From d5a755f2ba5a153d2bd039933ad80b42ed9cd701 Mon Sep 17 00:00:00 2001
From: Collin Barrett <6483057+collinbarrett@users.noreply.github.com>
Date: Sat, 31 May 2025 21:11:17 -0500
Subject: [PATCH] refactor(api): cache api responses

---
 .../CacheMiddleware.cs                        | 48 +++++++++++++++++++
 .../FilterLists.Directory.Api/Program.cs      |  1 +
 2 files changed, 49 insertions(+)
 create mode 100644 services/Directory/FilterLists.Directory.Api/CacheMiddleware.cs

diff --git a/services/Directory/FilterLists.Directory.Api/CacheMiddleware.cs b/services/Directory/FilterLists.Directory.Api/CacheMiddleware.cs
new file mode 100644
index 000000000..805cb7f7b
--- /dev/null
+++ b/services/Directory/FilterLists.Directory.Api/CacheMiddleware.cs
@@ -0,0 +1,48 @@
+namespace FilterLists.Directory.Api;
+
+internal class CachingMiddleware(RequestDelegate next, CachingMiddlewareOptions options)
+{
+    public async Task InvokeAsync(HttpContext context)
+    {
+        await next(context);
+
+        if (ShouldApplyCachingHeaders(context))
+        {
+            context.Response.Headers.CacheControl =
+                $"public, s-maxage={options.SharedCacheMaxAgeSeconds}, max-age={options.ClientCacheMaxAgeSeconds}";
+
+            if (options.AddExpiresHeader)
+                context.Response.Headers.Expires =
+                    DateTime.UtcNow.AddSeconds(options.SharedCacheMaxAgeSeconds).ToString("R");
+        }
+    }
+
+    private bool ShouldApplyCachingHeaders(HttpContext context)
+    {
+        return context.Request.Path.StartsWithSegments(options.ApiPathPrefix) &&
+               context.Request.Method == HttpMethods.Get &&
+               context.Response.StatusCode >= 200 &&
+               context.Response.StatusCode < 300 &&
+               !context.Response.Headers.ContainsKey("Cache-Control");
+    }
+}
+
+internal record CachingMiddlewareOptions
+{
+    public string ApiPathPrefix { get; set; } = "/api";
+    public int SharedCacheMaxAgeSeconds { get; set; } = 24 * 60 * 60; // Default 1 day
+    public int ClientCacheMaxAgeSeconds { get; set; } = 1 * 60 * 60; // Default 1 hour
+    public bool AddExpiresHeader { get; set; }
+}
+
+internal static class CachingMiddlewareExtensions
+{
+    public static IApplicationBuilder UseCustomApiCaching(
+        this IApplicationBuilder builder,
+        Action<CachingMiddlewareOptions>? configureOptions = null)
+    {
+        var options = new CachingMiddlewareOptions();
+        configureOptions?.Invoke(options);
+        return builder.UseMiddleware<CachingMiddleware>(options);
+    }
+}
\ No newline at end of file
diff --git a/services/Directory/FilterLists.Directory.Api/Program.cs b/services/Directory/FilterLists.Directory.Api/Program.cs
index 5182d8778..098493fd8 100644
--- a/services/Directory/FilterLists.Directory.Api/Program.cs
+++ b/services/Directory/FilterLists.Directory.Api/Program.cs
@@ -16,6 +16,7 @@
 
 app.UseExceptionHandler();
 app.UseCors();
+app.UseCustomApiCaching();
 app.MapEndpoints();
 app.MapDefaultEndpoints();
 app.UseSwagger(o => o.RouteTemplate = "{documentName}/openapi.json");