// 256 characters long
    assertEquals(4904844928629814570L, fingerprint(Strings.repeat("test", 64).getBytes(UTF_8)));
  }

  public void testStringsConsistency() {
    for (String s : Arrays.asList("", "some", "test", "strings", "to", "try")) {
      assertEquals(HASH_FN.newHasher().putUnencodedChars(s).hash(), HASH_FN.hashUnencodedChars(s));
    }
  }

  public void testUtf8() {
    char[] charsA = new char[128];

            getSubjectGenerator()
                .getSampleElements(getSubjectGenerator().getCollectionSize().getNumElements()));
    sort(entries, Helpers.<K, V>entryComparator(navigableMap.comparator()));

    // some tests assume SEVERAL == 3
    if (entries.size() >= 1) {
      a = entries.get(0);
      if (entries.size() >= 3) {
        b = entries.get(1);
        c = entries.get(2);
      }
    }
  }

   * @param callback the LineProcessor to use to handle the lines
   * @return the output of processing the lines
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue // some processors won't return a useful result
  @ParametricNullness
  public static <T extends @Nullable Object> T readLines(
      URL url, Charset charset, LineProcessor<T> callback) throws IOException {

```Python hl_lines="1  11-21"
{!> ../../docs_src/security/tutorial007.py!}
```

////

这类似于：

```Python
if not (credentials.username == "stanleyjobson") or not (credentials.password == "swordfish"):
    # Return some error
    ...
```

但使用 `secrets.compare_digest()`，可以防御**时差攻击**，更加安全。

### 时差攻击

什么是**时差攻击**？

假设攻击者试图猜出用户名与密码。

他们发送用户名为 `johndoe`，密码为 `love123`  的请求。

然后，Python 代码执行如下操作：

```Python hl_lines="14"
{!../../docs_src/background_tasks/tutorial001.py!}
```

`.add_task()` 接收以下参数：

* 在后台运行的任务函数(`write_notification`)。
* 应按顺序传递给任务函数的任意参数序列(`email`)。
* 应传递给任务函数的任意关键字参数(`message="some notification"`)。

## 依赖注入

使用 `BackgroundTasks` 也适用于依赖注入系统，你可以在多个级别声明 `BackgroundTasks` 类型的参数：在 *路径操作函数* 里，在依赖中(可依赖)，在子依赖中，等等。

**FastAPI** 知道在每种情况下该做什么以及如何复用同一对象，因此所有后台任务被合并在一起并且随后在后台运行：

//// tab | Python 3.10+

    $env:PATH = [Environment]::GetEnvironmentVariable('PATH', 'Machine') + ';C:\tools\LLVM\bin'; \
    [Environment]::SetEnvironmentVariable('PATH', $env:PATH, 'Machine');

# Install MSYS2, and add some extra tools.
RUN (New-Object Net.WebClient).DownloadFile( \
         'https://repo.msys2.org/distrib/x86_64/msys2-base-x86_64-20240113.tar.xz', \
         'msys2.tar.xz'); \

    // The initial state corresponds to the ASCII string "somepseudorandomlygeneratedbytes",
    // big-endian encoded. There is nothing special about this value; the only requirement
    // was some asymmetry so that the initial v0 and v1 differ from v2 and v3.
    private long v0 = 0x736f6d6570736575L;
    private long v1 = 0x646f72616e646f6dL;
    private long v2 = 0x6c7967656e657261L;

Проверьте, что всё сработало:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console
$ which pip

some/directory/fastapi/env/bin/pip
```

</div>

////

//// tab | Windows PowerShell

<div class="termy">

```console
$ Get-Command pip

some/directory/fastapi/env/bin/pip
```

</div>

////

        // just copy-off but includes a sum) and consideration of performance.
        //
        // TODO(allenl): There may be smarter ways to do this copy in some
        // cases, i.e. with a collective broadcast. We'll need to be careful
        // about things that are taken as inputs on the host or on their
        // existing device (for multi-device functions).

        return buildRedirectRequest(userResponse, method)
      }

      HTTP_CLIENT_TIMEOUT -> {
        // 408's are rare in practice, but some servers like HAProxy use this response code. The
        // spec says that we may repeat the request without modifications. Modern browsers also
        // repeat the request (even non-idempotent ones.)