### EventListener.Factory

In the preceding example we used a field, `callStartNanos`, to track the elapsed time of each event. This is handy, but it won’t work if multiple calls are executing concurrently. To accommodate this, use a `Factory` to create a new `EventListener` instance for each `Call`. This allows each listener to keep call-specific state.

  bufferA.writeUtf8(normalized)

  // 3. For each label, convert/validate Punycode.
  val decoded = Punycode.decode(bufferA.readUtf8()) ?: return null

  // 4.1 Validate.

  // Must be NFC.
  if (decoded != normalizeNfc(decoded)) return null

  // TODO: Must not begin with a combining mark.
  // TODO: Each character must be 'valid' or 'deviation'. Not mapped.

 * All comments are ignored.
 *
 * Regular lines contain fields separated by semicolons.
 *
 * The first element on each line is a single hex code point (like 0041) or a hex code point range
 * (like 0030..0039).
 *
 * The second element on each line is a mapping type, like `valid` or `mapped`.
 *
 * For lines that contain a mapping target, the next thing is a sequence of hex code points (like

 *  New: Reduce contention for applications that make a very high number of concurrent requests.
    Previously OkHttp used its connection pool as a lock when making changes to connections and
    calls. With this change each connection is locked independently.

 *  Upgrade: [Okio 2.7.0][okio_2_7_0].

    ```kotlin
    implementation("com.squareup.okio:okio:2.7.0")
    ```

import okio.Buffer
import okio.ByteString
import okio.ByteString.Companion.encodeUtf8
import okio.Source
import okio.Timeout

/**
 * Replicates a single upstream source into multiple downstream sources. Each downstream source
 * returns the same bytes as the upstream source. Downstream sources may read data either as it
 * is returned by upstream, or after the upstream source has been exhausted.
 *

    assertThat(b.code).isEqualTo(200)
    assertThat(server.takeRequest().sequenceNumber).isEqualTo(0)
    assertThat(
      server.takeRequest().sequenceNumber,
      "When connection: close is used, each request should get its own connection",
    ).isEqualTo(0)
  }

  @Test
  fun connectionCloseInResponse() {
    server.enqueue(MockResponse(headers = headersOf("Connection", "close")))

import okhttp3.HttpUrl
import okhttp3.Route
import okhttp3.internal.canParseAsIpAddress
import okhttp3.internal.immutableListOf
import okhttp3.internal.toImmutableList

/**
 * Selects routes to connect to an origin server. Each connection requires a choice of proxy server,
 * IP address, and TLS mode. Connections may also be recycled.
 */
class RouteSelector(
  private val address: Address,
  private val routeDatabase: RouteDatabase,

 * They don't specify whether a specific proxy server should be used or how to authenticate with that proxy server.

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/)

import kotlinx.serialization.decodeFromString
import kotlinx.serialization.json.Json

/**
 * A test from the [Web Platform To ASCII](https://github.com/web-platform-tests/wpt/blob/master/url/resources/toascii.json).
 *
 * Each test is a line of the file `toascii.json`.
 */
@Serializable
class WebPlatformToAsciiData {
  var input: String? = null
  var output: String? = null
  var comment: String? = null

/**
 * A one-shot stream from the origin server to the client application with the raw bytes of the
 * response body. Each response body is supported by an active connection to the webserver. This
 * imposes both obligations and limits on the client application.
 *
 * ### The response body must be closed.
 *
 * Each response body is backed by a limited resource like a socket (live network responses) or