* * If the proxy selector returns an empty list or null.
   *
   * Otherwise it lists the proxies in the order they will be attempted.
   *
   * @param url a URL with only the scheme, hostname, and port specified.
   */
  open fun proxySelectEnd(
    call: Call,
    url: HttpUrl,
    proxies: List<@JvmSuppressWildcards Proxy>,
  ) {
  }

  /**

 * connection the client has many options:
 *
 *  * **HTTP proxy:** a proxy server may be explicitly configured for the client. Otherwise, the
 *    [proxy selector][java.net.ProxySelector] is used. It may return multiple proxies to attempt.
 *  * **IP address:** whether connecting directly to an origin server or a proxy, opening a socket
 *    requires an IP address. The DNS server may return multiple IP addresses to attempt.
 *

//// tab | Python 3.8+

```Python hl_lines="10"
{!> ../../docs_src/header_params/tutorial002.py!}
```

////

/// warning | "Aviso"

Antes de definir `convert_underscores` como `False`, lembre-se de que alguns proxies e servidores HTTP não permitem o uso de cabeçalhos com sublinhados.

///

## Cabeçalhos duplicados

É possível receber cabeçalhos duplicados. Isso significa, o mesmo cabeçalho com vários valores.

        validator.validate(settings, problems);
        assertEquals(1, problems.messages.size());
        assertContains(
                problems.messages.get(0),
                "'proxies.proxy.id' must be unique" + " but found duplicate proxy with id " + id);
    }

    @Test
    void testValidateProxy() throws Exception {
        Settings settings = new Settings();

    }

    @Override public void proxySelectStart(Call call, HttpUrl url) {
      printEvent("proxySelectStart");
    }

    @Override public void proxySelectEnd(Call call, HttpUrl url, List<Proxy> proxies) {
      printEvent("proxySelectEnd");
    }

    @Override public void dnsStart(Call call, String domainName) {
      printEvent("dnsStart");
    }

     */
    public synchronized Proxy getActiveProxy() {
        if (activeProxy == null) {
            java.util.List<Proxy> proxies = getProxies();
            if (proxies != null && !proxies.isEmpty()) {
                for (Proxy proxy : proxies) {
                    if (proxy.isActive()) {
                        activeProxy = proxy;
                        break;
                    }

     * @return requested (de-)activation(s) of profile(s) in this execution. Never {@code null}.
     */
    ProfileActivation getProfileActivation();

    // Proxies
    List<Proxy> getProxies();

    MavenExecutionRequest setProxies(List<Proxy> proxies);

    MavenExecutionRequest addProxy(Proxy proxy);

    // Servers
    List<Server> getServers();

  protocols: List<Protocol>,
  connectionSpecs: List<ConnectionSpec>,
  /**
   * Returns this address's proxy selector. Only used if the proxy is null. If none of this
   * selector's proxies are reachable, a direct connection will be attempted.
   */
  @get:JvmName("proxySelector") val proxySelector: ProxySelector,
) {
  /**

///

```Python hl_lines="10"
{!> ../../docs_src/header_params/tutorial002.py!}
```

////

/// warning

Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

///

## Duplicate headers

It is possible to receive duplicate headers. That means, the same header with multiple values.

    override val call: Call,
    val url: HttpUrl,
  ) : CallEvent()

  data class ProxySelectEnd(
    override val timestampNs: Long,
    override val call: Call,
    val url: HttpUrl,
    val proxies: List<Proxy>?,
  ) : CallEvent() {
    override fun closes(event: CallEvent): Boolean = event is ProxySelectStart && call == event.call && url == event.url
  }

  data class DnsStart(
    override val timestampNs: Long,