n, err := io.Copy(io.MultiWriter(buf, md5w), ioutil.HardLimitReader(pReader, maxFanOutSize))
		if err != nil {
			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
			return
		}

		// Set the correct hex md5sum for the fan-out stream.
		fanOutOpts.MD5Hex = hex.EncodeToString(md5w.Sum(nil))

		concurrentSize := 100
		if runtime.GOMAXPROCS(0) < concurrentSize {
			concurrentSize = runtime.GOMAXPROCS(0)
		}