Confirm if HTTP connection uses Keep-Alive

[erickpintor]

To improve performance, FaunaDB allows http keep-alive connections. The should drivers issue requests with keep-alive header on.

The idle timeout for http connections is 5 seconds on the server, we should set it to a bit less on the client. 4 seconds should be fine.

[mtnbarreto]

From my understanding by default NSURLSession uses HTTP keep alive so not need to negotiate TCP stuff for each request.
Anyway i would like to check it.

Okay about the idle timeout.

[mtnbarreto]

It seems the client is not sending any Connection: close header so the connection should keep alive.

[erickpintor]

There is still an open question related to this: does swift keep a connection pool? If yes, we'll have to set it's idle timeout.

[mtnbarreto]

Apparently NSURLSession does't have such configuration. I'm almost sure it use a connection pool and in fact it support HTTP pipeline but probably it makes the decision about when close idle connections based on networking activity and trying to be as efficient as possible with the resources.

@erickpintor Here you have the NSURLSession configuration properties https://developer.apple.com/reference/foundation/nsurlsessionconfiguration. Maybe we should set up HTTPMaximumConnectionsPerHost.

Let me know your thoughts and the direction we should take on this.

[erickpintor]

From the docs.

... depending on your connection to the Internet, a session may use a lower limit than the one you specify. The default value is 6 in OS X, or 4 in iOS.

It doesn't seems wise to change it.

Considering that amount of concurrent connections, and the lack of configuration around idleness, I think is unlikely that it'll happen on normal devices.

We can close this for now.