default int readUnsignedShort() {
        return (readByte() & 0xFF) << 8 | readByte();
    }
Reads an unsigned short from the readable bytes.

@throws IllegalStateException if the {@link #readableBytes()} is less than {@code 2} bytes.
core/src/main/java/com/linecorp/armeria/common/stream/StreamDecoderInput.java