I'm working on a little proxy server that manages a bunch of tcp-ip connections that run in a selector loop. An external service talks to the proxy server via an http server embedded in the proxy server, and these requests go all the way through to a socket and then return the response from that socket in the response to the original http request.
I have concurrent requests (with a unique request id) coming in on the http server, the actual messages in these requests get stuck on queue and passed along to a bunch of socket connections (a certain socket will correspond to a message), and then the response gets dumped into a hash. The http request checks the hash periodically until it sees a response with the proper request id, or it times out. Here's an awesome system diagram if that makes no sense.
I'm totally new to using Java for http anything, so I figured I'd use Jetty and set up a simple request handler a la the Hello World example. Using a thread.sleep prevents concurrent requests, and continuations as far as I can tell requires events firing. I'd prefer the requests to check the hash once in a while as opposed to firing a connection event each time a socket puts a response in the hash, unless the events would fire by request id or something. That doesn't seem practical if there's a lot of traffic.
Cliffs:
- How do I make a handler (or servlet, if I need to go that far) wait for a bit or periodically while it's data becomes available without blocking everything else?
- Is there a better way to make the http request aware of data it should return as a response?
- Is this design bad, and if so, what's the alternative?
EDIT:
Here's my first stab at the problem. It works fine when the HTTP request points at an id which corresponds to a connected tcp client. If the id doesn't correspond to a connected client, jetty goes bonkers and gets into a loop and throws the following exception over and over. What I'd expect to happen is the request to time out because it cannot find any messages in the collector.
Mar 8, 2012 2:39:08 PM APIRequestHandler doPost
INFO: json: {"state": "255", "m": "set", "id": "00:00:00:00:00:06", "rid": "84955228696f11e1aa04c42c033c8bd7", "sid": "XXXXX"}
2012-03-08 14:39:08.526:WARN:oejs.ServletHandler:/
java.lang.IllegalStateException: ASYNCSTARTED,initial
at org.eclipse.jetty.server.AsyncContinuation.suspend(AsyncContinuation.java:365)
at org.eclipse.jetty.server.AsyncContinuation.suspend(AsyncContinuation.java:959)
at APIRequestHandler.doPost(APIRequestHandler.java:72)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:755)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:594)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:485)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1065)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:412)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:192)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:999)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:111)
at org.eclipse.jetty.server.Server.handle(Server.java:351)
at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:454)
at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:900)
at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:954)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:857)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:76)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:609)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:45)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:599)
at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:534)
at java.lang.Thread.run(Thread.java:680)
Servlet:
public void doPost(HttpServletRequest req, HttpServletResponse res)
throws java.io.IOException
{
String rid = req.getParameter("rid");
String msg = req.getParameter("json");
String id = req.getParameter("id");
// Send to tcp-ip channel
APIMessage m = new APIMessage();
m.rid = rid;
m.id = id;
m.json = msg + "\r\n";
queue.add(m);
this.selector.wakeup();
Continuation cc = ContinuationSupport.getContinuation(req);
res.setContentType("text/plain");
res.getWriter().println("Request: "+rid+"\tstart:\t"+new Date());
res.getWriter().flush();
int elapsed = 0;
String responseStr = "";
boolean timeoutHappened = true;
while(elapsed<this.timeout) // say 50 millis
{
if(collector.containsKey(rid)){
responseStr = collector.get(rid);
collector.remove(rid);
timeoutHappened = false;
break;
}
cc.setTimeout(10); // sleep 10 millis
cc.suspend();
}
if(!timeoutHappened)
{
logger.info("--->API http request found response in collector!");
logger.info("Respose: "+responseStr);
}
else // timed out
{
logger.info("--->API http request timed out!");
}
res.getWriter().println("Request: "+rid+"\tend:\t"+new Date());
if(cc.isInitial()!=true) {cc.complete();}
}
