Fix streaming CSV export #52
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Streaming was not working either in development (disable_streaming off) nor on production Heroku. Adding a Last-Modified header made it work. The problem would only manifest when using rack 2.2 or higher, and was caused by rack/rack#1416, where the `Rack::ETag` middleware changed it's behaviour to buffer the response and calculate an ETag digest even though the `Cache-Control: no-cache` header is set. This breaks the CSV streaming responses so to avoid that we use the hack outlined in rack/rack#1619 and set a Last-Modified header which triggers the `skip_caching?` condition in the `Rack::ETag` middleware. See activeadmin#6451 and alphagov/e-petitions@46413a7
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Streaming was not working either in development (disable_streaming off) nor on production Heroku. Adding a Last-Modified header made it work.
The problem would only manifest when using rack 2.2 or higher, and was caused by rack/rack#1416, where the
Rack::ETagmiddleware changed it's behaviour to buffer the response and calculate an ETag digest even though the
Cache-Control: no-cacheheader is set. This breaks the CSV streaming responses so to avoid that we use the hack outlined in rack/rack#1619 and set a Last-Modified header which triggers theskip_caching?condition in theRack::ETagmiddleware.See activeadmin#6451 and alphagov/e-petitions@46413a7