frontend: initial prototype

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

src/.gitignore

@@ -0,0 +1,6 @@
+# block vgo cache dir
+v/
+# temp gopath
+github.com
+golang.org
+google.golang.org

src/frontend/genproto.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -e
+
+PATH=$PATH:$GOPATH/bin
+protodir=../../pb
+
+protoc --go_out=plugins=grpc:genproto -I $protodir $protodir/demo.proto

src/frontend/main.go

@@ -0,0 +1,152 @@
+package main // import "frontend"
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+
+	"github.com/google/uuid"
+	"github.com/gorilla/mux"
+	"google.golang.org/grpc"
+
+	pb "frontend/genproto"
+)
+
+const (
+	port            = "8080"
+	defaultCurrency = "USD"
+	cookieMaxAge    = 60 * 60 * 48
+
+	cookieSessionID = "session-id"
+	cookieCurrency  = "currency"
+)
+
+var (
+	whitelistedCurrencies = map[string]bool{
+		"USD": true, "EUR": true, "CAD": true, "JPY": true}
+)
+
+type ctxKeySessionID struct{}
+
+type frontendServer struct {
+	productCatalogSvcAddr string
+	productCatalogSvcConn *grpc.ClientConn
+
+	cartSvcAddr string
+	cartSvcConn *grpc.ClientConn
+
+	currencySvcAddr string
+	currencySvcConn *grpc.ClientConn
+}
+
+func main() {
+	ctx := context.Background()
+
+	srvPort := port
+	if os.Getenv("PORT") != "" {
+		srvPort = os.Getenv("PORT")
+	}
+	svc := new(frontendServer)
+	// mustMapEnv(&svc.productCatalogSvcAddr, "PRODUCT_CATALOG_SERVICE_ADDR")
+	// mustMapEnv(&svc.cartSvcAddr, "CART_SERVICE_ADDR")
+	mustMapEnv(&svc.currencySvcAddr, "CURRENCY_SERVICE_ADDR")
+
+	var err error
+	svc.currencySvcConn, err = grpc.DialContext(ctx, svc.currencySvcAddr, grpc.WithInsecure())
+	if err != nil {
+		log.Fatalf("failed to connect currency service: %+v", err)
+	}
+
+	r := mux.NewRouter()
+	r.HandleFunc("/", svc.ensureSessionID(svc.homeHandler)).
+		Methods(http.MethodGet)
+	r.HandleFunc("/logout", svc.logoutHandler).
+		Methods(http.MethodGet)
+	r.HandleFunc("/setCurrency", svc.ensureSessionID(svc.setCurrencyHandler)).
+		Methods(http.MethodPost)
+	log.Printf("starting server on :" + srvPort)
+	log.Fatal(http.ListenAndServe("localhost:"+srvPort, r))
+}
+
+func (fe *frontendServer) ensureSessionID(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		var sessionID string
+		c, err := r.Cookie(cookieSessionID)
+		if err == http.ErrNoCookie {
+			u, _ := uuid.NewRandom()
+			sessionID = u.String()
+		} else if err != nil {
+			log.Printf("unrecognized cookie error: %+v", err)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		} else {
+			sessionID = c.Value
+		}
+		http.SetCookie(w, &http.Cookie{
+			Name:   cookieSessionID,
+			Value:  sessionID,
+			MaxAge: cookieMaxAge,
+		})
+		ctx := context.WithValue(r.Context(), ctxKeySessionID{}, sessionID)
+		r = r.WithContext(ctx)
+		next(w, r)
+	}
+}
+
+func (fe *frontendServer) homeHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[home] session_id=%+v", r.Context().Value(ctxKeySessionID{}))
+	currencies, err := fe.getCurrencies(r.Context())
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+	log.Printf("currencies: %+v", currencies)
+}
+
+func (fe *frontendServer) logoutHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[home] session_id=%+v", r.Context().Value(ctxKeySessionID{}))
+	for _, c := range r.Cookies() {
+		c.MaxAge = -1
+		http.SetCookie(w, c)
+	}
+	w.Header().Set("Location", "/")
+	w.WriteHeader(http.StatusFound)
+}
+
+func (fe *frontendServer) setCurrencyHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[setCurrency] session_id=%+v", r.Context().Value(ctxKeySessionID{}))
+	cur := r.FormValue("currency_code")
+	if cur != "" {
+		http.SetCookie(w, &http.Cookie{
+			Name:   cookieCurrency,
+			Value:  cur,
+			MaxAge: cookieMaxAge,
+		})
+	}
+	w.Header().Set("Location", "/")
+	w.WriteHeader(http.StatusFound)
+}
+
+func (fe *frontendServer) getCurrencies(ctx context.Context) ([]string, error) {
+	currs, err := pb.NewCurrencyServiceClient(fe.currencySvcConn).GetSupportedCurrencies(ctx, &pb.Empty{})
+	if err != nil {
+		return nil, err
+	}
+	var out []string
+	for _, c := range currs.CurrencyCodes {
+		if _, ok := whitelistedCurrencies[c]; ok {
+			out = append(out, c)
+		}
+	}
+	return out, nil
+}
+
+func mustMapEnv(target *string, envKey string) {
+	v := os.Getenv(envKey)
+	if v == "" {
+		panic(fmt.Sprintf("environment variable %q not set", envKey))
+	}
+	*target = v
+}