nginx 逻辑判断if语句使用

当nginx 需要多重过滤转发时，我们会用到逻辑判断if，下面是栗子：

upstream xx-12 {
        server ip:8080;
}
server {
        listen 8080 ssl;
        ssl_certificate /etc/nginx/conf.d/cert.pem;
        ssl_certificate_key /etc/nginx/conf.d/key.pem;
        ssl_prefer_server_ciphers  on;
        ssl_session_cache shared:SSL:1m;
        ssl_session_timeout 5m;
        client_max_body_size 50M;
        server_name _;
        location / {
                gzip on;
                gzip_min_length 1k;
                gzip_buffers 4 16k;
                gzip_comp_level 2;
                gzip_types text/plain application/x-javascript text/css application/xml                 
                text/javascript application/x-httpd-php image/jpeg image/gif image/png;
                gzip_vary off;
                gzip_disable "MSIE [1-6]\.";
                proxy_connect_timeout 30m;
                proxy_send_timeout 1d;
                proxy_read_timeout 1d;
                proxy_pass https://xx-12;
                proxy_redirect off;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "upgrade";
				if ($http_referer ~* "ip:8080/sm"){
					proxy_pass http://xx-12;
					break;
				} 
        }
}

if 语句可以过滤下一级路径，从而转发到实际的资源地址。