[🐛 Bug]: Informed driver port not being used - The port minus one is the port being used. Why?

What happened?

The selected port for the ChromeDriver doesn’t look right.

Why the port selected by the ChromeDriver receives a - 1 ?

def socket_lock
   @socket_lock ||= SocketLock.new(@port - 1, SOCKET_LOCK_TIMEOUT)
end

I took a look at the documentation, but I couldn’t find a reason.

See https://github.com/SeleniumHQ/selenium/blob/e3e492af0c9d9c99ce31b9dc036dbf75327e6f30/rb/lib/selenium/webdriver/common/service_manager.rb

How can we reproduce the issue?

Start a ChromeDriver by choosing a busy port.

Example

For this example, we’re choosing port 9999.

First, let’s make the port 9998 busy (port 9999 - 1)

python -m SimpleHTTPServer 9998

Second, let’s try to instantiate the ChromeDriver in the port 9999

 driver = Selenium::WebDriver.for(:chrome,  service: 
 Selenium::WebDriver::Chrome::Service.chrome(port: 9999))

Relevant log output

Operating System

Ubuntu 18.04

Selenium version

4.0.3

What are the browser(s) and version(s) where you see this issue?

N/A

What are the browser driver(s) and version(s) where you see this issue?

N/A

Are you using Selenium Grid?

No

[titusfortner]

Yeah, what we’re doing is locking the port - 1 with SocketLock#lock and then using PortProber#above to find the next available port to start the driver. This typically works fine because the port below the default ports is usually available.

I’m not sure why we do it this way, though. @twalpole or @p0deje do you have insight on this?

Bottom line is that Selenium will use the provided port, but you need to have the port below it available as well.

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