api: Implement bucket notification. (#2271)

* Implement basic S3 notifications through queues

Supports multiple queues and three basic queue types:

1. NilQueue -- messages don't get sent anywhere
2. LogQueue -- messages get logged
3. AmqpQueue -- messages are sent to an AMQP queue

* api: Implement bucket notification.

Supports two different queue types

- AMQP
- ElasticSearch.

* Add support for redis

vendor/github.com/streadway/amqp/confirms.go

@@ -0,0 +1,93 @@
+package amqp
+
+import "sync"
+
+// confirms resequences and notifies one or multiple publisher confirmation listeners
+type confirms struct {
+	m         sync.Mutex
+	listeners []chan Confirmation
+	sequencer map[uint64]Confirmation
+	published uint64
+	expecting uint64
+}
+
+// newConfirms allocates a confirms
+func newConfirms() *confirms {
+	return &confirms{
+		sequencer: map[uint64]Confirmation{},
+		published: 0,
+		expecting: 1,
+	}
+}
+
+func (c *confirms) Listen(l chan Confirmation) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	c.listeners = append(c.listeners, l)
+}
+
+// publish increments the publishing counter
+func (c *confirms) Publish() uint64 {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	c.published++
+	return c.published
+}
+
+// confirm confirms one publishing, increments the expecting delivery tag, and
+// removes bookkeeping for that delivery tag.
+func (c *confirms) confirm(confirmation Confirmation) {
+	delete(c.sequencer, c.expecting)
+	c.expecting++
+	for _, l := range c.listeners {
+		l <- confirmation
+	}
+}
+
+// resequence confirms any out of order delivered confirmations
+func (c *confirms) resequence() {
+	for c.expecting <= c.published {
+		sequenced, found := c.sequencer[c.expecting]
+		if !found {
+			return
+		}
+		c.confirm(sequenced)
+	}
+}
+
+// one confirms one publishing and all following in the publishing sequence
+func (c *confirms) One(confirmed Confirmation) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	if c.expecting == confirmed.DeliveryTag {
+		c.confirm(confirmed)
+	} else {
+		c.sequencer[confirmed.DeliveryTag] = confirmed
+	}
+	c.resequence()
+}
+
+// multiple confirms all publishings up until the delivery tag
+func (c *confirms) Multiple(confirmed Confirmation) {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	for c.expecting <= confirmed.DeliveryTag {
+		c.confirm(Confirmation{c.expecting, confirmed.Ack})
+	}
+}
+
+// Close closes all listeners, discarding any out of sequence confirmations
+func (c *confirms) Close() error {
+	c.m.Lock()
+	defer c.m.Unlock()
+
+	for _, l := range c.listeners {
+		close(l)
+	}
+	c.listeners = nil
+	return nil
+}