In a contest with testruns enabled, a participant can send send their own code with their own input to be ran in our evaluation environment.

The specified input file can either be a raw input file, or a zip archive containing a single file with the input data.

If the archive contains multiple files and its extension is not .zip,
the form will not show an error about multiple files,
but workers will detect that there's more than one file, and trigger a SystemError.

The form should validate the archive in the same (or more strict) way than workers do.
Particularly, the method of detecting if something is a zip should be the same in oioioi and workers.
Another way to do it would be to have oioioi explicitely tell the workers if the input is the zip or not. (The workers would still validate if there's only one archive member and unpack it, but wouldn't try to detect if the input is a zip or not.)