Validate Request Payloads

What you will practice

Requirements

• Register a `POST /users` route on the existing FastAPI `app` instance in `main.py`.
• Accept a JSON body with two fields: `name` (string) and `email` (string).
• On a valid payload, return HTTP `201` with the submitted data as the JSON body: `{"name": "...", "email": "..."}`.
• If `name` is missing or an empty string, return HTTP `400` with body `{"error": "name is required"}`.
• If `email` is missing or an empty string, return HTTP `400` with body `{"error": "email is required"}`.
• When both fields are invalid, report `name` first.

Starter files

What the judge checks

• Runs in the python environment with the python-pytest runner.
• Uses a 5000ms judge budget.
• Behavior rules include: Valid Payload Returns 201, Missing Name Returns 400, Missing Email Returns 400, Empty String Treated As Missing.

Constraints

• Use the existing FastAPI `app` instance — do not create a new one.
• The 400 error body must be `{"error": "<field_name> is required"}` — not Pydantic's default 422 format.
• Do not store or persist the user data — just validate and echo it back.

Example behavior

POST /users  {"name": "Alice", "email": "alice@example.com"}

201  {"name": "Alice", "email": "alice@example.com"}

POST /users  {"email": "alice@example.com"}

400  {"error": "name is required"}

Follow-up

This validates two required fields. Real APIs often validate dozens — format constraints, uniqueness checks, cross-field rules. How would you structure validation so adding a new rule is one line, not scattered conditionals?