Simple Time Server Using GQLGen

main.go

package main

import (
	"context"
	"net/http"
	"strings"
	"time"

	"github.com/99designs/gqlgen/handler"
)

//go:generate go run github.com/99designs/gqlgen

func main() {
	playgroundHandler := handler.Playground("What Time is It?", `/graphql`)
	exec := NewExecutableSchema(Config{Resolvers: root{}})
	graphqlHandler := handler.GraphQL(exec)
	http.HandleFunc("/graphql", func(w http.ResponseWriter, r *http.Request) {
		switch {
		case r.Method != `GET`:
			graphqlHandler.ServeHTTP(w, r)
		case canUpgrade(r, `websocket`):
			graphqlHandler.ServeHTTP(w, r)
		default:
			playgroundHandler.ServeHTTP(w, r)
		}
	})

	err := http.ListenAndServe(`localhost:8080`, nil)
	if err != nil {
		panic(err)
	}
}

func canUpgrade(r *http.Request, protocol string) bool {
	for _, v := range r.Header[`Upgrade`] {
		if strings.SplitN(v, " ", 2)[0] == protocol {
			return true
		}
	}
	return false
}

type root struct{}

func (_ root) Query() QueryResolver               { return query{} }
func (_ root) Subscription() SubscriptionResolver { return subscription{} }

type query struct{}

func (_ query) Time(_ context.Context) (string, error) {
	return time.Now().Format(timeFormat), nil
}

type subscription struct{}

func (r subscription) TimeChanged(ctx context.Context) (<-chan string, error) {
	ret := make(chan string)
	go r.trackTimeChanges(ctx, ret)
	return ret, nil
}

func (r subscription) trackTimeChanges(ctx context.Context, ret chan<- string) {
	t := time.NewTicker(time.Second)
	defer t.Stop()

	start := time.Now().Format(timeFormat)
	println(`.. starting to track time changes at`, start)
	defer println(`.. done tracking time changes since`, start)

	done := ctx.Done()
	select {
	case <-done:
		return
	case ret <- start:
	}

	for {
		select {
		case <-done:
			return
		case t := <-t.C:
			now := t.Format(timeFormat)
			select {
			case <-done:
				return
			case ret <- now:
			}
		}
	}
}

const timeFormat = `2006-01-02 15:04:05`

schema.graphql

package main

import (
	"context"
	"net/http"
	"strings"
	"time"

	"github.com/99designs/gqlgen/handler"
)

//go:generate go run github.com/99designs/gqlgen

func main() {
	playgroundHandler := handler.Playground("What Time is It?", `/graphql`)
	exec := NewExecutableSchema(Config{Resolvers: root{}})
	graphqlHandler := handler.GraphQL(exec)
	http.HandleFunc("/graphql", func(w http.ResponseWriter, r *http.Request) {
		switch {
		case r.Method != `GET`:
			graphqlHandler.ServeHTTP(w, r)
		case canUpgrade(r, `websocket`):
			graphqlHandler.ServeHTTP(w, r)
		default:
			playgroundHandler.ServeHTTP(w, r)
		}
	})

	err := http.ListenAndServe(`localhost:8080`, nil)
	if err != nil {
		panic(err)
	}
}

func canUpgrade(r *http.Request, protocol string) bool {
	for _, v := range r.Header[`Upgrade`] {
		if strings.SplitN(v, " ", 2)[0] == protocol {
			return true
		}
	}
	return false
}

type root struct{}

func (_ root) Query() QueryResolver               { return query{} }
func (_ root) Subscription() SubscriptionResolver { return subscription{} }

type query struct{}

func (_ query) Time(_ context.Context) (string, error) {
	return time.Now().Format(timeFormat), nil
}

type subscription struct{}

func (r subscription) TimeChanged(ctx context.Context) (<-chan string, error) {
	ret := make(chan string)
	go r.trackTimeChanges(ctx, ret)
	return ret, nil
}

func (r subscription) trackTimeChanges(ctx context.Context, ret chan<- string) {
	t := time.NewTicker(time.Second)
	defer t.Stop()

	start := time.Now().Format(timeFormat)
	println(`.. starting to track time changes at`, start)
	defer println(`.. done tracking time changes since`, start)

	done := ctx.Done()
	select {
	case <-done:
		return
	case ret <- start:
	}

	for {
		select {
		case <-done:
			return
		case t := <-t.C:
			now := t.Format(timeFormat)
			select {
			case <-done:
				return
			case ret <- now:
			}
		}
	}
}

const timeFormat = `2006-01-02 15:04:05`