[JENKINS-20128] reproduced the problem

test/src/test/groovy/hudson/cli/CLIActionTest.groovy

+package hudson.cli
+
+import hudson.remoting.Channel
+import org.junit.Rule
+import org.junit.Test
+import org.jvnet.hudson.test.JenkinsRule
+
+import java.util.concurrent.ExecutorService
+import java.util.concurrent.Executors
+
+/**
+ *
+ *
+ * @author Kohsuke Kawaguchi
+ */
+class CLIActionTest {
+    @Rule
+    public JenkinsRule j = new JenkinsRule()
+
+    ExecutorService pool;
+
+    /**
+     * Makes sure that the /cli endpoint is functioning.
+     */
+    @Test
+    public void testDuplexHttp() {
+        pool = Executors.newCachedThreadPool()
+        try {
+            FullDuplexHttpStream con = new FullDuplexHttpStream(new URL(j.URL,"cli"));
+            Channel ch = new Channel("test connection", pool, con.inputStream, con.outputStream);
+            ch.close();
+        } finally {
+            pool.shutdown();
+        }
+    }
+}