umqtt.simple: Add unsubscribe method.

Signed-off-by: Pedro Araoz <paraoz22@gmail.com>

Author: PedroAraoz

micropython/umqtt.simple/README.rst

@@ -53,6 +53,7 @@ follows MQTT control operations, and maps them to class methods:
 * ``ping()`` - Ping server (response is processed automatically by wait_msg()).
 * ``publish()`` - Publish a message.
 * ``subscribe()`` - Subscribe to a topic.
+* ``unsubscribe()`` - Unsubscribe to a topic.
 * ``set_callback()`` - Set callback for received subscription messages.
 * ``set_last_will()`` - Set MQTT "last will" message. Should be called
   *before* connect().

micropython/umqtt.simple/manifest.py

@@ -1,4 +1,4 @@
-metadata(description="Lightweight MQTT client for MicroPython.", version="1.6.0")
+metadata(description="Lightweight MQTT client for MicroPython.", version="1.7.0")
 
 # Originally written by Paul Sokolovsky.
 

micropython/umqtt.simple/umqtt/simple.py

@@ -175,6 +175,19 @@ def subscribe(self, topic, qos=0):
                     raise MQTTException(resp[3])
                 return
 
+    def unsubscribe(self, topic):
+        pkt = bytearray(b"\xa2\0\0\0")
+        self.pid += 1
+        struct.pack_into("!BH", pkt, 1, 2 + 2 + len(topic), self.pid)
+        self.sock.write(pkt)
+        self._send_str(topic)
+        while 1:
+            op = self.wait_msg()
+            if op == 0xB0:
+                resp = self.sock.read(3)
+                assert resp[1] == pkt[2] and resp[2] == pkt[3]
+                return
+
     # Wait for a single incoming MQTT message and process it.
     # Subscribed messages are delivered to a callback previously
     # set by .set_callback() method. Other (internal) MQTT