Go¶

Install¶

With HomeBrew (MacOS)¶

brew update
brew upgrade
brew install go

Install multiple versions

See Linux Package Management#Handling multiple versions

Style¶

https://github.com/Pungyeon/clean-go-article

Use camel style for variables.

Rules¶

function name¶

CamelCase, otherwise might have unexpected results

Init¶

go mod init <project_name>

Will generate go.mod

Dependencies¶

Install a specific module¶

go install <module_url>

You may see a lot of older Internet guides using go get, but it's deprecated. See https://go.dev/doc/go-get-install-deprecation.

Install current project's dependencies¶

Auto check your codes and update go.mod and install all required dependecies in go.mod to GOMODACHE if haven't

go mod tidy

Change module path¶

The go modules are stored in Go env GOMODCACHE (go env GOMODCACHE to check it)

You can change it to store the modules somewhere else

go env -w GOMODCACHE="/bruh"

go get from private domain/repo¶

Suppose you want to go get git.evilcorp.com/EVILPRODUCT/evil-event

Do this

export GOPRIVATE=git.evilcorp.com

Import¶

Go importing 101

https://stackoverflow.com/a/68710251/15493213

Run¶

go run <script.go>

Garbage Collection¶

Why Discord is switching from Go to Rust (2020) | Discord Blog

According to the blog, Go (at least v1.10 and before) will do garbage collection every 2 minutes, which may cause latency spikes.

This is allegedly fixed in v1.14. See Go runtime: 4 years later (2022) | Go Blog.

Internal Documentations¶

See https://tip.golang.org/doc/comment

Documenting your codes¶

To write a docstring for a package / function / everything, just comment before it.

// ankara mesi
// goooaallll
package mesi

This will be recognized by your IDE as well as the following tools.

CLI doc¶

To see the docstring of a package, external or internal

go doc <package name>

Web doc¶

Install godoc

go install golang.org/x/tools/cmd/godoc

In your project root, run

godoc -http=:6060 -v

Then go to http://localhost:6060/pkg/?m=all. Without m=all it will hide internal/. Related issue.

Environmental variables¶

Go Env¶

To see all Go env

go env

To see a specific Go env e.g. GOPATH

go env GOPATH

To set a Go env e.g. GOMODCACHE

go env -w GOMODCACHE="/bruh"

Dotenv¶

https://towardsdatascience.com/use-environment-variable-in-your-next-golang-project-39e17c3aaa66

go get github.com/joho/godotenv

godotenv.Load()
os.Getenv(<your_env>)

Viper¶

To use .env

viper.SetConfigFile(".env")
viper.ReadInConfig()

Slice¶

The internal of slice¶

Arrays, slices (and strings): The mechanics of 'append' | Go Blog

Slice is a slice of a fixed-sized array, with a pointer pointing to the start and a length value specifying the length.

type sliceHeader struct {
    Length        int
    ZerothElement *byte
}

slice := sliceHeader{
    Length:        50,
    ZerothElement: &buffer[100], // pointer to the underlying array
}

When copied or passed to a function, a change to the length won't apply to the original slice since the length is a value not a pointer.

Here we see that the contents of a slice argument can be modified by a function, but its header cannot. The length stored in the slice variable is not modified by the call to the function, since the function is passed a copy of the slice header, not the original.

func SubtractOneFromLength(slice []byte) []byte {
    slice = slice[0 : len(slice)-1]
    return slice
}

func main() {
    fmt.Println("Before: len(slice) =", len(slice))
    newSlice := SubtractOneFromLength(slice)
    fmt.Println("After:  len(slice) =", len(slice))
    fmt.Println("After:  len(newSlice) =", len(newSlice))
}

Before: len(slice) = 50
After:  len(slice) = 50
After:  len(newSlice) = 49

How append works¶

If the new length of slice is greater than the length of the underlying array, it will append() will first allocate a new array (length = 1.5 x new slice length), and the copy all the data into the new array. Since it's a different array, the address of the underlying array is obviously changed also.

If the original array is capable to hold all the new data already, it will simply copy the new data into the array.

// Append appends the elements to the slice.
// Efficient version.
func Append(slice []int, elements ...int) []int {
    n := len(slice)
    total := len(slice) + len(elements)
    if total > cap(slice) {
        // Reallocate. Grow to 1.5 times the new size, so we can still grow.
        newSize := total*3/2 + 1
        newSlice := make([]int, total, newSize)
        copy(newSlice, slice)
        slice = newSlice
    }
    slice = slice[:total]
    copy(slice[n:], elements)
    return slice
}

Slice of Values vs. Slice of Pointers¶

If the underlying array of your slice is big enough for your need, there is no point at using slice of pointers, as it will need to allocate a new piece of memory for the pointer for each entry in the slice.

However, if the your your slice will outgrow the underlying array when being appended, a new array with sufficient length will be allocated, copying all the data from the original array to the new one. This is when using slice of pointers is a better option, since only the pointers will need to be copied, not the entire values.

To test the performance difference yourself

main_test.go

package main

import (
    "testing"
)

type SmallStruct struct {
    A int
    B int
}

const (
    SLICE_LEN = 100
    ARRAY_LEN = 100
)

func BenchmarkSliceOfSmallStructs(b *testing.B) {
    b.ReportAllocs()
    for i := 0; i < b.N; i++ {
        slice := make([]SmallStruct, 0, ARRAY_LEN)
        for j := 0; j < SLICE_LEN; j++ {
            slice = append(slice, SmallStruct{A: j, B: j + 1})
        }
    }
}

func BenchmarkSliceOfPointersOfSmallStructs(b *testing.B) {
    b.ReportAllocs()
    for i := 0; i < b.N; i++ { // test count
        slice := make([]*SmallStruct, 0, ARRAY_LEN)
        for j := 0; j < SLICE_LEN; j++ {
            slice = append(slice, &SmallStruct{A: j, B: j + 1})
        }
    }
}

type BigStruct struct {
    F1, F2, F3, F4, F5, F6, F7                string
    I1, I2                                    int
    I3, I4, I5, I6, I7, I8, I9, I10, I11, I12 int
    A1, A2, A3, A4, A5, A6, A7                SmallStruct
    A8, A9, A10, A11, A12, A13, A14           SmallStruct
}

func BenchmarkSliceOfBigStructs(b *testing.B) {
    b.ReportAllocs()
    for i := 0; i < b.N; i++ {
        slice := make([]BigStruct, 0, ARRAY_LEN)
        for j := 0; j < SLICE_LEN; j++ {
            slice = append(slice, BigStruct{
                I1: j,
                I2: j + 1,
            })
        }
    }
}

func BenchmarkSliceOfPointersOfBigStructs(b *testing.B) {
    b.ReportAllocs()
    for i := 0; i < b.N; i++ {
        slice := make([]*BigStruct, 0, ARRAY_LEN)
        for j := 0; j < SLICE_LEN; j++ {
            slice = append(slice, &BigStruct{
                I1: j,
                I2: j + 1,
            })
        }
    }
}

To see direct ouputs

go test -bench . -count 3

To see analyzed outputs, install benchstat first

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

and then

go test -bench . -count 3 -benchmem >> benchmark.txt
benchstat benchmark.txt

See #Benchmarking for more

Output when SLICE_LEN = 100, ARRAY_LEN = 100:

goos: darwin
goarch: amd64
pkg: gslice
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
                                 │ benchmark.txt │
                                 │    sec/op     │
SliceOfSmallStructs-12               89.89n ± 4%
SliceOfPointersOfSmallStructs-12     2.133µ ± 8%
SliceOfBigStructs-12                 3.363µ ± 7%
SliceOfPointersOfBigStructs-12       8.597µ ± 3%
geomean                              1.534µ

                                 │ benchmark.txt  │
                                 │      B/op      │
SliceOfSmallStructs-12               0.000 ± 0%
SliceOfPointersOfSmallStructs-12   1.562Ki ± 0%
SliceOfBigStructs-12                 0.000 ± 0%
SliceOfPointersOfBigStructs-12     43.75Ki ± 0%
geomean                                         ¹
¹ summaries must be >0 to compute geomean

                                 │ benchmark.txt │
                                 │   allocs/op   │
SliceOfSmallStructs-12              0.000 ± 0%
SliceOfPointersOfSmallStructs-12    100.0 ± 0%
SliceOfBigStructs-12                0.000 ± 0%
SliceOfPointersOfBigStructs-12      100.0 ± 0%
geomean                                        ¹
¹ summaries must be >0 to compute geomean

Output when SLICE_LEN = 100, ARRAY_LEN = 10:

goos: darwin
goarch: amd64
pkg: gslice
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
                                 │ benchmark_raw.txt │
                                 │      sec/op       │
SliceOfSmallStructs-12                  880.6n ± 17%
SliceOfPointersOfSmallStructs-12        2.815µ ±  7%
SliceOfBigStructs-12                    20.41µ ± 15%
SliceOfPointersOfBigStructs-12          9.213µ ±  3%
geomean                                 4.646µ

                                 │ benchmark_raw.txt │
                                 │       B/op        │
SliceOfSmallStructs-12                  4.812Ki ± 0%
SliceOfPointersOfSmallStructs-12        3.906Ki ± 0%
SliceOfBigStructs-12                    147.2Ki ± 0%
SliceOfPointersOfBigStructs-12          46.09Ki ± 0%
geomean                                 18.90Ki

                                 │ benchmark_raw.txt │
                                 │     allocs/op     │
SliceOfSmallStructs-12                    4.000 ± 0%
SliceOfPointersOfSmallStructs-12          104.0 ± 0%
SliceOfBigStructs-12                      4.000 ± 0%
SliceOfPointersOfBigStructs-12            104.0 ± 0%
geomean                                   20.40                                        20.40

Please read Arrays, slices (and strings): The mechanics of 'append' | Go Blog if you're confused.

Discussions containing partial truths

Docstring¶

Comments directly above a function will become docstrings.

// this is an example function
// this function will return the result of a + b
func add(a int, b int) int {
    c := a + b
    return c
}

Interface¶

https://gobyexample.com/interfaces

type geometry interface {
    area() float64
    perim() float64
}

type rect struct {
    width, height float64
}
type circle struct {
    radius float64
}

func (r rect) area() float64 {
    return r.width * r.height
}
func (r rect) perim() float64 {
    return 2*r.width + 2*r.height
}

func (c circle) area() float64 {
    return math.Pi * c.radius * c.radius
}
func (c circle) perim() float64 {
    return 2 * math.Pi * c.radius
}

func measure(g geometry) {
    fmt.Println(g)
    fmt.Println(g.area())
    fmt.Println(g.perim())
}

func main() {
    r := rect{width: 3, height: 4}
    c := circle{radius: 5}
    measure(r)
    measure(c)
}

Channel¶

pipe

Dealing with Json¶

Read json from file¶

If your json has a clearly defined structure, then define your struct first

type struct myJsonObject {
    // my json schema
}

func getJsonFromFile() []myJsonObject {
    // read raw json from sample.json
    jsonFile, err := os.Open("sample.json")
    if err != nil {
        fmt.Println(err)
    }
    defer jsonFile.Close()
    var arrayOfJson []myJsonObject
    byteValue, _ := ioutil.ReadAll(jsonFile)
    json.Unmarshal(byteValue, &arrayOfJson)
    return arrayOfJson
}

https://tutorialedge.net/golang/parsing-json-with-golang/

grpc¶

sample

https://github.com/grpc/grpc-go/tree/master/examples/helloworld

proto file

https://stackoverflow.com/a/70587449/15493213

GORM¶

Go's ORM library

Execute raw query¶

db.EXEC("TRUNCATE TABLE services")

Enum¶

Note that AutoMigrate will not migrate enum changes. You can alter table directly, or drop the table and then let AutoMigrate recreate the tables (if not in production)

Use https://threedots.tech/post/safer-enums-in-go/

e.g.

type DataScope int

const (
    UNKNOWN_DATASCOPE DataScope = iota // -> 0
    NEW_CASE // -> 1
    PENDING_REVIEW // -> 2
    USER_REPLY // -> 3
)

type Report struct {
    DataScope  DataScope `gorm:"column:data_scope;type:enum('NEW_CASE', 'PENDING_REVIEW', 'USER_REPLY');index:,sort:desc" json:"dataScope"`
}

Use https://github.com/dmarkham/enumer to generate enumer file for DataScope.

go install github.com/dmarkham/enumer@latest

go run enumer -type=DataScope -sql

To map string back to enum, just use the URLTypeString function in the generated enumer file. But if you want to implement it manually,

package alphabets

type Alphabets int

const (
    A Alphabets = iota
    B
    C
)

var MapEnumStringToAlphabets = func() map[string]Alphabets {
    m := make(map[string]Alphabets)
    for i := A; i <= C; i++ {
        m[i.String()] = i
    }
    return m
}()

https://stackoverflow.com/a/75205150/15493213

But MySQL doesn't support specifying column, instead it always check the primary key for conflict check, so better use FirstOrCreate and the Update if RowsAffected is 0

res := r.dbClient.DB().
    WithContext(ctx).
    Model(&model.Report{}).
    Where("date = ?", date).
    FirstOrCreate(report)
err := res.Error
if err != nil {
    return err
}
if res.RowsAffected != 0 { // record created
    return nil
}
// update existing record
if err = r.dbClient.DB().
    WithContext(ctx).
    Model(&model.Report{}).
    Where("date = ?", date).
    Update("waiting_day", waitingDay).Error; err != nil {
    return err
}

hooks¶

https://gorm.io/docs/hooks.html

AfterFind
- auto execute after querying

Select 2 interlinked tables¶

Suppose you have 2 tables, Project & Incident. 1 project can have multiple incidents, but 1 incident only belongs to 1 project.

type Project struct {
    ID              uuid.UUID       `json:"id" gorm:"column:id;primary_key;type:varchar(64);not null"`

    Incidents []Incident `gorm:"foreignkey:IncidentID"`
}

type Incident struct {
    ID          uuid.UUID  `json:"id" gorm:"column:id;primary_key;type:varchar(64);not null"`
    ProjectID  uuid.UUID  `json:"project_id" gorm:"column:incident_id;type:varchar(64);not null"`

    Project Project `gorm:"foreignkey:ProjectID"`
}

You can query the project alongside its incident in GORM with

func (r projectRepository) GetProjectID(ctx context.Context, projectID uuid.UUID) (project *model.Project, err error) {
    if err := r.dbClient.DB().
        WithContext(ctx).
        Preload("Incidents").
        Where("id = ?", projectID).
        First(&project).Error; err != nil {
        return nil, err
    }
    return
}

If you look at its raw query, it still makes 2 seperate query for Project & Incident table, but at least you don't have to handle it youself.

Set a nullable field back to null¶

To set a nullable field of a record from having a value back to null, you can't use a simple pointer type when declaring a model, but a pointer to the corresponding type in the sql package.

type Model struct {
    Amount *sql.NullFloat64
}

// amount will not be updated
gorm.Updates(Model{Amount: nil})

// amount will be updated as a null
gorm.Updates(Model{Amount: &sql.NullFloat64{}})

// amount will be updated as a 10.50
gorm.Updates(Model{Amount: &sql.NullFloat64{Float64: 10.50, Valid: true}})

See https://stackoverflow.com/a/70596488/15493213

Error¶

You can add error manually, which is useful when writing unit tests

db.AddError(gorm.ErrInvalidTransaction)

or simply

db.Error = gorm.ErrInvalidTransaction

To revert, just reassign it to null

db.Error = nil

Logging¶

To print the raw query in your terminal

import (
    gormLogger "gorm.io/gorm/logger"
)

db.Config.Logger = gormLogger.Default.LogMode(gormLogger.Info)

AutoMigrate¶

You can let gorm migrate the tables for you. It does not migrate your tables completely however, for example it has some problems dealing with enum & foreign key.

models = []any{
    &modelA{},
    &modelB{},
}
db.AutoMigrate(models...)

ORM¶

#GORM ¶

Ent¶

From Facebook

https://entgo.io/

Migration¶

have automigration
uses #Atlas for versioned migration

db migration¶

golang-migrate¶

https://github.com/golang-migrate/migrate

Won't auto gen migration files

goose¶

https://github.com/pressly/goose

Won't auto gen migration files

Multiple reddit comments don't recommend it

Atlas¶

https://atlasgo.io/guides/orms/gorm

Auto gen migration files by comparing a blank MySQL db to a MySQL db holding your target tables.

Setup¶

Create a blank schema in local.

docker run --rm --name atlas-db-dev -d -p 23306:3306 -e MYSQL_DATABASE=dev -e MYSQL_ROOT_PASSWORD=pass mysql:8

docker run --rm --name atlas-db-dev -d -p 23306:3306 -e MYSQL_DATABASE=dev -e MYSQL_ROOT_PASSWORD=pass mysql:8

Create a blank schema (migration_target in this example) in your local mysql and run gorm AutoMigrate to fill it with the target schemas.

Starting with existing tables¶

doc

Generate baseline file

atlas migrate diff baseline \
  --dev-url "mysql://root:pass@:23306/dev" \
  --to "mysql://{username}:{password}@:3306/migration_target"

Apply 1st migration

atlas migrate apply \
  --url "mysql://{username}:{password}@:23306/{real_schema}" \
  --baseline "{baseline_title}"

Auto generate migration file¶

atlas migrate diff \
  --dev-url "mysql://root:pass@:23306/dev" \
  --to "mysql://{username}:{password}@:3306/migration_target"

Check migration status¶

atlas migrate status \
  --url "mysql://{username}:{password}@:3306/{real_schema}"

Run migrations¶

https://atlasgo.io/versioned/apply

atlas migrate apply \
  --url "mysql://{username}:{password}@:23306/{real_schema}"

Problems¶

when you want to alter a foreign key column type, you'll need to drop the key first and then add back later, but it won't write it for you in the auto generated migration files
no rollback

Goroutine¶

concurrency

With WaitGroup¶

wg.Add(n) -> n threads
wg.Wait() -> wait for all threads to end and then continue
go myfunction() -> Start a thread executing myfunction()

package main

import (
    "fmt"
    "sync"
)

func printStr(str string, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Println(str)
}

func main() {
    var wg sync.WaitGroup
    strList := []string{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j"}
    wg.Add(len(strList))
    for _, str := range strList {
        go printStr(str, &wg)
    }
    wg.Wait()
}

Limit amount of goroutines¶

package main

import "fmt"

const MAX = 20

func main() {
    sem := make(chan struct{}, MAX)
    for {
        sem <- struct{}{} // will block if there is MAX ints in sem
        go func() {
            fmt.Println("hello again, world")
            <-sem // removes an int from sem, allowing another to proceed
        }()
    }
}

https://stackoverflow.com/a/25306439/15493213

Fx - dependency injection¶

fx.New(
    fx.Provide(),
    fx.Invoke(),
).Run()

Context timeout¶

Default context timeout is 15s, to change it, specify it under fx.New()

fx.StartTimeout(time.Second*42)

Unit testing¶

Writing test files¶

Your test file should be in *_test.go format, in the same directory as your main file.

Functions should be in Test* format.

e.g.

// main.go
package mul

func Mul(a, b int) int {
    return a * b
}

// main_test.go
package mul // notice the same name

import (
    "testing"

    "github.com/stretchr/testify/assert"
)

func TestMul(t *testing.T) {
    assert.Equal(t, Mul(1, 2), 2)
}

Run something after each unit test¶

Using testify, you can add a TearDownTest() function, and it will run the function after each unit test.

For example, if you're using testcontainer and want to truncate your tables after each unit test, write that in the function.

Run Tests¶

To run all test files recursively

go test -v ./...

To run the test file in the current directory

go test -v

To run the test file in a specific package

go test -v <project name/package name>

-v for verbose

Save results to file

go test -v -cover -covermode=count -coverpkg=./... -coverprofile=coverage.out ./...
go test -json ./... > report.json

VsCode helper¶

You'll see a snippet allowing you to execute the test directly in VsCode. You can add additional flag in the settings.

For example, if you want it to always run with -v (verbose), add this in settings

`"go.testFlags": ["-v"]`

See https://github.com/Microsoft/vscode-go/issues/1377#issuecomment-347431580

assert equal of list ignoring order¶

assert.ElementsMatch()

https://github.com/stretchr/testify/issues/275#issuecomment-480823210

Benchmarking¶

Mock¶

GoMock¶

go install github.com/golang/mock/mockgen@latest

mockgen -source=doer/doer.go -destination=mocks/mock_doer.go --package mocks

sqlmock¶

https://pkg.go.dev/github.com/DATA-DOG/go-sqlmock

https://github.com/go-gorm/gorm/issues/1525#issuecomment-376164189

https://betterprogramming.pub/97ee73e36526

Gin¶

Binding parameters or body¶

You can bind the query parameters or json body to a struct.

To bind query parameters or form-data, specify form in struct tags. To bind json body, specify json in struct tags.

type Filter struct {
    Product    bool   `json:"product" form:"product"`
    SubProduct bool   `json:"sub_product" form:"sub_product"`
    Project    bool   `json:"project" form:"project"`
}

func (h topHandlers) HandleGetServices(c *gin.Context) {
    filter := &model.Filter{}
    // binding query params
    err := c.ShouldBind(filter)
    // binding json body
    err := c.ShouldBindJSON(filter)
    // rest of the codes
}

Don't forget to specify Content-Type: applicaiton/json in request header to bind json body.

mock¶

A helper function helping you set up a mock context and a recorder recording the reponse of your request

func MockGin() (*gin.Context, *httptest.ResponseRecorder) {
    w := httptest.NewRecorder()
    c, _ := gin.CreateTestContext(w)
    c.Request = &http.Request{
        Header: make(http.Header),
        URL:    &url.URL{},
        Body:   nil,
    }   
    return c, w
}

Create your mock request, send the context into your handler function, and see if the response code and data is correct

func TestGetService(){
    c, w := test_helper.MockGin()
    c.Request.URL.RawQuery = "id=1"

    expectedService := model.Service{}
    handler.HandleGetService(c) // assuming it will return a http status code and a model.Service struct, which will be recorded by w
    assert.Equal(suite.T(), http.StatusOK, w.Code)
    expected, _ := json.Marshal(expectedService)
    assert.Equal(suite.T(), string(expected), w.Body.String())
}

To emulate a post request with a json payload

    c, w := test_helper.MockGin()
    jsonPayload := `{
        "hi":  "there"
    }`
    c.Request.Body = io.NopCloser(strings.NewReader(jsonPayload))
    c.Request.Header.Set("Content-Type", "application/json")

Troubleshooting¶

problems in binding `bool` field with `binding:"required"` tag¶

You can only use *bool

https://github.com/gin-gonic/gin/issues/685

HTTP Client¶

Proxy¶

func NewHTTPClientWithProxy(proxyURL string) *resty.Client {
    client := resty.New()
    client.SetProxy(proxyURL)
    return client
}

proxyURL format: http://<username>:<password>@<host>:<port>

or http://<host>:<port> without authentication

Remember to use http even for https!

Logging with Logrus¶

github.com/sirupsen/logrus

Write to local file¶

logger := logrus.New()
currentTime := time.Now()
today := currentTime.Format("2006-01-02")
logFile := fmt.Sprintf("log_%s.txt", today)
f, err := os.OpenFile(logFile, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
if err != nil {
    fmt.Println("Failed to create logfile" + logFile)
    panic(err)
}
logger.SetOutput(f)

https://www.golinuxcloud.com/golang-logrus/

AES Encryption¶

Best practice: generate random IV each time and prepend it to your encrypted text. When decrypting, extract the IV from the encrypted text. See https://stackoverflow.com/questions/8041451/

Implementation

package main

import (
    "crypto/aes"
    "crypto/cipher"
    "crypto/rand"
    "encoding/base64"
    "fmt"
    "io"
)

func main() {
    originalText := "encrypt this golang"
    fmt.Println(originalText)

    key := []byte("example key 1234")

    // encrypt value to base64
    cryptoText := encrypt(key, originalText)
    fmt.Println(cryptoText)

    // encrypt base64 crypto to original value
    text := decrypt(key, cryptoText)
    fmt.Printf(text)
}

// encrypt string to base64 crypto using AES
func encrypt(key []byte, text string) string {
    // key := []byte(keyText)
    plaintext := []byte(text)

    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }

    // The IV needs to be unique, but not secure. Therefore it's common to
    // include it at the beginning of the ciphertext.
    ciphertext := make([]byte, aes.BlockSize+len(plaintext))
    iv := ciphertext[:aes.BlockSize]
    if _, err := io.ReadFull(rand.Reader, iv); err != nil {
        panic(err)
    }

    stream := cipher.NewCFBEncrypter(block, iv)
    stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)

    // convert to base64
    return base64.URLEncoding.EncodeToString(ciphertext)
}

// decrypt from base64 to decrypted string
func decrypt(key []byte, cryptoText string) string {
    ciphertext, _ := base64.URLEncoding.DecodeString(cryptoText)

    block, err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }

    // The IV needs to be unique, but not secure. Therefore it's common to
    // include it at the beginning of the ciphertext.
    if len(ciphertext) < aes.BlockSize {
        panic("ciphertext too short")
    }
    iv := ciphertext[:aes.BlockSize]
    ciphertext = ciphertext[aes.BlockSize:]

    stream := cipher.NewCFBDecrypter(block, iv)

    // XORKeyStream can work in-place if the two arguments are the same.
    stream.XORKeyStream(ciphertext, ciphertext)

    return fmt.Sprintf("%s", ciphertext)
}

https://gist.github.com/manishtpatel/8222606

AWS¶

S3¶

ls your bucket & get a file from your bucket

package main

import (
    "fmt"
    "os"

    "github.com/aws/aws-sdk-go/aws"
    "github.com/aws/aws-sdk-go/aws/credentials"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/s3"
    "github.com/joho/godotenv"
)

func main() {
    godotenv.Load()
    vosEndpoint := os.Getenv("VOS_ENDPOINT")
    vosKey := os.Getenv("VOS_KEY")
    vosSecret := os.Getenv("VOS_SECRET")
    sess, err := session.NewSession(&aws.Config{
        Credentials:      credentials.NewStaticCredentials(vosKey, vosSecret, ""),
        Endpoint:         aws.String(vosEndpoint),
        Region:           aws.String("us-east-1"),
        DisableSSL:       aws.Bool(false),
        S3ForcePathStyle: aws.Bool(true)},
    )
    if err != nil {
        panic(err)
    }

    svc := s3.New(sess)

    // ls all your buckets
    output, err := svc.ListBuckets(nil)
    if err != nil {
        panic(err)
    }
    fmt.Println(output)

    // get file from a bucket
    bucketName := "mybucket"
    fileName := "index.html"
    file, err := svc.GetObject(&s3.GetObjectInput{
        Bucket: aws.String(bucketName),
        Key:    aws.String(fileName),
    })
    if err != nil {
        panic(err)
    }
    defer file.Body.Close()
    fmt.Println(file)
}

Swaggo¶

https://github.com/swaggo/swag

Create API docs with go comments!

Install¶

go install github.com/swaggo/swag/cmd/swag@latest

Usage¶

//go:generate swag init --dir=<path/to/apis> --generalInfo=<path/to/swaggo-init-file> --output=<path/to/desired-doc-directory> --parseInternal --pd

In your swaggo init file

package handler

import (
    "net/http"

    _ "<path-to-doc-directory>"

    "github.com/gin-gonic/gin"
    swaggoFiles "github.com/swaggo/files"
    ginSwagger "github.com/swaggo/gin-swagger"
)

// @title My API
// @version 1.0
// @description This is my API

// @schemes http https
// @host localhost:8080
// @BasePath /api/v1

// RegisterSwaggoHandler swaggo
func RegisterSwaggoHandler(router *gin.Engine) {
    router.GET("/api/swagger", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, "/api/swagger/index.html") })
    router.GET("/api/swagger/*any", ginSwagger.WrapHandler(swaggoFiles.Handler))
}

Add comments before your API

// HandleGetServiceInfo Swagger
// @Summary      Get info
// @Description  Get info with id
// @Accept       json
// @Produce      json
// @Param        id      query    string    true    "id"
// @Success      200  {object}  model.Info
// @Failure      400  {string}  string ""
// @Failure      403  {string}  string ""
// @Failure      404  {string}  string ""
// @Router       /info [get]
func HandleGetInfo(){}

Add example values¶

type Product struct {
    ID       string            `json:"id" example:"1"`
    Name     string            `json:"name" example:"Product Name"`
    MiMappa  map[string]string `json:"mi_mappa" example:"key1:val1,key2:val2"`
}

See https://github.com/swaggo/swag/blob/master/example/object-map-example/controller/response.go

Define enums¶

type Product struct {
    ID       string            `json:"id" example:"1"`
    Name     string            `json:"name" example:"Product Name"`
    Type     string            `json:"name" enums:"TypeA,TypeB,TypeC" example:"TypeA"`
}

Troubleshooting¶

Some weird fake error¶

You may have internal packages of the same name. Please change one of them, even if you alias when importing.

See https://github.com/swaggo/swag/issues/817#issuecomment-1001845616.

Workspace¶

See https://earthly.dev/blog/go-workspaces/

Basically only use it when you want to use some local modules.

e.g. You're using a module github.com/alpha/beta, but you're also developing that module. Without workspace or replace in go.mod, you can only use what is on the web, but with workspace or replace in go.mod, you can use the local version.

With workspace, there will be a go.work file which you'll need to ignore in your repo before checking out, and with replace, you'll need to remove those lines in go.mod before checking out. The former saves more hassle when dealing with a lot of local modules.

Troubleshooting¶

VsCode: could not import strconv¶

command palette -> Go: Install/Update Tools

https://stackoverflow.com/a/64921674/15493213

VsCode: undeclared name¶

Scenario:

VsCode not recognizing functions in the same package

e.g.

bruh.go

package bruh

func Hello() string {
    return "Hello"
}

bruh_test.go

package bruh
import (
    "testing"

    "github.com/stretchr/testify/assert"
)

func TestHello(t *testing.T) {
    assert.Equal(t, Hello(), "Hello")
}

Yet it shows undeclared name: Hello on Hello()

Solution:

https://stackoverflow.com/a/59485684/15493213

/usr/local/Cellar/go/1.19.3/libexec/bin/go: no such file or directory¶

If you're using Homebrew, then change your GOROOT

export GOROOT=/usr/local/opt/go/libexec

If you have multiple versions installed, replace go with go@version. You can ls /usr/local/opt | grep go to check your versions.

See this Stack Overflow answer

VsCode: inline go generate not recognizing your go path¶

error:

executable file not found in $PATH

Just close the window and reopen. Reloading won't work!

Go¶

Install¶

With HomeBrew (MacOS)¶

Style¶

Rules¶

function name¶

Init¶

Dependencies¶

Install a specific module¶

Install current project's dependencies¶

Change module path¶

go get from private domain/repo¶

Import¶

Run¶

Garbage Collection¶

Internal Documentations¶

Documenting your codes¶

CLI doc¶

Web doc¶

Environmental variables¶

Go Env¶

Dotenv¶

Viper¶

Slice¶

The internal of slice¶

How append works¶

Slice of Values vs. Slice of Pointers¶

Docstring¶

Interface¶

Channel¶

Dealing with Json¶

Read json from file¶

grpc¶

GORM¶

Execute raw query¶

Enum¶

JSON¶

Transaction¶

Upsert¶

hooks¶

Select 2 interlinked tables¶

Set a nullable field back to null¶

Error¶

Logging¶

AutoMigrate¶

ORM¶

#GORM¶

Ent¶

Migration¶

db migration¶

golang-migrate¶

goose¶

Atlas¶

Setup¶

Starting with existing tables¶

Auto generate migration file¶

Check migration status¶

Run migrations¶

Problems¶

Goroutine¶

With WaitGroup¶

Limit amount of goroutines¶

Fx - dependency injection¶

Context timeout¶

Unit testing¶

Writing test files¶

Run something after each unit test¶

Run Tests¶

VsCode helper¶

assert equal of list ignoring order¶

Benchmarking¶

Mock¶

GoMock¶

sqlmock¶

Gin¶

Binding parameters or body¶

mock¶

Troubleshooting¶

problems in binding bool field with binding:"required" tag¶

HTTP Client¶

#GORM ¶

problems in binding `bool` field with `binding:"required"` tag¶