nginx 支持 WebSocket 協議

nginx.conf 的 http 段中：

map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;
}

vhost.conf 中：

location / {
    proxy_pass http://127.0.0.1:9875;
    proxy_set_header Host $host;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
}