Part1: gqlgen 으로 구독(Subscriptions) 서버 만들기

GraphQL 구독(Subscription) 기능을 통해 실시간으로 클라이언트에 이벤트를 스트리밍할 수 있습니다.

WebSocket 전송 추가

아래 코드는 go run github.com/99designs/gqlgen init 으로 만들어진 기본 코드입니다.

• server.go

package main

import (
 "log"
 "net/http"
 "os"

 "github.com/99designs/gqlgen/graphql/handler"
 "github.com/99designs/gqlgen/graphql/playground"
 "github.com/songtomtom/gqlgen-apollo-subscriptions/graph"
)

const defaultPort = "8080"

func main() {
 port := os.Getenv("PORT")
 if port == "" {
  port = defaultPort
 }

 srv := handler.NewDefaultServer(graph.NewExecutableSchema(graph.Config{Resolvers: &graph.Resolver{}}))

 http.Handle("/", playground.Handler("GraphQL playground", "/query"))
 http.Handle("/query", srv)

 log.Printf("connect to http://localhost:%s/ for GraphQL playground", port)
 log.Fatal(http.ListenAndServe(":"+port, nil))
}

Subscription 을 사용하려면 AddTransport(&transport.Websocket{}) 를 호출하여 클라이언트와 서버를 연결하세요.

• server.go

AddTransport(&transport.Websocket{}) 를 추가한 코드입니다.

package main

import (
	"github.com/99designs/gqlgen/graphql/handler/transport"
	"log"
	"net/http"
	"os"

	"github.com/99designs/gqlgen/graphql/handler"
	"github.com/99designs/gqlgen/graphql/playground"
	"github.com/songtomtom/gqlgen-apollo-subscriptions/graph"
)

const defaultPort = "8080"

func main() {
	port := os.Getenv("PORT")
	if port == "" {
		port = defaultPort
	}

	srv := handler.NewDefaultServer(graph.NewExecutableSchema(graph.Config{Resolvers: &graph.Resolver{}}))
	srv.AddTransport(&transport.Websocket{}) // <---- This is the important part!

	http.Handle("/", playground.Handler("GraphQL playground", "/query"))
	http.Handle("/query", srv)

	log.Printf("connect to http://localhost:%s/ for GraphQL playground", port)
	log.Fatal(http.ListenAndServe(":"+port, nil))
}

Subscription 스키마 정의

• schema.graphqls

"""
Make sure you have at least something in your `Query` type.
If you don't have a query the playground will be unable
to introspect your schema!
"""
type Query {
  placeholder: String
}

"""
`Time` is a simple type only containing the current time as
a unix epoch timestamp and a string timestamp.
"""
type Time {
  unixTime: Int!
  timeStamp: String!
}

"""
`Subscription` is where all the subscriptions your clients can
request. You can use Schema Directives like normal to restrict
access.
"""
type Subscription {
  """
  `currentTime` will return a stream of `Time` objects.
  """
  currentTime: Time!
}

CurrentTime 리졸버 개발

ch := make(chan *model.Time) 채널을 생성하고 ch 를 리턴하는 리졸버입니다. Go 의 채널은 클라이언트에 데이터를 보내는데 사용합니다.

• schema.resolvers.go

// CurrentTime is the resolver for the currentTime field.
func (r *subscriptionResolver) CurrentTime(ctx context.Context) (<-chan *model.Time, error) {
 // First you'll need to `make()` your channel. Use your type here!
 ch := make(chan *model.Time)

 // You can (and probably should) handle your channels in a central place outside of `schema.resolvers.go`.
 // For this example we'll simply use a Goroutine with a simple loop.
 go func() {
  for {
   // In our example we'll send the current time every second.
   time.Sleep(1 * time.Second)
   fmt.Println("Tick")

   // Prepare your object.
   currentTime := time.Now()
   t := &model.Time{
    UnixTime:  int(currentTime.Unix()),
    TimeStamp: currentTime.Format(time.RFC3339),
   }

   // The channel may have gotten closed due to the client disconnecting.
   // To not have our Goroutine block or panic, we do the send in a select block.
   // This will jump to the default case if the channel is closed.
   select {
   case ch <- t: // This is the actual send.
    // Our message went through, do nothing
   default: // This is run when our send does not work.
    fmt.Println("Channel closed.")
    // You can handle any deregistration of the channel here.
    return // We'll just return ending the routine.
   }
  }
 }()

 // We return the channel and no error.
 return ch, nil
}

CurrentTime 구독

subscription OnCurrentTime {
  currentTime {
    unixTime
    timeStamp
  }
}

1초 마다 시간이 바뀌는 값이 반환되어야 합니다.

{
  "data": {
    "currentTime": {
      "unixTime": 1672931488,
      "timeStamp": "2023-01-06T00:11:28+09:00"
    }
  }
}

Reference

• gqlgen - Subscriptions

Github

• songtomtom/gqlgen-apollo-subscriptions