[#1393] Support server switching

- This ensures that the SDK supports apps switching between different lightwalletd servers
- Synchronizer.validateServerEndpoint API added
- Demo app updated to leverage this new feature
- Changelog update
- Closes #1393

CHANGELOG.md

@@ -17,6 +17,13 @@ and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - `WalletBalanceFixture` class with mock values that are supposed to be used only for testing purposes 
 - `Memo.countLength(memoString: String)` to count memo length in bytes
+- `PersistableWallet.toSafeString` is a safe alternative for the regular [toString] function that prints only 
+  non-sensitive parts
+- `Synchronizer.validateServerEndpoint` this function checks whether the provided server endpoint is valid. 
+  The validation is based on comparing:
+  * network type
+  * sapling activation height
+  * consensus branch id
 
 ## [2.0.6] - 2024-01-30
 

demo-app/src/main/java/cash/z/ecc/android/sdk/demoapp/Navigation.kt

@@ -5,12 +5,17 @@ import android.content.ClipboardManager
 import android.content.Context
 import android.content.Intent
 import android.net.Uri
+import android.widget.Toast
+import androidx.activity.compose.BackHandler
 import androidx.activity.viewModels
 import androidx.compose.material3.SnackbarDuration
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation.NavHostController
 import androidx.navigation.NavOptionsBuilder
@@ -21,22 +26,27 @@ import cash.z.ecc.android.sdk.SdkSynchronizer
 import cash.z.ecc.android.sdk.demoapp.NavigationTargets.BALANCE
 import cash.z.ecc.android.sdk.demoapp.NavigationTargets.HOME
 import cash.z.ecc.android.sdk.demoapp.NavigationTargets.SEND
+import cash.z.ecc.android.sdk.demoapp.NavigationTargets.SERVER
 import cash.z.ecc.android.sdk.demoapp.NavigationTargets.TRANSACTIONS
 import cash.z.ecc.android.sdk.demoapp.NavigationTargets.WALLET_ADDRESS_DETAILS
 import cash.z.ecc.android.sdk.demoapp.ui.screen.addresses.view.Addresses
 import cash.z.ecc.android.sdk.demoapp.ui.screen.balance.view.Balance
 import cash.z.ecc.android.sdk.demoapp.ui.screen.home.view.Home
+import cash.z.ecc.android.sdk.demoapp.ui.screen.home.viewmodel.SecretState
 import cash.z.ecc.android.sdk.demoapp.ui.screen.home.viewmodel.WalletViewModel
 import cash.z.ecc.android.sdk.demoapp.ui.screen.send.view.Send
+import cash.z.ecc.android.sdk.demoapp.ui.screen.server.view.Server
 import cash.z.ecc.android.sdk.demoapp.ui.screen.transactions.view.Transactions
 import cash.z.ecc.android.sdk.demoapp.util.AndroidApiVersion
 import cash.z.ecc.android.sdk.demoapp.util.fromResources
+import cash.z.ecc.android.sdk.internal.Twig
 import cash.z.ecc.android.sdk.model.ZcashNetwork
+import cash.z.ecc.android.sdk.type.ServerValidation
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.launch
 
 @Composable
-@Suppress("LongMethod", "ktlint:standard:function-naming")
+@Suppress("LongMethod", "CyclomaticComplexMethod", "ktlint:standard:function-naming")
 internal fun ComposeActivity.Navigation() {
     val navController = rememberNavController()
 
@@ -63,6 +73,7 @@ internal fun ComposeActivity.Navigation() {
                         }
                     },
                     goTransactions = { navController.navigateJustOnce(TRANSACTIONS) },
+                    goServer = { navController.navigateJustOnce(SERVER) },
                     resetSdk = { walletViewModel.resetSdk() },
                     rewind = { walletViewModel.rewind() }
                 )
@@ -136,6 +147,76 @@ internal fun ComposeActivity.Navigation() {
                 )
             }
         }
+        composable(SERVER) {
+            val secretState = walletViewModel.secretState.collectAsStateWithLifecycle().value
+
+            val synchronizer = walletViewModel.synchronizer.collectAsStateWithLifecycle().value
+
+            Twig.info { "Current secrets state: $secretState" }
+
+            if (synchronizer == null || secretState !is SecretState.Ready) {
+                // Display loading indicator
+            } else {
+                val wallet = secretState.persistableWallet
+
+                Twig.info { "Current persisted wallet: ${wallet.toSafeString()}" }
+
+                val scope = rememberCoroutineScope()
+
+                var validationResult: ServerValidation by remember { mutableStateOf(ServerValidation.Valid) }
+
+                val onBack = {
+                    if (validationResult !is ServerValidation.Running) {
+                        navController.popBackStackJustOnce(SERVER)
+                    }
+                }
+
+                BackHandler { onBack() }
+
+                Server(
+                    buildInNetwork = ZcashNetwork.fromResources(application),
+                    onBack = onBack,
+                    onServerChange = { newEndpoint ->
+                        scope.launch {
+                            validationResult = ServerValidation.Running
+                            validationResult = synchronizer.validateServerEndpoint(application, newEndpoint)
+
+                            Twig.info { "Validation result: $validationResult" }
+
+                            when (validationResult) {
+                                ServerValidation.Valid -> {
+                                    walletViewModel.closeSynchronizer()
+
+                                    val newWallet =
+                                        wallet.copy(
+                                            endpoint = newEndpoint
+                                        )
+
+                                    Twig.info { "New wallet: ${newWallet.toSafeString()}" }
+
+                                    walletViewModel.persistExistingWallet(newWallet)
+
+                                    Toast.makeText(
+                                        applicationContext,
+                                        "Server saved",
+                                        Toast.LENGTH_SHORT
+                                    ).show()
+                                }
+                                is ServerValidation.InValid -> {
+                                    Twig.error { "Failed to validate the new endpoint: $newEndpoint" }
+                                }
+                                else -> {
+                                    // Should not happen
+                                    Twig.info { "Server validation state: $validationResult" }
+                                }
+                            }
+                        }
+                    },
+                    validationResult = validationResult,
+                    wallet = wallet,
+                )
+            }
+        }
         composable(TRANSACTIONS) {
             val synchronizer = walletViewModel.synchronizer.collectAsStateWithLifecycle().value
             if (null == synchronizer) {
@@ -225,5 +306,7 @@ object NavigationTargets {
 
     const val SEND = "send" // NON-NLS
 
+    const val SERVER = "server" // NON-NLS
+
     const val TRANSACTIONS = "transactions" // NON-NLS
 }

demo-app/src/main/java/cash/z/ecc/android/sdk/demoapp/ext/LightWalletEndpointDefaultExt.kt → demo-app/src/main/java/cash/z/ecc/android/sdk/demoapp/ext/LightWalletEndpointExt.kt

@@ -34,3 +34,8 @@ internal val LightWalletEndpoint.Companion.Testnet
             DEFAULT_PORT,
             isSecure = true
         )
+
+const val MIN_PORT_NUMBER = 1
+const val MAX_PORT_NUMBER = 65535
+
+internal fun LightWalletEndpoint.isValid() = host.isNotBlank() && port in MIN_PORT_NUMBER..MAX_PORT_NUMBER

demo-app/src/main/java/cash/z/ecc/android/sdk/demoapp/ui/screen/home/view/HomeView.kt

@@ -44,6 +44,7 @@ private fun ComposablePreviewHome() {
             goAddressDetails = {},
             goTransactions = {},
             goTestnetFaucet = {},
+            goServer = {},
             resetSdk = {},
             rewind = {},
         )
@@ -59,6 +60,7 @@ fun Home(
     goSend: () -> Unit,
     goAddressDetails: () -> Unit,
     goTransactions: () -> Unit,
+    goServer: () -> Unit,
     goTestnetFaucet: () -> Unit,
     resetSdk: () -> Unit,
     rewind: () -> Unit,
@@ -76,6 +78,7 @@ fun Home(
             walletSnapshot,
             goBalance = goBalance,
             goSend = goSend,
+            goServer = goServer,
             goAddressDetails = goAddressDetails,
             goTransactions = goTransactions
         )
@@ -155,8 +158,9 @@ private fun HomeMainContent(
     walletSnapshot: WalletSnapshot,
     goBalance: () -> Unit,
     goSend: () -> Unit,
+    goServer: () -> Unit,
     goAddressDetails: () -> Unit,
-    goTransactions: () -> Unit
+    goTransactions: () -> Unit,
 ) {
     Column(
         Modifier
@@ -179,6 +183,10 @@ private fun HomeMainContent(
             Text(text = stringResource(id = R.string.menu_transactions))
         }
 
+        Button(goServer) {
+            Text(text = stringResource(id = R.string.menu_server))
+        }
+
         Text(text = stringResource(id = R.string.home_status, walletSnapshot.status.toString()))
         if (walletSnapshot.status != Synchronizer.Status.SYNCED) {
             @Suppress("MagicNumber")

demo-app/src/main/java/cash/z/ecc/android/sdk/demoapp/ui/screen/home/viewmodel/WalletViewModel.kt

@@ -5,6 +5,7 @@ import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.viewModelScope
 import cash.z.ecc.android.bip39.Mnemonics
 import cash.z.ecc.android.bip39.toSeed
+import cash.z.ecc.android.sdk.SdkSynchronizer
 import cash.z.ecc.android.sdk.Synchronizer
 import cash.z.ecc.android.sdk.WalletCoordinator
 import cash.z.ecc.android.sdk.WalletInitMode
@@ -267,6 +268,18 @@ class WalletViewModel(application: Application) : AndroidViewModel(application)
             }
         }
     }
+
+    /**
+     * This safely and asynchronously stops the [Synchronizer].
+     */
+    fun closeSynchronizer() {
+        val synchronizer = synchronizer.value
+        if (null != synchronizer) {
+            viewModelScope.launch {
+                (synchronizer as SdkSynchronizer).close()
+            }
+        }
+    }
 }
 
 /**