feat(core): Capture # of dropped spans through beforeSendTransaction (#13022)

Fixes #12849.

This is a bit tricky because `beforeSendTransaction` can return a
promise, so in order to avoid dealing with this I put the # of spans on
the sdk metadata, and then compare that afterwards.

Author: mydea

packages/core/src/baseclient.ts

@@ -419,21 +419,21 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
   /**
    * @inheritDoc
    */
-  public recordDroppedEvent(reason: EventDropReason, category: DataCategory, _event?: Event): void {
-    // Note: we use `event` in replay, where we overwrite this hook.
-
+  public recordDroppedEvent(reason: EventDropReason, category: DataCategory, eventOrCount?: Event | number): void {
     if (this._options.sendClientReports) {
+      // TODO v9: We do not need the `event` passed as third argument anymore, and can possibly remove this overload
+      // If event is passed as third argument, we assume this is a count of 1
+      const count = typeof eventOrCount === 'number' ? eventOrCount : 1;
+
       // We want to track each category (error, transaction, session, replay_event) separately
       // but still keep the distinction between different type of outcomes.
       // We could use nested maps, but it's much easier to read and type this way.
       // A correct type for map-based implementation if we want to go that route
       // would be `Partial<Record<SentryRequestType, Partial<Record<Outcome, number>>>>`
       // With typescript 4.1 we could even use template literal types
       const key = `${reason}:${category}`;
-      DEBUG_BUILD && logger.log(`Adding outcome: "${key}"`);
-
-      // The following works because undefined + 1 === NaN and NaN is falsy
-      this._outcomes[key] = this._outcomes[key] + 1 || 1;
+      DEBUG_BUILD && logger.log(`Recording outcome: "${key}"${count > 1 ? ` (${count} times)` : ''}`);
+      this._outcomes[key] = (this._outcomes[key] || 0) + count;
     }
   }
 
@@ -778,6 +778,12 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
       .then(processedEvent => {
         if (processedEvent === null) {
           this.recordDroppedEvent('before_send', dataCategory, event);
+          if (isTransaction) {
+            const spans = event.spans || [];
+            // the transaction itself counts as one span, plus all the child spans that are added
+            const spanCount = 1 + spans.length;
+            this.recordDroppedEvent('before_send', 'span', spanCount);
+          }
           throw new SentryError(`${beforeSendLabel} returned \`null\`, will not send event.`, 'log');
         }
 
@@ -786,6 +792,18 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
           this._updateSessionFromEvent(session, processedEvent);
         }
 
+        if (isTransaction) {
+          const spanCountBefore =
+            (processedEvent.sdkProcessingMetadata && processedEvent.sdkProcessingMetadata.spanCountBeforeProcessing) ||
+            0;
+          const spanCountAfter = processedEvent.spans ? processedEvent.spans.length : 0;
+
+          const droppedSpanCount = spanCountBefore - spanCountAfter;
+          if (droppedSpanCount > 0) {
+            this.recordDroppedEvent('before_send', 'span', droppedSpanCount);
+          }
+        }
+
         // None of the Sentry built event processor will update transaction name,
         // so if the transaction name has been changed by an event processor, we know
         // it has to come from custom event processor added by a user

packages/core/test/lib/base.test.ts

@@ -1004,6 +1004,69 @@ describe('BaseClient', () => {
       expect(TestClient.instance!.event!.transaction).toBe('/adopt/dont/shop');
     });
 
+    test('calls `beforeSendTransaction` and drops spans', () => {
+      const beforeSendTransaction = jest.fn(event => {
+        event.spans = [{ span_id: 'span5', trace_id: 'trace1', start_timestamp: 1234 }];
+        return event;
+      });
+      const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN, beforeSendTransaction });
+      const client = new TestClient(options);
+
+      client.captureEvent({
+        transaction: '/dogs/are/great',
+        type: 'transaction',
+        spans: [
+          { span_id: 'span1', trace_id: 'trace1', start_timestamp: 1234 },
+          { span_id: 'span2', trace_id: 'trace1', start_timestamp: 1234 },
+          { span_id: 'span3', trace_id: 'trace1', start_timestamp: 1234 },
+        ],
+      });
+
+      expect(beforeSendTransaction).toHaveBeenCalled();
+      expect(TestClient.instance!.event!.spans?.length).toBe(1);
+
+      expect(client['_outcomes']).toEqual({ 'before_send:span': 2 });
+    });
+
+    test('calls `beforeSendSpan` and uses the modified spans', () => {
+      expect.assertions(3);
+
+      const beforeSendSpan = jest.fn(span => {
+        span.data = { version: 'bravo' };
+        return span;
+      });
+
+      const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN, beforeSendSpan });
+      const client = new TestClient(options);
+      const transaction: Event = {
+        transaction: '/cats/are/great',
+        type: 'transaction',
+        spans: [
+          {
+            description: 'first span',
+            span_id: '9e15bf99fbe4bc80',
+            start_timestamp: 1591603196.637835,
+            trace_id: '86f39e84263a4de99c326acab3bfe3bd',
+          },
+          {
+            description: 'second span',
+            span_id: 'aa554c1f506b0783',
+            start_timestamp: 1591603196.637835,
+            trace_id: '86f39e84263a4de99c326acab3bfe3bd',
+          },
+        ],
+      };
+
+      client.captureEvent(transaction);
+
+      expect(beforeSendSpan).toHaveBeenCalledTimes(2);
+      const capturedEvent = TestClient.instance!.event!;
+      for (const [idx, span] of capturedEvent.spans!.entries()) {
+        const originalSpan = transaction.spans![idx];
+        expect(span).toEqual({ ...originalSpan, data: { version: 'bravo' } });
+      }
+    });
+
     test('calls `beforeSend` and discards the event', () => {
       expect.assertions(4);