Hi all,
I am writing a restful twisted (8.1.0) server and am trying to return
useful error statuses from requests. The problem is that even
following the documentation extremely carefully I am getting an
AlreadyCalled Error every time I generate a failure. Here is my main
class (leaving out code that I feel is not relevant to the question:
from xml.dom import minidom
from twisted.web import server, resource
from FWGException import FWGException
class DeferredPostHandler(resource.Resource,minidom.Document):
NOT_IMPLEMENTED = 501
BAD_REQUEST = 400
def writeError(self, failure, request, *args, **kw):
failure.trap(FWGException)
request.setResponseCode(self.errorCode)
request.write("Error handling request: %s" %
failure.getErrorMessage())
request.finish()
def writeResult(self, result, request, *args, **kw):
self.writexml(request)
request.finish()
def render_GET(self, request):
self.process=self.db.runInteraction(self.processForm,request)
self.process.addCallbacks(self.writeResult, self.writeError,
[request], {}, [request], {})
return server.NOT_DONE_YET
I have a handler that extends this
from DeferredPostHandler import DeferredPostHandler
from twisted.web import http
from twisted.python.failure import Failure
from FWGException import FWGException
class CollectionAdminHandler(DeferredPostHandler):
def __init__(self, task, db, config):
DeferredPostHandler.__init__(self,db)
self.config = config
self.task = task
self.errorCode = http.OK
def processForm(self, cursor, request):
if self.task == 'add':
self.addCollection(cursor, request)
elif self.task == 'delete':
self.deleteCollection(cursor, request)
else:
self.errorCode = DeferredPostHandler.NOT_IMPLEMENTED
fail = Failure(FWGException("Unsupported Task"))
self.process.errback(fail)
def addCollection(self, cursor, request):
fail = None
if self.isValidAddRequest(request):
pass
else:
self.errorCode = DeferredPostHandler.BAD_REQUEST
fail = Failure(FWGException("Missing Parameter"))
if fail:
self.process.errback(fail);
def deleteCollection(self, cursor, request):
print 'Delete Collection'
def isValidAddRequest(self, request):
return 'title' in request.args and 'category' in request.args
and 'date' in request.args
Unfortunately whenever I call
self.process.errback(fail)
I get the following stack trace in my log
Traceback (most recent call last):
File "startserver.py", line 23, in <module>
reactor.run()
File "/Library/Python/2.5/site-packages/Twisted-8.1.0-py2.5-
macosx-10.5-i386.egg/twisted/internet/base.py", line 1048, in run
self.mainLoop()
File "/Library/Python/2.5/site-packages/Twisted-8.1.0-py2.5-
macosx-10.5-i386.egg/twisted/internet/base.py", line 1057, in mainLoop
self.runUntilCurrent()
--- <exception caught here> ---
File "/Library/Python/2.5/site-packages/Twisted-8.1.0-py2.5-
macosx-10.5-i386.egg/twisted/internet/base.py", line 677, in
runUntilCurrent
f(*a, **kw)
File "/Library/Python/2.5/site-packages/Twisted-8.1.0-py2.5-
macosx-10.5-i386.egg/twisted/internet/defer.py", line 243, in callback
self._startRunCallbacks(result)
File "/Library/Python/2.5/site-packages/Twisted-8.1.0-py2.5-
macosx-10.5-i386.egg/twisted/internet/defer.py", line 298, in
_startRunCallbacks
raise AlreadyCalledError
twisted.internet.defer.AlreadyCalledError:
I can not understand why this is happening :-( Can anybody help?
BTW I am using POST instead of PUT because my client can't do PUT
Conrad Winchester
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