The JSON object

It is expected that many websocket clients and servers will exchange data in JSON format. For Go programs this means that a Go object will be marshalled into JSON format as described in Chapter 4: Serialisation and then sent as a UTF-8 string, while the receiver will read this string and unmarshal it back into a Go object.

The websocket convenience object JSON will do this for you. It has methods Send and Receive for sending and receiving data, just like the Message object.

A client that sends a Person object in JSON format is

/* PersonClientJSON
 */
package main

import (
    "golang.org/x/net/websocket"
    "fmt"
    "os"
)

type Person struct {
    Name   string
    Emails []string
}

func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: ", os.Args[0], "ws://host:port")
        os.Exit(1)
    }
    service := os.Args[1]

    conn, err := websocket.Dial(service, "",
        "http://localhost")
    checkError(err)

    person := Person{Name: "Jan",
        Emails: []string{"[email protected]", "[email protected]"},
    }

    err = websocket.JSON.Send(conn, person)
    if err != nil {
        fmt.Println("Couldn't send msg " + err.Error())
    }
    os.Exit(0)
}

func checkError(err error) {
    if err != nil {
        fmt.Println("Fatal error ", err.Error())
        os.Exit(1)
    }
}

and a server that reads it is

/* PersonServerJSON
 */
package main

import (
    "golang.org/x/net/websocket"
    "fmt"
    "net/http"
    "os"
)

type Person struct {
    Name   string
    Emails []string
}

func ReceivePerson(ws *websocket.Conn) {
    var person Person
    err := websocket.JSON.Receive(ws, &person)
    if err != nil {
        fmt.Println("Can't receive")
    } else {

        fmt.Println("Name: " + person.Name)
        for _, e := range person.Emails {
            fmt.Println("An email: " + e)
        }
    }
}

func main() {

    http.Handle("/", websocket.Handler(ReceivePerson))
    err := http.ListenAndServe(":12345", nil)
    checkError(err)
}

func checkError(err error) {
    if err != nil {
        fmt.Println("Fatal error ", err.Error())
        os.Exit(1)
    }
}