feat: implement rss feed

.vscode/settings.json

@@ -2,6 +2,7 @@
   "cSpell.words": [
     "Antiforgery",
     "blazor",
+    "Entitize",
     "Hsts",
     "Markdig",
     "msedge"

src/Blog/Blog.csproj

@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="Markdig" Version="0.36.2" />
+    <PackageReference Include="System.ServiceModel.Syndication" Version="8.0.0" />
     <PackageReference Include="TestableIO.System.IO.Abstractions.Wrappers" Version="21.0.2" />
     <PackageReference Include="WebStoating.Markdig.Prism" Version="1.0.0" />
   </ItemGroup>

src/Blog/Program.cs

@@ -1,3 +1,8 @@
+using System.ServiceModel.Syndication;
+using System.Text;
+using System.Xml;
+using System.Xml.Linq;
+
 var builder = WebApplication.CreateBuilder(args);
 
 builder.Services.ConfigureOptions<FilePostServiceOptionsSetup>();
@@ -21,11 +26,73 @@ app.UseHttpsRedirection();
 app.UseStaticFiles();
 app.UseAntiforgery();
 
+app.UseStatusCodePagesWithRedirects("/Error/{0}");
+
+app
+  .MapGet("/rss", async (HttpContext context, IPostService postService) => 
+  {
+    var req = context.Request;
+    var url = $"{req.Scheme}://{req.Host}{req.PathBase}";
+    
+    var posts = await postService.GetPostsAsync();
+
+    var items = posts.Select(post =>
+    {
+      var uri = new Uri($"{url}/{post.Slug}");
+
+      var item = new SyndicationItem(
+        post.Title,
+        post.Lead,
+        uri,
+        post.Slug,
+        post.PublishedAt
+      );
+
+      return item;
+    });
+
+    var feed = new SyndicationFeed(
+      "journal",
+      "A blog by Stevan Freeborn",
+      new Uri(url)
+    )
+    {
+      Items = items,
+    };
+
+    XNamespace atom = "http://www.w3.org/2005/Atom";
+    feed.ElementExtensions.Add(
+      new XElement(atom + "link",
+        new XAttribute("href", url + "/rss"),
+        new XAttribute("rel", "self"),
+        new XAttribute("type", "application/rss+xml")
+      )
+    );
+
+    var settings = new XmlWriterSettings
+    {
+      Encoding = Encoding.UTF8,
+      NewLineHandling = NewLineHandling.Entitize,
+      Indent = true,
+      Async = true,
+    };
+
+    using var stream = new MemoryStream();
+    using var writer = XmlWriter.Create(stream, settings);
+
+    var rssFormatter = new Rss20FeedFormatter(feed, false);
+    rssFormatter.WriteTo(writer);
+    await writer.FlushAsync();
+
+    return Results.File(stream.ToArray(), "application/xml");
+  })
+  .WithDisplayName("RSS Feed")
+  .WithDescription("RSS feed for the blog");
+
 app
   .MapRazorComponents<App>()
   .AddInteractiveServerRenderMode();
 
-app.UseStatusCodePagesWithRedirects("/Error/{0}");
 
 app.Run();
 

test/Blog.Tests/EndToEnd/RssTests.cs

@@ -0,0 +1,37 @@
+using System.ServiceModel.Syndication;
+using System.Text;
+using System.Xml;
+using System.Xml.Linq;
+
+namespace Blog.Tests.EndToEnd;
+
+[TestFixture]
+public class RssTests : BlogTest
+{
+  [Test]
+  public async Task Task_Rss_WhenFetched_ItShouldReturnRssFeed()
+  {
+    var response = await Page.APIRequest.GetAsync("/rss");
+    response.Status.Should().Be((int)HttpStatusCode.OK);
+
+    var xml = await response.BodyAsync();
+    
+    var streamReader = new StreamReader(
+      new MemoryStream(xml), 
+      Encoding.UTF8
+    );
+
+
+    var settings = new XmlReaderSettings
+    {
+      Async = true
+    };
+
+    using var xmlReader = XmlReader.Create(streamReader, settings);
+    var feed = SyndicationFeed.Load(xmlReader);
+
+    feed.Title.Text.Should().Be("journal");
+    feed.Description.Text.Should().Be("A blog by Stevan Freeborn");
+    feed.Items.Should().HaveCount(2);
+  }
+}