walletunlocker: pass unlocked wallet back to lnd to avoid double unlock

walletunlocker/service.go

@@ -52,6 +52,13 @@ type WalletUnlockMsg struct {
 	// recovery should be attempted, such as after the wallet's initial
 	// creation, but before any addresses have been created.
 	RecoveryWindow uint32
+
+	// Wallet is the loaded and unlocked Wallet. This is returned
+	// through the channel to avoid it being unlocked twice (once to check
+	// if the password is correct, here in the WalletUnlocker and again
+	// later when lnd actually uses it). Because unlocking involves scrypt
+	// which is resource intensive, we want to avoid doing it twice.
+	Wallet *wallet.Wallet
 }
 
 // UnlockerService implements the WalletUnlocker service used to provide lnd
@@ -255,23 +262,19 @@ func (u *UnlockerService) UnlockWallet(ctx context.Context,
 	}
 
 	// Try opening the existing wallet with the provided password.
-	_, err = loader.OpenExistingWallet(password, false)
+	unlockedWallet, err := loader.OpenExistingWallet(password, false)
 	if err != nil {
 		// Could not open wallet, most likely this means that provided
 		// password was incorrect.
 		return nil, err
 	}
 
-	// We successfully opened the wallet, but we'll need to unload it to
-	// make sure lnd can open it later.
-	if err := loader.UnloadWallet(); err != nil {
-		// TODO: not return error here?
-		return nil, err
-	}
-
+	// We successfully opened the wallet and pass the instance back to
+	// avoid it needing to be unlocked again.
 	walletUnlockMsg := &WalletUnlockMsg{
 		Passphrase:     password,
 		RecoveryWindow: recoveryWindow,
+		Wallet:         unlockedWallet,
 	}
 
 	// At this point we was able to open the existing wallet with the