Tomcat servlet works on local machine but breaks on server

[Calvin Dobson]

m assuming I'm doing something simple and stupid since I'm new to this. But I have a working Tomcat servlet. On my local machine, when the connection is created with:

var webSocket = new WebSocket("ws://localhost:8080/myapp/websocketendpoint");

it works just fine. In fact, I accidentally loaded it to the server with that and of course it still worked :P.

However, whenever I try to run the servlet on the server itself:

var webSocket = new WebSocket("ws://11.22.33.44:8080/myapp/websocketendpoint");

it dies, saying that a connection cannot be established to the server. To be honest, I used this https://www.digitalocean.com/community/tutorials/install-tomcat-9-debian-9 to set up the server.  I thought I even briefly disabled the firewall.

[Bob Winter]

"It doesn't work" unfortunately isn't that much of an information. Unless the Exception is silently suppressed there's a rather helpful IOException telling you the issue. Most likely either a no route to host meaning the dns resolution failed or a connection refused which often means the firewall is blocking (unless the server isn't running at all).
So, to help us to help you to figure out the issue it's best to show us the error message (please post text output as text rather than taking a screenshot as it's hard to read on a mobile device).
I'm sure one here can spot the issue and give you some advice.

[Tim Moores]

That looks like JavaScript code - is there further information (or maybe error messages) in the browser console?

[Calvin Dobson]

Yes, I looked in the console.  The only message I seem to be able to get out of it goes along the lines of "could not connnect to server."  It doesn't include any other information about where in the protocol the process failed.  

[Calvin Dobson]

So I've managed to tease out some more debugging information:

This is Debain 9 and tomcat 9.
Firefox won't give an error code, chrome gives: failed: Error during WebSocket handshake: Unexpected response code: 500.  I think the error on the tomcat side is:

org.apache.catalina.startup.HostConfig.deployWAR Deployment of web application archive [/opt/tomcat/webapps/myapp-0.1-dev.war] has finished in [88] ms 20-May-2020 14:50:27.296 INFO [http-nio-8080-exec-3] org.apache.catalina.startup.HostConfig.undeploy Undeploying context [/myapp-0.1-dev] 20-May-2020 15:03:47.133 INFO [http-nio-8080-exec-11] org.apache.coyote.http11.Http11Processor.service Error parsing HTTP request header Note: further occurrences of HTTP request parsing errors will be logged at DEBUG level. java.lang.IllegalArgumentException: Invalid character found in the HTTP protocol [HTTP/1.10x0aHost:] at org.apache.coyote.http11.Http11InputBuffer.parseRequestLine(Http11InputBuffer.java:560) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:260) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748)


I tried it on FreeBSD, and this just changed the error to 404 from 500.  However  I also noticed that my subroutine which starts with

public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {

and prints a simple website works fine on my computer, but it doesn't work so well on the remote server.  Could a problem with web.xml cause this issue?