File fields exporter and importer sections
==========================================

File fields importer and exporter sections are used to extract data from
Archetypes file fields. The exporter section blueprint name is
``quintagroup.transmogrifier.fileexporter`` and the importer section blueprint
name is ``quintagroup.transmogrifier.fileimporter``.

Exporter needs relative path to the object, that have file fields. Improter
needs path and data for updating fields.

Both sections has ``path-key`` option which specify key in item where path to
object is stored (``_path`` is default) and ``files-key`` option that gives
key where XML data will be or is stored. Exporter section also has ``exclude-key``
option, that specifies key where list of file field names will be stored
(default is ``_excluded_fields``). These list will be used in marshaller
section.

Also this section provides condition option which, if specified, exports/imports
this or another binary field only if condition expression evaluates to true.

>>> import pprint
>>> binary = """
... [transmogrifier]
... pipeline =
...     binarysource
...     fileexporter
...     fileimporter
...     printer
...     dataprinter
... 
... [binarysource]
... blueprint = quintagroup.transmogrifier.tests.binarysource
... 
... [fileexporter]
... blueprint = quintagroup.transmogrifier.fileexporter
... condition = python:fname != 'image'
... 
... [dataprinter]
... blueprint = quintagroup.transmogrifier.tests.dataprinter
... print = 
...     _files
...     file-fields
...     data
... 
... [fileimporter]
... blueprint = quintagroup.transmogrifier.fileimporter
... 
... [printer]
... blueprint = collective.transmogrifier.sections.tests.pprinter
... """
>>> registerConfig(u'quintagroup.transmogrifier.tests.marshall', binary)
>>> transmogrifier(u'quintagroup.transmogrifier.tests.marshall') # doctest: +REPORT_NDIFF, +ELLIPSIS
{}
{'_path': 'not/existing/bar'}
{'_path': 'spam/eggs/notatcontent'}
{'_excluded_fields': ['image', 'file'],
 '_files': {'archive.tar.gz': {'content_type': 'application/x-tar',
                               'data': 'binary data',
                               'name': 'archive.tar.gz'},
            'file-fields': {'data': ...,
                            'name': '.file-fields.xml'}},
 '_path': 'spam/eggs/foo'}
<?xml version="1.0" encoding="utf-8"?>
<manifest>
  <field name="file">
    <filename>
      archive.tar.gz
    </filename>
    <mimetype>
      application/x-tar
    </mimetype>
  </field>
</manifest>
<BLANKLINE>
>>> pprint.pprint(plone.updated)
('archive.tar.gz', 'application/x-tar', 'binary data')

TODO: write test for getting data for fields from import context

The ``condition`` expression hass access to the following:

=================== ==========================================================
 ``item``            the current pipeline item
 ``transmogrifier``  the transmogrifier
 ``name``            the name of the splitter section
 ``options``         the splitter options
 ``modules``         sys.modules
 ``context``         the current content object
 ``fname``           the name of the field being processed
 ``filename``        the file name binary field is loaded into (import only)
 ``data``            data read from the file (import only)
 ``mimetype``        data mimetype (import only)
=================== ==========================================================