From 8ed99d9d791ed6bd8b897c705289b0464947e632 Mon Sep 17 00:00:00 2001
From: Yusuke Wada <yusuke@kamawada.com>
Date: Sun, 27 Apr 2025 20:12:13 +0900
Subject: [PATCH] feat(zod-validator): add `validationFunction` option (#1140)

Co-authored-by: migawka <migawka@amadeustech.dev>
---
 .changeset/tame-rooms-hide.md            |  5 ++
 packages/zod-validator/README.md         | 24 +++++++
 packages/zod-validator/src/index.test.ts | 82 ++++++++++++++++++++++++
 packages/zod-validator/src/index.ts      | 16 ++++-
 4 files changed, 124 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/tame-rooms-hide.md

diff --git a/.changeset/tame-rooms-hide.md b/.changeset/tame-rooms-hide.md
new file mode 100644
index 00000000..b0c0dd1e
--- /dev/null
+++ b/.changeset/tame-rooms-hide.md
@@ -0,0 +1,5 @@
+---
+'@hono/zod-validator': minor
+---
+
+feat: add `validationFunction` option
diff --git a/packages/zod-validator/README.md b/packages/zod-validator/README.md
index 5a5f5acc..ddd7a782 100644
--- a/packages/zod-validator/README.md
+++ b/packages/zod-validator/README.md
@@ -68,6 +68,30 @@ app.post(
 )
 ```
 
+### Custom validation function
+
+By default, this Validator validates values using `.safeParseAsync`.
+
+```ts
+await schema.safeParseAsync(value)
+```
+
+But, if you want to use the [`.passthrough`](https://zod.dev/?id=passthrough), you can specify your own function in `validationFunction`.
+
+```ts
+app.post(
+  '/',
+  zValidator('json', schema, undefined, {
+    validationFunction: async (schema, value) => {
+      return await schema.passthrough().safeParseAsync(value)
+    },
+  }),
+  (c) => {
+    // ...
+  }
+)
+```
+
 ## Author
 
 Yusuke Wada <https://github.com/yusukebe>
diff --git a/packages/zod-validator/src/index.test.ts b/packages/zod-validator/src/index.test.ts
index 23e21bd8..665d6899 100644
--- a/packages/zod-validator/src/index.test.ts
+++ b/packages/zod-validator/src/index.test.ts
@@ -378,3 +378,85 @@ describe('Case-Insensitive Headers', () => {
     type verify = Expect<Equal<Expected, Actual>>
   })
 })
+
+describe('With options + validationFunction', () => {
+  const app = new Hono()
+  const jsonSchema = z.object({
+    name: z.string(),
+    age: z.number(),
+  })
+
+  const route = app
+    .post('/', zValidator('json', jsonSchema), (c) => {
+      const data = c.req.valid('json')
+      return c.json({
+        success: true,
+        data,
+      })
+    })
+    .post(
+      '/extended',
+      zValidator('json', jsonSchema, undefined, {
+        validationFunction: async (schema, value) => {
+          return await schema.passthrough().safeParseAsync(value)
+        },
+      }),
+      (c) => {
+        const data = c.req.valid('json')
+        return c.json({
+          success: true,
+          data,
+        })
+      }
+    )
+
+  it('Should be ok due to passthrough schema', async () => {
+    const req = new Request('http://localhost/extended', {
+      body: JSON.stringify({
+        name: 'Superman',
+        age: 20,
+        length: 170,
+        weight: 55,
+      }),
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+      },
+    })
+    const res = await app.request(req)
+    expect(res).not.toBeNull()
+    expect(res.status).toBe(200)
+    expect(await res.json()).toEqual({
+      success: true,
+      data: {
+        name: 'Superman',
+        age: 20,
+        length: 170,
+        weight: 55,
+      },
+    })
+  })
+  it('Should be ok due to required schema', async () => {
+    const req = new Request('http://localhost', {
+      body: JSON.stringify({
+        name: 'Superman',
+        age: 20,
+      }),
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+      },
+    })
+    const res = await app.request(req)
+
+    expect(res).not.toBeNull()
+    expect(res.status).toBe(200)
+    expect(await res.json()).toEqual({
+      success: true,
+      data: {
+        name: 'Superman',
+        age: 20,
+      },
+    })
+  })
+})
diff --git a/packages/zod-validator/src/index.ts b/packages/zod-validator/src/index.ts
index 9af06db8..80d3b38c 100644
--- a/packages/zod-validator/src/index.ts
+++ b/packages/zod-validator/src/index.ts
@@ -1,7 +1,7 @@
 import type { Context, Env, Input, MiddlewareHandler, TypedResponse, ValidationTargets } from 'hono'
 import { validator } from 'hono/validator'
 import { ZodObject } from 'zod'
-import type { ZodError, ZodSchema, z } from 'zod'
+import type { SafeParseReturnType, ZodError, ZodSchema, z } from 'zod'
 
 export type Hook<
   T,
@@ -43,7 +43,14 @@ export const zValidator = <
 >(
   target: Target,
   schema: T,
-  hook?: Hook<z.infer<T>, E, P, Target>
+  hook?: Hook<z.infer<T>, E, P, Target>,
+  options?: {
+    validationFunction: (
+      schema: T,
+      value: ValidationTargets[Target]
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    ) => SafeParseReturnType<any, any> | Promise<SafeParseReturnType<any, any>>
+  }
 ): MiddlewareHandler<E, P, V> =>
   // @ts-expect-error not typed well
   validator(target, async (value, c) => {
@@ -63,7 +70,10 @@ export const zValidator = <
       )
     }
 
-    const result = await schema.safeParseAsync(validatorValue)
+    const result =
+      options && options.validationFunction
+        ? await options.validationFunction(schema, validatorValue)
+        : await schema.safeParseAsync(validatorValue)
 
     if (hook) {
       const hookResult = await hook({ data: validatorValue, ...result, target }, c)