From a64e16f681ca4682c0484e1b67ed85b45f83a00c Mon Sep 17 00:00:00 2001
From: Mia Winter <mia@miawinter.de>
Date: Thu, 11 Apr 2024 13:03:05 +0200
Subject: [PATCH] Added metrics to Webhook API (total events, errors)

---
 Wave/Controllers/WebhookController.cs |  7 ++++++-
 Wave/Program.cs                       |  7 +++++--
 Wave/Utilities/Metrics/ApiMetrics.cs  | 30 +++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 Wave/Utilities/Metrics/ApiMetrics.cs

diff --git a/Wave/Controllers/WebhookController.cs b/Wave/Controllers/WebhookController.cs
index d429fcf..67b4cc3 100644
--- a/Wave/Controllers/WebhookController.cs
+++ b/Wave/Controllers/WebhookController.cs
@@ -4,16 +4,19 @@
 using Microsoft.EntityFrameworkCore;
 using Wave.Data;
 using Wave.Data.Api.Mailtrap;
+using Wave.Utilities.Metrics;
 
 namespace Wave.Controllers;
 
 [ApiController]
 [Route("/api/[controller]")]
-public class WebhookController(ILogger<WebhookController> logger, ApplicationDbContext context) : ControllerBase {
+public class WebhookController(ILogger<WebhookController> logger, ApplicationDbContext context, ApiMetrics metrics) 
+		: ControllerBase {
 	[HttpPost("mailtrap/{apiKey}")]
 	[Authorize("EmailApi", AuthenticationSchemes = "ApiKeyInRoute")]
 	public async Task<IActionResult> Mailtrap(Webhook webhook, string apiKey) {
 		foreach (var webhookEvent in webhook.Events) {
+			metrics.WebhookEventReceived("Mailtrap", webhookEvent.Type.ToString());
 			var subscriber = await context.Set<EmailSubscriber>().FirstOrDefaultAsync(s => s.Email == webhookEvent.Email);
 
 			logger.LogDebug("Received Webhook event {EventType} for {email}", 
@@ -24,6 +27,7 @@ public class WebhookController(ILogger<WebhookController> logger, ApplicationDbC
 					"Received webhook event from mailtrap of type {EventType}, " +
 					"but failed to find subscriber with E-Mail {email}.", 
 					webhookEvent.Type, webhookEvent.Email);
+				metrics.WebhookEventError("Mailtrap", webhookEvent.Type.ToString(), "unknown email");
 				continue;
 			}
 
@@ -59,6 +63,7 @@ public class WebhookController(ILogger<WebhookController> logger, ApplicationDbC
 				case WebhookEventType.Click:
 				default:
 					logger.LogInformation("Received unsupported event {EventType} for {email}. Skipping.", webhookEvent.Type, webhookEvent.Email);
+					metrics.WebhookEventError("Mailtrap", webhookEvent.Type.ToString(), "unknown type");
 					return Ok();
 			}
 
diff --git a/Wave/Program.cs b/Wave/Program.cs
index a330303..49b4a5e 100644
--- a/Wave/Program.cs
+++ b/Wave/Program.cs
@@ -26,6 +26,7 @@
 using Serilog;
 using Serilog.Events;
 using Serilog.Sinks.Grafana.Loki;
+using Wave.Utilities.Metrics;
 
 #region Version Information
 
@@ -275,7 +276,7 @@
 
 #endregion
 
-#region Open Telemetry
+#region Open Telemetry & Metrics
 
 var features = builder.Configuration.GetSection(nameof(Features)).Get<Features>();
 if (features?.Telemetry is true) {
@@ -292,7 +293,7 @@
 		.AddMeter("Microsoft.AspNetCore.Http.Connections")
 		.AddMeter("Microsoft.AspNetCore.Http.Routing")
 		.AddMeter("Microsoft.AspNetCore.Diagnostics")
-		
+		.AddMeter("Wave.Api")
 		.AddPrometheusExporter());
 	
 	// Jaeger etc.
@@ -303,6 +304,8 @@
 			tracing.AddOtlpExporter(options => options.Endpoint = new Uri(otlpUrl));
 		});
 	}
+
+	builder.Services.AddSingleton<ApiMetrics>();
 }
 
 #endregion
diff --git a/Wave/Utilities/Metrics/ApiMetrics.cs b/Wave/Utilities/Metrics/ApiMetrics.cs
new file mode 100644
index 0000000..c28e1d1
--- /dev/null
+++ b/Wave/Utilities/Metrics/ApiMetrics.cs
@@ -0,0 +1,30 @@
+using System.Diagnostics.Metrics;
+
+namespace Wave.Utilities.Metrics;
+
+public class ApiMetrics {
+	private Counter<int> WebhookEventCounter { get; } 
+	private Counter<int> WebhookErrorCounter { get; } 
+
+	public ApiMetrics(IMeterFactory meterFactory) {
+		var meter = meterFactory.Create("Wave.Api");
+
+		WebhookEventCounter = meter.CreateCounter<int>("wave.webhook.events", "{events}",
+			description: "Counts the incoming webhook events");
+		WebhookErrorCounter = meter.CreateCounter<int>("wave.webhook.errors", "{events}",
+			description: "Counts errors in webhook events");
+	}
+
+	public void WebhookEventReceived(string api, string type) {
+		WebhookEventCounter.Add(1, 
+			new KeyValuePair<string, object?>("wave.webhook.event_type", type),
+			new KeyValuePair<string, object?>("wave.webhook.api", api));
+	}
+
+	public void WebhookEventError(string api, string type, string reason) {
+		WebhookErrorCounter.Add(1,
+			new KeyValuePair<string, object?>("wave.webhook.event_type", type),
+			new KeyValuePair<string, object?>("wave.webhook.api", api),
+			new KeyValuePair<string, object?>("wave.error.reason", reason));
+	}
+}
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