* [system DNS service][SYSTEM], which is the default. Some applications may provide their own
 * implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4 addresses,
 * or to force a specific known IP address.
 *
 * Implementations of this interface must be safe for concurrent use.
 */
fun interface Dns {
  /**

    // Write metadata to the end of the file.
    writeMetadata(upstreamSize)
    file!!.channel.force(false)

    // Once everything else is in place we can swap the dirty header for a clean one.
    writeHeader(PREFIX_CLEAN, upstreamSize, metadata.size.toLong())
    file!!.channel.force(false)

    // This file is complete.
    synchronized(this@Relay) {
      complete = true
    }

        val headers = request.headers

        if (requestBody != null) {
          // Request body headers are only present when installed as a network interceptor. When not
          // already present, force them to be included (if available) so their values are known.
          requestBody.contentType()?.let {
            if (headers["Content-Type"] == null) {
              logger.log("Content-Type: $it")
            }

 * doesn't cache partial responses.
 *
 * ## Force a Network Response
 *
 * In some situations, such as after a user clicks a 'refresh' button, it may be necessary to skip
 * the cache, and fetch data directly from the server. To force a full refresh, add the `no-cache`
 * directive:
 *
 * ```java
 * Request request = new Request.Builder()

     */
    @JvmField
    val FORCE_NETWORK = commonForceNetwork()

    /**
     * Cache control request directives that uses the cache only, even if the cached response is
     * stale. If the response isn't available in the cache or requires server validation, the call
     * will fail with a `504 Unsatisfiable Request`.
     */
    @JvmField
    val FORCE_CACHE = commonForceCache()

    /**

      }
    assertThat(requestsMade.size).isEqualTo(0)
    mockWebServer.dispatcher = dispatcher
    val url = mockWebServer.url("/").toUrl()
    val conn = url.openConnection() as HttpURLConnection
    conn.responseCode // Force the connection to hit the "server".
    // Make sure our dispatcher got the request.
    assertThat(requestsMade.size).isEqualTo(1)
  }

  @Test
  fun outOfOrderResponses() {
    val firstResponseCode = AtomicInteger()

    val bytes = ByteArray(byteCount)
    Random(0).nextBytes(bytes)
    return ByteString.of(*bytes)
  }

  private fun snapshot(): ByteString {
    randomAccessFile!!.getChannel().force(false)
    val source = file!!.source().buffer()
    return source.readByteString()
  }

  private fun write(data: ByteString) {
    val sink = file!!.sink().buffer()
    sink.write(data)
    sink.close()

1. Add an Emulator named `pixel5`, if you don't already have one

```
$ sdkmanager --install "system-images;android-29;google_apis;x86"
$ echo "no" | avdmanager --verbose create avd --force --name "pixel5" --device "pixel" --package "system-images;android-29;google_apis;x86" --tag "google_apis" --abi "x86"
```

2. Run an Emulator using Android Studio or from command line.

```

    client.newCall(request).execute().use { response ->
      assertEquals(200, response.code)
    }

    client.connectionPool.evictAll()
    assertEquals(0, client.connectionPool.connectionCount())

    // Force reuse. This appears flaky (30% of the time) even though sessions are reused.
    // javax.net.ssl.SSLHandshakeException: No new session is allowed and no existing
    // session can be resumed
    //

    var success = false
    try {
      if (connectionSpec.supportsTlsExtensions) {
        Platform.get().configureTlsExtensions(sslSocket, address.url.host, address.protocols)
      }

      // Force handshake. This can throw!
      sslSocket.startHandshake()
      // block for session establishment
      val sslSocketSession = sslSocket.session
      val unverifiedHandshake = sslSocketSession.handshake()