z3c.blobfile 0.1.3

File and Image Using Blob Support of ZODB -- Zope 3 Content Components

Blob File

This package provides an implementation of zope.app.file.interfaces.IFile which uses the Blob support introduced in ZODB 3.8. It’s main purpose is to provide an easy migration path for existing instances. For more advanced file implementations see zope.file and z3c.extfile.

The standard implementation in zope.app.file uses chunk objects to break big files into manageable parts. These chunks flow the server caches whereas blobs are directly consumed by the publisher. The main difference between this blob implementation and the old zope.app.file implementation can be seen in a replacement of the chunk objects by Blobs.

Detailed Documentation

Blob File Implementation

This implementation of zope.app.file.interfaces.IFile takes advantage of the new ZODB blob support and tries to be completely backward compatible to the existing file implementation in zope.app.file.

Compatibility with zope.app.file.File

The following tests mimic exactly the tests of the zope.app.file package.

Let’s test the constructor:

>>> from zope.app.file import File, Image

>>> file = File()
>>> file.contentType
''
>>> file.data
''

>>> file = File('Foobar')
>>> file.contentType
''
>>> file.data
'Foobar'

>>> file = File('Foobar', 'text/plain')
>>> file.contentType
'text/plain'
>>> file.data
'Foobar'

>>> file = File(data='Foobar', contentType='text/plain')
>>> file.contentType
'text/plain'
>>> file.data
'Foobar'

Let’s test the mutators:

>>> file = File()
>>> file.contentType = 'text/plain'
>>> file.contentType
'text/plain'

>>> file.data = 'Foobar'
>>> file.data
'Foobar'

>>> file.data = None
Traceback (most recent call last):
...
TypeError: Cannot set None data on a file.

Let’s test large data input:

>>> file = File()

Insert as string:

>>> file.data = 'Foobar'*60000
>>> file.getSize()
360000
>>> file.data == 'Foobar'*60000
True

Insert data as FileChunk:

>>> from zope.app.file.file import FileChunk
>>> fc = FileChunk('Foobar'*4000)
>>> file.data = fc
>>> file.getSize()
24000
>>> file.data == 'Foobar'*4000
True

Insert data from file object:

>>> import cStringIO
>>> sio = cStringIO.StringIO()
>>> sio.write('Foobar'*100000)
>>> sio.seek(0)
>>> file.data = sio
>>> file.getSize()
600000
>>> file.data == 'Foobar'*100000
True

Last, but not least, verify the interface:

>>> from zope.interface.verify import verifyClass
>>> zope.app.file.interfaces.IFile.implementedBy(File)
True
>>> verifyClass(zope.app.file.interfaces.IFile, File)
True

Test of Filerepresentation Adapters

>>> from zope.app.file.file import FileReadFile
>>> file = File()
>>> content = "This is some file\\ncontent."
>>> file.data = content
>>> file.contentType = "text/plain"
>>> FileReadFile(file).read() == content
True
>>> FileReadFile(file).size() == len(content)
True

>>> from zope.app.file.file import FileWriteFile
>>> file = File()
>>> content = "This is some file\\ncontent."
>>> FileWriteFile(file).write(content)
>>> file.data == content
True

Evolution of Existing Files

Please note that the following code is experimental. The code should not be used in production without careful testing. Backup your Data.fs and uncomment the following lines in the configure.zcml if you want to replace exiting zope.app.file.File instances.

<utility

component=”.generations.BlobFileSchemaManager” name=”z3c.blobfile” />

Let’s assume that you have already an existing database with zope.app.file content types:

>>> from z3c.blobfile import testing
>>> root = getRootFolder()

>>> root[u'file'] = File('A text file', contentType='text/plain')
>>> root[u'image'] = Image(testing.zptlogo)

Since the evolve step looks for implementations of IFile we also must provide a way to recognize other implementations than zope.app.file.File and Image. Let’s add a nonsense implementation as an example:

>>> root[u'custom'] = testing.MyFile()

Note that we cannot assume that these objects exist in isolation. Many of them probably are annotated, indexed, some even may be registered as utility etc. The evolution step throws the standard events when the objects are replaced and it’s up the application that this replacement is recognized accordingly. If your application has special needs you may subscribe to the FileReplacedEvent.

We will not test all relations to all other objects, since this is largely application dependent. Here we only take the ZopeDublinCore timestamps as an example that our evolution step leaves as many things untouched as possible.

>>> from zope.dublincore.interfaces import IZopeDublinCore
>>> import datetime

>>> IZopeDublinCore(root[u'file']).created = datetime.datetime.utcnow()
>>> t1 = IZopeDublinCore(root[u'file']).created
>>> IZopeDublinCore(root[u'file']).title = u'No evolution'

Now we perform the basic evolution steps. Since we expect some warning logs we need

>>> from zope.testing.loggingsupport import InstalledHandler
>>> import logging
>>> log_handler = InstalledHandler('z3c.blobfile.generations')

>>> from z3c.blobfile.generations.evolve1 import evolveZopeAppFile
>>> evolveZopeAppFile(root)
>>> transaction.commit()

>>> for record in log_handler.records:
...     print record.getMessage()
Unknown ...interfaces.IFile implementation z3c.blobfile.testing.MyFile

After the evolution step the class types have changed to the z3c.blobfile implementations:

>>> import z3c.blobfile
>>> isinstance(root[u'file'], z3c.blobfile.file.File)
True
>>> isinstance(root[u'image'], z3c.blobfile.image.Image)
True

Only the custom implementations remain untouched:

>>> isinstance(root[u'custom'], testing.MyFile)
True

The file data remain the same …

>>> root[u'file'].data
'A text file'
>>> root[u'file'].contentType
'text/plain'

>>> root[u'image'].data == testing.zptlogo
True

and so do the annotations:

>>> IZopeDublinCore(root[u'file']).created == t1
True
>>> IZopeDublinCore(root[u'file']).title
u'No evolution'

Even implementation details like the _data attribute still work:

>>> root[u'file']._data
'A text file'

CHANGES

Version 0.1.3 (2008-10-20)

• Bug: Don’t get/set image data twice on Image initialization.

• Cache file size and invalidate it on write access.

• Download file/image using new openDetached method that provides read-only file-like access to the blob, detached from the database connection.

Version 0.1.2 (2008-09-11)

• Bug: Set i18n domain in “overrides.zcml” to avoid warnings.

• Don’t expose Blob implementation details in add/upload forms. Also, “zope” translation domain has no translations for “Upload a File (Blob)”, it just has “Upload a File” translations, so use it.

Version 0.1.1 (2008-09-08)

• Bug: Register zope.app.wsgi.fileresult.FileResult as an adapter for BlobFile, making optimized file views really work.

• Bug: Also use optimized file view for z3c.blobfile.image.Image.

• Bug: Make blob versions of File and Image implement IBlobFile and IBlobImage interfaces respectively. This enables z3c.blobfile’s views.

• Bug: Use local ZopeMessageFactory. This fixes import error on Zope 2.10

Version 0.1.0 (2008-02-27)

• Initial Release