Fix duplicate cookies (#415)

* fix duplicate cookies in all cases

* Create shaggy-chicken-rhyme.md

Author: conico974

.changeset/shaggy-chicken-rhyme.md

@@ -0,0 +1,5 @@
+---
+"open-next": patch
+---
+
+Fix duplicate cookies

packages/open-next/src/http/openNextResponse.ts

@@ -148,6 +148,8 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
   getFixedHeaders(): OutgoingHttpHeaders {
     // Do we want to apply this on writeHead?
     this.fixHeaders(this.headers);
+    // This way we ensure that the cookies are correct
+    this.headers[SET_COOKIE_HEADER] = this._cookies;
     return this.headers;
   }
 
@@ -178,16 +180,7 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
     this.fixHeaders(this.headers);
     if (this._cookies.length > 0) {
       // For cookies we cannot do the same as for other headers
-      // We need to merge the cookies, and in this case, cookies generated by the routes or pages
-      // should be added after the ones generated by the middleware
-      // This prevents the middleware from overriding the cookies, especially for server actions
-      // which uses the same pathnames as the pages they're being called on
-      this.headers[SET_COOKIE_HEADER] = [
-        ...(parseCookies(
-          this.initialHeaders?.[SET_COOKIE_HEADER] as string | string[],
-        ) ?? []),
-        ...this._cookies,
-      ];
+      this.headers[SET_COOKIE_HEADER] = this._cookies;
     }
 
     if (this.streamCreator) {