How to set attachment MIME type for json import ?

[LeCobb]

Hello,

I am creating issues with json file importer on new JIRA instance. For this I extract information from the issues of an hold instance.

I include attachements in my json import file. These are created correctly on the new instance, however when i open them the format is not the correct one.

In an old issue I have a cpp file, for which the extraction gives :

I import my attachment like this :

It works, the attachment is created fine, but when I open it from JIRA to my web browser, it's HTML not cpp. 

How can I indicate the mimeType at the time of import ?

When I extract the previously created issue, the attachment has a mimeType different from "text/plain".

I couldn't find anything in the import documentation about this problem.

Thanks in advance for any help.

[LeCobb]

Can you at least tell me if this feature exists or not ? Thanks