[#1167] Step 3 - Download chain tip metadata from lightwalletd

- update chain tip action added

[#1167] Step 3 - Download chain tip metadata from lightwalletd

- roots removed from the ActionContext

[#1167] Step 3 - Download chain tip metadata from lightwalletd

- fallback to linear sync until next step is implemented

Sources/ZcashLightClientKit/Block/Actions/Action.swift

@@ -35,6 +35,7 @@ enum CBPState: CaseIterable {
     case migrateLegacyCacheDB
     case validateServer
     case updateSubtreeRoots
+    case updateChainTip
     case computeSyncControlData
     case download
     case scan

Sources/ZcashLightClientKit/Block/Actions/UpdateChainTipAction.swift

@@ -0,0 +1,39 @@
+//
+//  UpdateChainTipAction.swift
+//  
+//
+//  Created by Lukáš Korba on 01.08.2023.
+//
+
+import Foundation
+
+final class UpdateChainTipAction {
+    let rustBackend: ZcashRustBackendWelding
+    let service: LightWalletService
+    let logger: Logger
+
+    init(container: DIContainer) {
+        service = container.resolve(LightWalletService.self)
+        rustBackend = container.resolve(ZcashRustBackendWelding.self)
+        logger = container.resolve(Logger.self)
+    }
+}
+
+extension UpdateChainTipAction: Action {
+    var removeBlocksCacheWhenFailed: Bool { false }
+
+    func run(with context: ActionContext, didUpdate: @escaping (CompactBlockProcessor.Event) async -> Void) async throws -> ActionContext {
+        let latestBlockHeight = try await service.latestBlockHeight()
+
+        logger.info("Latest block height is \(latestBlockHeight)")
+        try await rustBackend.updateChainTip(height: Int32(latestBlockHeight))
+
+        // TODO: [#1169] Switching back to linear sync for now before step 5 & 6 are implemented
+        // https://github.com/zcash/ZcashLightClientKit/issues/1169
+        await context.update(state: .computeSyncControlData)
+
+        return context
+    }
+
+    func stop() async { }
+}

Sources/ZcashLightClientKit/Block/Actions/UpdateSubtreeRootsAction.swift

@@ -52,9 +52,7 @@ extension UpdateSubtreeRootsAction: Action {
             do {
                 try await rustBackend.putSaplingSubtreeRoots(startIndex: UInt64(request.startIndex), roots: roots)
 
-                // TODO: [#1167] Switching back to linear sync for now before step 3 & 4 are implemented
-                // https://github.com/zcash/ZcashLightClientKit/issues/1167
-                await context.update(state: .computeSyncControlData)
+                await context.update(state: .updateChainTip)
             } catch {
                 logger.debug("putSaplingSubtreeRoots failed with error \(error.localizedDescription)")
                 throw ZcashError.compactBlockProcessorPutSaplingSubtreeRoots(error)

Sources/ZcashLightClientKit/Block/CompactBlockProcessor.swift

@@ -216,6 +216,8 @@ actor CompactBlockProcessor {
                 action = ValidateServerAction(container: container, configProvider: configProvider)
             case .updateSubtreeRoots:
                 action = UpdateSubtreeRootsAction(container: container)
+            case .updateChainTip:
+                action = UpdateChainTipAction(container: container)
             case .computeSyncControlData:
                 action = ComputeSyncControlDataAction(container: container, configProvider: configProvider)
             case .download:
@@ -589,6 +591,8 @@ extension CompactBlockProcessor {
             break
         case .updateSubtreeRoots:
             break
+        case .updateChainTip:
+            break
         case .computeSyncControlData:
             break
         case .download: