2021-10-26 agreement

One 、 What is an agreement
A protocol or regulation commonly followed by computer communication .
Http The agreement is allowed HTML The language is transferred from the server to the client .

Two 、 The process from sending a request to receiving a request
1. After entering, the browser cache will be read , With cache , If you have a cache , Will read cache , No continue request server .
2.DNS The server performs domain name resolution , Find the corresponding... According to the domain name IP Address .
3. The client and server shake hands three times TCP link .
4. After creating the link, send Request request .
5. Server return Response, Parse the response , The final display page .

3、 ... and 、Url Format
agreement Request address or domain name port (Http Default port 80,https Default 443, If it is other ports, please indicate .) Access path Request parameters .

Four 、HTTP Message structure
1.Request
Request line Request method route HTTP Agreement version No
GET /baidu.com HTTP/1.1
Request header
Accept-Language
Host
Blank line
request Body
2.Response
Returns the line agreement Status code State description HTTP/1.1 200 OK
Returns the first
Content-Type
Contet-Length
Blank line
Body

5、 ... and 、GET and Post difference
1. First GET The request parameter is in Url In the address .Post In the request Body Inside , When the request is sent Post You can directly see the request parameters .
2.GET The request parameter has a length limit ,Post Generally no .
3.GET The data type of the request parameter is limited ,Post No, .
4.GET Can only Url code ,Post Support multiple coding methods .
5.GET The request parameters will be recorded in the browser ,Post Can't .
6.GET Only one request packet will be sent ,Post I'll send it twice , once header once data.

6、 ... and 、 Status code
1 The request is successful To continue processing
100 The request is successful , The client continues to send the rest of the request
2 The request is successful
200 Ask that everything be normal
202 Request received , But the request has not been completed .
3 Redirect
301
302
4 Client error
400 Grammar mistakes
404 Web page not found
5 Server error
503 Server not available
504 Overtime

7、 ... and 、 Request mode
8 Kind of
GET Post Put Header Delete Connect Trace options

8、 ... and 、BC framework CS framework
BS Browser server
CS Client server

Nine 、cookie and session The difference between
1.cookie Record information on the client side , Identify the user .session Is to record information on the server to determine the user identity .
2. because HTTP Protocol is stateless ,cookie In order to make up for the lack of agreement, we introduce cookie Mechanism .
3.cookie Equivalent to the pass issued by the client .
4.Cookie It's actually a short piece of text . The client requests the server , If the server needs to record the user status , Just use response Issue one to the client browser Cookie. The client browser will take Cookie Save up . When the browser requests the site again , The browser links the requested url with the Cookie Submit to the server together .5.cookie Use key-value Form preservation .6.Cookie It is not cross domain . according to Cookie standard , Browser access Google Only carry Google Of Cookie, Not carrying Baidu Of Cookie.7. Chinese belongs to Unicode character , In memory 4 Characters , And English belongs to ASCII character , It's just memory 2 Bytes .Cookie Use in Unicode Characters need to be correct for Unicode The characters are encoded , Otherwise, it will be disorderly .8.cookie except key-value attribute And the expiration date .Maxage=0 Delete Maxage=-1, Shutdown failure ,Maxage Is a positive number , How long will it expire .9.cookie It can be deleted and modified indirectly .10.HTTP Transmission transmission cookie when , Itself is not encrypted , There's a chance of being intercepted .

1.session Is the mechanism for the server to record the status of the client . Accordingly, the storage pressure of the server is increased .
2. When the client accesses the server , The server records information in some form .
3. For higher access speed ,session Generally accessed in memory .
4.session There is a timeout , After time, it will fail .
5.cookie On behalf of the customer ,session On behalf of the customer . adopt cookie ID,session Identify whether the same customer .

difference
1.cookie On the browser ,session On the server .2.cookie unsafe .3. Too many visits session It takes up server performance .4. Single cookie No more than 4k.

11、 ... and 、 Model
OSI Model 7 layer , The physical layer Data link layer The network layer Transport layer The session layer The presentation layer .TCP/IP Model 5 Physical layer Data link layer The network layer Transport layer application layer .

Twelve 、TCP UDP
All belong to the transport layer .TCP Link oriented services 1. First establish a link in the service , Then disconnect the service .2. During transmission , The packet does not need to carry the destination address .3. Ensure the security of transmission .UDP Unlinked Services 1. Don't link in advance , Send data directly .2. Each message has a carry address .3. The reliability of transmission is not guaranteed .

13、 ... and 、TCP Three handshakes and four waves
send out SYN SEQ ACK I want to start linking You can link to Confirm the link. I want to disconnect the link You can disconnect break link Confirm the disconnection .