polaris pwk 1725cgld full support

- significant improvements, correctnesses and stability fixes in
  protocol implementation
- correct handling of device appearances and disappearances
- flawlessly functioning telegram bot that re-renders kettle's state
  (temperature and other) in real time

3 files changed, 1093 insertions, 207 deletions

diff --git a/src/polaris/__init__.py b/src/polaris/__init__.py
index aa077ce..f1a7c1d 100644
--- a/src/polaris/__init__.py
+++ b/src/polaris/__init__.py
@@ -1,4 +1,12 @@
-# SPDX-License-Identifier: BSD-3-Clause
+# Polaris PWK 1725CGLD "smart" kettle python library
+# --------------------------------------------------
+# Copyright (C) Evgeny Zinoviev, 2022
+# License: BSD-3c
 
-from .kettle import Kettle
-from .protocol import Message, FrameType, PowerType
\ No newline at end of file
+from .kettle import Kettle, DeviceListener
+from .protocol import (
+    PowerType,
+    IncomingMessageListener,
+    ConnectionStatusListener,
+    ConnectionStatus
+)
\ No newline at end of file
diff --git a/src/polaris/kettle.py b/src/polaris/kettle.py
index 37f6813..1b995fd 100644
--- a/src/polaris/kettle.py
+++ b/src/polaris/kettle.py
@@ -1,97 +1,238 @@
-# SPDX-License-Identifier: BSD-3-Clause
+# Polaris PWK 1725CGLD smart kettle python library
+# ------------------------------------------------
+# Copyright (C) Evgeny Zinoviev, 2022
+# License: BSD-3c
 
 from __future__ import annotations
 
+import threading
 import logging
 import zeroconf
 
-import cryptography.hazmat.primitives._serialization
-from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey, X25519PublicKey
-from cryptography.hazmat.primitives import hashes
-
-from functools import partial
-from abc import ABC
-from ipaddress import ip_address
-from typing import Optional
+from abc import abstractmethod
+from ipaddress import ip_address, IPv4Address, IPv6Address
+from typing import Optional, List, Union
 
 from .protocol import (
-    Connection,
+    UDPConnection,
     ModeMessage,
-    HandshakeMessage,
     TargetTemperatureMessage,
-    Message,
-    PowerType
+    PowerType,
+    ConnectionStatus,
+    ConnectionStatusListener,
+    WrappedMessage
 )
 
-_logger = logging.getLogger(__name__)
-
 
-# Polaris PWK 1725CGLD IoT kettle
-class Kettle(zeroconf.ServiceListener, ABC):
-    macaddr: str
-    device_token: str
-    sb: Optional[zeroconf.ServiceBrowser]
-    found_device: Optional[zeroconf.ServiceInfo]
-    conn: Optional[Connection]
+class DeviceDiscover(threading.Thread, zeroconf.ServiceListener):
+    si: Optional[zeroconf.ServiceInfo]
+    _mac: str
+    _sb: Optional[zeroconf.ServiceBrowser]
+    _zc: Optional[zeroconf.Zeroconf]
+    _listeners: List[DeviceListener]
+    _valid_addresses: List[Union[IPv4Address, IPv6Address]]
+    _only_ipv4: bool
 
-    def __init__(self, mac: str, device_token: str):
+    def __init__(self, mac: str,
+                 listener: Optional[DeviceListener] = None,
+                 only_ipv4=True):
         super().__init__()
-        self.zeroconf = zeroconf.Zeroconf()
-        self.sb = None
-        self.macaddr = mac
-        self.device_token = device_token
-        self.found_device = None
-        self.conn = None
+        self.si = None
+        self._mac = mac
+        self._zc = None
+        self._sb = None
+        self._only_ipv4 = only_ipv4
+        self._valid_addresses = []
+        self._listeners = []
+        if isinstance(listener, DeviceListener):
+            self._listeners.append(listener)
+        self._logger = logging.getLogger(f'{__name__}.{self.__class__.__name__}')
+
+    def add_listener(self, listener: DeviceListener):
+        if listener not in self._listeners:
+            self._listeners.append(listener)
+        else:
+            self._logger.warning(f'add_listener: listener {listener} already in the listeners list')
+
+    def set_info(self, info: zeroconf.ServiceInfo):
+        valid_addresses = self._get_valid_addresses(info)
+        if not valid_addresses:
+            raise ValueError('no valid addresses')
+        self._valid_addresses = valid_addresses
+        self.si = info
+        for f in self._listeners:
+            try:
+                f.device_updated()
+            except Exception as exc:
+                self._logger.error(f'set_info: error while calling device_updated on {f}')
+                self._logger.exception(exc)
 
-    def find(self) -> zeroconf.ServiceInfo:
-        self.sb = zeroconf.ServiceBrowser(self.zeroconf, "_syncleo._udp.local.", self)
-        self.sb.join()
+    def add_service(self, zc: zeroconf.Zeroconf, type_: str, name: str) -> None:
+        self._add_update_service('add_service', zc, type_, name)
 
-        return self.found_device
+    def update_service(self, zc: zeroconf.Zeroconf, type_: str, name: str) -> None:
+        self._add_update_service('update_service', zc, type_, name)
 
-    # zeroconf.ServiceListener implementation
-    def add_service(self,
-                    zc: zeroconf.Zeroconf,
-                    type_: str,
-                    name: str) -> None:
-        if name.startswith(f'{self.macaddr}.'):
-            info = zc.get_service_info(type_, name)
+    def _add_update_service(self, method: str, zc: zeroconf.Zeroconf, type_: str, name: str) -> None:
+        info = zc.get_service_info(type_, name)
+        if name.startswith(f'{self._mac}.'):
+            self._logger.info(f'{method}: type={type_} name={name}')
+            try:
+                self.set_info(info)
+            except ValueError as exc:
+                self._logger.error(f'{method}: rejected: {str(exc)}')
+        else:
+            self._logger.debug(f'{method}: mac not matched: {info}')
+
+    def remove_service(self, zc: zeroconf.Zeroconf, type_: str, name: str) -> None:
+        if name.startswith(f'{self._mac}.'):
+            self._logger.info(f'remove_service: type={type_} name={name}')
+            # TODO what to do here?!
+
+    def run(self):
+        self._logger.info('starting zeroconf service browser')
+        ip_version = zeroconf.IPVersion.V4Only if self._only_ipv4 else zeroconf.IPVersion.All
+        self._zc = zeroconf.Zeroconf(ip_version=ip_version)
+        self._sb = zeroconf.ServiceBrowser(self._zc, "_syncleo._udp.local.", self)
+        self._sb.join()
+
+    def stop(self):
+        if self._sb:
             try:
-                self.sb.cancel()
+                self._sb.cancel()
             except RuntimeError:
                 pass
-            self.zeroconf.close()
-            self.found_device = info
+            self._sb = None
+        self._zc.close()
+        self._zc = None
+
+    def _get_valid_addresses(self, si: zeroconf.ServiceInfo) -> List[Union[IPv4Address, IPv6Address]]:
+        valid = []
+        for addr in map(ip_address, si.addresses):
+            if self._only_ipv4 and not isinstance(addr, IPv4Address):
+                continue
+            if isinstance(addr, IPv4Address) and str(addr).startswith('169.254.'):
+                continue
+            valid.append(addr)
+        return valid
 
-            assert self.device_curve == 29, f'curve type {self.device_curve} is not implemented'
-
-    def start_server(self, callback: callable):
-        addresses = list(map(ip_address, self.found_device.addresses))
-        self.conn = Connection(addr=addresses[0],
-                               port=int(self.found_device.port),
-                               device_pubkey=self.device_pubkey,
-                               device_token=bytes.fromhex(self.device_token))
+    @property
+    def pubkey(self) -> bytes:
+        return bytes.fromhex(self.si.properties[b'public'].decode())
 
-        # shake the kettle's hand
-        self._pass_message(HandshakeMessage(), callback)
-        self.conn.start()
+    @property
+    def curve(self) -> int:
+        return int(self.si.properties[b'curve'].decode())
 
-    def stop_server(self):
-        self.conn.interrupted = True
+    @property
+    def addr(self) -> Union[IPv4Address, IPv6Address]:
+        return self._valid_addresses[0]
 
     @property
-    def device_pubkey(self) -> bytes:
-        return bytes.fromhex(self.found_device.properties[b'public'].decode())
+    def port(self) -> int:
+        return int(self.si.port)
 
     @property
-    def device_curve(self) -> int:
-        return int(self.found_device.properties[b'curve'].decode())
+    def protocol(self) -> int:
+        return int(self.si.properties[b'protocol'].decode())
+
+
+class DeviceListener:
+    @abstractmethod
+    def device_updated(self):
+        pass
+
+
+class Kettle(DeviceListener, ConnectionStatusListener):
+    mac: str
+    device: Optional[DeviceDiscover]
+    device_token: str
+    conn: Optional[UDPConnection]
+    conn_status: Optional[ConnectionStatus]
+    _logger: logging.Logger
+    _find_evt: threading.Event
+
+    def __init__(self, mac: str, device_token: str):
+        super().__init__()
+        self.mac = mac
+        self.device = None
+        self.device_token = device_token
+        self.conn = None
+        self.conn_status = None
+        self._find_evt = threading.Event()
+        self._logger = logging.getLogger(f'{__name__}.{self.__class__.__name__}')
+
+    def device_updated(self):
+        self._find_evt.set()
+        self._logger.info(f'device updated, service info: {self.device.si}')
+
+    def connection_status_updated(self, status: ConnectionStatus):
+        self.conn_status = status
+
+    def discover(self, wait=True, timeout=None, listener=None) -> Optional[zeroconf.ServiceInfo]:
+        do_start = False
+        if not self.device:
+            self.device = DeviceDiscover(self.mac, listener=self, only_ipv4=True)
+            do_start = True
+            self._logger.debug('discover: started device discovery')
+        else:
+            self._logger.warning('discover: already started')
+
+        if listener is not None:
+            self.device.add_listener(listener)
+
+        if do_start:
+            self.device.start()
+
+        if wait:
+            self._find_evt.clear()
+            try:
+                self._find_evt.wait(timeout=timeout)
+            except KeyboardInterrupt:
+                self.device.stop()
+                return None
+            return self.device.si
+
+    def start_server_if_needed(self,
+                               incoming_message_listener=None,
+                               connection_status_listener=None):
+        if self.conn:
+            self._logger.warning('start_server_if_needed: server is already started!')
+            self.conn.set_address(self.device.addr, self.device.port)
+            self.conn.set_device_pubkey(self.device.pubkey)
+            return
+
+        assert self.device.curve == 29, f'curve type {self.device.curve} is not implemented'
+        assert self.device.protocol == 2, f'protocol {self.device.protocol} is not supported'
+
+        self.conn = UDPConnection(addr=self.device.addr,
+                                  port=self.device.port,
+                                  device_pubkey=self.device.pubkey,
+                                  device_token=bytes.fromhex(self.device_token))
+        if incoming_message_listener:
+            self.conn.add_incoming_message_listener(incoming_message_listener)
+
+        self.conn.add_connection_status_listener(self)
+        if connection_status_listener:
+            self.conn.add_connection_status_listener(connection_status_listener)
+
+        self.conn.start()
+
+    def stop_all(self):
+        # when we stop server, we should also stop device discovering service
+        if self.conn:
+            self.conn.interrupted = True
+            self.conn = None
+        self.device.stop()
+        self.device = None
+
+    def is_connected(self) -> bool:
+        return self.conn is not None and self.conn_status == ConnectionStatus.CONNECTED
 
     def set_power(self, power_type: PowerType, callback: callable):
-        self._pass_message(ModeMessage(power_type), callback)
+        message = ModeMessage(power_type)
+        self.conn.enqueue_message(WrappedMessage(message, handler=callback, ack=True))
 
     def set_target_temperature(self, temp: int, callback: callable):
-        self._pass_message(TargetTemperatureMessage(temp), callback)
-
-    def _pass_message(self, message: Message, callback: callable):
-        self.conn.send_message(message, partial(callback, self))
+        message = TargetTemperatureMessage(temp)
+        self.conn.enqueue_message(WrappedMessage(message, handler=callback, ack=True))
diff --git a/src/polaris/protocol.py b/src/polaris/protocol.py
index cc4e36a..5d7390f 100644
--- a/src/polaris/protocol.py
+++ b/src/polaris/protocol.py
@@ -1,39 +1,61 @@
-# SPDX-License-Identifier: BSD-3-Clause
+# Polaris PWK 1725CGLD "smart" kettle python library
+# --------------------------------------------------
+# Copyright (C) Evgeny Zinoviev, 2022
+# License: BSD-3c
 
 from __future__ import annotations
+
 import logging
 import socket
 import random
 import struct
 import threading
-import queue
+import time
 
-from enum import Enum
-from typing import Union, Optional, Any
+from abc import abstractmethod, ABC
+from enum import Enum, auto
+from typing import Union, Optional, Dict, Tuple, List
 from ipaddress import IPv4Address, IPv6Address
 
-import cryptography.hazmat.primitives._serialization
+import cryptography.hazmat.primitives._serialization as srlz
 
 from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey, X25519PublicKey
 from cryptography.hazmat.primitives import ciphers, padding, hashes
 from cryptography.hazmat.primitives.ciphers import algorithms, modes
 
-
+ReprDict = Dict[str, Union[str, int, float, bool]]
 _logger = logging.getLogger(__name__)
 
+PING_FREQUENCY = 3
+RESEND_ATTEMPTS = 5
+READ_TIMEOUT = 1
+ERROR_TIMEOUT = 15
+MESSAGE_QUEUE_REMOVE_DELAY = 13  # after what time to delete (and pass False to handlers, if needed) messages with phase=DONE from queue
+DISCONNECT_TIMEOUT = 15
+
 
-# drop-in replacement for Java API
+def safe_callback_call(f: callable,
+                       *args,
+                       logger: logging.Logger = None,
+                       error_message: str = None):
+    try:
+        return f(*args)
+    except Exception as exc:
+        logger.error(f'{error_message}, see exception below:')
+        logger.exception(exc)
+    return None
+
+
+# drop-in replacement for java.lang.System.arraycopy
 # TODO: rewrite
 def arraycopy(src, src_pos, dest, dest_pos, length):
     for i in range(length):
         dest[i + dest_pos] = src[i + src_pos]
 
 
-class FrameType(Enum):
-    ACK = 0
-    CMD = 1
-    AUX = 2
-    NAK = 3
+# "convert" unsigned byte to signed
+def u8_to_s8(b: int) -> int:
+    return struct.unpack('b', bytes([b]))[0]
 
 
 class PowerType(Enum):
@@ -44,23 +66,37 @@ class PowerType(Enum):
     # update: if I set it to '2', it just resets to '0'
 
 
+# low-level protocol structures
+# -----------------------------
+
+class FrameType(Enum):
+    ACK = 0
+    CMD = 1
+    AUX = 2
+    NAK = 3
+
+
 class FrameHead:
-    seq: int  # u8
+    seq: Optional[int]  # u8
     type: FrameType  # u8
-    length: int  # u16
+    length: int  # u16. This is the length of FrameItem's payload
 
     @staticmethod
     def from_bytes(buf: bytes) -> FrameHead:
         seq, ft, length = struct.unpack('<BBH', buf)
         return FrameHead(seq, FrameType(ft), length)
 
-    def __init__(self, seq: int, frame_type: FrameType, length: Optional[int] = None):
+    def __init__(self,
+                 seq: Optional[int],
+                 frame_type: FrameType,
+                 length: Optional[int] = None):
         self.seq = seq
         self.type = frame_type
         self.length = length or 0
 
     def pack(self) -> bytes:
         assert self.length != 0, "FrameHead.length has not been set"
+        assert self.seq is not None, "FrameHead.seq has not been set"
         return struct.pack('<BBH', self.seq, self.type.value, self.length)
 
 
@@ -84,30 +120,47 @@ class FrameItem:
         return bytes(ba)
 
 
+# high-level wrappers around FrameItem
+# ------------------------------------
+
+class MessagePhase(Enum):
+    WAITING = 0
+    SENT = 1
+    DONE = 2
+
+
 class Message:
     frame: Optional[FrameItem]
+    id: int
+
+    _global_id = 0
 
     def __init__(self):
         self.frame = None
 
+        # global internal message id, only useful for debugging purposes
+        self.id = self.next_id()
+
+    def __repr__(self):
+        return f'<{self.__class__.__name__} id={self.id} seq={self.frame.head.seq}>'
+
     @staticmethod
-    def from_encrypted(buf: bytes,
-                       inkey: bytes,
-                       outkey: bytes) -> Message:
-        # _logger.debug('[from_encrypted] buf='+buf.hex())
-        # print(f'buf len={len(buf)}')
+    def next_id():
+        _id = Message._global_id
+        Message._global_id += 1
+        return _id
+
+    @staticmethod
+    def from_encrypted(buf: bytes, inkey: bytes, outkey: bytes) -> Message:
+        _logger.debug(f'Message:from_encrypted: buf={buf.hex()}')
+
         assert len(buf) >= 4, 'invalid size'
         head = FrameHead.from_bytes(buf[:4])
 
         assert len(buf) == head.length + 4, f'invalid buf size ({len(buf)} != {head.length})'
-
         payload = buf[4:]
-
-        # byte b = paramFrameHead.seq;
         b = head.seq
 
-        # TODO check if protocol is 2, otherwise raise an exception
-
         j = b & 0xF
         k = b >> 4 & 0xF
 
@@ -123,15 +176,9 @@ class Message:
         decryptor = cipher.decryptor()
         decrypted_data = decryptor.update(payload) + decryptor.finalize()
 
-        # print(f'head.length={head.length} len(decr)={len(decrypted_data)}')
-        # if len(decrypted_data) > head.length:
         unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder()
         decrypted_data = unpadder.update(decrypted_data)
-        # try:
         decrypted_data += unpadder.finalize()
-        # except ValueError as exc:
-        #     _logger.exception(exc)
-        #     pass
 
         assert len(decrypted_data) != 0, 'decrypted data is null'
         assert head.seq == decrypted_data[0], f'decrypted seq mismatch {head.seq} != {decrypted_data[0]}'
@@ -145,29 +192,54 @@ class Message:
             return NakMessage(head.seq)
 
         elif head.type == FrameType.AUX:
+            # TODO implement AUX
             raise NotImplementedError('FrameType AUX is not yet implemented')
 
         elif head.type == FrameType.CMD:
-            cmd = decrypted_data[0]
+            type = decrypted_data[1]
             data = decrypted_data[2:]
-            return CmdMessage(head.seq, cmd, data)
+
+            cl = UnknownMessage
+
+            subclasses = [cl for cl in CmdIncomingMessage.__subclasses__() if cl is not SimpleBooleanMessage]
+            subclasses.extend(SimpleBooleanMessage.__subclasses__())
+
+            for _cl in subclasses:
+                # `UnknownMessage` is a special class that holds a packed command that we don't recognize.
+                # It will be used anyway if we don't find a match, so skip it here
+                if _cl == UnknownMessage:
+                    continue
+
+                if _cl.TYPE == type:
+                    cl = _cl
+                    break
+
+            m = cl.from_packed_data(data, seq=head.seq)
+            if isinstance(m, UnknownMessage):
+                m.set_type(type)
+            return m
 
         else:
             raise NotImplementedError(f'Unexpected frame type: {head.type}')
 
-    @property
-    def data(self) -> bytes:
+    def pack_data(self) -> bytes:
         return b''
 
-    def encrypt(self,
-                outkey: bytes,
-                inkey: bytes,
-                token: bytes,
-                pubkey: bytes):
+    @property
+    def seq(self) -> Union[int, None]:
+        try:
+            return self.frame.head.seq
+        except:
+            return None
+
+    @seq.setter
+    def seq(self, seq: int):
+        self.frame.head.seq = seq
 
+    def encrypt(self, outkey: bytes, inkey: bytes, token: bytes, pubkey: bytes):
         assert self.frame is not None
 
-        data = self.data
+        data = self._get_data_to_encrypt()
         assert data is not None
 
         b = self.frame.head.seq
@@ -199,7 +271,7 @@ class Message:
         arraycopy(data, 0, newdata, 1, len(data))
 
         newdata = bytes(newdata)
-        _logger.debug('payload to be sent: ' + newdata.hex())
+        _logger.debug('frame payload to be encrypted: ' + newdata.hex())
 
         padder = padding.PKCS7(algorithms.AES.block_size).padder()
         ciphertext = bytearray()
@@ -208,74 +280,143 @@ class Message:
 
         self.frame.setpayload(ciphertext)
 
-    def set_seq(self, seq: int):
-        self.frame.head.seq = seq
-
-    def __repr__(self):
-        return f'<{self.__class__.__name__} seq={self.frame.head.seq}>'
+    def _get_data_to_encrypt(self) -> bytes:
+        return self.pack_data()
 
 
-class AckMessage(Message):
-    def __init__(self, seq: int = 0):
+class AckMessage(Message, ABC):
+    def __init__(self, seq: Optional[int] = None):
         super().__init__()
-        self.frame = FrameItem(FrameHead(seq, FrameType.ACK, 0))
+        self.frame = FrameItem(FrameHead(seq, FrameType.ACK, None))
 
 
-class NakMessage(Message):
-    def __init__(self, seq: int = 0):
+class NakMessage(Message, ABC):
+    def __init__(self, seq: Optional[int] = None):
         super().__init__()
-        self.frame = FrameItem(FrameHead(seq, FrameType.NAK, 0))
+        self.frame = FrameItem(FrameHead(seq, FrameType.NAK, None))
 
 
 class CmdMessage(Message):
-    _type: Optional[int]
-    _data: bytes
+    type: Optional[int]
+    data: bytes
 
-    def __init__(self, seq=0,
-                 type: Optional[int] = None,
-                 data: bytes = b''):
-        super().__init__()
-        self._data = data
-        if type is not None:
-            self.frame = FrameItem(FrameHead(seq, FrameType.CMD))
-            self._type = type
-        else:
-            self._type = None
+    TYPE = None
 
-    @property
-    def data(self) -> bytes:
+    def _get_data_to_encrypt(self) -> bytes:
         buf = bytearray()
-        buf.append(self._type)
-        buf.extend(self._data)
+        buf.append(self.get_type())
+        buf.extend(self.pack_data())
         return bytes(buf)
 
+    def __init__(self, seq: Optional[int] = None):
+        super().__init__()
+        self.frame = FrameItem(FrameHead(seq, FrameType.CMD))
+        self.data = b''
+
+    def _repr_fields(self) -> ReprDict:
+        return {
+            'cmd': self.get_type()
+        }
+
     def __repr__(self):
         params = [
             __name__+'.'+self.__class__.__name__,
-            f'seq={self.frame.head.seq}',
-            # f'type={self.frame.head.type}',
-            f'cmd={self._type}'
+            f'id={self.id}',
+            f'seq={self.seq}'
         ]
-        if self._data:
-            params.append(f'data={self._data.hex()}')
+        fields = self._repr_fields()
+        if fields:
+            for k, v in fields.items():
+                params.append(f'{k}={v}')
+        elif self.data:
+            params.append(f'data={self.data.hex()}')
         return '<'+' '.join(params)+'>'
 
+    def get_type(self) -> int:
+        return self.__class__.TYPE
+
+
+class CmdIncomingMessage(CmdMessage):
+    @staticmethod
+    @abstractmethod
+    def from_packed_data(cls, data: bytes, seq: Optional[int] = None):
+        pass
+
+    @abstractmethod
+    def _repr_fields(self) -> ReprDict:
+        pass
+
+
+class CmdOutgoingMessage(CmdMessage):
+    @abstractmethod
+    def pack_data(self) -> bytes:
+        return b''
+
+
+class ModeMessage(CmdOutgoingMessage, CmdIncomingMessage):
+    TYPE = 1
+
+    pt: PowerType
+
+    def __init__(self, power_type: PowerType, seq: Optional[int] = None):
+        super().__init__(seq)
+        self.pt = power_type
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> ModeMessage:
+        assert len(data) == 1, 'data size expected to be 1'
+        mode, = struct.unpack('B', data)
+        return ModeMessage(PowerType(mode), seq=seq)
+
+    def pack_data(self) -> bytes:
+        return self.pt.value.to_bytes(1, byteorder='little')
 
-class ModeMessage(CmdMessage):
-    def __init__(self, power_type: PowerType):
-        super().__init__(type=1,
-                         data=(power_type.value).to_bytes(1, byteorder='little'))
+    def _repr_fields(self) -> ReprDict:
+        return {'mode': self.pt.name}
 
 
-class TargetTemperatureMessage(CmdMessage):
-    def __init__(self, temp: int):
-        super().__init__(type=2,
-                         data=bytes(bytearray([temp, 0])))
+class TargetTemperatureMessage(CmdOutgoingMessage, CmdIncomingMessage):
+    temperature: int
 
+    TYPE = 2
 
+    def __init__(self, temp: int, seq: Optional[int] = None):
+        super().__init__(seq)
+        self.temperature = temp
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> TargetTemperatureMessage:
+        assert len(data) == 2, 'data size expected to be 2'
+        nat, frac = struct.unpack('BB', data)
+        temp = int(nat + (frac / 100))
+        return TargetTemperatureMessage(temp, seq=seq)
+
+    def pack_data(self) -> bytes:
+        return bytes([self.temperature, 0])
+
+    def _repr_fields(self) -> ReprDict:
+        return {'temperature': self.temperature}
+
+
+class PingMessage(CmdIncomingMessage, CmdOutgoingMessage):
+    TYPE = 255
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> PingMessage:
+        assert len(data) == 0, 'no data expected'
+        return PingMessage(seq=seq)
+
+    def pack_data(self) -> bytes:
+        return b''
+
+    def _repr_fields(self) -> ReprDict:
+        return {}
+
+
+# This is the first protocol message. Sent by a client.
+# Kettle usually ACKs this, but sometimes i don't get any ACK and the very next message is HandshakeResponseMessage.
 class HandshakeMessage(CmdMessage):
-    def __init__(self):
-        super().__init__(type=0)
+    TYPE = 0
 
     def encrypt(self,
                 outkey: bytes,
@@ -297,20 +438,312 @@ class HandshakeMessage(CmdMessage):
         self.frame.setpayload(pld)
 
 
-# TODO
-# implement resending UDP messages if no answer has been received in a second
-# try at least 5 times, then give up
-class Connection(threading.Thread):
-    seq_no: int
+# Kettle either sends this right after the handshake, of first it ACKs the handshake then sends this.
+class HandshakeResponseMessage(CmdIncomingMessage):
+    TYPE = 0
+
+    protocol: int
+    fw_major: int
+    fw_minor: int
+    mode: int
+    token: bytes
+
+    def __init__(self,
+                 protocol: int,
+                 fw_major: int,
+                 fw_minor: int,
+                 mode: int,
+                 token: bytes,
+                 seq: Optional[int] = None):
+        super().__init__(seq)
+        self.protocol = protocol
+        self.fw_major = fw_major
+        self.fw_minor = fw_minor
+        self.mode = mode
+        self.token = token
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> HandshakeResponseMessage:
+        protocol, fw_major, fw_minor, mode = struct.unpack('<HBBB', data[:5])
+        return HandshakeResponseMessage(protocol, fw_major, fw_minor, mode, token=data[5:], seq=seq)
+
+    def _repr_fields(self) -> ReprDict:
+        return {
+            'protocol': self.protocol,
+            'fw': f'{self.fw_major}.{self.fw_minor}',
+            'mode': self.mode,
+            'token': self.token.hex()
+        }
+
+
+# Apparently, some hardware info.
+# On the other hand, if you look at com.syncleiot.iottransport.commands.CmdHardware, its mqtt topic is "mcu_firmware".
+# My device returns 1.1.1. The thing uses on ESP8266 MCU under the hood (or, more precisely, under a piece of cheap
+# plastic), so maybe 1.1.1 is the MCU fw revision.
+class DeviceHardwareMessage(CmdIncomingMessage):
+    TYPE = 143  # -113
+
+    hw: List[int]
+
+    def __init__(self, hw: List[int], seq: Optional[int] = None):
+        super().__init__(seq)
+        self.hw = hw
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> DeviceHardwareMessage:
+        assert len(data) == 3, 'invalid data size, expected 3'
+        hw = list(struct.unpack('<BBB', data))
+        return DeviceHardwareMessage(hw, seq=seq)
+
+    def _repr_fields(self) -> ReprDict:
+        return {'device_hardware': '.'.join(map(str, self.hw))}
+
+
+# This message is sent by kettle right after the HandshakeMessageResponse.
+# The diagnostic data is supposed to be sent to vendor, which we, obviously, not going to do.
+# So just ACK and skip it.
+class DeviceDiagnosticMessage(CmdIncomingMessage):
+    TYPE = 145  # -111
+
+    diag_data: bytes
+
+    def __init__(self, diag_data: bytes, seq: Optional[int] = None):
+        super().__init__(seq)
+        self.diag_data = diag_data
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> DeviceDiagnosticMessage:
+        return DeviceDiagnosticMessage(diag_data=data, seq=seq)
+
+    def _repr_fields(self) -> ReprDict:
+        return {'diag_data': self.diag_data.hex()}
+
+
+class SimpleBooleanMessage(ABC, CmdIncomingMessage):
+    value: bool
+
+    def __init__(self, value: bool, seq: Optional[int] = None):
+        super().__init__(seq)
+        self.value = value
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq: Optional[int] = None):
+        assert len(data) == 1, 'invalid data size, expected 1'
+        enabled, = struct.unpack('<B', data)
+        return cls(value=enabled == 1, seq=seq)
+
+    @abstractmethod
+    def _repr_fields(self) -> ReprDict:
+        pass
+
+
+class AccessControlMessage(SimpleBooleanMessage):
+    TYPE = 133  # -123
+
+    def _repr_fields(self) -> ReprDict:
+        return {'acl_enabled': self.value}
+
+
+class ErrorMessage(SimpleBooleanMessage):
+    TYPE = 7
+
+    def _repr_fields(self) -> ReprDict:
+        return {'error': self.value}
+
+
+class ChildLockMessage(SimpleBooleanMessage):
+    TYPE = 30
+
+    def _repr_fields(self) -> ReprDict:
+        return {'child_lock': self.value}
+
+
+class VolumeMessage(SimpleBooleanMessage):
+    TYPE = 9
+
+    def _repr_fields(self) -> ReprDict:
+        return {'volume': self.value}
+
+
+class BacklightMessage(SimpleBooleanMessage):
+    TYPE = 28
+
+    def _repr_fields(self) -> ReprDict:
+        return {'backlight': self.value}
+
+
+class CurrentTemperatureMessage(CmdIncomingMessage):
+    TYPE = 20
+
+    current_temperature: int
+
+    def __init__(self, temp: int, seq: Optional[int] = None):
+        super().__init__(seq)
+        self.current_temperature = temp
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> CurrentTemperatureMessage:
+        assert len(data) == 2, 'data size expected to be 2'
+        nat, frac = struct.unpack('BB', data)
+        temp = int(nat + (frac / 100))
+        return CurrentTemperatureMessage(temp, seq=seq)
+
+    def pack_data(self) -> bytes:
+        return bytes([self.current_temperature, 0])
+
+    def _repr_fields(self) -> ReprDict:
+        return {'current_temperature': self.current_temperature}
+
+
+class UnknownMessage(CmdIncomingMessage):
+    type: Optional[int]
+    data: bytes
+
+    def __init__(self, data: bytes, **kwargs):
+        super().__init__(**kwargs)
+        self.type = None
+        self.data = data
+
+    @classmethod
+    def from_packed_data(cls, data: bytes, seq=0) -> UnknownMessage:
+        return UnknownMessage(data, seq=seq)
+
+    def set_type(self, type: int):
+        self.type = type
+
+    def get_type(self) -> int:
+        return self.type
+
+    def _repr_fields(self) -> ReprDict:
+        return {
+            'type': self.type,
+            'data': self.data.hex()
+        }
+
+
+class WrappedMessage:
+    _message: Message
+    _handler: Optional[callable]
+    _validator: Optional[callable]
+    _logger: Optional[logging.Logger]
+    _phase: MessagePhase
+    _phase_update_time: float
+
+    def __init__(self,
+                 message: Message,
+                 handler: Optional[callable] = None,
+                 validator: Optional[callable] = None,
+                 ack=False):
+        self._message = message
+        self._handler = handler
+        self._validator = validator
+        self._logger = None
+        self._phase = MessagePhase.WAITING
+        self._phase_update_time = 0
+        if not validator and ack:
+            self._validator = lambda m: isinstance(m, AckMessage)
+
+    def setlogger(self, logger: logging.Logger):
+        self._logger = logger
+
+    def validate(self, message: Message):
+        if not self._validator:
+            return True
+        return self._validator(message)
+
+    def call(self, *args, error_message: str = None) -> None:
+        if not self._handler:
+            return
+        try:
+            self._handler(*args)
+        except Exception as exc:
+            logger = self._logger or logging.getLogger(self.__class__.__name__)
+            logger.error(f'{error_message}, see exception below:')
+            logger.exception(exc)
+
+    @property
+    def phase(self) -> MessagePhase:
+        return self._phase
+
+    @phase.setter
+    def phase(self, phase: MessagePhase):
+        self._phase = phase
+        self._phase_update_time = 0 if phase == MessagePhase.WAITING else time.time()
+
+    @property
+    def phase_update_time(self) -> float:
+        return self._phase_update_time
+
+    @property
+    def message(self) -> Message:
+        return self._message
+
+    @property
+    def id(self) -> int:
+        return self._message.id
+
+    @property
+    def seq(self) -> int:
+        return self._message.seq
+
+    @seq.setter
+    def seq(self, seq: int):
+        self._message.seq = seq
+
+    def __repr__(self):
+        return f'<{__name__}.{self.__class__.__name__} message={self._message.__repr__()}>'
+
+
+# Connection stuff
+# Well, strictly speaking, as it's UDP, there's no connection, but who cares.
+# ---------------------------------------------------------------------------
+
+class IncomingMessageListener:
+    @abstractmethod
+    def incoming_message(self, message: Message) -> Optional[Message]:
+        pass
+
+
+class ConnectionStatus(Enum):
+    NOT_CONNECTED = auto()
+    CONNECTING = auto()
+    CONNECTED = auto()
+    RECONNECTING = auto()
+    DISCONNECTED = auto()
+
+
+class ConnectionStatusListener:
+    @abstractmethod
+    def connection_status_updated(self, status: ConnectionStatus):
+        pass
+
+
+class UDPConnection(threading.Thread, ConnectionStatusListener):
+    inseq: int
+    outseq: int
     source_port: int
     device_addr: str
     device_port: int
     device_token: bytes
+    device_pubkey: bytes
     interrupted: bool
-    waiting_for_response: dict[int, callable]
+    response_handlers: Dict[int, WrappedMessage]
+    outgoing_queue: List[WrappedMessage]
     pubkey: Optional[bytes]
     encinkey: Optional[bytes]
     encoutkey: Optional[bytes]
+    inc_listeners: List[IncomingMessageListener]
+    conn_listeners: List[ConnectionStatusListener]
+    outgoing_time: float
+    outgoing_time_1st: float
+    incoming_time: float
+    status: ConnectionStatus
+    reconnect_tries: int
+
+    _addr_lock: threading.Lock
+    _iml_lock: threading.Lock
+    _csl_lock: threading.Lock
+    _st_lock: threading.Lock
 
     def __init__(self,
                  addr: Union[IPv4Address, IPv6Address],
@@ -318,36 +751,105 @@ class Connection(threading.Thread):
                  device_pubkey: bytes,
                  device_token: bytes):
         super().__init__()
-        self.logger = logging.getLogger(__name__+'.'+self.__class__.__name__)
+        self._logger = logging.getLogger(f'{__name__}.{self.__class__.__name__} <{hex(id(self))}>')
         self.setName(self.__class__.__name__)
-        # self.daemon = True
 
-        self.seq_no = -1
+        self.inseq = 0
+        self.outseq = 0
         self.source_port = random.randint(1024, 65535)
         self.device_addr = str(addr)
         self.device_port = port
         self.device_token = device_token
-        self.lock = threading.Lock()
-        self.outgoing_queue = queue.SimpleQueue()
-        self.waiting_for_response = {}
+        self.device_pubkey = device_pubkey
+        self.outgoing_queue = []
+        self.response_handlers = {}
         self.interrupted = False
+        self.outgoing_time = 0
+        self.outgoing_time_1st = 0
+        self.incoming_time = 0
+        self.inc_listeners = []
+        self.conn_listeners = [self]
+        self.status = ConnectionStatus.NOT_CONNECTED
+        self.reconnect_tries = 0
+
+        self._iml_lock = threading.Lock()
+        self._csl_lock = threading.Lock()
+        self._addr_lock = threading.Lock()
+        self._st_lock = threading.Lock()
 
         self.pubkey = None
         self.encinkey = None
         self.encoutkey = None
 
-        self.prepare_keys(device_pubkey)
-
-    def prepare_keys(self, device_pubkey: bytes):
+    def connection_status_updated(self, status: ConnectionStatus):
+        # self._logger.info(f'connection_status_updated: status = {status}')
+        with self._st_lock:
+            # self._logger.debug(f'connection_status_updated: lock acquired')
+            self.status = status
+            if status == ConnectionStatus.RECONNECTING:
+                self.reconnect_tries += 1
+            if status in (ConnectionStatus.CONNECTED, ConnectionStatus.NOT_CONNECTED, ConnectionStatus.DISCONNECTED):
+                self.reconnect_tries = 0
+
+    def _cleanup(self):
+        # erase outgoing queue
+        for wm in self.outgoing_queue:
+            wm.call(False,
+                    error_message=f'_cleanup: exception while calling cb(False) on message {wm.message}')
+        self.outgoing_queue = []
+        self.response_handlers = {}
+
+        # reset timestamps
+        self.incoming_time = 0
+        self.outgoing_time = 0
+        self.outgoing_time_1st = 0
+
+        self._logger.info('_cleanup: done')
+
+    def set_address(self, addr: Union[IPv4Address, IPv6Address], port: int):
+        with self._addr_lock:
+            if self.device_addr != str(addr) or self.device_port != port:
+                self.device_addr = str(addr)
+                self.device_port = port
+                self._logger.info(f'updated device network address: {self.device_addr}:{self.device_port}')
+
+    def set_device_pubkey(self, pubkey: bytes):
+        if self.device_pubkey.hex() != pubkey.hex():
+            self._logger.info(f'device pubkey has changed (old={self.device_pubkey.hex()}, new={pubkey.hex()})')
+            self.device_pubkey = pubkey
+            self._notify_cs(ConnectionStatus.RECONNECTING)
+
+    def get_address(self) -> Tuple[str, int]:
+        with self._addr_lock:
+            return self.device_addr, self.device_port
+
+    def add_incoming_message_listener(self, listener: IncomingMessageListener):
+        with self._iml_lock:
+            if listener not in self.inc_listeners:
+                self.inc_listeners.append(listener)
+
+    def add_connection_status_listener(self, listener: ConnectionStatusListener):
+        with self._csl_lock:
+            if listener not in self.conn_listeners:
+                self.conn_listeners.append(listener)
+
+    def _notify_cs(self, status: ConnectionStatus):
+        # self._logger.debug(f'_notify_cs: status={status}')
+        with self._csl_lock:
+            for obj in self.conn_listeners:
+                # self._logger.debug(f'_notify_cs: notifying {obj}')
+                obj.connection_status_updated(status)
+
+    def _prepare_keys(self):
         # generate key pair
         privkey = X25519PrivateKey.generate()
 
-        self.pubkey = bytes(reversed(privkey.public_key().public_bytes(encoding=cryptography.hazmat.primitives._serialization.Encoding.Raw,
-                                                                       format=cryptography.hazmat.primitives._serialization.PublicFormat.Raw)))
+        self.pubkey = bytes(reversed(privkey.public_key().public_bytes(encoding=srlz.Encoding.Raw,
+                                                                       format=srlz.PublicFormat.Raw)))
 
         # generate shared key
         device_pubkey = X25519PublicKey.from_public_bytes(
-            bytes(reversed(device_pubkey))
+            bytes(reversed(self.device_pubkey))
         )
         shared_key = bytes(reversed(
             privkey.exchange(device_pubkey)
@@ -362,51 +864,286 @@ class Connection(threading.Thread):
         self.encinkey = shared_sha256[:16]
         self.encoutkey = shared_sha256[16:]
 
+        self._logger.info('encryption keys have been created')
+
+    def _handshake_callback(self, r: MessageResponse):
+        # if got error for our HandshakeMessage, reset everything and try again
+        if r is False:
+            # self._logger.debug('_handshake_callback: set status=RECONNETING')
+            self._notify_cs(ConnectionStatus.RECONNECTING)
+        else:
+            # self._logger.debug('_handshake_callback: set status=CONNECTED')
+            self._notify_cs(ConnectionStatus.CONNECTED)
+
     def run(self):
+        self._logger.info('starting server loop')
+
         sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
         sock.bind(('0.0.0.0', self.source_port))
-        sock.settimeout(1)
+        sock.settimeout(READ_TIMEOUT)
 
         while not self.interrupted:
-            if not self.outgoing_queue.empty():
-                message = self.outgoing_queue.get()
-                message.encrypt(outkey=self.encoutkey,
-                                inkey=self.encinkey,
-                                token=self.device_token,
-                                pubkey=self.pubkey)
-                buf = message.frame.pack()
-                self.logger.debug('send: '+buf.hex())
-                self.logger.debug(f'sendto: {self.device_addr}:{self.device_port}')
-                sock.sendto(buf, (self.device_addr, self.device_port))
+            with self._st_lock:
+                status = self.status
+
+            if status in (ConnectionStatus.DISCONNECTED, ConnectionStatus.RECONNECTING):
+                self._cleanup()
+                if status == ConnectionStatus.DISCONNECTED:
+                    break
+
+            # no activity for some time means connection is broken
+            fail = False
+            fail_path = 0
+            if self.incoming_time > 0 and time.time() - self.incoming_time >= DISCONNECT_TIMEOUT:
+                fail = True
+                fail_path = 1
+            elif self.outgoing_time_1st > 0 and self.incoming_time == 0 and time.time() - self.outgoing_time_1st >= DISCONNECT_TIMEOUT:
+                fail = True
+                fail_path = 2
+
+            if fail:
+                self._logger.debug(f'run: setting status=RECONNECTING because of long inactivity, fail_path={fail_path}')
+                self._notify_cs(ConnectionStatus.RECONNECTING)
+
+            # establishing a connection
+            if status in (ConnectionStatus.RECONNECTING, ConnectionStatus.NOT_CONNECTED):
+                if status == ConnectionStatus.RECONNECTING and self.reconnect_tries >= 3:
+                    self._notify_cs(ConnectionStatus.DISCONNECTED)
+                    continue
+
+                self._reset_outseq()
+                self._prepare_keys()
+
+                # shake the imaginary kettle's hand
+                wrapped = WrappedMessage(HandshakeMessage(),
+                                         handler=self._handshake_callback,
+                                         validator=lambda m: isinstance(m, (AckMessage, HandshakeResponseMessage)))
+                self.enqueue_message(wrapped, prepend=True)
+                self._notify_cs(ConnectionStatus.CONNECTING)
+
+            # pick next (wrapped) message to send
+            wm = self._get_next_message()  # wm means "wrapped message"
+            if wm:
+                if not isinstance(wm.message, (AckMessage, NakMessage)):
+                    old_seq = wm.seq
+                    wm.seq = self.outseq
+                    self._set_response_handler(wm, old_seq=old_seq)
+                elif wm.seq is None:
+                    # ack/nak is a response to some incoming message (and it must have the same seqno that incoming
+                    # message had)
+                    raise RuntimeError(f'run: seq must be set for {wm.__class__.__name__}')
+
+                self._logger.debug(f'run: sending message: {wm.message}')
+                wm.message.encrypt(outkey=self.encoutkey, inkey=self.encinkey,
+                                   token=self.device_token, pubkey=self.pubkey)
+                buf = wm.message.frame.pack()
+                one_shot = isinstance(wm.message, (AckMessage, NakMessage, PingMessage))
+                # self._logger.debug(f'run: raw data to be sent: {buf.hex()}')
+
+                # sending the first time
+                if wm.phase == MessagePhase.WAITING:
+                    sock.sendto(buf, self.get_address())
+                # resending
+                elif wm.phase == MessagePhase.SENT:
+                    left = RESEND_ATTEMPTS
+                    while left > 0:
+                        sock.sendto(buf, self.get_address())
+                        left -= 1
+                        if left > 0:
+                            time.sleep(0.05)
+
+                if one_shot or wm.phase == MessagePhase.SENT:
+                    wm.phase = MessagePhase.DONE
+                else:
+                    wm.phase = MessagePhase.SENT
+
+                now = time.time()
+                self.outgoing_time = now
+                if not self.outgoing_time_1st:
+                    self.outgoing_time_1st = now
+
+            # receiving data
             try:
                 data = sock.recv(4096)
-                self.handle_incoming(data)
-            except TimeoutError:
+                self._handle_incoming(data)
+            except (TimeoutError, socket.timeout):
                 pass
 
-    def handle_incoming(self, buf: bytes):
-        self.logger.debug('handle_incoming: '+buf.hex())
-        message = Message.from_encrypted(buf, inkey=self.encinkey, outkey=self.encoutkey)
-        if message.frame.head.seq in self.waiting_for_response:
-            self.logger.info(f'received awaited message: {message}')
+        self._logger.info('bye...')
+
+    def _get_next_message(self) -> Optional[WrappedMessage]:
+        message = None
+        lpfx = '_get_next_message:'
+        remove_list = []
+        for wm in self.outgoing_queue:
+            if wm.phase == MessagePhase.DONE:
+                if isinstance(wm.message, (AckMessage, NakMessage)) or time.time() - wm.phase_update_time >= MESSAGE_QUEUE_REMOVE_DELAY:
+                    remove_list.append(wm)
+                continue
+            message = wm
+            break
+
+        for wm in remove_list:
+            self._logger.debug(f'{lpfx} rm path: removing id={wm.id} seq={wm.seq}')
+
+            # clear message handler
+            if wm.seq in self.response_handlers:
+                self.response_handlers[wm.seq].call(
+                    False, error_message=f'{lpfx} rm path: error while calling callback for seq={wm.seq}')
+                del self.response_handlers[wm.seq]
+
+            # remove from queue
             try:
-                f = self.waiting_for_response[message.frame.head.seq]
-                f(message)
-            except Exception as exc:
-                self.logger.exception(exc)
-            finally:
-                del self.waiting_for_response[message.frame.head.seq]
+                self.outgoing_queue.remove(wm)
+            except ValueError as exc:
+                self._logger.error(f'{lpfx} rm path: removing from outgoing_queue raised an exception: {str(exc)}')
+
+        # ping pong
+        if self.outgoing_time_1st != 0 and self.status == ConnectionStatus.CONNECTED:
+            now = time.time()
+            out_delta = now - self.outgoing_time
+            in_delta = now - self.incoming_time
+            if not message and max(out_delta, in_delta) > PING_FREQUENCY:
+                self._logger.debug(f'{lpfx} no activity: in for {in_delta:.2f}s, out for {out_delta:.2f}s, time to ping the damn thing')
+                message = WrappedMessage(PingMessage(), ack=True)
+
+        return message
+
+    def _handle_incoming(self, buf: bytes):
+        self.incoming_time = time.time()
+
+        incoming_message = Message.from_encrypted(buf, inkey=self.encinkey, outkey=self.encoutkey)
+        seq = incoming_message.seq
+
+        lpfx = f'handle_incoming({incoming_message.id}):'
+        self._logger.debug(f'{lpfx} received: {incoming_message}')
+
+        if isinstance(incoming_message, (AckMessage, NakMessage)):
+            seq_max = self.outseq
+            seq_name = 'outseq'
+        else:
+            seq_max = self.inseq
+            seq_name = 'inseq'
+            self.inseq = seq
+
+        if seq < seq_max < 0xfd:
+            self._logger.warning(f'{lpfx} dropping: seq={seq}, {seq_name}={seq_name}')
+            return
+
+        if seq not in self.response_handlers:
+            self._handle_incoming_cmd(incoming_message)
+            return
+
+        callback_value = None  # None means don't call a callback
+        handler = self.response_handlers[seq]
+
+        if handler.validate(incoming_message):
+            self._logger.info(f'{lpfx} response OK')
+            handler.phase = MessagePhase.DONE
+            callback_value = incoming_message
+            self._incr_outseq()
         else:
-            self.logger.info(f'received message (not awaited): {message}')
-
-    def send_message(self, message: Message, callback: callable):
-        seq = self.next_seqno()
-        message.set_seq(seq)
-        self.outgoing_queue.put(message)
-        self.waiting_for_response[seq] = callback
-
-    def next_seqno(self) -> int:
-        with self.lock:
-            self.seq_no += 1
-            self.logger.debug(f'next_seqno: set to {self.seq_no}')
-        return self.seq_no
+            self._logger.info(f'{lpfx} response is INVALID')
+
+            # It seems that we've received an incoming CmdMessage or PingMessage with the same seqno that our outgoing
+            # message had. Bad, but what can I say, this is quick-and-dirty made UDP based protocol and this sort of
+            # shit just happens.
+
+            # (To be fair, maybe my implementation is not perfect either. But hey, what did you expect from a
+            # reverse-engineered re-implementation of custom UDP-based protocol that some noname vendor uses for their
+            # cheap IoT devices? I think _that_ is _the_ definition of shit. At least my implementation is FOSS, which
+            # is more than you'll ever be able to say about them.)
+
+            # All this crapload of code below might not be needed at all, 'cause the protocol uses separate frame seq
+            # numbers for IN and OUT frames and this situation is not highly likely, as Theresa May could argue.
+            # After a handshake, a kettle sends us 10 or so CmdMessages, and then either we continuously ping it every
+            # 3 seconds, or kettle pings us. This in any case widens the gap between inseq and outseq.
+
+            # But! the seqno is only 1 byte in size and once it reaches 0xff, it circles back to zero. And that (plus,
+            # perhaps, some bad luck) gives a chance for a collision.
+
+            if handler.phase == MessagePhase.DONE or isinstance(handler.message, HandshakeMessage):
+                # no more attempts left, returning error back to user
+                # as to handshake, it cannot fail.
+                callback_value = False
+
+            # else:
+            #     # try resending the message
+            #     handler.phase_reset()
+            #     max_seq = self.outseq
+            #     wait_remap = {}
+            #     for m in self.outgoing_queue:
+            #         if m.seq in self.waiting_for_response:
+            #             wait_remap[m.seq] = (m.seq+1) % 256
+            #         m.set_seq((m.seq+1) % 256)
+            #         if m.seq > max_seq:
+            #             max_seq = m.seq
+            #     if max_seq > self.outseq:
+            #         self.outseq = max_seq % 256
+            #     if wait_remap:
+            #         waiting_new = {}
+            #         for old_seq, new_seq in wait_remap.items():
+            #             waiting_new[new_seq] = self.waiting_for_response[old_seq]
+            #         self.waiting_for_response = waiting_new
+
+            if isinstance(incoming_message, (PingMessage, CmdIncomingMessage)):
+                # handle incoming message as usual, as we need to ack/nak it anyway
+                self._handle_incoming_cmd(incoming_message)
+
+        if callback_value is not None:
+            handler.call(callback_value,
+                         error_message=f'{lpfx} error while calling callback for msg id={handler.message.id} seq={seq}')
+            del self.response_handlers[seq]
+
+    def _handle_incoming_cmd(self, incoming_message: Message):
+        if isinstance(incoming_message, (AckMessage, NakMessage)):
+            self._logger.debug(f'_handle_incoming_cmd({incoming_message.id}, seq={incoming_message.seq}): it\'s {incoming_message.__class__.__name__}, ignoring')
+            return
+
+        replied = False
+        with self._iml_lock:
+            for f in self.inc_listeners:
+                retval = safe_callback_call(f.incoming_message, incoming_message,
+                                            logger=self._logger,
+                                            error_message=f'_handle_incoming_cmd({incoming_message.id}, seq={incoming_message.seq}): error while calling message listener')
+                if isinstance(retval, Message):
+                    if isinstance(retval, (AckMessage, NakMessage)):
+                        retval.seq = incoming_message.seq
+                        self.enqueue_message(WrappedMessage(retval), prepend=True)
+                        replied = True
+                        break
+                    else:
+                        raise RuntimeError('are you sure your response is correct? only ack/nak are allowed')
+
+        if not replied:
+            self.enqueue_message(WrappedMessage(AckMessage(incoming_message.seq)), prepend=True)
+
+    def enqueue_message(self, wrapped: WrappedMessage, prepend=False):
+        self._logger.debug(f'enqueue_message: {wrapped.message}')
+        if not prepend:
+            self.outgoing_queue.append(wrapped)
+        else:
+            self.outgoing_queue.insert(0, wrapped)
+
+    def _set_response_handler(self, wm: WrappedMessage, old_seq=None):
+        if old_seq in self.response_handlers:
+            del self.response_handlers[old_seq]
+
+        seq = wm.seq
+        assert seq is not None, 'seq is not set'
+
+        if seq in self.response_handlers:
+            self._logger.warning(f'_set_response_handler(seq={seq}): handler is already set, cancelling it')
+            self.response_handlers[seq].call(False,
+                                             error_message=f'_set_response_handler({seq}): error while calling old callback')
+        self.response_handlers[seq] = wm
+
+    def _incr_outseq(self) -> None:
+        self.outseq = (self.outseq + 1) % 256
+
+    def _reset_outseq(self):
+        self.outseq = 0
+        self._logger.debug(f'_reset_outseq: set 0')
+
+
+MessageResponse = Union[Message, bool]