refactor: better node support for set-cookie header always being an array

Author: enisdenjo

docs/interfaces/Headers.md

@@ -6,7 +6,7 @@ Concrete interface that the headers map should implement.
 
 ## Indexable
 
-▪ [key: `string`]: `string` \| `undefined`
+▪ [key: `string`]: `string` \| `string`[] \| `undefined`
 
 ## Table of contents
 
@@ -15,6 +15,7 @@ Concrete interface that the headers map should implement.
 - [accept](Headers.md#accept)
 - [allow](Headers.md#allow)
 - [content-type](Headers.md#content-type)
+- [set-cookie](Headers.md#set-cookie)
 
 ## Properties
 
@@ -33,3 +34,13 @@ ___
 ### content-type
 
 • `Optional` **content-type**: `string`
+
+___
+
+### set-cookie
+
+• `Optional` **set-cookie**: `string` \| `string`[]
+
+Always an array in Node. Duplicates are added to it.
+Not necessarily true for other environments, make sure
+to check the type during runtime.

src/__tests__/utils/tserver.ts

@@ -33,7 +33,7 @@ export function startTServer(
         const [body, init] = await handle({
           url: req.url,
           method: req.method,
-          headers: req.headers as Record<string, string>,
+          headers: req.headers,
           body: await new Promise<string>((resolve) => {
             let body = '';
             req.on('data', (chunk) => (body += chunk));

src/common.ts

@@ -15,7 +15,13 @@ export interface Headers {
   accept?: string | undefined;
   allow?: string | undefined;
   'content-type'?: string | undefined;
-  [key: string]: string | undefined;
+  /**
+   * Always an array in Node. Duplicates are added to it.
+   * Not necessarily true for other environments, make sure
+   * to check the type during runtime.
+   */
+  'set-cookie'?: string | string[] | undefined;
+  [key: string]: string | string[] | undefined;
 }
 
 /**