harness-drone/server/pubsub/channel.go

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package pubsub
import (
"time"
)
type Channel struct {
record bool
history []interface{}
timeout time.Duration
closed chan bool
broadcast chan interface{}
subscribe chan *Subscription
unsubscribe chan *Subscription
subscriptions map[*Subscription]bool
}
func NewChannel(opts *Opts) *Channel {
return &Channel{
timeout: opts.Timeout,
record: opts.Record,
history: make([]interface{}, 0),
closed: make(chan bool),
broadcast: make(chan interface{}),
subscribe: make(chan *Subscription),
unsubscribe: make(chan *Subscription),
subscriptions: make(map[*Subscription]bool),
}
}
func (c *Channel) Publish(data interface{}) {
c.broadcast <- data
return
}
func (c *Channel) Subscribe() *Subscription {
s := NewSubscription(c)
c.subscribe <- s
return s
}
func (c *Channel) Close() {
go func() { c.closed <- true }()
}
func (c *Channel) start() {
// make sure we don't bring down the application
// if somehow we encounter a nil pointer or some
// other unexpected behavior.
defer func() {
recover()
}()
// timeout the channel after N duration
// ignore the timeout if set to 0
var timeout <-chan time.Time
if c.timeout > 0 {
timeout = time.After(c.timeout)
}
for {
select {
case sub := <-c.unsubscribe:
delete(c.subscriptions, sub)
close(sub.send)
case sub := <-c.subscribe:
c.subscriptions[sub] = true
// if we are recording the output
// we should send it to the subscriber
// upon first connecting.
if c.record && len(c.history) > 0 {
history := make([]interface{}, len(c.history))
copy(history, c.history)
go replay(sub, history)
}
case msg := <-c.broadcast:
// if we are recording the output, append
// the message to the history
if c.record {
c.history = append(c.history, msg)
}
// loop through each subscription and
// send the message.
for sub := range c.subscriptions {
select {
case sub.send <- msg:
// do nothing
default:
sub.Close()
}
}
case <-timeout:
c.Close()
case <-c.closed:
c.stop()
return
}
}
}
func replay(s *Subscription, history []interface{}) {
for _, msg := range history {
s.send <- msg
}
}
func (c *Channel) stop() {
for sub := range c.subscriptions {
sub.Close()
}
}