## HTTP protocol:
a request message: The client sends to the server-side data
* data format:
1. Request line
2. Request header
3. Request blank line
4. The request body
Second, a response message: The server sends the data to the client
* data format:
1. response line
1. composition: protocol / version response status codes status code description
2. response status code: the server tells the client browser to the current state of a request and response.
1. The status code is a 3-digit
2 Category:
1. 1xx: the server receiving the client message, but did not receive complete, waiting for a period of time, multi-state transmission 1xx code
2. 2xx: Success. Representatives: 200
3. 3xx: Redirection. Representative: 302 (redirect), 304 (cache access)
4. 4xx: Client Error.
Representative *:
* 404 (there is no corresponding resource request path)
* 405: doXxx embodiment no corresponding request method
5. 5xx: Server side error. Representative: 500 (internal server abnormal)
2 response header:
1. Format: first name: value
2. Common response headers:
1. Content-Type: The server tells the client response body of data formats and encoding format
2. Content-disposition: Open the server tells the client what format the response body data
* value:
* in-Line: default value, within the current open page
* attachment; filename = xxx: open response body attachment. Download
3. Response blank line
4. Response body: data transmission
* 响应字符串格式
HTTP/1.1 200 OK
Content-Type: text/html;charset=UTF-8
Content-Length: 101
Date: Wed, 06 Jun 2018 07:08:42 GMT
<html>
<head>
<title>$Title$</title>
</head>
<body>
hello , response
</body>
</html>