KeepAlive functionality in Server: Should we make it enabled permanently?

[sumawa]

There are two standard ways of verifying KeepAlive feature:

Keep Alive Test case 1

https://serverfault.com/a/554668

Getting "left intact" message while using curl

* Getting last two lines indicating keepAlive is still enabled 

		* Connection #0 to host localhost left intact
		* Closing connection 0

* And if keep-alive is not working, then it just outputs this line:

		* Closing connection #0

Keep Alive Test case 2

As per RFC https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.10

HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion of the response. For example,

       Connection: close

in either the request or the response header fields indicates that the connection SHOULD NOT be considered `persistent' (section 8.1) after the current request/response is complete.
HTTP/1.1 applications that do not support persistent connections MUST include the "close" connection option in every message.

Current behavior in zio-Http

We intend to enable / disable "keep alive" using

  private val server =
    Server.port(PORT) ++              // Setup port
      Server.paranoidLeakDetection ++ // Paranoid leak detection (affects performance)
      Server.app(fooBar +++ app)   //++     // Setup the Http app
//      Server.keepAlive.     // uncomment to enable keep alive 

Scenario 1. Explicitly enabling Server.keepAlive while creating Server

For Http 1.0

curl  --http1.0 -Iv http://localhost:8090/foo  

We get connection: close in response header (correct behavior) indicating no re-use

	< connection: close
	* Closing connection 0	

For Http 1.1 (Without Connection: close in request header)

We get "left intact" message indicating re-use (correct behaviour)

curl  --http1.1 -Iv http://localhost:8090/foo
	< 
	* Connection #0 to host localhost left intact
	* Closing connection 0

For Http 1.1 (WITH Connection: close in request header)

curl  --http1.1 -Iv -H "Connection: Close" http://localhost:8090/foo

We get Connection: close in response header indicating no re-use (correct behaviour)

	< connection: close
	* Closing connection 0

Scenario 2. Disabled Server.keepAlive while creating Server

The "proof" that keepAlive is still working even if we don't use Server.keepAlive

Run HelloWorldAdvanced in examples test (with Server.keepAlive disabled), and fire these curl requests from command line

 curl -Iv http://localhost:8090/foo --next http://localhost:8090/foo 2>&1 | grep -i '#0'

We see the message regarding Re-use

* Connected to localhost (::1) port 8090 (#0)
* Connection #0 to host localhost left intact
* Re-using existing connection! (#0) with host localhost
* Connected to localhost (::1) port 8090 (#0)
* Connection #0 to host localhost left intact	

Recommendation

* Allow keepAlive always and remove Server.keepAlive
* The user requests can use "Connection: close" in the request header to control re-use mechanism
* Also may be we can explore keepAliveTimeout mechanism rather, if there is a substantial use case.