How to propagate and handle context-aware errors in Go?

In Go, you can propagate and handle context-aware errors using the "errors" package along with the "context" package. Here's a step-by-step guide on how to achieve that:

Define a custom error type that includes a context.Context value. This will allow you to attach context information to the error. For example:

type MyError struct {
    ctx    context.Context
    errMsg string
}

Implement the error interface for your custom error type. This means implementing the Error() method that returns the error message. For example:

func (err *MyError) Error() string {
    return err.errMsg
}

When creating an error, attach the relevant context using the context package. For example:

func Something() error {
    ctx := context.WithValue(context.Background(), "key", "value")
    // ... do some processing
    if errOccurred {
        return &MyError{ctx, "An error occurred"}
    }
    return nil
}

To propagate the context-aware error, simply return it from your function or method.

func SomeFunction() error {
    // ...
    return Something()
}

When handling the error, you can retrieve the context information using the Context.Value() method. For example:

func HandleError(err error) {
    if myErr, ok := err.(*MyError); ok {
        value := myErr.ctx.Value("key")
        fmt.Println("Context value:", value)
    }

    // ... handle the error accordingly
}

By using this approach, you can propagate and handle context-aware errors in Go, allowing you to attach relevant context information and handle errors more effectively.