Plumtree gossip: don't subset REQUEST_SYNC fanout; make RequestSyncPacket.encode use const

bitchat.xcodeproj/project.pbxproj

@@ -41,6 +41,14 @@
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 		0481A3902E734CAE00FC845E /* CommandProcessorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A38F2E734CAE00FC845E /* CommandProcessorTests.swift */; };
 		0481A3912E734CAE00FC845E /* CommandProcessorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A38F2E734CAE00FC845E /* CommandProcessorTests.swift */; };
+		0481A3932E73730100FC845E /* RequestSyncPacket.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3922E73730100FC845E /* RequestSyncPacket.swift */; };
+		0481A3942E73730100FC845E /* RequestSyncPacket.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3922E73730100FC845E /* RequestSyncPacket.swift */; };
+		0481A3992E73730F00FC845E /* GossipSyncManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3952E73730F00FC845E /* GossipSyncManager.swift */; };
+		0481A39A2E73730F00FC845E /* PacketIdUtil.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3962E73730F00FC845E /* PacketIdUtil.swift */; };
+		0481A39B2E73730F00FC845E /* SeenPacketsBloomFilter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3972E73730F00FC845E /* SeenPacketsBloomFilter.swift */; };
+		0481A39C2E73730F00FC845E /* GossipSyncManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3952E73730F00FC845E /* GossipSyncManager.swift */; };
+		0481A39D2E73730F00FC845E /* PacketIdUtil.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3962E73730F00FC845E /* PacketIdUtil.swift */; };
+		0481A39E2E73730F00FC845E /* SeenPacketsBloomFilter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 0481A3972E73730F00FC845E /* SeenPacketsBloomFilter.swift */; };
 		048A4BE72E5CCCC300162C4A /* TransportConfig.swift in Sources */ = {isa = PBXBuildFile; fileRef = 048A4BE62E5CCCC300162C4A /* TransportConfig.swift */; };
 		048A4BE82E5CCCC300162C4A /* TransportConfig.swift in Sources */ = {isa = PBXBuildFile; fileRef = 048A4BE62E5CCCC300162C4A /* TransportConfig.swift */; };
 		048A4BE92E5CCCC300162C4B /* TransportConfig.swift in Sources */ = {isa = PBXBuildFile; fileRef = 048A4BE62E5CCCC300162C4A /* TransportConfig.swift */; };
@@ -233,6 +241,10 @@
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 		0481A38F2E734CAE00FC845E /* CommandProcessorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CommandProcessorTests.swift; sourceTree = "<group>"; };
+		0481A3922E73730100FC845E /* RequestSyncPacket.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RequestSyncPacket.swift; sourceTree = "<group>"; };
+		0481A3952E73730F00FC845E /* GossipSyncManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GossipSyncManager.swift; sourceTree = "<group>"; };
+		0481A3962E73730F00FC845E /* PacketIdUtil.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PacketIdUtil.swift; sourceTree = "<group>"; };
+		0481A3972E73730F00FC845E /* SeenPacketsBloomFilter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SeenPacketsBloomFilter.swift; sourceTree = "<group>"; };
 		048A4BE62E5CCCC300162C4A /* TransportConfig.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TransportConfig.swift; sourceTree = "<group>"; };
 		048A4C272E5FCD6600162C4A /* GeohashBookmarksStore.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GeohashBookmarksStore.swift; sourceTree = "<group>"; };
 		048A4C2A2E5FCE0300162C4A /* GeohashBookmarksStoreTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = GeohashBookmarksStoreTests.swift; sourceTree = "<group>"; };
@@ -372,9 +384,20 @@
 			path = Frameworks;
 			sourceTree = "<group>";
 		};
+		0481A3982E73730F00FC845E /* Sync */ = {
+			isa = PBXGroup;
+			children = (
+				0481A3952E73730F00FC845E /* GossipSyncManager.swift */,
+				0481A3962E73730F00FC845E /* PacketIdUtil.swift */,
+				0481A3972E73730F00FC845E /* SeenPacketsBloomFilter.swift */,
+			);
+			path = Sync;
+			sourceTree = "<group>";
+		};
 		0575DCBD15C7C719ADDCB67E /* Models */ = {
 			isa = PBXGroup;
 			children = (
+				0481A3922E73730100FC845E /* RequestSyncPacket.swift */,
 				11186E29A064E8D210880E1B /* BitchatPeer.swift */,
 			);
 			path = Models;
@@ -414,6 +437,7 @@
 				0575DCBD15C7C719ADDCB67E /* Models */,
 				637EDFDD042BDB5F2569A501 /* Noise */,
 				E78C7F4B6769C0A72F5DE544 /* Nostr */,
+				0481A3982E73730F00FC845E /* Sync */,
 				ADD53BCDA233C02E53458926 /* Protocols */,
 				D98A3186D7E4C72E35BDF7FE /* Services */,
 				9A78348821A7D3374607D4E3 /* Utils */,
@@ -829,6 +853,9 @@
 				923027D6F2F417AFA2488127 /* BitchatProtocol.swift in Sources */,
 				D450CF41F207BDE1A1AAA56E /* ChatViewModel.swift in Sources */,
 				B0CA7796B2B2AC2B33F84548 /* CompressionUtil.swift in Sources */,
+				0481A3992E73730F00FC845E /* GossipSyncManager.swift in Sources */,
+				0481A39A2E73730F00FC845E /* PacketIdUtil.swift in Sources */,
+				0481A39B2E73730F00FC845E /* SeenPacketsBloomFilter.swift in Sources */,
 				92D34E7A07C990C8A815B0CE /* ContentView.swift in Sources */,
 				5C93B4FDD0C448C3EDDBF8AE /* FavoritesPersistenceService.swift in Sources */,
 				047502B42E55FED60083520F /* MeshPeerList.swift in Sources */,
@@ -854,6 +881,7 @@
 				6A85FC357ACD85DBD9020845 /* NostrRelayManager.swift in Sources */,
 				749D8CF8A362B6CD0786782D /* NotificationService.swift in Sources */,
 				049BD3AF2E51ED60001A566B /* Transport.swift in Sources */,
+				0481A3942E73730100FC845E /* RequestSyncPacket.swift in Sources */,
 				E2DCF7817344F1CCDB8B7B2F /* SecureIdentityStateManager.swift in Sources */,
 				049BD3A02E51DBF4001A566B /* Packets.swift in Sources */,
 				047502892E5416250083520F /* Geohash.swift in Sources */,
@@ -894,6 +922,9 @@
 				6DE056E1EE9850E9FBF50157 /* BitchatProtocol.swift in Sources */,
 				7576A357B278E5733E9D9F33 /* ChatViewModel.swift in Sources */,
 				7DCA0DBCB8884E3B31C7BCE3 /* CompressionUtil.swift in Sources */,
+				0481A39C2E73730F00FC845E /* GossipSyncManager.swift in Sources */,
+				0481A39D2E73730F00FC845E /* PacketIdUtil.swift in Sources */,
+				0481A39E2E73730F00FC845E /* SeenPacketsBloomFilter.swift in Sources */,
 				1D9674FA5F998503831DC281 /* ContentView.swift in Sources */,
 				ACE2ED172C37F01561E50B71 /* FavoritesPersistenceService.swift in Sources */,
 				047502B62E55FED60083520F /* MeshPeerList.swift in Sources */,
@@ -919,6 +950,7 @@
 				BCD0EBACD82AF5E55C2CB2B9 /* NostrRelayManager.swift in Sources */,
 				61C81ED5F679D5E973EE0C07 /* NotificationService.swift in Sources */,
 				049BD3AE2E51ED60001A566B /* Transport.swift in Sources */,
+				0481A3932E73730100FC845E /* RequestSyncPacket.swift in Sources */,
 				68C4BE564735F6E7915274A2 /* SecureIdentityStateManager.swift in Sources */,
 				049BD3A22E51DBF4001A566B /* Packets.swift in Sources */,
 				047502872E5416250083520F /* Geohash.swift in Sources */,

bitchat/Models/RequestSyncPacket.swift

@@ -0,0 +1,62 @@
+import Foundation
+
+// REQUEST_SYNC payload TLV (type, length16, value)
+//  - 0x01: mBytes (uint16)
+//  - 0x02: k (uint8)
+//  - 0x03: bloom filter bits (opaque byte array of length mBytes)
+struct RequestSyncPacket {
+    let mBytes: Int
+    let k: Int
+    let bits: Data
+
+    func encode() -> Data {
+        var out = Data()
+        func putTLV(_ t: UInt8, _ v: Data) {
+            out.append(t)
+            let len = UInt16(v.count)
+            out.append(UInt8((len >> 8) & 0xFF))
+            out.append(UInt8(len & 0xFF))
+            out.append(v)
+        }
+        // mBytes
+        let mbBE = UInt16(mBytes).bigEndian
+        let mbData = withUnsafeBytes(of: mbBE) { Data($0) }
+        putTLV(0x01, mbData)
+        // k
+        putTLV(0x02, Data([UInt8(k & 0xFF)]))
+        // bits
+        putTLV(0x03, bits)
+        return out
+    }
+
+    static func decode(from data: Data) -> RequestSyncPacket? {
+        var off = 0
+        var mBytes: Int? = nil
+        var k: Int? = nil
+        var bits: Data? = nil
+
+        while off + 3 <= data.count {
+            let t = Int(data[off]); off += 1
+            guard off + 2 <= data.count else { return nil }
+            let len = (Int(data[off]) << 8) | Int(data[off+1]); off += 2
+            guard off + len <= data.count else { return nil }
+            let v = data.subdata(in: off..<(off+len)); off += len
+            switch t {
+            case 0x01:
+                if v.count == 2 {
+                    let mb = (Int(v[0]) << 8) | Int(v[1])
+                    mBytes = mb
+                }
+            case 0x02:
+                if v.count == 1 { k = Int(v[0]) }
+            case 0x03:
+                bits = v
+            default:
+                break // forward compatible; ignore unknown TLVs
+            }
+        }
+
+        guard let mb = mBytes, let kk = k, let bb = bits, mb == bb.count else { return nil }
+        return RequestSyncPacket(mBytes: mb, k: kk, bits: bb)
+    }
+}

bitchat/Protocols/BitchatProtocol.swift

@@ -125,6 +125,7 @@ enum MessageType: UInt8 {
     case announce = 0x01        // "I'm here" with nickname
     case message = 0x02         // Public chat message  
     case leave = 0x03           // "I'm leaving"
+    case requestSync = 0x21     // Bloom filter-based sync request (local-only)
     
     // Noise encryption
     case noiseHandshake = 0x10  // Handshake (init or response determined by payload)
@@ -138,6 +139,7 @@ enum MessageType: UInt8 {
         case .announce: return "announce"
         case .message: return "message"
         case .leave: return "leave"
+        case .requestSync: return "requestSync"
         case .noiseHandshake: return "noiseHandshake"
         case .noiseEncrypted: return "noiseEncrypted"
         case .fragment: return "fragment"

bitchat/Services/BLEService.swift

@@ -137,6 +137,9 @@ final class BLEService: NSObject {
     private var pendingDirectedRelays: [String: [String: (packet: BitchatPacket, enqueuedAt: Date)]] = [:]
     // Debounce for 'reconnected' logs
     private var lastReconnectLogAt: [String: Date] = [:]
+
+    // MARK: - Gossip Sync
+    private var gossipSyncManager: GossipSyncManager?
     
     // MARK: - Maintenance Timer
     
@@ -395,9 +398,15 @@ final class BLEService: NSObject {
         }
         timer.resume()
         maintenanceTimer = timer
-        
+
         // Publish initial empty state
         requestPeerDataPublish()
+
+        // Initialize gossip sync manager
+        let sync = GossipSyncManager(myPeerID: myPeerID)
+        sync.delegate = self
+        sync.start()
+        self.gossipSyncManager = sync
     }
     
     func setNickname(_ nickname: String) {
@@ -772,6 +781,8 @@ final class BLEService: NSObject {
                 self.messageDeduplicator.markProcessed(dedupID)
                 // Call synchronously since we're already on background queue
                 self.broadcastPacket(signedPacket)
+                // Track our own broadcast for sync
+                self.gossipSyncManager?.onPublicPacketSeen(signedPacket)
             }
         }
     }
@@ -1096,10 +1107,13 @@ final class BLEService: NSObject {
         }
 
         // For broadcast (no directed peer) and non-fragment, choose a subset deterministically
-        // Special-case announces: do NOT subset to maximize reach for presence
+        // Special-case control/presence messages: do NOT subset to maximize immediate coverage
         var selectedPeripheralIDs = Set(allowedPeripheralIDs)
         var selectedCentralIDs = Set(allowedCentralIDs)
-        if directedOnlyPeer == nil && packet.type != MessageType.fragment.rawValue && packet.type != MessageType.announce.rawValue {
+        if directedOnlyPeer == nil
+            && packet.type != MessageType.fragment.rawValue
+            && packet.type != MessageType.announce.rawValue
+            && packet.type != MessageType.requestSync.rawValue {
             let kp = subsetSizeForFanout(allowedPeripheralIDs.count)
             let kc = subsetSizeForFanout(allowedCentralIDs.count)
             selectedPeripheralIDs = selectDeterministicSubset(ids: allowedPeripheralIDs, k: kp, seed: messageID)
@@ -1130,6 +1144,12 @@ final class BLEService: NSObject {
         }
     }
 
+    // Directed send helper (unicast to a specific peerID) without altering packet contents
+    private func sendPacketDirected(_ packet: BitchatPacket, to peerID: String) {
+        guard let data = packet.toBinaryData(padding: false) else { return }
+        sendOnAllLinks(packet: packet, data: data, pad: false, directedOnlyPeer: peerID)
+    }
+
     // MARK: - Directed store-and-forward
     private func spoolDirectedPacket(_ packet: BitchatPacket, recipientPeerID: String) {
         let msgID = makeMessageID(for: packet)
@@ -1380,6 +1400,9 @@ final class BLEService: NSObject {
         case .message:
             handleMessage(packet, from: senderID)
             
+        case .requestSync:
+            handleRequestSync(packet, from: senderID)
+            
         case .noiseHandshake:
             handleNoiseHandshake(packet, from: senderID)
             
@@ -1580,12 +1603,17 @@ final class BLEService: NSObject {
             // Only notify of connection for new or reconnected peers when it is a direct announce
             if (packet.ttl == self.messageTTL) && (isNewPeer || isReconnectedPeer) {
                 self.delegate?.didConnectToPeer(peerID)
+                // Schedule initial unicast sync to this peer
+                self.gossipSyncManager?.scheduleInitialSyncToPeer(peerID, delaySeconds: 5.0)
             }
             
             self.requestPeerDataPublish()
             self.delegate?.didUpdatePeerList(currentPeerIDs)
         }
         
+        // Track for sync (include our own and others' announces)
+        gossipSyncManager?.onPublicPacketSeen(packet)
+
         // Send announce back for bidirectional discovery (only once per peer)
         let announceBackID = "announce-back-\(peerID)"
         let shouldSendBack = !messageDeduplicator.contains(announceBackID)
@@ -1607,6 +1635,15 @@ final class BLEService: NSObject {
             }
         }
     }
+
+    // Handle REQUEST_SYNC: decode payload and respond with missing packets via sync manager
+    private func handleRequestSync(_ packet: BitchatPacket, from peerID: String) {
+        guard let req = RequestSyncPacket.decode(from: packet.payload) else {
+            SecureLogger.warning("⚠️ Malformed REQUEST_SYNC from \(peerID)", category: .session)
+            return
+        }
+        gossipSyncManager?.handleRequestSync(fromPeerID: peerID, request: req)
+    }
     
     // Mention parsing moved to ChatViewModel
     
@@ -1647,6 +1684,11 @@ final class BLEService: NSObject {
             }
         }
 
+        // Track broadcast messages (recipientID == nil indicates broadcast)
+        if packet.recipientID == nil && packet.type == MessageType.message.rawValue {
+            gossipSyncManager?.onPublicPacketSeen(packet)
+        }
+
         guard accepted else {
             SecureLogger.warning("🚫 Dropping public message from unverified or unknown peer \(peerID.prefix(8))…", category: .security)
             return
@@ -1858,6 +1900,8 @@ final class BLEService: NSObject {
                 self?.broadcastPacket(signedPacket)
             }
         }
+        // Ensure our own announce is included in sync state
+        gossipSyncManager?.onPublicPacketSeen(signedPacket)
     }
     
     func sendDeliveryAck(for messageID: String, to peerID: String) {
@@ -2246,6 +2290,29 @@ final class BLEService: NSObject {
     }
 }
 
+// MARK: - GossipSyncManager Delegate
+extension BLEService: GossipSyncManager.Delegate {
+    func sendPacket(_ packet: BitchatPacket) {
+        if DispatchQueue.getSpecific(key: messageQueueKey) != nil {
+            broadcastPacket(packet)
+        } else {
+            messageQueue.async { [weak self] in self?.broadcastPacket(packet) }
+        }
+    }
+
+    func sendPacket(to peerID: String, packet: BitchatPacket) {
+        if DispatchQueue.getSpecific(key: messageQueueKey) != nil {
+            sendPacketDirected(packet, to: peerID)
+        } else {
+            messageQueue.async { [weak self] in self?.sendPacketDirected(packet, to: peerID) }
+        }
+    }
+
+    func signPacketForBroadcast(_ packet: BitchatPacket) -> BitchatPacket {
+        return noiseService.signPacket(packet) ?? packet
+    }
+}
+
 // MARK: - CBCentralManagerDelegate
 
 extension BLEService: CBCentralManagerDelegate {

bitchat/Sync/GossipSyncManager.swift

@@ -0,0 +1,168 @@
+import Foundation
+
+// Gossip-based sync manager using rotating Bloom filters
+final class GossipSyncManager {
+    protocol Delegate: AnyObject {
+        func sendPacket(_ packet: BitchatPacket)
+        func sendPacket(to peerID: String, packet: BitchatPacket)
+        func signPacketForBroadcast(_ packet: BitchatPacket) -> BitchatPacket
+    }
+
+    struct Config {
+        var seenCapacity: Int = 100          // recent broadcast messages kept
+        var bloomMaxBytes: Int = 256         // up to 256 bytes
+        var bloomTargetFpr: Double = 0.01    // 1%
+    }
+
+    private let myPeerID: String
+    private let config: Config
+    weak var delegate: Delegate?
+
+    // Bloom filter
+    private let bloom: SeenPacketsBloomFilter
+
+    // Storage: broadcast messages (ordered by insert), and latest announce per sender
+    private var messages: [String: BitchatPacket] = [:] // idHex -> packet
+    private var messageOrder: [String] = []
+    private var latestAnnouncementByPeer: [String: (id: String, packet: BitchatPacket)] = [:]
+
+    // Timer
+    private var periodicTimer: DispatchSourceTimer?
+    private let queue = DispatchQueue(label: "mesh.sync", qos: .utility)
+
+    init(myPeerID: String, config: Config = Config()) {
+        self.myPeerID = myPeerID
+        self.config = config
+        self.bloom = SeenPacketsBloomFilter(maxBytes: config.bloomMaxBytes, targetFpr: config.bloomTargetFpr)
+    }
+
+    func start() {
+        stop()
+        let timer = DispatchSource.makeTimerSource(queue: queue)
+        timer.schedule(deadline: .now() + 30.0, repeating: 30.0, leeway: .seconds(1))
+        timer.setEventHandler { [weak self] in self?.sendRequestSync() }
+        timer.resume()
+        periodicTimer = timer
+    }
+
+    func stop() {
+        periodicTimer?.cancel(); periodicTimer = nil
+    }
+
+    func scheduleInitialSyncToPeer(_ peerID: String, delaySeconds: TimeInterval = 5.0) {
+        queue.asyncAfter(deadline: .now() + delaySeconds) { [weak self] in
+            self?.sendRequestSync(to: peerID)
+        }
+    }
+
+    func onPublicPacketSeen(_ packet: BitchatPacket) {
+        let mt = MessageType(rawValue: packet.type)
+        let isBroadcastMessage = (mt == .message && packet.recipientID == nil)
+        let isAnnounce = (mt == .announce)
+        guard isBroadcastMessage || isAnnounce else { return }
+
+        let idBytes = PacketIdUtil.computeId(packet)
+        bloom.add(idBytes)
+        let idHex = idBytes.hexEncodedString()
+
+        if isBroadcastMessage {
+            if messages[idHex] == nil {
+                messages[idHex] = packet
+                messageOrder.append(idHex)
+                // Enforce capacity
+                let cap = max(1, config.seenCapacity)
+                while messageOrder.count > cap {
+                    let victim = messageOrder.removeFirst()
+                    messages.removeValue(forKey: victim)
+                }
+            }
+        } else if isAnnounce {
+            let sender = packet.senderID.hexEncodedString()
+            latestAnnouncementByPeer[sender] = (id: idHex, packet: packet)
+        }
+    }
+
+    private func sendRequestSync() {
+        let snap = bloom.snapshotActive()
+        let payload = RequestSyncPacket(mBytes: snap.mBytes, k: snap.k, bits: snap.bits).encode()
+        let pkt = BitchatPacket(
+            type: MessageType.requestSync.rawValue,
+            senderID: Data(hexString: myPeerID) ?? Data(),
+            recipientID: nil, // broadcast
+            timestamp: UInt64(Date().timeIntervalSince1970 * 1000),
+            payload: payload,
+            signature: nil,
+            ttl: 0 // local-only
+        )
+        let signed = delegate?.signPacketForBroadcast(pkt) ?? pkt
+        delegate?.sendPacket(signed)
+    }
+
+    private func sendRequestSync(to peerID: String) {
+        let snap = bloom.snapshotActive()
+        let payload = RequestSyncPacket(mBytes: snap.mBytes, k: snap.k, bits: snap.bits).encode()
+        var recipient = Data()
+        var temp = peerID
+        while temp.count >= 2 && recipient.count < 8 {
+            let hexByte = String(temp.prefix(2))
+            if let b = UInt8(hexByte, radix: 16) { recipient.append(b) }
+            temp = String(temp.dropFirst(2))
+        }
+        let pkt = BitchatPacket(
+            type: MessageType.requestSync.rawValue,
+            senderID: Data(hexString: myPeerID) ?? Data(),
+            recipientID: recipient,
+            timestamp: UInt64(Date().timeIntervalSince1970 * 1000),
+            payload: payload,
+            signature: nil,
+            ttl: 0 // local-only
+        )
+        let signed = delegate?.signPacketForBroadcast(pkt) ?? pkt
+        delegate?.sendPacket(to: peerID, packet: signed)
+    }
+
+    func handleRequestSync(fromPeerID: String, request: RequestSyncPacket) {
+        // Build membership checker from provided parameters
+        let mBits = request.mBytes * 8
+        let k = request.k
+        func mightContain(_ id: Data) -> Bool {
+            // Same hashing as local bloom; compute indices, check MSB-first bits in request.bits
+            var h1: UInt64 = 1469598103934665603
+            var h2: UInt64 = 0x27d4eb2f165667c5
+            for b in id { h1 = (h1 ^ UInt64(b)) &* 1099511628211; h2 = (h2 ^ UInt64(b)) &* 0x100000001B3 }
+            for i in 0..<k {
+                let combined = h1 &+ (UInt64(i) &* h2)
+                let idx = Int((combined & 0x7fff_ffff_ffff_ffff) % UInt64(mBits))
+                let byteIndex = idx / 8
+                let bitIndex = idx % 8
+                let byte = request.bits[byteIndex]
+                let bit = ((Int(byte) >> (7 - bitIndex)) & 1) == 1
+                if !bit { return false }
+            }
+            return true
+        }
+
+        // 1) Announcements: send latest per peer if requester lacks them
+        for (_, pair) in latestAnnouncementByPeer {
+            let (idHex, pkt) = pair
+            let idBytes = Data(hexString: idHex) ?? Data()
+            if !mightContain(idBytes) {
+                var toSend = pkt
+                toSend.ttl = 0
+                delegate?.sendPacket(to: fromPeerID, packet: toSend)
+            }
+        }
+
+        // 2) Broadcast messages: send all missing
+        let toSendMsgs = messageOrder.compactMap { messages[$0] }
+        for pkt in toSendMsgs {
+            let idBytes = PacketIdUtil.computeId(pkt)
+            if !mightContain(idBytes) {
+                var toSend = pkt
+                toSend.ttl = 0
+                delegate?.sendPacket(to: fromPeerID, packet: toSend)
+            }
+        }
+    }
+}
+

bitchat/Sync/PacketIdUtil.swift

@@ -0,0 +1,22 @@
+import Foundation
+import CryptoKit
+
+// Deterministic packet ID used for sync Bloom membership
+// ID = first 16 bytes of SHA-256 over: [type | senderID | timestamp | payload]
+enum PacketIdUtil {
+    static func computeId(_ packet: BitchatPacket) -> Data {
+        var hasher = SHA256()
+        hasher.update(data: Data([packet.type]))
+        hasher.update(data: packet.senderID)
+        var tsBE = packet.timestamp.bigEndian
+        withUnsafeBytes(of: &tsBE) { raw in hasher.update(data: Data(raw)) }
+        hasher.update(data: packet.payload)
+        let digest = hasher.finalize()
+        return Data(digest.prefix(16))
+    }
+
+    static func computeIdHex(_ packet: BitchatPacket) -> String {
+        return computeId(packet).hexEncodedString()
+    }
+}
+

bitchat/Sync/SeenPacketsBloomFilter.swift

@@ -0,0 +1,116 @@
+import Foundation
+
+// Rotating Bloom filter for recently seen packet IDs (16-byte IDs)
+final class SeenPacketsBloomFilter {
+    struct Snapshot { let mBytes: Int; let k: Int; let bits: Data }
+
+    private struct Filter { var mBits: Int; var k: Int; var bits: [UInt8]; var count: Int }
+
+    private let maxBytes: Int
+    private let targetFpr: Double
+    private let seed: UInt64 = 0x27d4eb2f165667c5
+
+    private let mBits: Int
+    private let kOptimal: Int
+    private let capacityOptimal: Int
+
+    private var active: Filter
+    private var standby: Filter
+    private var usingStandby: Bool = false
+    private let lock = NSLock()
+
+    init(maxBytes: Int = 256, targetFpr: Double = 0.01) {
+        self.maxBytes = max(1, maxBytes)
+        self.targetFpr = targetFpr
+        self.mBits = max(8, self.maxBytes * 8)
+        let (k, n) = SeenPacketsBloomFilter.deriveParams(mBits: self.mBits, fpr: targetFpr)
+        self.kOptimal = max(1, k)
+        self.capacityOptimal = max(1, n)
+        self.active = Filter(mBits: self.mBits, k: self.kOptimal, bits: [UInt8](repeating: 0, count: self.maxBytes), count: 0)
+        self.standby = Filter(mBits: self.mBits, k: self.kOptimal, bits: [UInt8](repeating: 0, count: self.maxBytes), count: 0)
+    }
+
+    private static func deriveParams(mBits: Int, fpr: Double) -> (Int, Int) {
+        // n ≈ -(m (ln 2)^2) / ln p ; k ≈ (m/n) ln 2
+        let ln2 = log(2.0)
+        let n = max(1, Int(Double(-mBits) * ln2 * ln2 / log(fpr)))
+        let k = max(1, Int(ceil((Double(mBits) / Double(n)) * ln2)))
+        return (k, n)
+    }
+
+    private func indicesFor(id: Data, mBits: Int, k: Int) -> [Int] {
+        var h1: UInt64 = 1469598103934665603 // FNV-1a 64-bit offset
+        var h2: UInt64 = seed
+        for b in id { // treat as unsigned bytes
+            h1 = (h1 ^ UInt64(b)) &* 1099511628211
+            h2 = (h2 ^ UInt64(b)) &* 0x100000001B3
+        }
+        var result = [Int]()
+        result.reserveCapacity(k)
+        for i in 0..<k {
+            let combined = h1 &+ (UInt64(i) &* h2)
+            let idx = Int((combined & 0x7fff_ffff_ffff_ffff) % UInt64(mBits))
+            result.append(idx)
+        }
+        return result
+    }
+
+    func add(_ id: Data) {
+        lock.lock(); defer { lock.unlock() }
+        let startStandbyAt = capacityOptimal / 2
+        if !usingStandby && active.count >= startStandbyAt {
+            standby = Filter(mBits: mBits, k: kOptimal, bits: [UInt8](repeating: 0, count: maxBytes), count: 0)
+            usingStandby = true
+        }
+        insert(into: &active, id: id)
+        if usingStandby { insert(into: &standby, id: id) }
+        if active.count >= capacityOptimal {
+            active = standby
+            standby = Filter(mBits: mBits, k: kOptimal, bits: [UInt8](repeating: 0, count: maxBytes), count: 0)
+            usingStandby = false
+        }
+    }
+
+    private func insert(into filter: inout Filter, id: Data) {
+        let idxs = indicesFor(id: id, mBits: filter.mBits, k: filter.k)
+        for i in idxs {
+            let byteIndex = i / 8
+            let bitIndex = i % 8
+            filter.bits[byteIndex] = UInt8(Int(filter.bits[byteIndex]) | (1 << (7 - bitIndex)))
+        }
+        filter.count &+= 1
+    }
+
+    func mightContain(_ id: Data) -> Bool {
+        lock.lock(); defer { lock.unlock() }
+        let a = active
+        let idx = indicesFor(id: id, mBits: a.mBits, k: a.k)
+        var inActive = true
+        for i in idx {
+            let byteIndex = i / 8
+            let bitIndex = i % 8
+            let set = ((Int(a.bits[byteIndex]) >> (7 - bitIndex)) & 1) == 1
+            if !set { inActive = false; break }
+        }
+        if inActive { return true }
+        if usingStandby {
+            let s = standby
+            let idx2 = indicesFor(id: id, mBits: s.mBits, k: s.k)
+            for i in idx2 {
+                let byteIndex = i / 8
+                let bitIndex = i % 8
+                let set = ((Int(s.bits[byteIndex]) >> (7 - bitIndex)) & 1) == 1
+                if !set { return false }
+            }
+            return true
+        }
+        return false
+    }
+
+    func snapshotActive() -> Snapshot {
+        lock.lock(); defer { lock.unlock() }
+        let a = active
+        return Snapshot(mBytes: a.bits.count, k: a.k, bits: Data(a.bits))
+    }
+}
+