Allow to re-obtain atomically with custom tokens

CHANGELOG.md

@@ -1,3 +1,7 @@
+## v0.9.4
+
+- Fix: allow to re-obtain locks with tokens [#71](https://github.com/bsm/redislock/pull/71)
+
 ## v0.9.3
 
 - Feature: allow custom lock tokens [#66](https://github.com/bsm/redislock/pull/66)

redislock.go

@@ -18,6 +18,12 @@ var (
 	luaRefresh = redis.NewScript(`if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("pexpire", KEYS[1], ARGV[2]) else return 0 end`)
 	luaRelease = redis.NewScript(`if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end`)
 	luaPTTL    = redis.NewScript(`if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("pttl", KEYS[1]) else return -3 end`)
+	luaObtain  = redis.NewScript(`
+if redis.call("set", KEYS[1], ARGV[1], "NX", "PX", ARGV[3]) then return redis.status_reply("OK") end
+
+local offset = tonumber(ARGV[2])
+if redis.call("getrange", KEYS[1], 0, offset-1) == string.sub(ARGV[1], 1, offset) then return redis.call("set", KEYS[1], ARGV[1], "PX", ARGV[3]) end
+`)
 )
 
 var (
@@ -31,7 +37,6 @@ var (
 // RedisClient is a minimal client interface.
 type RedisClient interface {
 	redis.Scripter
-	SetNX(ctx context.Context, key string, value interface{}, expiration time.Duration) *redis.BoolCmd
 }
 
 // Client wraps a redis client.
@@ -60,6 +65,7 @@ func (c *Client) Obtain(ctx context.Context, key string, ttl time.Duration, opt
 	}
 
 	value := token + opt.getMetadata()
+	ttlVal := strconv.FormatInt(int64(ttl/time.Millisecond), 10)
 	retry := opt.getRetryStrategy()
 
 	// make sure we don't retry forever
@@ -71,7 +77,7 @@ func (c *Client) Obtain(ctx context.Context, key string, ttl time.Duration, opt
 
 	var ticker *time.Ticker
 	for {
-		ok, err := c.obtain(ctx, key, value, ttl)
+		ok, err := c.obtain(ctx, key, value, len(token), ttlVal)
 		if err != nil {
 			return nil, err
 		} else if ok {
@@ -98,8 +104,14 @@ func (c *Client) Obtain(ctx context.Context, key string, ttl time.Duration, opt
 	}
 }
 
-func (c *Client) obtain(ctx context.Context, key, value string, ttl time.Duration) (bool, error) {
-	return c.client.SetNX(ctx, key, value, ttl).Result()
+func (c *Client) obtain(ctx context.Context, key, value string, tokenLen int, ttlVal string) (bool, error) {
+	_, err := luaObtain.Run(ctx, c.client, []string{key}, value, tokenLen, ttlVal).Result()
+	if err == redis.Nil {
+		return false, nil
+	} else if err != nil {
+		return false, err
+	}
+	return true, nil
 }
 
 func (c *Client) randomToken() (string, error) {

redislock_test.go

@@ -95,18 +95,39 @@ func TestObtain_custom_token(t *testing.T) {
 	rc := redis.NewClient(redisOpts)
 	defer teardown(t, rc)
 
-	lock, err := Obtain(ctx, rc, lockKey, time.Hour, &Options{Token: "foo", Metadata: "bar"})
+	// obtain lock
+	lock1, err := Obtain(ctx, rc, lockKey, time.Hour, &Options{Token: "foo", Metadata: "bar"})
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer lock.Release(ctx)
+	defer lock1.Release(ctx)
 
-	if exp, got := "foo", lock.Token(); exp != got {
-		t.Fatalf("expected %v, got %v", exp, got)
+	if exp, got := "foo", lock1.Token(); exp != got {
+		t.Errorf("expected %v, got %v", exp, got)
+	}
+	if exp, got := "bar", lock1.Metadata(); exp != got {
+		t.Errorf("expected %v, got %v", exp, got)
 	}
-	if exp, got := "bar", lock.Metadata(); exp != got {
+
+	// try to obtain again
+	_, err = Obtain(ctx, rc, lockKey, time.Hour, nil)
+	if exp, got := ErrNotObtained, err; !errors.Is(got, exp) {
 		t.Fatalf("expected %v, got %v", exp, got)
 	}
+
+	// allow to re-obtain lock if token is known
+	lock2, err := Obtain(ctx, rc, lockKey, time.Hour, &Options{Token: "foo", Metadata: "baz"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer lock2.Release(ctx)
+
+	if exp, got := "foo", lock2.Token(); exp != got {
+		t.Errorf("expected %v, got %v", exp, got)
+	}
+	if exp, got := "baz", lock2.Metadata(); exp != got {
+		t.Errorf("expected %v, got %v", exp, got)
+	}
 }
 
 func TestObtain_retry_success(t *testing.T) {