Not possible to connect to RosBridge

[GitRepJo]

Hi,

I installed the current version of node v10.19.0. on Ubuntu 20.04.2 LTS
I run node bin/rosbridge.js and node examples/index.js
However when i open http://localhost:3001/html/publisher.html in the browser i get the message.

Error in the backend! Connection closed.

No messages are received by the node index.js.

I changed the port of the node index.js to 3001 in index.js because 3000 was already used.

Any suggestions on how to narrow down on the error or get a more detailed error description?

[GitRepJo]

As already stated in #160 https://github.com/RobotWebTools/ros2-web-bridge/issues/160,
DEBUG=ros2-web-bridge* node bin/rosbridge.js provides more details.
It turns out, that the default port localhost:9090 was already blocked. Changing it to an open port worked well.
I checked for blocked ports with sudo nmap -sT -O localhost