HTTP message typically includes a client request message and a response message to the server of the server to the client. The client sends a request to the server, the request header contains the request method, URI, protocol version, and comprises a request modifiers, similar to the customer information and content MIME message structure. A server response status line, including the corresponding protocol version of the message, plus the success or error code comprises information server, the entity may be an entity meta information and content.
Http protocol defines a number of ways to interact with the server, there are four basic kinds, namely GET, POST, PUT, DELETE. URL address is used to describe a resource on a network, and in HTTP GET, POST, PUT, DELETE it corresponds to the investigation of this resource, change, add, delete four operations, our most common is the GET and POST . GET is generally used to get / query resource information, and POST are generally used to update resource information.
A, HTTP header information interpretation
HTTP header includes common header field, the request header, and response header entity header portion of four. Each header field consists of a domain name, a colon (:) and the value of three parts.
Universal head: the head is the client and the server can be used to provide some very useful common functions between the client, server and other applications, such as Date header.
Request header: Request packet is unique, they provide some additional information to the server, such as what type of client wants to receive data, such as Accept head.
Response header: the client to provide information to facilitate, for example, the end customer interaction, such as what type of head and Server server.
Entity head: head means for coping with the solid body portion, for example, an entity header may be used to illustrate the data type of the entity body portion, such as the Content-Type header.
Universal HTTP header
Common header field comprises a header field support request and response messages, the common header field comprises a header cache Cache-Control, Pragma header and informative Connection, Date, Transfer-Encoding, Update, Via.
1、Cache-Control
Cache-Control specify the request and response caching mechanism to follow. Cache-Control setting request message or the response message does not modify the cache of another processing procedure of message processing. Cache instruction request includes no-cache, no-store, max-age, max-stale, min-fresh, only-if-cached, the response message includes instructions public, private, no-cache, no- store, no-transform, must-revalidate, proxy-revalidate, max-age. Meaning of each instruction message is as follows:
no-cache: indicating a request or response message can not be cached, in fact, may be stored in the local cache, but prior to the original freshness authentication server, the cache can not be used to provide it to the client.
no-store: the cache should remove all traces of a document from memory as soon as possible, because it may contain sensitive information.
max-age: cache did not return a cached longer than a predetermined max-age second document, if over a predetermined second browser will not send a corresponding request to the server, the data returned directly from the cache; over this period was further processed by the server We decided to return the new data cache or still available. If also transmitted max-stale instructions of use may exceed its expiration time.
min-fresh: at least the next document within the specified seconds to keep it fresh, to accept its freshness lifetime greater than the current and the Age with min-fresh value of the cache object.
max-stale: instructs the client may receive a response message expires, if the specified value max-stale message, the client may receive a message in response to expiration but within the specified value.
only-if-cached: only when there are copies exist in the cache, the client will get a copy.
Public: indicates response may be any buffer cache, the cache can respond to any user with the content.
Private: indication for the whole or part of the message in response to a single user and can not be shared caching, the user can respond to a previous request for the cached content with the content.
2, Pragma
Pragma header field for containing instructions implement particular, is the most commonly used Pragma: no-cache. In HTTP / 1.1 protocol, its meaning and Cache- Control: the same no-cache.
3、Connection
Connection expressed the need for persistent connections. If here the value Servlet see "Keep-Alive", or see the request using HTTP 1.1 (HTTP 1.1 persistent connections default), it can take advantage of persistent connections, when the page containing a plurality of elements (e.g. Applet, pictures), significantly reducing the time required to download. To achieve this, Servlet need to send a Content-Length header in the response, the easiest method is to achieve: first write the contents of ByteArrayOutputStream, and then calculate its size before the official written content.
Close: Tell WEB server or proxy server, in response to the completion of this request, disconnected, this subsequent requests do not wait for a connection.
Keepalive: Tell WEB server or proxy server, upon completion of the response to this request, remain connected, wait for the current connection subsequent requests.
Keep-Alive: If the browser request remains connected to the head portion connected to the server indicating a desire to WEB how long (in seconds), as Keep-Alive: 300.
4、Date
Date header field indicates the time message sent by the server in response to include in the header, because the cache when evaluating freshness of use in response to which the time description format defined by RFC822. For example, Date: Mon, 31 Dec 2001 04:25:57 GMT. Date when the time described represents the world standard, the conversion cost in time, need to know the user's time zone.
5、Transfer-Encoding
WEB server indicate their body made of the response message (message body is not inside the object) how the encoding, such as whether the block (chunked), for example: Transfer-Encoding: chunked
6、Upgrade
It can specify another may be completely different protocol, such as HTTP / 1.1 client may send a HTTP / 1.0 request to the server, which contains a value of "HTTP / 1.1" Update the head, so that the client can test server whether to use HTTP / 1.1 up.
7、Via
Lists the response from the client to the OCS or in the opposite direction through which the proxy server, they request sent what protocol (and version).
When a client request arrives first proxy server, which will add its own Via header in the request sent inside, and fill in their own information, the next proxy server receives a request of a proxy server, it will Via header of the request before the request sent by itself inside a copy of the proxy server, and the related information to his back, so that when OCS receives a request last proxy server, checks the Via header, it know the route through which the request. For example: Via: 1.0 236-81.D07071953.sina.com.cn:80 (squid / 2.6.STABLE13)
HTTP request header
Request header is used to explain who or what sent the request, where the request originated, or preferences and capabilities of the client. The server may request the client information in the header analysis, trying to provide a better response to the client. Request-header field may contain the following fields Accept, Accept-Charset, Accept- Encoding, Accept-Language, Authorization, From, Host, If-Modified-Since, If-Match, If-None-Match, If-Range, If-Range , If-Unmodified-Since, Max-Forwards, Proxy-Authorization, Range, Referer, User-Agent. Extension of the request header fields required to support communications both sides, if you do not support the request header field is present, the general will as an entity header field processing.
8、Accept
WEB server told myself to accept what media types, * / * represents any type, type / * represents all sub-types under that type, type / sub-type.
9、Accept-Charset
Browser tells the server character set that he can receive.
10、Accept-Encoding
Affirming their own browser coding method received, generally designated compression method supports compression, support what compression method (gzip, deflate).
11、Accept-Language
Browser affirm their own language received. With a distinctive language character sets: Chinese language, Chinese has a variety of character sets, such as big5, gb2312, gbk and so on.
12、Authorization
When a client receives the WWW-Authenticate response from the WEB server, with the head to respond to their own authentication information to the WEB server.
13、If-Match
If the ETag target has not changed, in fact, also means that the object has not changed, only the implementation of an action request, access to documents.
14、If-None-Match
If the ETag object changes, but in fact it means that the object has changed, only to perform the requested action to obtain documents.
15、If-Modified-Since
If the requested object is modified in the head after a specified time, it performs the requested action (for example, returns the object), otherwise the code 304, tells the browser that the object is not modified. For example: If-Modified-Since: Thu, 10 Apr 2008 09:14:42 GMT
16、If-Unmodified-Since
If the requested object is not modified after a specified time of the head, it performs the required action (such as the return object).
17、If-Range
WEB browser tells the server object if my request has not changed, I was the missing piece to me, if the object has changed, put the entire object to me. ETag browser by sending a request to modify the object or the last time they know to the WEB server, allowed to determine whether the object is changed. Always used together with a Range header.
18、Range
Browser (such as multi-threaded downloading Flashget) WEB server tell which part they want to take an object. For example: Range: bytes = 1173546
19、Proxy-Authenticate
Response proxy browser, proxy authentication required to provide information.
20、Proxy-Authorization
Response proxy browser authentication request, provide their own identity.
21、Host
WEB server specified by the client they want to access the domain name / IP address and port number. As Host: rss.sina.com.cn
22、Referer
WEB browser indicates to the server what URL is clicked in the current request URL / URL from which page, for example: Referer: http: //www.ecdoer.com/
23、User-Agent
Browser to identify themselves (which browser). For example: User-Agent: Mozilla / 5.0 (Windows; U; Windows NT 5.1; zh-CN; rv: 1.8.1.14) Gecko / 20080404 Firefox / 2.0.0.14
HTTP response header
Response header to the client to provide some additional information, such as who is sending the response, responders, and even some special instructions related to the response. These headers help clients respond to treatment, and initiate requests better in the future. Response header field contains Age, Location, Proxy-Authenticate, Public, Retry- After, Server, Vary, Warning, WWW-Authenticate. Extension of the response header fields required to support communications both sides, if you do not support the existence of a response header field, generally will be treated as an entity header field.
24、Age
When the proxy server's cache with their own entity to respond to the request by the head of the entity from generation to show that now after more than a long time.
25、Server
WEB server showed himself to be what software and version information. For example: Server: Apache / 2.0.61 (Unix)
26、Accept-Ranges
WEB server indicate whether they accept the request for obtaining a part of an entity (such as a portion of a file) is. bytes: acceptance, none: non-acceptance.
27、Vary
WEB server tells Cache server with the contents of the head, under what conditions can respond to subsequent requests with objects returned in this response. If the source WEB server, upon receiving the first request message, the response header of the message as: Content-Encoding: gzip; Vary: Content-Encoding, then the analysis server Cache subsequent request header of the message, check Accept- encoding, whether with Vary header value in response to a previous agreement, that is, whether to use the same content encoding method, so you can prevent server Cache Cache with the entity after their response to the compression inside the browser does not have the ability to decompress. For example: Vary: Accept-Encoding.
HTTP entity header
Entity header provides a wealth of information about entities and their contents, the types of information relating to the object, the request method can effectively use various resources. In short, the head of the entity can inform the recipient what it is processed. Request and response messages can contain information about the entity, the entity information and entity-header field generally consists of entities. The entity header field contains the raw information about the entity, the entity header of the header information included Allow, Location, the content header Content-Base, Content-Encoding, Content-Language, Content-Length, Content-Location, Content-MD5, Content- Range, Content-Type, the cache head Etag, Expires, Last-Modified, extension-header.
28、Allow
The method that the server supports the request (such as GET, POST, etc.).
29、Location
It indicates that the client should go fetch the document for the receiving end positioned on the location (URL) resources. Location usually not directly, but through sendRedirect HttpServletResponse method, the method while setting the status code to 302.
30、Content-Base
Resolve the base URL to use when the body of a relative URL.
31、Content-Encoding
WEB server indicated you use what compression method (gzip, deflate) compression target response. For example: Content-Encoding: gzip
32、Content-Language
WEB server tells the browser that natural language understanding the most appropriate body to use.
33、Content-Length
WEB server tells the browser to the length or size of the object in response to their own, such as: Content-Length: 26012
34、Content-Location
The actual location of the resource is located.
35、Content-MD5
MD5 checksum and body.
36、Content-Range
Entity header is used to specify the position of the insertion portion of the overall entity, he also indicates the length of the entire entity. Returns a response to the client part of the server, it must describe the overall physical length of the response from the scope and coverage. The general format: Content-Range: bytes-unitSPfirst-byte-pos-last-byte-pos / entity-legth. For example, the first 500 bytes transmitted in the form of sub-fields: Content-Range: bytes0- 499/1234 If this section contains an http message (e.g., in response to a range request or a request for a range overlapping series), Content-Range range represented transmitted, Content-Length indicates the number of bytes actually transmitted.
37、Content-Type
WEB server tells the browser type of the object of their own responses. For example: Content-Type: application / xml
38、Etag
Is an object (such as URL) flag value, in relation to a target, such as a html file, if it is changed, it will not modify Etag, therefore, the role of ETag Last-Modified action with almost primarily for WEB server determines whether an object has changed. When such a request before a html file, get its ETag, when this time requesting the file, the browser will get the previous ETag value is sent to the WEB server, WEB server will then present the file with the ETag ETag comparison, then you know that the file has not changed.
39、Expires
After WEB server indicates that the entity will expire at what time, for the expired object only to verify its validity with WEB server, it can be used to respond to customer requests. The head HTTP / 1.0 in. For example: Expires: Sat, 23 May 2009 10:02:12 GMT
40、Last-Modified
WEB server think last modified objects, such as the last file modification time, last time produce dynamic pages, and so on. For example: Last-Modified: Tue, 06 May 2008 02:42:43 GMT
Two, HTTP Request Header information of
1, HTTP request method
Description: The main use of the "GET" and "POST".
Example: POST / test / tupian / cm HTTP / 1.1
Divided into three parts:
(1) POST: HTTP request method
(2) / test / tupian / cm: the address of the Web server requests the directory (or instructions)
(3) HTTP / 1.1: URI (Uniform Resource Identifier, Uniform Resource Identifier) and version
NOTE: In Ajax, the corresponding method attribute set.
2、Host
Description: web server domain name address request
3、User-Agent
Note: For more information HTTP client running the browser type. By this header information, web server may determine whether the client browser type current HTTP request.
Examples: User-Agent: Mozilla / 5.0 (Windows; U; Windows NT 5.1; zh-CN; rv: 1.8.1.11) Gecko / 20071127 Firefox / 2.0.0.11
4、Accept
Explanation: The content type of the client to receive the content type in the order of priorities that the client receives.
实例：Accept:text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
NOTE: Prototyp (1.5) Ajax code package, the Accept default setting is "text / javascript, text / html, application / xml, text / xml, * / *". This is because the default Ajax Json data acquisition mode returned by the server. In Ajax code, you can use the XMLHttpRequest object setRequestHeader function method to dynamically set the Header information.
5、Accept-Language
Description: Specifies the HTTP client browser to return to the language used to display information preference.
Example: Accept-Language: zh-cn, zh; q = 0.5 default Chinese herein.
6、Accept-Encoding
Description: Specifies the client browser to support web server returns the content compression encoding type. Representation allows the server to send the output to the client before the content is compressed to conserve bandwidth. The return compression format set here is that the client browser is capable of supporting.
实例：Accept-Encoding: gzip,deflate
Note: In fact, before Baidu many product lines, apache returned to the client page in the data, the data is compressed in gzip format.
7、Accept-Charset
Description: The browser can accept character encoding.
Example: Accept-Charset: gb2312, utf-8; q = 0.7, *; q = 0.7
8、Content-Type
Description: HTTP request to display this type of content submitted. Generally only when the post submission need to set the property.
实例：Content-type: application/x-www-form-urlencoded;charset:UTF-8
NOTE: For Content-Type attribute value can encode the following two types:
(1) "application / x-www-form-urlencoded": encoding type when the form data used by the server, the default value is the default "application / x-www-form-urlencoded". However, in a lot of text sent to the server, which is very low coding efficiency when text or binary data contains non-ASCII characters.
(2) "multipart / form-data": when the file upload, type of encoding used should be "multipart / form-data", it can either send the text data, binary data are also supported on the carrier.
When the data submission is alone, you can use "application / x-www-form-urlencoded"; when the file is submitted, it is necessary to use "multipart / form-data" encoding type.
Or specify the submission of the Content-Type charset property which character encoding. Generally not set, it just tells what character encoding used in the data submitted by the web server post.
In the development process in general, is a front-end engineering and back-end UI engineer what character encoding format to use to post a good discussion submitted, then the back-end ui engineer a fixed character encoding to parse the data submitted. So charset set here is not much.
9、Connection
Description: Indicates whether a persistent connection. If the web server to see here is "Keep-Alive", or see the request using HTTP 1.1 (HTTP 1.1 persistent connections default), it can take advantage of persistent connections, when a page contains multiple elements (eg Applet, pictures), significantly reducing the time required to download. To achieve this, web server needs to return to the client HTTP header information to send a Content-Length (return message body length) head, the easiest method is to achieve: first write the contents of ByteArrayOutputStream, then write in the official calculate its size before the content.
Example: Connection: keep-alive
10、Keep-Alive
Description: Keep-Alive display time for this HTTP connection. The client to server connection remain in effect when subsequent requests to the server appears, Keep-Alive feature prevents establish or re-establish the connection. Before the stop is connected to the HTTP request, then from the HTTP / 1.1 protocol, there is a long link, i.e. within a predetermined time Keep-Alive, the connection is not disconnected.
Examples: Keep-Alive: 300
11、cookie
Description: When an HTTP request, will save all the values in the cookie is sent with the domain name request to the web server.
12、Referer
Description: Contains a URL, URL of the page the user from accessing pages on behalf of the current request