feat: add periodic lisp-chat/client ping to maintain TCP/IP socket

Fixes #17

Author: ryukinix

src/client.lisp

@@ -13,6 +13,12 @@
 (defvar *io-lock* (make-lock "io mutex")
   "I/O Mutex for avoid terminal race conditions")
 
+(defvar *periodic-ping-interval* 30
+  "Interval in seconds to send a ping to the server")
+
+(defvar *stop* nil
+  "Stop sign to end the client")
+
 (defun erase-last-line ()
   "Erase the last line by using ANSI Escape codes"
   (format t "~C[1A~C[2K" #\Esc #\Esc))
@@ -32,26 +38,31 @@
   (write-line message (socket-stream socket))
   (finish-output (socket-stream socket)))
 
+(defun system-pongp (message)
+  "SYSTEM-PONGP detect if a pong response was received as systematic send"
+  (search "[@server]: pong (system)" message))
+
 ;; HACK: I don't know a better way to save state of cl-readline
 ;; before printing messages from server, so I'm cleaning all the stuff
 ;; before print a new message, and restore again. Maybe there is a
 ;; better way for doing that.
 (defun receive-message (message)
   "Receive a message and print in the terminal carefully with IO race conditions"
   (with-lock-held (*io-lock*)
-    (let ((line cl-readline:*line-buffer*)
-          (prompt cl-readline:+prompt+))
-      ;; erase
-      (cl-readline:replace-line "" nil)
-      (cl-readline:set-prompt "")
-      (cl-readline:redisplay)
-      ;; print message from server
-      (write-line message)
-      ;; restore
-      (cl-readline:replace-line (or line "") nil)
-      (setq cl-readline:*point* cl-readline:+end+)
-      (cl-readline:set-prompt prompt)
-      (cl-readline:redisplay))))
+    (unless (system-pongp message)
+     (let ((line cl-readline:*line-buffer*)
+           (prompt cl-readline:+prompt+))
+       ;; erase
+       (cl-readline:replace-line "" nil)
+       (cl-readline:set-prompt "")
+       (cl-readline:redisplay)
+       ;; print message from server
+       (write-line message)
+       ;; restore
+       (cl-readline:replace-line (or line "") nil)
+       (setq cl-readline:*point* cl-readline:+end+)
+       (cl-readline:set-prompt prompt)
+       (cl-readline:redisplay)))))
 
 (defun client-sender (socket username)
   "Routine to check new messages being typed by the user"
@@ -87,6 +98,14 @@
     (send-message username socket)
     username))
 
+(defun client-background-ping (socket)
+  "Maintain TCP/IP connection by sending periodic ping to maintain connection alive.
+
+The systematic pong is consumed and the @server response is not shown in the terminal
+"
+  (loop (sleep *periodic-ping-interval*)
+        (ignore-errors
+         (send-message "/ping system" socket))))
 
 (defun client-loop (host port)
   "Dispatch client threads for basic functioning system"
@@ -96,7 +115,10 @@
     (let ((sender (make-thread (lambda () (client-sender socket username))
                                :name "client sender"))
           (broadcast (make-thread (lambda () (server-broadcast socket))
-                                  :name "server broadcast")))
+                                  :name "server broadcast"))
+          (background-ping (make-thread (lambda () (client-background-ping socket))
+                                        :name "background ping")))
+      (join-thread background-ping)
       (join-thread sender)
       (join-thread broadcast))))
 

src/server.lisp

@@ -18,7 +18,7 @@
 (defvar *uptime* (multiple-value-list (get-decoded-time))
   "Uptime of server variable")
 (defparameter *commands-names*
-  '("/users" "/help" "/log" "/quit" "/uptime" "/nick")
+  '("/users" "/help" "/log" "/quit" "/uptime" "/nick" "/ping")
   "Allowed command names to be called by client user")
 (defparameter *clients* nil "List of clients")
 (defparameter *messages-stack* nil "Messages pending to be send by broadcasting")
@@ -105,6 +105,11 @@
   (declare (ignorable client args))
   (command-message (format nil "~{~a~^, ~}" (mapcar #'client-name *clients*))))
 
+(defun /ping (client &rest args)
+  "Return a list separated by commas of the currently logged users"
+  (declare (ignorable client args))
+  (command-message (format nil "pong ~a" args)))
+
 
 (defun /help (client &rest args)
   "Show a list of the available commands of lisp-chat"