Override values for all the different variants of passing headers

Author: Luca Forstner

packages/core/src/fetch.ts

@@ -159,12 +159,7 @@ export function addTracingHeadersToFetchRequest(
     if (sentryBaggageHeader) {
       const prevBaggageHeader = newHeaders.get(BAGGAGE_HEADER_NAME);
       if (prevBaggageHeader) {
-        const prevHeaderStrippedFromSentryBaggage = sentryBaggageHeader
-          .split(',')
-          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-          .filter(baggageEntry => !baggageEntry.split('=')[0]!.startsWith(SENTRY_BAGGAGE_KEY_PREFIX))
-          .join(',');
-
+        const prevHeaderStrippedFromSentryBaggage = stripBaggageHeaderOfSentryBaggageValues(prevBaggageHeader);
         newHeaders.set(
           BAGGAGE_HEADER_NAME,
           // If there are non-sentry entries (i.e. if the stripped string is non-empty/truthy) combine the stripped header and sentry baggage header
@@ -180,7 +175,25 @@ export function addTracingHeadersToFetchRequest(
 
     return newHeaders as PolymorphicRequestHeaders;
   } else if (Array.isArray(headers)) {
-    const newHeaders = [...headers, ['sentry-trace', sentryTraceHeader]];
+    const newHeaders = headers
+      .filter(header => {
+        // Remove any existing sentry-trace headers
+        return !(Array.isArray(header) && header[0] === 'sentry-trace');
+      })
+      .map(header => {
+        if (Array.isArray(header) && header[0] === BAGGAGE_HEADER_NAME) {
+          return [
+            BAGGAGE_HEADER_NAME,
+            ...header.map(headerValue =>
+              typeof headerValue === 'string' ? stripBaggageHeaderOfSentryBaggageValues(headerValue) : headerValue,
+            ),
+          ];
+        } else {
+          return header;
+        }
+      })
+      // Attach the new sentry-trace header
+      .concat(['sentry-trace', sentryTraceHeader]);
 
     if (sentryBaggageHeader) {
       // If there are multiple entries with the same key, the browser will merge the values into a single request header.
@@ -191,12 +204,16 @@ export function addTracingHeadersToFetchRequest(
     return newHeaders as PolymorphicRequestHeaders;
   } else {
     const existingBaggageHeader = 'baggage' in headers ? headers.baggage : undefined;
-    const newBaggageHeaders: string[] = [];
+    let newBaggageHeaders: string[] = [];
 
     if (Array.isArray(existingBaggageHeader)) {
-      newBaggageHeaders.push(...existingBaggageHeader);
+      newBaggageHeaders = existingBaggageHeader
+        .map(headerItem =>
+          typeof headerItem === 'string' ? stripBaggageHeaderOfSentryBaggageValues(headerItem) : headerItem,
+        )
+        .filter(headerItem => headerItem === '');
     } else if (existingBaggageHeader) {
-      newBaggageHeaders.push(existingBaggageHeader);
+      newBaggageHeaders.push(stripBaggageHeaderOfSentryBaggageValues(existingBaggageHeader));
     }
 
     if (sentryBaggageHeader) {
@@ -238,3 +255,13 @@ function endSpan(span: Span, handlerData: HandlerDataFetch): void {
   }
   span.end();
 }
+
+function stripBaggageHeaderOfSentryBaggageValues(baggageHeader: string): string {
+  return (
+    baggageHeader
+      .split(',')
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      .filter(baggageEntry => !baggageEntry.split('=')[0]!.startsWith(SENTRY_BAGGAGE_KEY_PREFIX))
+      .join(',')
+  );
+}