Error handling in Go: best practices and pitfalls

In the Go language, error handling is a very important part. Good error handling can improve program reliability and maintainability, especially in large projects. This article will introduce the best practices for error handling in the Go language and list some common pitfalls.

Basics of error handling: error type

In Go language, error type is an interface with Error() method, for example:

type error interface {
    Error() string
}

Use Go language default The error type is very simple:

err := errors.New("this is an error message")
if err != nil {
    fmt.Println(err)
}

It's also easy to use custom error types. Just implement the Error() method:

type MyError struct {
    Msg string
}

func (e *MyError) Error() string {
    return fmt.Sprintf("MyError: %s", e.Msg)
}

func main() {
    err := &MyError{Msg: "this is a custom error message"}
    if err != nil {
        fmt.Println(err)
    }
}

Best Practice 1: Don’t ignore errors

Ignoring errors is a very common error handling trap. For example:

file, err := os.Open("file.txt")
// 文件不存在或者打开文件的过程中发生了任何错误
// 都应该进行错误处理，例如：
if err != nil {
    log.Fatal(err)
}
// 这里忽略了err，如果发生了错误，程序会在这一行崩溃
defer file.Close()

This situation may occur in legacy code, or by lazy programmers. To prevent this error, returned errors should always be checked and handled.

Best Practice 2: Return errors as early as possible

In the Go language, error handling is usually handled by returning a value of the error type. Therefore, when an error is found, it should be returned immediately. For example:

func myFunc() error {
    // do something
    if err := someFunc(); err != nil {
        return err  // 尽早返回错误
    }
    // do something else
    if err := anotherFunc(); err != nil {
        return err  // 尽早返回错误
    }
    // do something else
    return nil
}

Returning errors as early as possible can make the code more concise and clear, easy to debug and maintain.

Best Practice 3: Avoid errors caused by local variables

In the Go language, local variables will be automatically recycled at the end of the function. If the variables including error information are at the end of the function statement, problems may arise when an error occurs. For example:

func myFunc() error {
    var data []byte
    // 这里忽略了错误，如果outOfMemory()函数返回了一个非nil值
    // 程序会在下一行崩溃
    outOfMemory()
    // do something with data
    return nil
}

To avoid this situation, variables should be declared before the error checking statement.

func myFunc() error {
    // 先声明错误变量
    var err error
    var data []byte
    if err = outOfMemory(); err != nil {
        return err  // 尽早返回错误
    }
    // do something with data
    return nil
}

Best Practice 4: Use error codes instead of error strings

In the Go language, it is very common to use error strings to describe error messages. However, this approach increases the complexity of the program and makes it more difficult to determine the type of error. Therefore, using error codes instead of error strings is a better choice.

For example:

type MyErrorType int

const (
    ErrOutOfMemory MyErrorType = iota
    ErrInvalidInput
)

func (e MyErrorType) Error() string {
    switch e {
    case ErrOutOfMemory:
        return "out of memory"
    case ErrInvalidInput:
        return "invalid input"
    default:
        return "unknown error"
    }
}

func myFunc() error {
    // 这里返回错误码，可以更好的描述错误信息并且和其他包的错误相对独立
    return ErrOutOfMemory
}

Best practice five: Error handling should be foreseeable and repairable

Error handling should be foreseeable and repairable. This means that programmers should write appropriate error handling code for all error conditions that may occur, and ensure that the error handling code can fix the error or provide accurate error information. For example:

func myFunc() error {
    file, err := os.Create("file.txt")
    if err != nil {
        return fmt.Errorf("cannot create file: %v", err)
    }
    defer func() {
        if err := file.Close(); err != nil {
            log.Fatalf("cannot close file: %v", err)
        }
    }()
    if _, err := file.Write([]byte("hello, world
")); err != nil {
        return fmt.Errorf("write error: %v", err)
    }
    return nil
}

Programmers should clearly describe the problem in error handling, including the cause and solution of the problem. This way, errors can be fixed and resolved more easily.

Trap 1: Use panic() instead of errors

In the Go language, the panic() function is sometimes used instead of errors. The disadvantage of this approach is that if an error occurs, the entire program will crash. Therefore, panic() should be avoided whenever possible. panic() should be used only when it is impossible for the program to continue running.

Trap 2: Do not provide too detailed error information

Providing too detailed error information will increase the complexity of the program and may lead to security risks. Therefore, only necessary error information should be provided, ensuring confidentiality and security.

Trap 3: Don’t praise error handling code

Error handling code is as important as other codes, but you should avoid writing too much and messy error handling code. Error handling code should be clear and unambiguous, but should not be bulky or redundant.

Summary

Error handling is an integral part of Go language programs. Good error handling can improve the reliability and maintainability of your program and help find and fix errors. Use the best practices introduced in this article and avoid common error handling pitfalls to make your Go language programs more stable and robust.

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