Python subscriber

examples/mqtt_arbitrary_buffer/python_subscriber/subscriber.py

@@ -0,0 +1,110 @@
+'''MQTT subscriber for Adafruit MQTT library mqtt_arbitrary_buffer example'''
+import paho.mqtt.client as mqtt
+import argparse
+import struct
+import array
+import sys
+
+feed_id = "RadESP"
+
+return_str =[
+    "Connection successful",
+    "incorrect protocol version",
+    "invalid client identifier",
+    "server unavailable",
+    "bad username or password",
+    "not authorised"
+    ]
+
+args = None
+
+# The callback for when the client receives a CONNACK response from the server.
+def on_connect(client, userdata, rc):
+    """callback function on connect. Subscribes or exits depending on outcome"""
+    print("MQTT: "),
+    print(return_str[rc])
+    if(rc > 1):
+        print("Connection refused - " + return_str[rc])
+        sys.exit(rc)
+    # Subscribing in on_connect() means that if we lose the connection and
+    # reconnect then subscriptions will be renewed.
+    else:
+        print(return_str[rc])
+        if(args.dry_run):
+            print("***Dry Run***")
+        client.subscribe(feed_id)
+
+def on_disconnect(client, userdata, rc):
+    """Callback for disconnect"""
+    if rc != 0:
+        print("Unexpected disconnection.")
+        client.reconnect()
+
+# The callback for when a PUBLISH message is received from the server.
+def on_message(client, userdata, msg):
+    try:
+        pMsg = parseMsg(msg.payload)
+        print("Received char Array: \"{}\", val1: {}, val2: {}, val3: {}...".format(pMsg[0], pMsg[1], pMsg[2], pMsg[3]))
+
+    except Exception as err:
+        print err
+
+
+
+def argBegin():
+    parser = argparse.ArgumentParser(description='MQTT subscriber for Adafruit MQTT library mqtt_arbitrary_buffer example')
+    parser.add_argument("--host", default="localhost", help='mqtt host to connect to. Defaults to localhost.')
+    parser.add_argument("-p", "--port", default=1883, help='network port to connect to. Defaults to 1883.')
+    parser.add_argument("-t", "--topic", nargs='*', required=True, help="mqtt topic to subscribe to. May be repeated multiple times.")
+    parser.add_argument("-k", "--keepalive", default=60, help="keep alive in seconds for this client. Defaults to 60.")
+
+    return parser.parse_args()
+
+
+def parseMsg(payload):
+    """Parses C struct from MQTT publisher Adafruit MQTT client to Python list"""
+
+    #values = payload    #TODO: remove extraneous values variable?
+    arr = array.array('B', payload) #convert python list to C-like array of unsigned char (B)
+
+    parsedStruct = struct.Struct('< 10s h L H') #define struct template (see below)
+    '''
+        Format of Struct from Adafruit MQTT client, Arduino, etc:
+
+        Adafruit MQTT client == Little endian (<)
+
+             Var NAME   | C TYPE (python symbol)    | size of member x bytes
+             -------------------------------------------------------------------
+              "charAry" |   uchar (s)               |   10s x 1 = 10 bytes
+              "val1"    |   int16 / short (h)       |   1h  x 2 =  2 bytes
+              "val2"    |   unsigned long (L)       |   1L  x 4 =  4 bytes
+              "val3"    |   uint16 / unsigned short |   1H  x 2 =  2 bytes
+              ------------------------------------------------------------------
+                                    Total packet size =         | 18 bytes |
+
+        See Section 7.3.2 of Python struct module documentation for complete format list
+        https://docs.python.org/2/library/struct.html
+    '''
+
+    charAry, val1, val2, val3 = parsedStruct.unpack_from(arr)
+    charAry = charAry.rstrip(' \t\r\n\0') #remove trailing white space from buffer
+    return charAry, val1, val2, val3
+
+
+def main():
+    """Wait for incoming message published by Adafruit MQTT client"""
+    global args
+    args = argBegin()
+    client = mqtt.Client()
+    client.on_connect = on_connect
+    client.on_message = on_message
+    client.connect(args.host, args.port, args.keepalive)
+
+    # Blocking call that processes network traffic, dispatches callbacks and
+    # handles reconnecting.
+    # Other loop*() functions are available that give a threaded interface and a
+    # manual interface.
+    client.loop_forever()
+
+if __name__ == '__main__':
+    sys.exit(main())