/** Returns the Content-Type header for this body. */
  abstract fun contentType(): MediaType?

  /**
   * Returns the number of bytes that will be written to sink in a call to [writeTo],
   * or -1 if that count is unknown.
   */
  @Throws(IOException::class)
  open fun contentLength(): Long = commonContentLength()

  /** Writes the content of this request to [sink]. */
  @Throws(IOException::class)