GraphQL Subscriptions allow you to stream events to your clients in real-time. This is easy to do in gqlgen and this recipe will show you how to setup a quick example.
Preparation
This recipe starts with the empty project after the quick start steps were followed. Although the steps are the same in an existing, more complex projects you will need to be careful to configure routing correctly.
In this recipe you will learn how to
- add WebSocket Transport to your server
- add the
Subscription
type to your schema - implement a real-time resolver.
Adding WebSocket Transport
To send real-time data to clients, your GraphQL server needs to have an open connection with the client. This is done using WebSockets.
To add the WebSocket transport change your main.go
by calling AddTransport(&transport.Websocket{})
on your query handler.
If you are using an external router, remember to send ALL /query
-requests to your handler!
Not just POST requests!
package main
import (
"log"
"net/http"
"os"
"github.com/99designs/gqlgen/graphql/handler"
"github.com/99designs/gqlgen/graphql/handler/transport"
"github.com/99designs/gqlgen/graphql/playground"
"github.com/example/test/graph"
"github.com/example/test/graph/generated"
)
const defaultPort = "8080"
func main() {
port := os.Getenv("PORT")
if port == "" {
port = defaultPort
}
srv := handler.NewDefaultServer(generated.NewExecutableSchema(generated.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))
}
Adding Subscriptions to your Schema
Next you’ll have to define the subscriptions in your schema in the Subscription
top-level type.
"""
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!
}
Implementing your Resolver
After regenerating your code with go run github.com/99designs/gqlgen generate
you’ll find a
new resolver for your subscription. It will look like any other resolver, except it expects
a <-chan *model.Time
(or whatever your type is). This is a
channel. Channels in Go are used to send objects to a
single receiver.
The resolver for our example currentTime
subscription looks as follows:
// 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
}
Trying it out
To try out your new subscription visit your GraphQL playground. This is exposed on
http://localhost:8080
by default.
Use the following query:
subscription {
currentTime {
unixTime
timeStamp
}
}
Run your query and you should see a response updating with the current timestamp every
second. To gracefully stop the connection click the Execute query
button again.
Adding Server-Sent Events transport
You can use instead of WebSocket (or in addition) Server-Sent Events
as transport for subscriptions. This can have advantages and disadvantages over transport via WebSocket and requires a
compatible client library, for instance graphql-sse. The connection between
server and client should be HTTP/2+. The client must send the subscription request via POST with
the header accept: text/event-stream
and content-type: application/json
in order to be accepted by the SSE transport.
The underling protocol is documented at distinct connections mode.
Add the SSE transport as first of all other transports, as the order is important. For that reason, New
instead of
NewDefaultServer
will be used.
srv := handler.New(generated.NewExecutableSchema(generated.Config{Resolvers: &graph.Resolver{}}))
srv.AddTransport(transport.SSE{}) // <---- This is the important
// default server
srv.AddTransport(transport.Options{})
srv.AddTransport(transport.GET{})
srv.AddTransport(transport.POST{})
srv.AddTransport(transport.MultipartForm{})
srv.SetQueryCache(lru.New(1000))
srv.Use(extension.Introspection{})
srv.Use(extension.AutomaticPersistedQuery{
Cache: lru.New(100),
})
The GraphQL playground does not support SSE yet. You can try out the subscription via curl:
curl -N --request POST --url http://localhost:8080/query \
--data '{"query":"subscription { currentTime { unixTime timeStamp } }"}' \
-H "accept: text/event-stream" -H 'content-type: application/json' \
--verbose
Full Files
Here are all files at the end of this tutorial. Only files changed from the end of the quick start are listed.
main.go
package main
import (
"log"
"net/http"
"os"
"github.com/99designs/gqlgen/graphql/handler"
"github.com/99designs/gqlgen/graphql/handler/transport"
"github.com/99designs/gqlgen/graphql/playground"
"github.com/example/test/graph"
"github.com/example/test/graph/generated"
)
const defaultPort = "8080"
func main() {
port := os.Getenv("PORT")
if port == "" {
port = defaultPort
}
srv := handler.NewDefaultServer(generated.NewExecutableSchema(generated.Config{Resolvers: &graph.Resolver{}}))
srv.AddTransport(&transport.Websocket{})
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))
}
schema.graphqls
type Query {
placeholder: String
}
type Time {
unixTime: Int!
timeStamp: String!
}
type Subscription {
currentTime: Time!
}
schema.resolvers.go
package graph
// This file will be automatically regenerated based on the schema, any resolver implementations
// will be copied through when generating and any unknown code will be moved to the end.
import (
"context"
"fmt"
"time"
"github.com/example/test/graph/generated"
"github.com/example/test/graph/model"
)
// Placeholder is the resolver for the placeholder field.
func (r *queryResolver) Placeholder(ctx context.Context) (*string, error) {
str := "Hello World"
return &str, nil
}
// CurrentTime is the resolver for the currentTime field.
func (r *subscriptionResolver) CurrentTime(ctx context.Context) (<-chan *model.Time, error) {
ch := make(chan *model.Time)
go func() {
for {
time.Sleep(1 * time.Second)
fmt.Println("Tick")
currentTime := time.Now()
t := &model.Time{
UnixTime: int(currentTime.Unix()),
TimeStamp: currentTime.Format(time.RFC3339),
}
select {
case ch <- t:
// Our message went through, do nothing
default:
fmt.Println("Channel closed.")
return
}
}
}()
return ch, nil
}
// Query returns generated.QueryResolver implementation.
func (r *Resolver) Query() generated.QueryResolver { return &queryResolver{r} }
// Subscription returns generated.SubscriptionResolver implementation.
func (r *Resolver) Subscription() generated.SubscriptionResolver { return &subscriptionResolver{r} }
type queryResolver struct{ *Resolver }
type subscriptionResolver struct{ *Resolver }