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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"
"fmt"
"log"
"net/http"
eh "github.com/firawe/eventhorizon"
"github.com/gorilla/websocket"
)
var upgrader = websocket.Upgrader{} // use default options
// EventHandler is a simple event handler for observing events.
type handler struct {
id string
ch chan eh.Event
}
// HandlerType implements the HandlerType method of the eventhorizon.EventHandler interface.
func (h *handler) HandlerType() eh.EventHandlerType {
return eh.EventHandlerType("websocket_" + h.id)
}
// HandleEvent implements the HandleEvent method of the eventhorizon.EventHandler interface.
func (h *handler) HandleEvent(ctx context.Context, event eh.Event) error {
select {
case h.ch <- event:
default:
return fmt.Errorf("missed event: %s", event)
}
return nil
}
// EventBusHandler is a Websocket handler for eventhorizon.Events. Events will
// be forwarded to all requests that have been upgraded to websockets.
// TODO: Send events as JSON.
func EventBusHandler(eventBus eh.EventBus, m eh.EventMatcher, id string) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
c, err := upgrader.Upgrade(w, r, nil)
if err != nil {
log.Print("upgrade:", err)
return
}
defer c.Close()
h := &handler{
id: id,
ch: make(chan eh.Event, 10),
}
eventBus.AddObserver(m, h)
for event := range h.ch {
if err := c.WriteMessage(websocket.TextMessage, []byte(event.String())); err != nil {
log.Println("write:", err)
break
}
}
})
}