Acknowledgements

Introduction

Acknowledgements comes in two flavors:

• With a callback function
• With a Promise

Type 1: With a callback

From client to server

Client

socket.timeout(5000).emit('request', { foo: 'bar' }, 'baz', (err, response) => {
  if (err) {
    // the server did not acknowledge the event in the given delay
  } else {
    console.log(response.status); // 'ok'
  }
});

Server

io.on('connection', (socket) => {
  socket.on('request', (arg1, arg2, callback) => {
    console.log(arg1); // { foo: 'bar' }
    console.log(arg2); // 'baz'
    callback({
      status: 'ok'
    });
  });
});

---

From server to client

Server

io.on('connection', (socket) => {
  socket.timeout(5000).emit('request', { foo: 'bar' }, 'baz', (err, response) => {
    if (err) {
      // the client did not acknowledge the event in the given delay
    } else {
      console.log(response.status); // 'ok'
    }
  });
});

Client

socket.on('request', (arg1, arg2, callback) => {
  console.log(arg1); // { foo: 'bar' }
  console.log(arg2); // 'baz'
  callback({
    status: 'ok'
  });
});

Type 2: With a promise

The emitWithAck() method provides the same functionality, but returns a Promise which will resolve once the other side acknowledges the event:

From client to server

Client

try {
  const response = await socket.timeout(5000).emitWithAck('request', { foo: 'bar' }, 'baz');
  console.log(response.status); // 'ok'
} catch (e) {
  // the server did not acknowledge the event in the given delay
}

Server

io.on('connection', (socket) => {
  socket.on('request', (arg1, arg2, callback) => {
    console.log(arg1); // { foo: 'bar' }
    console.log(arg2); // 'baz'
    callback({
      status: 'ok'
    });
  });
});

---

From server to client

Server

io.on('connection', async (socket) => {
  try {
    const response = await socket.timeout(5000).emitWithAck('request', { foo: 'bar' }, 'baz');
    console.log(response.status); // 'ok'
  } catch (e) {
    // the client did not acknowledge the event in the given delay
  }
});

Client

socket.on('request', (arg1, arg2, callback) => {
  console.log(arg1); // { foo: 'bar' }
  console.log(arg2); // 'baz'
  callback({
    status: 'ok'
  });
});