[Flight] Don't try to close debug channel twice (facebook#34340)

unstubbable · web-flow · commit aad7c664ffbd · 2025-08-29T17:22:39.000+02:00
When the debug channel was already closed, we must not try to close it
again when the Response gets garbage collected.

**Test plan:**

1. reduce the Flight fixture `App` component to a minimum [^1]
    - remove everything from `&lt;body&gt;`
    - delete the `console.log` statement
2. open the app in Firefox (seems to have a more aggressive GC strategy)
3. wait a few seconds

On `main`, you will see the following error in the browser console:

```
TypeError: Can not close stream after closing or error
```

With this change, the error is gone.

[^1]: It's a bit concerning that step 1 is needed to reproduce the
issue. Either GC is behaving differently with the unmodified App, or we
may hold on to the Response under certain conditions, potentially
creating a memory leak. This needs further investigation.
diff --git a/packages/react-client/src/ReactFlightClient.js b/packages/react-client/src/ReactFlightClient.js
@@ -1010,10 +1010,15 @@ export function reportGlobalError(
   if (__DEV__) {
     const debugChannel = response._debugChannel;
     if (debugChannel !== undefined) {
-      // If we don't have any more ways of reading data, we don't have to send any
-      // more neither. So we close the writable side.
+      // If we don't have any more ways of reading data, we don't have to send
+      // any more neither. So we close the writable side.
       closeDebugChannel(debugChannel);
       response._debugChannel = undefined;
+      // Make sure the debug channel is not closed a second time when the
+      // Response gets GC:ed.
+      if (debugChannelRegistry !== null) {
+        debugChannelRegistry.unregister(response);
+      }
     }
   }
 }
@@ -2434,7 +2439,7 @@ function ResponseInstance(
         // When a Response gets GC:ed because nobody is referring to any of the
         // objects that lazily load from the Response anymore, then we can close
         // the debug channel.
-        debugChannelRegistry.register(this, debugChannel);
+        debugChannelRegistry.register(this, debugChannel, this);
       }
     }
   }

Original file line number	Diff line number	Diff line change
`@@ -1010,10 +1010,15 @@ export function reportGlobalError(`
`1010`	`1010`	`if (__DEV__) {`
`1011`	`1011`	`const debugChannel = response._debugChannel;`
`1012`	`1012`	`if (debugChannel !== undefined) {`
`1013`		`- // If we don't have any more ways of reading data, we don't have to send any`
`1014`		`- // more neither. So we close the writable side.`
	`1013`	`+ // If we don't have any more ways of reading data, we don't have to send`
	`1014`	`+ // any more neither. So we close the writable side.`
`1015`	`1015`	`closeDebugChannel(debugChannel);`
`1016`	`1016`	`response._debugChannel = undefined;`
	`1017`	`+ // Make sure the debug channel is not closed a second time when the`
	`1018`	`+ // Response gets GC:ed.`
	`1019`	`+ if (debugChannelRegistry !== null) {`
	`1020`	`+ debugChannelRegistry.unregister(response);`
	`1021`	`+ }`
`1017`	`1022`	`}`
`1018`	`1023`	`}`
`1019`	`1024`	`}`
`@@ -2434,7 +2439,7 @@ function ResponseInstance(`
`2434`	`2439`	`// When a Response gets GC:ed because nobody is referring to any of the`
`2435`	`2440`	`// objects that lazily load from the Response anymore, then we can close`
`2436`	`2441`	`// the debug channel.`
`2437`		`- debugChannelRegistry.register(this, debugChannel);`
	`2442`	`+ debugChannelRegistry.register(this, debugChannel, this);`
`2438`	`2443`	`}`
`2439`	`2444`	`}`
`2440`	`2445`	`}`