Serve 503 when PocketBase is unavailable across all content pages

Elternbeirat.PocketBase/PocketBaseUnavailableException.cs

@@ -0,0 +1,49 @@
+namespace Elternbeirat.PocketBase;
+
+/// <summary>
+///     Thrown when PocketBase could not be reached, timed out, or returned a
+///     response that could not be read.
+/// </summary>
+/// <remarks>
+///     This is the one failure the content pages need to distinguish: the site is
+///     up but its data store is not, which is an HTTP 503, not a 404. Which
+///     low-level exceptions mean that (a transport error, a timeout, unreadable
+///     JSON) is <see cref="PocketBaseClient"/>'s concern; callers catch only this
+///     type and need not know how the client talks to PocketBase.
+/// </remarks>
+public sealed class PocketBaseUnavailableException : Exception
+{
+    /// <summary>
+    ///     Initializes a new instance with a default message.
+    /// </summary>
+    public PocketBaseUnavailableException()
+        : base("PocketBase is unavailable.")
+    {
+    }
+
+    /// <summary>
+    ///     Initializes a new instance with the given message.
+    /// </summary>
+    /// <param name="message">
+    ///     The message that describes the error.
+    /// </param>
+    public PocketBaseUnavailableException(string message)
+        : base(message)
+    {
+    }
+
+    /// <summary>
+    ///     Initializes a new instance with the given message and the underlying
+    ///     failure that caused it.
+    /// </summary>
+    /// <param name="message">
+    ///     The message that describes the error.
+    /// </param>
+    /// <param name="innerException">
+    ///     The transport, timeout, or deserialization exception that was caught.
+    /// </param>
+    public PocketBaseUnavailableException(string message, Exception innerException)
+        : base(message, innerException)
+    {
+    }
+}