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cl-conspack

Previously, I’ve posted about the cl-bert a serialization library. “cl-conspack” is also a serialization library with interesting features.

These features are:

  • compact binary representation;
  • support for object references;
  • and speed.

Let’s compare it with cl-bert:

POFTHEDAY> (bert:encode (list :hello
                              :lisp
                              :world!))
#(131 108 0 0 0 3 115 5 72 69 76 76 79
  115 4 76 73 83 80 115 6 87 79 82 76 68
  33 106)
POFTHEDAY> (length *)
28

POFTHEDAY> (conspack:encode (list :hello
                                  :lisp
                                  :world!))
#(40 4 131 64 5 72 69 76 76 79 131 64 4 76
  73 83 80 131 64 6 87 79 82 76 68 33 0)
POFTHEDAY> (length *)
27

As you can see, conspack’s result is one byte smaller, but we can squeeze more if we provide some knowledge about data to the “conspack”:

POFTHEDAY> (conspack:with-index (:hello :lisp :world!)
             (conspack:encode (list :hello
                                    :lisp
                                    :world!)))
#(40 4 176 177 178 0)
POFTHEDAY> (length *)
6 (3 bits, #x6, #o6, #b110)
POFTHEDAY> (conspack:with-index (:hello :lisp :world!)
             (conspack:decode **))
(:HELLO :LISP :WORLD!)
6

As you can see, now our data is only 6 bytes. This will work very good when you data uses many duplicate symbols.

In the next example, we will test how do links work:

POFTHEDAY> (defclass node ()
             ((name :type keyword
                    :initarg :name
                    :reader get-name)
              (next :type (or null
                              node)
                    :initform nil
                    :accessor get-next)))

POFTHEDAY> (defmethod print-object ((node node) stream)
             (format stream "<node ~A>" (get-name node)))

POFTHEDAY> (defparameter *first* (make-instance 'node :name :first))
POFTHEDAY> (defparameter *second* (make-instance 'node :name :second))

POFTHEDAY> (setf (get-next *first*)
                 *second*)

POFTHEDAY> (setf (get-next *second*)
                 *first*)

;; Now we need to tell cl-conspack which slots should be
;; serialized.
POFTHEDAY> (conspack:defencoding node
             name next)

POFTHEDAY> (conspack:tracking-refs ()
             (conspack:encode *first*))
#(242 56 2 130 64 4 78 79 68 69 129 64 9 80 79 70 84 72 69 68 65 89 240 130 64
  4 78 65 77 69 129 64 9 80 79 70 84 72 69 68 65 89 131 64 5 70 73 82 83 84 241
  130 64 4 78 69 88 84 129 64 9 80 79 70 84 72 69 68 65 89 56 2 130 64 4 78 79
  68 69 129 64 9 80 79 70 84 72 69 68 65 89 112 131 64 6 83 69 67 79 78 68 113
  114)

POFTHEDAY> (length *)
103

POFTHEDAY> (conspack:tracking-refs ()
             (conspack:decode **))
<node FIRST>

POFTHEDAY> (get-next *)
<node SECOND>

POFTHEDAY> (get-next *)
#S(CONSPACK::FORWARD-REF :TYPE :CDR :REF (NEXT . <node FIRST>) :DATUM NIL)

As you can see, “cl-conspack” broke the circular loop, but wasn’t able to restore it completely.

Probably, this could be improved.

Now let’s combine compression with object serialization. In the previous example, serialized data took 103 bytes. Let’s see how much we can squeeze:

POFTHEDAY> (conspack:with-index (node name next :first :second)
             (conspack:tracking-refs ()
               (conspack:encode *first*)))
#(242 56 2 176 240 177 179 241 178 56 2 176 112 180 113 114)

POFTHEDAY> (length *)
16

16 bytes. Not bad!

Seems, cl-conspack could be good for making a binary RPC protocol. By the way, it already has implementations not only for Common Lisp but also for Python and C.

See also