Opened 16 years ago

Closed 16 years ago

Last modified 11 years ago

#8222 closed Uncategorized (wontfix)

Storage should reset file's cursor after saving

Reported by: Julien Phalip Owned by: nobody
Component: File uploads/storage Version: dev
Severity: Normal Keywords:
Cc: Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

I had some trouble finding the cause of that problem. Basically, I was trying to save an uploaded image and then manipulate that image with PIL. But the following didn't work:

from PIL import Image

storage.save('/images/image.gif', uploaded_file) # Save the original
uploaded_image = Image.open(uploaded_file)
...

After debugging PIL I realised that it assumes the given file starts at position 0. Therefore, the following works:

from PIL import Image

storage.save('/images/image.gif', uploaded_file) # Save the original
uploaded_file.seek(0) # >> REWIND FILE <<
uploaded_image = Image.open(uploaded_file)
...

I think it would be good practice to automatically rewind the file after it's been saved, so that other tools can process the file without having to rewind it manually. That would feel more logical from an outside perspective.

Patch attached.

Attachments (2)

8222.file.storage.rewind.diff (1.1 KB ) - added by Julien Phalip 16 years ago.
Patch and regression tests
8222.storage.save.diff (1.2 KB ) - added by Julien Phalip 16 years ago.
Same patch, but changed the word 'rewind'

Download all attachments as: .zip

Change History (10)

by Julien Phalip, 16 years ago

Patch and regression tests

comment:1 by Julien Phalip, 16 years ago

Just a note about the tests I've written. I couldn't get temp_file.read() to return a unicode value 'some contents', even if creating it explicitly: ContentFile('some contents').
Maybe I've missed something simple there. What do you think?

by Julien Phalip, 16 years ago

Attachment: 8222.storage.save.diff added

Same patch, but changed the word 'rewind'

comment:2 by Julien Phalip, 16 years ago

Summary: Storage should rewind files after savingStorage should reset file's cursor after saving

'Rewind' is probably not the best word since we're dealing with direct file access :)

comment:3 by Jacob, 16 years ago

Component: UncategorizedFile uploads/storage
Triage Stage: UnreviewedAccepted

comment:4 by Julien Phalip, 16 years ago

Hmmm, I'm now wondering if this ticket is in fact valid...

FileSystemStorage._save() is supposed to close the file after it's been saved, right? In that case, it doesn't make sense to reset the cursor's position. Could Marty Alchin, or someone familiar enough with FileSystemStorage confirm this?

I believe that the reason uploaded_file still existed after saving was because I was testing on Windows, and that temporary uploaded files are not cleaned up properly on that platform. See ticket #8203.

If someone can confirm all that, then I guess this ticket is invalid. The right way would be to manipulate the file first, then save the manipulated version, and *lastly* save the original:

manipulated_image = Image.open(uploaded_file)
...
storage.save('/images/manipulated_image.gif', manipulated_image) # Save the manipulated image and close it.
storage.save('/images/image.gif', uploaded_file) # Save the original and close it.

comment:5 by Julien Phalip, 16 years ago

One question though: should closing the file after saving be enforced to every storage system?

Currently FileSystemStorage._save() seems to do it itself, but Storage.save() doesn't enforce it by default.

comment:6 by Jacob, 16 years ago

Resolution: wontfix
Status: newclosed

This change causes a test failure:

======================================================================
ERROR: test_large_upload (regressiontests.file_uploads.tests.FileUploadTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jacob/Projects/Django/upstream/tests/regressiontests/file_uploads/tests.py", line 53, in test_large_upload
    response = self.client.post('/file_uploads/verify/', post_data)
  File "/Users/jacob/Projects/Django/upstream/django/test/client.py", line 285, in post
    return self.request(**r)
  File "/Users/jacob/Projects/Django/upstream/django/core/handlers/base.py", line 86, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/Users/jacob/Projects/Django/upstream/tests/regressiontests/file_uploads/views.py", line 52, in file_upload_view_verify
    obj.testfile.save(largefile.name, largefile)
  File "/Users/jacob/Projects/Django/upstream/django/db/models/fields/files.py", line 74, in save
    self._name = self.storage.save(name, content)
  File "/Users/jacob/Projects/Django/upstream/django/core/files/storage.py", line 46, in save
    content.seek(0)
  File "/Users/jacob/Projects/Django/upstream/django/core/files/uploadedfile.py", line 88, in seek
    def seek(self, *args):          return self._file.seek(*args)
ValueError: I/O operation on closed file

----------------------------------------------------------------------

This is because depending on what type of file content is, seek() may not be valid after the file's been saved.

So I think you're right that this is invalid; you can always call seek() manually should you need to (or simply save the other file first, like you figured out).

comment:7 by Jacob, 12 years ago

milestone: 1.0

Milestone 1.0 deleted

comment:8 by anonymous, 11 years ago

Easy pickings: unset
Severity: Normal
Type: Uncategorized
UI/UX: unset
Note: See TracTickets for help on using tickets.
Back to Top