[client] Port the file drop bindings to iOS

The iOS SDK package gets the same platform handle the Android bindings
carry: transfers, receiving policy, and per-sender rules on one profile,
attached to the engine when the client starts. Payloads are path-based
rather than stream-based, since the app group container is readable from
both processes, and the platform sink is dropped for the same reason:
delivery lands on the filesystem directly. The default destination is
seeded in the constructor because the app process opens handles of its
own while the extension is down.

client/ios/NetBirdSDK/filedrop.go

@@ -0,0 +1,198 @@
+//go:build ios
+
+package NetBirdSDK
+
+import (
+	"errors"
+	"fmt"
+	"net/netip"
+	"path/filepath"
+	"sync"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/internal/filedrop"
+	"github.com/netbirdio/netbird/client/internal/profilemanager"
+)
+
+const filedropDataSubdir = "filedrop"
+
+// FileDrop is the platform-facing handle on one profile's file drop state.
+type FileDrop struct {
+	mu        sync.Mutex
+	configDir string
+	profileID string
+	manager   *filedrop.Manager
+	listener  FileDropListener
+}
+
+// NewFileDrop opens the file drop state of the given profile.
+func NewFileDrop(configDir, profileID string) (*FileDrop, error) {
+	if configDir == "" || profileID == "" {
+		return nil, errors.New("file drop requires a config dir and profile ID")
+	}
+
+	prefs, err := NewProfileManager(configDir).impl.ProfilePrefs(profileID)
+	if err != nil {
+		return nil, err
+	}
+
+	fd := &FileDrop{configDir: configDir, profileID: profileID}
+	manager, err := filedrop.NewManager(filedrop.ManagerConfig{
+		Profile: profilemanager.ID(profileID),
+		DataDir: filepath.Join(configDir, filedropDataSubdir, profileID),
+		Store:   filedrop.NewProfileStore(prefs),
+		Events:  fd.publish,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("create file drop manager: %w", err)
+	}
+
+	fd.manager = manager
+	ensureFileDropDestination(fd)
+	return fd, nil
+}
+
+// ProfileID returns the profile this handle belongs to.
+func (f *FileDrop) ProfileID() string {
+	return f.profileID
+}
+
+// SetListener installs the event listener, replacing any previous one.
+func (f *FileDrop) SetListener(listener FileDropListener) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.listener = listener
+}
+
+// Listener returns the installed event listener, nil when there is none.
+func (f *FileDrop) Listener() FileDropListener {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.listener
+}
+
+// RemoveListener stops event delivery.
+func (f *FileDrop) RemoveListener() {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.listener = nil
+}
+
+// Send starts an asynchronous transfer and returns its local transfer ID.
+func (f *FileDrop) Send(peerKey, peerName, peerIP string, payloads *FileDropPayloads) (string, error) {
+	if payloads == nil || payloads.Length() == 0 {
+		return "", errors.New("nothing to send")
+	}
+
+	addr, err := netip.ParseAddr(peerIP)
+	if err != nil {
+		return "", fmt.Errorf("parse peer address %q: %w", peerIP, err)
+	}
+
+	id, err := f.manager.Send(filedrop.PeerKey(peerKey), peerName, addr.Unmap(), payloads.items)
+	if err != nil {
+		return "", err
+	}
+	return string(id), nil
+}
+
+// Accept releases a pending incoming offer for download.
+func (f *FileDrop) Accept(transferID string) error {
+	return f.manager.Accept(filedrop.OfferID(transferID))
+}
+
+// Decline refuses a pending incoming offer.
+func (f *FileDrop) Decline(transferID string) error {
+	return f.manager.Decline(filedrop.OfferID(transferID))
+}
+
+// Cancel aborts a transfer in either direction.
+func (f *FileDrop) Cancel(transferID string) {
+	f.manager.Cancel(filedrop.OfferID(transferID))
+}
+
+// Transfers returns the history, newest first.
+func (f *FileDrop) Transfers() *FileDropTransferArray {
+	transfers := f.manager.Transfers()
+	items := make([]*FileDropTransfer, 0, len(transfers))
+	for _, t := range transfers {
+		items = append(items, toFileDropTransfer(t))
+	}
+	return &FileDropTransferArray{items: items}
+}
+
+// Transfer returns one history entry, or nil when it is unknown.
+func (f *FileDrop) Transfer(transferID string) *FileDropTransfer {
+	for _, t := range f.manager.Transfers() {
+		if string(t.ID) == transferID {
+			return toFileDropTransfer(t)
+		}
+	}
+	return nil
+}
+
+// DeleteTransfer removes one history entry, cancelling it when still live.
+func (f *FileDrop) DeleteTransfer(transferID string) {
+	f.manager.DeleteTransfer(filedrop.OfferID(transferID))
+}
+
+// Mode returns the base receiving mode.
+func (f *FileDrop) Mode() int {
+	return int(f.manager.Policy().Get().Mode)
+}
+
+// SetMode changes the base receiving mode.
+func (f *FileDrop) SetMode(mode int) error {
+	return f.manager.Policy().SetMode(filedrop.Mode(mode))
+}
+
+// DestinationDir returns the directory received files are delivered to.
+func (f *FileDrop) DestinationDir() string {
+	return f.manager.DestinationDir()
+}
+
+// SetDestinationDir persists the delivery directory.
+func (f *FileDrop) SetDestinationDir(dir string) error {
+	return f.manager.SetDestinationDir(dir)
+}
+
+// PeerRule returns the rule stored for one sender.
+func (f *FileDrop) PeerRule(peerKey string) int {
+	return int(f.manager.Policy().Get().Senders[filedrop.PeerKey(peerKey)])
+}
+
+// SetPeerRule sets or clears the exception for one sender.
+func (f *FileDrop) SetPeerRule(peerKey string, rule int) error {
+	return f.manager.SetSenderRule(filedrop.PeerKey(peerKey), filedrop.SenderRule(rule))
+}
+
+// Close stops the receiver and aborts every outgoing transfer.
+func (f *FileDrop) Close() error {
+	f.RemoveListener()
+	return f.manager.Close()
+}
+
+func (f *FileDrop) publish(kind filedrop.EventKind, transfer filedrop.Transfer) {
+	f.mu.Lock()
+	listener := f.listener
+	f.mu.Unlock()
+	if listener == nil {
+		return
+	}
+	listener.OnFileDropEvent(int(kind), toFileDropTransfer(transfer))
+}
+
+func defaultFileDropDir(configDir, profileID string) string {
+	return filepath.Join(configDir, filedropDataSubdir, profileID, "incoming")
+}
+
+func ensureFileDropDestination(fd *FileDrop) {
+	if fd.DestinationDir() != "" {
+		return
+	}
+	dir := defaultFileDropDir(fd.configDir, fd.profileID)
+	if err := fd.SetDestinationDir(dir); err != nil {
+		log.Warnf("failed to set default file drop destination: %v", err)
+	}
+}