plone.transformchain 1.2.0

Introduction

plone.transformchain provides methods to modify the response from a page published with repoze.zope2 or the “classic” ZPublisher before it is returned to the browser.

Register a uniquely named adapter from (published, request) providing the ITransform interface. published is the published object, e.g. a view; request is the current request.

The order of the transforms can be maintained using the order property of the adapter.

One of three methods will be called, depending on what type of input was obtained from the publisher and/or the previous method.

• transformBytes() is called if the input is a str (bytes) object

• transformUnicode() is called if the input is a unicode object

• transformIterable() is called if the input is another type of iterable

Each stage can return a byte string, a unicode string, or an iterable.

Most transformers will have a “natural” representation of the result, and will implement the respective method to return another value of the same representation, e.g. implement transformUnicode() to transform and return a unicode object. The other methods may then either be implemented to return None (do nothing) or convert the value to the appropriate type.

The first transformer in the chain is likely to get:

• A byte string if the transformer is running under the standard Zope 2 ZPublisher.

• An iterable if the transformer is running under repoze.zope2 or another WSGI pipeline.

Check self.request.response.getHeader('content-type') to see the type of result. The iterable, when unwound, will conform to this type, e.g. for “text/html”, ''.join(result) should be an HTML string.

The return value is passed to the next transform in the chain. The final transform should return a unicode string, an encoded string, or an iterable.

If a byte string or unicode string is returned by the last transform in the chain, the Content-Length header will be automatically updated.

Return None to signal that the result should not be changed from the previous transform.

Here is an example that uppercases everything:

from zope.component import adapter
from zope.interface import implementer
from zope.interface import Interface
from plone.transformchain.interfaces import ITransform

@implementer(ITransform)
@adapter(Interface, Interface) # any context, any request
class UpperTransform(object):

    order = 1000

    def __init__(self, published, request):
        self.published = published
        self.request = request

    def transformBytes(self, result, encoding):
        return result.upper()

    def transformUnicode(self, result, encoding):
        return result.upper()

    def transformIterable(self, result, encoding):
        return [s.upper() for s in result]

You could register this in ZCML like so:

<adapter factory=".transforms.UpperTransform" name="example.uppertransform" />

If you need to turn off transformations for a particular request, you can set a key in request.environ:

request.environ['plone.transformchain.disable'] = True

This will leave the response untouched and will not invoke any ITransform adapters at all.

Changelog