blueprint

Misc Golang routines

Application example

Applications are executed in a runtime context, instantiated from blueprint.Container. This container holds the main run cycle, and manages the startup/shutdown cycle of the application.

It is possible to register global destructor functions that will be called back in sequence when the application is terminated. To achieve this, any ordered application exit must use blueprint.Shutdown():

(...)
if err := doSomething(); err != nil {
	// perform application shutdown
	blueprint.Shutdown(err)
	os.exit(-1)
}

Simple API application example using blueprint.Container:

package main

import (
	"flag"
	"fmt"
	"github.com/gin-gonic/gin"
	"github.com/oddbit-project/blueprint"
	"github.com/oddbit-project/blueprint/config/provider"
	"github.com/oddbit-project/blueprint/log/zerolog/writer"
	"github.com/oddbit-project/blueprint/provider/httpserver"
	"github.com/rs/zerolog/log"
	"os"
)

const (
	VERSION = "9.9.0"
)

// CliArgs Command-line options
type CliArgs struct {
	ConfigFile  *string
	ShowVersion *bool
}

// Application sample application container
type Application struct {
	container  *blueprint.Container // runnable application container
	args       *CliArgs             // cli args
	httpServer *httpserver.Server   // our api server
}

// command-line args
var cliArgs = &CliArgs{
	ConfigFile:  flag.String("c", "config/sample.json", "Config file"),
	ShowVersion: flag.Bool("version", false, "Show version"),
}

// NewApplication Sample application factory
func NewApplication(args *CliArgs) (*Application, error) {
	cfg, err := provider.NewJsonProvider(*args.ConfigFile)
	if err != nil {
		return nil, err
	}
	return &Application{
		container:  blueprint.NewContainer(cfg),
		args:       args,
		httpServer: nil,
	}, nil
}

func (a *Application) Build() {
	// assemble internal dependencies of application
	// if some error occurs, generate fatal error & abort execution

	// initalize http server
	log.Info().Msg("Building Sample Application...")

	// initialize http server config
	httpConfig := httpserver.NewServerConfig()
	// fill parameters from config provider
	if err := a.container.Config.GetKey("server", httpConfig); err != nil {
		a.container.AbortFatal(err)
	}
	// Create http server from config
	var err error
	a.httpServer, err = httpConfig.NewServer()
	a.container.AbortFatal(err)

	// add http handler
	// endpoint: /v1/hello
	a.httpServer.Route().Group("/v1").GET(
		"/hello",
		func(ctx *gin.Context) {
			ctx.JSON(200, "Hello World")
		},
	)
}

func (a *Application) Run() {
	// register http destructor callback
	blueprint.RegisterDestructor(func() error {
		return a.httpServer.Shutdown(a.container.GetContext())
	})

	// Start  application - http server
	a.container.Run(func(app interface{}) error {
		go func() {
			log.Info().Msg(fmt.Sprintf("Running Sample Application API at https://%s:%d/v1/hello", a.httpServer.Config.Host, a.httpServer.Config.Port))
			a.container.AbortFatal(a.httpServer.Start())
		}()
		return nil
	})
}

func main() {
	// use zerolog as logger with console writer
	writer.UseDefaultWriter()

	flag.Parse()

	if *cliArgs.ShowVersion {
		log.Printf("Version: %s\n", VERSION)
		os.Exit(0)
	}

	app, err := NewApplication(cliArgs)
	if err != nil {
		log.Err(err).Msg("Initialization failed")
		os.Exit(-1)
	}

	// build application
	app.Build()

	// execute application
	app.Run()
}