With fast fallback, OkHttp attempts to connect to multiple web servers concurrently. It keeps whichever route connects first and cancels all of the others. Its rules are:

 * Prefer to alternate IP addresses from different address families, (IPv6 / IPv4), starting with IPv6.
 * Don't start a new attempt until 250 ms after the most recent attempt was started.
 * Keep whichever TCP connection succeeds first and cancel all the others.

---
name: fastapi
description: FastAPI best practices and conventions. Use when working with FastAPI APIs and Pydantic models for them. Keeps FastAPI code clean and up to date with the latest features and patterns, updated with new versions. Write new code or refactor and update old code.
---

# FastAPI

Official FastAPI skill to write code with best practices, keeping up to date with new versions and features.

## Use the `fastapi` CLI

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The LLM will probably translate this wrong. Interesting is only if it keeps the fixed translation when retranslating.

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The prompt designer may choose if they want to convert neutral quotes to typographic quotes. It is okay to leave them as is.

 * continues. See {@link QueueWorker#workOnQueue} for details.
 *
 * <p>{@code RuntimeException}s thrown by tasks are simply logged and the executor keeps trucking.
 * If an {@code Error} is thrown, the error will propagate and execution will stop until it is
 * restarted by a call to {@link #execute}.
 */
@J2ktIncompatible
@GwtIncompatible

For example, when you type `python` in the terminal, the operating system looks for a program called `python` in the **first directory** in that list.

If it finds it, then it will **use it**. Otherwise it keeps looking in the **other directories**.

### Installing Python and Updating the `PATH` { #installing-python-and-updating-the-path }

The benefit of a dedicated project for these tests are:
- `qa` projects are dedicated two specific usecases and easier to maintain
- It keeps the specific test logic separated from the common test logic.
- You can run those tests in parallel to other projects of the build.

#### Using test fixtures

Upgrading to OkHttp 4
=====================

OkHttp 4.x upgrades our implementation language from Java to Kotlin and keeps everything else the
same. We’ve chosen Kotlin because it gives us powerful new capabilities while integrating closely
with Java.

We spent a lot of time and energy on retaining strict compatibility with OkHttp 3.x. We’re even
keeping the package name the same: `okhttp3`!

There are three kinds of compatibility we’re tracking:

    MockReference(FinalizableReferenceQueue frq) {
      super(new Object(), frq);
    }

    @Override
    public void finalizeReferent() {
      finalizeReferentCalled = true;
    }
  }

  /**
   * Keeps a weak reference to the underlying reference queue. When this reference is cleared, we
   * know that the background thread has stopped and released its strong reference.
   */

  }

  /**
   * Regression test for an edge case where closing response body in the HTTP engine doesn't release
   * the corresponding stream allocation. This test keeps those response bodies alive and reads
   * them after the redirect has completed. This forces a connection to not be reused where it would
   * be otherwise.
   *
   *

Using a relative URL is important to make sure your application keeps working even in an advanced use case like [Behind a Proxy](../../advanced/behind-a-proxy.md).

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