text: #!/usr/bin/env python
  #
  # Copyright (c) 2019, Pycom Limited.
  #
  # This software is licensed under the GNU GPL version 3 or any
  # later version, with permitted additional terms. For more information
  # see the Pycom Licence v1.0 document supplied with this file, or
  # available at https://www.pycom.io/opensource/licensing
  #
  
  import usocket as socket
  import ustruct as struct
  from ubinascii import hexlify
  
  class MQTTException(Exception):
      pass
  
  class MQTTClient:
  
      def __init__(self, client_id, server, port=0, user=None, password=None, keepalive=0,
                   ssl=False, ssl_params={}):
          if port == 0:
              port = 8883 if ssl else 1883
          self.client_id = client_id
          self.sock = None
          self.addr = socket.getaddrinfo(server, port)[0][-1]
          self.ssl = ssl
          self.ssl_params = ssl_params
          self.pid = 0
          self.cb = None
          self.user = user
          self.pswd = password
          self.keepalive = keepalive
          self.lw_topic = None
          self.lw_msg = None
          self.lw_qos = 0
          self.lw_retain = False
  
      def _send_str(self, s):
          self.sock.write(struct.pack("!H", len(s)))
          self.sock.write(s)
  
      def _recv_len(self):
          n = 0
          sh = 0
          while 1:
              b = self.sock.read(1)[0]
              n |= (b & 0x7f) << sh
              if not b & 0x80:
                  return n
              sh += 7
  
      def set_callback(self, f):
          self.cb = f
  
      def set_last_will(self, topic, msg, retain=False, qos=0):
          assert 0 <= qos <= 2
          assert topic
          self.lw_topic = topic
          self.lw_msg = msg
          self.lw_qos = qos
          self.lw_retain = retain
  
      def connect(self, clean_session=True):
          self.sock = socket.socket()
          self.sock.connect(self.addr)
          if self.ssl:
              import ussl
              self.sock = ussl.wrap_socket(self.sock, **self.ssl_params)
          msg = bytearray(b"\x10\0\0\x04MQTT\x04\x02\0\0")
          msg[1] = 10 + 2 + len(self.client_id)
          msg[9] = clean_session << 1
          if self.user is not None:
              msg[1] += 2 + len(self.user) + 2 + len(self.pswd)
              msg[9] |= 0xC0
          if self.keepalive:
              assert self.keepalive < 65536
              msg[10] |= self.keepalive >> 8
              msg[11] |= self.keepalive & 0x00FF
          if self.lw_topic:
              msg[1] += 2 + len(self.lw_topic) + 2 + len(self.lw_msg)
              msg[9] |= 0x4 | (self.lw_qos & 0x1) << 3 | (self.lw_qos & 0x2) << 3
              msg[9] |= self.lw_retain << 5
          self.sock.write(msg)
          #print(hex(len(msg)), hexlify(msg, ":"))
          self._send_str(self.client_id)
          if self.lw_topic:
              self._send_str(self.lw_topic)
              self._send_str(self.lw_msg)
          if self.user is not None:
              self._send_str(self.user)
              self._send_str(self.pswd)
          resp = self.sock.read(4)
          assert resp[0] == 0x20 and resp[1] == 0x02
          if resp[3] != 0:
              raise MQTTException(resp[3])
          return resp[2] & 1
  
      def disconnect(self):
          self.sock.write(b"\xe0\0")
          self.sock.close()
  
      def ping(self):
          self.sock.write(b"\xc0\0")
  
      def publish(self, topic, msg, retain=False, qos=0):
          pkt = bytearray(b"\x30\0\0\0")
          pkt[0] |= qos << 1 | retain
          sz = 2 + len(topic) + len(msg)
          if qos > 0:
              sz += 2
          assert sz < 2097152
          i = 1
          while sz > 0x7f:
              pkt[i] = (sz & 0x7f) | 0x80
              sz >>= 7
              i += 1
          pkt[i] = sz
          #print(hex(len(pkt)), hexlify(pkt, ":"))
          self.sock.write(pkt, i + 1)
          self._send_str(topic)
          if qos > 0:
              self.pid += 1
              pid = self.pid
              struct.pack_into("!H", pkt, 0, pid)
              self.sock.write(pkt, 2)
          self.sock.write(msg)
          if qos == 1:
              while 1:
                  op = self.wait_msg()
                  if op == 0x40:
                      sz = self.sock.read(1)
                      assert sz == b"\x02"
                      rcv_pid = self.sock.read(2)
                      rcv_pid = rcv_pid[0] << 8 | rcv_pid[1]
                      if pid == rcv_pid:
                          return
          elif qos == 2:
              assert 0
  
      def subscribe(self, topic, qos=0):
          assert self.cb is not None, "Subscribe callback is not set"
          pkt = bytearray(b"\x82\0\0\0")
          self.pid += 1
          struct.pack_into("!BH", pkt, 1, 2 + 2 + len(topic) + 1, self.pid)
          #print(hex(len(pkt)), hexlify(pkt, ":"))
          self.sock.write(pkt)
          self._send_str(topic)
          self.sock.write(qos.to_bytes(1, "little"))
          while 1:
              op = self.wait_msg()
              if op == 0x90:
                  resp = self.sock.read(4)
                  #print(resp)
                  assert resp[1] == pkt[2] and resp[2] == pkt[3]
                  if resp[3] == 0x80:
                      raise MQTTException(resp[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
      # messages processed internally.
      def wait_msg(self):
          res = self.sock.read(1)
          self.sock.setblocking(True)
          if res is None:
              return None
          if res == b"":
              raise OSError(-1)
          if res == b"\xd0":  # PINGRESP
              sz = self.sock.read(1)[0]
              assert sz == 0
              return None
          op = res[0]
          if op & 0xf0 != 0x30:
              return op
          sz = self._recv_len()
          topic_len = self.sock.read(2)
          topic_len = (topic_len[0] << 8) | topic_len[1]
          topic = self.sock.read(topic_len)
          sz -= topic_len + 2
          if op & 6:
              pid = self.sock.read(2)
              pid = pid[0] << 8 | pid[1]
              sz -= 2
          msg = self.sock.read(sz)
          self.cb(topic, msg)
          if op & 6 == 2:
              pkt = bytearray(b"\x40\x02\0\0")
              struct.pack_into("!H", pkt, 2, pid)
              self.sock.write(pkt)
          elif op & 6 == 4:
              assert 0
  
      # Checks whether a pending message from server is available.
      # If not, returns immediately with None. Otherwise, does
      # the same processing as wait_msg.
      def check_msg(self):
          self.sock.setblocking(False)
          return self.wait_msg()
  