go-error-handling

# Go Error Handling

Master Go's error handling patterns including error wrapping, sentinel
errors, custom error types, and the errors package for robust applications.

## Basic Error Handling

**Creating and returning errors:**

```go
package main

import (
    "errors"
    "fmt"
)

func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, errors.New("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)
}
```

**Using fmt.Errorf:**

```go
func processFile(filename string) error {
    if filename == "" {
        return fmt.Errorf("filename cannot be empty")
    }
    // Process file...
    return nil
}
```

## Error Wrapping

**Wrapping errors with context (Go 1.13+):**

```go
import (
    "errors"
    "fmt"
    "os"
)

func readConfig(path string) error {
    _, err := os.Open(path)
    if err != nil {
        return fmt.Errorf("failed to read config: %w", err)
    }
    return nil
}

func main() {
    err := readConfig("config.json")
    if err != nil {
        fmt.Println(err)
        // Output: failed to read config: open config.json: no such file
    }
}
```

**Unwrapping errors:**

```go
func handleError(err error) {
    // Unwrap one level
    unwrapped := errors.Unwrap(err)
    if unwrapped != nil {
        fmt.Println("Unwrapped:", unwrapped)
    }

    // Check if specific error is in chain
    if errors.Is(err, os.ErrNotExist) {
        fmt.Println("File does not exist")
    }
}
```

## Sentinel Errors

**Defining and using sentinel errors:**

```go
package main

import (
    "errors"
    "fmt"
)

var (
    ErrNotFound     = errors.New("resource not found")
    ErrUnauthorized = errors.New("unauthorized access")
    ErrInvalidInput = errors.New("invalid input")
)

func getUser(id int) (string, error) {
    if id < 0 {
        return "", ErrInvalidInput
    }
    if id == 0 {