To have a server check the request's headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body.
要使服务器检查请求的头部，客户端必须在其初始请求中发送Expect: 100-continue作为头部，并在发送正文之前接收100 Continue状态代码。