Go Notes on Ricky

Go Snippet

Mon, 01 Jan 0001 00:00:00 +0000

ETCD TTL

func main() {
 // 创建 etcd 客户端
 cli, err := clientv3.New(clientv3.Config{
 Endpoints: []string{"localhost:2379"},
 DialTimeout: 5 * time.Second,
 })
 if err != nil {
 fmt.Println("Error connecting to etcd:", err)
 return
 }
 defer cli.Close()

 // 设置 TTL (单位为秒)
 ttl := int64(10) // 例如 10 秒
 resp, err := cli.Grant(context.TODO(), ttl)
 if err != nil {
 fmt.Println("Error creating lease:", err)
 return
 }

 // 使用 Lease ID 进行 Put 操作
 _, err = cli.Put(context.TODO(), "my-key", "my-value", clientv3.WithLease(resp.ID))
 if err != nil {
 fmt.Println("Error putting key with lease:", err)
 return
 }

 fmt.Println("Key with TTL successfully set.")
}

gRPC UnaryInterceptor

func unaryInterceptor(
 ctx context.Context,
 req any,
 info *googleGrpc.UnaryServerInfo,
 handler googleGrpc.UnaryHandler,
) (any, error) {
 // 打印被调用的方法名
 fmt.Println("Called method:", info.FullMethod)

 // 打印传入的请求参数
 fmt.Printf("Request: %+v\n", req)

 fmt.Printf("Meta: %+v\n", util.GetReqInfoFromCtx(ctx))
 // 调用实际的 handler
 response, err := handler(ctx, req)
 if err != nil {
 fmt.Println("err: ", err)
 }
 return response, err
}

isRunningTest

// isRunningTest 確認是否在跑測試
func isRunningTest() bool {
 return flag.Lookup("test.v") != nil
}

Go Tools

Mon, 01 Jan 0001 00:00:00 +0000

tools

benchstat

go install golang.org/x/perf/cmd/benchstat@latest

deadcode

go install golang.org/x/tools/cmd/deadcode@latest

httpstat

It’s like curl -v, with colours.

go get github.com/davecheney/httpstat

jsonnet

This an implementation of Jsonnet in pure Go

go get github.com/google/go-jsonnet/cmd/jsonnet

migrate

go install -tags 'mysql,sqlite,sqlite3' github.com/golang-migrate/migrate/v4/cmd/migrate@latest

protobuf

go install google.golang.org/protobuf/cmd/protoc-gen-go@lastest
go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@lastest
go install github.com/google/gnostic/cmd/protoc-gen-openapi@latest

gosec

Golang security checker

go get -u github.com/securego/gosec/cmd/gosec

govulncheck

go install golang.org/x/vuln/cmd/govulncheck@latest

vegeta

HTTP load testing tool and library

go get -u github.com/tsenart/vegeta

dasel

Select, put and delete data from JSON, TOML, YAML, XML and CSV files with a single tool. Supports conversion between formats and can be used as a Go package.

brew install dasel
go install github.com/tomwright/dasel/v2/cmd/dasel@master

hey

HTTP load generator, ApacheBench (ab) replacement, formerly known as rakyll/boom

brew install hey

slides

Terminal based presentation tool

brew install slides
go install github.com/maaslalani/slides@latest

gokart

A static analysis tool for securing Go code

go install github.com/praetorian-inc/gokart@latest

structslop

structslop is a static analyzer for Go that recommends struct field rearrangements to provide for maximum space/allocation efficiency.

go install -v github.com/orijtech/structslop/cmd/structslop@v0.0.8
go get github.com/orijtech/structslop/cmd/structslop

dive

A tool for exploring each layer in a docker image

brew install dive
go get github.com/wagoodman/dive

sttr

cross-platform, cli app to perform various operations on string

go install github.com/abhimanyu003/sttr@latest

gentool

Gen Tool is a single binary without dependencies can be used to generate structs from database

go install gorm.io/gen/tools/gentool@latest

wire

go install github.com/google/wire/cmd/wire@latest

ko

Build and deploy Go applications

go install github.com/google/ko@latest

Talisman

A tool to detect and prevent secrets from getting checked in

Array

Mon, 01 Jan 0001 00:00:00 +0000

array

package main

import (
 "fmt"
)

func main() {
 a := [5]int{1, 2, 3, 4, 5}
 t := a[3:4:4]
 fmt.Println(t[0])
}

A. 3
B. 4
C. compilation error

Answer

Try it
B

Channel

Mon, 01 Jan 0001 00:00:00 +0000

channel

package main

import (
 "fmt"
 "time"
)

func main() {
 ch := make(chan int, 1000)
 go func() {
 for i := 0; i < 10; i++ {
 ch <- i
 }
 }()
 go func() {
 for {
 a, ok := <-ch
 if !ok {
 fmt.Println("close")
 return
 }
 fmt.Println("a: ", a)
 }
 }()
 close(ch)
 fmt.Println("ok")
 time.Sleep(time.Second * 100)
}

Answer

Try it
ok
panic: send on closed channel

channel1

package main

import (
 "fmt"
)

func main() {
 c := make(chan int)
 close(c)
 val, _ := <-c
 fmt.Println(val)
}

Answer

Try it
0

Context

Mon, 01 Jan 0001 00:00:00 +0000

context

package main

import (
 "context"
 "fmt"
)

func f(ctx context.Context) {
 context.WithValue(ctx, "foo", -6)
}

func main() {
 ctx := context.TODO()
 f(ctx)
 fmt.Println(ctx.Value("foo"))
}

A. -6
B. 0
C. <nil>
D: panic

Answer

Try it
C

context1

package main

import(
 "fmt"
 "encoding/json"
 "context"
)

func main() {
 data, _ := json.Marshal(context.WithValue(context.Background(), "a", "b"))
 fmt.Println(string(data))
}

Answer

Try it
{"Context":{}}

Defer

Mon, 01 Jan 0001 00:00:00 +0000

defer

package main

import (
 "fmt"
)

func main() {
 defer_call()
}

func defer_call() {
 defer func() { fmt.Println("1") }()
 defer func() { fmt.Println("2") }()
 defer func() { fmt.Println("3") }()

 panic("4")
}

Answer

Try it
3
2
1
panic: 4

defer1

package main

import (
 "fmt"
)

type Person struct {
 age int
}

func main() {
 person := &Person{28}

 defer fmt.Println(person.age)

 defer func(p *Person) {
 fmt.Println(p.age)
 }(person)

 defer func() {
 fmt.Println(person.age)
 }()

 person.age = 29
}

Answer

Try it
29
29
28

defer2

package main

import (
 "fmt"
)

type Person struct {
 age int
}

func main() {
 person := &Person{28}

 defer fmt.Println(person.age)

 defer func(p *Person) {
 fmt.Println(p.age)
 }(person)

 defer func() {
 fmt.Println(person.age)
 }()

 person = &Person{29}
}

Answer

Try it
29
28
28

defer3

package main

import (
 "fmt"
)

var a bool = true

func main() {
 defer func() {
 fmt.Println("1")
 }()
 if a == true {
 fmt.Println("2")
 return
 }
 defer func() {
 fmt.Println("3")
 }()
}

Answer

Try it
2
1

defer4

package main

import "fmt"

type temp struct{}

func (t *temp) Add(elem int) *temp {
 fmt.Print(elem)
 return &temp{}
}

func main() {
 tt := &temp{}
 defer tt.Add(1).Add(2)
 tt.Add(3)
}

A. 132
B. 123
C. 312
D. 321

Answer

Try it
A

Goroutine

Mon, 01 Jan 0001 00:00:00 +0000

goroutine

package main

import (
 "fmt"
 "time"
)

func main() {
 ch1 := make(chan int)
 go fmt.Println(<-ch1)
 ch1 <- 5
 time.Sleep(1 * time.Second)
}

A. 5
B. deadlock
C. compilation error

Answer

Try it
B

Interface

Mon, 01 Jan 0001 00:00:00 +0000

interface

package main

import (
 "fmt"
)

type People interface {
 Show()
}

type Student struct{}

func (stu *Student) Show() {}

func live() People {
 var stu *Student
 return stu
}

func main() {
 if live() == nil {
 fmt.Println("AAAAAAA")
 } else {
 fmt.Println("BBBBBBB")
 }
}

Answer

Try it
BBBBBBB

interface1

package main

import (
 "fmt"
)

type People interface {
 Speak(string) string
}

type Student struct{}

func (stu *Student) Speak(think string) (talk string) {
 if think == "love" {
 talk = "You are a good boy"
 } else {
 talk = "hi"
 }
 return
}

func main() {
 var peo People = Student{}
 think := "love"
 fmt.Println(peo.Speak(think))
}

Answer

Try it
compilation error
cannot use Student{} (value of type Student) as People value in variable declaration: Student does not implement People (method Speak has pointer receiver)

interface2

package main

import "fmt"

type T1 struct {
 String func() string
}

func (T1) Error() string {
 return "T1.Error"
}

type T2 struct {
 Error func() string
}

func (T2) String() string {
 return "T2.String"
}

var t1 = T1{String: func() string { return "T1.String" }}
var t2 = T2{Error: func() string { return "T2.Error" }}

func main() {
 fmt.Println(t1.Error(), t1.String())
 fmt.Println(t2.Error(), t2.String())

 fmt.Println(t1, t2)
}

Answer

Try it
T1.Error T1.String
T2.Error T2.String
T1.Error T2.String

interface3

package main

import "fmt"

func main() {
 var p [100]int
 var m any = [...]int{99: 0}
 fmt.Println(p == m)
}

Answer

Try it
true

Iota

Mon, 01 Jan 0001 00:00:00 +0000

iota

package main

import "fmt"

const (
 x = iota
 _
 y
 z = "zz"
 k
 p = iota
)

func main() {
 fmt.Println(x, y, z, k, p)
}

Answer

Try it
0 2 zz zz 5

iota1

package main

import "fmt"

const (
 a = iota
 b = iota
)

const (
 name = "name"
 c = iota
 d = iota
)

func main() {
 fmt.Println(a, b, c, d)
}

Answer

Try it
0 1 1 2

JSON

Mon, 01 Jan 0001 00:00:00 +0000

json

package main

import (
 "encoding/json"
 "fmt"
)

type AutoGenerated struct {
 Age int `json:"age"`
 Name string `json:"name"`
 Child []int `json:"child"`
}

func main() {
 jsonStr1 := `{"age": 14,"name": "potter", "child":[1,2,3]}`
 a := AutoGenerated{}
 json.Unmarshal([]byte(jsonStr1), &a)
 aa := a.Child
 fmt.Println(aa)
 jsonStr2 := `{"age": 12,"name": "potter", "child":[3,4,5,7,8,9]}`
 json.Unmarshal([]byte(jsonStr2), &a)
 fmt.Println(aa)
}

A. [1 2 3] [1 2 3]
B. [1 2 3] [3 4 5]
C. [1 2 3] [3 4 5 6 7 8 9]
D. [1 2 3] [3 4 5 0 0 0]

Answer

Try it
B

json1

package main

import (
 "encoding/json"
 "fmt"
 "time"
)

func main() {
 t := struct {
 time.Time
 N int
 }{
 time.Date(2020, 12, 20, 0, 0, 0, 0, time.UTC),
 5,
 }

 m, _ := json.Marshal(t)
 fmt.Printf("%s", m)
}

A. {“Time”:“2020-12-20T00:00:00Z”,“N”:5}
B. “2020-12-20T00:00:00Z”
C. {“N”:5}
D. <nil>
E. 其他

Answer

Try it
B

Len

Mon, 01 Jan 0001 00:00:00 +0000

len

package main

func main() {
 var x *struct {
 s [][32]byte
 }

 println(len(x.s[99]))
}

A. panic
B. compilation error
C. 32
D. 0

Answer

Try it
C

len1

package main

const s = "Go101.org"

// len(s) == 9
// 1 << 9 == 512
// 512 / 128 == 4

var a byte = 1 << len(s) / 128
var b byte = 1 << len(s[:]) / 128

func main() {
 println(a, b)
}

A: 0 0
B: 0 4
C: 4 0
D: 4 4

Answer

Try it
C

len2

package main

var s = "Go101.org"

// len(s) == 9
// 1 << 9 == 512
// 512 / 128 == 4

var a byte = 1 << len(s) / 128
var b byte = 1 << len(s[:]) / 128

func main() {
 println(a, b)
}

A: 0 0
B: 0 4
C: 4 0
D: 4 4

Answer

Try it
A

Map

Mon, 01 Jan 0001 00:00:00 +0000

map

package main

import "fmt"

type Student struct {
 Name string
}

var list map[string]Student

func main() {

 list = make(map[string]Student)

 student := Student{"Aceld"}

 list["student"] = student
 list["student"].Name = "LDB"

 fmt.Println(list["student"])
}

Answer

Try it
compilation error
cannot assign to struct field list["student"].Name in map

map1

package main

func main() {
 m := make(map[int]int, 3)
 x := len(m)
 m[1] = m[1]
 y := len(m)
 println(x, y)
}

Answer

Try it
0 1

Print

Mon, 01 Jan 0001 00:00:00 +0000

print

package main

import "fmt"

type T struct {
 x int
}

func (t T) String() string { return "boo" }

func main() {
 t := T{123}
 fmt.Printf("%v\n", t)
 fmt.Printf("%#v\n", t)
}

Answer

Try it
boo
main.T{x:123}

print1

package main

import (
 "fmt"
)

func f(a ...int) {
 fmt.Printf("%#v\n", a)
}

func main() {
 f()
}

Answer

Try it
[]int(nil)

Race

Mon, 01 Jan 0001 00:00:00 +0000

race

type Stats struct {
 mutex sync.Mutex

 counters map[string]int
}

func (s *Stats) Snapshot() map[string]int {
 s.mutex.Lock()
 defer s.mutex.Unlock()

 return s.counters
}

func (s *Stats) Add(name string, num int) {
 s.mutex.Lock()
 defer s.mutex.Unlock()
 s.counters[name] = num
}

Answer

func (s *Stats) Snapshot() map[string]int {
s.mutex.Lock()
defer s.mutex.Unlock()
result := make(map[string]int, len(s.counters))
for k, v := range s.counters {
result[k] = v
}
return result
}

Select

Mon, 01 Jan 0001 00:00:00 +0000

select

package main

import "sync"

func main() {
 var wg sync.WaitGroup
 foo := make(chan int)
 bar := make(chan int)
 wg.Add(1)
 go func() {
 defer wg.Done()
 select {
 case foo <- <-bar:
 default:
 println("default")
 }
 }()
 wg.Wait()
}

Answer

Try it
fatal error: all goroutines are asleep - deadlock!

select1

package main

import "fmt"

func main() {
 ch1 := make(chan int)
 ch2 := make(chan int)
 go func() {
 ch1 <- 1
 }()

 go func() {
 select {
 case <-ch1:
 case ch2 <- 2:
 }
 }()

 fmt.Println(<-ch2)
}

A. 1
B. 2
C. No output, program is deadlocked
D. No output, program has finished execution.
E. else

Answer

Try it
B

Slice

Mon, 01 Jan 0001 00:00:00 +0000

slice

package main

import (
 "fmt"
)

func main() {
 var s1 []int
 var s2 = []int{}
 if __ == nil {
 fmt.Println("nil slice")
 }
 if __ != nil {
 fmt.Println("empty slice")
 }
}

A. s1, s2
B. s2, s1
C. s1, s1
D. s2, s2

Answer

Try it
A

slice1

package main

import (
 "fmt"
)

func main() {
 s := [3]int{1, 2, 3}
 a := s[:0]
 b := s[:2]
 c := s[1:2:cap(s)]
 fmt.Println(len(a), cap(a))
 fmt.Println(len(b), cap(b))
 fmt.Println(len(c), cap(c))
}

Answer

Try it
0 3
2 3
1 2

slice2

package main

import "fmt"

func main() {
 s1 := []int{1, 2, 3}
 s2 := s1[1:]
 s2[1] = 4
 fmt.Println(s1)
 s2 = append(s2, 5, 6, 7)
 fmt.Println(s1)
}

Answer

Try it
[1 2 4]
[1 2 4]

Variable

Mon, 01 Jan 0001 00:00:00 +0000

variable

A. p.name
B. (&p).name
C. (*p).name
D. p->name

Answer

AC

variable1

package main

import (
 "fmt"
)

func main() {
 var ans float64 = 15 + 25 + 5.2
 fmt.Println(ans)
}

A. 45
B. 45.0
C. 45.2
D. compliation error

Answer

Try it
C

variable2

package main

import (
 "fmt"
)

func main() {
 var ans float64 = 3 / 2
 fmt.Println(ans)
}

A. 1.5
B. 1
C. 0
D. compliation error

Answer

Try it
B

variable3

package main

func main() {
 const a int8 = -1
 var b int8 = -128 / a

 println(b)
}

Answer

Try it
compliation error
-128 / a (constant 128 of type int8) overflows int8

variable4

package main

func main() {
 var a int8 = -1
 var b int8 = -128 / a

 println(b)
}

Answer

Try it
-128

variable5

package main

import "fmt"

type MyInt1 int
type MyInt2 = int

func main() {
 var i int =0
 var i1 MyInt1 = i
 var i2 MyInt2 = i
 fmt.Println(i1, i2)
}

Answer

Try it
compilation error
cannot use i (variable of type int) as MyInt1 value in variable declaration

variable6

package main

import "fmt"

func main() {
 const X = 7.0
 var x any = X
 if y, ok := x.(int); ok {
 fmt.Println(y)
 } else {
 fmt.Println(int(y))
 }
}

A. 7
B. 7.0
C. 0
D. compilation error

Answer

Try it
C

Go Libraries

Mon, 01 Jan 0001 00:00:00 +0000