Middleware layer implemented in entry.server.tsx

[takumi-miyajima]

There are several arguments for the middleware layer.
ref: #1432

Why don't we work together to come up with a good implementation?

For example, I think it would be simple and powerful if we could export the following function to entry.server.tsx
If you have a better implementation or a better name, we would be glad to have you join the discussion.

// in `entry.server.tsx`
export const middleware = async ({
  request,
  context,
  params,
  getResponse,
}: {
  request: Request
  context: EntryContext
  params: Params
  getResponse: (request: Request, context: RouteContext) => Promise<Response>
}) => {
  // Create boiler templates for use in loaders and actions from context
  const { session, updateSession } = await withSession(request, context)
  const { db } = withDb(context)
  const routeContext = { session, db }

  // getResponse: handleDataRequest, handleResourceRequest, and handleDocumentRequest wrapped function in `@remix-run/server-runtime/server.ts`
  const response = await getResponse(request, routeContext)

  // Adapt boiler template to response
  await updateSession(response)

  return response
}

Known implementations:

• handleDataRequest
  Can only be used for json responses.
  Not called for document or resource requests.
  Also, only post-processing of responses is supported.

• beforeRequest | beforeResponse
  wip: proof of concept for request / response hooks #364
  If implemented on the @remix-run/{adapter} side, it cannot support an environment like vercel.

• Loaders or actions dynamically generated on each route
  Server code will be contained in Client side.
  This is undesirable in most cases.
  ref

Please let us know your thoughts.
Thanks!