Support Content-Disposition HTTP response header

[Syndesi]

The Content-Disposition HTTP response header can be used to transmit the file's name, including its file extension.

Within Ember Nexus, it should work in the following way:

• The Content-Disposition HTTP header is always set to attachment; filename="<name>.<extension>"
• The file name is decided by priority, starting with the following option:
  • The name-property of the current element, if it a) exists and b) is of type string.
  • The id of the current element, in string form.
• The extension is decided through the following options (already calculated during upload):
  • The original file extension, if the original upload contained a Content-Disposition header on its own.
  • A file extension determined by mime type lookup of the file itself.
  • If the extension can not be determined, the fallback extension .bin is used.
• The following constraints are placed on the file name:
  • The whole file name, i.e. <name>.<extension>, is limited to 255 characters - a normal limit by filesystems like NTFS, Btrfs, ext4 and exFAT are all limited to 256 bytes / chars. See also Wikipedia list of file system limits.
  • If the file name limit is exceeded, then the name part is truncated from the right as much as required. The extension itself can not be truncated.
  • Special characters need to be removed from the file name, notably: "*/:<>?\| source, Wikipedia

Note: The filename can not be directly changed by clients; they can only change the element's name. The file extension itself is linked to the representation, which can only be changed by re-uploading the file (or another representation).

Acceptance criteria:

• The Content-Disposition HTTP header is supported for file uploads.
• The Content-Disposition HTTP header is supported for file downloads.
• The file name is correctly generated, sanitized and truncated.
• Unit tests.
• Feature tests.
• Documentation.
• Todo: What about the RFC 5987 filename encoding? Should we support it? Is it easy to support?

See also:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Disposition
• https://en.wikipedia.org/wiki/List_of_filename_extensions_(A%E2%80%93E)