fixes for caching

GanjooRazor/Startup.cs

@@ -1,8 +1,11 @@
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.DataProtection;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Net.Http.Headers;
+using System;
 using System.IO;
 using System.Text.Encodings.Web;
 using System.Text.Unicode;
@@ -89,7 +92,36 @@ namespace GanjooRazor
 
             app.UseStatusCodePagesWithReExecute("/errors/{0}");
 
-            app.UseStaticFiles();
+            app.UseStaticFiles(new StaticFileOptions
+            {
+                OnPrepareResponse = ctx =>
+                {
+                    var path = ctx.Context.Request.Path.Value ?? "";
+                    var isExplicitlyVersioned = ctx.Context.Request.Query.ContainsKey("version") ||
+                                                 ctx.Context.Request.Query.ContainsKey("v");
+                    // /lib and /dist are third-party vendor code (jQuery, Bootstrap, TinyMCE, diff.js,
+                    // the jPlayer skin) that isn't hand-edited, so it's safe to treat the same as
+                    // explicitly-versioned assets even without a query string.
+                    var isVendorPath = path.StartsWith("/lib/", StringComparison.OrdinalIgnoreCase) ||
+                                        path.StartsWith("/dist/", StringComparison.OrdinalIgnoreCase);
+
+                    var headers = ctx.Context.Response.GetTypedHeaders();
+                    headers.CacheControl = new CacheControlHeaderValue
+                    {
+                        Public = true,
+                        // Versioned (?version=N / ?v=N) and vendor assets: the URL itself changes
+                        // whenever the content does, so a year-long cache is safe and is what should
+                        // eliminate most of the repeated p8.css/bk.js/user-panel.css/js downloads seen
+                        // in the IIS logs.
+                        // Everything else: no version query to rely on, so a conservative 6-hour cache
+                        // still cuts a lot of redundant requests without risking long-lived staleness
+                        // if someone edits chart.js/r2.js/etc. without remembering to bump a version.
+                        MaxAge = (isExplicitlyVersioned || isVendorPath)
+                            ? TimeSpan.FromDays(365)
+                            : TimeSpan.FromHours(6)
+                    };
+                }
+            });
 
             app.UseRouting();