Prevent websocket connections before establishment

Question

Our application is using websockets in an embedded jetty. The clients pass a http header containing an id. What we are trying to do is to block connections if a client with the same id is already connected. And no, we are not talking about user authentication here.

The only way to do this which we currently know is to implement this check in the @OnOpen-Callback of the Endpoint. The problem is that this method only gets called after the connection has already been established. So the connection state of the second client is toggling.

Instead we want to perform the check before the connection has been established. We thought about using a ServletFilter, but according to the answer of another question they are not supported for websocket communication.

Is there a way for the server to prevent the establishment of a websocket connection based on an arbitrary condition?

Answer 1

So the correct way seems to be to throw a RuntimeException in a custom Configurator class. At least that is how they do it in the jetty examples:

https://github.com/eclipse/jetty.project/blob/master/jetty-websocket/javax-websocket-server-impl/src/test/java/examples/MyAuthedConfigurator.java

That is still not a perfect solution, as there is no way to send a custom http status or websocket close code. On the client side this will result in a generic stacktrace:

java.io.IOException: Connect failure
    at org.eclipse.jetty.websocket.jsr356.ClientContainer.connect(ClientContainer.java:157)
    at org.eclipse.jetty.websocket.jsr356.ClientContainer.connectToServer(ClientContainer.java:180)
    at kam.cpush.ClientTestEndPoint.connect(ClientTestEndPoint.java:169)
    at kam.cpush.ClientTestEndPoint.connect(ClientTestEndPoint.java:155)
    at kam.cproxy.integrationtest.DuplicateControlChannelIT.connectToProxy(DuplicateControlChannelIT.java:72)
    at kam.cproxy.integrationtest.DuplicateControlChannelIT.testDuplicateChannelNotAllowed(DuplicateControlChannelIT.java:50)
    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.apache.maven.surefire.testng.TestNGExecutor.run(TestNGExecutor.java:115)
    at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.executeMulti(TestNGDirectoryTestSuite.java:205)
    at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.execute(TestNGDirectoryTestSuite.java:108)
    at org.apache.maven.surefire.testng.TestNGProvider.invoke(TestNGProvider.java:111)
    at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:203)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:155)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103)
Caused by: org.eclipse.jetty.websocket.api.UpgradeException: Didn't switch protocols
    at org.eclipse.jetty.websocket.client.io.UpgradeConnection.validateResponse(UpgradeConnection.java:314)
    at org.eclipse.jetty.websocket.client.io.UpgradeConnection.read(UpgradeConnection.java:241)
    at org.eclipse.jetty.websocket.client.io.UpgradeConnection.onFillable(UpgradeConnection.java:163)
    at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555)
    at java.lang.Thread.run(Thread.java:745)