The short answer is &#39;both&#39;.

XMPP is a set of application protocol for doing real-time chat (and many other things, for that matter) - it then has to be transported across the network somehow, so you need a transport binding. There are three main transport bindings for XMPP - 

 1. TCP/IP, which is what one usually uses on the Internet with native clients on devices
 2. HTTP (called BOSH), which is what one has traditionally used when using XMPP in the browser (as TCP-IP isn&#39;t available to Javascript apps in the browser)
 3.  Websockets, which is one one uses when doing XMPP in a modern browser.

So if you&#39;re developing a chat application in a browser, you&#39;d choose XMPP as the application protocol and you&#39;d use websockets (in a modern browser) or BOSH (in an older browser) as the network transport. If you use an XMPP library for Javascript like Stanza.io (https://github.com/otalk/stanza.io), it&#39;ll support both and you&#39;ll just be thinking about &#39;XMPP&#39; rather than the transport layer, other than at setup when you have to tell it what endpoint to connect to.

(You can&#39;t use &#39;just websockets&#39; for chat - you can use websockets without XMPP, but what this really means is that you&#39;re inventing your own application-layer protocol for chat, and the odds are you&#39;re going to save a lot of time and headaches by taking advantage of the work that&#39;s already gone into writing one with useful properties (security, identity, extensibility etc.) and for which there are existing libraries and servers by going XMPP instead.)

I&#39;m looking for a way to animate the drawing of a circle. I have been able to create the circle, but it draws it all together.

Here is my `CircleView` class: 

    import UIKit
    
    class CircleView: UIView {
      override init(frame: CGRect) {
        super.init(frame: frame)
        self.backgroundColor = UIColor.clearColor()
      }
      
      required init(coder aDecoder: NSCoder) {
        fatalError(&quot;init(coder:) has not been implemented&quot;)
      }
      
      
      override func drawRect(rect: CGRect) {
        // Get the Graphics Context
        var context = UIGraphicsGetCurrentContext();
        
        // Set the circle outerline-width
        CGContextSetLineWidth(context, 5.0);
        
        // Set the circle outerline-colour
        UIColor.redColor().set()
        
        // Create Circle
        CGContextAddArc(context, (frame.size.width)/2, frame.size.height/2, (frame.size.width - 10)/2, 0.0, CGFloat(M_PI * 2.0), 1)
        
        // Draw
        CGContextStrokePath(context);
      }
    }

And here is how I add it to the view hierarchy in my view controller:

    func addCircleView() {
        let diceRoll = CGFloat(Int(arc4random_uniform(7))*50)
        var circleWidth = CGFloat(200)
        var circleHeight = circleWidth
        // Create a new CircleView
        var circleView = CircleView(frame: CGRectMake(diceRoll, 0, circleWidth, circleHeight))
            
        view.addSubview(circleView)
    }

Is there a way to animate the drawing of the circle over 1 second? 

Example, part way through the animation it would look something like the blue line in this image:

![partial animation][1]


  [1]: http://i.stack.imgur.com/FP4Hum.png

Animate drawing of a circle

I want to track mutual locks in postgres constantly.

I came across [Locks Monitoring][1] article and tried to run the following query:

    SELECT bl.pid     AS blocked_pid,
         a.usename  AS blocked_user,
         kl.pid     AS blocking_pid,
         ka.usename AS blocking_user,
         a.query    AS blocked_statement
    FROM  pg_catalog.pg_locks         bl
     JOIN pg_catalog.pg_stat_activity a  ON a.pid = bl.pid
     JOIN pg_catalog.pg_locks         kl ON kl.transactionid = bl.transactionid AND kl.pid != bl.pid
     JOIN pg_catalog.pg_stat_activity ka ON ka.pid = kl.pid
    WHERE NOT bl.granted;

Unfortunately, it never returns non-empty result set. If I simplify given query to the following form:

    SELECT bl.pid     AS blocked_pid,
         a.usename  AS blocked_user,
         a.query    AS blocked_statement
    FROM  pg_catalog.pg_locks         bl
     JOIN pg_catalog.pg_stat_activity a  ON a.pid = bl.pid
    WHERE NOT bl.granted;

then it returns queries which are waiting to acquire a lock. But I cannot manage to change it so that it can return both blocked and blocker queries.

Any ideas?

  [1]: https://wiki.postgresql.org/wiki/Lock_Monitoring

How to detect query which holds the lock in Postgres?

I&#39;m about to develop a website that has near real time chat. I know that it can be implemented using xmpp or websocket protocols. I know also that the xmpp protocol has been developed in 1999 , and I guess it should be mature nowadays .On the other hand , the websocket protocol has been developed in 2011. 

 1. What was the need for websocket if xmpp was good in handling real time conversations?
 2.  What are the major differences between the 2 protocols? 
 3. And when should I choose one of them over the other?


Xmpp Vs Websocket

<p>I'm about to develop a website that has near real time chat. I know that it can be implemented using xmpp or websocket protocols. I know also that the xmpp protocol has been developed in 1999 , and I guess it should be mature nowadays .On the other hand , the websocket protocol has been developed in 2011.</p>
<ol>
<li>What was the need for websocket if xmpp was good in handling real time conversations?</li>
<li>What are the major differences between the 2 protocols?</li>
<li>And when should I choose one of them over the other?</li>
</ol>


Google Guava has a predicate that [always returns `true`][1]. Does Java 8 have something similar for its `Predicate`? I know I could use `(foo)-&gt;{return true;}`, but I want something pre-made, analogous to `Collections.emptySet()`.


  [1]: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Predicates.html#alwaysTrue%28%29

Built-in Java 8 predicate that always returns true?

We are implementing a REST API with Spring (4.1.1.). For certain HTTP requests, we would like to return a head with no body as a response. However, using `ResponseEntity&lt;Void&gt;` doesn&#39;t seem to work. When called with a `MockMvc` test, a 406 (Not acceptable) is returned. Using `ResponseEntity&lt;String&gt;` without a parameter value (`new  ResponseEntity&lt;String&gt;( HttpStatus.NOT_FOUND )`) works fine. 



Method:
   
    @RequestMapping( method = RequestMethod.HEAD, value = Constants.KEY )
    public ResponseEntity&lt;Void&gt; taxonomyPackageExists( @PathVariable final String key ) {

        LOG.debug( &quot;taxonomyPackageExists queried with key: {0}&quot;, key ); //$NON-NLS-1$

        final TaxonomyKey taxonomyKey = TaxonomyKey.fromString( key );

        LOG.debug( &quot;Taxonomy key created: {0}&quot;, taxonomyKey ); //$NON-NLS-1$

        if ( this.xbrlInstanceValidator.taxonomyPackageExists( taxonomyKey ) ) {

            LOG.debug( &quot;Taxonomy package with key: {0} exists.&quot;, taxonomyKey ); //$NON-NLS-1$

            return new ResponseEntity&lt;Void&gt;( HttpStatus.OK );

        } else {

            LOG.debug( &quot;Taxonomy package with key: {0} does NOT exist.&quot;, taxonomyKey ); //$NON-NLS-1$

            return new ResponseEntity&lt;Void&gt;( HttpStatus.NOT_FOUND );
        }

    }

Test case (TestNG):

    public class TaxonomyQueryControllerTest {

    private XbrlInstanceValidator   xbrlInstanceValidatorMock;
    private TaxonomyQueryController underTest;
    private MockMvc                 mockMvc;

    @BeforeMethod
    public void setUp() {
        this.xbrlInstanceValidatorMock = createMock( XbrlInstanceValidator.class );
        this.underTest = new TaxonomyQueryController( this.xbrlInstanceValidatorMock );
        this.mockMvc = MockMvcBuilders.standaloneSetup( this.underTest ).build();
    }

    @Test
    public void taxonomyPackageDoesNotExist() throws Exception {
        // record
        expect( this.xbrlInstanceValidatorMock.taxonomyPackageExists( anyObject( TaxonomyKey.class ) ) ).andStubReturn(
                false );

        // replay
        replay( this.xbrlInstanceValidatorMock );

        // do the test
        final String taxonomyKey = RestDataFixture.taxonomyKeyString;

        this.mockMvc.perform( head( &quot;/taxonomypackages/{key}&quot;, taxonomyKey ).accept( //$NON-NLS-1$
                MediaType.APPLICATION_XML ) ).andExpect( status().isNotFound() );

    }

    }

Fails with this stack trace: 

    FAILED: taxonomyPackageDoesNotExist
    java.lang.AssertionError: Status expected:&lt;404&gt; but was:&lt;406&gt;
	at org.springframework.test.util.AssertionErrors.fail(AssertionErrors.java:60)
	at org.springframework.test.util.AssertionErrors.assertEquals(AssertionErrors.java:89)
	at org.springframework.test.web.servlet.result.StatusResultMatchers$10.match(StatusResultMatchers.java:652)
	at org.springframework.test.web.servlet.MockMvc$1.andExpect(MockMvc.java:153)
	at de.zeb.control.application.xbrlstandalonevalidator.restservice.TaxonomyQueryControllerTest.taxonomyPackageDoesNotExist(TaxonomyQueryControllerTest.java:54)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
	at org.testng.internal.Invoker.invokeMethod(Invoker.java:714)
	at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
	at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
	at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
	at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
	at org.testng.TestRunner.privateRun(TestRunner.java:767)
	at org.testng.TestRunner.run(TestRunner.java:617)
	at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
	at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
	at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
	at org.testng.SuiteRunner.run(SuiteRunner.java:240)
	at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
	at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
	at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
	at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
	at org.testng.TestNG.run(TestNG.java:1057)
	at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:111)
	at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:204)
	at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:175)





Spring: Returning empty HTTP Responses with ResponseEntity&lt;Void&gt; doesn&#39;t work

I need to detect double clicks on a row of a `TableView`.

How can I listen for double clicks on any part of the row and get all data of this row to print it to the console?

Detect doubleclick on row of TableView JavaFX

Oh, those tricky Java 8 streams with lambdas. They are very powerful, yet the intricacies take a bit to wrap one&#39;s header around it all.

Let&#39;s say I have a `User` type with a property `User.getName()`. Let&#39;s say I have a map of those users `Map&lt;String, User&gt;` associated with names (login usernames, for example). Let&#39;s further say I have an instance of a comparator `UserNameComparator.INSTANCE` to sort usernames (perhaps with fancy collators and such).

So how do I get a list of the users in the map, sorted by username? I can ignore the map keys and do this:

    return userMap.values()
        .stream()
        .sorted((u1, u2) -&gt; {
          return UserNameComparator.INSTANCE.compare(u1.getName(), u2.getName());
        })
        .collect(Collectors.toList());

But that line where I have to extract the name to use the `UserNameComparator.INSTANCE` seems like too much manual work. Is there any way I can simply supply `User::getName` as some mapping function, just for the sorting, and still get the `User` instances back in the collected list?

Bonus: What if the thing I wanted to sort on were two levels deep, such as `User.getProfile().getUsername()`?

Sorting by property in Java 8 stream

I am using appcompat v7 to get the look consistent on Android 5 and less. It works rather well. However I cannot figure out how to change the bottom line color and the accent color for EditTexts. Is it possible? 

I have tried to define a custom `android:editTextStyle` (cf. below) but I only succeeded to change the full background color or text color but not the bottom line nor the accent color. Is there a specific property value to use? do I have to use a custom drawable image through the `android:background` property? is it not possible to specify a color in hexa?

     &lt;style name=&quot;Theme.App.Base&quot; parent=&quot;Theme.AppCompat.Light.DarkActionBar&quot;&gt;
         &lt;item name=&quot;android:editTextStyle&quot;&gt;@style/Widget.App.EditText&lt;/item&gt;
     &lt;/style&gt;

     &lt;style name=&quot;Widget.App.EditText&quot; parent=&quot;Widget.AppCompat.EditText&quot;&gt;
         ???
     &lt;/style&gt;

According to android API 21 sources, EditTexts with material design seem to use `colorControlActivated` and `colorControlNormal`. Therefore, I have tried to override these properties in the previous style definition but it has no effect. Probably appcompat does not use it. Unfortunately, I cannot find the sources for the last version of appcompat with material design. 

Changing EditText bottom line color with appcompat v7

I&#39;ve read that WS only works on HTTP, and that WSS works on both HTTP and HTTPS. Are WSS (Secure Web Socket) connections just as secure on an HTTP server as they are on an HTTPS server? Is a Web Socket Secure (WSS) connection still encrypted through TLS/SSL if the website/server is not?

WS on HTTP vs WSS on HTTPS

I&#39;ve recently set-up a local WebSocket server which works fine, however I&#39;m having a few troubles understanding how I should handle a sudden loss of connection which neither the client or server intentionally initiated, i.e: Server loses power, ethernet cables pulled out etc... I need the client&#39;s to know whether connection has been lost within ~10seconds.

Client side, connection is simply:

    var websocket_conn = new WebSocket(&#39;ws://192.168.0.5:3000&#39;);

	websocket_conn.onopen = function(e) {
		console.log(&#39;Connected!&#39;);
	};

	websocket_conn.onclose = function(e) {
		console.log(&#39;Disconnected!&#39;);
	};

I can manually trigger the connection disconnect which works fine,

    websocket_conn.close();

But if I simply pulled the ethernet cable out the back of the computer, or disabled the connection, `onclose` doesn&#39;t get called. I&#39;ve read in another post that it would eventually get called when [TCP detects loss of connectivity][1], but it&#39;s not in the timely manner that I need as the default for Firefox I believe is 10 minutes, and I don&#39;t really want to go around hundreds of computers `about:config` changing this value. The only other suggestion I&#39;ve read is to use a &#39;ping/pong&#39; keep-alive polling style method which seems counterintuitive to the idea of websockets.

Is there an easier way to detect this kind of disconnect behaviour? Are the old posts i&#39;m reading still up to date from a technical point, and the best method is still &#39;ping/pong&#39; style?

  [1]: https://stackoverflow.com/questions/11809267/how-do-i-know-if-connection-is-alive-with-websockets

Handling connection loss with websockets

I have, what I think to be, a very simple Spring WebSocket application.  However, I&#39;m trying to use path variables for the subscription as well as the message mapping.

I&#39;ve posted a paraphrased example  below. I would expect the `@SendTo` annotation to return back to the subscribers based on their `fleetId`.  ie, a `POST` to `/fleet/MyFleet/driver/MyDriver` should notify subscribers of `/fleet/MyFleet`, but I&#39;m not seeing this behavior.

It&#39;s worth noting that subscribing to literal `/fleet/{fleetId}` works.  Is this intended?  Am I missing some piece of configuration?  Or is this just not how it works?

I&#39;m not very familiar with WebSockets or this Spring project yet, so thanks in advance.

**Controller.java**

    ...
    @MessageMapping(&quot;/fleet/{fleetId}/driver/{driverId}&quot;)
	@SendTo(&quot;/topic/fleet/{fleetId}&quot;)
	public Simple simple(@DestinationVariable String fleetId, @DestinationVariable String driverId) {
		return new Simple(fleetId, driverId);
	}
    ...


**WebSocketConfig.java**

    @Configuration
    @EnableWebSocketMessageBroker
    public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
    	@Override
    	public void configureMessageBroker(MessageBrokerRegistry config) {
    		config.enableSimpleBroker(&quot;/topic&quot;);
    		config.setApplicationDestinationPrefixes(&quot;/live&quot;);
    	}
    
    	@Override
    	public void registerStompEndpoints(StompEndpointRegistry registry) {
    		registry.addEndpoint(&quot;/fleet&quot;).withSockJS();
    	}
    }

**index.html**

	var socket = new SockJS(&#39;/fleet&#39;);
	var stompClient = Stomp.over(socket);
	stompClient.connect({}, function(frame) {
        // Doesn&#39;t Work
        stompClient.subscribe(&#39;/topic/fleet/MyFleet&#39;, function(greeting) {
        // Works
		stompClient.subscribe(&#39;/topic/fleet/{fleetId}&#39;, function(greeting) {
			// Do some stuff
		});
	});

**Send Sample**

		stompClient.send(&quot;/live/fleet/MyFleet/driver/MyDriver&quot;, {}, JSON.stringify({
			// Some simple content
		}));

Path variables in Spring WebSockets @SendTo mapping

I have :

1. Apache 2.4 on port 80 of my server, with *[mod_proxy][1]* and *[mod_proxy_wstunnel][2]* enabled

2. Node.js + `socket.io` on port 3001 of the same server

Accessing `example.com` (with port 80) redirects to 2. thanks to [this method][3] with the following Apache configuration:

    &lt;VirtualHost *:80&gt;
        ServerName example.com
        ProxyPass / http://localhost:3001/
        ProxyPassReverse / http://localhost:3001/
        ProxyPass / ws://localhost:3001/
        ProxyPassReverse / ws://localhost:3001/
    &lt;/VirtualHost&gt;

It works for everything, except the websocket part : `ws://...` are not transmitted like it should by the proxy.

When I access the page on `example.com`, I have:

    Impossible to connect ws://example.com/socket.io/?EIO=3&amp;transport=websocket&amp;sid=n30rqg9AEqZIk5c9AABN.

Question: **How to make Apache proxy the WebSockets as well?** 


  [1]: https://httpd.apache.org/docs/2.4/mod/mod_proxy.html
  [2]: https://httpd.apache.org/docs/2.4/mod/mod_proxy_wstunnel.html
  [3]: https://stackoverflow.com/a/18604082/1422096

WebSockets and Apache proxy: how to configure mod_proxy_wstunnel?

I need to set an Authorization header to an HTML5 EventSource. As Server Sent Events seems to be disused since Websockets appeared, I cannot find any useful documentation. The approach I have already found is to pass the authorization data within the url... but I don&#39;t like this method.

I am using AngularJS and set interceptors on $httpProvider, but the EventSource is not intercepted by AngularJS, so I cannot add any header.

HTTP Authorization Header in EventSource (Server Sent Events)

What technology does Google Drive use to do real-time?

When I type in a Google Drive document that is being accessed by multiple users, the Chrome Developer Tools Network tab shows that there are no WebSockets.

I see that the two most frequent types of AJAX call have either &quot;bind?&quot; or &quot;save?&quot; in the URL. &quot;save?&quot; POST requests are made every time I type, which makes sense- normal AJAX for sending updates to the server.

When another user types, the most recent &quot;bind?&quot; GET call stays open, and the amount of data transferred over that connection increases. Periodically, &quot;bind?&quot;s are closed and new ones open up, and the logic seems to be some function of duration and data size. 

This isn&#39;t long-polling, since when the server sends updates it doesn&#39;t complete the response.

This doesn&#39;t seem to be server-sent events, since the content-type is &quot;text/plain&quot; instead of &quot;text/stream&quot;.

Is there a name for what Google is doing? If so, how can I try implementing this?


[![Chrome Dev Tools - editing a Google Drive document][1]][1]


  [1]: http://i.stack.imgur.com/AqkMu.png

What technology does Google Drive use to get real-time updates?

I&#39;m working on a new game project at the moment that will consist of a React Native front-end and a Lambda-based back-end. The app requires some real time features such as active user records, geofencing, etc.

I was looking at Firebase&#39;s Realtime Database that looks like a really elegant solution for real-time data sync but I don&#39;t think AWS has anything quite like it.

The 3 options I could think of for &quot;serverless&quot; realtime using only AWS services are:

**Option 1: AWS IoT Messaging over WebSockets**

This one is quite obvious, a managed WebSockets connection through the IoT SDK. I was thinking of triggering Lambdas in response to inbound and outbound events and just use WebSockets as the realtime layer, building custom handling logic on the app client as you typically would.

The downside to this, at least compared to Firebase, is that I will have to handle the data in the events myself which will add another layer of management on top of WebSockets and will have to be standardized with the API data layer in the application&#39;s stores.

Pros:

 - Scalable bi-directional realtime connection

Cons:

 - Only works when the app is open
 - Message structure needs to be implemented
 - Multiple transport layers to be managed

**Option 2: Push-triggered re-fetch**

Another option is to use push notifications as real-time triggers but use a regular HTTP request to API Gateway to actually get the updated payload.

I like this approach because it sticks to only one transport layer and a single source of truth for application state. It will also trigger updates when the app is not open since these are Push Notifications.

The downside is that this is a lot of custom work with potentially difficult mappings between push notifications to the data that needs to be fetched.

Pros:

 - Push notifications work even when app is closed
 - Single source of truth, transport layer

Cons:

 - Most custom solution
 - Will involve many more HTTP requests overall

**Option 3: Cognito Sync**
This is newer to me and I&#39;m not sure if it can actually be interfaced with from the server.

Cognito Sync offers user state sync. across devices complete with offline support and is part of the Cognito SDK which I&#39;ll be using anyway. It sounds like just what I&#39;m looking for but couldn&#39;t find any conclusive evidence as to whether it is possible to modify, or &quot;trigger&quot;, updates from AWS and not just from one of the devices.

Pros:

 - Provides an abstracted real-time data model
 - Connected to Cognito user records OOTB

Cons:

 - Not sure if can be modified or updated from Lambdas

&lt;br/&gt;

I&#39;m wondering if anyone has experience doing real-time on AWS as part of a Lambda-based architecture and if you have an opinion on what is the best way to proceed?

What would be the AWS equivalent to Firebase Realtime Database?

I started developing software for real-time systems a few months ago in C for space applications, and also for microcontrollers with C++. There&#39;s a rule of thumb in such systems that **one should never create heap objects** (so no malloc/new), because it makes the program **non-deterministic**. I wasn&#39;t able to verify the correctness of this statement when people tell me that. So, ***Is this a correct statement?***

The confusion for me is that as far as I know, determinism means that running a program twice will lead to the exact, same execution path. From my understanding this is an issue with multithreaded systems, since running the same program multiple times could have different threads running in different order every time.

Content Type	Original Author	Original Content on Stackoverflow
Question	Khafaga	View Question on Stackoverflow
Solution 1 - Java	Kev	View Answer on Stackoverflow

Xmpp Vs Websocket

Java Problem Overview

Java Solutions

Solution 1 - Java

How to detect query which holds the lock in Postgres?

Animate drawing of a circle

Attributions