nginx+lua搭建文件上传下载服务问题怎么解决

--文件下载服务写到 saverootpath .."/" .. filename 下面 
function download()
 local chunk_size = 4096
 local form,err=upload:new(chunk_size)
 if not form then
  ngx.log(ngx.err, "failed to new upload: ", err)
  ngx.exit(ngx.http_internal_server_error)
 end 
 form:set_timeout(100000)
 while true do
 local typ,res,err=form:read()
 if not typ then
  errormsg="failed to read :"..err
  return 1
 end
 if typ =="header" then
  local key=res[1]
  local value=res[2]
  if key =="content-disposition" then
  local kvlist=string.split(value,';')
   for _, kv in ipairs(kvlist) do
   local seg = string.trim(kv)
   if seg:find("filename") then
   local kvfile = string.split(seg, "=")
   filename = string.sub(kvfile[2], 2, -2)
   if filename then
    --获取文件后缀名字
    fileextension=getextension(filename)
    local linuxtime=tostring(os.time())
    filepath=saverootpath .."/" ..linuxtime..filename
    filetosave,errmsg = io.open(filepath, "w+")
    --存储的文件路径   
    --ngx.say("failed to open file ", filepath)
    if not filetosave then
    --ngx.say("failed to open file ", filepath .. errmsg)
    errormsg="打开文件失败"..filepath .. errmsg
    return 1
    end
   else
    errormsg="请求参数找不到文件名字"
    return 1
   end
   --跳出循环
   break 
   end
   end
  end
 elseif typ =="body" then
  if filetosave then
  filetosave:write(res)
  filemd5:update(res)
  end
 elseif typ =="part_end" then
  if filetosave then
  local md5_sum=filemd5:final()
  --ngx.say("md5: ", str.to_hex(md5_sum))
  filemd532=str.to_hex(md5_sum)
  filetosave:close()
  filetosave = nil
  end  
 elseif typ =="eof" then
  break
 else
  ngx.log(ngx.info, "do other things")
 end
 end
 return 0
end