I wrote my own presentation channel module which generates a zip file.
In the content processor class i check if the channel is opened in the preview mode and outputs a text instead of the zip. Now the client want's to download this page instead of displaying the text since the channel extension is zip. How can i force the preview to display the text?
That's because the preview server (an internal jetty within the default configuration) uses
application/zip as the mime type. You could try so change the mime type, but you probably have to re-apply that change after every FirstSpirit update. Please note that this would change the behaviour for all zip files, not just for your own presentation channel.