CODEWITHSUNDEEP
pythonasynchronoustwisted
sereizam
sereizam

Reputation: 2120

How to debug Protocol.dataReceived in Twisted

I'm new to twisted and I'm having trouble to debug my code within the dataReceived method of the twisted.internet.protocol.Protocol object.

Given some code like this

class Printer(Protocol):
    def dataReceived(self, data):
        print data # Works perfectly
        print toto # should trigger some error since "toto" is not defined
...
response.deliverBody(Printer())

I couldn't find a way to add an Errback on dataReceived. Is there a way ? an other way to debug its behavior ?

Thanks in advance for your help.

Upvotes: 1

Views: 194

Answers (1)

notorious.no
notorious.no

Reputation: 5107

You can't catch errors from dataReceived directly since that function isn't a deferred user's generally have control over. You can only call addErrback on deferred objects. Here is an example of how to catch errors:

from twisted.internet.protocol import Protocol
from twisted.internet.defer import Deferred

class Printer(Protocol):
    def dataReceived(self, data):
        d = Deferred()
        d.addCallback(self.display_data)
        d.addErrback(self.error_func)
        d.callback(data)

    def display_data(self, data):
        print(data)
        print(toto)    # this will raise NameError error

    def error_func(self, error):
        print('[!] Whoops here is the error: {0}'.format(error))

A deferred is created in the dataReceived function which will print data and the invalid toto variables. An errorback function (ie. self.error_func()) is chained to catch errors that occur in display_data(). You should strive very hard to not have errors in the dataReceived function itself. This isn't always possible but one should try. Hope this helps

Upvotes: 1

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