Proposal: Using io-ts to validate request/response

example_request.ts

type I = unknown;
type A = RequestOverWire // snake case, optionals
type O = RequestToUse // camelCase, all keys present, values defaulted
​
// frontend
const request: I = { id: 'my-id' };
const payload: A = requestSchema.decode(request);
if (isLeft(payload)) {
  displayErrors(payload);
} else {
  makeApiCall(payload);
}
​
// backend
const payload: A = requestSchema.decode(request);
if (isLeft(payload)) {
  return errorResponse(payload);
}
const requestToUse: O = requestSchema.encode(payload);

Notes:

• type A represents the request that’s sent/received: snake_cased, optional keys
• decode should do no transformation of I (except to trim keys with exact)
• sender is responsible for getting decode to succeed (converting to snake_case, making query params strings, etc.)
• type O represents the request to be consumed by the application: camelCased, all keys present
• encode is where most of the processing should go: snake_case to camelCase, setting of default values