WebClient

Currently known clients in Helidon that we should consider:

The "HTTP" protocol

1. HTTP/1.1 client
2. HTTP/2 client
3. Eventually HTTP/3 client
4. grpc client (uses HTTP/2 as the base protocol, useless without HTTP/2)

Non-HTTP

1. WebSocket client (upgrades from HTTP/1.1, but fallback to HTTP protocol is useless)

When I, as a user want to access a service using its client, I start with the knowledge of what protocol I want to use:

• HTTP (any version)
• grpc
• WebSocket

This should bet determined by the API I choose as a starting point. For HTTP, we should be able to provide order of preferences, depending on TLS support Plaintext:

• HTTP/1
• HTTP/2 using upgrade
• HTTP/2 prior knowledge

TLS:

• ALPN (lists supported protocols, decides based on response)

HttpClient http = HttpClient.builder()
    .versions(Http2Client.PROTOCOL) // ALPN (http,h2,h3)
    .addConfig(Http2ClientConfig.builder().usePriorKnowledge().build())
    .build();

Required features

1. allow ClientResponse<T> for cases where I do request(T.class), that is not AutoCloseable

Features that should be common:

1. Proxy support (first do a CONNECT, then use the "inner" protocol over the tunneled stream)
2. ClientService support (for HTTP based protocols - not for WebSocket)