microservices-demo/src/frontend/main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"cloud.google.com/go/profiler"
	"github.com/gorilla/mux"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"go.opencensus.io/exporter/stackdriver"
	"go.opencensus.io/plugin/ocgrpc"
	"go.opencensus.io/plugin/ochttp"
	"go.opencensus.io/plugin/ochttp/propagation/b3"
	"go.opencensus.io/trace"
	"google.golang.org/grpc"
)

const (
	port            = "8080"
	defaultCurrency = "USD"
	cookieMaxAge    = 60 * 60 * 48

	cookiePrefix    = "shop_"
	cookieSessionID = cookiePrefix + "session-id"
	cookieCurrency  = cookiePrefix + "currency"
)

var (
	whitelistedCurrencies = map[string]bool{
		"USD": true,
		"EUR": true,
		"CAD": true,
		"JPY": true,
		"GBP": true,
		"TRY": true}
)

type ctxKeySessionID struct{}

type frontendServer struct {
	productCatalogSvcAddr string
	productCatalogSvcConn *grpc.ClientConn

	currencySvcAddr string
	currencySvcConn *grpc.ClientConn

	cartSvcAddr string
	cartSvcConn *grpc.ClientConn

	recommendationSvcAddr string
	recommendationSvcConn *grpc.ClientConn

	checkoutSvcAddr string
	checkoutSvcConn *grpc.ClientConn

	shippingSvcAddr string
	shippingSvcConn *grpc.ClientConn
}

func main() {
	ctx := context.Background()
	log := logrus.New()
	log.Level = logrus.DebugLevel
	log.Formatter = &logrus.TextFormatter{}

	go initProfiling("frontend", "1.0.0")
	go initTracing(log)

	srvPort := port
	if os.Getenv("PORT") != "" {
		srvPort = os.Getenv("PORT")
	}
	addr := os.Getenv("LISTEN_ADDR")
	svc := new(frontendServer)
	mustMapEnv(&svc.productCatalogSvcAddr, "PRODUCT_CATALOG_SERVICE_ADDR")
	mustMapEnv(&svc.currencySvcAddr, "CURRENCY_SERVICE_ADDR")
	mustMapEnv(&svc.cartSvcAddr, "CART_SERVICE_ADDR")
	mustMapEnv(&svc.recommendationSvcAddr, "RECOMMENDATION_SERVICE_ADDR")
	mustMapEnv(&svc.checkoutSvcAddr, "CHECKOUT_SERVICE_ADDR")
	mustMapEnv(&svc.shippingSvcAddr, "SHIPPING_SERVICE_ADDR")

	mustConnGRPC(ctx, &svc.currencySvcConn, svc.currencySvcAddr)
	mustConnGRPC(ctx, &svc.productCatalogSvcConn, svc.productCatalogSvcAddr)
	mustConnGRPC(ctx, &svc.cartSvcConn, svc.cartSvcAddr)
	mustConnGRPC(ctx, &svc.recommendationSvcConn, svc.recommendationSvcAddr)
	mustConnGRPC(ctx, &svc.shippingSvcConn, svc.shippingSvcAddr)
	mustConnGRPC(ctx, &svc.checkoutSvcConn, svc.checkoutSvcAddr)

	r := mux.NewRouter()
	r.HandleFunc("/", svc.homeHandler).Methods(http.MethodGet, http.MethodHead)
	r.HandleFunc("/product/{id}", svc.productHandler).Methods(http.MethodGet, http.MethodHead)
	r.HandleFunc("/cart", svc.viewCartHandler).Methods(http.MethodGet, http.MethodHead)
	r.HandleFunc("/cart", svc.addToCartHandler).Methods(http.MethodPost)
	r.HandleFunc("/cart/empty", svc.emptyCartHandler).Methods(http.MethodPost)
	r.HandleFunc("/setCurrency", svc.setCurrencyHandler).Methods(http.MethodPost)
	r.HandleFunc("/logout", svc.logoutHandler).Methods(http.MethodGet)
	r.HandleFunc("/cart/checkout", svc.placeOrderHandler).Methods(http.MethodPost)
	r.PathPrefix("/static/").Handler(http.StripPrefix("/static/", http.FileServer(http.Dir("./static/"))))

	var handler http.Handler = r
	handler = &logHandler{log: log, next: handler} // add logging
	handler = ensureSessionID(handler)             // add session ID
	handler = &ochttp.Handler{                     // add opencensus instrumentation
		Handler:     handler,
		Propagation: &b3.HTTPFormat{}}

	log.Infof("starting server on " + addr + ":" + srvPort)
	log.Fatal(http.ListenAndServe(addr+":"+srvPort, handler))
}

func initTracing(log logrus.FieldLogger) {
	// TODO(ahmetb) this method is duplicated in other microservices using Go
	// since they are not sharing packages.
	for i := 1; i <= 3; i++ {
		log = log.WithField("retry", i)
		exporter, err := stackdriver.NewExporter(stackdriver.Options{})
		if err != nil {
			log.Warnf("failed to initialize stackdriver exporter: %+v", err)
		} else {
			trace.RegisterExporter(exporter)
			trace.ApplyConfig(trace.Config{DefaultSampler: trace.AlwaysSample()})
			log.Info("registered stackdriver tracing")
			return
		}
		d := time.Second * 20 * time.Duration(i)
		log.Debugf("sleeping %v to retry initializing stackdriver exporter", d)
		time.Sleep(d)
	}
	log.Warn("could not initialize stackdriver exporter after retrying, giving up")
}

func initProfiling(service, version string) {
	// TODO(ahmetb) this method is duplicated in other microservices using Go
	// since they are not sharing packages.
	for i := 1; i <= 3; i++ {
		if err := profiler.Start(profiler.Config{
			Service:        service,
			ServiceVersion: version,
			// ProjectID must be set if not running on GCP.
			// ProjectID: "my-project",
		}); err != nil {
			log.Printf("warn: failed to start profiler: %+v", err)
		}
		d := time.Second * 10 * time.Duration(i)
		log.Printf("sleeping %v to retry initializing stackdriver profiler", d)
		time.Sleep(d)
	}
	log.Printf("warning: could not initialize stackdriver profiler after retrying, giving up")
}

func mustMapEnv(target *string, envKey string) {
	v := os.Getenv(envKey)
	if v == "" {
		panic(fmt.Sprintf("environment variable %q not set", envKey))
	}
	*target = v
}

func mustConnGRPC(ctx context.Context, conn **grpc.ClientConn, addr string) {
	var err error
	*conn, err = grpc.DialContext(ctx, addr,
		grpc.WithInsecure(),
		grpc.WithTimeout(time.Second*3),
		grpc.WithStatsHandler(&ocgrpc.ClientHandler{}))
	if err != nil {
		panic(errors.Wrapf(err, "grpc: failed to connect %s", addr))
	}
}