add go-license

go-license/go.mod

@@ -0,0 +1,3 @@
+module git.rdctd.de/timo/blog/go-license
+
+go 1.23.2

go-license/license.go

@@ -0,0 +1,89 @@
+package golicense
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"time"
+)
+
+var (
+	secret            = []byte("superDuperSecret123!")
+	ErrorHmacMismatch = errors.New("checksum mismatch - not a valid license key")
+)
+
+type Data struct {
+	Feature1  bool
+	Feature2  int
+	ValidTill time.Time
+	CreatedAt time.Time
+}
+
+type Envelope struct {
+	Data     Data
+	Checksum []byte
+}
+
+func (e *Envelope) String() (string, error) {
+	d, err := json.Marshal(e)
+	if err != nil {
+		return "", err
+	}
+
+	str := base64.StdEncoding.EncodeToString(d)
+	return str, nil
+}
+
+func New(feature1 bool, feature2 int, expire int) (*Envelope, error) {
+	d := Data{
+		Feature1:  feature1,
+		Feature2:  feature2,
+		ValidTill: time.Now().AddDate(0, 0, expire),
+	}
+
+	e := Envelope{
+		Data: d,
+	}
+
+	db, err := json.Marshal(&d)
+	if err != nil {
+		return nil, err
+	}
+
+	hmac := hmac.New(sha256.New, secret)
+	hmac.Write(db)
+	dh := hmac.Sum(nil)
+
+	e.Checksum = dh
+
+	return &e, nil
+}
+
+func Verify(in string) (*Envelope, error) {
+	d, err := base64.StdEncoding.DecodeString(in)
+	if err != nil {
+		return nil, err
+	}
+
+	var e Envelope
+	if err := json.Unmarshal(d, &e); err != nil {
+		return nil, err
+	}
+
+	db, err := json.Marshal(e.Data)
+	if err != nil {
+		return nil, err
+	}
+
+	hm := hmac.New(sha256.New, secret)
+	hm.Write(db)
+	dh := hm.Sum(nil)
+
+	if !hmac.Equal(e.Checksum, dh) {
+		return nil, ErrorHmacMismatch
+	}
+
+	return &e, nil
+}

go-license/license_test.go

@@ -0,0 +1,57 @@
+package golicense
+
+import (
+	"testing"
+)
+
+func TestVerify(t *testing.T) {
+	e, err := New(true, 5, 365)
+	if err != nil {
+		t.Error(err)
+	}
+
+	key, err := e.String()
+	if err != nil {
+		t.Error(err)
+	}
+
+	e2, err := Verify(key)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if e2.Data.Feature1 != e.Data.Feature1 {
+		t.Error("Feature1 mismatch")
+	}
+
+	if e2.Data.Feature2 != e.Data.Feature2 {
+		t.Error("Feature2 mismatchh")
+	}
+}
+
+func TestVerifyMismatch(t *testing.T) {
+	e1, _ := New(true, 5, 365)
+
+	e2, _ := New(false, 5, 365)
+
+	key1, _ := e1.String()
+	key2, _ := e2.String()
+
+	if key1 == key2 {
+		t.Error("same keys, different license data")
+	}
+}
+
+func TestVerifyModifiedData(t *testing.T) {
+	e, _ := New(false, 5, 365)
+
+	e.Data.Feature1 = true
+
+	key, _ := e.String()
+
+	_, err := Verify(key)
+
+	if err != ErrorHmacMismatch {
+		t.Error("No HmacMismatch error")
+	}
+}