(in-package :cl-user)

;; User API functions
(defun read-byte-no-hang (stream &optional eof-error-p eof-value)
  (let ((byte (stream-read-byte-no-hang stream)))
    (cond ((eq ':eof byte)
           (if eof-error-p
               (error 'end-of-file :stream stream)
               eof-value))
          (t byte))))

#+CCL
(defmethod stream-read-byte-no-hang (stream)
  (ccl:with-input-timeout ((stream) 0)
    (handler-case
        (read-byte stream nil :eof)
      (ccl:input-timeout ()
        nil))))

#+SBCL
(defmethod stream-read-byte-no-hang (input-stream)
  (sb-sys:with-deadline (:seconds 0)
    (handler-case
        (read-byte input-stream nil :eof)
      (sb-sys:deadline-timeout ()
        nil))))