Hide ServerListPingEvent exceptions thrown by CB's LegacyPingHandler (#2378)

Fixes #2327.

Essentials/src/com/earth2me/essentials/EssentialsServerListener.java

@@ -10,12 +10,17 @@ import org.bukkit.event.server.ServerListPingEvent;
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
 import java.util.logging.Level;
 
 
 public class EssentialsServerListener implements Listener {
+    private static List<String> ignoredSLPECallers = Arrays.asList(
+        ".LegacyPingHandler.channelRead(" // CB responding to pings from pre-Netty clients
+    );
+
     private final transient IEssentials ess;
     private boolean unsupportedLogged = false;
     private boolean npeWarned = false;
@@ -46,22 +51,16 @@ public class EssentialsServerListener implements Listener {
         if (isPaperSample) {
             try {
                 List<String> playerNames = (List<String>) getSampleText.invoke(event, null);
-                Iterator<String> iterator = playerNames.iterator();
+                playerNames.removeIf(player -> ess.getUser(player).isVanished());
-                while (iterator.hasNext()) {
-                    String player = iterator.next();
-                    if (ess.getUser(player).isVanished()) {
-                        iterator.remove();
-                    }
-                }
                 setSampleText.invoke(event, playerNames);
             } catch (IllegalAccessException | InvocationTargetException | ClassCastException e) {
-                if (!unsupportedLogged) {
+                if (!unsupportedLogged && shouldWarnSLPECaller(e)) {
                     ess.getLogger().log(Level.WARNING, "Unable to hide players from server list ping "
-                            + "using Paper 1.12+ method!", e);
+                            + "using Paper 1.12 method!", e);
                     unsupportedLogged = true;
                 }
             } catch (NullPointerException e) {
-                if (!npeWarned) {
+                if (!npeWarned && shouldWarnSLPECaller(e)) {
                     npeWarned = true;
                     Exception ex = new Exception("A plugin has fired a ServerListPingEvent "
                             + "without implementing Paper's methods. Point the author to https://git.io/v7Xzl.");
@@ -79,11 +78,38 @@ public class EssentialsServerListener implements Listener {
                     }
                 }
             } catch (UnsupportedOperationException e) {
-                if (!unsupportedLogged) {
+                if (!unsupportedLogged && shouldWarnSLPECaller(e)) {
                     ess.getLogger().log(Level.WARNING, "Could not hide vanished players while handling " + event.getClass().getName(), e);
                     unsupportedLogged = true;
                 }
             }
         }
     }
+
+    /**
+     * Should we warn about this SLPE caller, or should we silently ignore it?
+     * This checks against the ignoredSLPECallers strings, and if it matches one of those, we
+     * return false.
+     *
+     * @param throwable A throwable caught by a catch block
+     * @return Whether or not to send a warning about this particular caller
+     */
+    private boolean shouldWarnSLPECaller(Throwable throwable) {
+        final int maxStackDepth = 20; // Limit the depth when searching through the stack trace
+        int depth = 0;
+        for (StackTraceElement element : throwable.getStackTrace()) {
+            depth++;
+            if (depth > maxStackDepth) {
+                break;
+            }
+
+            for (String ignoredString : ignoredSLPECallers) {
+                if (element.toString().contains(ignoredString)) {
+                    return false; // We know about this error and should ignore it, so don't warn
+                }
+            }
+        }
+
+        return true; // We don't know for certain that we can ignore this, so warn just to be safe
+    }
 }