ByteToMessageDecoder Class — netty Architecture

Source Code

codec-base/src/main/java/io/netty/handler/codec/ByteToMessageDecoder.java lines 78–604

public abstract class ByteToMessageDecoder extends ChannelInboundHandlerAdapter {

    /**
     * Cumulate {@link ByteBuf}s by merge them into one {@link ByteBuf}'s, using memory copies.
     */
    public static final Cumulator MERGE_CUMULATOR = new Cumulator() {
        @Override
        public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
            if (cumulation == in) {
                // when the in buffer is the same as the cumulation it is doubly retained, release it once
                in.release();
                return cumulation;
            }
            if (!cumulation.isReadable() && in.isContiguous()) {
                // If cumulation is empty and input buffer is contiguous, use it directly
                cumulation.release();
                return in;
            }
            try {
                final int required = in.readableBytes();
                if (required > cumulation.maxWritableBytes() ||
                    required > cumulation.maxFastWritableBytes() && cumulation.refCnt() > 1 ||
                    cumulation.isReadOnly()) {
                    // Expand cumulation (by replacing it) under the following conditions:
                    // - cumulation cannot be resized to accommodate the additional data
                    // - cumulation can be expanded with a reallocation operation to accommodate but the buffer is
                    //   assumed to be shared (e.g. refCnt() > 1) and the reallocation may not be safe.
                    return expandCumulation(alloc, cumulation, in);
                }
                cumulation.writeBytes(in, in.readerIndex(), required);
                in.readerIndex(in.writerIndex());
                return cumulation;
            } finally {
                // We must release in all cases as otherwise it may produce a leak if writeBytes(...) throw
                // for whatever release (for example because of OutOfMemoryError)
                in.release();
            }
        }
    };

    /**
     * Cumulate {@link ByteBuf}s by add them to a {@link CompositeByteBuf} and so do no memory copy whenever possible.
     * Be aware that {@link CompositeByteBuf} use a more complex indexing implementation so depending on your use-case
     * and the decoder implementation this may be slower than just use the {@link #MERGE_CUMULATOR}.
     */
    public static final Cumulator COMPOSITE_CUMULATOR = new Cumulator() {
        @Override
        public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
            if (cumulation == in) {
                // when the in buffer is the same as the cumulation it is doubly retained, release it once
                in.release();
                return cumulation;
            }
            if (!cumulation.isReadable()) {
                cumulation.release();
                return in;
            }
            CompositeByteBuf composite = null;
            try {
                if (cumulation instanceof CompositeByteBuf && cumulation.refCnt() == 1) {
                    composite = (CompositeByteBuf) cumulation;
                    // Writer index must equal capacity if we are going to "write"
                    // new components to the end
                    if (composite.writerIndex() != composite.capacity()) {
                        composite.capacity(composite.writerIndex());
                    }
                } else {
                    composite = alloc.compositeBuffer(Integer.MAX_VALUE).addFlattenedComponents(true, cumulation);
                }
                composite.addFlattenedComponents(true, in);
                in = null;
                return composite;
            } finally {
                if (in != null) {
                    // We must release if the ownership was not transferred as otherwise it may produce a leak
                    in.release();
                    // Also release any new buffer allocated if we're not returning it
                    if (composite != null && composite != cumulation) {
                        composite.release();
                    }
                }