fix bug in baggage merging

Author: Lms24

packages/node-core/src/utils/baggage.ts

@@ -24,8 +24,23 @@ export function mergeBaggageHeaders<Existing extends string | string[] | number
     return existing;
   }
 
-  // Start with existing entries, but Sentry entries from new baggage will overwrite
-  const mergedBaggageEntries = { ...existingBaggageEntries };
+  const newSentryBaggageEntries = Object.entries(newBaggageEntries).filter(([key]) =>
+    key.startsWith(SENTRY_BAGGAGE_KEY_PREFIX),
+  );
+
+  const oldBaggageEntriesWithoutSentry = existingBaggageEntries
+    ? Object.entries(existingBaggageEntries).filter(([key]) => !key.startsWith(SENTRY_BAGGAGE_KEY_PREFIX))
+    : [];
+
+  // If new baggage contains at least one sentry- value, we remove all old sentry- values
+  // otherwise, we keep old sentry- values. If we don't remove old sentry- values, we end
+  // up with an inconsistent dynamic sampling context propagation.
+  const mergedBaggageEntries = newSentryBaggageEntries.length
+    ? Object.fromEntries(oldBaggageEntriesWithoutSentry)
+    : existingBaggageEntries
+      ? Object.fromEntries(Object.entries(existingBaggageEntries))
+      : {};
+
   Object.entries(newBaggageEntries).forEach(([key, value]) => {
     // Sentry-specific keys always take precedence from new baggage
     // Non-Sentry keys only added if not already present

packages/node-core/test/utils/baggage.test.ts

@@ -69,7 +69,6 @@ describe('mergeBaggageHeaders', () => {
     expect(entries).toContain('third=party');
     expect(entries).toContain('sentry-environment=myEnv');
     expect(entries).toContain('sentry-release=2.1.0');
-    expect(entries).toContain('sentry-sample_rate=0.54');
     expect(entries).not.toContain('sentry-environment=staging');
     expect(entries).not.toContain('sentry-release=9.9.9');
   });
@@ -133,8 +132,7 @@ describe('mergeBaggageHeaders', () => {
     const existing = 'custom-key=value';
     const newBaggage = 'sentry-environment=production';
     const result = mergeBaggageHeaders(existing, newBaggage);
-    expect(result).toContain('custom-key=value');
-    expect(result).toContain('sentry-environment=production');
+    expect(result).toBe('custom-key=value,sentry-environment=production');
   });
 
   it('overwrites existing Sentry entries when keys conflict', () => {
@@ -153,4 +151,11 @@ describe('mergeBaggageHeaders', () => {
     expect(result).toContain('sentry-trace_id=123');
     expect(result).not.toContain('sentry-environment=staging');
   });
+
+  it('removes all sentry- values from old baggage and only adds new ones (if at least one new sentry- value is present)', () => {
+    const existing = 'sentry-trace_id=old,sentry-sampled=false,non-sentry=keep';
+    const newBaggage = 'sentry-trace_id=new,sentry-environment=new';
+    const result = mergeBaggageHeaders(existing, newBaggage);
+    expect(result).toBe('non-sentry=keep,sentry-trace_id=new,sentry-environment=new');
+  });
 });