fix(validator): Allow form data will mutliple values appended

src/validator/validator.test.ts

@@ -16,12 +16,7 @@ import type { ValidationFunction } from './validator'
 import { validator } from './validator'
 
 // Reference implementation for only testing
-const zodValidator = <
-  T extends ZodSchema,
-  E extends {},
-  P extends string,
-  Target extends keyof ValidationTargets
->(
+const zodValidator = <T extends ZodSchema, E extends {}, P extends string>(
   target: Target,
   schema: T
 ): MiddlewareHandler<
@@ -260,6 +255,20 @@ describe('FormData', () => {
       'foo[]': ['bar1', 'bar2'],
     })
   })
+
+  it('Should return `foo` as an array if multiple values are appended', async () => {
+    const form = new FormData()
+    form.append('foo', 'bar1')
+    form.append('foo', 'bar2')
+    const res = await app.request('/post', {
+      method: 'POST',
+      body: form,
+    })
+    expect(res.status).toBe(200)
+    expect(await res.json()).toEqual({
+      foo: ['bar1', 'bar2'],
+    })
+  })
 })
 
 describe('Malformed FormData request', () => {

src/validator/validator.ts

@@ -112,6 +112,8 @@ export const validator = <
               form[key] = [value]
             } else if (Array.isArray(form[key])) {
               ;(form[key] as unknown[]).push(value)
+            } else if (key in form) {
+              form[key] = [form[key] as string | File, value]
             }
           } else {
             form[key] = value