Short answer: No.

Long answer:

WebSocket runs over TCP, so on that level @EJP &#39;s answer applies. WebSocket can be &quot;intercepted&quot; by intermediaries (like WS proxies): those are allowed to reorder WebSocket control frames (i.e. WS pings/pongs), but not message frames when no WebSocket extension is in place. If there is a neogiated extension in place that in principle allows reordering, then an intermediary may only do so if it understands the extension and the reordering rules that apply.

It&#39;s not possible for them to arrive *in your application* out of order. Anything can happen on the network, but TCP will only present you the bytes in the order they were sent.

At the network layer TCP is suppose to guarantee that messages arrive in order.  At the application layer, errors can occur in the code and cause your messages to be out of order in the logic of your code. It could be the network stack your application is using or your application code itself.

If you asked me, can my Node.js application guarantee sending and receiving messages in order? I&#39;m going to have to say no. I&#39;ve run websocket applications connected to WiFi under high latency and low signal. It causes very strange behavior as if packets are dropped and messages are out of sequence. 

This article is a good read https://samsaffron.com/archive/2015/12/29/websockets-caution-required



Is there a way to receive multiple uploaded files with Flask? I&#39;ve tried the following:

    &lt;form method=&quot;POST&quot; enctype=&quot;multipart/form-data&quot; action=&quot;/upload&quot;&gt;
      &lt;input type=&quot;file&quot; name=&quot;file[]&quot; multiple=&quot;&quot;&gt;
      &lt;input type=&quot;submit&quot; value=&quot;add&quot;&gt;
    &lt;/form&gt;

And then printed the contents of `request.files[&#39;file&#39;]`:

    @app.route(&#39;/upload&#39;, methods=[&#39;POST&#39;])
    def upload():
      if not _upload_dir:
        raise ValueError(&#39;Uploads are disabled.&#39;)
    
      uploaded_file = flask.request.files[&#39;file&#39;]
      print uploaded_file
      media.add_for_upload(uploaded_file, _upload_dir)
      return flask.redirect(flask.url_for(&#39;_main&#39;))

If I upload multiple files, it only prints the first file in the set:  
  
    &lt;FileStorage: u&#39;test_file.mp3&#39; (&#39;audio/mp3&#39;)&gt;  
  
Is there a way to receive multiple files using Flask&#39;s built-in upload handling? Thanks for any help!

Uploading multiple files with Flask

I have a series of rows with columns and I want to select the value of an `input` field that is in a previous column to the `input` field (price input) that I am calling a function on when a key is released.

I have tried:

    quantity = $(this).parent().parent().children().val() ;
    quantity = $(this).parent().parent().children().closest(&#39;.inputQty&#39;, this).val() ;

But neither work.

An example of the DOM:

    &lt;div class=&quot;row&quot;&gt;
        &lt;div class=&quot;column&quot;&gt;&lt;input class=&quot;inputQty&quot; id=&quot;quantity0&quot; /&gt;&lt;/div&gt;
        &lt;div class=&quot;column&quot;&gt;&lt;input class=&quot;someOther&quot; id=&quot;Other0&quot; /&gt;&lt;/div&gt;
        &lt;div class=&quot;column&quot;&gt;
            &lt;div class=&quot;cSelect&quot;&gt;
                &lt;select id=&quot;currency0&quot;&gt;&lt;option&gt;&#163;&lt;/option&gt;&lt;/select&gt;
                &lt;input class=&quot;price&quot; id=&quot;price0&quot; /&gt;
            &lt;/div&gt;
        &lt;/div&gt;
    &lt;/div&gt;

Jquery find nearest matching element

If we send two messages over the same html5 websocket a split millisecond apart from each other, 

Is it theoretically possible for the messages to arrive in a different order than they were sent?

Can websocket messages arrive out-of-order?

<p>If we send two messages over the same html5 websocket a split millisecond apart from each other,</p>
<p>Is it theoretically possible for the messages to arrive in a different order than they were sent?</p>


## My Question(s) ##

 1. Are any of these methods preferred by a professional web designer?

 2. Are any of these methods prefereed by a web browser when drawing the website?

 3. Is this all just personal preference?

 4. Are there other techniques I&#39;m missing?

*Note: Above questions are in regards to designing a multi-column layout*

----------


float:left;
----------

http://jsfiddle.net/CDe6a/

![float:left image][1]

This is the method I always use when creating column layouts, and it seems to work just fine. The parent does collapse on itself though, so you just need to remember to `clear:both;` afterwards. Another *con* that I just found was the inability to align text vertically.

display:inline;
---------------

This seems to correct the problem of the collapsing parent, but adds whitespace.

http://jsfiddle.net/CDe6a/1/

![display:inline image][2]

Removing whitespace from html seems to be the easiest fix this problem, but is not desired if you are really picky about your html.

http://jsfiddle.net/CDe6a/2/

![no html whitespace image][3]

display:inline-block;
---------------------

Seems to behave exactly like `display:inline;`.

http://jsfiddle.net/CDe6a/3/

![display:inline-block image][2]

display:table-cell;
-------------------

http://jsfiddle.net/CDe6a/4/

![display:table-cell image][4]

Works perfect.

My thoughts:
------------

I&#39;m sure I&#39;m missing a ton of stuff, like certain exceptions that will break the layout but, `display:table-cell;` seems to work the best, and I think I will start replacing `float:left;` as I always seem to mess up on `clear:both;`. I&#39;ve read many articles and blogs about this on the web, but none of them give me a definite answer on what I should use when laying out my website.


  [1]: http://i.stack.imgur.com/oIMvg.png
  [2]: http://i.stack.imgur.com/aDgsb.png
  [3]: http://i.stack.imgur.com/qgnlL.png
  [4]: http://i.stack.imgur.com/BPtXn.png

float:left; vs display:inline; vs display:inline-block; vs display:table-cell;

I&#39;m not using CSS3. So I can&#39;t use `opacity` or `filter` attributes. Without using these attributes how can I make the `background-color` transparent of a `div`? It should be kind of the text box example in this [link][1]. Here the text box background color is transparent. I want to make the same, but without using the above mentioned attributes.


  [1]: http://www.w3schools.com/css/tryit.asp?filename=trycss_transparency

How to make div background color transparent in CSS

I have an array with objects inside of it, a few of the objects contain an underscore in the string.

Example:

    {&quot;name&quot;: &quot;My_name&quot;}

But I&#39;m calling the name function in multiple places, one such place is in an image tag where the underscore is necessary, using JavaScript I want to select a certain div with the name in it and replace the underscore with space.

Example:

    &lt;div&gt;
     &lt;div class=&quot;name&quot;&gt;
      My_name
     &lt;/div&gt;
     &lt;img src=&quot;My_name.jpg&quot;/&gt;
    &lt;/div&gt;

In the `div.name` I want it to say `My name` instead of `My_name`.



How to replace underscores with spaces?

I&#39;m reading http://www.html5rocks.com/en/tutorials/file/xhr2/ and trying to figure out the difference between an `ArrayBuffer` and a `Blob`.

Aren&#39;t both containers comprised of bits? Hence, couldn&#39;t both containers be viewed in many ways (as 32-bit chunks, 16-bit chunks, etc.)?

What is the difference between an ArrayBuffer and a Blob?

Seemed odd I couldn&#39;t find this one already asked, but here it goes!

I have an html &lt;select&gt; as follows:

    &lt;select id=&quot;select-meal-type&quot; multiple=&quot;multiple&quot;&gt;
        &lt;option value=&quot;1&quot;&gt;Breakfast&lt;/option&gt;
        &lt;option value=&quot;2&quot;&gt;Lunch&lt;/option&gt;
        &lt;option value=&quot;3&quot;&gt;Dinner&lt;/option&gt;
        &lt;option value=&quot;4&quot;&gt;Snacks&lt;/option&gt;
        &lt;option value=&quot;5&quot;&gt;Dessert&lt;/option&gt;
    &lt;/select&gt;

How do I get all the values(an array?) that the user has selected in javascript?

For example, if the user has selected Lunch and Snacks, I want an array of { 2, 4 }.

This seems like it should be a very simple task but I can&#39;t seem to do it. 

Thanks.

How to get all selected values from &lt;select multiple=multiple&gt;?

Is there a way to examine the status of a specific port from the Windows command line? I know I can use netstat to examine all ports but netstat is slow and looking at a specific port probably isn&#39;t.

Command line for looking at specific port

My question might sound stupid, but I just wanted to be sure:

- Is it possible to send an HTTP response before having the request for that resource?

Say for example you have an HTML page `index.html` that only shows a picture called `img.jpg`.
Now, if your server knows that a visitor will request the HTML file and then the jpg image every time:

Would it be possible for the server to send the image just after the HTML file to save time?

I know that HTTP is a synchronous protocol, so in theory it should not work, but I just wanted someone to confirm it (or not).

HTTP Response before Request

I would like to increase the RAM to at least 1 GB and I would like to configure “Host-Only” networking to use &quot;199.188.44.20&quot;.

This is my `Vagrantfile`:

&lt;!-- language: ruby --&gt;

    # -*- mode: ruby -*-
    # vi: set ft=ruby :

    Vagrant::Config.run do |config|
    
        config.vm.customize [&quot;modifyvm&quot;, :id, &quot;--memory&quot;, 1024]

        config.vm.network :hostonly, &quot;199.188.44.20&quot;
	
        config.vm.define :web do |web_config|
            web_config.vm.box = &quot;lucid32&quot;
            web_config.vm.forward_port 80, 8080

            web_config.vm.provision :puppet do |puppet|
                puppet.manifests_path = &quot;manifests&quot;
                puppet.manifest_file = &quot;lucid32.pp&quot;
            end
        end
	
        config.vm.define :web2 do |web2_config| 
            web2_config.vm.box = &quot;lucid32&quot;
            web2_config.vm.forward_port 80, 8081

            web2_config.vm.provision :puppet do |puppet|
                puppet.manifests_path = &quot;manifests&quot;
                puppet.manifest_file = &quot;myweb.pp&quot;
            end
        end
    end

However, when I run `vagrant up` I am getting:

&gt; _The VM failed to remain in the &quot;running&quot; state while attempting to boot. This is normally cause by a misconfiguration or host system incompatibles. Please open the VirtualBox GUI and attempt to boot the virtual machine manually to get more informative error message_

And, I am getting a `connection refuse` error when I try to log in to the VM.

How do I increase the RAM and set up host-only networking in Vagrant?

In Eclipse, I got this error:

    run:
         [java] Error creating the server socket.
         [java] Oct 04, 2012 5:31:38 PM cascadas.ace.AceFactory bootstrap
         [java] SEVERE: Failed to create world : java.net.BindException: Address already in use: JVM_Bind
         [java] Java Result: -1
    BUILD SUCCESSFUL
    Total time: 10 seconds

I&#39;m not sure why it came up  now, but it ran fine just a few hours ago. Do I need to restart my machine? How do i get to the bottom of it? I appreciate any tips or advice.

How do I resolve the &quot;java.net.BindException: Address already in use: JVM_Bind&quot; error?

I wanted to know the exact function of bind() in TCP. What does it mean by &#39;binding&#39; a local address to the socket? If it&#39;s assigning a port number to the socket, then why don&#39;t we use it in the client? I know that port is assigned by OS automatically in the client side, but I&#39;m not getting the big picture of how all of this works.

After bind(), we listen(). How is the bind related to listen()? Will the listen() know that bind() has been executed? If so, what changes does bind() make so that it is known? I mean, how does returning zero for successful execution help?

I&#39;ve gone through many definitions, but no where I could get all of this in detail. So if anyone can please explain this to me, I will be grateful.

Why is bind() used in TCP? Why is it used only on server side and not in client side?

Looking for Hello World Type Example of Web Sockets Implementation:

Here is [Socket Create][1] reference from php.net but this looks more low level than Web Sockets.

I want to use this Web Sockets as shown here on [caniuse.com][2] which is now implemented in all new major browsers.

A Google search turned up this [Nets.TutsPlus site][3] in which I can use the JavaScript example code...but I need to know how to implement the server-side in PHP not Java, Ruby, or Node.js as in the example.

Is PHP Socket Create relevant?  Does PHP natively support Web Sockets?  I guess just a point in the right direction for PHP implementation would help.

Actually the tutorial has a broken link to phpwebsockets...is this the library one should use?

[Websockets.org][4] has a test application, but no mention of PHP.


  [1]: http://www.php.net/manual/en/function.socket-create.php
  [2]: http://caniuse.com/#search=web%20sockets
  [3]: http://net.tutsplus.com/tutorials/javascript-ajax/start-using-html5-websockets-today/
  [4]: http://www.websocket.org

Is native PHP support for Web Sockets available?

HTML5 websockets are (and [have been for some time](https://stackoverflow.com/questions/6224771/disadvantages-of-websockets)) a hot topic as they elegantly enable *real-time* [server-side push](http://en.wikipedia.org/wiki/Push_technology#HTTP_server_push).

I currently have a working application with websockets powered by Tomcat 7.0.30 which includes [websocket support](http://www.tomcatexpert.com/blog/2012/05/01/how-apache-tomcat-implemented-websocket). But moving this to a production environment raises questions.

Mainly I would like to know the possible maximum number of connections that can operate (be *open*) concurrently per *browsing session*; a *browsing session* implies a single browser tab or window.

Do open websocket connections add up to the maximum number of connections that can be processed simultaneously by the Web server? E.g. [`MaxClients`](http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxclients) in Apache.

Conversely, is the maximum number of websockets for a single *browsing session* limited by the browser itself? As this [blog post](http://blog.dennis-boldt.de/?p=177) shows, up to April 2012, different browsers support varying amounts of *open* websocket connections. (I personally would aim for 1 open websocket per *browsing session*; but this info would still be good to know).

**TL/DR:**

 1. What limits the amount of possible websockets *per browsing session*? Is it the client? The server? Or a combination of both?
 2. Does the same limitation(s) apply to both `ws:` and `wss:` connections?

HTML5 websockets: max number of open connections?

I have a question about how to load balance web sockets.

I have a server which supports web sockets. Browsers connect to my site and each one opens a web socket to `www.mydomain.com`. That way, my social network app can push messages to the clients.

Traditionally, using just HTTP requests, I would scale up by adding a second server and a load balancer in front of the two web servers. 

With web sockets, the connection has to be directly with the web server, not the load balancers, because if a machine has a physical limit of say 64k open ports, and the clients were connecting to the load balancer, then I couldn&#39;t support more than 64k concurrent users.

So how do I -

1. get the client to connect directly to the web server (rather than the load balancer) when the page loads? Do I simply load the JavaScript from a node, and the load balancers (or whatever) randomly modifies the URL for the script, every time the page is initially requested?

2. handle a ripple start? The browser will notice that the connection is closed as the web server shuts down. I can write JavaScript code to attempt to reopen the connection, but the node will be gone for a while. So I guess I would have to go back to the load balancer to query the address of the next node to use?

3. I did wonder about the load balancers sending a redirect on the initial request, so that the browser initially requests `www.mydomain.com` and gets redirected to `www34.mydomain.com`. That works quite well, until the node goes down - and sites like Facebook don&#39;t do that. How do they do it?

Loadbalancing web sockets

I have read many posts on SO and the web regarding the keywords in my question title and learned a lot from them. Some of the questions I read are related to specific implementation challenges while others focus on general concepts. I just want to make sure I understood all of the concepts and the reasoning why technology X was invented over technology Y and so on. So here goes:

**Http Polling:** Basically AJAX, using XmlHttpRequest.

**Http Long Polling:** AJAX but the server holds on to the response unless the server has an update, as soon as the server has an update, it sends it and then the client can send another request. Disadvantage is the additional header data that needs to be sent back and forth causing additional overhead.

**Http Streaming:** Similar to long polling but the server responds with a header with &quot;Transfer Encoding: chunked&quot; and hence we do not need to initiate a new request every time the server sends some data (and hence save the additional header overhead). The drawback here is that we have to &quot;understand&quot; and figure out the structure of the data to distinguish between multiple chunks sent by the server.

**Java Applet, Flash, Silverlight:** They provide the ability to connect to socket servers over tcp/ip but since they are plugins, developers don&#39;t want to depend on them.

**WebSockets:** they are the new API which tries to address the short comings of above methods in the following manner:

 - The only advantage of WebSockets over plugins like Java Applets, Flash or Silverlight is that WebSockets are natively built into browsers and does not rely on plugins.
 - The only advantage of WebSockets over http streaming is that you don&#39;t have to make an effort to &quot;understand&quot; and parse the data received.
 - The only advantage of WebSockets over Long Polling is that of elimination of extra headers size &amp; opening and closing of socket connection for request.

Are there any other significant differences that I am missing? I&#39;m sorry if I am re-asking or combining many of the questions already on SO into a single question, but I just want to make perfect sense out of all the info that is out there on SO and the web regarding these concepts.

Thanks!

My Understanding of HTTP Polling, Long Polling, HTTP Streaming and WebSockets

I&#39;m assuming that WebRTC is an API that decodes/encodes audio and video, although the communication between the server and the clients is done via web sockets, or some other network protocol? I&#39;m a bit confused. Does WebRTC have its own communications protocol?

WebRTC and Websockets. Is there a difference

I am currently trying to set up a basic authentication system for my node.js app. For now I am using express (3.0.0rc5), passport (0.1.12) and socket.io (0.9.10) with Mongoose as Store for session data. I have also been playing around with `everyauth` but I didn&#39;t like to work with promises.

Current situation:

Authentication through passport (facebook strategy) is successful, a `session.sid` cookie is set on the client after the redirect and I am able to see a session document in my database. I can access the session cookie in `socket.io` through `socket.handshake.headers.cookie`. 

If I understood the passport concept correctly, after successful `authentication passport.serializeUser` is called which enables me to add information to the session. In my case the most important information is the email, so I set the serializer up in the following way:

    passport.serializeUser(function(user, done) {
      done(null, user.email);
    });

Now I am at the point where I have to use only the cookie information in my socket.io event to extract the email address from the session. 

    var connect = require(&#39;connect&#39;),
        parseSignedCookie = connect.utils.parseSignedCookie,
        cookie            = require(&#39;express/node_modules/cookie&#39;);

    io.on(&#39;connection&#39;, function(socket) {
        if(socket.handshake.headers.cookie) {
            var cookie = cookie.parse(socket.handshake.headers.cookie);
            var sessionID = parseSignedCookie(cookie[&#39;connect.sid&#39;], &#39;secret&#39;);
        }
    });

    passport.deserializeUser(function(id, done) {
        // so, what is supposed to be done here?
    });

So if I am not mistaken, the task is now to use `deserializeUser` to access the corresponding email address.

How would I do that? Any pointers are highly appreciated.

How to use passport with express and socket.io?

So I have an application running node js with socket.io as a backend and normal javascript as frontend. My application has a login system which currently simply has the client send its login data as soon as it&#39;s connected.

Now I figured it would be much nicer to have the login data sent along with the handshakeData, so I can directly have the user logged in while connecting (instead of after establishing a connection) respectively refuse authorization when the login data is invalid.

I&#39;m thinking it would be best to put my additional data in the header part of the handshakeData, so any ideas how I could do that? (Without having to modify socket.io if possible, but if it&#39;s the only way I can live with it)



Send custom data along with handshakeData in socket.io?

I construct my websocket connection with this code (e.g.):

    var socket = new WebSocket(&quot;ws://94.12.176.177:8080&quot;);

And I close the connection with this one:

    socket.close();

But how do I reestablish connection?

I&#39;ve done some research and tried several methods. This question could not help me: https://stackoverflow.com/questions/5898327/socket-io-reconnect-on-disconnect
It&#39;s the only result which close to what I&#39;m looking for.

The reason I want to do this is to allow users to stop sending data to the web temporary, and resending again after a period of time. Without reconnection, user have to refresh the page in order to resend. This may cause some data lost. Thank you.

How to reconnect to websocket after close connection

    Error: The connection to &lt;websocket&gt; was interrupted while the page was loading.
    Source File: localhost/socket.io/node_modules/socket.io-client/dist/socket.io.js
    Line: 2371

I am new to socket.io and I have tried to search for this, but I didn&#39;t get an answer.

Websocket is interrupted when I refresh page on Firefox. That&#39;s why server side is waiting to authorise client.

Here is code:
**server.js**
```javascript
var app = require(&#39;http&#39;).createServer(handler),
  io = require(&#39;socket.io&#39;).listen(app),
  fs = require(&#39;fs&#39;)

app.listen(8080);

function handler(req, res) {
  fs.readFile(__dirname + &#39;/index.html&#39;,
    function (err, data) {
      if (err) {
        res.writeHead(500);
        return res.end(&#39;Error loading index.html&#39;);
      }
      res.writeHead(200);
      res.end(data);
    });
}

io.sockets.on(&#39;connection&#39;, function (socket) {
  socket.emit(&#39;news&#39;, {
    hello: &#39;world&#39;
  });
  socket.on(&#39;my other event&#39;, function (data) {
    //alert(JSON.stringify(data));  
    console.log(data);
  });

});
```


**index.html**
```html
&lt;script src=&quot;node_modules/socket.io-client/dist/socket.io.js&quot;&gt;&lt;/script&gt;
&lt;script&gt;
  var socket = io.connect(&#39;http://localhost:8080&#39;);

  socket.on(&#39;news&#39;, function (data) {
    alert(JSON.stringify(data));
    console.log(data);
    socket.emit(&#39;my next event&#39;, { my: &#39;data&#39; });
  });

&lt;/script&gt;
```

Content Type	Original Author	Original Content on Stackoverflow
Question	Alex Lopatin	View Question on Stackoverflow
Solution 1 - Html	oberstet	View Answer on Stackoverflow
Solution 2 - Html	user207421	View Answer on Stackoverflow
Solution 3 - Html	manit	View Answer on Stackoverflow

Can websocket messages arrive out-of-order?

Html Problem Overview

Html Solutions

Solution 1 - Html

Solution 2 - Html

Solution 3 - Html

Jquery find nearest matching element

Uploading multiple files with Flask

Attributions