
     */
    Buffer fill(byte value);

    /**
     * Makes this buffer read-only. This is irreversible.
     * This operation is also idempotent, so calling this method multiple times on the same buffer makes no difference.
     *
     * @return This buffer instance.
     */
    Buffer makeReadOnly();

    /**
     * Queries if this buffer is read-only or not.
     *
     * @return {@code true} if this buffer is read-only, {@code false} otherwise.
     */
    boolean readOnly();

    /**
     * Copies the given length of data from this buffer into the given destination array, beginning at the given source
     * position in this buffer, and the given destination position in the destination array.
     * <p>
     * This method does not read or modify the {@linkplain #writerOffset() write offset} or the
     * {@linkplain #readerOffset() read offset}.
     *
     * @param srcPos The byte offset into this buffer from where the copying should start; the byte at this offset in
     *              this buffer will be copied to the {@code destPos} index in the {@code dest} array.
     * @param dest The destination byte array.
     * @param destPos The index into the {@code dest} array from where the copying should start.
     * @param length The number of bytes to copy.
     * @throws NullPointerException if the destination array is null.
     * @throws IndexOutOfBoundsException if the source or destination positions, or the length, are negative,
     * or if the resulting end positions reaches beyond the end of either this buffer, or the destination array.
     * @throws BufferClosedException if this buffer is closed.
     */
    void copyInto(int srcPos, byte[] dest, int destPos, int length);

    /**
     * Copies the given length of data from this buffer into the given destination byte buffer, beginning at the given
     * source position in this buffer, and the given destination position in the destination byte buffer.
     * <p>
     * This method does not read or modify the {@linkplain #writerOffset() write offset} or the
     * {@linkplain #readerOffset() read offset}, nor is the position of the destination buffer changed.
     * <p>
     * The position and limit of the destination byte buffer are also ignored, and do not influence {@code destPos}
     * or {@code length}.
     *
     * @param srcPos The byte offset into this buffer from where the copying should start; the byte at this offset in
     *              this buffer will be copied to the {@code destPos} index in the {@code dest} array.
     * @param dest The destination byte buffer.
     * @param destPos The index into the {@code dest} array from where the copying should start.
     * @param length The number of bytes to copy.
     * @throws NullPointerException if the destination buffer is null.
     * @throws IndexOutOfBoundsException if the source or destination positions, or the length, are negative,
     * or if the resulting end positions reaches beyond the end of either this buffer, or the destination array.
     * @throws java.nio.ReadOnlyBufferException if the destination buffer is read-only.
     * @throws BufferClosedException if this buffer is closed.
     */
    void copyInto(int srcPos, ByteBuffer dest, int destPos, int length);

    /**
     * Copies the given length of data from this buffer into the given destination buffer, beginning at the given
     * source position in this buffer, and the given destination position in the destination buffer.
     * <p>
     * This method does not read or modify the {@linkplain #writerOffset() write offset} or the
     * {@linkplain #readerOffset() read offset} on this buffer, nor on the destination buffer.
     * <p>
     * The read and write offsets of the destination buffer are also ignored, and do not influence {@code destPos}
     * or {@code length}.
     *
     * @param srcPos The byte offset into this buffer from where the copying should start; the byte at this offset in
     *              this buffer will be copied to the {@code destPos} index in the {@code dest} array.
     * @param dest The destination buffer.
     * @param destPos The index into the {@code dest} array from where the copying should start.
     * @param length The number of bytes to copy.
     * @throws NullPointerException if the destination buffer is null.
     * @throws IndexOutOfBoundsException if the source or destination positions, or the length, are negative,
     * or if the resulting end positions reaches beyond the end of either this buffer, or the destination array.
     * @throws BufferReadOnlyException if the destination buffer is read-only.
     * @throws BufferClosedException if this or the destination buffer is closed.
     */
    void copyInto(int srcPos, Buffer dest, int destPos, int length);

    /**
     * Writes into this buffer, all the readable bytes from the given buffer.
     * This updates the {@linkplain #writerOffset() write offset} of this buffer, and the
     * {@linkplain #readerOffset() reader offset} of the given buffer.
     *
     * @param source The buffer to read from.
     * @return This buffer.
     * @throws NullPointerException If the source buffer is {@code null}.
     */
    default Buffer writeBytes(Buffer source) {
        int size = source.readableBytes();
        int woff = writerOffset();
        source.copyInto(source.readerOffset(), this, woff, size);
        source.readerOffset(source.readerOffset() + size);
        writerOffset(woff + size);
        return this;
    }

    /**
     * Writes into this buffer, all the bytes from the given byte array.
     * This updates the {@linkplain #writerOffset() write offset} of this buffer by the length of the array.
     *
     * @param source The byte array to read from.
     * @return This buffer.
     */
    default Buffer writeBytes(byte[] source) {
        return writeBytes(source, 0, source.length);
    }

    /**
     * Writes into this buffer, all the bytes from the given byte array.
     * This updates the {@linkplain #writerOffset() write offset} of this buffer by the length of the array.
     *
     * @param source The byte array to read from.
     * @param srcPos Position in the {@code source} from where bytes should be written to this buffer.
     * @param length The number of bytes to copy.
     * @return This buffer.
     */
    default Buffer writeBytes(byte[] source, int srcPos, int length) {
        int woff = writerOffset();
        writerOffset(woff + length);
        for (int i = 0; i < length; i++) {
            setByte(woff + i, source[srcPos + i]);
        }
        return this;
    }

    /**
     * Resets the {@linkplain #readerOffset() read offset} and the {@linkplain #writerOffset() write offset} on this
     * buffer to zero, and return this buffer.
     *
     * @return This buffer instance.
     */
    default Buffer resetOffsets() {
        readerOffset(0);
        writerOffset(0);
        return this;
    }

    /**
     * Opens a cursor to iterate the readable bytes of this buffer. The {@linkplain #readerOffset() reader offset} and
     * {@linkplain #writerOffset() writer offset} are not modified by the cursor.
     * <p>
     * Care should be taken to ensure that the buffer's lifetime extends beyond the cursor and the iteration, and that
     * the {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified
     * while the iteration takes place. Otherwise, unpredictable behaviour might result.
     *
     * @return A {@link ByteCursor} for iterating the readable bytes of this buffer.
     */
    ByteCursor openCursor();

    /**
     * Opens a cursor to iterate the given number bytes of this buffer, starting at the given offset.
     * The {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified by
     * the cursor.
     * <p>
     * Care should be taken to ensure that the buffer's lifetime extends beyond the cursor and the iteration, and that
     * the {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified
     * while the iteration takes place. Otherwise, unpredictable behaviour might result.
     *
     * @param fromOffset The offset into the buffer where iteration should start.
     *                  The first byte read from the iterator will be the byte at this offset.
     * @param length The number of bytes to iterate.
     * @return A {@link ByteCursor} for the given stretch of bytes of this buffer.
     * @throws IllegalArgumentException if the length is negative, or if the region given by the {@code fromOffset} and
     * the {@code length} reaches outside the bounds of this buffer.
     */
    ByteCursor openCursor(int fromOffset, int length);

    /**
     * Opens a cursor to iterate the readable bytes of this buffer, in reverse.
     * The {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified by
     * the cursor.
     * <p>
     * Care should be taken to ensure that the buffer's lifetime extends beyond the cursor and the iteration, and that
     * the {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified
     * while the iteration takes place. Otherwise, unpredictable behaviour might result.
     *
     * @return A {@link ByteCursor} for the readable bytes of this buffer.
     */
    default ByteCursor openReverseCursor() {
        int woff = writerOffset();
        return openReverseCursor(woff == 0? 0 : woff - 1, readableBytes());
    }

    /**
     * Opens a cursor to iterate the given number bytes of this buffer, in reverse, starting at the given offset.
     * The {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified by
     * the cursor.
     * <p>
     * Care should be taken to ensure that the buffer's lifetime extends beyond the cursor and the iteration, and that
     * the {@linkplain #readerOffset() reader offset} and {@linkplain #writerOffset() writer offset} are not modified
     * while the iteration takes place. Otherwise, unpredictable behaviour might result.
     *
     * @param fromOffset The offset into the buffer where iteration should start.
     *                  The first byte read from the iterator will be the byte at this offset.
     * @param length The number of bytes to iterate.
     * @return A {@link ByteCursor} for the given stretch of bytes of this buffer.
     * @throws IllegalArgumentException if the length is negative, or if the region given by the {@code fromOffset} and
     * the {@code length} reaches outside the bounds of this buffer.
     */
    ByteCursor openReverseCursor(int fromOffset, int length);

    /**
     * Ensures that this buffer has at least the given number of bytes of
     * {@linkplain #writableBytes() available space for writing}.
     * If this buffer already has the necessary space, then this method returns immediately.
     * If this buffer does not already have the necessary space, then it will be expanded using the
     * {@link BufferAllocator} the buffer was created with.
     * This method is the same as calling {@link #ensureWritable(int, int, boolean)} where {@code allowCompaction} is
     * {@code false}.
     *
     * @param size The requested number of bytes of space that should be available for writing.
     * @return This buffer instance.
     * @throws IllegalStateException if this buffer is in a bad state.
     * @throws BufferClosedException if this buffer is closed.
     * @throws BufferReadOnlyException if this buffer is {@linkplain #readOnly() read-only}.
     */
    default Buffer ensureWritable(int size) {
        ensureWritable(size, 1, true);
        return this;
    }

    /**
     * Ensures that this buffer has at least the given number of bytes of
     * {@linkplain #writableBytes() available space for writing}.
     * If this buffer already has the necessary space, then this method returns immediately.
     * If this buffer does not already have the necessary space, then space will be made available in one or all of
     * the following available ways:
     *
     * <ul>
     *     <li>
     *         If {@code allowCompaction} is {@code true}, and sum of the read and writable bytes would be enough to
     *         satisfy the request, and it (depending on the buffer implementation) seems faster and easier to compact
     *         the existing buffer rather than allocation a new buffer, then the requested bytes will be made available
     *         that way. The compaction will not necessarily work the same way as the {@link #compact()} method, as the
     *         implementation may be able to make the requested bytes available with less effort than is strictly
     *         mandated by the {@link #compact()} method.
     *     </li>
     *     <li>
     *         Regardless of the value of the {@code allowCompaction}, the implementation may make more space available
     *         by just allocating more or larger buffers. This allocation would use the same {@link BufferAllocator}
     *         that this buffer was created with.
     *     </li>
     *     <li>
     *         If {@code allowCompaction} is {@code true}, then the implementation may choose to do a combination of
     *         compaction and allocation.
     *     </li>
     * </ul>
     *
     * @param size The requested number of bytes of space that should be available for writing.
     * @return This buffer instance.
     * @param minimumGrowth The minimum number of bytes to grow by. If it is determined that memory should be allocated
     *                     and copied, make sure that the new memory allocation is bigger than the old one by at least
     *                     this many bytes. This way, the buffer can grow by more than what is immediately necessary,
     *                     thus amortising the costs of allocating and copying.
     * @param allowCompaction {@code true} if the method is allowed to modify the
     *                                   {@linkplain #readerOffset() reader offset} and
     *                                   {@linkplain #writerOffset() writer offset}, otherwise {@code false}.
     * @throws BufferReadOnlyException if this buffer is {@linkplain #readOnly() read-only}.
     * @throws IllegalArgumentException if {@code size} or {@code minimumGrowth} are negative.
     * @throws IllegalStateException if this buffer is in a bad state.
     */
    Buffer ensureWritable(int size, int minimumGrowth, boolean allowCompaction);

    /**
     * Returns a copy of this buffer's readable bytes.
     * Modifying the content of the returned buffer will not affect this buffers contents.
     * The two buffers will maintain separate offsets. This method is identical to
     * {@code buf.copy(buf.readerOffset(), buf.readableBytes())}.
     * This method does not modify {@link #readerOffset()} or {@link #writerOffset()} of this buffer.
     * <p>
     * The copy is created with a {@linkplain #writerOffset() write offset} equal to the length of the copied data,
     * so that the entire contents of the copy is ready to be read.
     * <p>
     * The returned buffer will not be read-only, regardless of the {@linkplain #readOnly() read-only state} of this
     * buffer.
     *
     * @return A new buffer instance, with independent {@link #readerOffset()} and {@link #writerOffset()},
     * that contains a copy of the readable region of this buffer.
     * @throws BufferClosedException if this buffer is closed.
     */
    default Buffer copy() {
        int offset = readerOffset();
        int length = readableBytes();
        return copy(offset, length);
    }

    /**
     * Returns a copy of the given region of this buffer.
     * Modifying the content of the returned buffer will not affect this buffers contents.
     * The two buffers will  maintain separate offsets.
     * This method does not modify {@link #readerOffset()} or {@link #writerOffset()} of this buffer.
     * <p>
     * The copy is created with a {@linkplain #writerOffset() write offset} equal to the length of the copy,
     * so that the entire contents of the copy is ready to be read.
     * <p>
     * The returned buffer will not be read-only, regardless of the {@linkplain #readOnly() read-only state} of this
     * buffer.
     *
     * @param offset The offset where copying should start from. This is the offset of the first byte copied.
     * @param length The number of bytes to copy, and the capacity of the returned buffer.
     * @return A new buffer instance, with independent {@link #readerOffset()} and {@link #writerOffset()},
     * that contains a copy of the given region of this buffer.
     * @throws IllegalArgumentException if the {@code offset} or {@code length} reaches outside the bounds of the
     * buffer.
     * @throws BufferClosedException if this buffer is closed.
     */
    Buffer copy(int offset, int length);

    /**
     * Splits the buffer into two, at the {@linkplain #writerOffset() write offset} position.
     * <p>
     * The region of this buffer that contain the previously read and readable bytes, will be captured and returned in
     * a new buffer, that will hold its own ownership of that region. This allows the returned buffer to be
     * independently {@linkplain #send() sent} to other threads.
     * <p>
     * The returned buffer will adopt the {@link #readerOffset()} of this buffer, and have its {@link #writerOffset()}
     * and {@link #capacity()} both set to the equal to the write-offset of this buffer.
     * <p>
     * The memory region in the returned buffer will become inaccessible through this buffer. This buffer will have its
     * capacity reduced by the capacity of the returned buffer, and the read and write offsets of this buffer will both
     * become zero, even though their position in memory remain unchanged.
     * <p>
     * Effectively, the following transformation takes place:
     * <pre>{@code
     *         This buffer:
     *          +------------------------------------------+
     *         0|   |r/o                  |w/o             |cap
     *          +---+---------------------+----------------+
     *         /   /                     / \               \
     *        /   /                     /   \               \
     *       /   /                     /     \               \
     *      /   /                     /       \               \
     *     /   /                     /         \               \
     *    +---+---------------------+           +---------------+
     *    |   |r/o                  |w/o & cap  |r/o & w/o      |cap
     *    +---+---------------------+           +---------------+
     *    Returned buffer.                      This buffer.
     * }</pre>
     * When the buffers are in this state, both of the split parts retain an atomic reference count on the
     * underlying memory. This means that shared underlying memory will not be deallocated or returned to a pool, until
     * all the split parts have been closed.
     * <p>
     * Composite buffers have it a little easier, in that at most only one of the constituent buffers will actually be
     * split. If the split point lands perfectly between two constituent buffers, then a composite buffer can
     * simply split its internal array in two.
     * <p>
     * Split buffers support all operations that normal buffers do, including {@link #ensureWritable(int)}.
     * <p>
     * See the <a href="#split">Splitting buffers</a> section for details.
     *
     * @return A new buffer with independent and exclusive ownership over the previously read and readable bytes from
     * this buffer.
     */
    default Buffer split() {
        return split(writerOffset());
    }

    /**
     * Splits the buffer into two, at the given {@code splitOffset}.
     * <p>
     * The region of this buffer that precede the {@code splitOffset}, will be captured and returned in a new
     * buffer, that will hold its own ownership of that region. This allows the returned buffer to be independently
     * {@linkplain #send() sent} to other threads.
     * <p>
     * The returned buffer will adopt the {@link #readerOffset()} and {@link #writerOffset()} of this buffer,
     * but truncated to fit within the capacity dictated by the {@code splitOffset}.
     * <p>
     * The memory region in the returned buffer will become inaccessible through this buffer. If the
     * {@link #readerOffset()} or {@link #writerOffset()} of this buffer lie prior to the {@code splitOffset},
     * then those offsets will be moved forward, so they land on offset 0 after the split.
     * <p>
     * Effectively, the following transformation takes place:
     * <pre>{@code
     *         This buffer:
     *          +--------------------------------+
     *         0|               |splitOffset     |cap
     *          +---------------+----------------+
     *         /               / \               \
     *        /               /   \               \
     *       /               /     \               \
     *      /               /       \               \
     *     /               /         \               \
     *    +---------------+           +---------------+
     *    |               |cap        |               |cap
     *    +---------------+           +---------------+
     *    Returned buffer.            This buffer.
     * }</pre>
     * When the buffers are in this state, both of the split parts retain an atomic reference count on the
     * underlying memory. This means that shared underlying memory will not be deallocated or returned to a pool, until
     * all the split parts have been closed.
     * <p>
     * Composite buffers have it a little easier, in that at most only one of the constituent buffers will actually be
     * split. If the split point lands perfectly between two constituent buffers, then a composite buffer can
     * simply split its internal array in two.
     * <p>
     * Split buffers support all operations that normal buffers do, including {@link #ensureWritable(int)}.
     * <p>
     * See the <a href="#split">Splitting buffers</a> section for details.
     *
     * @param splitOffset The offset into this buffer where it should be split. After the split, the data at this offset
     *                    will be at offset zero in this buffer.
     * @return A new buffer with independent and exclusive ownership over the bytes from the beginning to the given
     * offset of this buffer.
     */
    Buffer split(int splitOffset);

    /**
     * Discards the read bytes, and moves the buffer contents to the beginning of the buffer.
     *
     * @return This buffer instance.
     * @throws BufferReadOnlyException if this buffer is {@linkplain #readOnly() read-only}.
     * @throws IllegalStateException if this buffer is in a bad state.
     */
    Buffer compact();

    /**
     * Get the number of "components" in this buffer. For composite buffers, this is the number of transitive
     * constituent buffers, while non-composite buffers only have one component.
     *
     * @return The number of components in this buffer.
     */
    int countComponents();

    /**
     * Get the number of "components" in this buffer, that are readable. These are the components that would be
     * processed by {@link #forEachReadable(int, ReadableComponentProcessor)}. For composite buffers, this is the
     * number of transitive constituent buffers that are readable, while non-composite buffers only have at most one
     * readable component.
     * <p>
     * The number of readable components may be less than the {@link #countComponents() component count}, if not all of
     * them have readable data.
     *
     * @return The number of readable components in this buffer.
     */
    int countReadableComponents();

    /**
     * Get the number of "components" in this buffer, that are writable. These are the components that would be
     * processed by {@link #forEachWritable(int, WritableComponentProcessor)}. For composite buffers, this is the
     * number of transitive constituent buffers that are writable, while non-composite buffers only have at most one
     * writable component.
     * <p>
     * The number of writable components may be less than the {@link #countComponents() component count}, if not all of
     * them have space for writing.
     *
     * @return The number of writable components in this buffer.
     */
    int countWritableComponents();

    /**
     * Processes all readable components of this buffer, and return the number of components processed.
     * <p>
     * The given {@linkplain ReadableComponentProcessor processor} is called for each readable component in this buffer,
     * and passed a component index, for the given component in the iteration, and a {@link ReadableComponent} object
     * for accessing the data within the given component.
     * <p>
     * The component index is specific to the particular invocation of this method. The first call to the consumer will
     * be passed the given initial index, and the next call will be passed the initial index plus one, and so on.
     * <p>
     * The {@linkplain ReadableComponentProcessor component processor} may stop the iteration at any time by returning
     * {@code false}.
     * This will cause the number of components processed to be returned as a negative number (to signal early return),
     * and the number of components processed may then be less than the
     * {@linkplain #countReadableComponents() readable component count}.
     * <p>
     * <strong>Note</strong> that the {@link ReadableComponent} instance passed to the consumer could be reused for
     * multiple calls, so the data must be extracted from the component in the context of the iteration.
     * <p>
     * The {@link ByteBuffer} instances obtained from the component, share lifetime with that internal component.
     * This means they can be accessed as long as the internal memory store remain unchanged. Methods that may cause
     * such changes are {@link #split(int)}, {@link #split()}, {@link #compact()}, {@link #ensureWritable(int)},
     * {@link #ensureWritable(int, int, boolean)}, and {@link #send()}.
     * <p>
     * The best way to ensure this doesn't cause any trouble, is to use the buffers directly as part of the iteration.
     * <p>
     * <strong>Note</strong> that the arrays, memory addresses, and byte buffers exposed as components by this method,
     * should not be used for changing the buffer contents. Doing so may cause undefined behaviour.
     * <p>
     * Changes to position and limit of the byte buffers exposed via the processed components, are not reflected back to
     * this buffer instance.
     *
     * @param initialIndex The initial index of the iteration, and the index that will be passed to the first call to
     *                    the {@linkplain ReadableComponentProcessor#process(int, ReadableComponent) processor}.
     * @param processor The processor that will be used to process the buffer components.
     * @return The number of readable components processed, as a positive number if all readable components were
     * processed, or as a negative number if the iteration was stopped because
     * {@link ReadableComponentProcessor#process(int, ReadableComponent)} returned {@code false}.
     * In any case, the number of components processed may be less than {@link #countComponents()}.
     */
    <E extends Exception> int forEachReadable(int initialIndex, ReadableComponentProcessor<E> processor) throws E;

    /**
     * Process all writable components of this buffer, and return the number of components processed.
     * <p>
     * The given {@linkplain WritableComponentProcessor processor} is called for each writable component in this buffer,
     * and passed a component index, for the given component in the iteration, and a {@link WritableComponent} object
     * for accessing the data within the given component.
     * <p>
     * The component index is specific to the particular invocation of this method. The first call to the consumer will
     * be passed the given initial index, and the next call will be passed the initial index plus one, and so on.
     * <p>
     * The {@link WritableComponentProcessor component processor} may stop the iteration at any time by returning
     * {@code false}.
     * This will cause the number of components processed to be returned as a negative number (to signal early return),
     * and the number of components processed may then be less than the
     * {@linkplain #countReadableComponents() readable component count}.
     * <p>
     * <strong>Note</strong> that the {@link WritableComponent} instance passed to the consumer could be reused for
     * multiple calls, so the data must be extracted from the component in the context of the iteration.
     * <p>
     * The {@link ByteBuffer} instances obtained from the component, share lifetime with that internal component.
     * This means they can be accessed as long as the internal memory store remain unchanged. Methods that may cause
     * such changes are {@link #split(int)}, {@link #split()}, {@link #compact()}, {@link #ensureWritable(int)},
     * {@link #ensureWritable(int, int, boolean)}, and {@link #send()}.
     * <p>
     * The best way to ensure this doesn't cause any trouble, is to use the buffers directly as part of the iteration.
     * <p>
     * Changes to position and limit of the byte buffers exposed via the processed components, are not reflected back to
     * this buffer instance.
     *
     * @param initialIndex The initial index of the iteration, and the index that will be passed to the first call to
     *                    the {@linkplain WritableComponentProcessor#process(int, WritableComponent) processor}.
     * @param processor The processor that will be used to process the buffer components.
     * @return The number of writable components processed, as a positive number if all writable components were
     * processed, or as a negative number if the iteration was stopped because
     * {@link WritableComponentProcessor#process(int, WritableComponent)} returned {@code false}.
     * In any case, the number of components processed may be less than {@link #countComponents()}.
     */
    <E extends Exception> int forEachWritable(int initialIndex, WritableComponentProcessor<E> processor) throws E;
}