override fun contentType(): MediaType? = TODO()

        override fun contentLength(): Long = TODO()

        override fun isDuplex(): Boolean = TODO()

        override fun isOneShot(): Boolean = TODO()

        override fun writeTo(sink: BufferedSink) = TODO()
      }
    requestBody = "".toRequestBody(null)
    requestBody = "".toRequestBody("".toMediaTypeOrNull())

    most common use of duplex calls is [gRPC][grpc_http2].

 *  New: Prevent OkHttp from retransmitting a request body by overriding `RequestBody.isOneShot()`.
    This is most useful when writing the request body is destructive.

 *  New: We've added `requestFailed()` and `responseFailed()` methods to `EventListener`. These

              return null
            }

            override fun writeTo(sink: BufferedSink) {
              sink.writeUtf8("attempt " + attempt++)
            }

            override fun isOneShot(): Boolean {
              return true
            }
          },
      )
    val response = client.newCall(request).execute()
    assertThat(response.code).isEqualTo(503)