This library should be a drop in replacement for monkeylib-binary-data described in Peter Seibel's excellent book: you should start here.

It also contains the following optionals enhancements.

definition/access of octet size of objects

When defining a new binary-type, in addition to :reader and :writer definition, you can set a :size to calculate the octet size of this new type. You can then access this size with type-size

Here is an example from common-datatypes.lisp (that comes with binary-io ;-)

;;; Unsigned integers
(define-binary-type unsigned-integer (bits)
  (:reader (fd)
       (assert (equal (stream-element-type fd) '(unsigned-byte 8)))
       (let ((byte-indexes (byte-indexes bits *endianness*))
         (value 0))
         (dolist (i byte-indexes value)
           (setf (ldb (byte 8 i) value) (read-byte fd)))))
  (:writer (fd value)
       (assert (equal (stream-element-type fd) '(unsigned-byte 8)))
       (let ((byte-indexes (byte-indexes bits *endianness*)))
         (dolist (i byte-indexes)
           (write-byte (ldb (byte 8 i) value) fd))))
  (:size () (ceiling bits 8)))

(define-binary-type u2 () (unsigned-integer :bits 16))

(type-size 'u2) ;; -> 2

There is also an object-size method for binary class.

(define-binary-class test-size ()
  ((a u2)
   (b u2)))

(object-size 'test-size) ;; -> 4

optional initform for slots

You can precise an optional initform for a slot as a third value in the slot spec of a binary class definition:

(define-binary-class foo-header ()
  ((tag (8bit-string :length 4 :terminator #\Nul) "FOO")
   (counter u2 0)))

(tag (make-instance 'foo-header)) ;; -> "FOO"
Peter Seibel <>