From 290c7f7fde5e604b2a8ac90f93b15e143ea09a92 Mon Sep 17 00:00:00 2001
From: Arda TANRIKULU <ardatanrikulu@gmail.com>
Date: Mon, 26 Dec 2022 14:48:28 +0300
Subject: [PATCH] Ping/pong for SSE (#2150)

* Ping/pong for SSE

* Update packages/graphql-yoga/src/plugins/resultProcessor/push.ts

Co-authored-by: Denis Badurina <badurinadenis@gmail.com>

Co-authored-by: Denis Badurina <badurinadenis@gmail.com>
---
 .changeset/wise-geckos-beam.md                   |  5 +++++
 .../src/plugins/resultProcessor/push.ts          | 16 +++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/wise-geckos-beam.md

diff --git a/.changeset/wise-geckos-beam.md b/.changeset/wise-geckos-beam.md
new file mode 100644
index 0000000000..4240e34455
--- /dev/null
+++ b/.changeset/wise-geckos-beam.md
@@ -0,0 +1,5 @@
+---
+'graphql-yoga': minor
+---
+
+Ping the client every 12 seconds to keep the connection alive
diff --git a/packages/graphql-yoga/src/plugins/resultProcessor/push.ts b/packages/graphql-yoga/src/plugins/resultProcessor/push.ts
index 22676fa7e0..d2517c7c95 100644
--- a/packages/graphql-yoga/src/plugins/resultProcessor/push.ts
+++ b/packages/graphql-yoga/src/plugins/resultProcessor/push.ts
@@ -9,6 +9,8 @@ export function processPushResult(
   result: ResultProcessorInput,
   fetchAPI: FetchAPI,
 ): Response {
+  const timeoutInSeconds = 12
+
   const headersInit = {
     'Content-Type': 'text/event-stream',
     Connection: 'keep-alive',
@@ -20,9 +22,19 @@ export function processPushResult(
 
   let iterator: AsyncIterator<MaybeArray<ExecutionResult>>
 
+  let pingInterval: number
   const textEncoder = new fetchAPI.TextEncoder()
   const readableStream = new fetchAPI.ReadableStream({
-    start() {
+    start(controller) {
+      // ping client every 12 seconds to keep the connection alive
+      pingInterval = setInterval(() => {
+        if (!controller.desiredSize) {
+          clearInterval(pingInterval)
+          return
+        }
+        controller.enqueue(textEncoder.encode(':\n\n'))
+      }, timeoutInSeconds * 1000) as unknown as number
+
       if (isAsyncIterable(result)) {
         iterator = result[Symbol.asyncIterator]()
       } else {
@@ -45,10 +57,12 @@ export function processPushResult(
         controller.enqueue(textEncoder.encode(`data: ${chunk}\n\n`))
       }
       if (done) {
+        clearInterval(pingInterval)
         controller.close()
       }
     },
     async cancel(e) {
+      clearInterval(pingInterval)
       await iterator.return?.(e)
     },
   })