plone.app.blob 1.0b4

Overview

This package aims to be an add-on for Plone 3.x integrating ZODB 3.8’s blob support, which allows large binary data to be managed by the ZODB, but separately from your usual FileStorage database, i.e. Data.fs. This has several advantages, most importantly a much smaller Data.fs and better performance both cpu- as well as memory-wise.

Contents

Status

At the moment the integration for “File” content should be stable, but still needs more field testing. It is being successfully used in several production deployments, though. The provided blob-based content type should safely usable as a drop-in replacement for ATFile. As such it has been successfully tested against all CMFPlone and ATContentTypes tests. Please use the provided test-compatibility.sh script to run these tests for yourself.

Image support is still in an alpha stadium and not enabled by default. It can be activated by applying the respective profile via the portal setup tool.

More detailed information about the integration and the current status can be found in the corresponding plone enhancement ticket.

Requirements

Plone 3.0 or newer is required. The package has been tested with all versions from 3.0 up to and including 3.2.2. However, as all versions before 3.0.4 require a workaround described in the Troubleshooting section below, it is recommended to use Plone 3.0.4 or a more recent version.

Installation

The easiest way to get ZODB blob support in Plone 3 using this package is to work with installations based on zc.buildout. Other types of installations should also be possible, but might turn out to be somewhat tricky — please see the FAQ section below.

To get started you will simply need to add the package to your “eggs” and “zcml” sections, run buildout, restart your Plone instance and install the “plone.app.blob” package using the quick-installer or via the “Add-on Products” section in “Site Setup”.

A sample buildout configuration file, i.e. buildout.cfg, could look like this:

[buildout]
parts = plone zope2 instance
find-links =
    http://dist.plone.org
    http://download.zope.org/ppix/
    http://download.zope.org/distribution/
    http://effbot.org/downloads
eggs = elementtree

[plone]
recipe = plone.recipe.plone

[zope2]
recipe = plone.recipe.zope2install
url = ${plone:zope2-url}

[instance]
recipe = plone.recipe.zope2instance
zope2-location = ${zope2:location}
blob-storage = var/blobstorage
user = admin:admin
products = ${plone:products}
eggs =
    ${buildout:eggs}
    ${plone:eggs}
    plone.app.blob
zcml = plone.app.blob

You can also use this buildout configuration to create a fresh Plone installation. To do so you would store it as buildout.cfg — preferably in an empty directory, download bootstrap.py into the same directory and issue the following commands:

$ python bootstrap.py
$ ./bin/buildout
$ ./bin/instance fg

After that you create a “Plone Site” via the ZMI as usual and either select the “plone.app.blob” extension profile at creation time or again install the “plone.app.blob” package using one of the above mentioned methods.

For your convenience a working buildout configuration, including bootstrap.py and buildout.cfg, is provided as a subversion checkout at http://svn.plone.org/svn/plone/plone.app.blob/buildouts/plone-3.x.

A sample ZEO buildout configuration could look like this:

[buildout]
parts = plone zope2 zeo client1 client2
find-links =
  http://dist.plone.org
  http://download.zope.org/ppix/
  http://download.zope.org/distribution/
  http://effbot.org/downloads
eggs = elementtree

[plone]
recipe = plone.recipe.plone

[zope2]
recipe = plone.recipe.zope2install
url = ${plone:zope2-url}

[zeo]
recipe = plone.recipe.zope2zeoserver
zope2-location = ${zope2:location}
zeo-address = 127.0.0.1:8100
zeo-var = ${buildout:directory}/var
blob-storage = ${zeo:zeo-var}/blobstorage
eggs = plone.app.blob

[client1]
recipe = plone.recipe.zope2instance
zope2-location = ${zope2:location}
zeo-address = ${zeo:zeo-address}
blob-storage = ${zeo:blob-storage}
zeo-client = on
shared-blob = on
user = admin:admin
products = ${plone:products}
eggs =
  ${buildout:eggs}
  ${plone:eggs}
  plone.app.blob
zcml = plone.app.blob

[client2]
recipe = plone.recipe.zope2instance
http-address = 8081
zope2-location = ${client1:zope2-location}
zeo-client = ${client1:zeo-client}
zeo-address = ${client1:zeo-address}
blob-storage = ${client1:blob-storage}
shared-blob = ${client1:shared-blob}
user = ${client1:user}
products = ${client1:products}
eggs = ${client1:eggs}
zcml = ${client1:zcml}

Please note the configuration options blob-storage and shared-blob specified in [client1] and [client2]. To enable blob support on a ZEO client (or standalone instance) you always have to specify a path in the blob-storage configuration option. If shared-blob is set to “on”, the ZEO client will assume it can read blob files directly from within the path specified in the blob-storage option. This path might also refer to a network share in case the ZEO client and server are installed on separate machines. However, to stream blob files trough the ZEO connection you will have to set the shared-blob option to “off”. The path specified in the blob-storage option will be ignored in this situation, but it needs to be set nevertheless.

More detailed instructions on how to set things up as well as some background information on blobs — or in other words the story of an “early adopter” — can be found in Ken Manheimer’s wiki. This is a highly useful resource and recommended read for people trying to give blobs a spin. Please note however, that most of the recipe changes described in these instructions have already been incorporated in the particular recipes by now.

In addition, more information on how to use buildout is available in the accompanying README.txt as well as in Martin’s excellent buildout tutorial on plone.org.

Migrating existing content

In-place content migration is provided for existing “File” and “Image” content. The Products.contentmigration package is required for this to work. To install this package you will again need to add its name to the “eggs” and “zcml” section of your buildout.cfg, so that it reads like:

[instance]
...
eggs +=
    plone.app.blob
    Products.contentmigration
zcml +=
    plone.app.blob
    Products.contentmigration

You can also refer to the above mentioned sample buildout.cfg for details.

In order to then migrate your existing file content to blobs you can use the migration interfaces provided at http://<site>/@@blob-file-migration to migrate “File” content as well as http://<site>/@@blob-image-migration for “Image” content respectively. <site> will need to be replaced with the URL of your “Plone Site” object here, of course. The pages will show you the number of available ATFile or ATImage instances and then lets you convert these to the provided blob content types by clicking a button.

Please refer to the next section if you encounter any errors during migration.

Troubleshooting

The following are some known issues, that will hopefully be resolved soon enough. In the meantime here are the recommended workarounds:

“FileFieldException: Value is not File or String (…)” Exception

Symptom

After upgrading your buildout you’re getting an error like the following during blob migration:

Traceback (innermost last):
  File ".../basemigrator/walker.py", line 174, in migrate
  ...
  File ".../Archetypes/Field.py", line 931, in _process_input
FileFieldException: Value is not File or String (...)

Problem

Your version of archetypes.schemaextender has been upgraded to 1.1 while running buildout. You either didn’t run it in non-newest mode (-N) or have not pinned down the version of archetypes.schemaextender.

Solution

Downgrade archetypes.schemaextender to version 1.0 for the moment. You can do this by adding a version pin like:

[versions] archetypes.schemaextender = 1.0

to your buildout.cfg. A proper fix to add compatibility to the latest version is being worked on.

“AttributeError: ‘NoneType’ object has no attribute ‘getAccessor’” Exception

Symptom

After upgrading from version 1.0b2 or earlier you’re getting an error like the following when trying to view blob-based content:

Traceback (innermost last):
  Module ZPublisher.Publish, line 119, in publish
  ...
  Module Products.ATContentTypes.content.base, line 300, in get_content_type
AttributeError: 'NoneType' object has no attribute 'getAccessor'

Problem

Recent versions have added support for sub-types based on marker interfaces and your existing blob-based content hasn’t been marked yet.

Solution

Upgrade to at least 1.0b4, re-install “plone.app.blob” via the quick-installer and reset all sub-types by accessing the @@blob-maintenance/resetSubtypes view.

“Invalid plugin id” Exception

Symptom

When trying to create a “Plone Site” you’re getting an error like:

Error Type: KeyError
Error Value: 'Invalid plugin id: credentials_basic_auth'

Problem

Your version of Products.PluggableAuthService is too old — you need 1.5.2 or newer (please see http://www.zope.org/Collectors/PAS/59 for more information about this).

Solution

Please use the provided buildout, add the 1.5 branch as an svn:external to the products/ directory of your buildout or upgrade to Plone 3.0.4 by re-running buildout.

“unknown type name: ‘blobstorage’”

Symptom

When running buildout you’re getting an error like:

Error: unknown type name: 'blobstorage'
(line 36 in file:///.../parts/instance/etc/zope.conf)

Problem

Your version of the plone.recipe.zope2instance recipe is too old — you need to have at least version 1.0.

Solution

Make sure you’re running buildout with neither “-N” nor “-o” and you also don’t have:

newest = false

in your ~/.buildout/default.cfg. Alternatively, running buildout with option “-n” should update the recipe to the latest version.

missing distribution for required “zdaemon” and “ZConfig” eggs

Symptom

When running buildout you’re getting errors like:

Getting distribution for 'zdaemon>=1.4a2,<1.4.999'.
While:
  Installing instance.
  Getting distribution for 'zdaemon>=1.4a2,<1.4.999'.
Error: Couldn't find a distribution for 'zdaemon>=1.4a2,<1.4.999'.

or:

Getting distribution for 'ZConfig>=2.4a2,<2.4.999'.
While:
  Installing instance.
  Getting distribution for 'ZConfig>=2.4a2,<2.4.999'.
Error: Couldn't find a distribution for 'ZConfig>=2.4a2,<2.4.999'.

Problem

zdaemon and ZConfig eggs have only been released to the Cheeseshop starting from more recent versions, i.e. 2.0 and 2.5 respectively. Older distributions in egg format are only available from http://download.zope.org/distribution

Solution

Add the above link to the find-links setting of the [buildout] section in your buildout.cfg, like:

find-links =
    http://download.zope.org/distribution/
    ...

“ZRPCError: bad handshake ‘Z303’”

Symptom

With a ZEO setup you are getting errors like:

ZRPCError: bad handshake 'Z303'

Problem

You probably haven’t added plone.app.blob to the eggs setting in your [zeo] buildout part. Without it the ZEO server will not use the required version 3.8 of ZODB and hence not support blobs.

Solution

Add the string plone.app.blob to the eggs setting in the [zeo] section (i.e. the one using the plone.recipe.zope2zeoserver recipe) in your buildout.cfg, like:

[zeo]
...
eggs = plone.app.blob
...

“AttributeError: ‘NoneType’ object has no attribute ‘product’” during migration

Symptom

After installing “plone.app.blob” via the quick-installer or applying the “plone.app.blob: ATFile replacement” profile you are seeing migration errors like:

Traceback (innermost last):
  Module ZPublisher.Publish, line 119, in publish
  Module ZPublisher.mapply, line 88, in mapply
  Module ZPublisher.Publish, line 42, in call_object
  Module plone.app.blob.browser.migration, line 24, in __call__
  Module plone.app.blob.migrations, line 42, in migrateATFiles
  Module Products.contentmigration.basemigrator.walker, line 126, in go
  Module Products.contentmigration.basemigrator.walker, line 205, in migrate
MigrationError: MigrationError for obj at /... (File -> Blob):
Traceback (most recent call last):
  File ".../Products/contentmigration/basemigrator/walker.py", line 174, in migrate
    migrator.migrate()
  File ".../Products/contentmigration/basemigrator/migrator.py", line 185, in migrate
    method()
  File ".../Products/contentmigration/archetypes.py", line 111, in beforeChange_schema
    archetype = getType(self.dst_meta_type, fti.product)
AttributeError: 'NoneType' object has no attribute 'product'

Problem

The current migration code has been written to convert existing “File” content to the “Blob” content type provided by the base “plone.app.blob” profile. However, that type isn’t known when just installing the “ATFile replacement” profile. The latter is probably what you want to install, though, as former “File” content will keep the same portal type, i.e. “File” after being migrated. This way no apparent changes are visible, which might help with avoiding confusion.

Solution

For now you might work around this by either applying the “plone.app.blob” profile via the ZMI in /portal_setup. This will install the above mentioned “Blob” content type. After that migration will work, but your former “File” content will have the “Blob” content type.

If that’s not what you want, simply change line line 17 in plone/app/blob/migrations.py (which is probably contained in an egg directory located somewhere like eggs/plone.app.blob-1.0b2-py2.4.egg/ relative to your buildout/installation) from:

dst_portal_type = 'Blob'

to:

dst_portal_type = 'File'

After that migration should use the new “File” type, based on ZODB blobs. Once you’ve migrated you might remove or disable the “Blob” type from /portal_types again. A future version of “plone.app.blob” will try auto-detect the correct target type for the migration (or at least allow to specify it) to make this more convenient.

If you have already migrated to “Blob” content, but would rather like to have “File” items, you can change the two previous lines to:

src_portal_type = 'Blob'
src_meta_type = 'ATBlob'

and re-run the blob migration. This will convert your “Blob”s to show up as “File”s again. You should probably pack your ZODB afterwards to avoid having its blob storage occupy twice as much disk space as actually needed (the extra migration will create new blobs).

FAQ

Is it possible to use “plone.app.blob” in installations not based on zc.buildout?

Yes, but that would require some additional steps, since it depends on ZODB 3.8, but Plone currently ships with Zope 2.10, which still comes with ZODB 3.7. So, to make things work you could either install the required versions of all additionally needed packages into your lib/python/ directory or use the respective eggs and make sure they get preferred over their older versions on import, for example by setting up PYTHONPATH.

Alternatively it should also be possible to install the package using easy_install, which would automatically install its dependencies including ZODB 3.8, too. Again you would need to set up your PYTHONPATH to make sure the desired versions are used. However, installing the package like this is likely to have side effects on other Zope/Plone instances on your system, so you probably want to use virtualenv here at least.

Overall, to get started without too much pain, a buildout-based installation is recommended — for example the provided buildout.

Will this be available for Plone 2.5.x?

Yes, support for the 2.5 series is planned and next on the agenda.

What about image support, i.e. a drop-in for ATImage content?

While just replacing the primary field in ATImage’s schemata should probably already work quite well, proper image support is planned for a later release. “proper” here means using a sub-typing approach as presented by Rocky Burt in Naples, which will have several advantages including a cleaner and better structured code, but will also take a little longer to implement.

Strange messages like Exception exceptions.OSError: (2, 'No such file or directory', '.../tmpZvxjZB') in <bound method _TemporaryFileWrapper.__del__ of <closed file '<fdopen>', mode 'w+b' at 0x7317650>> ignored get written to the logs whenever a file is uploaded. Is that an error or something to worry about?

No, that’s fine, it’s just a small annoyance, that should be fixed eventually. In case you care, the problem is that the zope publisher creates a temporary file for each upload it receives. Once the upload has finished that temporary file is passed to the blob machinery, which moves it into its blob storage. However, at the end of the request the wrapper class for temporary files tries to remove the file as well, since well, it’s supposed to be temporary. At that time the file is already gone though, and the above warning is issued.

Feedback

Any kind of feedback like bug reports, suggestions, feature requests and most preferably success stories is most welcome and much appreciated. Especially, it would be interesting to hear about success or problems with migration of existing content and installations on platforms other than OSX.

So please feel free to post comments to the above mentioned plone enhancement ticket, file tickets in the issue tracker or contact me on #plone, through the plone developer mailing list or directly via email.

Changelog

(name of developer listed in brackets)

1.0b5 Unreleased

• Fix registration of blob-based image scale adapter to prevent getting 404s for content other than images. This fixes the second issue related to http://plone.org/products/plone.app.blob/issues/19 [witsch]

1.0b4 Released May 19, 2009

• Provide maintenance view for (re)setting blob sub-types, which can also be used to fix things after upgrading from 1.0b2 or earlier. This fixes http://plone.org/products/plone.app.blob/issues/19 [witsch]

1.0b3 Released May 15, 2009

• Clean up GenericSetup profiles to allow separate installation of replacement types for “File” and “Image” content. [witsch]

• Add index accessor to make indexing of file content work again. This fixes http://plone.org/products/plone.app.blob/issues/12 [witsch]

• Make code more robust in case of missing blob files. This fixes http://plone.org/products/plone.app.blob/issues/10 [witsch]

• Make tests clean up their temporary blob directories. [stefan]

• Remove quota argument from DemoStorage calls. [stefan]

• Add workaround to prevent breakage with CMFEditions (blob-based content can still not be versioned, though). [witsch]

• Add missing acquisition-wrapper, also allowing to remove circular references between instance and field, which broke pickling. [witsch]

• Fix helper for determining image sizes to not break for non-image content. [witsch]

• Use PIL for determining image sizes as the OFS code cannot handle certain types of JPEGs. [witsch]

• Added missing metadata.xml to the default profile. [hannosch]

• Only use the file name for id generation for the replacement types, i.e. “File” and “Image”, but not custom types. This fixes http://plone.org/products/plone.app.blob/issues/3 [witsch]

• Fix issue where the mime-type registry returned an empty tuple when looking up an unknown mime-type. This fixes http://plone.org/products/plone.app.blob/issues/1 [witsch]

1.0b2 Released February 29, 2008

• Reverted fix for Windows that closed the file upload object in order to work around a problem with reading from the blob file afterwards. [witsch]

1.0b1 Released February 28, 2008

• Minor bug fixes and cleanups [witsch]

• Fix for a problem regarding file uploads on Windows, where renaming the still open temporary file isn’t allowed and hence caused an error. Now the file is closed before the call to consumeFile(). [rochael]

• Fix for Windows regarding the generation of the temporary file used for file uploads so that it doesn’t get deleted after being moved to the blob storare [rochael]

• Change file size calculation so as not to need to reopen the file, which broke on Windows [rochael]

• Changed the primary field of the blob content types to not to be “searchable” as this causes indexing of the blob content making ram consumption go through the roof [witsch]

1.0a2 Released December 12, 2007

• Various minor bug fixes regarding migration, content icons etc [witsch]

• String value are now wrapped using StringIO to make them adaptable, so that their mime-type can be guessed as well. [naro]

• Added alternative GenericSetup profile to allow to replace ATFile as the “File” content type [witsch]

1.0a1 Released December 7, 2007

• Initial version [witsch]

• Initial package structure. [zopeskel]