go_encryptedstring/encryptedString.go

package encryptedstring

import (
	"encoding/hex"
	"encoding/xml"
	"fmt"
	"strings"
)

// IPotentiallyUnencrypted describes an interface for a struct which was potentially not encrypted
type IPotentiallyUnencrypted interface {
	// WasUnencrypted determines wheter the value was set from data marked as unencrypted
	WasUnencrypted() bool
}

// EncryptedString is a string wrapper which will en-/decrypt the actual value upon (un)marshalling
type EncryptedString struct {
	data string
}

// New returns a new EncryptedString instance with a specific value
func New(value string) EncryptedString {
	es := EncryptedString{}
	es.encrypt(value)
	return es
}

// Value returns the current value
func (es EncryptedString) Value() string {
	if decrypted, err := es.decrypt(); err == nil {
		return decrypted
	}
	return ""
}

// String implements the fmt.Stringer interface
func (es EncryptedString) String() string {
	if es.WasUnencrypted() {
		if data, err := getEncryptionProvider().Encrypt([]byte(es.data)); err == nil {
			return defaultIdentifier + hex.EncodeToString(data)
		}
	} else if strings.HasPrefix(es.data, defaultIdentifier) {
		return es.data
	}
	return ""
}

// SetValue sets the current value
func (es *EncryptedString) SetValue(newValue string) {
	es.encrypt(newValue)
}

// WasUnencrypted determines wheter the value was set from data marked as unencrypted
func (es EncryptedString) WasUnencrypted() bool {
	return !strings.HasPrefix(es.data, defaultIdentifier)
}

// MarshalJSON satisfies the json.Marshaler interface
func (es EncryptedString) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf("\"%s\"", es.String())), nil
}

// UnmarshalJSON satisfies the json.Unmarshaler interface
func (es *EncryptedString) UnmarshalJSON(data []byte) error {
	cleanData, ok := unquoteBytes(data)
	if ok {
		es.data = string(cleanData)
		if _, err := es.decrypt(); err == nil {
			return nil
		}
	}
	return fmt.Errorf("'%s' cannot be unmarshalled from JSON", string(data))
}

// MarshalXML satisfies the xml.Marshaler interface
func (es EncryptedString) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
	err := e.EncodeToken(start)
	if nil != err {
		return err
	}
	stringValue := es.String()
	err = e.EncodeToken(xml.CharData([]byte(stringValue)))
	if nil != err {
		return err
	}
	err = e.EncodeToken(xml.EndElement{
		Name: start.Name,
	})
	if nil != err {
		return err
	}
	return e.Flush()
}

// UnmarshalXML satisfies the xml.Unmarshaler interface
func (es *EncryptedString) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
	var (
		token xml.Token
		err   error
	)

Loop:
	for {
		if token, err = d.Token(); err != nil {
			return err
		}

		if token == nil {
			break
		}

		switch se := token.(type) {
		case xml.StartElement:
			return fmt.Errorf("bad XML syntax")
		case xml.CharData:
			stringData := strings.Trim(string(se), " \t\r\n")
			if 0 < len(stringData) {
				es.data = stringData
				if _, err = es.decrypt(); err != nil {
					return err
				}
			}
		case xml.EndElement:
			break Loop
		}
	}

	return nil
}

// MarshalText satisfies the TextMarshaler interface
func (es EncryptedString) MarshalText() (text []byte, err error) {
	return []byte(es.String()), nil
}

// UnmarshalText satisfies the TextUnmarshaler interface
func (es *EncryptedString) UnmarshalText(text []byte) error {
	es.data = string(text)
	if _, err := es.decrypt(); err != nil {
		return err
	}
	return nil
}

func (es *EncryptedString) encrypt(value string) {
	payload := []byte(value)
	additionalBytes := len(payload) % 16
	for i := 0; i < additionalBytes; i++ {
		payload = append(payload, 0)
	}
	if encrypted, err := getEncryptionProvider().Encrypt(payload); err == nil {
		es.data = defaultIdentifier + hex.EncodeToString(encrypted)
	}
}

func (es *EncryptedString) decrypt() (decrypted string, err error) {
	if strings.HasPrefix(es.data, defaultIdentifier) {
		var payload []byte
		payload, err = hex.DecodeString(es.data[len(defaultIdentifier):])
		if err == nil {
			if unencrypted, err := getEncryptionProvider().Decrypt(payload); err == nil {
				for len(unencrypted) > 0 {
					if unencrypted[len(unencrypted)-1] == 0 {
						unencrypted = unencrypted[:len(unencrypted)-1]
					} else {
						break
					}
				}
				decrypted = string(unencrypted)
			}
		}
	} else {
		decrypted = es.data
	}
	return
}