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handler.go
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handler.go
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// Copyright © 2019 The Things Network Foundation, The Things Industries B.V.
//
// 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 events
import (
"context"
"time"
)
// Handler interface for event listeners.
type Handler interface {
Notify(Event)
}
type handlerFunc struct {
handler func(Event)
}
func (f handlerFunc) Notify(evt Event) { f.handler(evt) }
// HandlerFunc makes the func implement the Handler interface.
func HandlerFunc(handler func(Event)) Handler {
return &handlerFunc{handler}
}
// Channel is a channel of Events that can be used as an event handler.
// The channel should be buffered, events will be dropped if the channel blocks.
// It is typically not safe to close this channel until you're absolutely sure
// that it is no longer registered as an event handler.
type Channel chan Event
// Notify implements the Handler interface.
func (ch Channel) Notify(evt Event) {
select {
case ch <- evt:
default:
channelDropped.WithLabelValues(evt.Name()).Inc()
}
}
// ReceiveTimeout returns the next event from the channel or returns nil after a timeout.
func (ch Channel) ReceiveTimeout(timeout time.Duration) Event {
select {
case evt := <-ch:
return evt
case <-time.After(timeout):
return nil
}
}
// ReceiveContext returns the next event from the channel or returns nil when the context is done.
func (ch Channel) ReceiveContext(ctx context.Context) Event {
select {
case evt := <-ch:
return evt
case <-ctx.Done():
return nil
}
}
// ContextHandler delivers events to the Handler as long as ctx.Err() is non-nil.
func ContextHandler(ctx context.Context, handler Handler) Handler {
return &contextHandler{Context: ctx, Handler: handler}
}
type contextHandler struct {
context.Context
Handler
}
func (hdl contextHandler) Notify(evt Event) {
if hdl.Err() == nil {
hdl.Handler.Notify(evt)
}
}