Class: Fly::RegionalDatabase::ReplayableRequestMiddleware

Inherits:
Object
  • Object
show all
Defined in:
lib/fly-ruby/regional_database.rb

Instance Method Summary collapse

Constructor Details

#initialize(app) ⇒ ReplayableRequestMiddleware 



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# File 'lib/fly-ruby/regional_database.rb', line 46

def initialize(app)
  @app = app
end

Instance Method Details

#call(env) ⇒ Object 



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# File 'lib/fly-ruby/regional_database.rb', line 62

def call(env)
  request = Rack::Request.new(env)

  # Does this request satisfiy a condition for replaying in the primary region?
  #
  # 1. Its HTTP method matches those configured for automatic replay
  # 2. It arrived before the threshold defined by the last write request.
  #    This threshold helps avoid the same client from missing its own
  #    write due to replication lag.

  if Fly.configuration.in_secondary_region?
    if replayable_http_method?(request.request_method)
      return RegionalDatabase.replay_in_primary_region!(state: "http_method")
    elsif within_replay_threshold?(request.cookies[Fly.configuration.replay_threshold_cookie])
      return RegionalDatabase.replay_in_primary_region!(state: "threshold")
    end
  end

  status, headers, body = @app.call(env)

  response = Rack::Response.new(body, status, headers)
  replay_state = replay_request_state(request.get_header("HTTP_FLY_REPLAY_SRC"))

  # Request was replayed, but not by a threshold, so set a threshold within which
  # all requests should be replayed to the primary region
  if replay_state && replay_state != "threshold"
    response.set_cookie(
      Fly.configuration.replay_threshold_cookie,
      Time.now.to_i + Fly.configuration.replay_threshold_in_seconds
    )
  end

  response.finish
end

#replay_request_state(header_value) ⇒ Object 



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# File 'lib/fly-ruby/regional_database.rb', line 58

def replay_request_state(header_value)
  header_value&.slice(/(?:^|;)state=([^;]*)/, 1)
end

#replayable_http_method?(http_method) ⇒ Boolean 



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# File 'lib/fly-ruby/regional_database.rb', line 54

def replayable_http_method?(http_method)
  Fly.configuration.replay_http_methods.include?(http_method)
end

#within_replay_threshold?(threshold) ⇒ Boolean 



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# File 'lib/fly-ruby/regional_database.rb', line 50

def within_replay_threshold?(threshold)
  threshold && (threshold.to_i - Time.now.to_i) > 0
end