kapetan-io / errors

golang errors package with support for contextual logging with slog

Errors

Is a drop in replacement library for std "errors" package with support for optional fields to support the only handle errors once rule while not losing context where the error occurred.

Usage

Attach fields to an error message using standard types or optionally use slog.Attr attributes.

err := errors.Fields{
    "key1", "value1",
    slog.String("key2", "value2"),
    slog.Duration("expired", time.Second),
}.Errorf("message")

// Extract those attributes when reporting errors via slog
slog.Info("an error occurred!", errors.ToAttr(err))
// INFO an error occurred! err=message key1=value1 key2=value2 expired=1s

Use standard introspection functions to extract fields

var f errors.HasFields
if errors.As(wrap, &f) {
    slog.Error("this error has log fields", f.Fields()...)
}

Each call on the call stack can add to the list of fields as needed.

Convenience to std error library methods

Provides pass through access to the standard errors.Is(), errors.As(), errors.Unwrap() so you don't need to import this package and the standard error package.

Support for standard golang introspection functions

Errors wrapped with errors.Fields{} are compatible with standard library introspection functions errors.Unwrap(), errors.Is() and errors.As()

ErrQuery := errors.New("query error")
wrap := errors.Fields{"key1", "value1"}.Errorf("message: %w", err)
errors.Is(wrap, ErrQuery) // == true

Custom Error types

You can even implement custom error types which can pass along fields by implementing the errors.HasFields interface.

type ErrHasFields struct {
	M string
	F []any
}

func (e *ErrHasFields) Error() string {
	return e.M
}

func (e *ErrHasFields) Fields() []any {
	return e.F
}