repoze.bfg.httprequest 0.4

Adaptable request interfaces.

Overview

The motivation for this package is to encourage the use of request type adaptation instead of depending on packages with request type definitions.

Instead of subclassing the request interface, we encourage an adaptation pattern:

>>> from repoze.bfg.interfaces import IRequest
>>> IGZipRequest = IRequest({'http_accept_encoding': 'gzip'})

An event handler listens for the INewRequest event and automatically marks the request with interfaces as needed to adapt the request to the request types that it may apply for.

To complete the example above, a request would come in with an HTTP environment like the following:

{‘http_accept_encoding’: ‘compress, gzip’}

Since we’ve previouly adapted the request to an accept-encoding of ‘gzip’, the adaptation machinery will mark the interface such that this environment will match the IGZipRequest interface.

This would be an alternative to subclassing, where we would manually have to set up an event listener that interprets the request environment and marks the request with the interface.

>>> class IGZipRequest(IRequest):
...     """Marker interface for requests for gzipped response."""

Credits

Stefan Eletzhofer <[e-mail]> and Malthe Borch <[e-mail]>.

Adaptable HTTP request interfaces

Suppose we want to adapt on requests that have an “http_accept_encoding” that calls for a gzipped response, we’d set up an interface as follows:

>>> from repoze.bfg.interfaces import IRequest
>>> IGZipRequest = IRequest({'http_accept_encoding': 'gzip'})

Let’s now craft a request that will match this interface.

>>> class TestRequest(object):
...     interface.implements(IRequest)
...
...     def __init__(self, environ):
...         self.environ = environ

>>> request = TestRequest({'http_accept_encoding': 'compress, gzip'})

At this point, the request has not been prepared for adaptation.

>>> from repoze.bfg.events import NewRequest
>>> from zope.event import notify
>>> notify(NewRequest(request))

We expect the request to implement the IGZipRequest interface.

>>> IGZipRequest.providedBy(request)
True

To get more flexibility, we can supply a match function:

>>> IAlternativeGZipRequest = IRequest(
...    {'http_accept_encoding': lambda value: 'gzip' in value})

>>> notify(NewRequest(request))
>>> IAlternativeGZipRequest.providedBy(request)
True

Suppose now we’d also like to support requests for documents in German.

>>> IGermanLanguageRequest = IRequest({'http_accept_language': 'de'})

We’ll create a new request, which, besides asking a gzipped response, also asks for the content in German.

>>> request = TestRequest(
...     {'http_accept_encoding': 'compress, gzip', 'http_accept_language': 'de'})

>>> notify(NewRequest(request))

Verify that the request provides the adapted interfaces.

>>> IGermanLanguageRequest.providedBy(request)
True

>>> IGZipRequest.providedBy(request)
True

Now, as you would expect, we can adapt a request interface that combines these two environments.

>>> IZippedGerman = IRequest(
...    {'http_accept_encoding': 'gzip', 'http_accept_language': 'de'})
>>> notify(NewRequest(request))

>>> IZippedGerman.providedBy(request)
True

Note that this interface extends the two interfaces that were created for each of the environment pairs of it.

>>> IZippedGerman.isOrExtends(IGermanLanguageRequest)
True

>>> IZippedGerman.isOrExtends(IGZipRequest)
True

Let’s try a request that doesn’t match.

>>> IZippedFrench = IRequest(
...     {'http_accept_encoding': 'gzip', 'http_accept_language': 'fr'})
>>> notify(NewRequest(request))

>>> IZippedFrench.providedBy(request)
False

Adapted requests are global with respect to the environment:

>>> IRequest({'http_accept_encoding': 'gzip'}) is IRequest({'http_accept_encoding': 'gzip'})
True

Pickle-support

The adapted interface are created dynamically and would therefore not be locatable by the pickle module. To remedy this, an import hook is added on package initialization.

(The repoze.bfg packages pickles configuration actions in order to improve startup time, and therefore it’s important that the adapted interfaces are pickable.)

>>> from pickle import dumps, loads
>>> p = dumps(IGZipRequest)

Now, we’ll pretend that we the repoze.bfg.httprequest.interfaces has not yet been imported. This will make pickle import it when we load back the pickle.

>>> import sys
>>> del sys.modules['repozehttprequestinterfaces']

We’ll reinitialize the interfaces module.

>>> loads(p)
<IHTTPRequest http_accept_encoding=gzip>