check(!closed) { "closed" }

      if (noMoreParts) return null

      // Read a boundary, skipping the remainder of the preceding part as necessary.
      if (partCount == 0 && source.rangeEquals(0L, dashDashBoundary)) {
        // This is the first part. Consume "--" followed by the boundary.
        source.skip(dashDashBoundary.size.toLong())
      } else {