From 585ddef540fc72479c646d252f503bef46722230 Mon Sep 17 00:00:00 2001
From: enisdenjo <badurinadenis@gmail.com>
Date: Thu, 28 Sep 2023 10:37:30 -0700
Subject: [PATCH 1/2] fail

---
 src/__tests__/server.ts | 55 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/src/__tests__/server.ts b/src/__tests__/server.ts
index ea2b1de8..74758e7b 100644
--- a/src/__tests__/server.ts
+++ b/src/__tests__/server.ts
@@ -635,6 +635,61 @@ describe('Connect', () => {
       expect(event.wasClean).toBeTruthy();
     });
   });
+
+  it("should have acknowledged connection even if ack message send didn't resolve", (done) => {
+    let sent: Promise<void> | null = null;
+    let resolveSend = () => {
+      // noop
+    };
+    makeServer({
+      schema,
+      onSubscribe(ctx) {
+        expect(ctx.acknowledged).toBeTruthy();
+        resolveSend();
+        done();
+      },
+    }).opened(
+      {
+        protocol: GRAPHQL_TRANSPORT_WS_PROTOCOL,
+        send: async () => {
+          // if already set, this is a subsequent send happening after the test
+          if (sent) {
+            return;
+          }
+
+          // message was sent and delivered to the client...
+          sent = new Promise((resolve) => {
+            resolve();
+          });
+          await sent;
+
+          // ...but something else is slow - leading to a potential race condition on the `acknowledged` flag
+          await new Promise<void>((resolve) => (resolveSend = resolve));
+        },
+        close: (code, reason) => {
+          fail(`Unexpected close with ${code}: ${reason}`);
+        },
+        onMessage: async (cb) => {
+          cb(stringifyMessage({ type: MessageType.ConnectionInit }));
+          await sent;
+          cb(
+            stringifyMessage({
+              id: '1',
+              type: MessageType.Subscribe,
+              payload: { query: '{ getValue }' },
+            }),
+          );
+        },
+        onPing: () => {
+          /**/
+        },
+        onPong: () => {
+          /**/
+        },
+      },
+      {},
+    );
+  });
 });
 
 describe('Ping/Pong', () => {

From 538795f9f08d0e4f59de3fd8b44af52cd4a088e7 Mon Sep 17 00:00:00 2001
From: enisdenjo <badurinadenis@gmail.com>
Date: Thu, 28 Sep 2023 10:37:33 -0700
Subject: [PATCH 2/2] fix

---
 src/server.ts | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/server.ts b/src/server.ts
index 32860347..94b585cb 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -613,6 +613,11 @@ export function makeServer<
             if (permittedOrPayload === false)
               return socket.close(CloseCode.Forbidden, 'Forbidden');
 
+            // we should acknowledge before send to avoid race conditions (like those exampled in https://github.com/enisdenjo/graphql-ws/issues/501)
+            // even if the send fails/throws, the connection should be closed because its malfunctioning
+            // @ts-expect-error: I can write
+            ctx.acknowledged = true;
+
             await socket.send(
               stringifyMessage<MessageType.ConnectionAck>(
                 isObject(permittedOrPayload)
@@ -627,9 +632,6 @@ export function makeServer<
                 replacer,
               ),
             );
-
-            // @ts-expect-error: I can write
-            ctx.acknowledged = true;
             return;
           }
           case MessageType.Ping: {