2006-10-08 Complication

* Add a framed average peer clock skew calculator
    * Add config property "router.clockOffsetSanityCheck" to determine
      if NTP-suggested clock offsets get sanity checked (default "true")
    * Reject NTP-suggested clock offsets if they'd increase peer clock skew
      by more than 5 seconds, or make it more than 20 seconds total
    * Decrease log level in getMedianPeerClockSkew()

history.txt

@@ -1,4 +1,12 @@
-$Id: history.txt,v 1.529 2006-09-27 01:00:33 jrandom Exp $
+$Id: history.txt,v 1.530 2006-09-29 18:54:19 zzz Exp $
+
+2006-10-08  Complication
+    * Add a framed average peer clock skew calculator
+    * Add config property "router.clockOffsetSanityCheck" to determine
+      if NTP-suggested clock offsets get sanity checked (default "true")
+    * Reject NTP-suggested clock offsets if they'd increase peer clock skew
+      by more than 5 seconds, or make it more than 20 seconds total
+    * Decrease log level in getMedianPeerClockSkew()
 
 2006-09-29  zzz
     * i2psnark: Second try at synchronization fix - synch addRequest()

router/java/src/net/i2p/router/CommSystemFacade.java

@@ -39,6 +39,12 @@ public abstract class CommSystemFacade implements Service {
      */
     public Long getMedianPeerClockSkew() { return null; }
     
+    /**
+     * Return framed average clock skew of connected peers in seconds, or null if we cannot answer.
+     * CommSystemFacadeImpl overrides this.
+     */
+    public Long getFramedAveragePeerClockSkew(int percentToInclude) { return null; }
+    
     /**
      * Determine under what conditions we are remotely reachable.
      *

router/java/src/net/i2p/router/RouterClock.java

@@ -31,9 +31,6 @@ public class RouterClock extends Clock {
      */
     public void setOffset(long offsetMs, boolean force) {
 
-        // To test new routines, calculate median peer clock skew
-        Long medianPeerClockSkew = _context.commSystem().getMedianPeerClockSkew();
-
         if (false) return;
         long delta = offsetMs - _offset;
         if (!force) {
@@ -56,7 +53,36 @@ public class RouterClock extends Clock {
                 _alreadyChanged = true;
                 return;
             }
+
+            // If so configured, check sanity of proposed clock offset
+            if (Boolean.valueOf(_context.getProperty("router.clockOffsetSanityCheck","true")).booleanValue() == true) {
+
+                // Try calculating peer clock skew
+                Long peerClockSkew = _context.commSystem().getFramedAveragePeerClockSkew(50);
+
+                if (peerClockSkew != null) {
+
+                    // Predict the effect of applying the proposed clock offset
+                    long currentPeerClockSkew = peerClockSkew.longValue();
+                    long predictedPeerClockSkew = currentPeerClockSkew + (delta / 1000l);
+
+                    // Fail sanity check if applying the offset would increase peer clock skew
+                    if ((Math.abs(predictedPeerClockSkew) > (Math.abs(currentPeerClockSkew) + 5)) ||
+                        (Math.abs(predictedPeerClockSkew) > 20)) {
+
+                        getLog().error("Ignoring clock offset " + offsetMs + "ms (current " + _offset +
+                                       "ms) since it would increase peer clock skew from " + currentPeerClockSkew +
+                                       "s to " + predictedPeerClockSkew + "s. Broken server in pool.ntp.org?");
+                        return;
+                    } else {
+                        getLog().debug("Approving clock offset " + offsetMs + "ms (current " + _offset +
+                                       "ms) since it would decrease peer clock skew from " + currentPeerClockSkew +
+                                       "s to " + predictedPeerClockSkew + "s.");
+                    }
+                }
+            } // check sanity
         }
+
         if (_alreadyChanged) {
             if (delta > 15*1000)
                 getLog().log(Log.CRIT, "Updating clock offset to " + offsetMs + "ms from " + _offset + "ms");

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

@@ -15,9 +15,9 @@ import net.i2p.CoreVersion;
  *
  */
 public class RouterVersion {
-    public final static String ID = "$Revision: 1.464 $ $Date: 2006-09-27 01:00:37 $";
+    public final static String ID = "$Revision: 1.465 $ $Date: 2006-09-29 18:54:17 $";
     public final static String VERSION = "0.6.1.25";
-    public final static long BUILD = 11;
+    public final static long BUILD = 12;
     public static void main(String args[]) {
         System.out.println("I2P Router version: " + VERSION + "-" + BUILD);
         System.out.println("Router ID: " + RouterVersion.ID);

router/java/src/net/i2p/router/transport/CommSystemFacadeImpl.java

@@ -84,11 +84,53 @@ public class CommSystemFacadeImpl extends CommSystemFacade {
         Collections.sort(skews);
         // Pick out median
         Long medianPeerClockSkew = (Long) (skews.get(skews.size() / 2));
-        if (_log.shouldLog(Log.WARN))
+        if (_log.shouldLog(Log.INFO))
-            _log.warn("Our median peer clock skew is " + medianPeerClockSkew + " s.");
+            _log.info("Our median peer clock skew is " + medianPeerClockSkew + " s.");
         return medianPeerClockSkew;
     }
     
+    /**
+     * Framed average clock skew of connected peers in seconds, or null if we cannot answer.
+     * Average is calculated over the middle "percentToInclude" peers.
+     */
+    public Long getFramedAveragePeerClockSkew(int percentToInclude) {
+        if (_manager == null) {
+            if (_log.shouldLog(Log.INFO))
+                _log.info("Returning null for framed averege peer clock skew (no transport manager)!");
+            return null;
+        }
+        Vector skews = _manager.getClockSkews();
+        if (skews == null) {
+            if (_log.shouldLog(Log.ERROR))
+                _log.error("Returning null for framed average peer clock skew (no data)!");
+            return null;
+        }
+        if (skews.size() < 5) {
+            if (_log.shouldLog(Log.ERROR))
+                _log.error("Returning null for framed average peer clock skew (only " + skews.size() + " peers)!");
+            return null;
+        }
+        // Going to calculate, sort them
+        Collections.sort(skews);
+        // Calculate frame size
+        int frameSize = (skews.size() * percentToInclude / 100);
+        int first = (skews.size() / 2) - (frameSize / 2);
+        int last = (skews.size() / 2) + (frameSize / 2);
+        // Sum skew values
+        long sum = 0;
+        for (int i = first; i < last; i++) {
+            long value = ((Long) (skews.get(i))).longValue();
+            if (_log.shouldLog(Log.DEBUG))
+                _log.debug("Adding clock skew " + i + " valued " + value + " s.");
+            sum = sum + value;
+        }
+        // Calculate average
+        Long framedAverageClockSkew = new Long(sum / frameSize);
+        if (_log.shouldLog(Log.INFO))
+            _log.info("Our framed average peer clock skew is " + framedAverageClockSkew + " s.");
+        return framedAverageClockSkew;
+    }
+    
     public List getBids(OutNetMessage msg) {
         return _manager.getBids(msg);
     }