Refactor Markdown content negotiation into dedicated middleware

Author: maartenba

server/src/Docs.Web/ContentNegotiationMiddleware.cs

@@ -0,0 +1,43 @@
+namespace Docs.Web;
+
+/// <summary>
+/// Middleware that serves .md files when the client sends Accept: text/markdown.
+/// </summary>
+public class ContentNegotiationMiddleware : IMiddleware
+{
+    private readonly IWebHostEnvironment _environment;
+
+    public ContentNegotiationMiddleware(IWebHostEnvironment environment)
+    {
+        _environment = environment;
+    }
+
+    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
+    {
+        var accept = context.Request.Headers.Accept.ToString();
+        if (accept.Contains("text/markdown", StringComparison.OrdinalIgnoreCase))
+        {
+            var requestPath = context.Request.Path.Value?.TrimEnd('/') ?? "";
+
+            // Try the exact path with .md extension, then index.md inside the directory
+            var candidates = new[]
+            {
+                Path.Combine(_environment.WebRootPath, requestPath.TrimStart('/') + ".md"),
+                Path.Combine(_environment.WebRootPath, requestPath.TrimStart('/'), "index.md")
+            };
+
+            foreach (var mdPath in candidates)
+            {
+                if (File.Exists(mdPath))
+                {
+                    context.Response.ContentType = "text/markdown; charset=utf-8";
+                    context.Response.Headers.TryAdd("content-signal", "ai-train=yes, search=yes, ai-input=yes");
+                    await context.Response.SendFileAsync(mdPath);
+                    return;
+                }
+            }
+        }
+
+        await next(context);
+    }
+}

server/src/Docs.Web/Program.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using Docs.Web;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -7,6 +8,9 @@
 // Add response compression
 builder.Services.AddResponseCompression();
 
+// Content negotiation middleware
+builder.Services.AddTransient<ContentNegotiationMiddleware>();
+
 var app = builder.Build();
 
 app.MapDefaultEndpoints();
@@ -52,35 +56,7 @@
 app.UseResponseCompression();
 
 // Content negotiation: serve .md file when Accept: text/markdown
-app.Use(async (context, next) =>
-{
-    var accept = context.Request.Headers.Accept.ToString();
-    if (accept.Contains("text/markdown", StringComparison.OrdinalIgnoreCase))
-    {
-        var webHostEnvironment = context.RequestServices.GetRequiredService<IWebHostEnvironment>();
-        var requestPath = context.Request.Path.Value?.TrimEnd('/') ?? "";
-
-        // Try the exact path with .md extension, then index.md inside the directory
-        var candidates = new[]
-        {
-            Path.Combine(webHostEnvironment.WebRootPath, requestPath.TrimStart('/') + ".md"),
-            Path.Combine(webHostEnvironment.WebRootPath, requestPath.TrimStart('/'), "index.md")
-        };
-
-        foreach (var mdPath in candidates)
-        {
-            if (File.Exists(mdPath))
-            {
-                context.Response.ContentType = "text/markdown; charset=utf-8";
-                context.Response.Headers["content-signal"] = "ai-train=yes, search=yes, ai-input=yes";
-                await context.Response.SendFileAsync(mdPath);
-                return;
-            }
-        }
-    }
-
-    await next();
-});
+app.UseMiddleware<ContentNegotiationMiddleware>();
 
 // Add trailing slash redirect middleware (replicate nginx behavior)
 app.Use(async (context, next) =>