限制连接到网络服务的客户端数量

Question

How can I limit the number of clients connected to my service? I tried with a simple counter, but if a client exits without close their connection I don't have how get it.

Please could somebody give me ideas in order to get it?

const MAX_CLIENTS = 5
var ConnectedClients int
func main() {
    ConnectedClients = 0
    server, err := net.Listen(CONN_TYPE, net.JoinHostPort(CONN_HOST, CONN_PORT))
    if err != nil {
        fmt.Println("Error Listening", err.Error())
        os.Exit(1)
    }
    defer server.Close()
    fmt.Println("Listening on ", net.JoinHostPort(CONN_HOST, CONN_PORT))
    for {
        conn, err := server.Accept()
        if err != nil {
            fmt.Println("Error acepting: ", err.Error())
            os.Exit(1)
        }

        ConnectedClients += 1
        fmt.Println("Connected with:", conn.RemoteAddr())
        fmt.Println("Clients:", ConnectedClients)

        if ConnectedClients > MAX_CLIENTS {
            fmt.Println("Limit reached! Disconnecting:", conn.RemoteAddr())
            conn.Close()
        }
        go handleRequest(conn)
    }
}

func handleRequest(conn net.Conn) {
    //This defer will never run.... :-(
    defer func() {
        fmt.Println("Connection closed with client:", conn.RemoteAddr())
        ConnectedClients -= 1
        conn.Close()
    }()
    ...
    ...
}

Answer 1

Actually it might be the issue in the code you have not shared with us (those ...)

Connection will exit - sooner or later. The assumption is that in your connection handler you have to do some read/write operations, so the best way forward would be use read/write timeout (deadlines) to raise errors which you going to handle as needed.

Please, check the use of SetReadDeadline/SetWriteDeadline in documentation http://golang.org/pkg/net/#IPConn.SetReadDeadline or as used in this answer - https://stackoverflow.com/a/12741495/93767

Once you fix the handler part you can use client counting without any issues.