@Pikne @thiemowmde I'd like to start working on a more meaningful error message. To be sure I'm not misunderstanding:
The file extension of this file https://et.wikipedia.org/wiki/Fail:Kilingi_Nomme_suurvapp.png is png, but the detected mime type is gif. Is it the gif that's wrong or the png? If it's the gif, how could a user fix this?

Thanks for clarifying. Johanna

In T218083#5215415, @JStrodt_WMDE wrote:

To be sure I'm not misunderstanding: The file extension of this file https://et.wikipedia.org/wiki/Fail:Kilingi_Nomme_suurvapp.png is png, but the detected mime type is gif. Is it the gif that's wrong or the png? If it's the gif, how could a user fix this?

Yes, file type "gif" is correct, file extension "png" is not. It would be nice if extension could be corrected during import, either manually or automatically.

If changing it during import would be overly complicated, then the error message could inform user that file type and extension do not match, and that one could retry after correcting the extension on source wiki. The latter means that file needs to be moved under new title that has correct extension (on most Wikimedia wikis you need to be an administrator to do that).

If file type and extension do not match, but the file type is not permitted anyway, then it should display a different error message (T222783).

In case FileImporter can't solve these issues automatically, I suggest this error message:

"The extension of the file you are importing (.png) does not match its MIME type (gif). To fix this, rename the original file so that it ends in .gif. This is usually done by admins. After that, you can try another import."

@Pikne What do you think?

Yes, this error message would probably do in case the extension cannot be corrected during import.

Here are the internal errors, they look promising:

UploadBase::verifyExtension: mime type image/gif mismatches file extension png, rejecting file
[FileImporter] FileImporter\Services\UploadBase\ValidatingUploadBase::validateFile checks failed

Side note: FileRevisionFromRemoteUrl doesn't short-circuit after title or file type validation, I'm wondering why. Maybe to render a more verbose error message?

I'd like to change it to short-circuit...

@JStrodt_WMDE I've made some changes to the code which allow us to bubble up errors from MediaWiki core, which currently uses the filetype-mime-mismatch message:

I suppose there are three options to align us with the acceptance criteria:

• Update the MediaWiki core error message to use our more elaborate text. This would have to be slightly reworded to not reference "import", since it might also be displayed in UploadWizard.
• Special-case our code to catch the core error message, and wrap with a custom message bearing our new text.
• Display the core error message as it is currently worded.

Change 513586 had a related patch set uploaded (by Awight; owner: Awight):
[mediawiki/extensions/FileImporter@master] Return some localizable error messages from upload validation

https://gerrit.wikimedia.org/r/513586

@awight I would be ok with using the core message for now, since we are showing this from our blocking error page anyways.
Since in the screenshot you posted the message is shown o top of the file import preview page, I'm pasting the blocking error page mock in here again to be sure we have the same thing in mind:

In T218083#5226032, @Lea_WMDE wrote:

Since in the screenshot you posted the message is shown o top of the file import preview page, I'm pasting the blocking error page mock in here again to be sure we have the same thing in mind:

Thanks for pointing this out! Do you mind if we split the error page into a new task, since it affects all import errors and isn't specific to this one?

This error page exists already (I think it was done back then: T189439: Error situations (wrong file format, abuse filter failure...) lead to an error page )

In T218083#5226038, @Lea_WMDE wrote:

This error page exists already (I think it was done back then: T189439: Error situations (wrong file format, abuse filter failure...) lead to an error page )

Cool, I see now. However, reading the code I also see that our error page is only displayed for unrecoverable errors that happen during the import "planning" phase, but not for any of the errors that occur during the "actually import" phase.

Change 513586 merged by jenkins-bot:
[mediawiki/extensions/FileImporter@master] Return some localizable error messages from upload validation

https://gerrit.wikimedia.org/r/513586