Make site resilient to basket API being down

src/WebApp/Components/Layout/CartMenu.razor

@@ -17,6 +17,7 @@
 @code {
     IDisposable? basketStateSubscription;
     private IReadOnlyCollection<BasketItem>? basketItems;
+    private bool? basketUnavailable;
 
     [CascadingParameter]
     public required HttpContext HttpContext { get; set; }
@@ -30,14 +31,7 @@
         // component to re-render with the updated data.
         basketStateSubscription = Basket.NotifyOnChange(EventCallback.Factory.Create(this, UpdateBasketItemsAsync));
 
-        try
-        {
-            await UpdateBasketItemsAsync();
-        }
-        catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.Unauthorized)
-        {
-            await LogOutService.LogOutAsync(HttpContext);
-        }
+        await UpdateBasketItemsAsync();
     }
 
     public void Dispose()
@@ -47,6 +41,17 @@
 
     private async Task UpdateBasketItemsAsync()
     {
-        basketItems = await Basket.GetBasketItemsAsync();
+        try
+        {
+            basketItems = await Basket.GetBasketItemsAsync();
+        }
+        catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.Unauthorized)
+        {
+            await LogOutService.LogOutAsync(HttpContext);
+        }
+        catch
+        {
+            basketUnavailable = true;
+        }
     }
 }

src/WebApp/Components/Pages/Cart/CartPage.razor

@@ -11,7 +11,13 @@
 <SectionContent SectionName="page-header-title">Shopping bag</SectionContent>
 
 <div class='cart'>
-    @if (basketItems is null)
+    @if (basketUnavailable == true)
+    {
+        <p class="validation-message">
+            Your shopping bag is currently unavailable. Please try again later.
+        </p>
+    }
+    else if (basketItems is null)
     {
         <p>Loading...</p>
     }
@@ -86,6 +92,7 @@
 
 @code {
     private IReadOnlyCollection<BasketItem>? basketItems;
+    private bool? basketUnavailable;
 
     [SupplyParameterFromForm]
     public int? UpdateQuantityId { get; set; }
@@ -95,7 +102,14 @@
 
     protected override async Task OnInitializedAsync()
     {
-        basketItems = await Basket.GetBasketItemsAsync();
+        try
+        {
+            basketItems = await Basket.GetBasketItemsAsync();
+        }
+        catch
+        {
+            basketUnavailable = true;
+        }
     }
 
     private decimal? TotalPrice => basketItems?.Sum(i => i.Quantity * i.UnitPrice);
@@ -112,7 +126,15 @@
     {
         var id = UpdateQuantityId!.Value;
         var quantity = UpdateQuantityValue!.Value;
-        await Basket.SetQuantityAsync(id, quantity);
-        basketItems = await Basket.GetBasketItemsAsync();
+
+        try
+        {
+            await Basket.SetQuantityAsync(id, quantity);
+            basketItems = await Basket.GetBasketItemsAsync();
+        }
+        catch
+        {
+            basketUnavailable = true;
+        }
     }
 }

src/WebApp/Components/Pages/Item/ItemPage.razor

@@ -38,7 +38,7 @@
                         Add to shopping bag
                     </button>
                 }
-                else
+                else if (!isLoggedIn)
                 {
                     <button type="submit" title="Log in to purchase">
                         <svg width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" xmlns="http://www.w3.org/2000/svg">
@@ -54,6 +54,10 @@
             {
                 <p class="validation-message">There was an issue adding the item to your shopping bag. <br />Please try again.</p>
             }
+            else if (isLoggedIn && basketUnavailable == true)
+            {
+                <p class="validation-message">Your shopping bag is currently unavailable. <br />Please try again later.</p>
+            }
 
             @if (numInCart > 0)
             {
@@ -75,6 +79,7 @@ else if (notFound)
     private int numInCart;
     private bool isLoggedIn;
     private bool notFound;
+    private bool? basketUnavailable;
 
     [Parameter]
     public int ItemId { get; set; }
@@ -88,17 +93,32 @@ else if (notFound)
 
     protected override async Task OnInitializedAsync()
     {
+        isLoggedIn = HttpContext.User.Identity?.IsAuthenticated == true;
+
         try
         {
-            isLoggedIn = HttpContext.User.Identity?.IsAuthenticated == true;
             item = await CatalogService.GetCatalogItem(ItemId);
-            await UpdateNumInCartAsync();
         }
         catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.NotFound)
         {
             HttpContext.Response.StatusCode = 404;
             notFound = true;
         }
+
+        StateHasChanged();
+
+        if (!notFound && item is not null)
+        {
+            try
+            {
+                await UpdateNumInCartAsync();
+                basketUnavailable = false;
+            }
+            catch
+            {
+                // Ignore basket errors on page load
+            }
+        }
     }
 
     private async Task AddToCartAsync()
@@ -116,6 +136,8 @@ else if (notFound)
                 await BasketState.AddAsync(item);
                 await UpdateNumInCartAsync();
 
+                basketUnavailable = false;
+
                 if (WasLoggedOut)
                 {
                     // Remove the flag from the URL by forcing a full page navigation
@@ -131,6 +153,10 @@ else if (notFound)
                 Nav.NavigateTo(loginUrl, HttpContext, forceFullNavigation: true);
                 return;
             }
+            catch
+            {
+                basketUnavailable = true;
+            }
         }
     }
 

src/WebApp/Extensions/NavigationManagerExtensions.cs

@@ -13,6 +13,13 @@ public static void NavigateTo(this NavigationManager navigationManager, string u
         }
 
         // Workaround to force Blazor enhanced navigation to do a full redirect to an internal URL from an enhanced form handler
-        httpContext.Response.Headers["blazor-enhanced-nav-redirect-location"] = url;
+        if (!httpContext.Response.HasStarted)
+        {
+            httpContext.Response.Headers["blazor-enhanced-nav-redirect-location"] = url;
+        }
+        else
+        {
+            throw new InvalidOperationException("Cannot force a full redirect when response has already started, e.g. when Streaming Rendering is enabled.");
+        }
     }
 }