[JENKINS-8856] evacuate stdout at OS level to avoid interference with

JVM.

changelog.html

@@ -67,6 +67,9 @@ Upcoming changes</a>
   <li class=bug>
     Jenkins didn't start on IBM JDK.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-10810">issue 10810</a>)
+  <li class=rfe>
+    stdin/stdout based remote slaves, such as ones launched via SSH or script, now does a better redirect to avoid interference with JVM output to stdout.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-8856">issue 8856</a>)
 </ul>
 </div><!--=TRUNK-END=-->
 

core/src/main/java/hudson/util/jna/GNUCLibrary.java

@@ -72,6 +72,10 @@ public interface GNUCLibrary extends Library {
     int chown(String fileName, int uid, int gid);
     int chmod(String fileName, int i);
 
+    int dup(int old);
+    int dup2(int old, int _new);
+    int close(int fd);
+
     // see http://www.gnu.org/s/libc/manual/html_node/Renaming-Files.html
     int rename(String oldname, String newname);
 

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

+package jenkins.slaves;
+
+import hudson.Extension;
+import hudson.FilePath;
+import hudson.model.Computer;
+import hudson.model.TaskListener;
+import hudson.remoting.Callable;
+import hudson.remoting.Channel;
+import hudson.remoting.StandardOutputStream;
+import hudson.slaves.ComputerListener;
+import hudson.util.jna.GNUCLibrary;
+
+import java.io.File;
+import java.io.FileDescriptor;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.lang.reflect.Constructor;
+import java.util.logging.Logger;
+
+/**
+ * @author Kohsuke Kawaguchi
+ */
+@Extension
+public class StandardOutputSwapper extends ComputerListener {
+    @Override
+    public void preOnline(Computer c, Channel channel, FilePath root, TaskListener listener)  {
+        if (disabled)   return;
+
+        try {
+            if (channel.call(new ChannelSwapper()))
+                listener.getLogger().println("Evacuated stdout");
+        } catch (Throwable e) {
+            LOGGER.fine("Fatal problem swapping file descriptors " + c.getName());
+        }
+    }
+
+    private static final class ChannelSwapper implements Callable<Boolean,Exception> {
+        public Boolean call() throws Exception {
+            if (File.pathSeparatorChar==';')    return false;   // Windows
+            
+            OutputStream o = Channel.current().getUnderlyingOutput();
+            if (o instanceof StandardOutputStream) {
+                StandardOutputStream stdout = (StandardOutputStream)o;
+
+                // duplicate the OS file descriptor and create FileOutputStream around it
+                int out = GNUCLibrary.LIBC.dup(1);
+                if (out<0)      throw new IOException("Failed to dup(1)");
+                Constructor<FileDescriptor> c = FileDescriptor.class.getDeclaredConstructor(int.class);
+                c.setAccessible(true);
+                FileOutputStream fos = new FileOutputStream(c.newInstance(out));
+
+                // swap it into channel so that it'll use the new file descriptor
+                stdout.swap(fos);
+
+                // close fd=1 (stdout) and duplicate fd=2 (stderr) into fd=1 (stdout)
+                GNUCLibrary.LIBC.close(1);
+                GNUCLibrary.LIBC.dup2(2,1);
+                return true;
+            }
+            return false;
+        }
+    }
+
+    private static final Logger LOGGER = Logger.getLogger(StandardOutputSwapper.class.getName());
+    public static boolean disabled = Boolean.getBoolean(StandardOutputSwapper.class.getName()+".disabled");
+}

pom.xml

@@ -133,7 +133,7 @@ THE SOFTWARE.
       <dependency>
         <groupId>org.jenkins-ci.main</groupId>
         <artifactId>remoting</artifactId>
-        <version>2.4</version>
+        <version>2.5</version>
       </dependency>
     </dependencies>
   </dependencyManagement>