First, what is the HTTP protocol
HTTP is a shorthand for the Hypertext Transfer Protocol (Hypertext Transfer Protocol), which is an application- layer protocol to the TCP/IP protocol that defines how Web clients request Web pages from a Web server. And how the server delivers Web pages to clients.
noun Interpretation in the definition:
What is hypertext? Hypertext is a Web text that organizes the text information of various spaces together by means of hyperlinks. What is the application layer protocol? Network designers use hierarchical way to organize network protocols and implement the hardware and software of these protocols, historically, a more important protocol organization model is the five-layer Internet protocol stack, from the top level to the bottom, respectively, the application layer, Transport layer, network layer, link layer, physical layer. Among them, the common protocol of Application layer is HTTP, SMTP, FTP, etc., Transport layer protocol has TCP, UDP, etc., network layer has IP and so on. Second, the HTTP protocol features 1. HTTP uses TCP as its transport layer protocol, and TCP provides reliable data transfer services for HTTP. Using a hierarchical structure, the HTTP protocol does not have to worry about data loss or the details of how TCP recovers from data loss and sequence failures in the network. 2. HTTP is a
Stateless Protocol, the server sends the requested file to the client without saving any information about the customer (the cookie should be used if it needs to be saved). 3. http/1.0 use non-persistent connection, http/1.1 use
Continuous Connection。 Using persistent connections, you do not have to allocate TCP buffers and keep TCP variables multiple times in the client and server, while avoiding twice times the RTT delivery delay for each transport object. The default mode for HTTP is to use a continuous connection with pipelining. HTTP message Format 1. The request message example is as follows: GET /somedir/page.html http/1.1host: www.someschool.educonnection: CLOSEUSER-AGENT:MOZILLA/5.0ACCEPT-LANGUAGE:FR-------------------------------------------------------First line: Request Lineother Lines:header line Requests Line: Method field-URL field-HTTP version field where the Method field is preferable get, post, HEAD, PUT, delete, etc. defaults to get request, after URL With parameters, there is a size limit, no more than 1K form submission indicated with post, passed in the entity, no size limit the head method is often used for debugging, returning only HTTP messages, not returning the request object Connection:close means not using persistent connections Common request headers: accept:text/html,image/* Customer acceptable data types Accept-charset:iso-8859-1 The character set encoding accept-encoding to be used to accept data: Gzip,compress Accepted data compression formats ACCEPT-LANGUAGE:EN-US,ZH-CN accepted locales host:www.it315.org:80 Virtual host name If-modified-since:tue, 18:23:51 GMT cache resource Last acquisition time referer:http://www.it315.org/index.jsp The current request from which link user-agent:mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0) Client Information cookie connection:close/kEep-alive Specify whether to stay connected Date:tue, 18:23:51 GMT Current time 2. Response messages Examples are as follows: http/1.1 OkConnection:closeDate:Tue, 15:44:04 gmtserver:apache/2.2.3 (CentOS) last-modif Ied:tue, 15:11:03 gmtcontent-length:6821content-type:text/html (data, data, data ...) -------------------------------------------------------First line:status linelast line: entity bodyother Lines : header line status Line: Protocol version-Status code-status information status codes and status information common are: OK301 Moved Permanently400 bad Request404 not found505 HTTP Version not supported-------------------------------------------------------100 ~ 199 indicates successful reception, the client needs to continue committing to complete the process, 200 ~ 299 indicates successful reception and completion of the entire process 300 ~ 399 to complete the request, the customer needs further refinement of the request, such as 302 request redirection, 304, 307 notification using cache 400 ~ 499 client request with Error 500 ~ 599 Server Side Error Common response header: Lo cation:http://www.it315.org/index.jsp Mate 302 implements request redirection Server:apache Tomcat Server basic information Content-encoding:gzip Compressed format used by the server to send data content-length:80 Send data size CONTENT-LANGUAGE:ZH-CN send data using locale Content-type:text/html; charset=gb2312 Basic information about the data currently being sent Last-modified:tue, 18:23:51 GMT cache related refresh:1;url=http:// www.it315.org timed Refresh to a urlcontent-disposition:attachment;filename=aaa.zip header transfer-encoding related to downloads: chunked Data transmission type, one block transmission set-cookie:ss=q0=5lb_nq; Path=/search Settings cookieetag:w/"83794-1208174400000" and cache related expires: -1 Specifies the time of the resource cache, If the value is 0 or 1 browse does not cache the resource Cache-control:no-cache If No-cache then notifies the browser not to cache Pragma:no-cache If No-cache is notified that the browser is not cached for historical reasons, the above three are used to control the cache while using connection:close/keep-alive to keep the connection Date:tue, 2000 18:23:51 gmt Current Time third, Telnet demo telnet cis.poly.edu 80
HTTP protocol Preliminary parsing
