json_websockets.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"strconv"
	"time"

	"golang.org/x/net/websocket"
)

type Input struct {
	Num string
}

type Output struct {
	Num   int
	Error string
}

func main() {
	// a websocket handler that reads in a number, attempts to parse it
	// with Atoi(), then responds.
	wsh := func(ws *websocket.Conn) {
		for {
			var input Input
			if err := websocket.JSON.Receive(ws, &input); err != nil {
				log.Println(err)
				return
			}
			num, err := strconv.Atoi(input.Num)
			msg := ""
			if err != nil {
				msg = err.Error()
			}
			if err := websocket.JSON.Send(ws, &Output{num, msg}); err != nil {
				log.Println(err)
				return
			}
		}
	}

	go func() {
		log.Fatal(http.ListenAndServe(":7070", websocket.Handler(wsh)))
	}()
	// give the server a chance to start up
	time.Sleep(time.Second)

	// make a request to the server
	origin := "http://localhost/"
	url := "ws://localhost:7070/"
	ws, err := websocket.Dial(url, "", origin)
	if err != nil {
		log.Fatal(err)
	}
	// send a bunch of numbers over the websocket in JSON form
	vals := []string{"7", "8", "foo"}
	for _, n := range vals {
		if err := websocket.JSON.Send(ws, &Input{n}); err != nil {
			log.Fatal(err)
		}
	}

	// recieve the response from the websocket one at a time
	for range vals {
		var output Output
		if err := websocket.JSON.Receive(ws, &output); err != nil {
			log.Fatal(err)
		}
		fmt.Printf("'%d' '%s'\n", output.Num, output.Error)
	}
}