sslSocket.wantClientAuth = true
          sslSocket.startHandshake()
          return@submit sslSocket.session.handshake()
        }
      }
    }
  }

  private fun doClientHandshake(
    client: HandshakeCertificates,
    serverAddress: InetSocketAddress,
  ): Future<Handshake> {
    return executorService.submit<Handshake> {
      SocketFactory.getDefault().createSocket().use { rawSocket ->

  @Test
  fun racingReaders() {
    val pipe = Pipe(1024)
    val sink = pipe.sink.buffer()
    val relay = edit(file, pipe.source, metadata, 5)
    val future1 = executor.submit(sourceReader(relay.newSource()))
    val future2 = executor.submit(sourceReader(relay.newSource()))
    Thread.sleep(500)
    sink.writeUtf8("abcdefghij")
    Thread.sleep(500)
    sink.writeUtf8("klmnopqrst")
    sink.close()

- Favour a working external library if appropriate.  There are many examples of OkHttp libraries that can sit on top or hook in via existing APIs.
- Get working code on a personal branch with tests before you submit a PR.
- OkHttp is a small and light dependency.  Don't introduce new dependencies or major new functionality.

    assertThat(buffer.readUtf8()).isEqualTo(expected)
  }

  @Test
  fun fieldAndTwoFiles() {
    val expected =
      """
      |--AaB03x
      |Content-Disposition: form-data; name="submit-name"
      |
      |Larry
      |--AaB03x
      |Content-Disposition: form-data; name="files"
      |Content-Type: multipart/mixed; boundary=BbC04y
      |
      |--BbC04y

0002 0.554 connectionReleased
0002 0.554 callEnd
0001 0.624 responseBodyEnd
0001 0.624 connectionReleased
0001 0.624 callEnd
```

The `EventListener.Factory` also makes it possible to limit metrics to a subset of calls. This one captures metrics on a random 10%:

```java
class MetricsEventListener extends EventListener {
  private static final Factory FACTORY = new Factory() {

original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted to Licensor for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner. For the purposes of this definition, "submitted" means any form of electronic, verbal, or written communication sent to the Licensor or its representatives, including but not limited to communication on electronic...

        .throttleBody(1, 750, TimeUnit.MILLISECONDS)
        .build(),
    )
    val call = client.newCall(Request(server.url("/a")))
    val executor = Executors.newSingleThreadExecutor()
    val result = executor.submit<Response?> { call.execute() }
    Thread.sleep(100) // wait for it to go in flight.
    call.cancel()
    assertFailsWith<IOException> {
      result.get()!!.body.bytes()
    }

        }
        for (varyField in value.split(',')) {
          result.add(varyField.trim())
        }
      }
      return result ?: emptySet()
    }

    /**
     * Returns the subset of the headers in this's request that impact the content of this's body.
     */
    fun Response.varyHeaders(): Headers {
      // Use the request headers sent over the network, since that's what the response varies on.

          )
      } else {
        issuerKeyPair = subjectKeyPair
        issuer = subject
      }
      val signatureAlgorithm = signatureAlgorithm(issuerKeyPair)

      // Subset of certificate data that's covered by the signature.
      val tbsCertificate =
        TbsCertificate(
          // v3:
          version = 2L,
          serialNumber = serialNumber ?: BigInteger.ONE,

          .matches(Regex(prefix.pattern + regex.pattern, RegexOption.DOT_MATCHES_ALL))
      }

    fun assertNoMoreLogs() {
      assertThat(logs.size, "More messages remain: ${logs.subList(index, logs.size)}")
        .isEqualTo(index)
    }

    override fun log(message: String) {
      logs.add(message)
    }
  }

  companion object {