feat(backup): Add backup/restore to the server

api/http/offlinegate/offlinegate.go

@@ -0,0 +1,71 @@
+package offlinegate
+
+import (
+	"log"
+	"net/http"
+	"sync"
+	"time"
+
+	httperror "github.com/portainer/libhttp/error"
+)
+
+// OfflineGate is a entity that works similar to a mutex with a signaling
+// Only the caller that have Locked an gate can unlock it, otherw will be blocked with a call to Lock.
+// Gate provides a passthrough http middleware that will wait for a locked gate to be unlocked.
+// For a safety reasons, middleware will timeout
+type OfflineGate struct {
+	lock        *sync.Mutex
+	signalingCh chan interface{}
+}
+
+// NewOfflineGate creates a new gate
+func NewOfflineGate() *OfflineGate {
+	return &OfflineGate{
+		lock: &sync.Mutex{},
+	}
+}
+
+// Lock locks readonly gate and returns a function to unlock
+func (o *OfflineGate) Lock() func() {
+	o.lock.Lock()
+	o.signalingCh = make(chan interface{})
+	return o.unlock
+}
+
+func (o *OfflineGate) unlock() {
+	if o.signalingCh == nil {
+		return
+	}
+
+	close(o.signalingCh)
+	o.signalingCh = nil
+	o.lock.Unlock()
+}
+
+// Watch returns a signaling channel.
+// Unless channel is nil, client needs to watch for a signal on a channel to know when gate is unlocked.
+// Signal channel is disposable: onced signaled, has to be disposed and acquired again.
+func (o *OfflineGate) Watch() chan interface{} {
+	return o.signalingCh
+}
+
+// WaitingMiddleware returns an http handler that waits for the gate to be unlocked before continuing
+func (o *OfflineGate) WaitingMiddleware(timeout time.Duration, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		signalingCh := o.Watch()
+
+		if signalingCh != nil {
+			if r.Method != "GET" && r.Method != "HEAD" && r.Method != "OPTIONS" {
+				select {
+				case <-signalingCh:
+				case <-time.After(timeout):
+					log.Println("error: Timeout waiting for the offline gate to signal")
+					httperror.WriteError(w, http.StatusRequestTimeout, "Timeout waiting for the offline gate to signal", http.ErrHandlerTimeout)
+				}
+			}
+		}
+
+		next.ServeHTTP(w, r)
+
+	})
+}