什么是417状态码?
在请求的Expect报头字段中给出的期望1至少有一个入站服务器无法满足。
417代码参考
Rails HTTP状态符号: expectation_failed
Go HTTP状态常量http。StatusExpectationFailed
Symfony HTTP状态常数响应:HTTP_EXPECTATION_FAILED
Python2 HTTP状态常量httplib。EXPECTATION_FAILED
Python3+ HTTP状态常量http.client.EXPECTATION_FAILED
Python3.5+ HTTP状态常量http.HTTPStatus.EXPECTATION_FAILED
