*
     * Performance: O(1) operation using concurrent queue
     *
     * @return a byte buffer for SMB operations
     * @throws IllegalStateException if buffer size exceeds maximum allowed
     */
    static public byte[] getBuffer() {
        // Try to get from cache first - O(1) operation
        byte[] buf = bufferQueue.poll();
        if (buf != null) {

    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> dep: Raise HTTPException
        dep -->> handler: Auto forward exception
        handler -->> client: HTTP error response
        operation -->> dep: Raise other exception
        dep -->> handler: Auto forward exception
    end
    operation ->> client: Return response to client

        } else if (isRetryable()) {
            log.warn("Retryable SMB error: {} in operation '{}' (attempt {}/{})", getMessage(), operationName, attemptNumber,
                    retryPolicy.getMaxAttempts());
        } else {
            log.error("Non-retryable SMB error: {} in operation '{}'", getMessage(), operationName);
        }
    }

    /**
     * Check if this exception is retryable

# ミドルウェア

**FastAPI** アプリケーションにミドルウェアを追加できます。

「ミドルウェア」は、すべての**リクエスト**に対して、それがあらゆる特定の*path operation*によって処理される前に機能する関数です。また、すべての**レスポンス**に対して、それを返す前に機能します。

* ミドルウェアはアプリケーションに届いたそれぞれの**リクエスト**を受け取ります。
* その後、その**リクエスト**に対して何かを実行したり、必要なコードを実行したりできます。
* 次に、アプリケーションの残りの部分に**リクエスト**を渡して (*path operation* によって) 処理させます。
* 次に、ミドルウェアはアプリケーション (の *path operation*) によって生成された**レスポンス**を受け取ります。
* その**レスポンス**に対して何かを実行したり、必要なコードを実行したりできます。
* そして、**レスポンス**を返します。

```mermaid
sequenceDiagram

participant client as Client
participant handler as Exception handler
participant dep as Dep with yield
participant operation as Path Operation
participant tasks as Background tasks

    Note over client,operation: Can raise exceptions, including HTTPException
    client ->> dep: Start request
    Note over dep: Run code up to yield
    opt raise Exception

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).

{* ../../docs_src/security/tutorial002_an_py310.py hl[30:32] *}

## Recap { #recap }

You can now get the current user directly in your *path operation function*.

We are already halfway there.

We just need to add a *path operation* for the user/client to actually send the `username` and `password`.

You can set the *path operation decorator* parameter `response_model_exclude_unset=True`:

{* ../../docs_src/response_model/tutorial004_py310.py hl[22] *}

and those default values won't be included in the response, only the values actually set.

So, if you send a request to that *path operation* for the item with ID `foo`, the response (not including default values) will be:

    }

    /**
     * Execute an operation with circuit breaker protection
     *
     * @param <T> return type
     * @param operation the operation to execute
     * @return operation result
     * @throws CIFSException if circuit is open or operation fails
     */
    public <T> T executeWithCircuitBreaker(Supplier<T> operation) throws CIFSException {
        // Backpressure control

                            * `security_scopes.scopes` will contain `["me"]` for the *path operation* `read_users_me`, because it is declared in the dependency `get_current_active_user`.