ZOOKEEPER-1871: Add an option to zkCli to wait for connection before executing commands

-waitforconnection option will make zk client wait for -timeout time to connect to zk server.  timeout time is 30ms by default but can be specified explicitly for a session using -timeout option in command line.

Author: Mukti <muktikrishnan94@gmail.com>

Reviewers: maoling <maoling@apache.org>, Mohammad Arshad <arshad@apache.org>

Closes #1626 from MuktiKrishnan/ZOOKEEPER-1871-master and squashes the following commits:

2947514b2 [Mukti] ZOOKEEPER-1871: Removed statement which was re-creating zookeeper admin in ZooKeeperMain.java and added documentation for waitforconnection in zookeeperCLI.md and
c475d46ff [Mukti] ZOOKEEPER-1871: Add an option to zkCli to wailt for connection before executing commands

zookeeper-docs/src/main/resources/markdown/zookeeperCLI.md

@@ -24,6 +24,8 @@ Enter into the ZooKeeper-cli
 bin/zkCli.sh
 # connect to the remote host with timeout:3s
 bin/zkCli.sh -timeout 3000 -server remoteIP:2181
+# connect to the remote host with -waitforconnection option to wait for connection success before executing commands
+bin/zkCli.sh -waitforconnection -timeout 3000 -server remoteIP:2181
 # connect with a custom client configuration properties file
 bin/zkCli.sh -client-configuration /path/to/client.properties
 ```

zookeeper-server/src/main/java/org/apache/zookeeper/ZooKeeperMain.java

@@ -32,6 +32,8 @@ import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
@@ -68,6 +70,7 @@ public class ZooKeeperMain {
 
     protected ZooKeeper zk;
     protected String host = "";
+    private CountDownLatch connectLatch = null;
 
     public boolean getPrintWatches() {
         return printWatches;
@@ -106,6 +109,13 @@ public class ZooKeeperMain {
                 ZooKeeperMain.printMessage("WATCHER::");
                 ZooKeeperMain.printMessage(event.toString());
             }
+            if (connectLatch != null) {
+                // connection success
+                if (event.getType() == Event.EventType.None
+                    && event.getState() == Event.KeeperState.SyncConnected) {
+                    connectLatch.countDown();
+                }
+            }
         }
 
     }
@@ -168,6 +178,8 @@ public class ZooKeeperMain {
                         options.put("readonly", "true");
                     } else if (opt.equals("-client-configuration")) {
                         options.put("client-configuration", it.next());
+                    } else if (opt.equals("-waitforconnection")) {
+                        options.put("waitforconnection", "true");
                     }
                 } catch (NoSuchElementException e) {
                     System.err.println("Error: no argument found for option " + opt);
@@ -261,7 +273,19 @@ public class ZooKeeperMain {
             }
         }
 
-        zk = new ZooKeeperAdmin(host, Integer.parseInt(cl.getOption("timeout")), new MyWatcher(), readOnly, clientConfig);
+        if (cl.getOption("waitforconnection") != null) {
+            connectLatch = new CountDownLatch(1);
+        }
+
+        int timeout = Integer.parseInt(cl.getOption("timeout"));
+        zk = new ZooKeeperAdmin(host, timeout, new MyWatcher(), readOnly, clientConfig);
+        if (connectLatch != null) {
+            if (!connectLatch.await(timeout, TimeUnit.MILLISECONDS)) {
+                zk.close();
+                throw new IOException(KeeperException.create(KeeperException.Code.CONNECTIONLOSS));
+            }
+        }
+
     }
 
     public static void main(String[] args) throws IOException, InterruptedException {

zookeeper-server/src/test/java/org/apache/zookeeper/ZooKeeperTest.java

@@ -774,4 +774,25 @@ public class ZooKeeperTest extends ClientBase {
         });
     }
 
+    @Test
+    public void testWaitForConnection() throws Exception {
+        // get a wrong port number
+        int invalidPort = PortAssignment.unique();
+        long timeout = 3000L; // millisecond
+        String[] args1 = {"-server", "localhost:" + invalidPort, "-timeout",
+                Long.toString(timeout), "-waitforconnection", "ls", "/"};
+        long startTime = System.currentTimeMillis();
+        // try to connect to a non-existing server so as to wait until wait_timeout
+        try {
+            ZooKeeperMain zkMain = new ZooKeeperMain(args1);
+            fail("IOException was expected");
+        } catch (IOException e) {
+            // do nothing
+        }
+        long endTime = System.currentTimeMillis();
+        assertTrue(endTime - startTime >= timeout,
+                "ZooKeeeperMain does not wait until the specified timeout");
+
+    }
+
 }