backend: add ManualReconnect method and call on iOS

When the iOS app goes into the background, its TCP
connetions (Electrum server connetions) are killed after a
while (~30s).

When the user goes back into the app, we want to immediatelly trigger
a reconnect, not waiting for the regular 30s reconnect timer.

backend/backend.go

@@ -538,6 +538,43 @@ func (backend *Backend) Coin(code coinpkg.Code) (coinpkg.Coin, error) {
 	return coin, nil
 }
 
+// ManualReconnect triggers reconnecting to Electrum servers if their connection is down.
+// Only coin connections that were previously established are reconnected.
+// Calling this is a no-op for coins that are already connected.
+func (backend *Backend) ManualReconnect() {
+	var electrumCoinCodes []coinpkg.Code
+	if backend.arguments.Testing() {
+		electrumCoinCodes = []coinpkg.Code{
+			coinpkg.CodeTBTC,
+			coinpkg.CodeTLTC,
+		}
+	} else {
+		electrumCoinCodes = []coinpkg.Code{
+			coinpkg.CodeBTC,
+			coinpkg.CodeLTC,
+		}
+	}
+	backend.log.Info("Manually reconnecting")
+	for _, code := range electrumCoinCodes {
+		c, err := backend.Coin(code)
+		if err != nil {
+			backend.log.WithError(err).Errorf("could not find coin: %s", code)
+			continue
+		}
+		btcCoin, ok := c.(*btc.Coin)
+		if !ok {
+			backend.log.Errorf("Expected %s to be a btc coin", code)
+			continue
+		}
+		blockchain := btcCoin.Blockchain()
+		if blockchain == nil {
+			// Not initialized yet
+			continue
+		}
+		blockchain.ManualReconnect()
+	}
+}
+
 // Testing returns whether this backend is for testing only.
 func (backend *Backend) Testing() bool {
 	return backend.arguments.Testing()

backend/bridgecommon/bridgecommon.go

@@ -166,6 +166,18 @@ func UsingMobileDataChanged() {
 	})
 }
 
+// ManualReconnect exposes the ManualReconnect backend method.
+func ManualReconnect() {
+	mu.Lock()
+	defer mu.Unlock()
+
+	if globalBackend == nil {
+		return
+	}
+	globalBackend.ManualReconnect()
+
+}
+
 // BackendEnvironment implements backend.Environment.
 type BackendEnvironment struct {
 	NotifyUserFunc      func(string)

backend/coins/btc/blockchain/blockchain.go

@@ -118,4 +118,5 @@ type Interface interface {
 	Close()
 	ConnectionError() error
 	RegisterOnConnectionErrorChangedEvent(func(error))
+	ManualReconnect()
 }

backend/coins/btc/electrum/failoverclient.go

@@ -156,6 +156,10 @@ func (f *failoverClient) TransactionGet(txHash chainhash.Hash) (*wire.MsgTx, err
 	})
 }
 
+func (f *failoverClient) ManualReconnect() {
+	f.failover.ManualReconnect()
+}
+
 func (f *failoverClient) Close() {
 	f.failover.Close()
 }

backend/mobileserver/mobileserver.go

@@ -227,8 +227,13 @@ func CancelAuth() {
 	bridgecommon.CancelAuth()
 }
 
-// AuthResult triggers an auth feeedback notification (auth-ok/auth-err) towards the frontend,
+// AuthResult triggers an auth feedback notification (auth-ok/auth-err) towards the frontend,
 // depending on the input value.
 func AuthResult(ok bool) {
 	bridgecommon.AuthResult(ok)
 }
+
+// ManualReconnect wraps bridgecommon.ManualReconnet
+func AuthResult() {
+	bridgecommon.ManualReconnect()
+}