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switch.go
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/
switch.go
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/*
* Copyright 2018 Comcast Cable Communications Management, LLC
*
* 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 handlers
import (
"net/http"
"sync/atomic"
)
// SwitchHandler is an HTTP Wrapper that allows users to update the underlying handler in-place
// once associated with a net.Listener
type SwitchHandler struct {
mux http.Handler
oldMux http.Handler
reloading int32
}
// NewSwitchHandler returns a New *SwitchHandler
func NewSwitchHandler(router http.Handler) *SwitchHandler {
return &SwitchHandler{mux: router, oldMux: router}
}
// ServeHTTP serves an HTTP Request
func (s *SwitchHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
if s.isReloading() {
s.oldMux.ServeHTTP(w, r)
return
}
s.mux.ServeHTTP(w, r)
}
// Update atomically changes the underlying handler without impacting user requests or uptime
func (s *SwitchHandler) Update(h http.Handler) {
s.oldMux = s.mux
s.setReloading(true)
s.mux = h
s.setReloading(false)
}
// Handler returns the current mux
func (s *SwitchHandler) Handler() http.Handler {
if s.isReloading() {
return s.oldMux
}
return s.mux
}
func (s *SwitchHandler) isReloading() bool {
return atomic.LoadInt32(&s.reloading) != 0
}
func (s *SwitchHandler) setReloading(isReloading bool) {
if isReloading {
atomic.StoreInt32(&s.reloading, 1)
return
}
atomic.StoreInt32(&s.reloading, 0)
}