Redmine

Attachments with Unicode upper-case filenames (like TestТест.png aka Test\xd0\xa2\xd0\xb5\xd1\x81\xd1\x82.png) are not shown when included in wiki inline image macro.

Steps to reproduce:
1. Make a wiki page
2. Attach a file named TestТест.png
3. Write in a wiki page a macro !TestТест.png!

Expected:
- The image is shown as an attachment

Actual:
- The image is not shown because an attachment is not found
- The 404 error is in logs because Redmine tries to extract a generic resource, not an attachment

I have investigated this issue and it seems that the ApplicationHelper#parse_inline_attachments method downcases filenames and then those names are compared against the database in Attachment#latest_attach using String#casecmp. The casecmp method (do not confuse with a newer String#casecmp? method!) cannot deal with Unicode so the comparison fails. This bug can or can not be seen if an attachment name is downcased because casecmp can successfully compare downcased strings because their byte representation is the same.

The problem can be fixed easily just by avoiding calling String#downcase in ApplicationHelper#parse_inline_attachments.
Comparing ASCII filenames with any cases should still work without changes (because of casecmp).
Comparing Unicode filenames should work fine because we do not bother with changing filename at all.

I wrote a patch consisting of:
1. Test AttachmentTest#test_latest_should_get_with_unicode_downcase that reproduces a problem with an attachment search (passes before and after the fix).
2. Test ApplicationHelperTest#test_attached_images_with_textile_and_uppercase_non_ascii_filename that reproduces a problem with inline image macro (passes after the fix).
3. Small fix to ApplicationHelper#parse_inline_attachments that avoids calling downcase.

Related issues:
- #27780 can fix the problem just by calling String#casecmp? but it is ruby-2.4 only
- #20369 introduced the problem in 3.2.0

About system:

Environment:
  Redmine version                3.4.7.stable
  Ruby version                   2.4.4-p296 (2018-03-28) [x86_64-darwin17]
  Rails version                  4.2.11
  Environment                    production
  Database adapter               SQLite
SCM:
  Subversion                     1.10.0
  Mercurial                      4.8.2
  Git                            2.20.1
  Filesystem
Redmine plugins:
  no plugin installed