[wildfly-dev] WF 8.0 HTTP Upgrade help needed
Przemyslaw Bielicki
pbielicki at gmail.com
Fri Apr 4 02:51:07 EDT 2014
Hi Stuart,
thx for the explanations. There is a problem anyway - if you set both read
and write listeners from the handler it won't work at all as in the write
listener ServletOutputStream.isReady() will be returning true all the time
(why not? the output is ready to send some data at the same time in is
ready to read some data), and the read listener will be ignored (as the
tread is focused on the writer). The solution here is not to have while
(out.isReady()) loop in the writer but a simple check if (out.isReady()),
but then you have to call onWritePossible yourself. It means you need to
pass a write listener reference to the read listener - it's smells more
than a bit.
I think I have my conclusion, that is: it is impossible to achieve
full-duplex (thus multiplexing) in an upgraded protocol using Servlet 3.1
API as there is "only ever one IO thread per connection" (I didn't find
such limitation in the specification - can you point out the section in
which it is said there should be on thread per connection?). In order to
achieve multiplexing one have to explicitly create a separate thread
dealing with either reading or writing the data.
Also, using Servlet 3.1 it is impossible to achieve non-blocking read and
write and multiplexing on the same connection, even using a separate thread.
I will contact the specification owners to see their opinion.
Many thanks,
Przemyslaw
On Fri, Apr 4, 2014 at 12:33 AM, Stuart Douglas
<stuart.w.douglas at gmail.com>wrote:
>
>
> Przemyslaw Bielicki wrote:
>
>> I tried - exactly the same results.
>>
>> Another weird observation is that ServletOutputStream.isReady() is
>> returning true even after the connection is closed
>> (ServletInputStream.isFinished() is correctly returning true).
>>
>> Here's the scenario that works but I can write back the data only once:
>> 1. In HttpUpgradeHandler I set only the ReadListener
>> 2. I switch the protocol and send some data
>> 3. ReadListener gets activated i.e. onDataAvailable() is called.
>> 4. I process the input data, read as much as possible and put the input
>> into the queue
>> 5. From within ReadListener I set the WriteListener
>> 6. WriteListener.onWritePossible() gets called and I process the data -
>> I clean the queue
>> 7. As long as I'm in WriteListener.onWritePossible()
>> (while.out.isReady() is constantly returning true, which is a correct
>> bahavior) the ReadListener is on-hold. I can send as much data as I like
>> but onDataAvailable() is not called
>> 8. Only when I leave WriteListener.onWritePossible() method the
>> ReadListener.onDataAvailable() is called again and I can consume the
>> input data again.
>> 9. I can process the input data again i.e. put it into the queue but
>> WriteListener.onWritePossible() is never called again. When I try to
>> reset it I get IllegalStateException
>>
>> Either the specification or implementation seem not very mature....
>> Wildfly behavior is consistent with the one of Tomcat.
>>
>
> As Remy said this is expected.
> Basically there is only ever one IO thread per connection, so only one
> method will be active at a time.
>
> The reason why your listener method is not being called again would become
> apparent if you look at the javadoc for the read/write listeners:
>
> Subsequently the container will invoke this method if and only
> if {@link javax.servlet.ServletOutputStream#isReady()} method
> has been called and has returned <code>false</code>.
>
> Basically what this means is that the listener is only invoked if
> isReady() returns false at some point. If you have read some data and then
> you want to echo it you should call the onWritePossible method yourself,
> after you have received the data.
>
> Stuart
>
>
>
>
>> At the moment I conclude that the non-blocking write is not possible in
>> Servlet 3.1.
>>
>> I would appreciate if someone can provide an example that actually works
>> or explain why the weird behavior I observe is correct (is it?)
>>
>> Cheers,
>> Przemyslaw
>>
>>
>>
>>
>> On Thu, Apr 3, 2014 at 6:18 AM, Stuart Douglas
>> <stuart.w.douglas at gmail.com <mailto:stuart.w.douglas at gmail.com>> wrote:
>>
>> Can you try with the latest development build of Wildfly (from
>> https://ci.jboss.org/hudson/__job/WildFly-latest-master/
>> <https://ci.jboss.org/hudson/job/WildFly-latest-master/>).
>>
>>
>> There have been some fixes in this area, so your problem may have
>> already been fixed.
>>
>> Stuart
>>
>>
>> PB wrote:
>>
>> Hi,
>>
>> I'm testing the HTTP Upgrade feature of WF 8.0 and I'm facing
>> some banal
>> problem. Basically my ReadListener is NEVER called.
>> Here's the code:
>>
>> @WebServlet(urlPatterns = "/upgrade")
>> public class UpgradeServlet extends HttpServlet {
>> @Override
>> protected void doGet(HttpServletRequest req,
>> HttpServletResponse
>> resp) throws ServletException, IOException {
>> if
>> ("upgrade".equalsIgnoreCase(__req.getHeader("Connection"))) {
>> req.upgrade(EchoHandler.class)__;
>>
>> }
>> }
>> }
>>
>> public class EchoHandler implements HttpUpgradeHandler {
>> @Override
>> public void init(WebConnection wc) {
>> try {
>> ServletInputStream in = wc.getInputStream();
>> ServletOutputStream out = wc.getOutputStream();
>>
>> BlockingQueue<String> queue = new
>> LinkedBlockingQueue<String>();
>> in.setReadListener(new EchoReadListener(queue, in));
>> out.setWriteListener(new EchoWriteListener(queue, out));
>> } catch (IOException e) {
>> throw new IllegalStateException(e);
>> }
>> }
>>
>> public class EchoReadListener implements ReadListener {
>> @Override
>> public void onDataAvailable() throws IOException {
>> while (in.isReady()) {
>> int length = in.read(buffer);
>> String input = new String(buffer, 0, length);
>> if (false == queue.offer(input)) {
>> System.err.println("'" + input + "' input was ignored");
>> }
>> }
>> }
>>
>> I'm connecting to WF using telnet and sending the upgrade request:
>> GET /example-webapp/upgrade HTTP/1.1
>> Host: localhost
>> Connection: upgrade
>> Upgrade: echo
>>
>> and I'm getting correct response:
>>
>> HTTP/1.1 101 Switching Protocols
>> Connection: Upgrade
>> X-Powered-By: Undertow 1
>> Server: Wildfly 8
>> Content-Length: 0
>>
>> which means that from now on the protocol between my telnet
>> client and
>> WF is pure TCP.
>> So, I start typing some text, hit Enter and.... nothing happens.
>> onDataAvailable() is NEVER called. More so, this makes WF totally
>> irresponsive - my whole webapp is dead.
>>
>> I believe, I'm doing something wrong - any ideas what exactly?
>> There is
>> also a slight chance that Upgrade feature in WF is f****d :)
>> Anyway, WF should not block even in case my upgraded protocol is
>> not
>> working correctly?
>>
>> Many thanks,
>> Przemyslaw
>>
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