http2: fix zombie session crash on socket close

src/node_http2.cc

@@ -1766,7 +1766,14 @@ void Http2Session::OnStreamAfterWrite(WriteWrap* w, int status) {
   Debug(this, "write finished with status %d", status);
 
   MaybeNotifyGracefulCloseComplete();
-  CHECK(is_write_in_progress());
+  // Guard against write callback being invoked when write is not in progress.
+  // This can happen with zombie sessions where the underlying socket is closed
+  // but the session hasn't been properly notified. Instead of crashing, we
+  // silently handle the inconsistent state. (Ref: https://github.com/nodejs/node/issues/61304)
+  if (!is_write_in_progress()) {
+    Debug(this, "write callback invoked but write not in progress, possible zombie session");
+    return;
+  }
   set_write_in_progress(false);
 
   // Inform all pending writes about their completion.

test/parallel/test-http2-socket-close-zombie-session.js

@@ -0,0 +1,97 @@
+// Flags: --expose-internals
+'use strict';
+
+// Regression test for https://github.com/nodejs/node/issues/61304
+// When the underlying socket is closed at the OS level without
+// sending RST/FIN (e.g., network black hole), the HTTP/2 session
+// enters a zombie state where it believes the connection is alive
+// but the socket is actually dead. Subsequent write attempts should
+// fail gracefully rather than crash with assertion failures.
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const assert = require('assert');
+const h2 = require('http2');
+const { kSocket } = require('internal/http2/util');
+const fixtures = require('../common/fixtures');
+
+const server = h2.createSecureServer({
+  key: fixtures.readKey('agent1-key.pem'),
+  cert: fixtures.readKey('agent1-cert.pem')
+});
+
+server.on('stream', common.mustCall((stream) => {
+  stream.respond({ ':status': 200 });
+  stream.end('hello');
+}));
+
+server.listen(0, common.mustCall(() => {
+  const client = h2.connect(`https://localhost:${server.address().port}`, {
+    rejectUnauthorized: false
+  });
+
+  let firstRequestDone = false;
+
+  // First request to establish connection
+  const req1 = client.request({ ':path': '/' });
+  req1.on('response', common.mustCall(() => {
+    firstRequestDone = true;
+  }));
+  req1.on('data', () => {});
+  req1.on('end', common.mustCall(() => {
+    // Connection is established, now simulate network black hole
+    // by destroying the underlying socket without proper close
+    const socket = client[kSocket];
+
+    // Verify session state before socket destruction
+    assert.strictEqual(client.closed, false);
+    assert.strictEqual(client.destroyed, false);
+
+    // Destroy the socket to simulate OS-level connection loss
+    // This mimics what happens when network drops packets without RST/FIN
+    socket.destroy();
+
+    // The session should handle this gracefully
+    // Prior to fix: this would cause assertion failures in subsequent writes
+    // After fix: session should close properly
+
+    setImmediate(() => {
+      // Try to send another request into the zombie session
+      // With the fix, the session should close gracefully without crashing
+      try {
+        const req2 = client.request({ ':path': '/test' });
+        // The request may or may not emit an error event,
+        // but it should not receive a response
+        req2.on('error', () => {
+          // Acceptable: error event fires
+        });
+        req2.on('response', common.mustNotCall(
+          'Should not receive response from zombie session'
+        ));
+        req2.end();
+      } catch (err) {
+        // Also acceptable: synchronous error on request creation
+        assert(err);
+      }
+
+      // Verify session eventually closes
+      client.on('close', common.mustCall(() => {
+        server.close();
+      }));
+
+      // Force cleanup if session doesn't close naturally
+      setTimeout(() => {
+        if (!client.destroyed) {
+          client.destroy();
+        }
+        if (server.listening) {
+          server.close();
+        }
+      }, 1000);
+    });
+  }));
+
+  req1.end();
+}));