From 3089712084b7ceb40914947e8ab109867512fe13 Mon Sep 17 00:00:00 2001
From: Ahmet Alp Balkan <ahmetb@google.com>
Date: Thu, 28 Jun 2018 00:20:26 -0700
Subject: [PATCH] frontend: error page

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>
---
 src/frontend/handlers.go          | 52 ++++++++++++++++++-------------
 src/frontend/templates/error.html |  7 +++--
 2 files changed, 35 insertions(+), 24 deletions(-)

diff --git a/src/frontend/handlers.go b/src/frontend/handlers.go
index 7e84bac..abb18cb 100644
--- a/src/frontend/handlers.go
+++ b/src/frontend/handlers.go
@@ -36,7 +36,7 @@ func ensureSessionID(next http.HandlerFunc) http.HandlerFunc {
 				MaxAge: cookieMaxAge,
 			})
 		} else if err != nil {
-			http.Error(w, fmt.Sprintf("unrecognized cookie error: %+v", err), http.StatusInternalServerError)
+			renderHTTPError(w, fmt.Errorf("unrecognized cookie error: %+v", err), http.StatusInternalServerError)
 			return
 		} else {
 			sessionID = c.Value
@@ -51,17 +51,17 @@ func (fe *frontendServer) homeHandler(w http.ResponseWriter, r *http.Request) {
 	log.Printf("[home] session_id=%s currency=%s", sessionID(r), currentCurrency(r))
 	currencies, err := fe.getCurrencies(r.Context())
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	products, err := fe.getProducts(r.Context())
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve products: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve products: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	cart, err := fe.getCart(r.Context(), sessionID(r))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
@@ -73,7 +73,7 @@ func (fe *frontendServer) homeHandler(w http.ResponseWriter, r *http.Request) {
 	for i, p := range products {
 		price, err := fe.convertCurrency(r.Context(), p.GetPriceUsd(), currentCurrency(r))
 		if err != nil {
-			http.Error(w, err.Error(), http.StatusInternalServerError)
+			renderHTTPError(w, err, http.StatusInternalServerError)
 			return
 		}
 		ps[i] = productView{p, price}
@@ -93,36 +93,36 @@ func (fe *frontendServer) homeHandler(w http.ResponseWriter, r *http.Request) {
 func (fe *frontendServer) productHandler(w http.ResponseWriter, r *http.Request) {
 	id := mux.Vars(r)["id"]
 	if id == "" {
-		http.Error(w, "product id not specified", http.StatusBadRequest)
+		renderHTTPError(w, fmt.Errorf("product id not specified"), http.StatusBadRequest)
 		return
 	}
 	log.Printf("[productHandler] id=%s currency=%s session=%s", id, currentCurrency(r), sessionID(r))
 	p, err := fe.getProduct(r.Context(), id)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve product: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve product: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	currencies, err := fe.getCurrencies(r.Context())
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	cart, err := fe.getCart(r.Context(), sessionID(r))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	price, err := fe.convertCurrency(r.Context(), p.GetPriceUsd(), currentCurrency(r))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to convert currency: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to convert currency: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	recommendations, err := fe.getRecommendations(r.Context(), sessionID(r), []string{id})
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to get product recommendations: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to get product recommendations: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
@@ -147,19 +147,19 @@ func (fe *frontendServer) addToCartHandler(w http.ResponseWriter, r *http.Reques
 	quantity, _ := strconv.ParseUint(r.FormValue("quantity"), 10, 32)
 	productID := r.FormValue("product_id")
 	if productID == "" || quantity == 0 {
-		http.Error(w, "invalid form input", http.StatusBadRequest)
+		renderHTTPError(w, fmt.Errorf("invalid form input"), http.StatusBadRequest)
 		return
 	}
 	log.Printf("[addToCart] product_id=%s qty=%d session_id=%s", productID, quantity, sessionID(r))
 
 	p, err := fe.getProduct(r.Context(), productID)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve product: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve product: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	if err := fe.insertCart(r.Context(), sessionID(r), p.GetId(), int32(quantity)); err != nil {
-		http.Error(w, fmt.Sprintf("failed to add to cart: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to add to cart: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	w.Header().Set("location", "/cart")
@@ -170,7 +170,7 @@ func (fe *frontendServer) emptyCartHandler(w http.ResponseWriter, r *http.Reques
 	log.Printf("[emptyCart] session_id=%s", sessionID(r))
 
 	if err := fe.emptyCart(r.Context(), sessionID(r)); err != nil {
-		http.Error(w, fmt.Sprintf("failed to empty cart: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to empty cart: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	w.Header().Set("location", "/")
@@ -181,24 +181,24 @@ func (fe *frontendServer) viewCartHandler(w http.ResponseWriter, r *http.Request
 	log.Printf("[viewCart] session_id=%s", sessionID(r))
 	currencies, err := fe.getCurrencies(r.Context())
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	cart, err := fe.getCart(r.Context(), sessionID(r))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	recommendations, err := fe.getRecommendations(r.Context(), sessionID(r), cartIDs(cart))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to get product recommendations: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to get product recommendations: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
 	shippingCost, err := fe.getShippingQuote(r.Context(), cart, currentCurrency(r))
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to get shipping quote: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to get shipping quote: %+v", err), http.StatusInternalServerError)
 		return
 	}
 
@@ -212,12 +212,12 @@ func (fe *frontendServer) viewCartHandler(w http.ResponseWriter, r *http.Request
 	for i, item := range cart {
 		p, err := fe.getProduct(r.Context(), item.GetProductId())
 		if err != nil {
-			http.Error(w, fmt.Sprintf("could not retrieve product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
+			renderHTTPError(w, fmt.Errorf("could not retrieve product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
 			return
 		}
 		price, err := fe.convertCurrency(r.Context(), p.GetPriceUsd(), currentCurrency(r))
 		if err != nil {
-			http.Error(w, fmt.Sprintf("could not convert currency for product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
+			renderHTTPError(w, fmt.Errorf("could not convert currency for product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
 			return
 		}
 
@@ -280,7 +280,7 @@ func (fe *frontendServer) placeOrderHandler(w http.ResponseWriter, r *http.Reque
 				Country:       country},
 		})
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to complete the order: %+v", err), http.StatusInternalServerError)
+		renderHTTPError(w, fmt.Errorf("failed to complete the order: %+v", err), http.StatusInternalServerError)
 		return
 	}
 	log.Printf("order #%s completed", order.GetOrder().GetOrderId())
@@ -359,6 +359,14 @@ func (fe *frontendServer) setCurrencyHandler(w http.ResponseWriter, r *http.Requ
 	w.WriteHeader(http.StatusFound)
 }
 
+func renderHTTPError(w http.ResponseWriter, err error, code int) {
+	w.WriteHeader(code)
+	templates.ExecuteTemplate(w, "error", map[string]interface{}{
+		"error":       err.Error(),
+		"status_code": code,
+		"status":      http.StatusText(code)})
+}
+
 func currentCurrency(r *http.Request) string {
 	c, _ := r.Cookie(cookieCurrency)
 	if c != nil {
diff --git a/src/frontend/templates/error.html b/src/frontend/templates/error.html
index 5a1b125..24e167a 100644
--- a/src/frontend/templates/error.html
+++ b/src/frontend/templates/error.html
@@ -6,8 +6,11 @@
             <div class="container bg-light py-3 px-lg-5 py-lg-5">
                 <h1>Uh, oh!</h1>
                 <p>Something has failed. Below are some details for debugging.</p>
-                <pre>
-                    {{.errorMsg}}
+                
+                <p><strong>HTTP Status:</strong> {{.status_code}} {{.status}}</p>
+                <pre class="border border-danger"
+                    style="white-space: pre-wrap; word-break: keep-all;">
+                    {{- .error -}}
                 </pre>
             </div>
         </div>