Merge pull request #2026 from bcgov/metrics

Metrics & etags
bcgov · Dec 11, 2024 · ba2149e · ba2149e
2 parents ed61335 + 9ca475a
commit ba2149e
Show file tree

Hide file tree

Showing 7 changed files with 109 additions and 17 deletions.
diff --git a/src/backend/TrafficCourts/Staff.Service/Middleware/ETagMiddleware.cs b/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)}\"";
+        }
+    }
+}
diff --git a/src/backend/TrafficCourts/Staff.Service/Program.cs b/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;

diff --git a/src/backend/TrafficCourts/TrafficCourts.Core/Diagnostics/OperationMetrics.cs b/src/backend/TrafficCourts/TrafficCourts.Core/Diagnostics/OperationMetrics.cs
@@ -35,6 +35,8 @@ protected OperationMetrics(IMeterFactory factory, string meterName, string name,
         _timer = new Timer(_meter, $"{name}.operation.duration", "ms", $"Elapsed time spent executing a {description} operation");
     }
 
+    protected Meter Meter => _meter;
+
     /// <summary>
     /// Begins a named operation
     /// </summary>
@@ -62,6 +64,6 @@ public ITimerOperation BeginOperation([CallerMemberName] string operation = null
 
     public void Dispose()
     {
-        _meter.Dispose();
+        Meter.Dispose();
     }
 }
diff --git a/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/ETagHandler.cs b/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/ETagHandler.cs
@@ -1,4 +1,5 @@
 using Microsoft.Extensions.Caching.Memory;
+using OpenTelemetry.Metrics;
 using System.Diagnostics.Metrics;
 
 namespace TrafficCourts.OrdsDataService;
@@ -33,17 +34,12 @@ public class ETagHandler : DelegatingHandler
     public const string NoCache = "no-cache";
 
     private readonly IMemoryCache _cache;
+    private readonly IOrdsDataServiceOperationMetrics _metrics;
 
-    private readonly Counter<long> _cacheHitCounter;
-    private readonly Counter<long> _cacheMissCounter;
-
-    public ETagHandler(IMemoryCache cache, IMeterFactory factory)
+    internal ETagHandler(IMemoryCache cache, IOrdsDataServiceOperationMetrics metrics)
     {
         _cache = cache ?? throw new ArgumentNullException(nameof(cache));
-
-        var meter = factory.Create(OrdsDataServiceOperationMetrics.MeterName);
-        _cacheHitCounter = meter.CreateCounter<long>("ordsdataservice_etag_cache_hits");
-        _cacheMissCounter = meter.CreateCounter<long>("ordsdataservice_etag_cache_misses");
+        _metrics = metrics ?? throw new ArgumentNullException(nameof(metrics));
     }
 
     protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
@@ -69,20 +65,19 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
         var pathTag = new KeyValuePair<string, object?>("path", request.RequestUri!.AbsolutePath);
         var expirationTag = new KeyValuePair<string, object?>("expiration-secs", (int)expiration.TotalSeconds);
 
-        // already had the response
+        // already have the response
         if (response.StatusCode == System.Net.HttpStatusCode.NotModified)
         {
-            _cacheHitCounter.Add(1, pathTag, expirationTag);
+            _metrics.RecordEtagCacheHit(pathTag, expirationTag);
             response = CreateResponse(request, cacheEntry);
             return response;
         }
-        else
-        {
-            _cacheMissCounter.Add(1, pathTag, expirationTag); // this same request was different than the cached response
-        }
 
         if (response.Headers.ETag != null)
         {
+            // only increment the cache miss if we have a etag
+            _metrics.RecordEtagCacheMiss(pathTag, expirationTag);
+
             var responseBody = await response.Content.ReadAsByteArrayAsync(cancellationToken);
 
             // create response template

diff --git a/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/IOrdsDataServiceOperationMetrics.cs b/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/IOrdsDataServiceOperationMetrics.cs
@@ -4,4 +4,13 @@ namespace TrafficCourts.OrdsDataService;
 
 internal interface IOrdsDataServiceOperationMetrics : IOperationMetrics
 {
+    /// <summary>
+    /// Records a OrdsDataService ETag cache hit.
+    /// </summary>
+    void RecordEtagCacheHit(KeyValuePair<string, object?> tag1, KeyValuePair<string, object?> tag2);
+
+    /// <summary>
+    /// Records a OrdsDataService ETag cache miss.
+    /// </summary>
+    void RecordEtagCacheMiss(KeyValuePair<string, object?> tag1, KeyValuePair<string, object?> tag2);
 }
diff --git a/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/OrdsDataServiceExtensions.cs b/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/OrdsDataServiceExtensions.cs
@@ -32,8 +32,8 @@ public static void AddOrdsDataService(this IServiceCollection services, IConfigu
         .AddHttpMessageHandler(sp =>
         {
             var cache = sp.GetRequiredService<Caching.Memory.IMemoryCache>();
-            var factory = sp.GetRequiredService<IMeterFactory>();
-            ETagHandler handler = new ETagHandler(cache, factory);
+            var metrics = sp.GetRequiredService<IOrdsDataServiceOperationMetrics>();
+            ETagHandler handler = new ETagHandler(cache, metrics);
             return handler;
         });
 

diff --git a/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/OrdsDataServiceOperationMetrics.cs b/src/backend/TrafficCourts/TrafficCourts.OrdsDataService/OrdsDataServiceOperationMetrics.cs
@@ -9,9 +9,23 @@ internal class OrdsDataServiceOperationMetrics : OperationMetrics, IOrdsDataServ
 {
     public const string MeterName = "OrdsDataService";
 
+    private readonly Counter<long> _cacheHitCounter;
+    private readonly Counter<long> _cacheMissCounter;
+
     public OrdsDataServiceOperationMetrics(IMeterFactory factory) : base(factory, MeterName, "ordsdataservice", "ORDS Data Service")
     {
+        _cacheHitCounter = Meter.CreateCounter<long>("ordsdataservice.etag.cache.hits");
+        _cacheMissCounter = Meter.CreateCounter<long>("ordsdataservice.etag.cache.misses");
     }
+
+    /// <summary>
+    /// Records a OrdsDataService ETag cache hit.
+    /// </summary>
+    public void RecordEtagCacheHit(KeyValuePair<string, object?> tag1, KeyValuePair<string, object?> tag2) => _cacheHitCounter.Add(1, tag1, tag2);
+    /// <summary>
+    /// Records a OrdsDataService ETag cache miss.
+    /// </summary>
+    public void RecordEtagCacheMiss(KeyValuePair<string, object?> tag1, KeyValuePair<string, object?> tag2) => _cacheMissCounter.Add(1, tag1, tag2);
 }
 
 public static class TracerProviderBuilderExtensions