check(currentPart == this) { "closed" }

        source.timeout().intersectWith(timeout) {
          return when (val limit = currentPartBytesRemaining(maxResult = byteCount)) {
            0L -> -1L // No more bytes in this part.
            else -> source.read(sink, limit)
          }
        }

        error("unreachable") // TODO(jwilson): fix intersectWith() to return T.
      }