fix(node): Add conditions to TracingHanlder.startTransaction (#5485)

Currently, our TracingHandler always starts a transaction, whether or not tracing is enabled. It also traces OPTIONS and HEAD requests, which it shouldn't. This fixes both of those problems by checking both the current client's options (for tracing enablement) and the incoming request's method before starting a transaction.

packages/node/src/handlers.ts

@@ -33,6 +33,24 @@ export function tracingHandler(): (
     res: http.ServerResponse,
     next: (error?: any) => void,
   ): void {
+    const hub = getCurrentHub();
+    const options = hub.getClient()?.getOptions();
+
+    if (!options || req.method?.toUpperCase() === 'OPTIONS' || req.method?.toUpperCase() === 'HEAD') {
+      return next();
+    }
+
+    // TODO: This is the `hasTracingEnabled` check, but we're doing it manually since `@sentry/tracing` isn't a
+    // dependency of `@sentry/node`. Long term, that function should probably move to `@sentry/hub.
+    if (!('tracesSampleRate' in options) && !('tracesSampler' in options)) {
+      __DEBUG_BUILD__ &&
+        logger.warn(
+          'Sentry `tracingHandler` is being used, but tracing is disabled. Please enable tracing by setting ' +
+            'either `tracesSampleRate` or `tracesSampler` in your `Sentry.init()` options.',
+        );
+      return next();
+    }
+
     // If there is a trace header set, we extract the data from it (parentSpanId, traceId, and sampling decision)
     const traceparentData =
       req.headers && isString(req.headers['sentry-trace']) && extractTraceparentData(req.headers['sentry-trace']);
@@ -53,7 +71,7 @@ export function tracingHandler(): (
     );
 
     // We put the transaction on the scope so users can attach children to it
-    getCurrentHub().configureScope(scope => {
+    hub.configureScope(scope => {
       scope.setSpan(transaction);
     });
 

packages/node/test/handlers.test.ts

@@ -150,14 +150,16 @@ describe('tracingHandler', () => {
 
   const sentryTracingMiddleware = tracingHandler();
 
-  let req: http.IncomingMessage, res: http.ServerResponse, next: () => undefined;
+  let hub: Hub, req: http.IncomingMessage, res: http.ServerResponse, next: () => undefined;
 
   function createNoOpSpy() {
     const noop = { noop: () => undefined }; // this is wrapped in an object so jest can spy on it
     return jest.spyOn(noop, 'noop') as any;
   }
 
   beforeEach(() => {
+    hub = new Hub(new NodeClient(getDefaultNodeClientOptions({ tracesSampleRate: 1.0 })));
+    jest.spyOn(sentryCore, 'getCurrentHub').mockReturnValue(hub);
     req = {
       headers,
       method,
@@ -181,6 +183,33 @@ describe('tracingHandler', () => {
     expect(startTransaction).toHaveBeenCalled();
   });
 
+  it("doesn't create a transaction when handling a `HEAD` request", () => {
+    const startTransaction = jest.spyOn(sentryCore, 'startTransaction');
+    req.method = 'HEAD';
+
+    sentryTracingMiddleware(req, res, next);
+
+    expect(startTransaction).not.toHaveBeenCalled();
+  });
+
+  it("doesn't create a transaction when handling an `OPTIONS` request", () => {
+    const startTransaction = jest.spyOn(sentryCore, 'startTransaction');
+    req.method = 'OPTIONS';
+
+    sentryTracingMiddleware(req, res, next);
+
+    expect(startTransaction).not.toHaveBeenCalled();
+  });
+
+  it("doesn't create a transaction if tracing is disabled", () => {
+    delete hub.getClient()?.getOptions().tracesSampleRate;
+    const startTransaction = jest.spyOn(sentryCore, 'startTransaction');
+
+    sentryTracingMiddleware(req, res, next);
+
+    expect(startTransaction).not.toHaveBeenCalled();
+  });
+
   it("pulls parent's data from tracing header on the request", () => {
     req.headers = { 'sentry-trace': '12312012123120121231201212312012-1121201211212012-0' };