Service Framework

Warning

This section is incomplete.

Mitogen includes a simple framework for implementing services exposed to other contexts, with some built-in subclasses to capture common designs. This is a work in progress, and new functionality will be added as common usage patterns emerge.

Overview

Service

• User-supplied class with explicitly exposed methods.

• May be auto-imported/constructed in a child from a parent simply by calling it

• Identified in calls by its canonical name (e.g. mypkg.mymod.MyClass) by default, but may use any naming scheme the configured activator understands.

• Children receive refusals if the class is not already activated by a aprent

• Has an associated Select instance which may be dynamically loaded with receivers over time, on_message_received() invoked if any receiver becomes ready.

Invoker

• Abstracts mechanism for calling a service method and verifying permissions.

• Built-in ‘service.Invoker’: concurrent execution of all methods on the thread pool.

• Built-in ‘service.SerializedInvoker’: serialization of all calls on a single thread borrowed from the pool while any request is pending.

• Built-in ‘service.DeduplicatingInvoker’: requests are aggregated by distinct (method, kwargs) key, only one such method ever executes, return value is cached and broadcast to all request waiters. Waiters do not block additional pool threads.

Activator

• Abstracts mechanism for activating a service and verifying activation permission.

• Built-in activator looks for service by fully.qualified.ClassName using Python import mechanism, and only permits parents to trigger activation.

Pool

• Manages a fixed-size thread pool, mapping of service name to Invoker, and an aggregate Select over every activate service’s Selects.

• Constructed automatically in children in response to the first CALL_SERVICE message sent to them by a parent.

• Must be constructed manually in parent context.

• Has close() and add() methods.

Example

import mitogen
import mitogen.service


class FileService(mitogen.service.Service):
    """
    Simple file server, for demonstration purposes only! Use of this in
    real code would be a security vulnerability as it would permit children
    to read any file from the master's disk.
    """

    @mitogen.service.expose(policy=mitogen.service.AllowAny())
    @mitogen.service.arg_spec(spec={
        'path': str
    })
    def read_file(self, path):
        with open(path, 'rb') as fp:
            return fp.read()


def download_file(source_context, path):
    s = source_context.call_service(
        service_name=FileService,  # may also be string 'pkg.mod.FileService'
        method_name='read_file',
        path=path,
    )

    with open(path, 'w') as fp:
        fp.write(s)


def download_some_files(source_context, paths):
    for path in paths:
        download_file(source_context, path)


@mitogen.main()
def main(router):
    pool = mitogen.service.Pool(router, services=[
        FileService(router),
    ])

    remote = router.ssh(hostname='k3')
    remote.call(download_some_files,
        source_context=router.myself(),
        paths=[
            '/etc/passwd',
            '/etc/hosts',
        ]
    )
    pool.stop()

Reference

Built-in Services