Nginx 删除斜杠

我正在使用openresty，下面是我的配置

location ~ ^/shorten.json/(?<url>.*)$ {
    content_by_lua '
      local cjson = require "cjson"
      local parser = require "redis.parser"
      local id = 1234
      local url = ngx.var.url
      local sUrl = "http://" .. ngx.var.host .. "/" .. id
      ngx.location.capture("/storenew",
        { args = { id = "/"..tostring(id), url = url } }
      )
      ngx.header.content_type = "application/json; charset=utf-8"
      ngx.say(cjson.encode({ shortUrl = sUrl }))
    ';
  }

location ~ ^/storenew$ {
    internal;

    redis2_query select 0;
    set_unescape_uri $id $arg_id;
    set_unescape_uri $url $arg_url;
    redis2_query set $id $url;
    redis2_query expire $id 1209600;

    redis2_query select 5;
    redis2_query incr count;

    redis2_pass 127.0.0.1:6379;
  }

它返回我并用/1234键在redis中保存一个条目

当我取这个redis条目时，我得到了这个

http:/facebook.com，即删除一个斜杠

请帮忙

http://example.com/shorten.json/https%3A%2F%2Ffacebook.com