Add API etag support to avoid sending content to browsers possible

src/backend/TrafficCourts/Staff.Service/Middleware/ETagMiddleware.cs

@@ -0,0 +1,69 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace TrafficCourts.Staff.Service.Middleware;
+
+public class ETagMiddleware
+{
+    private readonly RequestDelegate _next;
+
+    public ETagMiddleware(RequestDelegate next)
+    {
+        _next = next;
+    }
+
+    public async Task InvokeAsync(HttpContext context)
+    {
+        // Only handle GET requests
+        if (context.Request.Method != HttpMethods.Get)
+        {
+            await _next(context);
+            return;
+        }
+
+        // capture the response body
+        Stream originalBodyStream = context.Response.Body;
+
+        // create new response body stream
+        using var memoryStream = new MemoryStream();
+        context.Response.Body = memoryStream;
+        await _next(context);
+
+        // Only generate ETag for successful responses
+        if (context.Response.StatusCode == StatusCodes.Status200OK)
+        {
+            // Generate ETag based on the response content
+            memoryStream.Seek(0, SeekOrigin.Begin);
+            var content = await new StreamReader(memoryStream).ReadToEndAsync();
+            var eTag = GenerateETag(content);
+
+            // Check the If-None-Match header
+            if (context.Request.Headers.TryGetValue("If-None-Match", out Microsoft.Extensions.Primitives.StringValues value) && value == eTag)
+            {
+                context.Response.StatusCode = StatusCodes.Status304NotModified;
+                context.Response.Headers.ETag = eTag;
+                context.Response.Body = originalBodyStream;
+                context.Response.ContentLength = 0; // Ensure the response body is empty
+                return;
+            }
+
+            // Include the ETag in the response headers
+            context.Response.Headers.ETag = eTag;
+
+            // Write the response body back to the original stream
+            memoryStream.Seek(0, SeekOrigin.Begin);
+            await memoryStream.CopyToAsync(originalBodyStream);
+        }
+
+        context.Response.Body = originalBodyStream;
+    }
+
+    private string GenerateETag(string content)
+    {
+        using (var md5 = MD5.Create())
+        {
+            var hash = md5.ComputeHash(Encoding.UTF8.GetBytes(content));
+            return $"\"{Convert.ToBase64String(hash)}\"";
+        }
+    }
+}

src/backend/TrafficCourts/Staff.Service/Program.cs

@@ -3,6 +3,7 @@
 using TrafficCourts.Configuration.Validation;
 using TrafficCourts.Diagnostics;
 using TrafficCourts.Staff.Service;
+using TrafficCourts.Staff.Service.Middleware;
 
 var builder = WebApplication.CreateBuilder(args);
 var logger = builder.GetProgramLogger();
@@ -18,6 +19,8 @@
 app.UseAuthentication();
 app.UseAuthorization();
 
+app.UseMiddleware<ETagMiddleware>();
+
 app.UseFastEndpoints(c => {
     c.Endpoints.RoutePrefix = "api";
     c.Endpoints.PrefixNameWithFirstTag = true;