/
broker.go
165 lines (135 loc) · 4.1 KB
/
broker.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
package handlers
import (
"fmt"
"log"
"net/http"
)
// Broker is responsible
// for keeping a list of which clients (browsers) are currently attached
// and broadcasting events (messages) to those clients.
//
type Broker struct {
// Create a map of clients, the keys of the map are the channels
// over which we can push messages to attached clients. (The values
// are just booleans and are meaningless.)
//
clients map[chan string]bool
// Channel into which new clients can be pushed
//
newClients chan chan string
// Channel into which disconnected clients should be pushed
//
defunctClients chan chan string
// Channel into which messages are pushed to be broadcast out
// to attahed clients.
//
Messages chan string
}
// This Broker method starts a new goroutine. It handles
// the addition & removal of clients, as well as the broadcasting
// of messages out to clients that are currently attached.
//
func (b *Broker) Start() {
// Start a goroutine
//
go func() {
// Loop endlessly
//
for {
// Block until we receive from one of the
// three following channels.
select {
case s := <-b.newClients:
// There is a new client attached and we
// want to start sending them messages.
b.clients[s] = true
log.Println("Added new client")
case s := <-b.defunctClients:
// A client has dettached and we want to
// stop sending them messages.
delete(b.clients, s)
close(s)
log.Println("Removed client")
case msg := <-b.Messages:
// There is a new message to send. For each
// attached client, push the new message
// into the client's message channel.
for s, _ := range b.clients {
s <- msg
}
log.Printf("Broadcast message to %d clients", len(b.clients))
}
}
}()
}
// This Broker method handles and HTTP request at the "/events/" URL.
//
func (b *Broker) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Make sure that the writer supports flushing.
//
f, ok := w.(http.Flusher)
if !ok {
http.Error(w, "Streaming unsupported!", http.StatusInternalServerError)
return
}
// Create a new channel, over which the broker can
// send this client messages.
messageChan := make(chan string)
// Add this client to the map of those that should
// receive updates
b.newClients <- messageChan
// Listen to the closing of the http connection via the CloseNotifier
notify := w.(http.CloseNotifier).CloseNotify()
go func() {
<-notify
// Remove this client from the map of attached clients
// when `EventHandler` exits.
b.defunctClients <- messageChan
log.Println("HTTP connection just closed.")
}()
// Set the headers related to event streaming.
w.Header().Set("Content-Type", "text/event-stream")
w.Header().Set("Cache-Control", "no-cache")
w.Header().Set("Connection", "keep-alive")
// Don't close the connection, instead loop 10 times,
// sending messages and flushing the response each time
// there is a new message to send along.
//
// NOTE: we could loop endlessly; however, then you
// could not easily detect clients that dettach and the
// server would continue to send them messages long after
// they're gone due to the "keep-alive" header. One of
// the nifty aspects of SSE is that clients automatically
// reconnect when they lose their connection.
//
// A better way to do this is to use the CloseNotifier
// interface that will appear in future releases of
// Go (this is written as of 1.0.3):
// https://code.google.com/p/go/source/detail?name=3292433291b2
//
for {
// Read from our messageChan.
msg, open := <-messageChan
if !open {
// If our messageChan was closed, this means that the client has
// disconnected.
break
}
// Write to the ResponseWriter, `w`.
fmt.Fprintf(w, "data: Message: %s\n\n", msg)
// Flush the response. This is only possible if
// the repsonse supports streaming.
f.Flush()
}
// Done.
log.Println("Finished HTTP request at ", r.URL.Path)
}
// NewBroker creates a new broker instance
func NewBroker() *Broker {
return &Broker{
make(map[chan string]bool),
make(chan (chan string)),
make(chan (chan string)),
make(chan string),
}
}