1、 Go knowledge check and remedy + practical course notes youth training camp notes

Go Knowledge checking and filling + Practical course notes | Youth Camp notes

This is my participation 「 The third youth training camp - Back end field 」 The third part of note creation activities 1 Notes

It is divided into simple basic grammar to check and fill gaps and notes of the final practical project

Check for defects and make up for omissions ：

Map：

map The assignment of is completely unordered , It has nothing to do with the content and order of insertion

Structure ：

Pass in the structure pointer as a parameter in the method , It can be modified , In some cases, the overhead of copying structures can be avoided

string library ：

a := "hello"
fmt.Println(strings.Contains(a, "ll"))                // true
fmt.Println(strings.Count(a, "l"))                    // 2
fmt.Println(strings.HasPrefix(a, "he"))               // true
fmt.Println(strings.HasSuffix(a, "llo"))              // true
fmt.Println(strings.Index(a, "ll"))                   // 2
fmt.Println(strings.Join([]string{
    "he", "llo"}, "-")) // he-llo
fmt.Println(strings.Repeat(a, 2))                     // hellohello
fmt.Println(strings.Replace(a, "e", "E", -1))         // hEllo
fmt.Println(strings.Split("a-b-c", "-"))              // [a b c]
fmt.Println(strings.ToLower(a))                       // hello
fmt.Println(strings.ToUpper(a))                       // HELLO

fmt package ：

+v: Print out more details

fmt.Printf("p=%+v\n", p) // p={x:1 y:2}

#v: Print out more detailed content

fmt.Printf("p=%#v\n", p) // p=main.point{x:1, y:2}

JSON：

Serialize to a string ：

a := userInfo{
    Name: "wang", Age: 18, Hobby: []string{
    "Golang", "TypeScript"}}
	buf, err := json.Marshal(a)
	if err != nil {
    
		panic(err)
	}
	fmt.Println(buf)         // [123 34 78 97...]
	fmt.Println(string(buf)) // {"Name":"wang","age":18,"Hobby":["Golang","TypeScript"]}

Deserialize back to structure ：

var b userInfo
	err = json.Unmarshal(buf, &b)
	if err != nil {
    
		panic(err)
	}
	fmt.Printf("%#v\n", b) // main.userInfo{Name:"wang", Age:18, Hobby:[]string{"Golang", "TypeScript"}}

Get the timestamp ：

now := time.Now()
fmt.Println(now.Unix()) // 1648738080

Type conversion ：

This method always forgets

// String to number 
n2, _ := strconv.Atoi("123") 
// 123

// The number is converted to a string 
strconv.Itoa(n2)
// "123"

rand random number

The corresponding random number seed is generated by the timestamp generated by the time the project is started each time ：

maxNum := 100
rand.Seed(time.Now().UnixNano())
secretNumber := rand.Intn(maxNum)

The client parses the response

Convert a string into a stream

Because if you pass in a stream instead of a string , Prevent if the parameter file is large , It will waste a lot of time

client := &http.Client{
    }
var data = strings.NewReader(`{"trans_type":"en2zh","source":"good"}`)

Add a blog you wrote before （golang Of Panic）

You can put panic Understand as a kind of try catch

Used only to catch fatal errors , It should not be used to report common errors ： For example, when something should not happen happens , We should call panic（ An array 、 Null pointer exception, etc ）

When an exception occurs and is panic When capturing , The program will break , And then execute defer

stay go Language design , The function gets a multiple return value , Although very miscellaneous , Use... Every time if err != nil

however , Really catch exceptions and throw , It has to be used panic
The sample code

Practice notes ：

SOCKS5 proxy server

SOCKS5 The protocol is a clear text transmission protocol , The purpose is to open a hole in the firewall , Let the authorized users have the ability to access the resources through a single port

Activation effect ：

​ After starting the program ,

• Mode one ： Configure and use this proxy in the browser , At this point, we open the web page , Proxy server logs , It will print out the domain name of the website you visit or IP, This shows that our network traffic is through this proxy server .
• Mode two ： Test our proxy server on the command line . We can use cur-soci5 + Proxy address , Followed by an accessible URL, If the proxy server works properly , that curt The command will return normally .

socks5 How the protocol works

​ Normal browser to visit a website , If you don't go through the proxy server , Will first establish with each other's website TCP Connect , Then shake hands three times . After shaking hands HTTP request , Then the service returns HTTP Respond to .

​ If you set up a proxy server , The process will become more complicated . The first is the browser and socks5 The agent establishes TCP Connect ,socks5 The agent then establishes with the real server TCP Connect . It can be divided into four stages , handshake phase 、 Authentication phase 、 Request stage 、relay Stage .
​ The first handshake stage , Liuziqi will socks5 Agent sends request , The content of the request package includes the version number of a protocol , There are also supported authentication types , socks5 Will choose an authentication method , Back to the browser . If you return 00 That means you don't need certification , If other types are returned, the authentication process will begin .

( The certification process ：

​ First step , The browser will send a package to the proxy server , This package has three fields ; First field ：version, That is, the protocol version number , Fixed is 5; Second field ：methods, Number of certified methods ; Third field ： Every method The coding ,0 Representatives don't need certification ,2 On behalf of user name and password authentication
here , The proxy server also needs to return a response, The return package includes two fields , One is version One is method, That is, the authentication method we selected , At present, we are only ready to implement the method without authentication , That is to say 0)

​ The third stage is the request stage , After authentication, the browser will towards socks5 Initiate request . The main information includes version number , Type of request , Generally, it's mainly connection request , Represents hope socks5 The server goes to a domain name or a IP Address a port to establish TCP Connect , After the proxy server receives the response , It will establish a connection with the back-end server , Then return the response .
​ The fourth stage is relay Stage , At this time, the browser will send a normal sending request , Then after the proxy server receives the request , It will directly convert the request to the real server . Then if the real server returns a response , The response will also be sent to the proxy server , The proxy server doesn't care about the details of sending traffic , It can be HTTP Traffic , It could be something else TCP Traffic .

Establish connection with back-end server , Then return the response .
​ The fourth stage is relay Stage , At this time, the browser will send a normal sending request , Then after the proxy server receives the request , It will directly convert the request to the real server . Then if the real server returns a response , The response will also be sent to the proxy server , The proxy server doesn't care about the details of sending traffic , It can be HTTP Traffic , It could be something else TCP Traffic .