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/allocator.go

@@ -0,0 +1,106 @@
+package amqp
+
+import (
+	"bytes"
+	"fmt"
+	"math/big"
+)
+
+const (
+	free      = 0
+	allocated = 1
+)
+
+// allocator maintains a bitset of allocated numbers.
+type allocator struct {
+	pool *big.Int
+	last int
+	low  int
+	high int
+}
+
+// NewAllocator reserves and frees integers out of a range between low and
+// high.
+//
+// O(N) worst case space used, where N is maximum allocated, divided by
+// sizeof(big.Word)
+func newAllocator(low, high int) *allocator {
+	return &allocator{
+		pool: big.NewInt(0),
+		last: low,
+		low:  low,
+		high: high,
+	}
+}
+
+// String returns a string describing the contents of the allocator like
+// "allocator[low..high] reserved..until"
+//
+// O(N) where N is high-low
+func (a allocator) String() string {
+	b := &bytes.Buffer{}
+	fmt.Fprintf(b, "allocator[%d..%d]", a.low, a.high)
+
+	for low := a.low; low <= a.high; low++ {
+		high := low
+		for a.reserved(high) && high <= a.high {
+			high++
+		}
+
+		if high > low+1 {
+			fmt.Fprintf(b, " %d..%d", low, high-1)
+		} else if high > low {
+			fmt.Fprintf(b, " %d", high-1)
+		}
+
+		low = high
+	}
+	return b.String()
+}
+
+// Next reserves and returns the next available number out of the range between
+// low and high.  If no number is available, false is returned.
+//
+// O(N) worst case runtime where N is allocated, but usually O(1) due to a
+// rolling index into the oldest allocation.
+func (a *allocator) next() (int, bool) {
+	wrapped := a.last
+
+	// Find trailing bit
+	for ; a.last <= a.high; a.last++ {
+		if a.reserve(a.last) {
+			return a.last, true
+		}
+	}
+
+	// Find preceeding free'd pool
+	a.last = a.low
+
+	for ; a.last < wrapped; a.last++ {
+		if a.reserve(a.last) {
+			return a.last, true
+		}
+	}
+
+	return 0, false
+}
+
+// reserve claims the bit if it is not already claimed, returning true if
+// succesfully claimed.
+func (a *allocator) reserve(n int) bool {
+	if a.reserved(n) {
+		return false
+	}
+	a.pool.SetBit(a.pool, n-a.low, allocated)
+	return true
+}
+
+// reserved returns true if the integer has been allocated
+func (a *allocator) reserved(n int) bool {
+	return a.pool.Bit(n-a.low) == allocated
+}
+
+// release frees the use of the number for another allocation
+func (a *allocator) release(n int) {
+	a.pool.SetBit(a.pool, n-a.low, free)
+}