HTTPBinUtil get and parse the request header by requesting `http(s)://httpbin.org`.

HTTPRequestHeaders 代表发起HTTP请求时的请求头部分信息 其中`X-Forwarded-For`和`X-Real-Ip`可以计算出Client的公网IP `Via` 一般是在HTTP请求经由代理转发后增加的字段.

RateLimiter contains some rate limit to control the rate of some operations, such as network request frequency, etc.

RequestHeadersGetter 获取HTTP请求头的接口。.