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python-kasa/docs/source/topics.md

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Topics

   :local:

These topics aim to provide some details on the design and internals of this library. You might be interested in this if you want to improve this library, or if you are just looking to access some information that is not currently exposed.

(topics-initialization)=

Initialization

Use {func}~kasa.Discover.discover to perform udp-based broadcast discovery on the network. This will return you a list of device instances based on the discovery replies.

If the device's host is already known, you can use to construct a device instance with {meth}~kasa.Device.connect().

The {meth}~kasa.Device.connect() also enables support for connecting to new KASA SMART protocol and TAPO devices directly using the parameter {class}~kasa.DeviceConfig. Simply serialize the {attr}~kasa.Device.config property via {meth}~kasa.DeviceConfig.to_dict() and then deserialize it later with {func}~kasa.DeviceConfig.from_dict() and then pass it into {meth}~kasa.Device.connect().

(topics-discovery)=

Discovery

Discovery works by sending broadcast UDP packets to two known TP-link discovery ports, 9999 and 20002. Port 9999 is used for legacy devices that do not use strong encryption and 20002 is for newer devices that use different levels of encryption. If a device uses port 20002 for discovery you will obtain some basic information from the device via discovery, but you will need to await {func}Device.update() <kasa.Device.update()> to get full device information. Credentials will most likely be required for port 20002 devices although if the device has never been connected to the tplink cloud it may work without credentials.

To query or update the device requires authentication via {class}Credentials <kasa.Credentials> and if this is invalid or not provided it will raise an {class}AuthenticationException <kasa.AuthenticationException>.

If discovery encounters an unsupported device when calling via {meth}Discover.discover_single() <kasa.Discover.discover_single> it will raise a {class}UnsupportedDeviceException <kasa.UnsupportedDeviceException>. If discovery encounters a device when calling {func}Discover.discover() <kasa.Discover.discover>, you can provide a callback to the on_unsupported parameter to handle these.

(topics-deviceconfig)=

DeviceConfig

The {class}DeviceConfig class can be used to initialise devices with parameters to allow them to be connected to without using discovery. This is required for newer KASA and TAPO devices that use different protocols for communication and will not respond on port 9999 but instead use different encryption protocols over http port 80. Currently there are three known types of encryption for TP-Link devices and two different protocols. Devices with automatic firmware updates enabled may update to newer versions of the encryption without separate notice, so discovery can be helpful to determine the correct config.

To connect directly pass a {class}DeviceConfig object to {meth}Device.connect().

A {class}DeviceConfig can be constucted manually if you know the {attr}DeviceConfig.connection_type values for the device or alternatively the config can be retrieved from {attr}Device.config post discovery and then re-used.

(topics-update-cycle)=

Update Cycle

When {meth}~kasa.Device.update() is called, the library constructs a query to send to the device based on :ref:supported modules <modules>. Internally, each module defines {meth}~kasa.modules.Module.query() to describe what they want query during the update.

The returned data is cached internally to avoid I/O on property accesses. All properties defined both in the device class and in the module classes follow this principle.

While the properties are designed to provide a nice API to use for common use cases, you may sometimes want to access the raw, cached data as returned by the device. This can be done using the {attr}~kasa.Device.internal_state property.

(topics-modules-and-features)=

Modules and Features

The functionality provided by all {class}~kasa.Device instances is (mostly) done inside separate modules. While the individual device-type specific classes provide an easy access for the most import features, you can also access individual modules through {attr}kasa.Device.modules. You can get the list of supported modules for a given device instance using {attr}~kasa.Device.supported_modules.

If you only need some module-specific information,
you can call the wanted method on the module to avoid using {meth}`~kasa.Device.update`.

(topics-protocols-and-transports)=

Protocols and Transports

The library supports two different TP-Link protocols, IOT and SMART. IOT is the original Kasa protocol and SMART is the newer protocol supported by TAPO devices and newer KASA devices. The original protocol has a target, command, args interface whereas the new protocol uses a different set of commands and has a method, parameters interface. Confusingly TP-Link originally called the Kasa line "Kasa Smart" and hence this library used "Smart" in a lot of the module and class names but actually they were built to work with the IOT protocol.

In 2021 TP-Link started updating the underlying communication transport used by Kasa devices to make them more secure. It switched from a TCP connection with static XOR type of encryption to a transport called KLAP which communicates over http and uses handshakes to negotiate a dynamic encryption cipher. This automatic update was put on hold and only seemed to affect UK HS100 models.

In 2023 TP-Link started updating the underlying communication transport used by Tapo devices to make them more secure. It switched from AES encryption via public key exchange to use KLAP encryption and negotiation due to concerns around impersonation with AES. The encryption cipher is the same as for Kasa KLAP but the handshake seeds are slightly different. Also in 2023 TP-Link started releasing newer Kasa branded devices using the SMART protocol. This appears to be driven by hardware version rather than firmware.

In order to support these different configurations the library migrated from a single protocol class TPLinkSmartHomeProtocol to support pluggable transports and protocols. The classes providing this functionality are:

  • {class}BaseProtocol <kasa.protocols.BaseProtocol>

  • {class}IotProtocol <kasa.protocols.IotProtocol>

  • {class}SmartProtocol <kasa.protocols.SmartProtocol>

  • {class}BaseTransport <kasa.transports.BaseTransport>

  • {class}XorTransport <kasa.transports.XorTransport>

  • {class}AesTransport <kasa.transports.AesTransport>

  • {class}KlapTransport <kasa.transports.KlapTransport>

  • {class}KlapTransportV2 <kasa.transports.KlapTransportV2>

(topics-errors-and-exceptions)=

Errors and Exceptions

The base exception for all library errors is {class}KasaException <kasa.exceptions.KasaException>.

  • If the device returns an error the library raises a {class}DeviceError <kasa.exceptions.DeviceError> which will usually contain an error_code with the detail.
  • If the device fails to authenticate the library raises an {class}AuthenticationError <kasa.exceptions.AuthenticationError> which is derived from {class}DeviceError <kasa.exceptions.DeviceError> and could contain an error_code depending on the type of failure.
  • If the library encounters and unsupported deviceit raises an {class}UnsupportedDeviceError <kasa.exceptions.UnsupportedDeviceError>.
  • If the device fails to respond within a timeout the library raises a {class}TimeoutError <kasa.exceptions.TimeoutError>.
  • All other failures will raise the base {class}KasaException <kasa.exceptions.KasaException> class.