Changed the communication protocol: the first 4 bytes of each message

represent the message length

scontrini.rkt

@@ -12,6 +12,12 @@
 	(let ((file (open-input-file "pizza_list.json")))
 		(read-json file)))
 
+; Send the pizza list as a JSON, prepending it with 4 bytes that contain the list length
+(define (send-pizzas-list output)
+	(let ((pizzas-list (get-pizzas-list)))
+		(write-bytes (integer->integer-bytes (bytes-length (jsexpr->bytes pizzas-list)) 4 #f) output)
+		(write-json pizzas-list output)))
+
 ; Print the to-print string on the printer
 ; TODO add synchronization to avoid race conditions
 (define (printer-print to-print)
@@ -33,20 +39,18 @@
 		(case (hash-ref parsed-json 'command)
 			(("print") (printer-print (hash-ref parsed-json 'text)))
 			(("pizza") (printer-print (format-pizza (hash-ref parsed-json 'pizzas))))
-			(("get-pizzas") (write-json (get-pizzas-list) output)))))
+			(("get-pizzas") (send-pizzas-list output))
+			(else (displayln "Unknown command")))))
 
-; Execute the command specified in the JSON
+; Parse the JSON and execute the command specified in it
+;
+; Each message starts with the length of the JSON object, put into the first 4 bytes
 (define (execute-commands input output)
-	(let ((message ""))
-		(let loop-until-eof ((str (read-string 1 input)))
-			(if (eof-object? str)
-				(begin
-					(parse-json message output)
-					(close-input-port input)
-					(close-output-port output))
-				(begin
-					(set! message (string-append message str))
-					(loop-until-eof (read-string 1 input)))))))
+  	; read the first 4 bytes, little-endian, unsigned
+	(let ((message-length (integer-bytes->integer (read-bytes 4 input) #f)))
+		(parse-json (bytes->string/utf-8 (read-bytes message-length input)) output)
+		(close-input-port input)
+		(close-output-port output)))
 
 ; Wait on a port and spawn new threads on each connection
 (define (wait-for-connection)