feat: join room, rooms.Update transactional

rooms/rooms_manager.go

@@ -3,6 +3,7 @@ package rooms
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 
@@ -37,11 +38,10 @@ func (r *Room) UnmarshalBinary(data []byte) error {
 
 // let's check whether it will be possible to save nested structs
 
-var ctx = context.Background()
-
 type RoomManager interface {
 	Get(roomName string) (Room, bool, error)
 	Save(room Room) error
+	Update(ctx context.Context, roomName string, f func(fromRoom Room) (toRoom Room)) error
 }
 const roomRedisPrefix = "room"
 func roomNameToRedisId(roomName string) string {
@@ -55,7 +55,7 @@ type RedisRM struct {
 
 func (redisRM RedisRM) Get(roomName string) (Room, bool, error) {
 	var readRoom Room
-	err := redisRM.Rdb.Get(ctx, roomNameToRedisId(roomName)).Scan(&readRoom)
+	err := redisRM.Rdb.Get(context.TODO(), roomNameToRedisId(roomName)).Scan(&readRoom)
 	if err == redis.Nil {
 		return Room{}, false, nil
 	}
@@ -67,7 +67,43 @@ func (redisRM RedisRM) Get(roomName string) (Room, bool, error) {
 	return readRoom, true, nil
 }
 
+var maxRetries int = 20
+func (redisRM RedisRM) Update(ctx context.Context, roomName string, f func(fromRoom Room) (toRoom Room)) error {
+	// transactional function
+	roomKey := roomNameToRedisId(roomName)
+	txf := func (tx *redis.Tx) error {
+		var savedRoom Room
+		err := tx.Get(ctx, roomKey).Scan(&savedRoom)
+		if err != nil {
+			return err
+		}
+
+		room := f(savedRoom)
+
+		_, err = tx.Pipelined(ctx, func(pipe redis.Pipeliner) error {
+			pipe.Set(ctx, roomKey, &room, 0)
+			return nil
+		})
+
+		return err
+	}
+	for i := 0; i < maxRetries; i++ {
+		err := redisRM.Rdb.Watch(ctx, txf, roomKey)
+		if err == nil {
+			return nil // success
+		}
+		if err == redis.TxFailedErr {
+			// optimistic lock will keep spinning
+			continue
+		}
+		// non tx errror are returned, including redis.Nil
+		return err
+	}
+
+	return errors.New("update reached maximum amount of retries")
+}
+
 func (redisRM RedisRM) Save(room Room) error {
-	err := redisRM.Rdb.Set(ctx, roomNameToRedisId(room.Name), &room, 0).Err() // maybe even set expiration?
+	err := redisRM.Rdb.Set(context.TODO(), roomNameToRedisId(room.Name), &room, 0).Err() // maybe even set expiration?
 	return err
 }