extracting json part from the error message.

errors.go

// CustomError stores a part of the complete API error 
type CustomError struct {
	Code   string `json:"code"`
	Reason string `json:"reason"`
}

// Error implements the error interface
func (e *CustomError) Error() string {
	return fmt.Sprintf("%s - %s", e.Code, e.Reason)
}

var jsonRegex *regexp.Regexp
var once sync.Once
var regexErr error

func getJSONRegex() (*regexp.Regexp, error) {

	once.Do(func() {
		jsonRegex, regexErr = regexp.Compile(`\{.*\}`)
	})
	return jsonRegex, regexErr

}

// extractJSON uses regex to find JSON content within a string
func extractJSON(s string) (string, error) {
	re, err := getJSONRegex()
	if err != nil {
		return "", fmt.Errorf("failed to compile regex: %v", err)
	}
	match := re.FindString(s)
	if match == "" {
		return "", fmt.Errorf("no JSON object found in the string")
	}
	return match, nil
}

// ParseErrorResponse extracts and parses the JSON error response
func ParseErrorResponse(errorMsg string) (*CustomError, error) {
	jsonStr, err := extractJSON(errorMsg)
	if err != nil {
		return nil, fmt.Errorf("failed to extract JSON: %v", err)
	}

	var customErr CustomError
	err = json.Unmarshal([]byte(jsonStr), &customErr)
	if err != nil {
		return nil, fmt.Errorf("failed to parse error response: %v", err)
	}
	return &customErr, nil
}