扭曲：等待推迟到'完成'

Question

How can I 'throw' deferred's into the reactor so it gets handled somewhere down the road?

Situation

I have 2 programs running on localhost.

1. A twisted jsonrpc service (localhost:30301)
2. A twisted webservice (localhost:4000)

When someone connects to the webservice, It needs to send a query to the jsonrpc service, wait for it to come back with a result, then display the result in the web browser of the user (returning the value of the jsonrpc call).

I can't seem to figure out how to return the value of the deferred jsonrpc call. When I visit the webservice with my browser I get a HTML 500 error code (did not return any byte) and Value: < Deferred at 0x3577b48 >.

It returns the deferred object and not the actual value of the callback.

Been looking around for a couple of hours and tried a lot of different variations before asking.

from txjsonrpc.web.jsonrpc import Proxy
from twisted.web import resource
from twisted.web.server import Site
from twisted.internet import reactor


class Rpc():
    def __init__(self, child):
        self._proxy = Proxy('http://127.0.0.1:30301/%s' % child)

    def execute(self, function):
        return self._proxy.callRemote(function)


class Server(resource.Resource):
    isLeaf = True

    def render_GET(self, request):
        rpc = Rpc('test').execute('test')

        def test(result):
            return '<h1>%s</h1>' % result

        rpc.addCallback(test)
        return rpc

site = Site(Server())
reactor.listenTCP(4000, site)
print 'Running'
reactor.run()

Answer 1

The problem you're having here is that web's IResource is a very old interface, predating even Deferred .

The quick solution to your problem is to use Klein , which provides a nice convenient high-level wrapper around twisted.web for writing web applications, among other things, adding lots of handling for Deferred s throughout the API.

The slightly more roundabout way to address it is to read the chapter of the Twisted documentation that is specifically about asynchronous responses in twisted.web.