Validate a request body

You want a POST route that rejects a malformed JSON body with a 400 before your handler runs, and hands the handler typed, validated fields. Put a body schema on the route descriptor.

Inline route

1. Define a body schema from @flare-ts/lib/schema.
2. Pass it in route options as { body: schema }.
3. Read the validated body from scope.input.body.

import { FlareHost, FlareResponse } from "@flare-ts/core";
import { node } from "@flare-ts/core/node";
import { schema, str, int } from "@flare-ts/lib/schema";

const host = new FlareHost(node);

host.http.post(
  "/users",
  { body: schema({ name: str.min(1), age: int.min(0) }) },
  (_ctx, scope) => {
    const { body } = scope.input;
    return new FlareResponse(201, { name: body.name, age: body.age });
  },
);

const app = host.build();
app.run();

Body validation runs after before middleware and immediately before the handler. A present-but-invalid body returns 400 with field errors before the handler runs. An empty or missing body arrives as body === null and is not rejected, so guard for it when a field is required.

Controller route

Group descriptors in httpContract and use ctx.extract:

import { ControllerBase, FlareHost, httpContract } from "@flare-ts/core";
import { Post } from "@flare-ts/core/decorators";
import { node } from "@flare-ts/core/node";
import { model, str, int } from "@flare-ts/lib/schema";

class CreateUser extends model({ name: str.min(1), age: int.min(0) }) {}

const UserContract = httpContract({
  create: { body: CreateUser },
});

class UsersController extends ControllerBase {
  public static override deps = [];
  public static override state = [];
  public static override contract = UserContract;

  @Post("")
  create() {
    const { body } = this.ctx.extract(UserContract.create);
    return this.created({ name: body.name, age: body.age });
  }
}

const host = new FlareHost(node);
host.http.controller("/users", UsersController);

const app = host.build();
app.run();

Notes

• Validation happens once per request at the boundary. You don’t re-validate inside the handler.
• Add route and query to the same descriptor. Inline handlers read all fields from scope.input.
• To cap body size, add maxBodyBytes to the descriptor. Oversized bodies return 413.

Related

• HTTP contracts
• Request limits and bodies
• Schema: primitives and model()