Issue with truncated Japanese filenames when downloading from SharePoint Online has been resolved

This article is a repost of an article published on Hatena Blog on March 30, 2017.

https://docs.microsoft.com/ja-jp/archive/blogs/sharepoint_support/13-sharepoint?WT.mc_id=M365-MVP-5002941

In SharePoint Online, an issue occurred where downloading files with long Japanese filenames would result in the filename being truncated. This issue appears to have been resolved recently.

Note that the same issue has also been resolved for OneDrive for Business.

The change involves sending attachment; filename*=UTF-8'' in the HTTP Content-Disposition header. This allows supported browsers to correctly download files even with long Japanese names. Previously, filename="" was used to transmit filenames up to 13 double-byte characters. Therefore, if you download with a browser that does not support the new format, the filename will still be truncated as before.