Serialization

Fastify’s performance is enhanced by solving the serialization problem when using JSON.stringify and JSON.parse.

Deep dive into this topic by watching Matteo Collina’s talk:

These concepts are a Fastify feature, in which Kita takes full advantage of.

Kita runs at build time, inferring all I/O types for each route and generating route schemas. This enables Fastify to use a super fast serializer and super fast validator.

Parsing the request

Kita uses Ts Json Schema Generator under the hood to transform TypeScript AST TypeNodes into a JSON schema.

This is what powers the complex transformation of code types into JSON schemas. Take a look at the following example:

Example definition

export interface CreateUser {
  /**
   * The name of the user
   *
   * @minLength 3
   * @maxLength 20
   */
  name: string;

  /**
   * The email of the user
   *
   * @format email
   */
  email: string;

  /**
   * The age of the user
   *
   * @minimum 0
   * @maximum 150
   */
  age: number;
}

Type Schema

{
  "CreateUserRequest": {
    "additionalProperties": false,
    "properties": {
      "age": {
        "description": "The age of the user",
        "maximum": 150,
        "minimum": 0,
        "type": "number"
      },
      "email": {
        "description": "The email of the user",
        "format": "email",
        "type": "string"
      },
      "name": {
        "description": "The name of the user",
        "maxLength": 20,
        "minLength": 3,
        "type": "string"
      }
    },
    "required": ["name", "email", "age"],
    "type": "object"
  }
}

You can use the above interface inside a route handler:

Example route

import type { Body } from '@kitajs/runtime';

interface CreateUser {
  name: string;
  email: string;
  age: number;
}

export function post(data: Body<CreateUser>) {
  return true;
}

Route Schema

{
  "paths": {
    "/": {
      "post": {
        "operationId": "postIndex",
        "requestBody": {
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/CreateUserRequest"
              }
            }
          }
        },
        "responses": {
          "2XX": {
            "description": "Default Response",
            "content": {
              "application/json": {
                "schema": {
                  "type": "boolean"
                }
              }
            }
          }
        }
      }
    }
  }
}

The above schema is handled by Fastify & Ajv, ensuring that the request body matches the expected types as well as the constraints defined in the interface, such as @minLength, @maxLength, @format, @minimum, and @maximum.

Ajv, the library used underneath, is trusted by millions of developers and multiple big companies for its speed and reliability.