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/gopkg.in/olivere/elastic.v3/search_queries_missing.go

@@ -0,0 +1,67 @@
+// Copyright 2012-2015 Oliver Eilhard. All rights reserved.
+// Use of this source code is governed by a MIT-license.
+// See http://olivere.mit-license.org/license.txt for details.
+
+package elastic
+
+// MissingQuery returns documents that have only null values or no value
+// in the original field.
+//
+// For details, see:
+// https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-missing-query.html
+type MissingQuery struct {
+	name      string
+	queryName string
+	nullValue *bool
+	existence *bool
+}
+
+// NewMissingQuery creates and initializes a new MissingQuery.
+func NewMissingQuery(name string) *MissingQuery {
+	return &MissingQuery{name: name}
+}
+
+// QueryName sets the query name for the query that can be used when
+// searching for matched filters hit.
+func (q *MissingQuery) QueryName(queryName string) *MissingQuery {
+	q.queryName = queryName
+	return q
+}
+
+// NullValue indicates whether the missing filter automatically includes
+// fields with null value configured in the mappings. Defaults to false.
+func (q *MissingQuery) NullValue(nullValue bool) *MissingQuery {
+	q.nullValue = &nullValue
+	return q
+}
+
+// Existence indicates whether the missing filter includes documents where
+// the field doesn't exist in the docs.
+func (q *MissingQuery) Existence(existence bool) *MissingQuery {
+	q.existence = &existence
+	return q
+}
+
+// Source returns JSON for the query.
+func (q *MissingQuery) Source() (interface{}, error) {
+	// {
+	//   "missing" : {
+	//     "field" : "..."
+	//   }
+	// }
+
+	source := make(map[string]interface{})
+	params := make(map[string]interface{})
+	source["missing"] = params
+	params["field"] = q.name
+	if q.nullValue != nil {
+		params["null_value"] = *q.nullValue
+	}
+	if q.existence != nil {
+		params["existence"] = *q.existence
+	}
+	if q.queryName != "" {
+		params["_name"] = q.queryName
+	}
+	return source, nil
+}