[JENKINS-48761] - Restore binary compatibility with agents running old Remoting versions

core/src/main/java/hudson/Launcher.java

@@ -1289,7 +1289,7 @@ public abstract class Launcher {
         }
 
         public RemoteProcess call() throws IOException {
-            final Channel channel = getOpenChannelOrFail();
+            final Channel channel = _getOpenChannelOrFail();
             Launcher.ProcStarter ps = new LocalLauncher(listener).launch();
             ps.cmds(cmd).masks(masks).envs(env).stdin(in).stdout(out).stderr(err).quiet(quiet);
             if(workDir!=null)   ps.pwd(workDir);
@@ -1308,7 +1308,11 @@ public abstract class Launcher {
                         Channel taskChannel = null;
                         try {
                             // Sync IO will fail automatically if the channel is being closed, no need to use getOpenChannelOrFail()
-                            taskChannel = Channel.currentOrFail();
+                            // TODOL Replace by Channel#currentOrFail() when Remoting version allows
+                            taskChannel = Channel.current();
+                            if (taskChannel == null) {
+                                throw new IOException("No Remoting channel associated with this thread");
+                            }
                             taskChannel.syncIO();
                         } catch (Throwable t) {
                             // this includes a failure to sync, agent.jar too old, etc

core/src/main/java/hudson/model/Computer.java

@@ -1426,7 +1426,7 @@ public /*transient*/ abstract class Computer extends Actionable implements Acces
 
     private static final class DumpExportTableTask extends MasterToSlaveCallable<String,IOException> {
         public String call() throws IOException {
-            final Channel ch = getChannelOrFail();
+            final Channel ch = _getChannelOrFail();
             StringWriter sw = new StringWriter();
             try (PrintWriter pw = new PrintWriter(sw)) {
                 ch.dumpExportTable(pw);

core/src/main/java/hudson/slaves/ChannelPinger.java

@@ -134,7 +134,7 @@ public class ChannelPinger extends ComputerListener {
         @Override
         public Void call() throws IOException {
             // No sense in setting up channel pinger if the channel is being closed
-            setUpPingForChannel(getOpenChannelOrFail(), null, pingTimeoutSeconds, pingIntervalSeconds, false);
+            setUpPingForChannel(_getOpenChannelOrFail(), null, pingTimeoutSeconds, pingIntervalSeconds, false);
             return null;
         }
 

core/src/main/java/hudson/slaves/SlaveComputer.java

@@ -38,6 +38,7 @@ import hudson.model.TaskListener;
 import hudson.model.User;
 import hudson.remoting.Channel;
 import hudson.remoting.ChannelBuilder;
+import hudson.remoting.ChannelClosedException;
 import hudson.remoting.Launcher;
 import hudson.remoting.VirtualChannel;
 import hudson.security.ACL;
@@ -867,7 +868,11 @@ public class SlaveComputer extends Computer {
                 // ignore this error.
             }
 
-            Channel.currentOrFail().setProperty("slave",Boolean.TRUE); // indicate that this side of the channel is the slave side.
+            try {
+                _getChannelOrFail().setProperty("slave",Boolean.TRUE); // indicate that this side of the channel is the slave side.
+            } catch (ChannelClosedException e) {
+                throw new IllegalStateException(e);
+            }
 
             return null;
         }

core/src/main/java/jenkins/security/MasterToSlaveCallable.java

 package jenkins.security;
 
 import hudson.remoting.Callable;
+import hudson.remoting.Channel;
+import hudson.remoting.ChannelClosedException;
 import org.jenkinsci.remoting.RoleChecker;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import javax.annotation.Nonnull;
 
 
 /**
@@ -11,10 +17,31 @@ import org.jenkinsci.remoting.RoleChecker;
  * @since 1.587 / 1.580.1
  */
 public abstract class MasterToSlaveCallable<V, T extends Throwable> implements Callable<V,T> {
+
+    private static final long serialVersionUID = 1L;
+
     @Override
     public void checkRoles(RoleChecker checker) throws SecurityException {
         checker.check(this,Roles.SLAVE);
     }
 
-    private static final long serialVersionUID = 1L;
+    //TODO: replace by Callable#getChannelOrFail() once Minimal supported Remoting version is 3.15 or above
+    @Restricted(NoExternalUse.class)
+    protected static Channel _getChannelOrFail() throws ChannelClosedException {
+        final Channel ch = Channel.current();
+        if (ch == null) {
+            throw new ChannelClosedException("No channel associated with the thread", null);
+        }
+        return ch;
+    }
+
+    //TODO: replace by Callable#getOpenChannelOrFail() once Minimal supported Remoting version is 3.15 or above
+    @Restricted(NoExternalUse.class)
+    protected static Channel _getOpenChannelOrFail() throws ChannelClosedException {
+        final Channel ch = _getChannelOrFail();
+        if (ch.isClosingOrClosed()) { // TODO: Since Remoting 2.33, we still need to explicitly declare minimal Remoting version
+            throw new ChannelClosedException("The associated channel " + ch + " is closing down or has closed down", ch.getCloseRequestCause());
+        }
+        return ch;
+    }
 }

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

@@ -39,7 +39,7 @@ public class StandardOutputSwapper extends ComputerListener {
     private static final class ChannelSwapper extends MasterToSlaveCallable<Boolean,Exception> {
         public Boolean call() throws Exception {
             if (File.pathSeparatorChar==';')    return false;   // Windows
-            Channel c = getOpenChannelOrFail();
+            Channel c = _getOpenChannelOrFail();
             StandardOutputStream sos = (StandardOutputStream) c.getProperty(StandardOutputStream.class);
             if (sos!=null) {
                 swap(sos);