sse/sse.go

// Copyright 2013 Alexandre Fiori
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package sse

import (
	"bufio"
	"errors"
	"fmt"
	"net"

	"github.com/fiorix/go-web/http"
)

var ErrNoHijack = errors.New("Server does not support hijacking")

// MessageEvent is the container of Server-Sent events (SSE), push notifications.
type MessageEvent struct {
	Data  string // message content
	Id    string // id of the message (int?)
	Event string // name of the event
	Retry int    // client reconnection time, in milliseconds
}

// ServeEvents prepares the request for SSE, push notifications.
// Caveat: ResponseWriter.Status() returns 0 after ServeEvents is called.
func ServeEvents(w http.ResponseWriter) (net.Conn, *bufio.ReadWriter, error) {
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("Content-Type", "text/event-stream")
	hj, ok := w.(http.Hijacker)
	if !ok {
		return nil, nil, ErrNoHijack
	}
	conn, buf, err := hj.Hijack()
	fmt.Fprintf(conn, "HTTP/1.1 200 OK\r\n")
	w.Header().Write(conn)
	fmt.Fprintf(conn, "\r\n")
	return conn, buf, err
}

// SendEvent sends a push notification to the peer (usually a browser).
// Browsers can handle these events in JavaScript:
// http://www.w3schools.com/html/html5_serversentevents.asp
func SendEvent(buf *bufio.ReadWriter, m *MessageEvent) (err error) {
	if m.Data != "" {
		fmt.Fprintf(buf, "data: %s\n", m.Data)
	}
	if m.Event != "" {
		fmt.Fprintf(buf, "event: %s\n", m.Event)
	}
	if m.Id != "" {
		fmt.Fprintf(buf, "id: %s\n", m.Id)
	}
	if m.Retry >= 1 {
		fmt.Fprintf(buf, "retry: %d\n", m.Retry)
	}
	_, err = fmt.Fprintf(buf, "\n")
	if err == nil {
		err = buf.Flush()
	}
	return
}