Fix: Do not use lua cjson library to encode task to json

Go and Lua json libraries encodes json differently (e.g. order of
key/value) and caused a bug when removing tasks that was previously
encoded by Lua json library and redis was receiving a string generated
by Go json library.

internal/rdb/rdb.go

@@ -133,24 +133,29 @@ func (r *RDB) Schedule(msg *TaskMessage, processAt time.Time) error {
 // Retry moves the task from in-progress to retry queue, incrementing retry count
 // and assigning error message to the task message.
 func (r *RDB) Retry(msg *TaskMessage, processAt time.Time, errMsg string) error {
-	bytes, err := json.Marshal(msg)
+	bytesToRemove, err := json.Marshal(msg)
 	if err != nil {
 		return fmt.Errorf("could not marshal %+v to json: %v", msg, err)
 	}
+	modified := *msg
+	modified.Retried++
+	modified.ErrorMsg = errMsg
+	bytesToAdd, err := json.Marshal(&modified)
+	if err != nil {
+		return fmt.Errorf("could not marshal %+v to json: %v", modified, err)
+	}
 	// 	KEYS[1] -> asynq:in_progress
 	//  KEYS[2] -> asynq:retry
-	//  ARGV[1] -> TaskMessage value
+	//  ARGV[1] -> TaskMessage value to remove from InProgress queue
-	//  ARGV[2] -> error message
+	//  ARGV[2] -> TaskMessage value to add to Retry queue
 	//  ARGV[3] -> retry_at UNIX timestamp
 	script := redis.NewScript(`
 	redis.call("LREM", KEYS[1], 0, ARGV[1])
-	local msg = cjson.decode(ARGV[1])
+	redis.call("ZADD", KEYS[2], ARGV[3], ARGV[2])
-	msg["Retried"] = msg["Retried"] + 1
-	msg["ErrorMsg"] = ARGV[2]
-	redis.call("ZADD", KEYS[2], ARGV[3], cjson.encode(msg))
 	return redis.status_reply("OK")
 	`)
-	_, err = script.Run(r.client, []string{inProgressQ, retryQ}, string(bytes), errMsg, processAt.Unix()).Result()
+	_, err = script.Run(r.client, []string{inProgressQ, retryQ},
+		string(bytesToRemove), string(bytesToAdd), processAt.Unix()).Result()
 	return err
 }
 
@@ -160,30 +165,34 @@ func (r *RDB) Retry(msg *TaskMessage, processAt time.Time, errMsg string) error
 func (r *RDB) Kill(msg *TaskMessage, errMsg string) error {
 	const maxDeadTask = 10
 	const deadExpirationInDays = 90
-	bytes, err := json.Marshal(msg)
+	bytesToRemove, err := json.Marshal(msg)
 	if err != nil {
 		return fmt.Errorf("could not marshal %+v to json: %v", msg, err)
 	}
+	modified := *msg
+	modified.ErrorMsg = errMsg
+	bytesToAdd, err := json.Marshal(&modified)
+	if err != nil {
+		return fmt.Errorf("could not marshal %+v to json: %v", modified, err)
+	}
 	now := time.Now()
 	limit := now.AddDate(0, 0, -deadExpirationInDays).Unix() // 90 days ago
 	// KEYS[1] -> asynq:in_progress
 	// KEYS[2] -> asynq:dead
-	// ARGV[1] -> TaskMessage value
+	// ARGV[1] -> TaskMessage value to remove from InProgress queue
-	// ARGV[2] -> error message
+	// ARGV[2] -> TaskMessage value to add to Dead queue
 	// ARGV[3] -> died_at UNIX timestamp
 	// ARGV[4] -> cutoff timestamp (e.g., 90 days ago)
 	// ARGV[5] -> max number of tasks in dead queue (e.g., 100)
 	script := redis.NewScript(`
 	redis.call("LREM", KEYS[1], 0, ARGV[1])
-	local msg = cjson.decode(ARGV[1])
+	redis.call("ZADD", KEYS[2], ARGV[3], ARGV[2])
-	msg["ErrorMsg"] = ARGV[2]
-	redis.call("ZADD", KEYS[2], ARGV[3], cjson.encode(msg))
 	redis.call("ZREMRANGEBYSCORE", KEYS[2], "-inf", ARGV[4])
 	redis.call("ZREMRANGEBYRANK", KEYS[2], 0, -ARGV[5])
 	return redis.status_reply("OK")
 	`)
 	_, err = script.Run(r.client, []string{inProgressQ, deadQ},
-		string(bytes), errMsg, now.Unix(), limit, maxDeadTask).Result()
+		string(bytesToRemove), string(bytesToAdd), now.Unix(), limit, maxDeadTask).Result()
 	return err
 }