Make createCors({ origins }) to accept function

src/createCors.spec.ts

@@ -30,6 +30,52 @@ describe('createCors(options)', () => {
 
       expect(response.headers.get('Access-Control-Max-Age')).toBe('60')
     })
+
+    it('origins should be array of string', async () => {
+      const { preflight } = createCors({
+        origins: ['http://localhost:3000', 'http://localhost:4000']
+      })
+      const router = Router().all('*', preflight)
+
+      const generateRequest = (origin: string) => new Request('https://foo.bar', {
+        method: 'OPTIONS',
+        headers: {
+          'Access-Control-Request-Method': 'GET',
+          'Access-Control-Request-Headers': 'content-type',
+          origin,
+        }
+      })
+
+      const response1 = await router.handle(generateRequest('http://localhost:3000'))
+      expect(response1.headers.get('Access-Control-Allow-Origin')).toBe('http://localhost:3000')
+      const response2 = await router.handle(generateRequest('http://localhost:4000'))
+      expect(response2.headers.get('Access-Control-Allow-Origin')).toBe('http://localhost:4000')
+      const response3 = await router.handle(generateRequest('http://localhost:5000'))
+      expect(response3.headers.get('Access-Control-Allow-Origin')).toBe(null)
+    })
+
+    it('origins should be function returns boolean', async () => {
+      const { preflight } = createCors({
+        origins: (origin) => origin.startsWith('https://') && origin.endsWith('.example.com')
+      })
+      const router = Router().all('*', preflight)
+
+      const generateRequest = (origin: string) => new Request('https://foo.bar', {
+        method: 'OPTIONS',
+        headers: {
+          'Access-Control-Request-Method': 'GET',
+          'Access-Control-Request-Headers': 'content-type',
+          origin,
+        }
+      })
+
+      const response1 = await router.handle(generateRequest('https://secure.example.com'))
+      expect(response1.headers.get('Access-Control-Allow-Origin')).toBe('https://secure.example.com')
+      const response2 = await router.handle(generateRequest('https://another-secure.example.com'))
+      expect(response2.headers.get('Access-Control-Allow-Origin')).toBe('https://another-secure.example.com')
+      const response3 = await router.handle(generateRequest('http://unsecure.example.com'))
+      expect(response3.headers.get('Access-Control-Allow-Origin')).toBe(null)
+    })
   })
 
   describe('preflight (middleware)', () => {

src/createCors.ts

@@ -1,7 +1,7 @@
 import { IRequest } from './Router'
 
-export interface CorsOptions {
-  origins?: string[]
+export type CorsOptions = {
+  origins?: string[] | ((origin: string) => boolean)
   maxAge?: number
   methods?: string[]
   headers?: any
@@ -13,6 +13,9 @@ export const createCors = (options: CorsOptions = {}) => {
   const { origins = ['*'], maxAge, methods = ['GET'], headers = {} } = options
 
   let allowOrigin: any
+  const isAllowOrigin = typeof origins === 'function' 
+    ? origins
+    : (origin: string) => (origins.includes(origin) || origins.includes('*'))
 
   // Initial response headers.
   const rHeaders = {
@@ -30,10 +33,8 @@ export const createCors = (options: CorsOptions = {}) => {
     const useMethods = [...new Set(['OPTIONS', ...methods])]
     const origin = r.headers.get('origin') || ''
 
-    // Set allowOrigin globally.
-    allowOrigin = (origins.includes(origin) || origins.includes('*')) && {
-      'Access-Control-Allow-Origin': origin,
-    }
+    // set allowOrigin globally
+    allowOrigin = isAllowOrigin(origin) && { 'Access-Control-Allow-Origin': origin }
 
     // Check if method is OPTIONS.
     if (r.method === 'OPTIONS') {