Duplicate request passed to Dispatcher

[ismasan]

So that we have a snapshot of the request in case Rack middleware mutates the original request

The problem

Rack middleware such as Rack::URLMap (used for mounting Rack apps under a path prefix) adds the prefix to Request#env['SCRIPT_NAME'], and then clear it out once the mounted app as served a response.

map '/sourced' do
  run MyMountedApp
end

However, Datastar's async fibers run after the host app has returned a response, by which time the middleware has reset the script name from '/sourced' back to ''. Any code (such as template rendering) that assumes the expected path prefix (ex for URL building) will break.

The solution

When initialising the Datastar Dispatcher, make sure to make a copy of the request, so that middleware mutating the original request doesn't mutate the one held by SSE fibers.