MYNEWT-822 newtmgr bll - reconn on spvtmo.

The first data packet to be exchanged over a BLE connection has a high
probability of triggering a disconnect. The sending controller uses this
packet to determine if the connection attempt was successful in the
first place, and it does not get retried if it gets dropped.

In the case of newtmgr, the first data packet gets sent during ATT MTU
negotiation. The bhd (blehostd) transports recover from a disconnect
during ATT MTU negotiation by reopening the session.

The ble transports (native BLE) do not recover from such a disconnect.
We should add the same recovery logic for the ble transports that has
already been implemented for bhd.

newtmgr/bll/bll_oic_sesn.go

@@ -196,31 +196,55 @@ func (bls *BllOicSesn) exchangeMtu() error {
 	return nil
 }
 
-func (bls *BllOicSesn) Open() error {
+// @return bool                 Whether to retry the open attempt; false
+//                                  on success.
+//         error                The cause of a failed open; nil on success.
+func (bls *BllOicSesn) openOnce() (bool, error) {
 	if bls.IsOpen() {
-		return nmxutil.NewSesnAlreadyOpenError(
+		return false, nmxutil.NewSesnAlreadyOpenError(
 			"Attempt to open an already-open bll session")
 	}
 
 	d, err := omp.NewDispatcher(true, 3)
 	if err != nil {
-		return err
+		return false, err
 	}
 	bls.d = d
 
 	if err := bls.connect(); err != nil {
-		return err
+		return false, err
 	}
 
 	if err := bls.exchangeMtu(); err != nil {
-		return err
+		return true, err
 	}
 
 	if err := bls.discoverAll(); err != nil {
-		return err
+		return false, err
 	}
 
 	if err := bls.subscribe(); err != nil {
+		return false, err
+	}
+
+	return false, nil
+}
+
+func (bls *BllOicSesn) Open() error {
+	var err error
+
+	for i := 0; i < bls.cfg.ConnTries; i++ {
+		var retry bool
+
+		retry, err = bls.openOnce()
+		if !retry {
+			break
+		}
+	}
+
+	if err != nil {
+		// Ensure the session is closed.
+		bls.Close()
 		return err
 	}
 

newtmgr/bll/bll_plain_sesn.go

@@ -140,25 +140,49 @@ func (bps *BllPlainSesn) exchangeMtu() error {
 	return nil
 }
 
-func (bps *BllPlainSesn) Open() error {
+// @return bool                 Whether to retry the open attempt; false
+//                                  on success.
+//         error                The cause of a failed open; nil on success.
+func (bps *BllPlainSesn) openOnce() (bool, error) {
 	if bps.IsOpen() {
-		return nmxutil.NewSesnAlreadyOpenError(
+		return false, nmxutil.NewSesnAlreadyOpenError(
 			"Attempt to open an already-open bll session")
 	}
 
 	if err := bps.connect(); err != nil {
-		return err
+		return false, err
 	}
 
 	if err := bps.exchangeMtu(); err != nil {
-		return err
+		return true, err
 	}
 
 	if err := bps.discoverAll(); err != nil {
-		return err
+		return false, err
 	}
 
 	if err := bps.subscribe(); err != nil {
+		return false, err
+	}
+
+	return false, nil
+}
+
+func (bps *BllPlainSesn) Open() error {
+	var err error
+
+	for i := 0; i < bps.cfg.ConnTries; i++ {
+		var retry bool
+
+		retry, err = bps.openOnce()
+		if !retry {
+			break
+		}
+	}
+
+	if err != nil {
+		// Ensure the session is closed.
+		bps.Close()
 		return err
 	}
 

newtmgr/bll/bll_sesn_cfg.go

@@ -32,11 +32,13 @@ type BllSesnCfg struct {
 	AdvFilter    ble.AdvFilter
 	PreferredMtu int
 	ConnTimeout  time.Duration
+	ConnTries    int
 }
 
 func NewBllSesnCfg() BllSesnCfg {
 	return BllSesnCfg{
 		PreferredMtu: 527,
 		ConnTimeout:  10 * time.Second,
+		ConnTries:    3,
 	}
 }