# Pastebin PHHt4I89
(defun recv-string-or-array-bytes (socket &key dontwait (encoding cffi:*default-foreign-encoding*))
  "Receive a message part from a socket as a string."
  (pzmq:with-message msg
    (pzmq:msg-recv msg socket :dontwait dontwait)
    (values
     (let* ((data (pzmq:msg-data msg))
            (len (pzmq:msg-size msg))
            (all-graphic-p (loop for index from 0 below len
                                 always (graphic-char-p (cffi:mem-aref data :uint8 index)))))
       (if all-graphic-p
           (cffi:foreign-string-to-lisp data :count len :encoding encoding)
           (let ((array-bytes (make-array len :element-type 'ext:byte8)))
             (loop for index from 0 below len
                   do (setf (aref array-bytes index) (cffi:mem-aref data :uint8 index)))
             array-bytes)))
     (pzmq:getsockopt socket :rcvmore))))