fix(sdk): support custom metrics (#446)

Author: doronkopit5

packages/sample-app/src/sample_decorators.ts

@@ -31,6 +31,7 @@ class SampleOpenAI {
       prompt: `Tell me a joke about ${jokeSubject}`,
       model: "gpt-3.5-turbo-instruct",
     });
+    traceloop.reportCustomMetric("test_metric", 50.2);
 
     return completion.choices[0].text;
   }

packages/traceloop-sdk/src/lib/node-server-sdk.ts

@@ -8,6 +8,7 @@ export * from "./tracing/decorators";
 export * from "./tracing/manual";
 export * from "./tracing/association";
 export * from "./tracing/score";
+export * from "./tracing/custom-metric";
 export * from "./prompts";
 
 initInstrumentations();

packages/traceloop-sdk/src/lib/tracing/custom-metric.ts

@@ -0,0 +1,27 @@
+import { context, diag, trace } from "@opentelemetry/api";
+
+/**
+ * Reports a custom metric to the current active span.
+ *
+ * This function allows you to add a custom metric to the current span in the trace.
+ * If there is no active span, a warning will be logged.
+ *
+ * @param {string} metricName - The name of the custom metric.
+ * @param {number} metricValue - The numeric value of the custom metric.
+ *
+ * @example
+ * reportCustomMetric('processing_time', 150);
+ */
+export const reportCustomMetric = (metricName: string, metricValue: number) => {
+  const currentContext = context.active();
+  const currentSpan = trace.getSpan(currentContext);
+
+  if (currentSpan) {
+    currentSpan.setAttribute(
+      `traceloop.custom_metric.${metricName}`,
+      metricValue,
+    );
+  } else {
+    diag.warn(`No active span found to report custom metric: ${metricName}`);
+  }
+};