Socket.IO enables real-time bidirectional event-based communication. It consists of:
- a Golang server (this repository)
- a Javascript client library for the browser (or a Node.js client)
Some implementations in other languages are also available:
Its main features are:
Connections are established even in the presence of:
- proxies and load balancers.
- personal firewall and antivirus software.
For this purpose, it relies on Engine.IO for golang, which first establishes a long-polling connection, then tries to upgrade to better transports that are "tested" on the side, like WebSocket. Please see the Goals section for more information.
Unless instructed otherwise a disconnected client will try to reconnect forever, until the server is available again. Please see the available reconnection options here.
A heartbeat mechanism is implemented at the Engine.IO level, allowing both the server and the client to know when the other one is not responding anymore.
That functionality is achieved with timers set on both the server and the client, with timeout values (the pingInterval and pingTimeout parameters) shared during the connection handshake. Those timers require any subsequent client calls to be directed to the same server, hence the sticky-session requirement when using multiples nodes.
Any serializable data structures can be emitted, including:
- []byte and io.Reader
Sample code:
import (
"github.com/zishang520/socket.io/socket"
)
io.On("connection", func(clients ...any) {
client := clients[0].(*socket.Socket)
client.Emit("request" /* … */) // emit an event to the socket
io.Emit("broadcast" /* … */) // emit an event to all connected sockets
client.On("reply", func(...any) { /* … */ }) // listen to the event
})In order to create separation of concerns within your application (for example per module, or based on permissions), Socket.IO allows you to create several Namespaces, which will act as separate communication channels but will share the same underlying connection.
Within each Namespace, you can define arbitrary channels, called Rooms, that sockets can join and leave. You can then broadcast to any given room, reaching every socket that has joined it.
This is a useful feature to send notifications to a group of users, or to a given user connected on several devices for example.
Note: Socket.IO is not a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the ack id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server (like ws://echo.websocket.org) either. Please see the protocol specification here.
The following example attaches socket.io to a plain engine.io *types.CreateServer listening on port 3000.
package main
import (
"github.com/zishang520/engine.io/types"
"github.com/zishang520/engine.io/utils"
"github.com/zishang520/socket.io/socket"
"os"
"os/signal"
"syscall"
)
func main() {
httpServer := types.CreateServer(nil)
io := socket.NewServer(httpServer, nil)
io.On("connection", func(clients ...any) {
client := clients[0].(*socket.Socket)
client.On("event", func(datas ...any) {
})
client.On("disconnect", func(...any) {
})
})
httpServer.Listen("127.0.0.1:3000", nil)
exit := make(chan struct{})
SignalC := make(chan os.Signal)
signal.Notify(SignalC, os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
go func() {
for s := range SignalC {
switch s {
case os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT:
close(exit)
return
}
}
}()
<-exit
httpServer.Close(nil)
os.Exit(0)
}other: Use http.Handler interface
package main
import (
"github.com/zishang520/engine.io/types"
"github.com/zishang520/engine.io/utils"
"github.com/zishang520/socket.io/socket"
"os"
"os/signal"
"syscall"
)
func main() {
httpServer := types.CreateServer(nil)
io := socket.NewServer(nil, nil)
httpServer.Handle("/socket.io", io.ServeHandler(nil))
io.On("connection", func(clients ...any) {
client := clients[0].(*socket.Socket)
client.On("event", func(datas ...any) {
})
client.On("disconnect", func(...any) {
})
})
httpServer.Listen("127.0.0.1:3000", nil)
exit := make(chan struct{})
SignalC := make(chan os.Signal)
signal.Notify(SignalC, os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
go func() {
for s := range SignalC {
switch s {
case os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT:
close(exit)
return
}
}
}()
<-exit
io.Close(nil)
httpServer.Close(nil)
os.Exit(0)
}Please see the documentation here.
In order to see all the debug output, run your app with the environment variable
DEBUG including the desired scope.
To see the output from all of Socket.IO's debugging scopes you can use:
DEBUG=socket.io*
make test