asyncvarlink

This is a pure Python implementation of the varlink IPC protocol based on asyncio. The main differences to he reference implementation are:

• Usage of asyncio instead of synchronous threading
• Where the reference implementation parses a varlink interface description as a source of truth, this implementation derives a varlink interface description from a typed Python class to describe an interface.
• Even though the varlink faq explicitly renders passing file descriptors out of scope, systemd uses it and it is an important feature also implemented here.

Client usage

The VarlinkServiceInterface class represents the org.varlink.service introspection interface. We can use it to introspect systemd-hostnamed.

import asyncio
from asyncvarlink import VarlinkClientProtocol, connect_unix_varlink
from asyncvarlink.serviceinterface import VarlinkServiceInterface

async def main() -> None:
    t, p = await connect_unix_varlink(
        VarlinkClientProtocol, "/run/systemd/io.systemd.Hostname"
    )
    i = p.make_proxy(VarlinkServiceInterface)
    print(await i.GetInfo())
    t.close()

asyncio.run(main())

Server usage

Here is an example for defining an interface. If it is to be used by a server, the methods need to be implemented of course, but on the client side, typed stubs will do.

import asyncio
import collections.abc
import enum
from asyncvarlink import VarlinkInterface, varlinkmethod

class Direction(enum.Enum):
    left = "left"
    right = "right"

class DemoInterface(VarlinkInterface, name="com.example.demo"):
    @varlinkmethod(return_parameter="direction")
    def Reverse(self, *, value: Direction) -> Direction:
        return Direction.left if value == Direction.right else Direction.right

    @varlinkmethod(return_parameter="value")
    def Range(self, *, count: int) -> collections.abc.Iterator[int]:
        return iter(range(count))

    @varlinkmethod
    async def Sleep(self, *, delay: float) -> None:
        await asyncio.sleep(delay)

Setting up a service is now a matter of plugging things together.

import asyncio
import sys
from asyncvarlink import VarlinkInterfaceRegistry, VarlinkTransport
from asyncvarlink.serviceinterface import VarlinkServiceInterface

registry = VarlinkInterfaceRegistry()
registry.register_interface(
    VarlinkServiceInterface(
        "ExampleVendor",
        "DemonstrationProduct",
        "1.0",
        "https://github.com/helmutg/asyncvarlink",
        registry,
    ),
)
registry.register_interface(DemoInterface())
VarlinkTransport(
    asyncio.get_event_loop(),
    sys.stdin.fileno(),
    sys.stdout.fileno(),
    registry.protocol_factory(),
)

When communicating via stdio, varlinkctl from systemd may be used to interact with a service. Registering a VarlinkServiceInterface implementing the org.varlink.service introspection interface is optional.

Documentation

The source for sphinxdoc documentation resides below docs/. A rendered version is published on github pages.

Collaboration

The primary means of collaborating on this project is github. If you prefer not to use a centralized forge, sending inquiries and patches to Helmut is also welcome.

License

LGPL-2.0-or-later