fix(node): support undici headers as strings or arrays (#10938)

Author: jessezhang91

packages/node/src/integrations/undici/index.ts

@@ -309,8 +309,13 @@ function setHeadersOnRequest(
   sentryTrace: string,
   sentryBaggageHeader: string | undefined,
 ): void {
-  const headerLines = request.headers.split('\r\n');
-  const hasSentryHeaders = headerLines.some(headerLine => headerLine.startsWith('sentry-trace:'));
+  let hasSentryHeaders: boolean;
+  if (Array.isArray(request.headers)) {
+    hasSentryHeaders = request.headers.some(headerLine => headerLine === 'sentry-trace');
+  } else {
+    const headerLines = request.headers.split('\r\n');
+    hasSentryHeaders = headerLines.some(headerLine => headerLine.startsWith('sentry-trace:'));
+  }
 
   if (hasSentryHeaders) {
     return;

packages/node/src/integrations/undici/types.ts

@@ -224,7 +224,9 @@ export interface UndiciRequest {
   // Originally was Dispatcher.HttpMethod, but did not want to vendor that in.
   method?: string;
   path: string;
-  headers: string;
+  // string for undici@<=6.6.2 and string[] for undici@>=6.7.0.
+  // see for more information: https://github.com/getsentry/sentry-javascript/issues/10936
+  headers: string | string[];
   addHeader(key: string, value: string): RequestWithSentry;
 }