# README

Service Locator

Implements a very simple service locator that does allows for modular initialization with a deterministic init order.

A module has a simple 4 phase lifecycle: Init, Start, Reload and Stop. You can enable or disable a feature in the config. This hooks into the watching infrastructure, so you can also enable or disable modules by just editing config or changing a remote value.

Name	Description
Init	Called on initial creation of the module
Start	Called when the module is started, or enabled at runtime
Reload	Called when the config has changed and the module needs to reconfigure itself
Stop	Called when the module is stopped, or disabled at runtime

Each module is identified by a unique name, this defaults to its package name,

Usage

To use it, a package that serves as a module needs to export a method or variable that implements the Module interface.

package orders

import "github.com/casualjim/go-appserver/locator"

var Module = locator.MakeModule(
  locator.Init(func(app locator.Application) error {
    orders := new(ordersService)
    locator.Set("ordersService", orders)
    orders.app = app
    return nil
  }),
  locator.Reload(func(app locator.Application) error {
    // you can reconfigure the services that belong to this module here
    return nil
  })
)

type Order struct {
  ID      int64
  Product int64
}

type odersService struct {
  app locator.Application
}

func (o *ordersService) Create(o *Order) error {
  var db OrdersStore
  o.app.Get("ordersDb", &db)
  return db.Save(o)
}

In the main package you would then write a main function that could look like this:

func main() {
  app := locator.New()
  app.RegisterModule(orders.Module)

  if err := app.Init(); err != nil {
    app.Logger().Fatalln(err)
  }

  app.Logger().Infoln("application initialized, starting...")

  if err := app.Start(); err != nil {
    app.Logger().Fatalln(err)
  }

  app.Logger().Infoln("application initialized, starting...")
  // do a blocking operation here, like run a http server

  if err := app.Stop(); err != nil {
    app.Logger().Fatalln(err)
  }
}