Para enviar algo a todos los clientes, usa:

io.sockets.emit('response', data);

Para recibir de clientes, usted usa:

socket.on('cursor', function(data) {
  ...
});

¿Cómo puedo combinar los dos para que cuando reciba un mensaje en el servidor de un cliente, envíe ese mensaje a todos los usuarios excepto al que envía el mensaje?

socket.on('cursor', function(data) {
  io.sockets.emit('response', data);
});

¿Tengo que hackearlo enviando la identificación del cliente con el mensaje y luego verificando el lado del cliente o hay una manera más fácil?

Aquí está mi lista (actualizada para 1.0) :

// sending to sender-client only
socket.emit('message', "this is a test");

// sending to all clients, include sender
io.emit('message', "this is a test");

// sending to all clients except sender
socket.broadcast.emit('message', "this is a test");

// sending to all clients in 'game' room(channel) except sender
socket.broadcast.to('game').emit('message', 'nice game');

// sending to all clients in 'game' room(channel), include sender
io.in('game').emit('message', 'cool game');

// sending to sender client, only if they are in 'game' room(channel)
socket.to('game').emit('message', 'enjoy the game');

// sending to all clients in namespace 'myNamespace', include sender
io.of('myNamespace').emit('message', 'gg');

// sending to individual socketid
socket.broadcast.to(socketid).emit('message', 'for your eyes only');

// list socketid
for (var socketid in io.sockets.sockets) {}
 OR
Object.keys(io.sockets.sockets).forEach((socketid) => {});

De la respuesta @LearnRPG pero con 1.0:

 // send to current request socket client
 socket.emit('message', "this is a test");

 // sending to all clients, include sender
 io.sockets.emit('message', "this is a test"); //still works
 //or
 io.emit('message', 'this is a test');

 // sending to all clients except sender
 socket.broadcast.emit('message', "this is a test");

 // sending to all clients in 'game' room(channel) except sender
 socket.broadcast.to('game').emit('message', 'nice game');

 // sending to all clients in 'game' room(channel), include sender
 // docs says "simply use to or in when broadcasting or emitting"
 io.in('game').emit('message', 'cool game');

 // sending to individual socketid, socketid is like a room
 socket.broadcast.to(socketid).emit('message', 'for your eyes only');

Para responder al comentario de @Crashalot, socketidproviene de:

var io = require('socket.io')(server);
io.on('connection', function(socket) { console.log(socket.id); })

Aquí hay una respuesta más completa sobre lo que ha cambiado de 0.9.x a 1.x.

 // send to current request socket client
 socket.emit('message', "this is a test");// Hasn't changed

 // sending to all clients, include sender
 io.sockets.emit('message', "this is a test"); // Old way, still compatible
 io.emit('message', 'this is a test');// New way, works only in 1.x

 // sending to all clients except sender
 socket.broadcast.emit('message', "this is a test");// Hasn't changed

 // sending to all clients in 'game' room(channel) except sender
 socket.broadcast.to('game').emit('message', 'nice game');// Hasn't changed

 // sending to all clients in 'game' room(channel), include sender
 io.sockets.in('game').emit('message', 'cool game');// Old way, DOES NOT WORK ANYMORE
 io.in('game').emit('message', 'cool game');// New way
 io.to('game').emit('message', 'cool game');// New way, "in" or "to" are the exact same: "And then simply use to or in (they are the same) when broadcasting or emitting:" from http://socket.io/docs/rooms-and-namespaces/

 // sending to individual socketid, socketid is like a room
 io.sockets.socket(socketid).emit('message', 'for your eyes only');// Old way, DOES NOT WORK ANYMORE
 socket.broadcast.to(socketid).emit('message', 'for your eyes only');// New way

Quería editar la publicación de @soyuka pero mi revisión fue rechazada por una revisión por pares.

broadcast.emit envía el mensaje a todos los demás clientes (excepto al remitente)

socket.on('cursor', function(data) {
  socket.broadcast.emit('msg', data);
});

Emitir cheatsheet

io.on('connect', onConnect);

function onConnect(socket){

  // sending to the client
  socket.emit('hello', 'can you hear me?', 1, 2, 'abc');

  // sending to all clients except sender
  socket.broadcast.emit('broadcast', 'hello friends!');

  // sending to all clients in 'game' room except sender
  socket.to('game').emit('nice game', "let's play a game");

  // sending to all clients in 'game1' and/or in 'game2' room, except sender
  socket.to('game1').to('game2').emit('nice game', "let's play a game (too)");

  // sending to all clients in 'game' room, including sender
  io.in('game').emit('big-announcement', 'the game will start soon');

  // sending to all clients in namespace 'myNamespace', including sender
  io.of('myNamespace').emit('bigger-announcement', 'the tournament will start soon');

  // sending to individual socketid (private message)
  socket.to(<socketid>).emit('hey', 'I just met you');

  // sending with acknowledgement
  socket.emit('question', 'do you think so?', function (answer) {});

  // sending without compression
  socket.compress(false).emit('uncompressed', "that's rough");

  // sending a message that might be dropped if the client is not ready to receive messages
  socket.volatile.emit('maybe', 'do you really need it?');

  // sending to all clients on this node (when using multiple nodes)
  io.local.emit('hi', 'my lovely babies');

};

Para los espacios de nombres dentro de las salas, la lista de clientes en una sala (similar a la respuesta de Nav) es uno de los dos enfoques que he encontrado que funcionará. El otro es usar excluir. P.EJ

socket.on('message',function(data) {
    io.of( 'namespace' ).in( data.roomID ).except( socket.id ).emit('message',data);
}

Otros casos

io.of('/chat').on('connection', function (socket) {
    //sending to all clients in 'room' and you
    io.of('/chat').in('room').emit('message', "data");
};

Se actualizó la lista para obtener más documentación.

socket.emit('message', "this is a test"); //sending to sender-client only
socket.broadcast.emit('message', "this is a test"); //sending to all clients except sender
socket.broadcast.to('game').emit('message', 'nice game'); //sending to all clients in 'game' room(channel) except sender
socket.to('game').emit('message', 'enjoy the game'); //sending to sender client, only if they are in 'game' room(channel)
socket.broadcast.to(socketid).emit('message', 'for your eyes only'); //sending to individual socketid
io.emit('message', "this is a test"); //sending to all clients, include sender
io.in('game').emit('message', 'cool game'); //sending to all clients in 'game' room(channel), include sender
io.of('myNamespace').emit('message', 'gg'); //sending to all clients in namespace 'myNamespace', include sender
socket.emit(); //send to all connected clients
socket.broadcast.emit(); //send to all connected clients except the one that sent the message
socket.on(); //event listener, can be called on client to execute on server
io.sockets.socket(); //for emiting to specific clients
io.sockets.emit(); //send to all connected clients (same as socket.emit)
io.sockets.on() ; //initial connection from a client.

Espero que esto ayude.

usa esta codificación

io.sockets.on('connection', function (socket) {

    socket.on('mousemove', function (data) {

        socket.broadcast.emit('moving', data);
    });

este socket.broadcast.emit () emitirá todo en la función excepto para el servidor que está emitiendo

Estoy usando espacios de nombres y habitaciones. Encontré

socket.broadcast.to('room1').emit('event', 'hi');

para trabajar donde

namespace.broadcast.to('room1').emit('event', 'hi');

No

(si alguien más se enfrenta a ese problema)