lua 遍历Header头部

local headers = ngx.req.get_headers()
ngx.say("headers begin", "<br/>")
ngx.say("Host : ", headers["Host"], "<br/>")
ngx.say("user-agent : ", headers["user-agent"], "<br/>")
ngx.say("user-agent : ", headers.user_agent, "<br/>")
for k,v in pairs(headers) do
    if type(v) == "table" then
        ngx.say(k, " : ", table.concat(v, ","), "<br/>")
    else
        ngx.say(k, " : ", v, "<br/>")
    end
end