forked from looplab/eventhorizon
/
eventbus.go
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/
eventbus.go
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// Copyright (c) 2017 - The Event Horizon authors.
//
// 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 httputils
import (
"context"
"log"
"net/http"
"sync"
"github.com/gorilla/websocket"
eh "github.com/2908755265/eventhorizon"
"github.com/2908755265/eventhorizon/codec/json"
)
// EventBusHandler is a simple event handler for observing events.
type EventBusHandler struct {
// Use the default options.
upgrader websocket.Upgrader
chs []chan eh.Event
chsMu sync.RWMutex
codec eh.EventCodec
}
// NewEventBusHandler creates a new EventBusHandler.
func NewEventBusHandler() *EventBusHandler {
return &EventBusHandler{
codec: &json.EventCodec{},
}
}
// HandlerType implements the HandlerType method of the eventhorizon.EventHandler interface.
func (h *EventBusHandler) HandlerType() eh.EventHandlerType {
return eh.EventHandlerType("websocket")
}
// HandleEvent implements the HandleEvent method of the eventhorizon.EventHandler interface.
func (h *EventBusHandler) HandleEvent(ctx context.Context, event eh.Event) error {
h.chsMu.RLock()
defer h.chsMu.RUnlock()
// Send to all websocket connections.
for _, ch := range h.chs {
select {
case ch <- event:
default:
log.Printf("eventhorizon: publish queue full in websocket event bus: %s", event)
}
}
return nil
}
// ServeHTTP implements the ServeHTTP method of the http.Handler interface
// by upgrading requests to websocket connections which will receive all events.
func (h *EventBusHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
c, err := h.upgrader.Upgrade(w, r, nil)
if err != nil {
log.Printf("eventhorizon: could not upgrade websocket: %s", err)
return
}
defer c.Close()
ch := make(chan eh.Event, 10)
h.chsMu.Lock()
h.chs = append(h.chs, ch)
h.chsMu.Unlock()
for event := range ch {
data, err := h.codec.MarshalEvent(context.Background(), event)
if err != nil {
log.Printf("eventhorizon: could not marshal websocket event: %s", err)
break
}
if err := c.WriteMessage(websocket.TextMessage, data); err != nil {
log.Printf("eventhorizon: could not write to websocket: %s", err)
break
}
}
}