Go: error handling

  • Go
  • Gabriele Romanato

Programming is inevitably accompanied by errors and unforeseen situations. Effective error handling is an essential part of any software application, as it can affect the stability, reliability and maintainability of the code. In Go, a programming language developed by Google, error handling is addressed in a unique and consistent way, following the languages best practices. In this article, well explore recommended strategies and techniques for handling errors in Go.

Errors as values

A distinctive feature of error handling in Go is the use of errors as values. Instead of throwing exceptions as in many other programming languages, Go uses data types named error to represent error situations. An error is simply an interface that has an Error() method that returns a string describing the error. For example: 


package main

import (
    "fmt"
)

func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, fmt.Errorf("division by zero")
    }
    return a / b, nil
}

func main() {
    result, err := divide(10, 0)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("Result:", result)
}

This approach puts the programmer in full control of error handling and promotes clarity in the code flow.

Error Handling

In Go, error handling is often done using the "check and handle" idiom. This means that after each function call that might return an error, you should check whether an error was returned and, if any, handle it appropriately. This helps avoid silent errors that could lead to unexpected behavior. 


file, err := os.Open("file.txt")
if err != nil {
    fmt.Println("Error opening file:", err)
    return
}
defer file.Close()

// Altre operazioni sul file

In the example above, the os.Open function will return an error if the requested file cannot be opened. Error checking is immediate and if the file open fails, the error will be handled and program flow will be stopped.

Use context

Go provides the context package which offers a way to manage the timeout, cancellation and expiration of operations. This is especially useful when working with network calls or other operations that may take too much time. 


package main

import (
    "context"
    "fmt"
    "net/http"
    "time"
)

func main() {
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()

    req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://example.com", nil)
    if err != nil {
        fmt.Println("Error creating request:", err)
        return
    }

    client := http.DefaultClient
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error making request:", err)
        return
    }
    defer resp.Body.Close()

    // Altre operazioni sulla risposta
}

Error logging

Error logging is a crucial practice for diagnosing and debugging applications. Go offers the log package for basic logging, but many developers prefer more advanced libraries like logrus or zap for more flexibility and functionality. 


package main

import (
    "fmt"
    "log"

    "github.com/sirupsen/logrus"
)

func main() {
    logFile, err := os.Open("app.log")
    if err != nil {
        log.Fatal("Error opening log file:", err)
        return
    }
    defer logFile.Close()

    log.SetOutput(logFile)

    // Utilizzo del logger
    log.Println("App started")
    // ...
    log.Println("App finished")
}

Custom errors

In situations where the standard error types provided by Go arent enough, you can create your own errors by defining new types that implement the error interface. This can help identify and handle specific error situations in your application. 


package main

import (
    "fmt"
)

type CustomError struct {
    ErrorCode int
    Message   string
}

func (e CustomError) Error() string {
    return fmt.Sprintf("Error %d: %s", e.ErrorCode, e.Message)
}

func process(data []int) error {
    if len(data) == 0 {
        return CustomError{ErrorCode: 100, Message: "Empty data"}
    }
    // Altre operazioni
    return nil
}

func main() {
    data := []int{}
    err := process(data)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    fmt.Println("Processing completed successfully")
}

Conclusions

Error handling is a crucial aspect of writing reliable and stable applications. In Go, the approach to error handling through the concept of errors as values, the use of defer , the use of the context package, and the creation of custom errors all contribute to clearer, more robust and maintainable code. Following error handling best practices in Go will not only improve code quality, but will also make it easier to debug and maintain your application in the long run.

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