SkillApi: Inter-Skill RPC

SkillApi provides a MessageBus-based remote procedure call (RPC) mechanism. Methods decorated with @skill_api_method are exposed on the bus. Any other skill (or application) can call them by fetching a SkillApi proxy object.

Source: ovos_workshop/skills/api.py

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Overview

The bus message protocol for SkillApi has two phases:

1. Discovery: the caller sends <skill_id>.public_api on the bus. The target skill responds with a dict mapping method names to their bus message type and docstring.
2. Call: the caller sends a Message of the method's registered type with {"args": [...], "kwargs": {...}}. The target skill responds with {"result": <return value>}.

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@skill_api_method Decorator

skill_api_method is defined in ovos_workshop/decorators/__init__.py:77. Tag a skill method as part of the public API. The method must be defined on an OVOSSkill subclass.

from ovos_workshop.decorators import skill_api_method

class MySkill(OVOSSkill):

    @skill_api_method
    def get_temperature(self, city: str) -> float:
        """Return the current temperature for the given city."""
        return self._fetch_temperature(city)

The decorator sets func.api_method = True. During skill initialization, OVOSSkill discovers all methods with this attribute and registers a bus listener for each one at <skill_id>.<method_name>.

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SkillApi Class

SkillApi is defined in ovos_workshop/skills/api.py:20.

Class Attribute: bus

SkillApi.bus is defined in ovos_workshop/skills/api.py:27. A class-level reference to the MessageBusClient. Must be set before calling SkillApi.get().

SkillApi.connect_bus(mycroft_bus)

SkillApi.connect_bus is defined in ovos_workshop/skills/api.py:29. Register the bus client. Call this once during application startup.

from ovos_workshop.skills.api import SkillApi

SkillApi.connect_bus(bus)

SkillApi.get(skill, api_timeout=3)

SkillApi.get is defined in ovos_workshop/skills/api.py:65. Fetches the public API for the given skill and returns a proxy object. Returns None if the skill is not running or does not expose any API methods.

@staticmethod
def get(skill: str, api_timeout: int = 3) -> Optional[object]:

Parameter	Description
skill	The skill_id of the target skill.
api_timeout	Seconds to wait for each remote method call (default 3).

Raises RuntimeError if SkillApi.bus has not been set.

The returned proxy object has one attribute per exposed method. Calling proxy.method_name(*args, **kwargs) sends the corresponding bus message and returns the result field of the response. Returns None on timeout.

SkillApi.__init__(method_dict, timeout=3)

SkillApi.__init__ is defined in ovos_workshop/skills/api.py:34. Normally you do not construct SkillApi directly. Use SkillApi.get() instead. The constructor builds a dynamic method for every entry in method_dict.

Parameter	Description
method_dict	Dict mapping method names to {"help": <docstring>, "type": <bus message type>}.
timeout	Default timeout in seconds for each remote call.

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Bus Message Protocol

Discovery

Request: <skill_id>.public_api (no data)

Response: <skill_id>.public_api with data:

{
  "get_temperature": {
    "help": "Return the current temperature for the given city.",
    "type": "my-weather-skill.get_temperature"
  }
}

Method Call

Request: my-weather-skill.get_temperature with data:

{"args": ["London"], "kwargs": {}}

Response: same message type with data:

{"result": 18.5}

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Full Example

Exposing methods (server skill)

from ovos_workshop.skills.ovos import OVOSSkill
from ovos_workshop.decorators import skill_api_method


class WeatherSkill(OVOSSkill):

    @skill_api_method
    def get_temperature(self, city: str) -> float:
        """Return the current temperature in Celsius for the given city."""
        # … real implementation …
        return 18.5

    @skill_api_method
    def get_forecast(self, city: str, days: int = 3) -> list:
        """Return a weather forecast list for the given city."""
        return [{"day": i, "condition": "sunny"} for i in range(days)]

Calling methods (client skill or app)

from ovos_workshop.skills.ovos import OVOSSkill
from ovos_workshop.skills.api import SkillApi


class MyClientSkill(OVOSSkill):

    def initialize(self):
        SkillApi.connect_bus(self.bus)

    def handle_ask_weather(self, message):
        weather_api = SkillApi.get("my-weather-skill.author")
        if weather_api is None:
            self.speak("Weather skill is not available.")
            return

        temp = weather_api.get_temperature("London")
        if temp is None:
            self.speak("No response from weather skill.")
            return

        self.speak(f"It is {temp} degrees in London.")

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