gio:file-info-content-type (info)

info -- a g:file-info instance
ctype -- a string for the content type

The g:file-info-content-type function gets the content type of the file. It is an error to call this function if info does not contain the G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE attribute.

The (setf g:file-info-content-type) function sets the content type attribute for a given info.