HTTP protocol--Request and response

1. Introduction

HTTP is an object-oriented protocol belonging to the application layer, which is suitable for distributed hypermedia information System because of its simple and fast way. It was proposed in 1990, after several years of use and development, has been continuously improved and expanded. Currently used in the WWW is the sixth edition of Http/1.0, http/1.1 standardization work is in progress, and Http-ng (Next Generation of HTTP) has been proposed.

The main features of the HTTP protocol can be summarized as follows:

1. Support client/server mode.

2. Simple and fast: When a customer requests a service from the server, it simply transmits the request method and path. The request method commonly has, POST. Each method specifies a different type of contact between the customer and the server. Because the HTTP protocol is simple, the HTTP server's program size is small, so the communication speed is fast.

3. Flexible: HTTP allows the transfer of any type of data object. The type being transmitted is marked by Content-type.

4. 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.

5. 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.

2. HTTP request and Response

2.1 HTTP request--method

GET	Request to get the resource represented by Request-uri
POST	Append new data to the resource identified by Request-uri
HEAD	Request for a response message header for a resource identified by Request-uri
PUT	The request server stores a resource and uses Request-uri as its identity
DELETE	Requesting the server to delete resources identified by Request-uri
TRACE	Request Server Loopback received request information, primarily for testing or diagnostics

2.2 HTTP request--Common response code

Status code	Describe	Client request succeeded
200	Ok	Client request succeeded
206	Partial Content	Return part of the request entity
301	Moved Permanently	Target permanent movement
60W	Found	Find Target (target is moved temporarily)
304	Not Modified	Target not modified
400	Bad Request	Client requests have syntax errors and cannot be understood by the server
403	Forbidden	The server received the request but refused to provide the service
404	Not Found	Request resource does not exist
413	Request Entity Too Large	Request entity too large
500	Internal Server Error	An unpredictable error occurred on the server that prevented the client from completing the request
502	Bad Gateway	Gateway error, which may be caused by network failure or excessive load.
504	Gateway Timeout	Connection timed out

3. Common HTTP header fields

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2. Accept (identifies entity types that the browser can accept)
6. Accept-charset/accept-language (character set and language)
10. Accept-encoding (Accept encoded format gzip or Deflat)
14. Cache-control (Cache policy. Example: Cache-control:no-cache)
18. Pragma (callout. Example: Pragma:no-cache)
22. Connection (connection parameter.) Example: Connection:close)
26. Date (day. Example: DATE:MON,31DEC200104:25:57GMT)
30. Content-type (Identifies the entity type.  For example: content-type:text/html. Mime.types file example)
34. Transfer-encoding (transfer encoding. Chunk)
38. Content-length (solid length)
42. Set-cookie/cookie
46. User-agent (Browser ID)
50. Host (target host)
54. Expires
58. Last-modified
62. Range/content-range
66. Content-disposition
70. Referer (reference, usually the URL of the previous visit)

4. HTTP protocol format and structure---examples

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2. Get/index.shtml http/1.1
4. Host:www.google.com
6. user-agent:mozilla/5.0 (Windows; U Windows NT 5.1; ZH-CN; rv:1.9.0.5) gecko/2008120122 firefox/3.0.5
8. accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
10. accept-language:zh-cn,zh;q=0.5
12. Accept-encoding:gzip,deflate
14. accept-charset:gb2312,utf-8;q=0.7,*;q=0.7
16. keep-alive:300
18. Connection:keep-alive
22. http/1.x OK
24. Date:tue, 08:26:37 GMT
26. server:apache/2.2.8 (Unix) php/5.2.6
28. Accept-ranges:bytes
30. Keep-alive:timeout=5, max=99
32. Connection:keep-alive
34. Transfer-encoding:chunked
36. content-type:text/html; Charset=utf-8

HTTP protocol--Request and response