在尝试获取IP时，所有标准标头值都包含不正确的值。
req.ip: ::ffff:172.17.0.5
req.headers['x-forwarded-for']: 169.254.160.2
req.socket.remoteAddress: ::ffff:172.17.0.5
所有这些都导致了错误的ip。
解决方案：
- 使用
let ip = req.headers['x-appengine-user-ip']或 - 使用
app.set('trust proxy', true);使用Express的信任代理设置
解释：https://cloud.google.com/appengine/docs/flexible/nodejs/runtime#https_and_forwarding_proxies
应用程序引擎终止负载平衡器上的HTTPS连接，并将请求转发到您的应用程序。用户的IP地址在标准
X-Forwarded-For报头和X-Appengine-User-Ip报头中都可用。需要此信息的应用程序应将其web框架配置为信任代理。
每个请求的标头值的完整列表：
{
"host": "<APP_ID>.appspot.com",
"x-real-ip": "169.254.160.2",
"x-forwarded-for": "169.254.160.2",
"x-google-real-ip": "169.254.160.2",
"x-appengine-user-ip": "2620:0:1002:100a:2c4b:4f6b:7851:a9d9",
"x-appengine-api-ticket": "aad4544d4e04a1a0",
"x-appengine-user-email": "",
"x-appengine-auth-domain": "gmail.com",
"x-appengine-user-id": "",
"x-appengine-user-nickname": "",
"x-appengine-user-organization": "",
"x-appengine-user-is-admin": "0",
"x-appengine-request-id-hash": "A104B85B",
"x-appengine-request-log-id": "5748c500ff00ff09eec9a104b85b0001737e736d6172742d737061726b2d39333632320001323031363035323774313530323538000100",
"x-appengine-https": "on",
"x-appengine-datacenter": "us6",
"x-appengine-default-version-hostname": "smart-spark-93622.appspot.com",
"cache-control": "max-age=0",
"accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
"upgrade-insecure-requests": "1",
"save-data": "on",
"user-agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.63 Safari/537.36",
"accept-language": "en-US,en;q=0.8",
"x-appengine-country": "US",
"x-appengine-region": "ca",
"x-appengine-city": "san francisco",
"x-appengine-citylatlong": "37.774929,-122.419416",
"x-cloud-trace-context": "4a77265a7fa3e11be8cccebce59f7702/9314487514850703289;o=5"
}
可以看出，x-forwarded-for正被设置为x-google-real-ip。因此，用户的ip现在可以在x-appengine-user-ip中使用。