"prefix": "/healthz/ready"
          },
          "route": {
           "cluster": "agent"
          }
         }
        ]
       }
      ]
     },
     "last_updated": "2023-11-29T09:58:27.299Z"
    },
    {
     "route_config": {
      "@type": "type.googleapis.com/envoy.config.route.v3.RouteConfiguration",
      "virtual_hosts": [
       {
        "name": "backend",
        "domains": [
         "*"

           "prefix": "/healthz/ready"
          },
          "route": {
           "cluster": "agent"
          }
         }
        ]
       }
      ]
     },
     "last_updated": "2023-11-29T09:58:27.299Z"
    },
    {
     "route_config": {
      "@type": "type.googleapis.com/envoy.config.route.v3.RouteConfiguration",
      "virtual_hosts": [
       {
        "name": "backend",
        "domains": [
         "*"

    // https://github.com/google/guava/issues/2996
    // no data, just testing that there's no StackOverflowException
    assertEquals(-1, tenMillionEmptySources().read());
  }

  public void testReadArray_noStackOverflow() throws IOException {
    // https://github.com/google/guava/issues/2996
    // no data, just testing that there's no StackOverflowException

    // https://github.com/google/guava/issues/2996
    // no data, just testing that there's no StackOverflowException
    assertEquals(-1, tenMillionEmptySources().read());
  }

  public void testReadArray_noStackOverflow() throws IOException {
    // https://github.com/google/guava/issues/2996
    // no data, just testing that there's no StackOverflowException

某些情况下，需要向客户端返回错误提示。

这里所谓的客户端包括前端浏览器、其他应用程序、物联网设备等。

需要向客户端返回错误提示的场景主要如下：

- 客户端没有执行操作的权限
- 客户端没有访问资源的权限
- 客户端要访问的项目不存在
- 等等 ...

遇到这些情况时，通常要返回 **4XX**（400 至 499）**HTTP 状态码**。

**4XX** 状态码与表示请求成功的 **2XX**（200 至 299） HTTP 状态码类似。

只不过，**4XX** 状态码表示客户端发生的错误。

大家都知道**「404 Not Found」**错误，还有调侃这个错误的笑话吧？

## 使用 `HTTPException`

向客户端返回 HTTP 错误响应，可以使用 `HTTPException`。

### 导入 `HTTPException`

```Python hl_lines="1"

* etc.

In these cases, you would normally return an **HTTP status code** in the range of **400** (from 400 to 499).

This is similar to the 200 HTTP status codes (from 200 to 299). Those "200" status codes mean that somehow there was a "success" in the request.

The status codes in the 400 range mean that there was an error from the client.

Remember all those **"404 Not Found"** errors (and jokes)?