HTTP Introduction HTTP Works HTTP three-point considerations:

Introduction to HTTP

The HTTP protocol is an abbreviation for the Hyper Text Transfer Protocol (Hypertext Transfer Protocol), which is used to transfer hypertext to the local browser from the World Wide Web (www:world Wide Web) server.

HTTP is a TCP/IP communication protocol that transmits data (HTML files, image files, query results, and so on).

How HTTP Works

The HTTP protocol works on the client-server architecture. The browser sends all requests via URLs to the HTTP server, which is the Web servers, as an HTTP client.

The Web server has: Apache server, IIS server (Internet information Services) and so on.

The Web server sends a response message to the client, based on the received request.

The HTTP default port number is 80, but you can also change to 8080 or another port.

HTTP three-point considerations:

• HTTP is no connection: the meaning of no connection is to limit the processing of only one request per connection. When the server finishes processing the customer's request and receives the customer's answer, the connection is disconnected. In this way, the transmission time can be saved.
• HTTP is media Independent: This means that any type of data can be sent over HTTP as long as the client and the server know what to do with the data content. The client and server specify that the appropriate Mime-type content type be used.
• HTTP is stateless: The HTTP protocol is a stateless protocol. Stateless means that the protocol has no memory capacity for transactional processing. A lack of state means that if the previous information is required for subsequent processing, it must be re-routed, which may cause the amount of data to be transferred per connection to increase. On the other hand, it responds faster when the server does not need the previous information.

The HTTP protocol communication flow is shown in the table:

HTTP status Code

When a viewer accesses a webpage, the browser of the viewer makes a request to the server where the page is located. When a Web page is received and displayed by the browser, the server on which the page resides returns a message header (server header) that contains the HTTP status code to respond to the browser's request.

HTTP status code in English is HTTP status code.

The following are the common HTTP status codes:

• 200-Successful request
• 301-Resources (Web pages, etc.) are permanently transferred to other URLs
• 404-The requested resource (Web page, etc.) does not exist
• 500-Internal Server error

HTTP status Code classification

The HTTP status code consists of three decimal digits, the first decimal number defines the type of the status code, and the latter two numbers do not have a function of classification. There are 5 types of HTTP status codes:

HTTP status Code classification

category	Category Description
1**	Information, the server receives the request and requires the requestor to continue the operation
2**	Successful, the operation is successfully received and processed
3**	Redirect, requires further action to complete the request
4**	Client error, request contains syntax error or cannot complete request
5**	Server error, the server has an error while processing the request

HTTP Status Code list:

HTTP status Code list

Status Code	Status Code English name	Chinese Description
100	Continue	Go on. The client should continue its request
101	Switching protocols	Switch protocols. The server switches the protocol based on the client's request. You can only switch to a more advanced protocol, for example, a new version of the protocol that switches to HTTP
200	Ok	The request was successful. Typically used for Get and post requests
201	Created	has been created. A new resource was successfully requested and created
202	Accepted	has been accepted. The request has been accepted, but the completion is not processed
203	Non-authoritative Information	Non-authorized information. The request was successful. But the meta information returned is not on the original server, but a copy
204	No Content	No content. The server processed successfully, but the content was not returned. Make sure the browser continues to display the current document without updating the page
205	Reset Content	Resets the content. The server processing succeeds, and the user terminal (for example: browser) should reset the document view. The browser's form fields can be cleared by this return code
206	Partial Content	Part of the content. The server successfully processed a partial GET request
300	Multiple Choices	Multiple options. The requested resource can include multiple locations, which can return a list of resource characteristics and addresses for use in the user terminal (for example: browser) selection
301	Moved Permanently	Move permanently. The requested resource has been permanently moved to the new URI, the return information will include the new URI, and the browser will automatically redirect to the new URI. Any future new requests should be replaced with a new URI
60W	Found	Temporary move. Similar to 301. But resources are only temporarily moved. The client should continue to use the original URI
303	See other	See other addresses. Similar to 301. Viewing with Get and post requests
304	Not Modified	Not modified. The requested resource is not modified and no resources are returned when the server returns this status code. Clients typically cache accessed resources by providing a header indicating that the client wants to return only the resources modified after the specified date
305	Use Proxy	Use a proxy. The requested resource must be accessed through the proxy
306	Unused	HTTP status codes that have been discarded
307	Temporary Redirect	Temporary redirection. Similar to 302. REDIRECT with GET request
400	Bad Request	Client request syntax error, server does not understand
401	Unauthorized www.jusho.cn	Request for user authentication
402	Payment Required	Reserved for future use
403	Forbidden	The server understands the request from the requesting client, but refuses to execute the request
50U	Not Found www.pipixiaa.com	The server could not find the resource (Web page) based on the client's request. With this code, the Web designer can set up a personalized page that "the resource you requested could not be found"
405	Method not allowed	The method in the client request is forbidden
50W	Not acceptable	The server cannot complete the request based on the content attributes requested by the client
407	Proxy Authentication Required	The request requires the authentication of the agent, similar to 401, but the requestor should use the proxy for authorization
408	Request time-out	The server waits for a client to send a request that is too long and times out
409	Conflict	It is possible for the server to complete a put request from the client to return this code when the server handles the request and a conflict occurs
410	Gone www.foodtvl.com	The resource requested by the client no longer exists. 410 is different from 404, if the resource is now permanently deleted and can use 410 code, the site designer can specify a new location for the resource through 301 code
411	Length Required	The server cannot process request information sent by the client without content-length
412	Precondition Failed	Prerequisite error for client request information
413	Request Entity Too Large	The request was rejected because the requested entity was too large to be processed by the server. To prevent successive requests from the client, the server may close the connection. If only the server is temporarily unable to process, it will contain a retry-after response message
414	Request-uri Too Large	The requested URI is too long (the URI is usually the URL) and the server cannot process
415	Unsupported Media Type	The server cannot process the media format that was included with the request
416	Requested range not satisfiable	Invalid scope for client request
417	Expectation Failed	Server failed to satisfy expect request header information
500	Internal Server Error	Server internal error, unable to complete request
501	Not implemented	The server does not support the requested feature and cannot complete the request
502	Bad Gateway	A server acting as a gateway or proxy that received an invalid request from the remote server
503	Service unavailable	Due to overloading or system maintenance, the server is temporarily unable to process client requests. The length of the delay can be included in the server's Retry-after header information
504	Gateway time-out	A server that acts as a gateway or proxy and does not get requests from the remote server in time
505	HTTP Version not supported	The server does not support the version of the requested HTTP protocol and cannot complete processing

HTTP Introduction HTTP Works HTTP three-point considerations: