Prevent InvalidStateException when response has already ended.

[feg624]

This PR prevents the scenario described on the stacktrace below. It happens when a prior handler than the template handler, breaks the handler chain while performing some validation. This change first checks whether the response has already ended before trying to write the template result to the response.

Jun 18, 2018 8:34:57 PM io.vertx.ext.web.impl.RoutingContextImplBase
SEVERE: Unexpected exception in route
java.lang.IllegalStateException: Response has already been written
at io.vertx.core.http.impl.HttpServerResponseImpl.checkValid(HttpServerResponseImpl.java:545)
at io.vertx.core.http.impl.HttpServerResponseImpl.putHeader(HttpServerResponseImpl.java:189)
at io.vertx.ext.web.handler.impl.TemplateHandlerImpl.lambda$handle$0(TemplateHandlerImpl.java:50)
at io.vertx.ext.web.templ.impl.PebbleTemplateEngineImpl.render(PebbleTemplateEngineImpl.java:89)
at io.vertx.ext.web.handler.impl.TemplateHandlerImpl.handle(TemplateHandlerImpl.java:48)
at io.vertx.ext.web.handler.impl.TemplateHandlerImpl.handle(TemplateHandlerImpl.java:28)
at io.vertx.ext.web.impl.RouteImpl.handleContext(RouteImpl.java:219)
at io.vertx.ext.web.impl.RoutingContextImplBase.iterateNext(RoutingContextImplBase.java:120)
at io.vertx.ext.web.impl.RoutingContextImpl.next(RoutingContextImpl.java:133)
at com.fegsoft.pricinglist.AppServerVerticle.lambda$5(AppServerVerticle.java:128)
at io.vertx.core.eventbus.impl.EventBusImpl.lambda$convertHandler$1(EventBusImpl.java:349)
at io.vertx.core.eventbus.impl.HandlerRegistration.deliver(HandlerRegistration.java:223)
at io.vertx.core.eventbus.impl.HandlerRegistration.handle(HandlerRegistration.java:200)
at io.vertx.core.eventbus.impl.EventBusImpl.lambda$deliverToHandler$3(EventBusImpl.java:533)
at io.vertx.core.impl.ContextImpl.lambda$wrapTask$2(ContextImpl.java:339)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:886)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.lang.Thread.run(Thread.java:745)

[feg624]

I've added more changes to the PR, so that the RoutingContext is available after reroute. These changes may not be good enough, but allows to start discussions about it.

[feg624]

I reverted the last commit, as I realized it was working as designed. However, I still think that the TemplateHandlerImpl should check whether the response has already ended.

[pmlopes]

I think this fix is applied in the wrong place. Any handler can break the chain so this issue affects not just the template engine but any handler. I think the check should be done in the iteration.