I'm still busy trying to get MQTT (using Mosquitto MQTT) running for me in
Scheme. I have the following code, and this works fine when compiling.
Note, that I have defined the `on_message` callback as external, so
basically a C function in the end. This forces me to use this code compiled.
Ideally, in a next step, I'd like to put everything into a Chicken module
in a way that will also be usable in the interpreter. Therefore my question:
*What would I have to do to be able to use pure Scheme functions as
callbacks here?*
Any hint and help appreciated ...
> ;; csc -I /usr/include -L "-l mosquitto" mqtt.scm
>
> (import (chicken memory))
> (import (chicken blob))
> (import bind)
> (bind-rename/pattern "_" "-")
> (bind* "struct mosquitto_message{
> int mid;
> char *topic;
> void *payload;
> int payloadlen;
> int qos;
> ___bool retain;
> };")
> (bind* "int mosquitto_lib_init();")
> (bind* "int mosquitto_lib_cleanup();")
> (bind* "int mosquitto_lib_version(___out int *major,
> ___out int *minor,
> ___out int *revision);")
> (bind* "struct mosquitto *mosquitto_new(const char *id,
> ___bool clean_session,
> void *obj);")
> (bind* "void mosquitto_destroy(struct mosquitto *mosq);")
> (bind* "int mosquitto_connect(struct mosquitto *mosq,
> const char *host,
> int port,
> int keepalive);")
> (bind* "int mosquitto_publish(struct mosquitto *mosq,
> ___out int *mid,
> const char *topic,
> ___length(payload) int payloadlen,
> ___blob payload /* const void *payload */,
> int qos,
> ___bool retain);")
> (bind* "___safe int mosquitto_loop(struct mosquitto *mosq, int timeout,
> int max_packets);")
> (bind* "___safe int mosquitto_loop_forever(struct mosquitto * mosq, int
> timeout, int max_packets);")
> (bind* "int mosquitto_subscribe(struct mosquitto *mosq,
> int *mid,
> const char *sub,
> int qos);")
> (bind* "int mosquitto_unsubscribe(struct mosquitto *mosq,
> int *mid,
> const char *sub);")
> ;; setting callbacks
> (bind* "void mosquitto_connect_callback_set(struct mosquitto *mosq,
> void (*on_connect)(struct
> mosquitto *, void *, int));")
> ;;(bind* "mosquitto_disconnect_callback_set")
> ;;(bind* "mosquitto_publish_callback_set")
> ;; NB: the last type of return value in the vallback is 'const struct *'
> according
> ;; to mosquitto.h; however, it seems impossible to encode this in the
> ;; Scheme callback function using combinations of 'c-pointer' and
> 'const'
> (bind* "void mosquitto_message_callback_set(struct mosquitto *mosq,
> void (*on_message)(struct
> mosquitto *,
> void *,
> struct mosquitto_message *));")
> ;;(bind* "mosquitto_subscribe_callback_set")
> ;;(bind* "mosquitto_unsubscribe_callback_set")
> ;;(bind* "mosquitto_log_callback_set")
> (mosquitto-lib-init)
> (display (mosquitto-lib-version))
> ;; on-connect callback
> (define-external (on_connect ((c-pointer "struct mosquitto") mosq)
> ((c-pointer void) userdata)
> (int returncode))
> void
> (begin
> (display "connected to broker ... returncode: ")
> (display returncode)
> (newline)))
> ;; on-message callback
> (define-external (on_message ((c-pointer "struct mosquitto") mosq)
> ((c-pointer void) userdata)
> ((c-pointer "struct mosquitto_message") msg))
> void
> (let* ((len (mosquitto-message-payloadlen msg))
> (*payload (mosquitto-message-payload msg))
> (payload (make-blob len))
> (mid (mosquitto-message-mid msg))
> (topic (mosquitto-message-topic msg))
> (qos (mosquitto-message-qos msg))
> (retain (mosquitto-message-retain msg))
> ;; int mid; char* topic; int qos; bool retain
> )
> (if (> len 0)
> (move-memory! *payload payload len))
> (display "Wow! ... there was a message!\n")
> (display (blob->string payload)) (newline)
> (display retain)
> (newline)))
> (let-values (((res major minor revision) (mosquitto-lib-version)))
> (display major) (newline)
> (display minor) (newline)
> (display revision) (newline))
> ;; #f is equivalent to C's NULL
> (define mqttc (mosquitto-new #f #t #f))
> (display "mqtt client address\n")
> (display mqttc) (newline)
> (mosquitto-connect-callback-set mqttc #$on_connect)
> (mosquitto-message-callback-set mqttc #$on_message)
> (display "connect to broker\n")
> (display (mosquitto-connect mqttc "localhost" 1883 60))
> (newline)
> (mosquitto-subscribe mqttc #f "greetings/#" 0)
> (define payload (string->blob "gluck, gluck!"))
> (mosquitto-publish mqttc "chicken/call" payload 0 #f)
> (let loop ()
> (mosquitto-loop mqttc -1 1)
> (loop))
> ;;(mosquitto-loop-forever mqttc -1 1)
> ;; (mosquitto-loop mqttc -1 1)
> (mosquitto-destroy mqttc)
> (mosquitto-lib-cleanup)
--
Christoph Lange
Lotsarnas Väg 8
430 83 Vrångö
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