type inference for c.req.json()

[tmokmss]

What is the feature you are proposing?

When I define a route handler with the following code, the variable foo is infered as any, where I want it to be string without additional type annotation.

{
  const route = createRoute({
    method: 'post',
    path: '/',
    request: {
      body: {
        content: {
          'application/json': {
            schema: z.object({
              foo: z.string(),
            }),
          },
        },
      },
    },
    responses: {
      200: {
        description: 'success',
      },
    },
  });

  app.openapi(route, async (c) => {
    const { foo } = await c.req.json();
    return c.json({}, 200);
  });
}

It appears the HonoRequest type already has enough information to infer the json type:

However foo is inferred as any:

c.req.json<{foo:string}>() works, but it would be great if we can avoid adding (seemingly) redundant type annotation, like how c.req.valid('query') works.

Let me know if I'm misusing something, thanks!

[tmokmss]

I found c.req.valid('json') seems to work as expected, but not sure why c.req.json is async whereas c.req.valid is sync function? Is there any behavioural difference?

[EdamAme-x]

@tmokmss
Already called internally
https://github.com/honojs/hono/blob/main/src/validator/validator.ts#L78

[yusukebe]

Hi @tmokmss

Please use c.req.valid('json') in the app.openapi for the Zod OpenAPI. And it's expected that the object returned from c.req.json() is not typed. If you want to add type, pass the generics, as you said:

c.req.json<{ foo: string }>()

[tmokmss]

@EdamAme-x @yusukebe Thanks for the guidance!
Still not sure how the async function works in sync call but I'll look into the code later 🙏

[EdamAme-x]

Still not sure how the async function works in sync call but I'll look into the code later 🙏

The c.req.json is called and validated in the async middleware before c.req.valid is called.
After that, the validated data is kept in the Context so that it can be called sync.

[tmokmss]

@EdamAme-x That makes sense! I just started learning hono and you helped me a lot :) thank you so much!