Update Synchronizer and Processor APIs to enable changing the server.

Actual implementation is in a subsequent commit.

src/main/java/cash/z/ecc/android/sdk/SdkSynchronizer.kt

@@ -78,7 +78,7 @@ class SdkSynchronizer internal constructor(
      * the underlying channel to connect to the same service, and use other APIs
      * (such as darksidewalletd) because channels are heavyweight.
      */
-    val channel: ManagedChannel get() = (processor.downloader.lightwalletService as LightWalletGrpcService).channel
+    val channel: ManagedChannel get() = (processor.downloader.lightWalletService as LightWalletGrpcService).channel
 
     var isStarted = false
 
@@ -223,7 +223,18 @@ class SdkSynchronizer internal constructor(
      */
     override suspend fun getServerInfo(): Service.LightdInfo = processor.downloader.getServerInfo()
 
-    
+    /**
+     * Changes the server that is being used to download compact blocks. This will throw an
+     * exception if it detects that the server change is invalid e.g. switching to testnet from
+     * mainnet.
+     */
+    override suspend fun changeServer(host: String, port: Int, errorHandler: (Throwable) -> Unit) {
+        val info =
+            (processor.downloader.lightWalletService as LightWalletGrpcService).connectionInfo
+        processor.downloader.changeService(LightWalletGrpcService(info.appContext, host, port))
+    }
+
+
     //
     // Storage APIs
     //

src/main/java/cash/z/ecc/android/sdk/Synchronizer.kt

@@ -5,6 +5,7 @@ import cash.z.ecc.android.sdk.block.CompactBlockProcessor
 import cash.z.ecc.android.sdk.block.CompactBlockProcessor.WalletBalance
 import cash.z.ecc.android.sdk.db.entity.ConfirmedTransaction
 import cash.z.ecc.android.sdk.db.entity.PendingTransaction
+import cash.z.ecc.android.sdk.ext.ZcashSdk
 import cash.z.ecc.android.sdk.validate.AddressType
 import cash.z.ecc.android.sdk.validate.ConsensusMatchType
 import cash.z.wallet.sdk.rpc.Service
@@ -221,6 +222,18 @@ interface Synchronizer {
      */
     suspend fun getServerInfo(): Service.LightdInfo
 
+    /**
+     * Gracefully change the server that the Synchronizer is currently using. In some cases, this
+     * will require waiting until current network activity is complete. Ideally, this would protect
+     * against accidentally switching between testnet and mainnet, by comparing the service info of
+     * the existing server with that of the new one.
+     */
+    suspend fun changeServer(
+        host: String,
+        port: Int = ZcashSdk.DEFAULT_LIGHTWALLETD_PORT,
+        errorHandler: (Throwable) -> Unit = { throw it }
+    )
+
 
     //
     // Error Handling

src/main/java/cash/z/ecc/android/sdk/block/CompactBlockProcessor.kt

@@ -170,7 +170,7 @@ class CompactBlockProcessor(
         if (!updateRanges()) {
             twig("Disconnection detected! Attempting to reconnect!")
             setState(Disconnected)
-            downloader.lightwalletService.reconnect()
+            downloader.lightWalletService.reconnect()
             ERROR_CODE_RECONNECT
         } else if (currentInfo.lastDownloadRange.isEmpty() && currentInfo.lastScanRange.isEmpty()) {
             twig("Nothing to process: no new blocks to download or scan, right now.")