((type :initform 0 :initarg :type :type octet :accessor tlv-type)

    (length :initform 0 :initarg :length :type (unsigned-byte 16) :accessor tlv-length)

    (value :initform (make-array 0 :element-type 'octet) :initarg :value :type octet-vector :accessor tlv-value))

   (:documentation "TypeLengthValue object.

 TLVs are a common packet format in communication protocols. Objects of

 this type are assumed to have a 1 byte TYPE, a 2 byte LENGTH, and a

 VALUE which is an OCTET-VECTOR of length LENGTH."))

     (let ((buf (make-array (+ 3 length) :element-type 'octet)))

       (setf (subseq buf 1 2) (integer-to-octets length 16))

       (unless (= 0 length)

         (setf (subseq buf 4) value))

 (defun make-tlv (type length &optional (value #.(make-array 0 :element-type 'octet)))

   (make-instance 'tlv :type type :length length :value value))

 (defmethod serialize ((obj tlv) (format (eql :string)) &key stream (external-format :default))

   (declare (ignore format stream))

   (sb-ext:octets-to-string (serialize obj :bytes) :external-format external-format))

 (defmethod deserialize ((from simple-array) (format (eql :tlv)) &key)

   (declare (ignore format))

   (let ((type (aref from 0))

         (length (octets-to-integer (subseq from 1 3))))

     (if (= 0 length)

         (make-tlv type length)

         (let ((value (subseq from 3 (+ 3 length))))

           (funcall #'make-tlv type length value)))))

 (defmethod deserialize ((from stream) (format (eql :tlv)) &key)

   (let ((type (read-byte from))

         (l (make-array 2 :element-type 'octet :adjustable t)))

     (read-sequence l from)

     (let ((length (octets-to-integer (coerce l 'octet-vector) 2)))

       (if (= 0 length)

           (make-tlv type length nil)

           (let ((value (make-array length :element-type 'octet)))

             (read-sequence value from)

             (make-tlv type length value))))))

 (defmethod serde ((from tlv) (to simple-array))

   (with-slots (type length value) from

     (setf (aref to 0) type)

     (replace to (integer-to-octets length 16) :start1 1 :start2 2)

     (unless (= 0 length)

       (replace to value :start1 3 :end1 (+ 3 length)))

     to))

 #+nil

 (describe

  (deserialize

   (serialize (make-instance 'tlv) :bytes)

   :tlv))