HTTP/2 - Enable HTTP/2, ALPN & NPN by default

[aluccaroni]

For performance reason enable by default HTTP/2, Application Layer Protocol Negotiation and Next Protocol Negotiation.

We should have all the building blocks (Netty, boringSSL) to do so

[hamadodene]

With the migration to reactor netty, it is possible to enable HTTP2 support on both the server and client sides.
See https://projectreactor.io/docs/netty/release/reference/index.html#_http2 for server side
See https://projectreactor.io/docs/netty/release/reference/index.html#_http2_2 for client side.

Two http2 modes can be enabled:

1. H2 for http2 with ciphertext
2. H2C for Http with plaintext.
   With H2 you will need to provide a certificate for text encryption.

In my opinion both H2 and H2C need to be supported client side and server side. The administrator will have to decide which one to enable.

I would expect a configuration like this for server side:

listener.1.protocol=HTTP11,H2
listener.1.sslcertificate=example.p12   //mandatory if H2 is configured
listener.1.sslpassword=example 

listener.2.protocol=HTTP11,H2C

For client side:

client.protocol=HTTP11,H2
client.sslcertificate=example.p12  //mandatory if H2 is configured
client.sslpassword=example
 

or

client.protocol=HTTP11,H2C
Note:
A listener can support HTTP11+H2 or HTTP11 + H2C.
But it can NOT support HTTP11+H2+H2C. Basically you cannot configure H2 and H2C on the same listener. We will have to manage this in such a way that it is not possible.

[hamadodene]

I did some testing and based on what said here https://projectreactor.io/docs/netty/release/reference/index.html#_protocol_selection , it seems that in our case, on the listener we can support HTTP11+H2 or HTTP11 +H2C.
So it's not possible to support HTTP11+H2+H2C on the same listener.

Does it make sense to you too? @pv3nturi

[aluccaroni]

@hamadodene it shouldn't be a problem since we have different listener for http and https (different port). I don't see a case where we need a listener with H2+H2C

[hamadodene]

@aluccaroni I agree with you