[Feature Request] remove hard coded "Connection: Close" for using persistent connection with geckodriver

[astmaih]

Meta -

OS: Windows Server

Selenium Version: 3.14.0

Browser: Firefox

Browser Version: 61.0

because geckodriver in verion 0.21.0 now supports http keep_alive connections, the selenium standalone server should now also support keep_alive connections to avoid TCP connection spamming. For this, i kindy request to remove the hard coded "Connection: close" code from PassThrough.java:

selenium/java/server/src/org/openqa/selenium/grid/session/remote/Passthrough.java

Line 86 in 33e2d10

// None of this "keep alive" nonsense.

selenium/java/server/src/org/openqa/selenium/grid/session/remote/Passthrough.java

Line 87 in 33e2d10

connection.setRequestProperty("Connection", "close");

or, at least, make keep_alive connections configurable.

Expected Behavior -

for one running test, the connection from the Selenium Server to the geckodriver should be persistent and be reused.

Actual Behavior -

For every command sended from the test to the browser, the selenium server opens a new tcp connection. After opening and using for one single command, every Connection stays in the TIME_WAITE state for 4 minutes. For complex selenium tests (using 3 parallel test-builds with more than 30 tests each build), after some time we get more than 5000 connections at the keep_alive state and sometimes the following error when the selenium server tries to open a new connection for the next command:

10:38:19.214 INFO - I/O exception (java.net.BindException) caught when processing request to {}->http://127.0.0.1:7057: Address already in use: connect

[diemol]

This was already implemented via ed716b5 and 663fee6