fix(offlinegate): fix data race in offlinegate EE-2713 (#6626)

api/http/offlinegate/offlinegate.go

@@ -3,69 +3,48 @@ package offlinegate
 import (
 	"log"
 	"net/http"
-	"sync"
+	"strings"
 	"time"
 
 	httperror "github.com/portainer/libhttp/error"
+	lock "github.com/viney-shih/go-lock"
 )
 
-// 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.
+// OfflineGate is an entity that works similar to a mutex with signaling
+// Only the caller that has Locked a gate can unlock it, otherwise it 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
+// For safety reasons, the middleware will timeout
 type OfflineGate struct {
-	lock        *sync.Mutex
-	signalingCh chan interface{}
+	lock *lock.CASMutex
 }
 
 // NewOfflineGate creates a new gate
 func NewOfflineGate() *OfflineGate {
 	return &OfflineGate{
-		lock: &sync.Mutex{},
+		lock: lock.NewCASMutex(),
 	}
 }
 
 // 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
+	return o.lock.Unlock
 }
 
 // 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)
-				}
-			}
+		if r.Method == "GET" || r.Method == "HEAD" || r.Method == "OPTIONS" || strings.HasPrefix(r.URL.Path, "/api/backup") || strings.HasPrefix(r.URL.Path, "/api/restore") {
+			next.ServeHTTP(w, r)
+			return
 		}
 
+		if !o.lock.RTryLockWithTimeout(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)
+			return
+		}
 		next.ServeHTTP(w, r)
-
+		o.lock.RUnlock()
 	})
 }