Validating JSON inputs in Cloud Functions and Cloud APIs

[skyrpex]

See this code example which is a mixture of Wing and TypeScript. Showcases the use of theoretical generics to restrict the shape of the data a function accepts.

bring cloud;

interface CreateUserOptions {
    name: str;
    age?: num;
}

let createUser = new cloud.Function<CreateUserOptions>(inflight (user) => {
    log(user);
    //  ^^^^ type CreateUserOptions
});

// Valid
createUser({
    name: "skyrpex",
    age: 30,
});

// Invalid
createUser({
    age: 30
});

If the Cloud Function is used inside the app, there's no need to validate the input data since the type checking system will make sure no invalid data is used. Now, if we use a Cloud API instead, this function will be exposed to the outside and thus the data will need to be validated since it can't be trusted:

// ...

let api = new cloud.Api();
api.post("/user", inflight (request: cloud.ApiRequest) => {
    log(request.body);
    //          ^^^^ type string | undefined

    createUser(request.body);
    //                 ^^^^ Error: `string | undefined` is not assignable to `CreateUserOptions`

    // In TypeScript, I would use zod to validate the data
    let options = zod.object({
        name: zod.string(),
        age: zod.number().optional(),
    }).parse(Json.parse(request.body));

    log(options);
    //  ^^^^^^^ type { name: string; age?: number | undefined; }

    // Now, `options` matches the type `CreateUserOptions`
    createUser(options);
});

Since Wing is the compiler, it should be technically possible to generate the following:

• Validation code under the hood for simple types
• A conditional version of every function: is called from within the app, there's no need to validate. Validate the input otherwise

This is just an example of a concept and the API design is not ideal. I like the DX that trpc offers, just check it out. But I'd like to highlight:

• Integrates with zod
• Allows creating reusable routers
• Allows navigating to the definition and implementation of the router endpoints using cmd+click