2nd/10_Wiki/Topic_Programming/Architecture/API-Contract-Definition.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-api-contract-definition	API Contract Definition	10_Wiki/Topics	verified	self	API Contract OpenAPI Contract Schema-First API Contract-First Design	none	A	0.95	applied	api openapi contract schema design		2026-05-10	pending	language framework yaml openapi-3.1

API Contract Definition

매 한 줄

"매 API 의 shape (path, method, schema, error, auth) 을 매 machine-readable spec 으로 매 먼저 정의하고 매 그 후 server/client 가 매 그것을 따른다." OpenAPI 3.1 (REST), gRPC .proto, GraphQL SDL, AsyncAPI (event), JSON Schema 가 매 dominant. 2026 현재 매 LLM 이 매 spec 을 읽어 매 client / mock / test 를 매 generate — 매 contract-first 가 매 AI 시대의 매 default.

매 핵심

매 contract-first vs code-first

• Contract-first: 매 spec → 매 server stub + 매 client SDK. 매 multi-team / multi-language 의 default.
• Code-first: 매 code → 매 spec generated (FastAPI, NestJS Swagger). 매 single team 에서 매 빠름.
• 2026 추세: 매 contract-first 가 매 LLM-friendly + 매 mock-driven dev 에 유리.

매 standard 별 사용처

• OpenAPI 3.1: 매 REST/HTTP. 매 JSON Schema 2020-12 align.
• gRPC + protobuf: 매 internal high-perf, 매 strong typing.
• GraphQL SDL: 매 client-driven query, 매 BFF.
• AsyncAPI 3: 매 Kafka / NATS / WebSocket event.
• JSON Schema: 매 payload validation, 매 LLM structured output.

매 contract testing

• Provider tests: 매 server 가 매 spec 을 만족하는지 검증 (매 schemathesis, dredd, prism).
• Consumer-driven contracts: 매 Pact — 매 client 가 매 expectation 을 매 publish, 매 server 가 매 verify.

매 응용

1. SDK auto-generation (Stainless, Speakeasy, OpenAPI Generator).
2. Mock server (Prism, Mockoon).
3. Fuzz / property test (Schemathesis).

💻 패턴

1) OpenAPI 3.1 minimal

openapi: 3.1.0
info: { title: Orders API, version: 1.2.0 }
servers: [{ url: https://api.example.com/v1 }]
paths:
  /orders/{id}:
    get:
      operationId: getOrder
      parameters:
        - { name: id, in: path, required: true, schema: { type: string, format: uuid } }
      responses:
        '200':
          content: { application/json: { schema: { $ref: '#/components/schemas/Order' } } }
        '404': { description: Not found }
components:
  schemas:
    Order:
      type: object
      required: [id, total]
      properties:
        id:    { type: string, format: uuid }
        total: { type: number, minimum: 0 }
        status: { type: string, enum: [pending, paid, shipped, canceled] }

2) gRPC proto

syntax = "proto3";
package orders.v1;

service Orders {
  rpc Get (GetReq) returns (Order);
  rpc Stream (StreamReq) returns (stream Event);
}
message GetReq  { string id = 1; }
message Order   { string id = 1; double total = 2; Status status = 3; }
enum Status { PENDING = 0; PAID = 1; SHIPPED = 2; CANCELED = 3; }

3) GraphQL SDL

type Order {
  id: ID!
  total: Float!
  status: Status!
}
enum Status { PENDING PAID SHIPPED CANCELED }
type Query { order(id: ID!): Order }

4) AsyncAPI 3 (Kafka event)

asyncapi: 3.0.0
info: { title: Orders Events, version: 1.0.0 }
channels:
  orders.created:
    address: orders.created
    messages:
      OrderCreated:
        payload: { $ref: '#/components/schemas/Order' }
operations:
  publishOrderCreated:
    action: send
    channel: { $ref: '#/channels/orders.created' }

5) Server stub generation

# 매 OpenAPI → TypeScript Express
npx openapi-generator-cli generate -i openapi.yaml -g typescript-node -o ./gen
# 매 OpenAPI → Python (FastAPI server)
npx openapi-typescript openapi.yaml -o gen/types.ts

6) Schemathesis property-based test

schemathesis run openapi.yaml --base-url=http://localhost:8000 \
  --checks=all --hypothesis-deadline=2000

7) Pact consumer test (TS)

import { Pact } from '@pact-foundation/pact';
const provider = new Pact({ consumer: 'web', provider: 'orders' });
await provider.addInteraction({
  state: 'order 1 exists',
  uponReceiving: 'a get for order 1',
  withRequest: { method: 'GET', path: '/v1/orders/1' },
  willRespondWith: { status: 200, body: { id: '1', total: 99 } }
});

8) JSON Schema for LLM structured output

order_schema = {
  "type": "object",
  "required": ["id", "total"],
  "properties": {"id":{"type":"string"},"total":{"type":"number"}}
}
client.messages.create(
  model="claude-opus-4-7",
  tools=[{"name":"return_order","input_schema":order_schema}],
  tool_choice={"type":"tool","name":"return_order"},
  messages=[...]
)

매 결정 기준

상황	Standard
매 public REST	OpenAPI 3.1
매 internal microservices	gRPC + protobuf
매 client-shaped query	GraphQL
매 event-driven	AsyncAPI 3
매 LLM structured output	JSON Schema

기본값: 매 contract-first + 매 OpenAPI 3.1 + 매 SDK auto-gen + 매 schemathesis CI. 매 internal 은 gRPC.

🔗 Graph

• 부모: API Design
• 변형: OpenAPI · gRPC
• 응용: Contract Testing
• Adjacent: JSON Schema · Pact

🤖 LLM 활용

언제: 매 spec → SDK / mock / test scaffold 자동 생성, 매 spec lint, 매 changelog diff. 언제 X: 매 LLM 이 매 spec 을 매 invent — 매 source-of-truth 는 매 git-tracked spec file.

❌ 안티패턴

• Spec drift: 매 server 가 매 spec 과 매 다름. 매 schemathesis CI 로 차단.
• No versioning: 매 breaking change 를 매 same path 에 push. 매 /v1 → /v2 또는 매 deprecated header.
• Anyof everywhere: 매 spec 이 매 너무 permissive → 매 client 의 매 type narrowing 불가.
• Code-first without lint: 매 generated spec 이 매 inconsistent (매 nullable, 매 enum).
• Mock-only test: 매 contract test 없이 매 mock 만 사용 → 매 prod fail.

🧪 검증 / 중복

• Verified (OpenAPI 3.1 spec, AsyncAPI 3.0 spec, Pact docs, Schemathesis docs).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — OpenAPI/gRPC/GraphQL/AsyncAPI 4-standard + contract testing