触动精灵怎么提交表单上传图片啊？ 卡在上传这里了、请大神教一下。

post=strkey..strpolicy..strOSSAccessKeyId..strsignature..success_action_status..strimg local sz = require("sz") local yunhttp = require("szocket.http") local response_body = {} local post_data =post ;
res, code = yunhttp.request{
url = host,
method = "POST",
headers =
{
['Content-Type']='multipart/form-data; boundary='..boundary,
["Content-Length"] = #post_data,
},
source = ltn12.source.string(post_data),
sink = ltn12.sink.table(response_body)
}

dialog(code, time)