Add missing context for subscription loaders (#567)

lib/subscription-connection.js

@@ -197,7 +197,7 @@ module.exports = class SubscriptionConnection {
         pubsub: sc,
         lruGatewayResolvers: this.lruGatewayResolvers,
         reply: {
-          [kLoaders]: subscriptionLoaders && subscriptionLoaders.create(),
+          [kLoaders]: subscriptionLoaders && subscriptionLoaders.create(context),
           [kEntityResolvers]: this.entityResolvers,
           request: { headers: {} }
         }

test/subscription.js

@@ -1876,3 +1876,176 @@ test('subscription server works with fastify-websocket', t => {
     }))
   })
 })
+
+test('subscription passes context to its loaders', t => {
+  const app = Fastify()
+  t.teardown(async () => {
+    await app.close()
+  })
+
+  const sendTestMutation = () => {
+    app.inject({
+      method: 'POST',
+      url: '/graphql',
+      body: {
+        query: `
+          mutation {
+            addNotification(message: "Hello World") {
+              id
+            }
+          }
+        `
+      }
+    }, () => {})
+  }
+
+  const emitter = mq()
+  const schema = `
+    type Notification {
+      id: ID!
+      message: String
+    }
+
+    type Query {
+      notifications: [Notification]
+    }
+
+    type Mutation {
+      addNotification(message: String): Notification
+    }
+
+    type Subscription {
+      notificationAdded: Notification
+    }
+  `
+
+  let idCount = 1
+  const notifications = [{
+    id: idCount,
+    message: 'Notification message'
+  }]
+
+  const loaders = {
+    Notification: {
+      message: async (queries, context) => {
+        t.ok(context, 'context is not missing')
+        const { username } = context
+        return queries.map(({ obj }) => `${obj.message} ${username}`)
+      }
+    }
+  }
+
+  const resolvers = {
+    Query: {
+      notifications: () => notifications
+    },
+    Mutation: {
+      addNotification: async (_, { message }) => {
+        const id = idCount++
+        const notification = {
+          id,
+          message
+        }
+        notifications.push(notification)
+        await emitter.emit({
+          topic: 'NOTIFICATION_ADDED',
+          payload: {
+            notificationAdded: notification
+          }
+        })
+
+        return notification
+      }
+    },
+    Subscription: {
+      notificationAdded: {
+        subscribe: (root, args, { pubsub, topic }) => pubsub.subscribe(topic)
+      }
+    }
+  }
+
+  app.register(GQL, {
+    schema,
+    resolvers,
+    loaders,
+    subscription: {
+      emitter,
+      context: () => ({
+        topic: 'NOTIFICATION_ADDED',
+        username: 'foobar'
+      })
+    }
+  })
+
+  app.listen(0, err => {
+    t.error(err)
+
+    const ws = new WebSocket('ws://localhost:' + (app.server.address()).port + '/graphql', 'graphql-ws')
+    const client = WebSocket.createWebSocketStream(ws, { encoding: 'utf8', objectMode: true })
+    t.teardown(client.destroy.bind(client))
+    client.setEncoding('utf8')
+
+    client.write(JSON.stringify({
+      type: 'connection_init'
+    }))
+
+    client.write(JSON.stringify({
+      id: 1,
+      type: 'start',
+      payload: {
+        query: `
+          subscription {
+            notificationAdded {
+              id
+              message
+            }
+          }
+        `
+      }
+    }))
+
+    client.write(JSON.stringify({
+      id: 2,
+      type: 'start',
+      payload: {
+        query: `
+          subscription {
+            notificationAdded {
+              id
+              message
+            }
+          }
+        `
+      }
+    }))
+
+    client.write(JSON.stringify({
+      id: 2,
+      type: 'stop'
+    }))
+
+    client.on('data', chunk => {
+      const data = JSON.parse(chunk)
+
+      if (data.id === 1 && data.type === 'data') {
+        t.equal(chunk, JSON.stringify({
+          type: 'data',
+          id: 1,
+          payload: {
+            data: {
+              notificationAdded: {
+                id: '1',
+                message: 'Hello World foobar'
+              }
+            }
+          }
+        }))
+
+        client.end()
+        t.end()
+      } else if (data.id === 2 && data.type === 'complete') {
+        sendTestMutation()
+      }
+    })
+  })
+})