Telnet switch (#8913)

* Added telnet switch.

* Lint.

* Coverage

* Added port parameter to Telnet switch.

* Removed optimistic attribute from Telnet switch.

* Code cleanup.

.coveragerc

@@ -570,6 +570,7 @@ omit =
     homeassistant/components/switch/rest.py
     homeassistant/components/switch/rpi_rf.py
     homeassistant/components/switch/tplink.py
+    homeassistant/components/switch/telnet.py
     homeassistant/components/switch/transmission.py
     homeassistant/components/switch/wake_on_lan.py
     homeassistant/components/telegram_bot/*

homeassistant/components/switch/telnet.py

@@ -0,0 +1,144 @@
+"""
+Support for switch controlled using a telnet connection.
+
+For more details about this platform, please refer to the documentation at
+https://home-assistant.io/components/switch.telnet/
+"""
+import logging
+import telnetlib
+from datetime import timedelta
+
+import voluptuous as vol
+
+from homeassistant.components.switch import (SwitchDevice, PLATFORM_SCHEMA,
+                                             ENTITY_ID_FORMAT)
+from homeassistant.const import (
+    CONF_RESOURCE, CONF_NAME, CONF_SWITCHES, CONF_VALUE_TEMPLATE,
+    CONF_COMMAND_OFF, CONF_COMMAND_ON, CONF_COMMAND_STATE, CONF_PORT)
+import homeassistant.helpers.config_validation as cv
+
+_LOGGER = logging.getLogger(__name__)
+
+DEFAULT_PORT = 23
+
+SWITCH_SCHEMA = vol.Schema({
+    vol.Required(CONF_COMMAND_ON): cv.string,
+    vol.Required(CONF_COMMAND_OFF): cv.string,
+    vol.Optional(CONF_COMMAND_STATE): cv.string,
+    vol.Optional(CONF_NAME): cv.string,
+    vol.Optional(CONF_PORT, default=DEFAULT_PORT): cv.port,
+    vol.Required(CONF_RESOURCE): cv.string,
+    vol.Required(CONF_VALUE_TEMPLATE): cv.template,
+})
+
+PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
+    vol.Required(CONF_SWITCHES): vol.Schema({cv.slug: SWITCH_SCHEMA}),
+})
+
+SCAN_INTERVAL = timedelta(seconds=10)
+
+
+# pylint: disable=unused-argument
+def setup_platform(hass, config, add_devices, discovery_info=None):
+    """Find and return switches controlled by telnet commands."""
+    devices = config.get(CONF_SWITCHES, {})
+    switches = []
+
+    for object_id, device_config in devices.items():
+        value_template = device_config.get(CONF_VALUE_TEMPLATE)
+
+        if value_template is not None:
+            value_template.hass = hass
+
+        switches.append(
+            TelnetSwitch(
+                hass,
+                object_id,
+                device_config.get(CONF_RESOURCE),
+                device_config.get(CONF_PORT),
+                device_config.get(CONF_NAME, object_id),
+                device_config.get(CONF_COMMAND_ON),
+                device_config.get(CONF_COMMAND_OFF),
+                device_config.get(CONF_COMMAND_STATE),
+                value_template
+            )
+        )
+
+    if not switches:
+        _LOGGER.error("No switches added")
+        return False
+
+    add_devices(switches)
+
+
+class TelnetSwitch(SwitchDevice):
+    """Representation of a switch that can be toggled using telnet commands."""
+
+    def __init__(self, hass, object_id, resource, port, friendly_name,
+                 command_on, command_off, command_state, value_template):
+        """Initialize the switch."""
+        self._hass = hass
+        self.entity_id = ENTITY_ID_FORMAT.format(object_id)
+        self._resource = resource
+        self._port = port
+        self._name = friendly_name
+        self._state = False
+        self._command_on = command_on
+        self._command_off = command_off
+        self._command_state = command_state
+        self._value_template = value_template
+
+    def _telnet_command(self, command):
+        try:
+            telnet = telnetlib.Telnet(self._resource, self._port)
+            telnet.write(command.encode('ASCII') + b'\r')
+            response = telnet.read_until(b'\r', timeout=0.2)
+            return response.decode('ASCII').strip()
+        except IOError as error:
+            _LOGGER.error(
+                'Command "%s" failed with exception: %s',
+                command, repr(error))
+            return None
+
+    @property
+    def name(self):
+        """Return the name of the switch."""
+        return self._name
+
+    @property
+    def should_poll(self):
+        """Only poll if we have state command."""
+        return self._command_state is not None
+
+    @property
+    def is_on(self):
+        """Return true if device is on."""
+        return self._state
+
+    @property
+    def assumed_state(self):
+        """Default ist true if no state command is defined, false otherwise."""
+        return self._command_state is None
+
+    def update(self):
+        """Update device state."""
+        response = self._telnet_command(self._command_state)
+        if response:
+            rendered = self._value_template \
+                .render_with_possible_json_value(response)
+            self._state = rendered == "True"
+        else:
+            _LOGGER.warning(
+                "Empty response for command: %s", self._command_state)
+
+    def turn_on(self, **kwargs):
+        """Turn the device on."""
+        self._telnet_command(self._command_on)
+        if self.assumed_state:
+            self._state = True
+
+    def turn_off(self, **kwargs):
+        """Turn the device off."""
+        self._telnet_command(self._command_off)
+        if self.assumed_state:
+            self._state = False