SSU2: Implement ack-immediate flag

Use a single ack timer for each session rather than
creating a new one for every ack
Log tweaks

history.txt

@@ -1,3 +1,12 @@
+2022-08-29 zzz
+ * SSU2: Implement ack-immediate flag
+
+2022-08-28 zzz
+ * Console:
+   - Add notification and summary bar info on deadlock
+   - Linkify router hash even if not in netdb
+ * Util: Add option to gzip router logs
+
 2022-08-25 zzz
  * Router: Fix deadlock via rebuildRouterAddress() and UDPTransport
  * SSU2:

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Git";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 2;
+    public final static long BUILD = 3;
 
     /** for example "-test" */
     public final static String EXTRA = "";

router/java/src/net/i2p/router/transport/udp/PacketBuilder2.java

@@ -275,6 +275,11 @@ class PacketBuilder2 {
         //if (_log.shouldDebug())
         //    _log.debug("Packet " + pktNum + " before encryption:\n" + HexDump.dump(data, 0, off));
 
+        // ack immediate flag
+        if (numFragments > 0) {
+            data[SHORT_HEADER_FLAGS_OFFSET] = peer.getFlags();
+        }
+
         encryptDataPacket(packet, peer.getSendCipher(), pktNum, peer.getSendHeaderEncryptKey1(), peer.getSendHeaderEncryptKey2());
         setTo(packet, peer.getRemoteIPAddress(), peer.getRemotePort());
         //if (_log.shouldDebug())
@@ -351,8 +356,8 @@ class PacketBuilder2 {
      *  This will also include acks, a new token block, and padding.
      */
     public UDPPacket buildSessionDestroyPacket(int reason, PeerState2 peer) {
-            if (_log.shouldWarn())
-                _log.warn("Sending termination " + reason + " to : " + peer);
+        if (_log.shouldDebug())
+            _log.debug("Sending termination " + reason + " to : " + peer);
         List<Block> blocks = new ArrayList<Block>(2);
         if (peer.getKeyEstablishedTime() - _context.clock().now() > EstablishmentManager.IB_TOKEN_EXPIRATION / 2 &&
             !_context.router().gracefulShutdownInProgress()) {

router/java/src/net/i2p/router/transport/udp/PeerState.java

@@ -2214,6 +2214,17 @@ public class PeerState {
         }
     }
 
+    /**
+     * SSU 2 only
+     *
+     * @since 0.9.56
+     */
+    protected boolean shouldRequestImmediateAck() {
+        synchronized(_sendWindowBytesRemainingLock) {
+            return _sendWindowBytesRemaining < _sendWindowBytes / 3;
+        }
+    }
+
     /**
      * Transfer the basic activity/state from the old peer to the current peer
      *

router/java/src/net/i2p/router/transport/udp/PeerState2.java

@@ -63,6 +63,8 @@ public class PeerState2 extends PeerState implements SSU2Payload.PayloadCallback
      */
     private final SSU2Bitfield _ackedMessages;
     private final ConcurrentHashMap<Long, List<PacketBuilder.Fragment>> _sentMessages;
+    private final ACKTimer _ackTimer;
+
     private long _sentMessagesLastExpired;
     private byte[] _ourIP;
     private int _ourPort;
@@ -140,6 +142,7 @@ public class PeerState2 extends PeerState implements SSU2Payload.PayloadCallback
             // For outbound, SessionConfirmed is packet 0
             _packetNumber.set(1);
         }
+        _ackTimer = new ACKTimer();
     }
 
     // SSU 1 overrides
@@ -197,7 +200,7 @@ public class PeerState2 extends PeerState implements SSU2Payload.PayloadCallback
     protected synchronized void messagePartiallyReceived(long now) {
         if (_wantACKSendSince <= 0) {
             _wantACKSendSince = now;
-            new ACKTimer();
+            _ackTimer.schedule();
         }
     }
 
@@ -490,6 +493,11 @@ public class PeerState2 extends PeerState implements SSU2Payload.PayloadCallback
                     ECNReceived();
             }   //// !_dead
 
+            boolean ackImmediate = (header.data[SHORT_HEADER_FLAGS_OFFSET] & 0x01) != 0 && _context.getBooleanProperty("ssu2.ackImmediate");
+            if (ackImmediate) {
+                _ackTimer.scheduleImmediate();
+            }
+
         } catch (Exception e) {
             if (_log.shouldWarn())
                 _log.warn("Bad encrypted packet on: " + this + '\n' + HexDump.dump(data, off, len), e);
@@ -958,16 +966,50 @@ public class PeerState2 extends PeerState implements SSU2Payload.PayloadCallback
         return rv;
     }
 
+    /**
+     *  Flag byte to be sent in header
+     *
+     *  @since 0.9.56
+     */
+    byte getFlags() {
+        return shouldRequestImmediateAck() ? (byte) 0x01 : 0;
+    }
+
     /**
      *  A timer to send an ack-only packet.
      */
     private class ACKTimer extends SimpleTimer2.TimedEvent {
+
+        /**
+         *  Caller must schedule
+         */
         public ACKTimer() {
             super(_context.simpleTimer2());
+        }
+
+        /**
+         *  Ack soon, based on the current RTT
+         *
+         *  @since 0.9.56
+         */
+        public void schedule() {
             long delta = Math.max(10, Math.min(_rtt/6, ACK_FREQUENCY));
             if (_log.shouldDebug())
                 _log.debug("Sending delayed ack in " + delta + ": " + PeerState2.this);
-            schedule(delta);
+            reschedule(delta, true);
+        }
+
+        /**
+         *  Ack almost immediately
+         *
+         *  @since 0.9.56
+         */
+        public void scheduleImmediate() {
+            _wantACKSendSince = _context.clock().now();
+            long delta = Math.min(_rtt/16, 5);
+            if (_log.shouldDebug())
+                _log.debug("Sending immediate ack in " + delta + ": " + PeerState2.this);
+            reschedule(delta, true);
         }
 
         /**