palo/Scontrini-Daemon
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Changed the communication protocol: the first 4 bytes of each message

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represent the message length
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palo 2023-10-28 00:01:05 +02:00
parent 0145ff15cb
commit 46c32a90bb
1 changed files with 16 additions and 12 deletions
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26
scontrini.rkt
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@ -12,6 +12,12 @@
(let ((file (open-input-file "pizza_list.json"))) (let ((file (open-input-file "pizza_list.json")))
(read-json file))) (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 ; Print the to-print string on the printer
; TODO add synchronization to avoid race conditions ; TODO add synchronization to avoid race conditions
(define (printer-print to-print) (define (printer-print to-print)
@ -33,20 +39,18 @@
(case (hash-ref parsed-json 'command) (case (hash-ref parsed-json 'command)
(("print") (printer-print (hash-ref parsed-json 'text))) (("print") (printer-print (hash-ref parsed-json 'text)))
(("pizza") (printer-print (format-pizza (hash-ref parsed-json 'pizzas)))) (("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) (define (execute-commands input output)
(let ((message "")) ; read the first 4 bytes, little-endian, unsigned
(let loop-until-eof ((str (read-string 1 input))) (let ((message-length (integer-bytes->integer (read-bytes 4 input) #f)))
(if (eof-object? str) (parse-json (bytes->string/utf-8 (read-bytes message-length input)) output)
(begin
(parse-json message output)
(close-input-port input) (close-input-port input)
(close-output-port output)) (close-output-port output)))
(begin
(set! message (string-append message str))
(loop-until-eof (read-string 1 input)))))))
; Wait on a port and spawn new threads on each connection ; Wait on a port and spawn new threads on each connection
(define (wait-for-connection) (define (wait-for-connection)