[JENKINS-57993] Avoid printing stack traces for some common agent conditions.

core/src/main/java/hudson/TcpSlaveAgentListener.java

@@ -43,13 +43,13 @@ import hudson.slaves.OfflineCause;
 import java.io.DataOutputStream;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.io.UnsupportedEncodingException;
 import java.net.SocketAddress;
 import java.util.Arrays;
 import jenkins.AgentProtocol;
 
 import java.io.BufferedWriter;
 import java.io.DataInputStream;
+import java.io.EOFException;
 import java.io.IOException;
 import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
@@ -286,7 +286,11 @@ public final class TcpSlaveAgentListener extends Thread {
                     // try to clean up the socket
                 }
             } catch (IOException e) {
-                LOGGER.log(Level.WARNING,"Connection #"+id+" failed",e);
+                if (e instanceof EOFException) {
+                    LOGGER.log(Level.INFO, "Connection #{0} failed: {1}", new Object[] {id, e});
+                } else {
+                    LOGGER.log(Level.WARNING, "Connection #" + id + " failed", e);
+                }
                 try {
                     s.close();
                 } catch (IOException ex) {

core/src/main/java/jenkins/slaves/DefaultJnlpSlaveReceiver.java

@@ -24,6 +24,7 @@ import jenkins.util.SystemProperties;
 import org.jenkinsci.remoting.engine.JnlpConnectionState;
 
 import java.io.IOException;
+import java.nio.channels.ClosedChannelException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -181,7 +182,9 @@ public class DefaultJnlpSlaveReceiver extends JnlpAgentReceiver {
     public void channelClosed(@NonNull JnlpConnectionState event) {
         final String nodeName = event.getProperty(JnlpConnectionState.CLIENT_NAME_KEY);
         IOException cause = event.getCloseCause();
-        if (cause != null) {
+        if (cause instanceof ClosedChannelException) {
+            LOGGER.log(Level.INFO, "{0} for {1} terminated: {2}", new Object[] {Thread.currentThread().getName(), nodeName, cause});
+        } else if (cause != null) {
             LOGGER.log(Level.WARNING, Thread.currentThread().getName() + " for " + nodeName + " terminated",
                     cause);
         }