[nginx] 对UA为空的请求返回403

<code>       location / {
            <span>if</span> (<span>$http_user_agent</span> = <span>""</span>){
                access_log off;
                <span>return</span><span>403</span>;
            }

            default_<span>type</span>   text/html;
            content_by_lua <span>'
                ngx.say("<h1>你好 baby </h1>")
            '</span>;
        }</code>

<code>lzz<span>@ubuntu</span><span>:conf</span><span>$ </span>curl <span>'http://localhost'</span>
<h1>你好 baby /h1></h1></code>

<code>lzz@ubuntu:conf$ curl -H "User-Agent:" 'http://localhost'
<span>html</span>><span>head</span>><span>title</span>>403 Forbidden<span><span>title</span>></span><span><span>head</span>></span><span>body</span><span>bgcolor</span>=<span>"white"</span>><span>center</span>><span>h1</span>>403 Forbidden<span><span>h1</span>></span><span><span>center</span>></span><span>hr</span>><span>center</span>>ngx_openresty/1.2.6.1<span><span>center</span>></span><span><span>body</span>></span><span><span>html</span>></span></code>