From b5b79b94f2d634510b20d819f498b2aadad04c0b Mon Sep 17 00:00:00 2001
From: Eric Eastwood <contact@ericeastwood.com>
Date: Mon, 29 Aug 2022 14:13:13 -0500
Subject: [PATCH] Manually instrument some archive logic (#44)

---
 server/fetch-events-in-range.js               |  3 +-
 server/fetch-room-data.js                     |  3 +-
 .../1-render-hydrogen-to-string.js            |  3 +-
 server/tracing/trace-utilities.js             | 62 +++++++++++++++++++
 4 files changed, 68 insertions(+), 3 deletions(-)
 create mode 100644 server/tracing/trace-utilities.js

diff --git a/server/fetch-events-in-range.js b/server/fetch-events-in-range.js
index 582c1e5..36ae229 100644
--- a/server/fetch-events-in-range.js
+++ b/server/fetch-events-in-range.js
@@ -4,6 +4,7 @@ const assert = require('assert');
 const urlJoin = require('url-join');
 
 const { fetchEndpointAsJson } = require('./lib/fetch-endpoint');
+const { traceFunction } = require('./tracing/trace-utilities');
 
 const config = require('./lib/config');
 const matrixServerUrl = config.get('matrixServerUrl');
@@ -140,4 +141,4 @@ async function fetchEventsInRange(accessToken, roomId, startTs, endTs, limit) {
   };
 }
 
-module.exports = fetchEventsInRange;
+module.exports = traceFunction(fetchEventsInRange);
diff --git a/server/fetch-room-data.js b/server/fetch-room-data.js
index 7bf03b6..48b0915 100644
--- a/server/fetch-room-data.js
+++ b/server/fetch-room-data.js
@@ -4,6 +4,7 @@ const assert = require('assert');
 
 const urlJoin = require('url-join');
 const { fetchEndpointAsJson } = require('./lib/fetch-endpoint');
+const { traceFunction } = require('./tracing/trace-utilities');
 
 const config = require('./lib/config');
 const matrixServerUrl = config.get('matrixServerUrl');
@@ -48,4 +49,4 @@ async function fetchRoomData(accessToken, roomId) {
   };
 }
 
-module.exports = fetchRoomData;
+module.exports = traceFunction(fetchRoomData);
diff --git a/server/hydrogen-render/1-render-hydrogen-to-string.js b/server/hydrogen-render/1-render-hydrogen-to-string.js
index dbdf841..6c9c40d 100644
--- a/server/hydrogen-render/1-render-hydrogen-to-string.js
+++ b/server/hydrogen-render/1-render-hydrogen-to-string.js
@@ -8,6 +8,7 @@ const fork = require('child_process').fork;
 
 const assert = require('assert');
 const RethrownError = require('../lib/rethrown-error');
+const { traceFunction } = require('../tracing/trace-utilities');
 
 // The render should be fast. If it's taking more than 5 seconds, something has
 // gone really wrong.
@@ -105,4 +106,4 @@ async function renderHydrogenToString(options) {
   }
 }
 
-module.exports = renderHydrogenToString;
+module.exports = traceFunction(renderHydrogenToString);
diff --git a/server/tracing/trace-utilities.js b/server/tracing/trace-utilities.js
new file mode 100644
index 0000000..ccc9c0d
--- /dev/null
+++ b/server/tracing/trace-utilities.js
@@ -0,0 +1,62 @@
+'use strict';
+
+const assert = require('assert');
+const opentelemetryApi = require('@opentelemetry/api');
+
+const packageInfo = require('../../package.json');
+assert(packageInfo.name);
+assert(packageInfo.version);
+
+const tracer = opentelemetryApi.trace.getTracer(packageInfo.name, packageInfo.version);
+
+/**
+ * Wraps an existing function to instrument it with OpenTelemetry tracing. Now
+ * whenever the function runs, it will create a span with the given name. It's
+ * basically `tracer.startActiveSpan` with some sensible default behaviors to
+ * automatically end spans:
+ * - when function completes successfully, status of span also set
+ * - when function throws (exception recorded against span)
+ * - if function returns a Promise, the promise is resolved
+ * @param name Span name, passed through to `tracer.startActiveSpan`
+ * @param fn The function to wrap
+ * @returns The wrapped function
+ *
+ * via
+ * https://github.com/open-telemetry/opentelemetry-js-api/issues/164#issuecomment-1174925516
+ */
+function trace(name, fn) {
+  return function (...args) {
+    return tracer.startActiveSpan(name, async (span) => {
+      try {
+        const result = await Promise.resolve(fn(...args));
+        span.setStatus({
+          code: opentelemetryApi.SpanStatusCode.OK,
+        });
+        return result;
+      } catch (e) {
+        const err = e;
+        span.recordException(err);
+        span.setStatus({
+          code: opentelemetryApi.SpanStatusCode.ERROR,
+          message: err.message,
+        });
+        throw err;
+      } finally {
+        span.end();
+      }
+    });
+  };
+}
+
+/**
+ * Wraps an existing function to instrument it with OpenTelemetry tracing. The
+ * span name will be the name of the function.
+ */
+function traceFunction(fn) {
+  return trace(fn.name, fn);
+}
+
+module.exports = {
+  trace,
+  traceFunction,
+};