Amazon DynamoDB で作るサーバーレスなゲーム用フレンドマイクロサービス

{
    "eventID": "380271641178688a170beb2fabd6c401",
    "eventName": "INSERT",
    "eventVersion": "1.1",
    "eventSource": "aws:dynamodb",
    "awsRegion": "us-east-1",
    "dynamodb": {
        "ApproximateCreationDateTime": 1659342437,
        "Keys": {
            "friend_id": {
                "S": "playerB"
            },
            "player_id": {
                "S": "playerA"
            }
        },
        "NewImage": {
            "friend_id": {
                "S": "playerB"
            },
            "last_updated": {
                "N": "1659342437340"
            },
            "player_id": {
                "S": "playerA"
            },
            "state": {
                "S": "Requested"
            }
        },
        "SequenceNumber": "23469600000000008634076814",
        "SizeBytes": 98,
        "StreamViewType": "NEW_AND_OLD_IMAGES"
    },
    "eventSourceARN": "arn:aws:dynamodb:us-east-1:123456789012:table/Friend/stream/2022-07-27T07:25:17.774"
}

    // 複数の Handler に対して使うイベントソースの共通プロパティを定義
    const streamEventSourceProps: StreamEventSourceProps = {
      startingPosition: StartingPosition.LATEST,
      batchSize: 5,
      retryAttempts: 1,
      onFailure: stateHandleDLQ,
      reportBatchItemFailures: true,
    };
    
    // player B に変更を行う Handler に紐付け
    requestStateHandler.addEventSource(
      // friendTable から流れる Streams にフィルターを付ける 
      new DynamoEventSource(friendTable, {
        filters: [
          // フィルターの中身を定義
          FilterCriteria.filter({
            eventName: FilterRule.isEqual("INSERT"),
            dynamodb: {
              NewImage: {
                state: { S: FilterRule.isEqual(State.Requested) },
              },
            },
          }),
        ],
        ...streamEventSourceProps,
      })
    );

  const rejectParam: DocumentClient.DeleteItemInput = {
    TableName: friendTableName,
    // PK はプレーヤー B、SK はプレーヤー A
    Key: {
      "player_id": playerBId,
      "friend_id": playerAId,
    },
    // state=Friends というコンディションの時のみ Delete
    ConditionExpression: "#state = :friends",
    ExpressionAttributeNames: {
      "#state": "state",
    },
    ExpressionAttributeValues: {
      ":friends": Friends,
    },
  };

const rejectParam: DocumentClient.DeleteItemInput = {
    TableName: friendTableName,
    ... // 上記のパラメータの内容
  };
  try {
    await db.delete(rejectParam).promise();
  } catch (e: any) {
    if (e.name == "ConditionalCheckFailedException") {
      // 想定しているエラーなのでここを無視する。
      return;
    }
    throw e;
  }

  const friendParam: DocumentClient.PutItemInput = {
    TableName: friendTableName,
    Item: {
      "player_id": playerBId,
      "friend_id": playerAId,
      state: Pending,
      last_updated: timeStamp,
    },
    // 申請時にはプレーヤー B のデータが無い事を条件にする
    ConditionExpression: `attribute_not_exists(player_id)`,
  };

const updateReceiverParams: DocumentClient.TransactWriteItem = {
    Update: {
      TableName: friendTableName,
      Key: {
        "player_id": playerAId,
        "friend_id": playerBId,
      },
      // プレーヤー A も申請をしているので state=Requested
      ConditionExpression: "#state = :requested",
      // 両プレーヤーが申請しているので Friends に変更
      UpdateExpression: "SET #state = :friends, #last_updated = :last_updated",
      ExpressionAttributeNames: {
        "#state": "state",
        "#last_updated": "last_updated",
      },
      ExpressionAttributeValues: {
        ":requested": Requested,
        ":friends": Friends,
        ":last_updated": timeStamp,
      },
    },
  };

  const updateRequesterParam: DocumentClient.TransactWriteItem = {
    Update: {
      TableName: friendTableName,
      Key: {
        "player_id": playerBId,
        "friend_id": playerAId,
      },
      // プレーヤー B も申請しているので state=Requested
      ConditionExpression: "#state = :requested",
      // 両プレーヤーが申請しているので Friends に変更
      UpdateExpression: "SET #state = :friends, #last_updated = :last_updated",
      ExpressionAttributeNames: {
        "#state": "state",
        "#last_updated": "last_updated",
      },
      ExpressionAttributeValues: {
        ":requested": Requested,
        ":friends": Friends,
        ":last_updated": timeStamp,
      },
    },
  };