printEvent("callStart");
  }

  @Override public void callEnd(Call call) {
    printEvent("callEnd");
  }

  ...
}
```

We can use this listener to race a pair of concurrent HTTP requests:

```java
Request washingtonPostRequest = new Request.Builder()
    .url("https://www.washingtonpost.com/")
    .build();
client.newCall(washingtonPostRequest).enqueue(new Callback() {

    // punctuation space
    assertThat(parse("http://h/\u2008").encodedPath).isEqualTo("/%E2%80%88")
    // thin space
    assertThat(parse("http://h/\u2009").encodedPath).isEqualTo("/%E2%80%89")
    // hair space
    assertThat(parse("http://h/\u200a").encodedPath).isEqualTo("/%E2%80%8A")
    // zero-width space
    assertThat(parse("http://h/\u200b").encodedPath).isEqualTo("/%E2%80%8B")
    // zero-width non-joiner

  @JvmOverloads
  constructor(
    val requiredPlatformName: String? = null,
    val platform: Platform? = null,
  ) : BeforeEachCallback, AfterEachCallback, InvocationInterceptor {
    private val versionChecks = mutableListOf<Pair<Matcher<out Any>, Matcher<out Any>>>()

    override fun beforeEach(context: ExtensionContext) {
      setupPlatform()
    }

    override fun afterEach(context: ExtensionContext) {
      resetPlatform()
    }

 *
 * All start/connect/acquire events will eventually receive a matching end/release event, either
 * successful (non-null parameters), or failed (non-null throwable). The first common parameters of
 * each event pair are used to link the event in case of concurrent or repeated events e.g.
 * `dnsStart(call, domainName)` → `dnsEnd(call, domainName, inetAddressList)`.
 *
 * Events are typically nested with this structure:
 *

   * request is transmitted. This is only interesting for duplex calls where the request and
   * response may be interleaved.
   *
   * Read this value only once for each enter/exit pair because its value can change.
   */
  private fun doReadTimeout() = !connection.client || sink.closed || sink.finished

  /**
   * A source that reads the incoming data frames of a stream. Although this class uses

  private lateinit var server: MockWebServer
  private lateinit var client: OkHttpClient

  val listener = RecordingEventListener()

  fun setUp(mode: Pair<CancelMode, ConnectionType>) {
    this.cancelMode = mode.first
    this.connectionType = mode.second

    if (connectionType == H2) {
      platform.assumeHttp2Support()
    }

    cipherSuitesAsString.intersect(socketEnabledCipherSuites, CipherSuite.ORDER_BY_NAME)
  } else {
    socketEnabledCipherSuites
  }
}

internal fun MediaType?.chooseCharset(): Pair<Charset, MediaType?> {
  var charset: Charset = Charsets.UTF_8
  var finalContentType: MediaType? = this
  if (this != null) {
    val resolvedCharset = this.charset()
    if (resolvedCharset == null) {

import okio.Buffer
import okio.ForwardingSink
import okio.ForwardingSource
import okio.Sink
import okio.Source
import okio.buffer

/**
 * Transmits a single HTTP request and a response pair. This layers connection management and events
 * on [ExchangeCodec], which handles the actual I/O.
 */
class Exchange(
  internal val call: RealCall,
  internal val eventListener: EventListener,

              // observation that the header entries we care about are in adjacent pairs, and we
              // always know the first index of the pair.
              if (STATIC_HEADER_TABLE[headerNameIndex - 1].value == value) {
                headerIndex = headerNameIndex
              } else if (STATIC_HEADER_TABLE[headerNameIndex].value == value) {

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