[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/relay/client/peer_subscription.go

@@ -0,0 +1,191 @@
+package client
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/relay/messages"
+)
+
+const (
+	OpenConnectionTimeout = 30 * time.Second
+)
+
+type relayedConnWriter interface {
+	Write(p []byte) (n int, err error)
+}
+
+// PeersStateSubscription manages subscriptions to peer state changes (online/offline)
+// over a relay connection. It allows tracking peers' availability and handling offline
+// events via a callback. We get online notification from the server only once.
+type PeersStateSubscription struct {
+	log             *log.Entry
+	relayConn       relayedConnWriter
+	offlineCallback func(peerIDs []messages.PeerID)
+
+	listenForOfflinePeers map[messages.PeerID]struct{}
+	waitingPeers          map[messages.PeerID]chan struct{}
+	mu                    sync.Mutex // Mutex to protect access to waitingPeers and listenForOfflinePeers
+}
+
+func NewPeersStateSubscription(log *log.Entry, relayConn relayedConnWriter, offlineCallback func(peerIDs []messages.PeerID)) *PeersStateSubscription {
+	return &PeersStateSubscription{
+		log:                   log,
+		relayConn:             relayConn,
+		offlineCallback:       offlineCallback,
+		listenForOfflinePeers: make(map[messages.PeerID]struct{}),
+		waitingPeers:          make(map[messages.PeerID]chan struct{}),
+	}
+}
+
+// OnPeersOnline should be called when a notification is received that certain peers have come online.
+// It checks if any of the peers are being waited on and signals their availability.
+func (s *PeersStateSubscription) OnPeersOnline(peersID []messages.PeerID) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	for _, peerID := range peersID {
+		waitCh, ok := s.waitingPeers[peerID]
+		if !ok {
+			// If meanwhile the peer was unsubscribed, we don't need to signal it
+			continue
+		}
+
+		waitCh <- struct{}{}
+		delete(s.waitingPeers, peerID)
+		close(waitCh)
+	}
+}
+
+func (s *PeersStateSubscription) OnPeersWentOffline(peersID []messages.PeerID) {
+	s.mu.Lock()
+	relevantPeers := make([]messages.PeerID, 0, len(peersID))
+	for _, peerID := range peersID {
+		if _, ok := s.listenForOfflinePeers[peerID]; ok {
+			relevantPeers = append(relevantPeers, peerID)
+		}
+	}
+	s.mu.Unlock()
+
+	if len(relevantPeers) > 0 {
+		s.offlineCallback(relevantPeers)
+	}
+}
+
+// WaitToBeOnlineAndSubscribe waits for a specific peer to come online and subscribes to its state changes.
+func (s *PeersStateSubscription) WaitToBeOnlineAndSubscribe(ctx context.Context, peerID messages.PeerID) error {
+	// Check if already waiting for this peer
+	s.mu.Lock()
+	if _, exists := s.waitingPeers[peerID]; exists {
+		s.mu.Unlock()
+		return errors.New("already waiting for peer to come online")
+	}
+
+	// Create a channel to wait for the peer to come online
+	waitCh := make(chan struct{}, 1)
+	s.waitingPeers[peerID] = waitCh
+	s.listenForOfflinePeers[peerID] = struct{}{}
+	s.mu.Unlock()
+
+	if err := s.subscribeStateChange(peerID); err != nil {
+		s.log.Errorf("failed to subscribe to peer state: %s", err)
+		s.mu.Lock()
+		if ch, exists := s.waitingPeers[peerID]; exists && ch == waitCh {
+			close(waitCh)
+			delete(s.waitingPeers, peerID)
+			delete(s.listenForOfflinePeers, peerID)
+		}
+		s.mu.Unlock()
+		return err
+	}
+
+	// Wait for peer to come online or context to be cancelled
+	timeoutCtx, cancel := context.WithTimeout(ctx, OpenConnectionTimeout)
+	defer cancel()
+	select {
+	case _, ok := <-waitCh:
+		if !ok {
+			return fmt.Errorf("wait for peer to come online has been cancelled")
+		}
+
+		s.log.Debugf("peer %s is now online", peerID)
+		return nil
+	case <-timeoutCtx.Done():
+		s.log.Debugf("context timed out while waiting for peer %s to come online", peerID)
+		if err := s.unsubscribeStateChange([]messages.PeerID{peerID}); err != nil {
+			s.log.Errorf("failed to unsubscribe from peer state: %s", err)
+		}
+		s.mu.Lock()
+		if ch, exists := s.waitingPeers[peerID]; exists && ch == waitCh {
+			close(waitCh)
+			delete(s.waitingPeers, peerID)
+			delete(s.listenForOfflinePeers, peerID)
+		}
+		s.mu.Unlock()
+		return timeoutCtx.Err()
+	}
+}
+
+func (s *PeersStateSubscription) UnsubscribeStateChange(peerIDs []messages.PeerID) error {
+	msgErr := s.unsubscribeStateChange(peerIDs)
+
+	s.mu.Lock()
+	for _, peerID := range peerIDs {
+		if wch, ok := s.waitingPeers[peerID]; ok {
+			close(wch)
+			delete(s.waitingPeers, peerID)
+		}
+
+		delete(s.listenForOfflinePeers, peerID)
+	}
+	s.mu.Unlock()
+
+	return msgErr
+}
+
+func (s *PeersStateSubscription) Cleanup() {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	for _, waitCh := range s.waitingPeers {
+		close(waitCh)
+	}
+
+	s.waitingPeers = make(map[messages.PeerID]chan struct{})
+	s.listenForOfflinePeers = make(map[messages.PeerID]struct{})
+}
+
+func (s *PeersStateSubscription) subscribeStateChange(peerID messages.PeerID) error {
+	msgs, err := messages.MarshalSubPeerStateMsg([]messages.PeerID{peerID})
+	if err != nil {
+		return err
+	}
+
+	for _, msg := range msgs {
+		if _, err := s.relayConn.Write(msg); err != nil {
+			return err
+		}
+
+	}
+	return nil
+}
+
+func (s *PeersStateSubscription) unsubscribeStateChange(peerIDs []messages.PeerID) error {
+	msgs, err := messages.MarshalUnsubPeerStateMsg(peerIDs)
+	if err != nil {
+		return err
+	}
+
+	var connWriteErr error
+	for _, msg := range msgs {
+		if _, err := s.relayConn.Write(msg); err != nil {
+			connWriteErr = err
+		}
+	}
+	return connWriteErr
+}