- To send an HTTP request:A request consists of four parts: a request line, a request header, a blank line, and a request data
- The
- request line
- Request line consists of three tokens: The request method, the request URI, and the HTTP version, separated by a space. For example, the get /index.html http/1.1
- HTTP specification defines 8 possible request methods:
- GET     &N bsp; retrieves a simple request to identify a resource in the URI
head As with the Get method, the server returns only the status row and header, and does not return the request document
post The server accepts requests that are written to data in the client output stream
put The server holds the request data as a request for the new content of the specified URI
delete Server Delete Request for named resource in URI
options Request for Request method information supported by the server
trace Web server feedback HTTP request and its header request
connect a method that has been documented but not currently implemented, reserved for tunneling
- Request Header: Consists of a keyword/value pair, one pair per line, a keyword and a value separated by a colon (:).
-
- The request header notifies the server about the functionality and identity of the client, and a typical request header is marked with:
- User-agent Client Manufacturer and version
- List of content types that are recognized by the Accept client
- Content-length number of data bytes attached to the request
- Blank line: The last request header is followed by a blank line, sending a carriage return and regression, notifying the server that there are no more headers.
- Request data: The Content-type and content-length headers are most commonly used to transmit data using post.
- The
- service side accepts the request and returns an HTTP response: the Web server resolves the request and locates the specified resource. The server writes a copy of the resource to the socket, where it is read by the client.
- A response consists of four parts; status line, response header, blank line, response data
- status line: The status line consists of three tokens: HTTP version, response code, and response description.
- http version: Indicates to the client the highest version that it can understand.
- Response Code: A 3-bit numeric code that indicates the success or failure of the request and, if it fails, the cause.
- Response Description: Explains the readability of the response code.
- For example: Http/1.1 200 ok
- HTTP response: HTTP response code:
1xx: Information, request received, continue processing
2XX: Success, Behavior is successfully accepted, understood and adopted BR>3XX: Redirect, in order to complete the request, the action must be performed further
4xx: Client error:
2. Response header: Like the request header, they indicate the server's function, identifying the details of the response data.
3. Blank line: The last response header is followed by a blank line that sends a carriage return and regression, indicating that the server no longer has a header label.
4. Response data: HTML documents and images, i.e. HTML itself.
- The server closes the connection and the browser resolves the response:
- The browser parses the status line first to see the status code indicating whether the request was successful.
- Each response header is then parsed, and the header tells the following bytes of HTML.
- Reads the response data HTML, formats it according to the syntax and semantics of the HTML, and displays it in a browser window.
- An HTML document may contain other resource references that need to be loaded, the browser recognizes these references, and then makes additional requests to other resources, which are cycled multiple times.
- Stateless connections: The HTTP model is stateless, indicating that the Web server does not remember requests from the same client when processing a request.
- HTTP response code:
- The response code is divided into five types, denoted by their first digit:
1.1XX: Information, request received, continue processing
2.2XX: Success, Behavior is successfully accepted, understood and adopted
3.3XX: Redirect, in order to complete the request, the action must be further performed
4.4XX: Client error, request contains syntax error or request cannot be implemented
5.5XX: Server error, server cannot implement an apparently invalid request
- The following table shows each response code and what it means:
100 continue
101 Group Exchange Association
OK
201 was created
202 are adopted
203 Non-authorised information
204 No Content
205 Resetting Content
206 part of the content
300 + Options
301 Permanently transmitted
302 found
303 See other
304 not changed
305 using Proxies
307 Temporary redirection
400 Error request
401 Not authorized
402 Request for payment
403 Forbidden
404 Not Found
405 Methods not allowed
406 Not Accepted
407 Request for Proxy authorization
408 Request timed out
409 conflicts
410 Out of date
411 length of the requirement
412 Premise not established
413 The request instance is too large
414 Request URI too large
415 Unsupported media types
416 The range of requests that cannot be satisfied
417 Expectations of failure
500 Internal Server Error
501 Not used
502 Gateway Error
503 Unavailable Services
504 Gateway Timeout
505 HTTP version is not supported
- HTTP Header:The header is made up of a primary key/value pair. They describe the properties of the client or server, the resources being transferred, and the connection that should be implemented.
Four different types of head labels:
1. Generic header: Can be used for a request or for a response, and is associated with a transaction as a whole rather than a specific resource.
2. Request Header: Allows the client to pass information about itself and the form of the desired response.
3. Response header: The server and the response to transmit its own information.
4. Entity Header: Defines the information for the transmitted resource. Can be used for requests or for responses.
Header Format:<name>:<value><crlf>
The following table describes the headers used in the http/1.1
Accept defines the types of media that clients can handle, sorted by priority;
In a comma-delimited list, you can define multiple types and use wildcard characters. Example: accept:image/jpeg,image/png,*/*
Accept-charset defines the character sets that the client can handle, sorted by priority;
In a comma-delimited list, you can define multiple types and use wildcard characters. Example: Accept-charset:iso-8859-1,*,utf-8
Accept-encoding defines the encoding mechanism that the client can understand. Example: accept-encoding:gzip,compress
Accept-language defines a list of natural languages that the client is willing to accept. Example: Accept-language:en,de
Accept-ranges a response header that allows the server to indicate that it will accept requests for the resource component at a given offset and length.
The value of the header is understood as the unit of measure for the requested range. such as Accept-ranges:bytes or Accept-ranges:none
Age allows the server to specify the length of time, in seconds, that has elapsed since the server generated the response.
The header is used primarily for caching responses. Example: age:30
Allow a response header that defines a list of HTTP methods supported by the Zhiyuan in the request URI. Example: Allow:get,put
AUTHORIZATION a response header that defines the authorization (domain and encoded user ID and password) necessary to access a resource.
Example: Authorization:basic yxv0ag9yonboaww=
Cache-control a generic header for defining cache directives. Example: cache-control:max-age=30
Connection a generic header that indicates whether the socket connection is saved as open. Example: Connection:close or Connection:keep-alive
Content-base an entity header that defines a base URI in order to resolve relative URLs within the entity scope.
If you do not define a content-base header to resolve relative URLs, use the content-location URI (present and absolute) or use a URI request.
Example: content-base:http://www.myweb.com
Content-encoding a type of media modifier that indicates how an entity is encoded. Example: Content-encoding:zip
The content-language is used to specify the natural language type of the data in the input stream. Example: Content-language:en
CONTENT-LENGTH Specifies the length of the bytes contained in the request or response data. Example: content-length:382
CONTENT-LOCATION Specifies the resource location (URI) contained in the request or response.
If it is a must. To the URL it also acts as a starting point for the relative URL of the parsed entity.
Example: Content-location:http://www.myweb.com/news
A MD5 Digest of the CONTENT-MD5 entity used as a checksum.
Both the sender and the receiver calculate the MD5 summary, and the recipient compares the value that it calculates with the value passed in this header.
Example: content-md5: <base64 of MD5 digest>
The Content-range is sent along with some entities, indicating the low and high byte offsets of the inserted bytes, as well as the total length of the entity.
Example: content-range:1001-2000/5000
Contern-type indicates the MIME type of the entity being sent or received. Example: content-type:text/html
Date when the HTTP message was sent. Example: DATE:MON,10PR 18:42:51 GMT
ETag an entity header that assigns a unique identifier to the resource being sent.
For resources that can use multiple URL requests, the etag can be used to determine whether the actual resource being sent is the same resource.
For example: ETag: "208f-419e-30f8dc99"
Expires the validity period of the specified entity. Example: expires:mon,05 Dec 12:00:00 GMT
form a request header, given the e-mail address of the human user who controls the user agent. For example: from: [email protected]
Host name of the resource being requested by host. This domain is mandatory for requests that use http/1.1. Example: Host:www.myweb.com
If-modified-since If a GET request is included, the request is conditionally dependent on the last modified date of the resource.
If this header appears, and the resource has been modified since the specified date, a 304 response code should be reversed.
Example: IF-MODIFIED-SINCE:MON,10PR 18:42:51 GMT
If-match if included in a request, specify one or more entity tags. Only the resources whose etag is labeled with the list are sent.
Example: If-match: "208f-419e-308dc99"
If-none-match If a request is included, specify one or more entity tags. The resource's etag does not match any one of the criteria in the list, and the operation executes.
Example: If-none-match: "208f-419e-308dc99"
If-range an entity tag for the specified resource, and the client already has a copy of this resource. Must be used in conjunction with the range header.
If this entity has not been modified since it was last retrieved by the client, the server sends only the specified range, otherwise it will send the entire resource.
Example: Range:byte=0-499<crlf>if-range: "208f-419e-30f8dc99"
If-unmodified-since This entity is returned only if the requested entity has not been modified since the specified date.
Example: IF-UNMODIFIED-SINCE:MON,10PR 18:42:51 GMT
last-modified Specifies the date and time that the requested resource was last modified. Example: LAST-MODIFIED:MON,10PR 18:42:51 GMT
Location for a resource that has already been moved, it is used to redirect the requestor to another position.
Used in conjunction with status Code 302 (temporary movement) or 301 (permanent move).
Example: location:http://www2.myweb.com/index.jsp
Max-forwards a request header for the trace method to specify the maximum number of proxies or gateways that the request is routed through the gateway.
The proxy or gateway should reduce this number before passing the request. Example: Max-forwards:3
Pragma a generic header that sends implementation-related information. Example: Pragma:no-cache
Proxy-authenticate is similar to Www-authenticate, which is intentionally requesting authentication from the next server only from the request chain (proxy).
Example: Proxy-authenticate:basic realm-admin
Proxy-proxy-authorization is similar to authorization, but does not intentionally deliver anything that is further than the instant server chain.
Example: Proxy-proxy-authorization:basic yxv0ag9yonboaww=
The public list shows the set of methods supported by the server. Example: Public:options,mget,mhead,get,head
range specifies the offset range of a unit of measure and a partially requested resource. Example: range:bytes=206-5513
Refener a Request header field that indicates the initial resource that generated the request. For an HTML form, it contains the address of the Web page for this form.
Example: refener:http://www.myweb.com/news/search.html
Retry-after a response header domain that is sent by the server in conjunction with a status code of 503 (unable to provide a service) to indicate how long to wait before requesting a request again.
This time can be a date, or it can be a unit of seconds. Example: retry-after:18
Server A header that identifies the Web server software and its version number. Example: server:apache/2.0.46 (WIN32)
Transfer-encoding a generic header that indicates the type of transformation that corresponds to the message body that is reversed by the receiving party. Example: transfer-encoding:chunked
Upgrade allows the server to specify a new protocol or a new protocol version, which is used in conjunction with response Encoding 101 (switching protocol).
Example: upgrade:http/2.0
User-agent defines the type of software used to generate the request (typically, such as a Web browser).
For example: user-agent:mozilla/4.0 (compatible; MSIE 5.5; Windows NT; Digext)
Vary a response header that is used to indicate that a response entity is selected from the available response representations using server-driven negotiation. Example: Vary: *
Via a generic header that contains all intermediate hosts and protocols to satisfy the request. Example: via:1.0 fred.com, 1.1 wilma.com
The Warning is used to provide a response header for response status supplemental information. Example: warning:99 www.myweb.com Piano needs tuning
Www-authenticate a response header that prompts the user agent to provide a user name and password, which is used in conjunction with status Code 401 (not authorized). Responds to an authoritative header.
Example: Www-authenticate:basic realm=zxm.mgmt
HTTP request model and header information reference
