### Import `APIRouter`

You import it and create an "instance" the same way you would with the class `FastAPI`:

```Python hl_lines="1  3" title="app/routers/users.py"
{!../../../docs_src/bigger_applications/app/routers/users.py!}
```

### *Path operations* with `APIRouter`

And then you use it to declare your *path operations*.

Use it the same way you would use the `FastAPI` class:

You could load it at the top level of the module/file, but that would also mean that it would **load the model** even if you are just running a simple automated test, then that test would be **slow** because it would have to wait for the model to load before being able to run an independent part of the code.

 *  Fix: Don't crash if a TLS tunnel's response body is truncated.
 *  Fix: Don't track unusable routes beyond their usefulness. We had a bug where we could track
    certain bad routes indefinitely; now we only track the ones that could be necessary.
 *  Fix: Defer proxy selection until a proxy is required. This saves calls to `ProxySelector` on
    calls that use a pooled connection.


## Version 4.3.1

author:
  using_gitstream: {{ (pr.author | isEnabledUser ) }}

# Perhaps a task could generate this list from the CODEOWNERS, or both this and CODEOWNERS could be generated from different single source of truth?
# Keys like `- build_infrastructure:` do not mean anything, they just need to be unique

    It won't be serialized with a model, etc.

    Make sure it has the data you want it to have, and that the values are valid JSON (if you are using `JSONResponse`).

!!! note "Technical Details"
    You could also use `from starlette.responses import JSONResponse`.

    And also that you are not sending any data that should have been filtered by a `response_model`.

### More info

!!! note "Technical Details"
    You could also use `from starlette.responses import Response` or `from starlette.responses import JSONResponse`.

# Read the "|" not as "or", but as a "pipe", taking the output of the previous command and passing it to the next command.
# This section could also appear ahead of the automations section.

# This function calculates the estimated time to review and makes it available in the automation above.
# The name `calc`, and the nesting is arbitrary.
calc:

That way, the sub-application will know to use that path prefix for the docs UI.

And the sub-application could also have its own mounted sub-applications and everything would work correctly, because FastAPI handles all these `root_path`s automatically.

    it may slow down the tests for not running in parallel and may cause the
    test to timeout but it could be useful when you need to execute a single
    test or more in general your filtered/selected tests have a very low
    execution time and the sharding
    [could create an overhead on the test execution](https://github.com/bazelbuild/bazel/issues/2113#issuecomment-264054799).

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3

import okio.IOException

interface Callback {
  /**
   * Called when the request could not be executed due to cancellation, a connectivity problem or
   * timeout. Because networks can fail during an exchange, it is possible that the remote server
   * accepted the request before the failure.
   */
  fun onFailure(