WebSocket via HTTP proxy

As you might know, WebSocket can be used for bi-directional "real-time" communication with multiple clients. What does that mean in proxy environments and how this even works? WebSocket uses HTTP upgrade mechanism specified in HTTP 1.1 and by design requires open (TCP) connection.

HTTP CONNECT is there for exactly these usecases. It is usually used for tunneling HTTPS via proxy, but it can be used for WebSocket as well.

I will describe complete "proxified" handshake using captured connection of Tyrus Client connecting to public echo service - echo.websocket.org. Please note that we are directly using Tyrus API - not WebSocket specification (JSR-356), because we need to set a proxy.

final ClientManager client = ClientManager.createClient();

client.getProperties().put(
  GrizzlyClientSocket.PROXY_URI, "http://my.proxy:8080"
);
final Session session = client.connectToServer(new Endpoint() {

  @Override
  public void onOpen(Session session, EndpointConfig config) {
    session.addMessageHandler(new MessageHandler.Whole<String>() {
      @Override
      public void onMessage(String message) {
        System.out.println("# Message received: " + message);
      }
    });
  }
}, ClientEndpointConfig.Builder.create().build(),
   URI.create("ws://echo.websocket.org"));

session.getBasicRemote().sendText("test message");

BTW, Tyrus Client proxy support can be improved, currently it does not support proxy authentication, JDK's ProxySelector and so on. Please vote/comment on TYRUS-204 if you lack some of the mentioned options or anything else related to proxy support.

Current modern browsers do support this out of the box, so all you need is to set your HTTP proxy and described handshake will be done automatically. There might be limitation for parallel open connection in browser tab/instance, but I don't have any exact data about this.

Also, you might ask whether there is some need to server-side support - simple answer is "no". HTTP containers will see regular connection (from proxy), there is no additional work or overhead on that side.

Lets see our dumped communication:

client > proxy
CONNECT echo.websocket.org:80 HTTP/1.1
Host: echo.websocket.org
Proxy-Connection: keep-alive
Connection: keep-alive

Firstly, client need to send a request to proxy for new "permanent" connection. As already mentioned, CONNECT method handles this. First argument is a hostname (echo.websocket.org) and standard HTTP version.

proxy > client
HTTP/1.0 200 Connection established

If you are lucky, your proxy does support CONNECT and allows you to create connection (HTTP 200 is returned).

client > proxy
GET / HTTP/1.1
Connection: Upgrade
Host: echo.websocket.org
Origin: echo.websocket.org
Sec-WebSocket-Key : sDD3Wk7PMRCPE9+C0VyOcQ==
Sec-WebSocket-Version: 13
Upgrade: websocket

This is standard WebSocket handshake request, which will be passed to target HTTP container.

proxy > client
HTTP/1.1 101 Web Socket Protocol Handshake
Upgrade: WebSocket
Connection: Upgrade
Sec-WebSocket-Accept: 8TNIHr7bJHqQadjXYvqLql6RFEA=
Date: Tue, 16 Jul 2013 15:30:53 GMT
...

And there is a valid response to our handshake request, connection is established and communication can be started; there is nothing else different than in proxy-less environment. Please note that proxies do have limited resources and your request may be turned down because proxy "CONNECT" pool is empty.

Conclusion here is that WebSocket can work via proxies without any limitation, it just introduces different kind of traffic than pure HTTP and might cause some additional requirements related to proxy performance in case you are going to use WebSocket for long-running client connections.

Comments:

Hi Pavel,

Thanks for the explanation, that really did help me to understand the handshake. I have a scenario, wherein the connection initiation is successful and the proxy returns a HTTP/1.0 200 Connection established, but the SSL handshake fails.

HTTP/1.0 500 handshakefailed
Via: 1.0 10.X.X.X (McAfee Web Gateway 7.2.0.1.0.13253)
Content-Type: text/html
Cache-Control: no-cache
Content-Length: 2063
Proxy-Connection: Close

Any suggestions why is it failing?

Posted by Srini on September 04, 2013 at 08:05 AM CEST #

Hi Srini,

you should add -Djavax.net.debug=all (see http://docs.oracle.com/javase/1.5.0/docs/guide/security/jsse/ReadDebug.html for more details). It usually is certificate issue, in your case it might be because the other side does not have properly signed certificate and you don't have truststore and/or keystore properly set on client side.

Feel free to send more details to users@tyrus.java.net.

Posted by guest on September 09, 2013 at 10:11 AM CEST #

Finally some extra info on websokets and proxies...not much on the web. I read this article on WS & proxies that every other article seemed to link to http://www.infoq.com/articles/Web-Sockets-Proxy-Servers
Problem is its dated 2010 yet the protocol was standaridzed end of 2011 and there is a part on '_Proxy Usage_:' that explains that the client can send info to a proxy asking it to connect to the given server. To me this sounds like there shouldnt be any problems as put out in the 2010 article but wasnt sure because i know about proxies but not their nitty gritties. Your article supports what I thought but i'd like to know for sure, are there any limitatons to HTTP proxy traversal when using Websockets?

Posted by tom on December 06, 2013 at 11:15 PM CET #

Hi Tom,

there are limitations, but it is very unlikely you will hit them - it is the same as for creating HTTPS connections. From what I know, the theoretical limit would be something around 60k parallel connections for one proxy. Also depends on the proxy software itself, the number of "CONNECT"s is usually capped there to be able to process other standard http requests.

Posted by Pavel on December 06, 2013 at 11:34 PM CET #

Hi Pavel,
for a work flow system, I've build and which may handle advertisement production for multiple customers (news providers) within a single instance.
Internaly it is based on ip-reachability of all components.
In some cases it is necessary to integrate the personality who recorded the commercial ad order (somewher, within the customers LAN).
I'm on with WEB Sockets to allow the quasi synchronous connection to connect to the data base and via RMI to the Production server.
At the moment I'v started to build a test application using the NETBEAN IDE 8.0.2.
This IDE is based on JSR_API.
You used tyrus the uese proxies.
Could you plaese lat me know, which implementation I should use in my case.

Jochen

Posted by Jochen Seliger on May 12, 2015 at 10:29 AM CEST #

Hey Jochen,

I'm not sure whether I understood the question; Netbeans itself are not shipping with Java EE implementation by default. However, you can download prepackaged bundle with Glassfish, which does contain Tyrus - then you should be all set to start your work with Tyrus. Or you can use libraries from some other supported application server and then you will use their implementation, which might or might not be Tyrus.

The usecase is not really clear to me - I don't know where in your design you plan to use WebSocket. You can create more comprehensive description and share it on users@tyrus.java.net - responding there is much easier than here.

Thanks,
Pavel

Posted by Pavel on May 12, 2015 at 11:02 AM CEST #

Hi Pavel,
as I'm not sure yet, if I should use tyrus or JAVA7 (with JSR356), I'm not sure where to post my questions.
Concerning your question:
I'v build a work flow solution, which will speed up the advertisement production for newsproviders (mainly for newspapers).
Internally (between the compoments of the solution) I need a visibility of all components cross over [LAN or VPN]).
The solution is build to handle productions for unlimited number of customers (newspapers).
As the customers commercial advertisement systems will have work stations, spread over an unknown range of network structures, where in some cases the recorders of the commercial order, should be incorporabable into the work flow processing, we will provide an easy way to do that.
The needed part within the work flow logic is already implemented.
But the quasi synchronous connection quasi from any computer is the question.
Generally there could be opened an VPN, including all mashines.
But if an customers will handle production, lets say one in UK, one on Polans one in China, the establishing of one or several VPN's will be slightly complicated.
Therefor I'd like to have the opportunity, to let our special WF-Clients to get connected to an WEB-Service, running at the central WF-Instance and letting them them retrieve and use the jdbc-Connection and the RMI-reagistries (for and backwars)to connect to the relavant production server by a client and to exchange messages from any connected clienet to any other client.
That's the scenario, where I need the WEB-socket connection, first to retrieve the DBConnection and the RMI-registry and run the connection via these objects.

Regards
Jochen

Posted by guest on May 12, 2015 at 02:27 PM CEST #

Hi Jochen,

seems like you are looking for "TCP over WebSocket". Maybe not exactly TCP, you certainly could use some higher level protocols.. well. Not saying this is a bad idea (on the contrary - this should nicely get you around most firewalls, proxies and other nasty stuff out there, since WebSocket is HTTP at the very beginning), but it is not something which we do have implemented in Tyrus.

There are some people which are using WebSocket protocol as a tunnel for almost anything, like RFC 7118 (SIP over WebSocket), RFC 7395 (XMPP over WebSocket) and others. (see https://datatracker.ietf.org/doc/search/?name=websocket&sort=&rfcs=on&activedrafts=on for more complete result).

I doubt you want to create new standard, but you can! :)

So you can use websocket for your project and it should work (no guaranties about effectiveness etc), but it will mean significant investment in proprietary solution. I know about one company which do specialize on WebSocket applications - look for Kaazing, they might have something which will almost suite your needs, but you should also consider the VPN based solution you mentioned - in the long run, it could be cheaper and more sustainable one. Anyway, this is really out of scope of this article/blog, so I should stop now :) feel free to contact me privately if you think I can help more.

Regards,
Pavel

Posted by Pavel on May 12, 2015 at 03:24 PM CEST #

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