fix(server): ResponseHeadersPlugin context reference issues (#293)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Refactor**
- Enhanced response header management to ensure consistent propagation
of custom header values during API responses.
  
- **Tests**
- Reorganized and expanded test cases to verify proper header handling
and context management, improving overall reliability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dinwwwh

packages/server/src/plugins/response-headers.test.ts

@@ -3,48 +3,112 @@ import { OpenAPIHandler } from '../../../openapi/src/adapters/fetch/openapi-hand
 import { os } from '../builder'
 import { ResponseHeadersPlugin } from './response-headers'
 
-it('responseHeadersPlugin', async () => {
-  const router = os
-    .$context<ResponseHeadersPluginContext>()
-    .use(({ context, next }) => {
-      context.resHeaders?.set('x-custom-1', 'mid')
-      context.resHeaders?.set('x-custom-2', 'mid')
-      context.resHeaders?.set('x-custom-3', 'mid')
-      context.resHeaders?.set('x-custom-4', 'mid')
-
-      return next()
-    })
-    .route({
-      method: 'GET',
-      path: '/ping',
-      outputStructure: 'detailed',
+describe('responseHeadersPlugin', () => {
+  it('works', async () => {
+    const router = os
+      .$context<ResponseHeadersPluginContext>()
+      .use(({ context, next }) => {
+        context.resHeaders?.set('x-custom-1', 'mid')
+        context.resHeaders?.set('x-custom-2', 'mid')
+        context.resHeaders?.set('x-custom-3', 'mid')
+        context.resHeaders?.set('x-custom-4', 'mid')
+
+        return next()
+      })
+      .route({
+        method: 'GET',
+        path: '/ping',
+        outputStructure: 'detailed',
+      })
+      .handler(() => {
+        return {
+          headers: {
+            'x-custom-1': 'value',
+            'x-custom-2': ['1', '2'],
+            'x-custom-3': undefined,
+          },
+        }
+      })
+
+    const handler = new OpenAPIHandler(router, {
+      plugins: [
+        new ResponseHeadersPlugin(),
+      ],
     })
-    .handler(() => {
-      return {
-        headers: {
-          'x-custom-1': 'value',
-          'x-custom-2': ['1', '2'],
-          'x-custom-3': undefined,
-        },
-      }
+
+    const { response } = await handler.handle(new Request('https://example.com/ping'))
+
+    if (!response) {
+      throw new Error('response is undefined')
+    }
+
+    expect(response.headers.get('x-custom-1')).toBe('value, mid')
+    expect(response.headers.get('x-custom-2')).toBe('1, 2, mid')
+    expect(response.headers.get('x-custom-3')).toBe('mid')
+    expect(response.headers.get('x-custom-4')).toBe('mid')
+
+    await handler.handle(new Request('https://example.com/not_found'))
+  })
+
+  it('should clone the context to avoid reference issues', async () => {
+    const router = os
+      .$context<ResponseHeadersPluginContext>()
+      .route({
+        method: 'GET',
+        path: '/ping',
+      })
+      .handler(() => 'ping')
+
+    const interceptor = vi.fn(({ next }) => next())
+
+    const handler = new OpenAPIHandler(router, {
+      plugins: [
+        new ResponseHeadersPlugin(),
+      ],
+      interceptors: [
+        interceptor,
+      ],
     })
 
-  const handler = new OpenAPIHandler(router, {
-    plugins: [
-      new ResponseHeadersPlugin(),
-    ],
+    const context = { a: 'value' }
+    await handler.handle(new Request('https://example.com/ping'), { context })
+
+    expect(interceptor).toHaveBeenCalledOnce()
+    expect(interceptor).toHaveBeenCalledWith(expect.objectContaining({
+      context: { ...context, resHeaders: expect.any(Headers) },
+    }))
+
+    expect(interceptor.mock.calls[0]![0].context).not.toBe(context)
   })
 
-  const { response } = await handler.handle(new Request('https://example.com/ping'))
+  it('should use the provided resHeaders when already defined', async () => {
+    const router = os
+      .$context<ResponseHeadersPluginContext>()
+      .route({
+        method: 'GET',
+        path: '/ping',
+      })
+      .handler(() => 'ping')
 
-  if (!response) {
-    throw new Error('response is undefined')
-  }
+    const interceptor = vi.fn(({ next }) => next())
 
-  expect(response.headers.get('x-custom-1')).toBe('value, mid')
-  expect(response.headers.get('x-custom-2')).toBe('1, 2, mid')
-  expect(response.headers.get('x-custom-3')).toBe('mid')
-  expect(response.headers.get('x-custom-4')).toBe('mid')
+    const handler = new OpenAPIHandler(router, {
+      plugins: [
+        new ResponseHeadersPlugin(),
+      ],
+      interceptors: [
+        interceptor,
+      ],
+    })
+
+    const context = { a: 'value', resHeaders: new Headers() }
+    await handler.handle(new Request('https://example.com/ping'), { context })
 
-  await handler.handle(new Request('https://example.com/not_found'))
+    expect(interceptor).toHaveBeenCalledOnce()
+    expect(interceptor).toHaveBeenCalledWith(expect.objectContaining({
+      context,
+    }))
+
+    expect(interceptor.mock.calls[0]![0].context.resHeaders).toBe(context.resHeaders)
+  })
 })

packages/server/src/plugins/response-headers.ts

@@ -9,19 +9,23 @@ export class ResponseHeadersPlugin<T extends ResponseHeadersPluginContext> imple
     options.rootInterceptors ??= []
 
     options.rootInterceptors.push(async (interceptorOptions) => {
-      const headers = new Headers()
+      const resHeaders = interceptorOptions.context.resHeaders ?? new Headers()
 
-      interceptorOptions.context.resHeaders = headers
-
-      const result = await interceptorOptions.next()
+      const result = await interceptorOptions.next({
+        ...interceptorOptions,
+        context: {
+          ...interceptorOptions.context,
+          resHeaders,
+        },
+      })
 
       if (!result.matched) {
         return result
       }
 
       const responseHeaders = result.response.headers
 
-      for (const [key, value] of headers) {
+      for (const [key, value] of resHeaders) {
         if (Array.isArray(responseHeaders[key])) {
           responseHeaders[key].push(value)
         }