## Technical Details { #technical-details }

FastAPI implements some SSE best practices out of the box.

* Send a **"keep alive" `ping` comment** every 15 seconds when there hasn't been any message, to prevent some proxies from closing the connection, as suggested in the [HTML specification: Server-Sent Events](https://html.spec.whatwg.org/multipage/server-sent-events.html#authoring-notes).

        str | None,
        Doc(
            """
            Optional event type name.

            Maps to `addEventListener(event, ...)` on the browser. When omitted,
            the browser dispatches on the generic `message` event.
            """
        ),
    ] = None
    id: Annotated[
        str | None,
        AfterValidator(_check_id_no_null),
        Doc(
            """
            Optional event ID.

{* ../../docs_src/custom_response/tutorial009c_py310.py hl[9:14,17] *}

现在，不再是返回：

```json
{"message": "Hello World"}
```

...这个响应将返回：

```json
{
  "message": "Hello World"
}
```

当然，你很可能会找到比格式化 JSON 更好的方式来利用这一点。😉

### `orjson` 或响应模型 { #orjson-or-response-model }

        is IllegalArgumentException -> {
          assertEquals("Android internal error", ioe.message)
        }

        is CertificateException -> {
          assertTrue(ioe.cause?.cause is IllegalArgumentException)
          assertEquals(
            true,
            ioe.cause
              ?.cause
              ?.message
              ?.startsWith("Invalid input to toASCII"),
          )
        }

        }
    }

    private void handleChecksumFailure(String checksumPolicy, String message, Throwable cause)
            throws ChecksumFailedException {
        if (ArtifactRepositoryPolicy.CHECKSUM_POLICY_FAIL.equals(checksumPolicy)) {
            throw new ChecksumFailedException(message, cause);
        } else if (!ArtifactRepositoryPolicy.CHECKSUM_POLICY_IGNORE.equals(checksumPolicy)) {

        }, "A PACDecodingException should be thrown for a malformed token.");

        assertEquals("Malformed kerberos ticket", exception.getMessage(), "The exception message should indicate a malformed ticket.");
    }

    /**
     * Test constructor with an empty token.
     * Empty token causes readObject() to return null, which leads to NullPointerException.
     */
    @Test

{* ../../docs_src/background_tasks/tutorial001_py310.py hl[14] *}

`.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 { #dependency-injection }

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：

            throw AssertionError("unsupported hashAlgorithm: ${pin.hashAlgorithm}")
          }
        }
      }
    }

    // If we couldn't find a matching pin, format a nice exception.
    val message =
      buildString {
        append("Certificate pinning failure!")
        append("\n  Peer certificate chain:")
        for (element in peerCertificates) {
          append("\n    ")

        try {
            ReflectionValueExtractor.evaluate("h.value[1]", new ValueHolder("string"));
        } catch (Exception e) {
            // TODO assert exception message
        }
    }

    /**
     * <p>testIllegalMappedType.</p>
     *
     * @throws Exception if any.
     */
    @Test
    public void testIllegalMappedType() throws Exception {

        String message = String.format(
            Locale.ROOT,
            "The %s must be set to a JDK installation directory for Java %d but is [%s] corresponding to [%s]",
            description,
            expectedVersion,
            javaHome,
            actualVersion
        );

        throw new GradleException(message);
    }