Add new error type to send response headers

[thedae]

Added a way to write response headers on error

Usage

If the triggered error implements a Headers() map[string][]string, the returned map will be written as response headers. For example, when implementing a quota system, you could return a 429 with a Retry-After response header like this:

type errProxyQuotaExceeded struct {
	error
	headers map[string][]string
}

func NewErrProxyQuotaExceeded(blockedFor string) error {
	err := errProxyQuotaExceeded{error: errors.New("quota exceeded")}

	err.headers = map[string][]string{
		'Retry-After': {blockedFor},
	}
	return err
}

func (errProxyQuotaExceeded) StatusCode() int {
	return http.StatusTooManyRequests
}

func (e errProxyQuotaExceeded) Headers() map[string][]string {
	return e.headers
}

[github-actions]

This pull request was marked as resolved a long time ago and now has been automatically locked as there has not been any recent activity after it. You can still open a new issue and reference this link.