featurebase/event.go

// Copyright 2017 Pilosa Corp.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package pilosa

// NodeEventType are the types of events that can be sent from the
// ChannelEventDelegate.
type NodeEventType int

const (
	NodeJoin NodeEventType = iota
	NodeLeave
	NodeUpdate
)

// NodeEvent is a single event related to node activity in the cluster.
type NodeEvent struct {
	Event NodeEventType
	Node  *Node
}

// EventHandler is the interface for the pilosa object which knows how to
// handle broadcast messages. (Hint: this is implemented by pilosa.Server)
type EventHandler interface {
	ReceiveEvent(e *NodeEvent) error
}

// EventReceiver is the interface for the object which will listen for and
// decode broadcast messages before passing them to pilosa to handle. The
// implementation of this could be an http server which listens for messages,
// gets the protobuf payload, and then passes it to
// EventHandler.ReceiveMessage.
type EventReceiver interface {
	// Start starts listening for broadcast messages - it should return
	// immediately, spawning a goroutine if necessary.
	Start(EventHandler) error
}

type nopEventReceiver struct{}

func (n *nopEventReceiver) Start(e EventHandler) error { return nil }

// NopEventReceiver is a no-op implementation of the EventReceiver.
var NopEventReceiver = &nopEventReceiver{}