Merge pull request #1195 from LukasKorba/1189-Implement-continuity-check-and-RewindAction

[#1189] implement continuity check and rewind action

Sources/ZcashLightClientKit/Block/Actions/Action.swift

@@ -13,6 +13,7 @@ actor ActionContext {
     var syncControlData: SyncControlData
     let preferredSyncAlgorithm: SyncAlgorithm
     var supportedSyncAlgorithm: SyncAlgorithm?
+    var requestedRewindHeight: BlockHeight?
     var totalProgressRange: CompactBlockRange = 0...0
     var lastScannedHeight: BlockHeight?
     var lastDownloadedHeight: BlockHeight?
@@ -34,6 +35,7 @@ actor ActionContext {
     func update(lastDownloadedHeight: BlockHeight) async { self.lastDownloadedHeight = lastDownloadedHeight }
     func update(lastEnhancedHeight: BlockHeight?) async { self.lastEnhancedHeight = lastEnhancedHeight }
     func update(supportedSyncAlgorithm: SyncAlgorithm) async { self.supportedSyncAlgorithm = supportedSyncAlgorithm }
+    func update(requestedRewindHeight: BlockHeight) async { self.requestedRewindHeight = requestedRewindHeight }
 }
 
 enum CBPState: CaseIterable {
@@ -43,6 +45,7 @@ enum CBPState: CaseIterable {
     case updateSubtreeRoots
     case updateChainTip
     case processSuggestedScanRanges
+    case rewind
     case computeSyncControlData
     case download
     case scan

Sources/ZcashLightClientKit/Block/Actions/ProcessSuggestedScanRangesAction.swift

@@ -27,13 +27,6 @@ extension ProcessSuggestedScanRangesAction: Action {
         let scanRanges = try await rustBackend.suggestScanRanges()
         
         if let firstRange = scanRanges.first {
-            // 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 {
-                // TODO: [#1189] handle rewind, https://github.com/zcash/ZcashLightClientKit/issues/1189
-                // REWIND to download.start height HERE
-            }
-            
             let lowerBound = firstRange.range.lowerBound - 1
             let upperBound = firstRange.range.upperBound - 1
             
@@ -55,7 +48,14 @@ extension ProcessSuggestedScanRangesAction: Action {
             await context.update(syncControlData: syncControlData)
             await context.update(totalProgressRange: lowerBound...upperBound)
             
-            await context.update(state: .download)
+            // 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 {
+                await context.update(requestedRewindHeight: lowerBound + 1)
+                await context.update(state: .rewind)
+            } else {
+                await context.update(state: .download)
+            }
         } else {
             await context.update(state: .finished)
         }

Sources/ZcashLightClientKit/Block/Actions/RewindAction.swift

@@ -0,0 +1,48 @@
+//
+//  RewindAction.swift
+//  
+//
+//  Created by Lukáš Korba on 09.08.2023.
+//
+
+import Foundation
+
+final class RewindAction {
+    let downloader: BlockDownloader
+    let rustBackend: ZcashRustBackendWelding
+    let downloaderService: BlockDownloaderService
+    let logger: Logger
+
+    init(container: DIContainer) {
+        downloader = container.resolve(BlockDownloader.self)
+        rustBackend = container.resolve(ZcashRustBackendWelding.self)
+        downloaderService = container.resolve(BlockDownloaderService.self)
+        logger = container.resolve(Logger.self)
+    }
+    
+    private func update(context: ActionContext) async -> ActionContext {
+        await context.update(state: .download)
+        return context
+    }
+}
+
+extension RewindAction: Action {
+    var removeBlocksCacheWhenFailed: Bool { false }
+
+    func run(with context: ActionContext, didUpdate: @escaping (CompactBlockProcessor.Event) async -> Void) async throws -> ActionContext {
+        guard let rewindHeight = await context.requestedRewindHeight else {
+            return await update(context: context)
+        }
+        
+        logger.debug("Executing rewind.")
+        await downloader.rewind(latestDownloadedBlockHeight: rewindHeight)
+        try await rustBackend.rewindToHeight(height: Int32(rewindHeight))
+        
+        // clear cache
+        try await downloaderService.rewind(to: rewindHeight)
+        
+        return await update(context: context)
+    }
+
+    func stop() async { }
+}

Sources/ZcashLightClientKit/Block/Actions/ScanAction.swift

@@ -63,9 +63,15 @@ extension ScanAction: Action {
                 // ScanAction is controlled locally so it must report back the updated scanned height
                 await context.update(lastScannedHeight: lastScannedHeight)
             }
+        } catch ZcashError.rustScanBlocks(let errorMsg) {
+            if isContinuityError(errorMsg) {
+                await context.update(requestedRewindHeight: batchRange.lowerBound - 10)
+                await context.update(state: .download)
+                return context
+            } else {
+                throw ZcashError.rustScanBlocks(errorMsg)
+            }
         } catch {
-            // TODO: [#1189] check isContinuityError, https://github.com/zcash/ZcashLightClientKit/issues/1189
-            // if YES, REWIND to height at what error occured - at least 1 block
             throw error
         }
 
@@ -74,3 +80,11 @@ extension ScanAction: Action {
 
     func stop() async { }
 }
+
+private extension ScanAction {
+    func isContinuityError(_ errorMsg: String) -> Bool {
+        errorMsg.contains("The parent hash of proposed block does not correspond to the block hash at height")
+        || errorMsg.contains("Block height discontinuity at height")
+        || errorMsg.contains("note commitment tree size provided by a compact block did not match the expected size at height")
+    }
+}

Sources/ZcashLightClientKit/Block/CompactBlockProcessor.swift

@@ -230,6 +230,8 @@ actor CompactBlockProcessor {
                 action = UpdateChainTipAction(container: container)
             case .processSuggestedScanRanges:
                 action = ProcessSuggestedScanRangesAction(container: container)
+            case .rewind:
+                action = RewindAction(container: container)
             case .computeSyncControlData:
                 action = ComputeSyncControlDataAction(container: container, configProvider: configProvider)
             case .download:
@@ -607,6 +609,8 @@ extension CompactBlockProcessor {
             break
         case .processSuggestedScanRanges:
             break
+        case .rewind:
+            break
         case .computeSyncControlData:
             break
         case .download: