How to handle errors in Go?

Handling errors in Go is an important aspect of writing robust and reliable code. Go's error handling philosophy encourages explicit handling of errors, making it clear when and where errors can occur. Here are some common techniques and best practices for handling errors in Go:

1. Use the error Type:

Go uses the built-in error type to represent errors. A function that might encounter an error typically returns a value of type error. You can create custom error types or use the errors.New() function to create simple error instances.

import "errors"

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

2. Check Errors Explicitly:

Always check the returned error value after calling a function that can return an error. Ignoring errors can lead to unexpected behavior. Use conditional statements or if err != nil to handle errors.

result, err := divide(10, 2)
if err != nil {
    fmt.Println("Error:", err)
} else {
    fmt.Println("Result:", result)
}

3. Handle Errors at the Right Level:

Handle errors at the appropriate level of your code. If a function cannot recover from an error, it should return the error to its caller. If a function can recover or handle the error locally, it can do so and continue execution.

4. Use Multiple Return Values:

Functions can return multiple values, including an error. This allows you to return both the result and an error status, making error handling more idiomatic and efficient.

5. panic and recover:

Go has the panic and recover mechanisms for handling exceptional situations, but they are typically used for severe errors and should not be used for regular error handling. panic causes the program to halt and exit, and recover is used to catch and handle panics.

6. Error Wrapping:

Go 1.13 introduced the errors.Wrap() function and related functions in the errors package for creating wrapped errors. Wrapping errors provides additional context about where an error occurred while preserving the original error message.

import "github.com/pkg/errors"

func readFile(filename string) ([]byte, error) {
    data, err := ioutil.ReadFile(filename)
    if err != nil {
        return nil, errors.Wrap(err, "readFile failed")
    }
    return data, nil
}

7. Use fmt.Errorf():

The fmt package provides the Errorf() function to create formatted error messages. This is useful for including dynamic information in error messages.

func connectToDatabase(username, password string) error {
    if username == "" || password == "" {
        return fmt.Errorf("username and password are required")
    }
    // Connect logic...
    return nil
}

8. Logging Errors:

Logging errors helps with debugging and understanding the flow of your program. Use a logging package like log or a structured logging library to log errors along with relevant context.

9. Handle Errors in a Central Place:

For more complex applications, consider centralizing error handling logic to make it consistent across the application. This can help with logging, reporting, and maintaining error handling strategies.

In summary, Go emphasizes explicit error handling to ensure robust and reliable code. By checking errors explicitly, using multiple return values, and considering error wrapping, you can write code that gracefully handles errors and provides useful diagnostic information when things go wrong.