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Http uses connection oriented TCP as the transport layer protocol.Http itself has no connection.
Request message
CRLF is carriage return and line feed Request message with GET method
Request message with POST method
method
OPTIONS: This method enables the server to return all HTTP request methods supported by the resource.Use '*' instead of the resource name to send OPTIONS requests to the Web server to test whether the server functions normally.
HEAD: Like the GET method, it sends a request for a specified resource to the server.Only the server will not return this part of the resource.The advantage of this method is that "information about the resource" (meta information or metadata) can be obtained without transferring all the content.
GET: Issue a Display request to the specified resource.The GET method should only be used to read data, and should not be used in operations that produce "side effects", such as Web Applications.One reason is that GET may be accessed randomly by web spiders.See safety method
POST: Submit data to the specified resource and request the server to process (for example, submit a form or upload a file).The data is included in the request text.This request may create a new resource, modify an existing resource, or both.
PUT: upload the latest content to the specified resource location.
DELETE: The request server deletes the resource identified by Request URI.
TRACE: Echo the request received by the server, mainly for testing or diagnosis.
CONNECT: HTTP/1.1 protocol is reserved for proxy servers that can change the connection to pipeline mode.Usually used for links to SSL encryption servers (via unencrypted HTTP proxy servers).
Although there are eight HTTP request methods, we usually use get and post in practical applications. Other request methods can also be realized indirectly through these two methods.
URL
URL generally consists of<protocol>://<host>:<port number>/<path>
agreement
Http -- Hypertext Transfer Protocol Resources
Https -- Hypertext transport protocol using secure socket layer
Absolute URL displays the full path of the file, which means that the location of the absolute URL itself is independent of the location of the referenced actual file.
Relative URLs use the location of the folder containing the URL itself as a reference point to describe the location of the target folder.
If the path omits the URL, it refers to a home page on the Internet.
The first URL omits the path, representing the home page that Baidu knows.
The second is the relative path of the file 1742817.html, indicating its location.
They all use the https protocol.The port number is omitted.
Version No
The protocol used to be HTTP/1.0 is now upgraded to HTTP/1.1.What is the difference between the two?
The time required to request a World Wide Web document is2 * RTT+document transmission time。Because it takes three handshakes to establish a TCP connection with the server, the third handshaking takes the data related to the sending request, and then the HTTP server response message has four interactions in total, that is, 2 * RTT time.In addition to some other costs, the World Wide Web server needs to serve a large number of customers, so every time you browse, you need to establish a connection,HTTP/1.0Non persistent connection (short link)The server is heavily burdened.HTTP/1.1 usesContinuous connection (long link), the server still maintains the connection after sending the response.
Continuous linking is also divided into pipeline mode and non pipeline mode.The non pipeline mode requires that the next browsing request can only be sent after the customer sends a response.In pipeline mode, the client can send the next request without waiting for a response, and the server can respond continuously after receiving the request without waiting, saving time.
The continuous connection of HTTP 1.1 also needs to add new request headers to help implement it.
For example,When the value of the Connection request header is Keep Alive, the client notifies the server to keep the connection after returning the result of this request;When the value of the Connection request header is close, the client notifies the server to close the connection after returning the result of this request.
HTTP 1.1 also provides request headers and response headers related to identity authentication, state management, cache caching and other mechanisms.
HTTP message header field
From aboveHTTPThere are four types of header fieldsGeneral header field，Request header field，Response header field，Entity header field。
General header field: header used by both request message and response message.
Request header field: header used when sending request message from client to server.
Response header field: the header used when the response message is returned from the server to the client.
Entity header field: header used for the entity part of request message and response message.
HTTP/1.1 header field
General header field
First field name
explain
Cache
Control cache behavior
Connection
Hop by hop header and connection management
Date
Date and time of message creation
Pragma
Message instruction
Trailer
List of headers at the end of the message
Transfer-Encoding
Specify the transmission coding mode of the message body
Upgrade
Upgrade to another agreement
Via
Information about proxy server
Warning
Error Notification
Request header field
First field name
explain
Accept
Media types that the user agent can handle
Accept-Charset
Preferred character set
Accept-Encoding
Priority content encoding
Accept-Language
Preferred language (natural language)
Authorization
Web Authentication Information
Expect
Expect specific server behavior
From
User's email address
Host
Server where the requested resource resides
if-Match
Compare Entity Tag (ETag)
if-Modified-Since
Compare the update time of resources
if-None-Match
Compare entity tags (as opposed to if Match)
if-Range
Send range request of entity Byte when resources are not updated
if-Unmodified-Since
Compare the update time of resources (as opposed to if Modified Since)
Max-Forwards
Maximum number of transmission hops
Proxy-Authorization
The proxy server requires the client's authentication information
Range
Entity's byte range request
Referer
The original method to obtain the URI in the request
TE
Priority of transmission code
User-Agent
HTTP client program information
Response header field
First field name
explain
Accept-Ranges
Whether to accept byte range request
Age
Estimating the resource creation time
ETag
Matching information of resources
Location
Redirect the client to the specified URI
Proxy-Authenticate
Authentication information of proxy server to client
Reter-After
Timing requirements for re launching request
Server
HTTP server installation information
Vary
Management information of proxy server cache
WWW-Authenticate
Server to client authentication information
Entity header field
First field name
explain
Allow
HTTP methods supported by resources
Content-Encoding
Applicable coding method of entity
Content-Language
Natural language of entity subject
Content-Length
Size of entity body (unit: bytes)
Content-Location
Replace the URI of the corresponding resource
Content-MD5
Message digest of entity subject
Content-Range
Location range of entity body
Content-Type
Media type of entity subject
Expires
Date and time when the entity principal expires
Last-Modified
Date and time when the resource was last modified
Http operation procedure
Http is a transaction oriented application layer protocol.Each World Wide Web site has a server process that constantly listens to TCP port 80 to find that a browser sends a connection request to it. Once the connection is established, the browser sends a page browsing request to the World Wide Web server.The browser and server must follow the specified format and certain rules, which are the hypertext transfer protocol http.
Use HTTP/1.0 to describe the event after the user sends a browsing request (enter a URL in the browser address or click an optional event, and the browser will automatically find the page to be connected).
1. Browser analysis URL.
2. Request DNS to resolve the IP address of the domain name.
3. Get the IP address.
3. The browser server establishes a TCP connection (IP address+port number).
4. Issue the file fetching command, such as GET/question/1742817.html in the URL above
5. The server responds by sending 1742817.html to the browser.
6. Release the TCP connection.
7. The browser displays the text in html.
Response message
Status codes and phrases
1xx: Indication - indicates that the request has been received and continues processing.
2xx: Success – indicates that the request has been successfully received, understood and accepted.
3xx: Redirect – Further action is required to complete the request.
4xx: Client error - The request has syntax errors or cannot be implemented.
5xx: Server side error - the server failed to implement a legitimate request.
Common status codes and status descriptions are as follows.
200 OK: The client request is successful.
400 Bad Request: The client request has syntax errors and cannot be understood by the server.
401 Unauthorized: The request is unauthorized. This status code must be used together with the WWW Authenticate header field.
403 Forbidden: The server received the request but refused to provide the service.
404 Not Found: The request resource does not exist. For example, an incorrect URL was entered.
500 Internal Server Error: Unexpected error occurred on the server.
503 Server Unavailable: The server is currently unable to process client requests and may recover after a period of time. For example, HTTP/1.1 200 OK (CRLF).
Difference between GET method and POST method
Reference link 1. For GET submission, the requested data will be attached to the URL (that is, the data will be placed in the HTTP protocol header<request line>)?Split URL and transmit data, and connect multiple parameters with&;For example, login. action?name=hyddd&password=idontknow&verify=%E4%BD%A0 %E5%A5%BD。If the data is English letters/numbers, send it as it is. If it is a space, convert it to+. If it is Chinese/other characters, directly encrypt the string with BASE64. The result is as follows:% E4% BD% A0% E5% A5% BD, where XX in% XX is ASCII represented by the symbol in hexadecimal.
POST submission: Place the submitted data in the HTTP package body<request body>.The red font in the above example indicates the actual transmission data
Therefore,The data submitted by GET will be displayed in the address bar, while the address bar will not be changed for POST submission
2. Size of transmitted data:
First of all,The HTTP protocol does not limit the size of the transmitted data,The HTTP protocol specification also does not limit the URL length.However, the limitations in actual development mainly include:
GET: Certain browsers and servers have restrictions on the URL length. For example, IE has 2083 bytes (2K+35) for the URL length.For other browsers, such as NetscapeFireFox, etc., has no length limit in theory, and its limit depends on the support of the operating system.
Therefore, when GET is submitted, the transmission data will be limited by the URL length.
POST: Since the value is not transferred through URL, the data is not limited theoretically.However, in fact, each Web server will limit the size of post submission data,Apache and IIS6 have their own configurations.
3. Safety: POST is more secure than GET.Note: The security mentioned here is not the same concept as the "security" mentioned by GET above.The above "security" only means no data modification, while the security here means real security. For example, when data is submitted through GET, the user name and password will appear in clear text on the URL, because (1) the login page may be cached by the browser, (2) other people can view the browser's history, so others can get your account and password.
