Why is the pkg/errors tripartite library more recommended for go language error handling?

Hello everyone , I am a frank.

01

Introduce

Go Language project development , We usually need to deal with errors in code logic ,Go Official standard library errors It provides us with some methods , such as New,Unwarp,Is and As.

among , What we use most is New, however , In our reality Go Project under development , Will use some layered design , such as MVC,Clean Architecture etc. .

In projects that use hierarchical design , If we use Go Standard library errors Wrong definition , You will encounter the problem of error coverage .

02

About the standard library errors Error coverage problem

Go Standard library errors Of New Method , Only a simple error message can be defined , In the project code of hierarchical design , You will encounter the problem of error coverage , For example, our sample project code , It uses Clean Architecture Layered design .

Project hierarchical directory ：

.
├── app
│   └── main.go
├── domain
│   └── user.go
├── go.mod
├── go.sum
└── user
    ├── delivery
    │   └── http
    │       └── user.go
    ├── repository
    │   └── mysql
    │       └── user.go
    └── usecase
        └── user.go

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In the example project , So let's use Go Standard library errors Of New Method definition error , The code snippet is as follows ：

repository layer ：

func (m *mysqlUserRepository) GetUserById(ctx context.Context, user *domain.User) (err error) {
 _, err = m.DB.Get(user)
 fmt.Printf("mysqlUserRepository || GetUserById() || uid=%v || err=%v\n", user.Id, err)
 return
}

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usecase layer ：

func (u *userUsecase) GetUserById(ctx context.Context, user *domain.User) (err error) {
 if user.Id == 0 {
  err = errors.New("invalid request parameter")
 }
 err = u.userRepo.GetUserById(ctx, user)
 fmt.Printf("userUsecase || GetUserById() || uid=%v || err=%v\n", user.Id, err)
 return
}

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delivery layer ：

func (u *UserHandler) GetUserById(c echo.Context) error {
 idP, err := strconv.Atoi(c.Param("id"))
 if err != nil {
  return c.JSON(http.StatusNotFound, err)
 }
 id := int64(idP)
 ctx := c.Request().Context()
 user := &domain.User{
  Id: id,
 }
 err = u.UserUsecase.GetUserById(ctx, user)
 if err != nil {
  err = errors.New("UserUsecase error")
  fmt.Printf("UserHandler || GetUserById() || uid=%v || err=%+v\n", id, err)
  return c.JSON(http.StatusInternalServerError, err)
 }
 return c.JSON(http.StatusOK, user)
}

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Read the above three pieces of code , We can find out , We have error handling code in each layer , We deliberately use the wrong request parameters , And write the password of the database connection incorrectly , The error that triggered the application .

Output results ：

mysqlUserRepository || GetUserById() || uid=1 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
userUsecase || GetUserById() || uid=1 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
UserHandler || GetUserById() || uid=1 || err=UserUsecase error

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Read the output , We can find out ,usecase Layer definition error , The called repository Layer returns error coverage ;delivery Layer definition errors will usecase Error coverage returned by layer .

Because we printed errors on each layer , Check carefully , You can still locate the error , But it's still complicated , Not only do printing errors at each level make the code less elegant , And it can't quickly locate the error .

How to solve this problem ？ Use a tripartite Library github.com/pkg/errors Replace Go Standard library errors.

03

Three party Library pkg/errors

Use a tripartite Library pkg/errors It can solve the problem that the error information of call stack overlaps each other in the project of hierarchical design , It can output wrong stack information for us , New error messages can be added to the existing error messages , So as to solve the problem that the output error information lacks context .

So let's revise that Part 02 Example code for , take Go Standard library errors Replace with a third-party library pkg/errors, I believe careful readers have found , Because the names of these two bags are the same , And they all have New Method , So it's convenient to replace , Just replace the imported package .

Sample code ：

import (
 // "errors"
 "fmt"
 "github.com/labstack/echo/v4"
 "github.com/pkg/errors"
 "github.com/weirubo/learn_go/lesson41/domain"
 "net/http"
 "strconv"
)

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Output result after replacement ：

mysqlUserRepository || GetUserById() || uid=0 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
userUsecase || GetUserById() || uid=0 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
UserHandler || GetUserById() || uid=0 || err=UserUsecase error
github.com/weirubo/learn_go/lesson41/user/delivery/http.(*UserHandler).GetUserById
        /Users/frank/GolandProjects/learn_go/lesson41/user/delivery/http/user.go:36
github.com/labstack/echo/v4.(*Echo).add.func1
        /Users/frank/go/pkg/mod/github.com/labstack/echo/[email protected]/echo.go:520
github.com/labstack/echo/v4.(*Echo).ServeHTTP
        /Users/frank/go/pkg/mod/github.com/labstack/echo/[email protected]/echo.go:630
net/http.serverHandler.ServeHTTP
        /usr/local/go/src/net/http/server.go:2916
net/http.(*conn).serve
        /usr/local/go/src/net/http/server.go:1966
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1571

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Read the output above , We can find that the error handling package consists of Go Standard library errors Replace with a third-party library pkg/errors after , The output results are not only Go Standard library errors Error messages for , Wrong stack information is also output .

So far, , We just switched the imported package , The error message contains the wrong stack information , however , Our error coverage problem has not been solved , We also need to use third-party libraries pkg/errors Of Wrap Method , Let's change the code again , take New Replace the method with Wrap Method .

delivery layer ：

...
if err != nil {
  // err = errors.New("UserUsecase error")
  err = errors.Wrap(err, "UserUsecase error")
  fmt.Printf("UserHandler || GetUserById() || uid=%v || err=%+v\n", id, err)
  return c.JSON(http.StatusInternalServerError, err)
 }
...

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Read the code above , We modify delivery Layer error handling code , take New Replace the method with Wrap Method , It can be based on the existing error information , Attach new error information and wrong stack information .

Output results ：

mysqlUserRepository || GetUserById() || uid=0 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
userUsecase || GetUserById() || uid=0 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
UserHandler || GetUserById() || uid=0 || err=Error 1045: Access denied for user 'root'@'172.17.0.1' (using password: YES)
UserUsecase error
github.com/weirubo/learn_go/lesson41/user/delivery/http.(*UserHandler).GetUserById
        /Users/frank/GolandProjects/learn_go/lesson41/user/delivery/http/user.go:37
github.com/labstack/echo/v4.(*Echo).add.func1
        /Users/frank/go/pkg/mod/github.com/labstack/echo/[email protected]/echo.go:520
github.com/labstack/echo/v4.(*Echo).ServeHTTP
        /Users/frank/go/pkg/mod/github.com/labstack/echo/[email protected]/echo.go:630
net/http.serverHandler.ServeHTTP
        /usr/local/go/src/net/http/server.go:2916
net/http.(*conn).serve
        /usr/local/go/src/net/http/server.go:1966
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1571

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Read the above output , We can find it in delivery Error message defined by layer , No more override calls usecase The error message returned by the layer method , Both are output normally .

It should be noted that , Output error information and stack information at the same time , Placeholders need to use %+v, Don't output stack information at every layer , This will repeatedly print stack information , Usually, if the stack information is printed on the lower layer , Don't print stack information on the upper layer .

Besides , Three party Library pkg/errors The other two methods WithMessage and WithStack It's also more commonly used , They are based on the existing error messages , Attach new error information and wrong stack information , We are in the actual project development , You can choose to use the appropriate method as needed .

04

summary

In this article, we talked about using Go Standard library errors Limitations and deficiencies of error handling , In order to solve its shortcomings , We introduced the use of third-party libraries pkg/errors Replace Go Standard library errors, And third-party library pkg/errors How to use several common methods of .

About the third-party library pkg/errors More ways , Interested readers can read the document to learn how to use .

Reference material ：

1. https://pkg.go.dev/github.com/pkg/[email protected]
2. https://pkg.go.dev/errors
3. https://dave.cheney.net/2016/06/12/stack-traces-and-the-errors-package
4. https://morioh.com/p/777d15fe7828