[#1206] Frequent call of update chain tip

- The State Machine has been slightly updated so it measures time when it lastly updated chain tip. If it happened more than 10mins ago, it calls the .updateChainTip action once again before the download-scan-enhance loop continues
- updated unit test

[#1206] Frequent call of update chain tip (#1207)

- whenever updateChainTip is called, it's followed by suggestScanRanges logic

Sources/ZcashLightClientKit/Block/Actions/Action.swift

@@ -18,6 +18,8 @@ actor ActionContext {
     var totalProgressRange: CompactBlockRange = 0...0
     /// Amount of blocks that have been processed so far
     var processedHeight: BlockHeight = 0
+    /// Update chain tip must be called repeatadly, this value stores the previous update and help to decide when to call it again
+    var lastChainTipUpdateTime: TimeInterval = 0.0
     var lastScannedHeight: BlockHeight?
     var lastDownloadedHeight: BlockHeight?
     var lastEnhancedHeight: BlockHeight?
@@ -38,6 +40,7 @@ actor ActionContext {
         self.totalProgressRange = totalProgressRange
     }
     func update(processedHeight: BlockHeight) async { self.processedHeight = processedHeight }
+    func update(lastChainTipUpdateTime: TimeInterval) async { self.lastChainTipUpdateTime = lastChainTipUpdateTime }
     func update(lastScannedHeight: BlockHeight) async { self.lastScannedHeight = lastScannedHeight }
     func update(lastDownloadedHeight: BlockHeight) async { self.lastDownloadedHeight = lastDownloadedHeight }
     func update(lastEnhancedHeight: BlockHeight?) async { self.lastEnhancedHeight = lastEnhancedHeight }

Sources/ZcashLightClientKit/Block/Actions/EnhanceAction.swift

@@ -30,7 +30,7 @@ final class EnhanceAction {
         if lastScannedHeight >= latestBlockHeight {
             await context.update(state: .clearCache)
         } else {
-            await context.update(state: .download)
+            await context.update(state: .updateChainTip)
         }
 
         return context

Sources/ZcashLightClientKit/Block/Actions/ProcessSuggestedScanRangesAction.swift

@@ -25,7 +25,7 @@ extension ProcessSuggestedScanRangesAction: Action {
     func run(with context: ActionContext, didUpdate: @escaping (CompactBlockProcessor.Event) async -> Void) async throws -> ActionContext {
         logger.info("Getting the suggested scan ranges from the wallet database.")
         let scanRanges = try await rustBackend.suggestScanRanges()
-        
+
         if let firstRange = scanRanges.first {
             let lowerBound = firstRange.range.lowerBound - 1
             let upperBound = firstRange.range.upperBound - 1
@@ -42,7 +42,7 @@ extension ProcessSuggestedScanRangesAction: Action {
                 latestScannedHeight [DB]:       \(lowerBound)
                 firstUnenhancedHeight [DB]:     \(lowerBound + 1)
                 """)
-            
+
             await context.update(lastScannedHeight: lowerBound)
             await context.update(lastDownloadedHeight: lowerBound)
             await context.update(syncControlData: syncControlData)
@@ -61,7 +61,7 @@ extension ProcessSuggestedScanRangesAction: Action {
                 logger.info("Setting the total range for Spend before Sync to \(minHeight...maxHeight).")
                 await context.update(totalProgressRange: minHeight...maxHeight)
             }
-            
+
             // If there is a range of blocks that needs to be verified, it will always
             // be returned as the first element of the vector of suggested ranges.
             if firstRange.priority == .verify {

Sources/ZcashLightClientKit/Block/Actions/UpdateChainTipAction.swift

@@ -17,19 +17,31 @@ final class UpdateChainTipAction {
         rustBackend = container.resolve(ZcashRustBackendWelding.self)
         logger = container.resolve(Logger.self)
     }
+    
+    func updateChainTip(_ context: ActionContext, time: TimeInterval) async throws {
+        let latestBlockHeight = try await service.latestBlockHeight()
+        
+        logger.info("Latest block height is \(latestBlockHeight)")
+        try await rustBackend.updateChainTip(height: Int32(latestBlockHeight))
+        await context.update(lastChainTipUpdateTime: time)
+    }
 }
 
 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))
-        
-        await context.update(state: .processSuggestedScanRanges)
+        let lastChainTipUpdateTime = await context.lastChainTipUpdateTime
+        let now = Date().timeIntervalSince1970
 
+        // Update chain tip can be called from different contexts
+        if await context.prevState == .updateSubtreeRoots || now - lastChainTipUpdateTime > 600 {
+            try await updateChainTip(context, time: now)
+            await context.update(state: .processSuggestedScanRanges)
+        } else if await context.prevState == .enhance {
+            await context.update(state: .download)
+        }
+        
         return context
     }
 

Tests/OfflineTests/CompactBlockProcessorActions/EnhanceActionTests.swift

@@ -50,7 +50,7 @@ final class EnhanceActionTests: ZcashTestCase {
         )
     }
 
-    func testEnhanceAction_decideWhatToDoNext_DownloadExpected() async throws {
+    func testEnhanceAction_decideWhatToDoNext_UpdateChainTipExpected() async throws {
         let enhanceAction = setupAction()
         underlyingDownloadRange = CompactBlockRange(uncheckedBounds: (1000, 2000))
         underlyingScanRange = CompactBlockRange(uncheckedBounds: (1000, 2000))
@@ -60,8 +60,8 @@ final class EnhanceActionTests: ZcashTestCase {
         let nextState = await nextContext.state
 
         XCTAssertTrue(
-            nextState == .download,
-            "testEnhanceAction_decideWhatToDoNext_DownloadExpected is expected to be .download but received \(nextState)"
+            nextState == .updateChainTip,
+            "testEnhanceAction_decideWhatToDoNext_DownloadExpected is expected to be .updateChainTip but received \(nextState)"
         )
     }