1 files changed, 40 insertions, 0 deletions
diff --git a/packages/integrations/node/src/createOutgoingHttpHeaders.ts b/packages/integrations/node/src/createOutgoingHttpHeaders.ts
new file mode 100644
index 000000000..5b99cfa4f
--- /dev/null
+++ b/packages/integrations/node/src/createOutgoingHttpHeaders.ts
@@ -0,0 +1,40 @@
+import type { OutgoingHttpHeaders } from 'http';
+
+/**
+ * Takes in a nullable WebAPI Headers object and produces a NodeJS OutgoingHttpHeaders object suitable for usage
+ * with ServerResponse.writeHead(..) or ServerResponse.setHeader(..)
+ * 
+ * @param webHeaders WebAPI Headers object
+ * @returns NodeJS OutgoingHttpHeaders object with multiple set-cookie handled as an array of values
+ */
+export const createOutgoingHttpHeaders = (webHeaders: Headers | undefined | null): OutgoingHttpHeaders | undefined => {
+  if (!webHeaders) {
+    return undefined;
+  }
+
+  // re-type to access Header.getSetCookie()
+  const headers = webHeaders as HeadersWithGetSetCookie;
+
+  // at this point, a multi-value'd set-cookie header is invalid (it was concatenated as a single CSV, which is not valid for set-cookie)
+  const nodeHeaders: OutgoingHttpHeaders = Object.fromEntries(headers.entries());
+
+  if (Object.keys(nodeHeaders).length === 0) {
+    return undefined;
+  }
+
+  // if there is > 1 set-cookie header, we have to fix it to be an array of values
+  if (headers.has('set-cookie')) {
+    const cookieHeaders = headers.getSetCookie();
+    if (cookieHeaders.length > 1) {
+      // the Headers.entries() API already normalized all header names to lower case so we can safely index this as 'set-cookie'
+      nodeHeaders['set-cookie'] = cookieHeaders;
+    }
+  }
+
+  return nodeHeaders;
+};
+
+interface HeadersWithGetSetCookie extends Headers {
+  // the @astrojs/webapi polyfill makes this available (as of undici@5.19.0), but tsc doesn't pick it up on the built-in Headers type from DOM lib
+  getSetCookie(): string[];
+}