*
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */
  fun takeEvent(
    eventClass: Class<out ConnectionEvent>? = null,
    elapsedMs: Long = -1L,
  ): ConnectionEvent {

    assertThat(source1.readUtf8(10)).isEqualTo("abcdefghij")
    assertThat(source1.exhausted()).isTrue()
    source1.close()
    assertThat(relay1.isClosed).isTrue()

    // Since relay1 is closed, new sources cannot be created.
    assertThat(relay1.newSource()).isNull()
    val relay2 = read(file)
    assertThat(relay2.metadata()).isEqualTo(metadata)
    val source2 = relay2.newSource()!!.buffer()

  val bodySize: Long,
  /** The body of this POST request. This may be truncated. */
  val body: Buffer,
  /**
   * The index of this request on its HTTP connection. Since a single HTTP connection may serve
   * multiple requests, each request is assigned its own sequence number.
   */
  val sequenceNumber: Int,
  socket: Socket,
  /**

            try {
              plan.connectTcp()
            } catch (e: Throwable) {
              ConnectResult(plan, throwable = e)
            }
          // Only post a result if this hasn't since been canceled.
          if (plan in tcpConnectsInFlight) {
            connectResults.put(connectResult)
          }
          return -1L
        }
      },
    )
    return null
  }

Since HTTP requests frequently happen in parallel, connection pooling must be thread-safe.

These are the primary classes involved with establishing, sharing, and terminating connections:

Some requests will have a cached response. When this cached response isn’t fresh, OkHttp can do a _conditional GET_ to download an updated response if it’s newer than what’s cached. This requires headers like `If-Modified-Since` and `If-None-Match` to be added.

## Rewriting Responses

### [Fast Fallback](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback/)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

   * prefix. On the IBM JVM all cipher suites have the "SSL_" prefix.
   *
   * Prior to OkHttp 3.3.1 we accepted either form and consider them equivalent. And since OkHttp
   * 3.7.0 this is also true. But OkHttp 3.3.1 through 3.6.0 treated these as different.
   */
  @Test
  fun forJavaName_fromLegacyEnumName() {

   *
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */
  fun takeEvent(
    eventClass: Class<out CallEvent>? = null,
    elapsedMs: Long = -1L,
  ): CallEvent {

   * due to any of:
   *
   *  * A stale connection. The request was made on a reused connection and that reused connection
   *    has since been closed by the server.
   *  * A client timeout (HTTP 408).
   *  * A authorization challenge (HTTP 401 and 407) that is satisfied by the [Authenticator].