lua 遍历Header头部

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