jnr-ffi example

libc.clj

(ns libc
  (:require [jise.core :refer [defclass]])
  (:import (jnr.ffi LibraryLoader
                    Pointer
                    Struct
                    Struct$SignedLong
                    Struct$time_t)
           (jnr.ffi.annotations Out Transient)))

;;
;;
;; Minimum Working Example for JNR/Clojure
;;
;;

(definterface LibCPrint
  (^int puts [^String x])
  (^int fflush [^jnr.ffi.Pointer stream]))

(def +cprint+ (-> (LibraryLoader/create LibCPrint)
                  (.load "c")))

;; This prints "Hello World" on a newline when run
(comment 
  
  (do (.puts +cprint+ "Hello World")
      (.fflush +cprint+ nil))

  (jnr.ffi.Runtime/getRuntime +cprint+)
  )


;;
;; Clojure Port of Gettimeofday
;;
;; JNR Reference: https://github.com/jnr/jnr-ffi-examples/blob/master/gettimeofday/src/main/java/gettimeofday/Gettimeofday.java
;; Clojure Reference: https://github.com/lvh/caesium/blob/master/src/caesium/binding.clj
;;



;; DOES NOT COMPILE
^{:public true}
(defclass Timeval [jnr.ffi.Struct]

  ^:public
  (def ^Struct$time_t tv_sec)

  ^:public
  (def ^Struct$SignedLong tv_usec)

  ^:public
  (defm Timeval [^jnr.ffi.Runtime rt]
    (super rt)
    (set! (.tv_sec this) (Struct$time_t.))
    (set! (.tv_usec this) (Struct$SignedLong.))))


(definterface LibCTimeOfDay
  (^int gettimeofday [^libc.Timeval ^{jnr.ffi.annotations.Out {}
                                      jnr.ffi.annotations.Transient {}} tv
                      ^jnr.ffi.Pointer stream]))

(def +ctimeofday+
  (-> (LibraryLoader/create LibCTimeOfDay)
      (.load "c")))


(comment
  
  (def +rt+ (jnr.ffi.Runtime/getRuntime +ctimeofday+))
  
  (def +tv+ (TimeVal. +rt+))

  ;; Prints out Time of day
  (do (.gettimeofday +tv+)
      (println (format "sec: %d, usec: %d"
                       (.. +tv+ -tv_sec get)
                       (.. +tv+ -tv_usec get)))))