/london-departure-times

London departure times app

Primary LanguageGo

London Transport Live Arrivals

Just an experiment in Go.

Development

Requirements

  • Go >= 1.5
  • Glide is used as a dependency manager. This requires GO15VENDOREXPERIMENT=1 to be set.
  • To manage assets, the app uses Webpack. To recompile the assets, install Node.js, then run npm install webpack -g and then, in the app folder, npm install, and then webpack.

Running

The app requires a set of TFL API credentials, which can be obtained here. TFL_APP_ID and TFL_APP_KEY have to be available as environment variables (or can be added to a .env file in the app's directory).

Implementation details

The app uses the gin-gonic framework for serving web requests.

On the client side, Bacon.js is used, instead of a more traditional MVC framework: I love the reactive approach, and I find it greatly simplifies event-driven code.

To fetch live line updates, the app implements a poller that demultiplexes the incoming requests, and allows to have a predetermined concurrency and polling interval. This has been the most interesting part of the implementation, and the ease with which it came together really sold me on Go!

Code structure

  • main.go is the entry point, which starts the poller and the gin router
  • api.go defines the public API structures.
  • tfl.go provides the main TFL client structure, the common TFL API structures, and an initializer which constructs the sub-services (implemented in tflstops.go, tflarrivals.go and tflstoppoints.go) in charge of calling the specific API endpoints.
  • tflpoller.go is responsible for receiving "arrivals" requests, adding them to a poll loop, and returning the most up-to-date information available (if any).