A presentation at EuRuKo in in Budapest, Hungary by Mehdi Lahmam
Middleware all the things
At Trainline, we sell train tickets, across EU and UK.
How does it work? Frontends Rails API Connections API aka connection with carriers APIs
A bunch of middlewares Requests are processed by generated apps on the fly, which are stacks of middlewares.
Request (an environment Hash) Connections API env[:params][:action] Base::Builder.app do use DoSomething use AnotherThing # insert a bunch of cool stuff here end
Connections API An action (an app) Middleware 1 ① down ↓ ↑ ④ up Middleware 2 ② down ↓ ↑ ③ up Middleware 3 ⃔ → ⑤ env[:callback] ⃔
% tree lib/pacon/actions -L 1 lib/pacon/actions ├── book.rb ├── book_subscription.rb ├── cancel.rb ├── emit.rb ├── emit_subscription.rb ├── estimate_exchange.rb ├── estimate_refund.rb ├── exchange.rb ├── exchange_pay.rb ├── exchange_search.rb ├── fetch_pnr.rb ├── fetch_subscription.rb ├── fetch_travel_document.rb ├── immediate_cancel.rb ├── load_timetable.rb ├── pay.rb ├── refund.rb └── search.rb
def self.search Base::Builder.app do use Base::LogAction use Base::VolatileStations use Base::InitResultCache use Base::LogSearchFruitfulness use Base::AvoidFruitlessSearch use Base::ReportAndBlockCombinations use Base::TryAgain use Base::SearchWindow use Base::FilterUnsellableFolderMix use Base::FilterTimetableResults use Base::TooManyPassengers use Base::WarnDifferentStation use Base::Parallel end end
def self.search Base::Builder.app do use Base::LogAction use Base::VolatileStations use Base::InitResultCache use Base::LogSearchFruitfulness use Base::AvoidFruitlessSearch use Base::ReportAndBlockCombinations use Base::TryAgain use Base::SearchWindow use Base::FilterUnsellableFolderMix use Base::FilterTimetableResults use Base::TooManyPassengers use Base::WarnDifferentStation use Base::Parallel end end Will call SNCF.search, DB.search…
module SNCF class << self def search Base::Builder.app do use SNCF::Stations use SNCF::ExtractFoldersFromJourneys # tons of very secret sauce use SNCF::HttpRequest end end end end
Event Machine FTW The whole is based on Event Machine to coordinate all the parallel requests made to carriers APIs.
This short talk describes the heart of Trainline EU architecture, heavily inspired by Rack itself, based on apps and stacks of middlewares, on top on EventMachine.
The slides has been made live at EuRuKo 2017 and talk done there :)
for free. You
can too.