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serverSideEmit(..., callback) does not deliver events until heartbeat is triggered

Abierto
  • ¿Algo no está bien?
#16 1 comentario 0 reacciones 0 asignados Ver en GitHub

@Harjot2022 ya está trabajando en esto.

Desde el 22/3/2026.

  • #18 de @wangxpych — cerrado sin fusionar

Evaluación

Dificultad
3/5
Tiempo estimado
1-2 días
Aptitud para principiantes
52/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Estancado
Stack tecnológico
postgresql, typescript
Área
backend, databases, distributed-systems

Línea de trabajo

Start with the Postgres adapter's serverSideEmit(..., callback) and heartbeat or server discovery flow, using the minimal reproduction in the issue. Compare callback-based emits with emits without callbacks and verify that all connected servers receive the event and return acknowledgements before any dummy emit is sent.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Environment

  • @socket.io/postgres-adapter: 0.4.0
  • socket.io: 4.8.x
  • pg: 8.16.x
  • Node.js: 22
  • PostgreSQL: 14.x

Problem description

When using serverSideEmit(..., callback), the callback is invoked with:

(err, responses) => {
  console.log(err);       // null
  console.log(responses); // [] ← empty
}

The event is never delivered to any other server, and the handler (io.on(...)) is never triggered on them.

However, if each individual server sends at least one serverSideEmit() (even a dummy one), things start working — the events are delivered and acknowledged as expected.

Note: If serverSideEmit() is used without a callback, the event is delivered to other servers even before they have sent any emits themselves. The issue only affects the ACK-based communication (serverSideEmit(..., callback)).

Root cause

The Postgres adapter does not deliver serverSideEmit(..., callback) events to other servers unless those servers have already started sending their own heartbeats.

Until a server sends a serverSideEmit():

  • It is connected and listening on the correct LISTEN channel
  • It can receive broadcast events without callback
  • But it will not be discoverable by other servers for ACK-based communication (serverSideEmit(..., callback))

As a result:

  • The initiating server sends a request and waits for ACKs
  • But other servers ignore the request because they don't recognize the source as active
  • The callback returns with responses = []

Minimal reproduction

// on all servers:
io.on("test-ack", (data, callback) => {
  console.log("received:", data);
  callback("ack from " + process.pid);
});

// on emitter server:
setTimeout(() => {
  io.serverSideEmit("test-ack", "hello", (err, responses) => {
    console.log("err:", err);           // null
    console.log("responses:", responses); // [] if heartbeat not yet started on other servers
  });
}, 1000);

Workaround

Ensure that every server sends a dummy serverSideEmit() after startup to trigger the heartbeat:

io.serverSideEmit("__init__", "poke");

This ensures each server becomes discoverable by others and can participate in ACK-based messaging.

Lenguaje dominante
TypeScript
Estrellas
27
Forks
9
Sin PR fusionados en 30 d

Preparar el entorno

  • Incluye un Dockerfile o un archivo de Docker Compose
  • Sin plantilla de pull request
  • Sin guía de contribución

Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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