2nd/10_Wiki/Topics/Coding/Backend_gRPC_Patterns.md

---
id: backend-grpc-patterns
title: gRPC — Proto / Streaming / 인터셉터
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [backend, grpc, protobuf, streaming, vibe-coding]
tech_stack: { language: "TS / Go / Java", applicable_to: ["Backend"] }
applied_in: []
aliases: [protobuf, gRPC stream, unary, server streaming, bidi, ConnectRPC]
---

# gRPC

> Service-to-service RPC 표준. **Proto schema → 타입 안전 코드 generate**. HTTP/2 = 한 connection 다중 stream. JSON/REST 보다 빠르고 타입 안전. 브라우저 사용은 **gRPC-Web 또는 ConnectRPC**.

## 📖 핵심 개념
- 4 RPC 종류: unary / server stream / client stream / bidi stream.
- Proto3 syntax: enum / oneof / map / repeated.
- Interceptor: middleware (auth, logging, retry).
- Deadline: 모든 호출 timeout 명시.

## 💻 코드 패턴

### Proto 정의
```proto
syntax = "proto3";
package user.v1;

service UserService {
  rpc GetUser(GetUserRequest) returns (User);
  rpc StreamUsers(ListUsersRequest) returns (stream User);
  rpc CreateUsers(stream CreateUserRequest) returns (BulkResult);
  rpc Chat(stream ChatMessage) returns (stream ChatMessage);
}

message User {
  string id = 1;
  string email = 2;
  google.protobuf.Timestamp created_at = 3;
  optional string name = 4;
}

message GetUserRequest { string id = 1; }
```

### Server (Node + ts-proto + @grpc/grpc-js)
```ts
import * as grpc from '@grpc/grpc-js';

const server = new grpc.Server();
server.addService(UserServiceService, {
  getUser: async (call, cb) => {
    const u = await db.user.findUnique({ where: { id: call.request.id } });
    if (!u) return cb({ code: grpc.status.NOT_FOUND, message: 'user' });
    cb(null, u);
  },
  streamUsers: async (call) => {
    const it = db.user.streamAll();
    for await (const u of it) call.write(u);
    call.end();
  },
});

server.bindAsync('0.0.0.0:50051', grpc.ServerCredentials.createInsecure(), () => {
  server.start();
});
```

### Client + deadline + retry
```ts
const client = new UserServiceClient('localhost:50051', grpc.credentials.createInsecure());

client.getUser({ id: 'u1' }, { deadline: Date.now() + 5000 }, (err, res) => {
  if (err?.code === grpc.status.NOT_FOUND) ...
});
```

### Interceptor (auth)
```ts
const authInterceptor: grpc.Interceptor = (opts, nextCall) => {
    return new grpc.InterceptingCall(nextCall(opts), {
        start(metadata, listener, next) {
            metadata.add('authorization', `Bearer ${token}`);
            next(metadata, listener);
        },
    });
};

const client = new UserServiceClient(addr, creds, { interceptors: [authInterceptor] });
```

### ConnectRPC (browser-friendly)
```ts
// HTTP/1+JSON, HTTP/2+protobuf 다 지원. CORS 친화.
import { createPromiseClient } from '@connectrpc/connect';
import { createConnectTransport } from '@connectrpc/connect-web';

const t = createConnectTransport({ baseUrl: 'https://api.example.com' });
const client = createPromiseClient(UserService, t);
const u = await client.getUser({ id: 'u1' });
```

### Streaming (server-side)
```ts
const stream = client.streamUsers({});
stream.on('data', (u) => console.log(u));
stream.on('end', () => console.log('done'));
stream.on('error', (e) => console.error(e));
```

### Versioning
```proto
package user.v1;
// 새 필드는 새 number 부여. 기존 number / type 절대 변경 금지.
// breaking 시 user.v2 새 패키지.
```

## 🤔 의사결정 기준
| 상황 | 추천 |
|---|---|
| 내부 service-to-service | gRPC |
| 브라우저 호출 | ConnectRPC / gRPC-Web |
| public REST API | REST or GraphQL |
| 실시간 양방향 | bidi stream / WebSocket |
| 부분 업데이트 | google.protobuf.FieldMask |
| Batching | repeated field 또는 client stream |

## ❌ 안티패턴
- **Deadline 없음**: 영원히 hang.
- **Stream cancel 안 함**: 서버 자원 소진.
- **Proto field number 재사용**: prod 데이터 깨짐.
- **enum 0 안 만들고 시작**: default unknown 부재.
- **Optional 안 쓰고 string 빈 문자열 = null**: 모호.
- **Server reflection prod 켬**: schema 노출.
- **TLS 없는 prod**: token 노출.

## 🤖 LLM 활용 힌트
- Proto3 + ts-proto / buf 권장.
- ConnectRPC 가 modern + browser 친화.
- Deadline + Interceptor 항상.

## 🔗 관련 문서