Serve 503 when PocketBase is unavailable across all content pages

Elternbeirat.Web/Features/Pages/ContentPage.razor

@@ -1,14 +1,18 @@
 @page "/{Slug}"
 
-@if (_page is null)
+@if (_unavailable)
 {
-    <PageTitle>Nicht gefunden</PageTitle>
+    <PageTitle>Vorübergehend nicht erreichbar</PageTitle>
+    <p>Die Seite ist gerade nicht erreichbar. Bitte später erneut versuchen.</p>
 }
-else
+else if (_page is not null)
 {
     <PageTitle>@_page.Title</PageTitle>
     <article>
+        <h1>@_page.Title</h1>
         @Body
     </article>
     <PageEmbeds Embed="_page.Embed" />
 }
+@* No page and not unavailable: the slug was unknown; NavigationManager.NotFound()
+   already ran in OnParametersSetAsync and renders the not-found page. *@

Elternbeirat.Web/Features/Pages/ContentPage.razor.cs

@@ -8,9 +8,9 @@ namespace Elternbeirat.Web.Features.Pages;
 public partial class ContentPage
 {
     [LoggerMessage(
-        Level = LogLevel.Warning,
-        Message = "Could not load page '{slug}' from PocketBase.")]
-    private static partial void LogLoadFailed(
+        Level = LogLevel.Error,
+        Message = "Could not load page '{Slug}' from PocketBase; content source is unavailable.")]
+    private static partial void LogSourceUnavailable(
         ILogger logger,
         string slug,
         Exception exception);
@@ -24,11 +24,19 @@ public partial class ContentPage
     [Inject]
     private ILogger<ContentPage> Logger { get; set; } = null!;
 
+    [Inject]
+    private NavigationManager Navigation { get; set; } = null!;
+
     [CascadingParameter]
     private HttpContext? HttpContext { get; set; }
 
     private Page? _page;
 
+    // Set when the content source could not be reached or read. The markup then
+    // shows a "temporarily unavailable" note instead of a not-found page, matching
+    // the 503 this sets on the response.
+    private bool _unavailable;
+
     // The page body rendered from Markdown to HTML, ready to emit as a
     // MarkupString in the markup.
     private MarkupString Body => (MarkupString)Markdown.ToHtml(_page?.Body);
@@ -37,24 +45,23 @@ public partial class ContentPage
     {
         try
         {
-            var pages = await PocketBase.GetPagesAsync();
+            var pages = await PocketBase.GetPagesAsync(HttpContext?.RequestAborted ?? CancellationToken.None);
             _page = pages.FirstOrDefault(
-                p => string.Equals(p.Slug, Slug, StringComparison.OrdinalIgnoreCase));
+                page => string.Equals(page.Slug, Slug, StringComparison.OrdinalIgnoreCase));
         }
-        catch (HttpRequestException ex)
+        catch (PocketBaseUnavailableException exception)
         {
-            // Source unreachable -> treat as "not found" rather than a 500. The
-            // 404 branch below serves the friendly /not-found page.
-            LogLoadFailed(Logger, Slug, ex);
-            _page = null;
+            // The site works, its data store is down: 503, not 404.
+            LogSourceUnavailable(Logger, Slug, exception);
+            _unavailable = true;
+            SourceUnavailable.SetStatus(HttpContext);
+            return;
         }
 
-        // Unknown slug (or unreachable source) -> 404, so
-        // UseStatusCodePagesWithReExecute serves the /not-found page instead of an
-        // empty 200 response.
-        if (_page is null && HttpContext is not null)
+        if (_page is null)
         {
-            HttpContext.Response.StatusCode = StatusCodes.Status404NotFound;
+            // The source answered, but there is no page with this slug: a genuine 404.
+            Navigation.NotFound();
         }
     }
 }