Added an exponential back-off to polling open groups when they fail to poll

SessionMessagingKit/Database/Migrations/_001_InitialSetupMigration.swift

@@ -140,6 +140,9 @@ enum _001_InitialSetupMigration: Migration {
             t.column(.sequenceNumber, .integer).notNull()
             t.column(.inboxLatestMessageId, .integer).notNull()
             t.column(.outboxLatestMessageId, .integer).notNull()
+            t.column(.pollFailureCount, .integer)
+                .notNull()
+                .defaults(to: 0)
         }
         
         /// Create a full-text search table synchronized with the OpenGroup table

SessionMessagingKit/Database/Models/OpenGroup.swift

@@ -26,6 +26,7 @@ public struct OpenGroup: Codable, Identifiable, FetchableRecord, PersistableReco
         case sequenceNumber
         case inboxLatestMessageId
         case outboxLatestMessageId
+        case pollFailureCount
     }
     
     public var id: String { threadId }  // Identifiable
@@ -86,6 +87,9 @@ public struct OpenGroup: Codable, Identifiable, FetchableRecord, PersistableReco
     /// updated whenever this value changes)
     public let outboxLatestMessageId: Int64
     
+    /// The number of times this room has failed to poll since the last successful poll
+    public let pollFailureCount: Int64
+    
     // MARK: - Relationships
     
     public var thread: QueryInterfaceRequest<SessionThread> {
@@ -117,7 +121,8 @@ public struct OpenGroup: Codable, Identifiable, FetchableRecord, PersistableReco
         infoUpdates: Int64,
         sequenceNumber: Int64 = 0,
         inboxLatestMessageId: Int64 = 0,
-        outboxLatestMessageId: Int64 = 0
+        outboxLatestMessageId: Int64 = 0,
+        pollFailureCount: Int64 = 0
     ) {
         self.threadId = OpenGroup.idFor(roomToken: roomToken, server: server)
         self.server = server.lowercased()
@@ -133,6 +138,7 @@ public struct OpenGroup: Codable, Identifiable, FetchableRecord, PersistableReco
         self.sequenceNumber = sequenceNumber
         self.inboxLatestMessageId = inboxLatestMessageId
         self.outboxLatestMessageId = outboxLatestMessageId
+        self.pollFailureCount = pollFailureCount
     }
 }
 
@@ -159,7 +165,8 @@ public extension OpenGroup {
                 infoUpdates: 0,
                 sequenceNumber: 0,
                 inboxLatestMessageId: 0,
-                outboxLatestMessageId: 0
+                outboxLatestMessageId: 0,
+                pollFailureCount: 0
             )
         }
         
@@ -192,7 +199,8 @@ extension OpenGroup: CustomStringConvertible, CustomDebugStringConvertible {
             "infoUpdates: \(infoUpdates)",
             "sequenceNumber: \(sequenceNumber)",
             "inboxLatestMessageId: \(inboxLatestMessageId)",
-            "outboxLatestMessageId: \(outboxLatestMessageId))"
+            "outboxLatestMessageId: \(outboxLatestMessageId)",
+            "pollFailureCount: \(pollFailureCount))"
         ].joined(separator: ", ")
     }
 }

SessionMessagingKit/Sending & Receiving/Pollers/OpenGroupPoller.swift

@@ -15,7 +15,8 @@ extension OpenGroupAPI {
 
         // MARK: - Settings
         
-        private static let pollInterval: TimeInterval = 4
+        private static let minPollInterval: TimeInterval = 3
+        private static let maxPollInterval: Double = (60 * 60)
         internal static let maxInactivityPeriod: Double = (14 * 24 * 60 * 60)
         
         // MARK: - Lifecycle
@@ -28,10 +29,7 @@ extension OpenGroupAPI {
             guard !hasStarted else { return }
             
             hasStarted = true
-            timer = Timer.scheduledTimerOnMainThread(withTimeInterval: Poller.pollInterval, repeats: true) { _ in
-                self.poll(using: dependencies).retainUntilComplete()
-            }
-            poll(using: dependencies).retainUntilComplete()
+            pollRecursively(using: dependencies)
         }
 
         @objc public func stop() {
@@ -41,6 +39,30 @@ extension OpenGroupAPI {
 
         // MARK: - Polling
         
+        private func pollRecursively(using dependencies: OpenGroupManager.OGMDependencies = OpenGroupManager.OGMDependencies()) {
+            guard hasStarted else { return }
+            
+            let minPollFailureCount: TimeInterval = Storage.shared
+                .read { db in
+                    try OpenGroup
+                        .filter(OpenGroup.Columns.server == server)
+                        .select(min(OpenGroup.Columns.pollFailureCount))
+                        .asRequest(of: TimeInterval.self)
+                        .fetchOne(db)
+                }
+                .defaulting(to: 0)
+            let nextPollInterval: TimeInterval = getInterval(for: minPollFailureCount, minInterval: Poller.minPollInterval, maxInterval: Poller.maxPollInterval)
+            
+            poll(using: dependencies).retainUntilComplete()
+            timer = Timer.scheduledTimerOnMainThread(withTimeInterval: nextPollInterval, repeats: false) { [weak self] timer in
+                timer.invalidate()
+                
+                Threading.pollerQueue.async {
+                    self?.pollRecursively(using: dependencies)
+                }
+            }
+        }
+        
         @discardableResult
         public func poll(using dependencies: OpenGroupManager.OGMDependencies = OpenGroupManager.OGMDependencies()) -> Promise<Void> {
             return poll(isBackgroundPoll: false, isPostCapabilitiesRetry: false, using: dependencies)
@@ -83,6 +105,14 @@ extension OpenGroupAPI {
                             cache.timeSinceLastPoll[server] = Date().timeIntervalSince1970
                             UserDefaults.standard[.lastOpen] = Date()
                         }
+                        
+                        // Reset the failure count
+                        Storage.shared.writeAsync { db in
+                            try OpenGroup
+                                .filter(OpenGroup.Columns.server == server)
+                                .updateAll(db, OpenGroup.Columns.pollFailureCount.set(to: 0))
+                        }
+                        
                         SNLog("Open group polling finished for \(server).")
                         seal.fulfill(())
                     }
@@ -97,7 +127,24 @@ extension OpenGroupAPI {
                         )
                         .done(on: OpenGroupAPI.workQueue) { [weak self] didHandleError in
                             if !didHandleError {
-                                SNLog("Open group polling failed due to error: \(error).")
+                                // Increase the failure count
+                                let pollFailureCount: Int64 = Storage.shared
+                                    .read { db in
+                                        try OpenGroup
+                                            .filter(OpenGroup.Columns.server == server)
+                                            .select(max(OpenGroup.Columns.pollFailureCount))
+                                            .asRequest(of: Int64.self)
+                                            .fetchOne(db)
+                                    }
+                                    .defaulting(to: 0)
+                                
+                                Storage.shared.writeAsync { db in
+                                    try OpenGroup
+                                        .filter(OpenGroup.Columns.server == server)
+                                        .updateAll(db, OpenGroup.Columns.pollFailureCount.set(to: (pollFailureCount + 1)))
+                                }
+                                
+                                SNLog("Open group polling failed due to error: \(error). Setting failure count to \(pollFailureCount).")
                             }
                             
                             self?.isPolling = false
@@ -265,4 +312,11 @@ extension OpenGroupAPI {
             }
         }
     }
+    
+    // MARK: - Convenience
+
+    fileprivate static func getInterval(for failureCount: TimeInterval, minInterval: TimeInterval, maxInterval: TimeInterval) -> TimeInterval {
+        // Arbitrary backoff factor...
+        return min(maxInterval, minInterval + pow(2, failureCount))
+    }
 }

SessionUtilitiesKit/Database/Storage.swift

@@ -200,6 +200,14 @@ public final class Storage {
                 WHERE openGroup.infoUpdates = -1
             """)
             // TODO: Remove this once everyone has updated
+            let openGroupTableInfo: [Row] = (try? Row.fetchAll(db, sql: "PRAGMA table_info(openGroup)"))
+                .defaulting(to: [])
+            if !openGroupTableInfo.contains(where: { $0["name"] == "pollFailureCount" }) {
+                try? db.execute(literal: """
+                    ALTER TABLE openGroup
+                    ADD pollFailureCount INTEGER NOT NULL DEFAULT 0
+                """)
+            }
             
             onComplete(finalError, needsConfigSync)
         }