DNS、TCP 与 TLS：一次 HTTPS 请求经过哪些阶段

import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Optional;
public class Main {
    record Entry(String value, long expires) {}
    static final class Cache {
        private final Map<String,Entry> data = new HashMap<>();
        private long last = -1;
        private void time(long now) {
            if (now < 0 || now < last) throw new IllegalArgumentException("time");
            last = now;
        }
        private String key(String host) {
            if (host == null || !host.matches("[A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*"))
                throw new IllegalArgumentException("ASCII teaching host");
            return host.toLowerCase(Locale.ROOT);
        }
        void put(String host, String value, long ttl, long now) {
            String key = key(host);
            if (value == null || ttl < 0) throw new IllegalArgumentException("entry");
            long expires = Math.addExact(now,ttl);
            time(now);
            if (ttl == 0) data.remove(key); // 零 TTL 不保留旧值。
            else data.put(key,new Entry(value,expires));
        }
        Optional<String> get(String host, long now) {
            String key = key(host); time(now);
            Entry entry = data.get(key);
            if (entry == null) return Optional.empty();
            if (now >= entry.expires()) { // 到期边界立即失效。
                data.remove(key); return Optional.empty();
            }
            return Optional.of(entry.value());
        }
    }
    static void require(boolean condition) {
        if (!condition) throw new AssertionError();
    }
    public static void main(String[] args) {
        Cache c = new Cache();
        c.put("Example.test","A",5,0);
        // 命中、大小写、恰好过期和刷新后的新期限。
        require(c.get("example.test",4).equals(Optional.of("A")));
        require(c.get("EXAMPLE.TEST",5).isEmpty());
        c.put("example.test","B",10,5);
        c.put("example.test","C",1,6);
        require(c.get("example.test",7).isEmpty());
        c.put("example.test","D",10,7);
        c.put("example.test","ignored",0,8);
        require(c.get("example.test",8).isEmpty());
        require(c.get("missing.test",8).isEmpty());
        boolean rejected = false;
        try { c.get("example.test",7); } catch (IllegalArgumentException e) { rejected = true; }
        require(rejected);
        System.out.println("PASS 6");
    }
}