Expose negotiated protocol version

[tnull]

The v1.6 upgrade negotiated and stored the server protocol version during connection setup, but omitted the documented public API for reading it.

Add protocol_version() so callers can reuse the negotiated value. Only fall back to server.version when no cached version exists.

[oleonardolima]

utACK f78ed74

Overall it looks good! I pushed a commit fixing the CI, though.

[caarloshenriq]

tACK fadedd9

I wrote this example to validate:

use electrum_client::{Client, Config, ElectrumApi, Socks5Config};
use std::env;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let url = env::args().nth(1).expect("uso: cargo run --example test_protocol_version -- <url> [socks5_addr]");
    let proxy = env::args().nth(2);

    let config = Config::builder()
        .validate_domain(false)
        .socks5(proxy.map(Socks5Config::new))
        .build();

    let client = Client::from_config(&url, config)?;
    println!("{} -> protocol_version = {}", url, client.protocol_version()?);

    let features = client.server_features()?;
    println!("server_features = {:#?}", features);

    Ok(())
}

and tested using these electrum url's

➜  rust-electrum-client git:(pr-213) - cargo run --example test_protocol_version -- "ssl://testnet.aranguren.org:51002"
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s
     Running `target/debug/examples/test_protocol_version 'ssl://testnet.aranguren.org:51002'`
ssl://testnet.aranguren.org:51002 -> protocol_version = 1.6
server_features = ServerFeaturesRes {
    server_version: "Fulcrum 2.1.1",
    genesis_hash: [
        0,
        0,
        0,
        0,
        9,
        51,
        234,
        1,
        173,
        14,
        233,
        132,
        32,
        151,
        121,
        186,
        174,
        195,
        206,
        217,
        15,
        163,
        244,
        8,
        113,
        149,
        38,
        248,
        215,
        127,
        73,
        67,
    ],
    protocol_min: "1.4",
    protocol_max: "1.6",
    hash_function: Some(
        "sha256",
    ),
    pruning: None,
}
➜  rust-electrum-client git:(pr-213) - cargo run --example test_protocol_version -- "tcp://blackie.c3-soft.com:57005"
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
     Running `target/debug/examples/test_protocol_version 'tcp://blackie.c3-soft.com:57005'`
tcp://blackie.c3-soft.com:57005 -> protocol_version = 1.6
server_features = ServerFeaturesRes {
    server_version: "Fulcrum 2.1.1",
    genesis_hash: [
        0,
        0,
        0,
        0,
        9,
        51,
        234,
        1,
        173,
        14,
        233,
        132,
        32,
        151,
        121,
        186,
        174,
        195,
        206,
        217,
        15,
        163,
        244,
        8,
        113,
        149,
        38,
        248,
        215,
        127,
        73,
        67,
    ],
    protocol_min: "1.4",
    protocol_max: "1.6",
    hash_function: Some(
        "sha256",
    ),
    pruning: None,
}
➜  rust-electrum-client git:(pr-213) - cargo run --example test_protocol_version -- "ssl://blackie.c3-soft.com:62002"
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.14s
     Running `target/debug/examples/test_protocol_version 'ssl://blackie.c3-soft.com:62002'`
ssl://blackie.c3-soft.com:62002 -> protocol_version = 1.6
server_features = ServerFeaturesRes {
    server_version: "Fulcrum 2.1.1",
    genesis_hash: [
        0,
        0,
        0,
        0,
        29,
        212,
        16,
        196,
        154,
        120,
        134,
        104,
        206,
        38,
        117,
        23,
        24,
        204,
        121,
        116,
        116,
        211,
        21,
        42,
        95,
        192,
        115,
        221,
        68,
        253,
        159,
        123,
    ],
    protocol_min: "1.4",
    protocol_max: "1.6",
    hash_function: Some(
        "sha256",
    ),
    pruning: None,
}

➜  rust-electrum-client git:(pr-213) - cargo run --example test_protocol_version -- "tcp://5dfr3ossuq3kxyc4zsgwqarh37yzlp7b6jc2j7h2gjq6jp7d7zg6fnid.onion:62001" "127.0.0.1:9050"
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
     Running `target/debug/examples/test_protocol_version 'tcp://5dfr3ossuq3kxyc4zsgwqarh37yzlp7b6jc2j7h2gjq6jp7d7zg6fnid.onion:62001' '127.0.0.1:9050'`
tcp://5dfr3ossuq3kxyc4zsgwqarh37yzlp7b6jc2j7h2gjq6jp7d7zg6fnid.onion:62001 -> protocol_version = 1.6
server_features = ServerFeaturesRes {
    server_version: "Fulcrum 2.1.0",
    genesis_hash: [
        0,
        0,
        0,
        0,
        29,
        212,
        16,
        196,
        154,
        120,
        134,
        104,
        206,
        38,
        117,
        23,
        24,
        204,
        121,
        116,
        116,
        211,
        21,
        42,
        95,
        192,
        115,
        221,
        68,
        253,
        159,
        123,
    ],
    protocol_min: "1.4",
    protocol_max: "1.6",
    hash_function: Some(
        "sha256",
    ),
    pruning: None,
}

[oleonardolima]

@caarloshenriq did you manage to test it against a server that didn't support v1.6 ?