multi: allow client to link autopilot sessions

autopilotserver/interface.go

@@ -29,7 +29,7 @@ type Autopilot interface {
 	// remains active.
 	RegisterSession(ctx context.Context, pubKey *btcec.PublicKey,
 		mailboxAddr string, devServer bool,
-		featureConf map[string][]byte, prevLocal *btcec.PublicKey,
+		featureConf map[string][]byte, linkedGroupKey *btcec.PublicKey,
 		linkSig []byte) (*btcec.PublicKey, error)
 
 	// ActivateSession attempts to inform the autopilot server that the

cmd/litcli/autopilot.go

@@ -65,6 +65,11 @@ var addAutopilotSessionCmd = cli.Command{
 				"perform actions on. In the " +
 				"form of: peerID1,peerID2,...",
 		},
+		cli.StringFlag{
+			Name: "group_id",
+			Usage: "The hex encoded group ID of the session " +
+				"group to link this one to",
+		},
 	},
 }
 
@@ -224,6 +229,14 @@ func initAutopilotSession(ctx *cli.Context) error {
 		}
 	}
 
+	var groupID []byte
+	if ctx.IsSet("group_id") {
+		groupID, err = hex.DecodeString(ctx.String("group_id"))
+		if err != nil {
+			return err
+		}
+	}
+
 	resp, err := client.AddAutopilotSession(
 		ctxb, &litrpc.AddAutopilotSessionRequest{
 			Label:                  ctx.String("label"),
@@ -231,6 +244,7 @@ func initAutopilotSession(ctx *cli.Context) error {
 			MailboxServerAddr:      ctx.String("mailboxserveraddr"),
 			DevServer:              ctx.Bool("devserver"),
 			Features:               featureMap,
+			LinkedGroupId:          groupID,
 		},
 	)
 	if err != nil {

session_rpcserver.go

@@ -10,6 +10,8 @@ import (
 	"time"
 
 	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightninglabs/lightning-node-connect/mailbox"
 	"github.com/lightninglabs/lightning-terminal/accounts"
 	"github.com/lightninglabs/lightning-terminal/autopilotserver"
@@ -1010,6 +1012,52 @@ func (s *sessionRpcServer) AddAutopilotSession(ctx context.Context,
 		caveats = append(caveats, firewall.MetaPrivacyCaveat)
 	}
 
+	// If a previous session ID has been set to link this new one to, we
+	// first check if we have the referenced session, and we make sure it
+	// has been revoked.
+	var (
+		linkedGroupID      *session.ID
+		linkedGroupSession *session.Session
+	)
+	if len(req.LinkedGroupId) != 0 {
+		var groupID session.ID
+		copy(groupID[:], req.LinkedGroupId)
+
+		// Check that the group actually does exist.
+		groupSess, err := s.cfg.db.GetSessionByID(groupID)
+		if err != nil {
+			return nil, err
+		}
+
+		// Ensure that the linked session is in fact the first session
+		// in its group.
+		if groupSess.ID != groupSess.GroupID {
+			return nil, fmt.Errorf("can not link to session "+
+				"%x since it is not the first in the session "+
+				"group %x", groupSess.ID, groupSess.GroupID)
+		}
+
+		// Now we need to check that all the sessions in the group are
+		// no longer active.
+		ok, err := s.cfg.db.CheckSessionGroupPredicate(
+			groupID, func(s *session.Session) bool {
+				return s.State == session.StateRevoked ||
+					s.State == session.StateExpired
+			},
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		if !ok {
+			return nil, fmt.Errorf("a linked session in group "+
+				"%x is still active", groupID)
+		}
+
+		linkedGroupID = &groupID
+		linkedGroupSession = groupSess
+	}
+
 	s.sessRegMu.Lock()
 	defer s.sessRegMu.Unlock()
 
@@ -1021,14 +1069,32 @@ func (s *sessionRpcServer) AddAutopilotSession(ctx context.Context,
 	sess, err := session.NewSession(
 		id, localPrivKey, req.Label, session.TypeAutopilot, expiry,
 		req.MailboxServerAddr, req.DevServer, perms, caveats,
-		featureConfig, privacy, nil,
+		featureConfig, privacy, linkedGroupID,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error creating new session: %v", err)
 	}
 
+	// If this session is being linked to a previous one, then we need to
+	// use the previous session's local private key to sign the new
+	// session's public key in order to prove to the Autopilot server that
+	// the two session's belong to the same owner.
+	var (
+		linkSig        []byte
+		prevSessionPub *btcec.PublicKey
+	)
+	if linkedGroupID != nil {
+		privKey := linkedGroupSession.LocalPrivateKey
+		pubKey := sess.LocalPublicKey.SerializeCompressed()
+
+		msg := chainhash.HashB(pubKey)
+		linkSig = ecdsa.Sign(privKey, msg).Serialize()
+
+		prevSessionPub = linkedGroupSession.LocalPublicKey
+	}
+
 	// Register all the privacy map pairs for this session ID.
-	privDB := s.cfg.privMap(sess.ID)
+	privDB := s.cfg.privMap(sess.GroupID)
 	err = privDB.Update(func(tx firewalldb.PrivacyMapTx) error {
 		for r, p := range privacyMapPairs {
 			err := tx.NewPair(r, p)
@@ -1045,7 +1111,7 @@ func (s *sessionRpcServer) AddAutopilotSession(ctx context.Context,
 	// Attempt to register the session with the Autopilot server.
 	remoteKey, err := s.cfg.autopilot.RegisterSession(
 		ctx, sess.LocalPublicKey, sess.ServerAddr, sess.DevServer,
-		featureConfig, nil, nil,
+		featureConfig, prevSessionPub, linkSig,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error registering session with "+