public MessageHeaderDecoder wrap(final DirectBuffer buffer, final int offset)
    {
        if (buffer != this.buffer)
        {
            this.buffer = buffer;
        }
        this.offset = offset;

        return this;
    }
Message identifiers and length of message root.
sbe-tool/src/main/java/uk/co/real_logic/sbe/ir/generated/MessageHeaderDecoder.java