They're also concrete: each URL identifies a specific path (like `/square/okhttp`) and query (like `?q=sharks&lang=en`). Each webserver hosts many URLs.

### [Addresses](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-address/)

Addresses specify a webserver (like `github.com`) and all of the **static** configuration necessary to connect to that server: the port number, HTTPS settings, and preferred network protocols (like HTTP/2).

        executor,
        null,
        object : DnsResolver.Callback<List<InetAddress>> {
          override fun onAnswer(
            addresses: List<InetAddress>,
            rCode: Int,
          ) {
            callback.onResponse(hostname, addresses)
          }

          override fun onError(e: DnsResolver.DnsException) {
            callback.onFailure(
              hostname,

// Endpoint represents a single logical "backend" implementing a service.
message Endpoint {
  // addresses of this endpoint. The contents of this field are interpreted
  // according to the corresponding EndpointSlice addressType field. Consumers
  // must handle different types of addresses in the context of their own
  // capabilities. This must contain at least one address but no more than

		// the 'for=' capture, which we ignore. In the case of multiple IP
		// addresses (for=8.8.8.8, 8.8.4.4, 172.16.1.20 is valid) we only
		// extract the first, which should be the client IP.
		if match := forRegex.FindStringSubmatch(fwd); len(match) > 1 {
			// IPv6 addresses in Forwarded headers are quoted-strings. We strip
			// these quotes.
			addr = strings.Trim(match[1], `"`)
		}
	}

  # outbound connections.
  # If "REDIRECT", use iptables REDIRECT to NAT and redirect to Envoy.
  # The "REDIRECT" mode loses source addresses during redirection.
  # If "TPROXY", use iptables TPROXY to redirect to Envoy.
  # The "TPROXY" mode preserves both the source and destination IP
  # addresses and ports, so that they can be used for advanced filtering
  # and manipulation.
  # The "TPROXY" mode also configures the sidecar to run with the

     * fallbacks to prevent the host machine's various IP addresses from interfering.
     */
    private val SINGLE_INET_ADDRESS_DNS =
      Dns { hostname ->
        val addresses = Dns.SYSTEM.lookup(hostname)
        listOf(addresses[0])
      }

    private operator fun Throwable?.plus(throwable: Throwable): Throwable {
      if (this != null) {

     * <li>indexed properties (java.util.List or array instance) should be contains <code>(\\w+)\\[(\\d+)\\]</code>
     * pattern, i.e. "user.addresses[1].street"</li>
     * <li>mapped properties should be contains <code>(\\w+)\\((.+)\\)</code> pattern,
     *  i.e. "user.addresses(myAddress).street"</li>
     * </ul>
     *
     * @param expression not null expression
     * @param root       not null object

import okio.Buffer

/**
 * Quick and dirty pattern to differentiate IP addresses from hostnames. This is an approximation
 * of Android's private InetAddress#isNumeric API.
 *
 * This matches IPv6 addresses as a hex string containing at least one colon, and possibly
 * including dots after the first colon. It matches IPv4 addresses as strings containing only

// Addr2line is a minimal simulation of the GNU addr2line tool,
// just enough to support pprof.
//
// Usage:
//
//	go tool addr2line binary
//
// Addr2line reads hexadecimal addresses, one per line and with optional 0x prefix,
// from standard input. For each input address, addr2line prints two output lines,
// first the name of the function containing the address and second the file:line

    // 2 6to4 addresses differing in the embedded IPv4 address should
    // hash to the different values.
    assertThat(InetAddresses.getCoercedIPv4Address(InetAddresses.forString("2002:0102:0304::1")))
        .isNotEqualTo(
            InetAddresses.getCoercedIPv4Address(InetAddresses.forString("2002:0506:0708::1")));

    // 2 6to4 addresses NOT differing in the embedded IPv4 address should