* Then it returns the **response**.

/// note | Technical Details

If you have dependencies with `yield`, the exit code will run *after* the middleware.

If there were any background tasks (covered in the [Background Tasks](background-tasks.md){.internal-link target=_blank} section, you will see it later), they will run *after* all the middleware.

///

## Create a middleware { #create-a-middleware }

Just use any kind of model, any kind of class, any kind of database that you need for your application. **FastAPI** has you covered with the dependency injection system.

## Code size { #code-size }

This example might seem verbose. Keep in mind that we are mixing security, data models, utility functions and *path operations* in the same file.

	if debugNoExit {
		freeze := func(_ int) {
			// Infinite blocking op
			<-make(chan struct{})
		}

		// Override the logger os.Exit()
		logger.ExitFunc = freeze

		defer func() {
			if err := recover(); err != nil {
				fmt.Println("panic:", err)
				fmt.Println("")
				fmt.Println(string(debug.Stack()))
			}
			freeze(-1)
		}()
	}

	// Run the app - exit on error.

    @Override
    public Set<K> keySet() {
      /*
       * We can't use StandardKeySet, as NavigableMapTestSuiteBuilder assumes that our keySet is a
       * NavigableSet. We test StandardKeySet in the superclass, so it's still covered.
       */
      return navigableKeySet();
    }

    @Override
    public Collection<V> values() {
      return new StandardValues();
    }

    @Override
    public String toString() {

                          (N predecessor) -> EndpointPair.ordered(predecessor, node)),
                      Iterators.transform(
                          // filter out 'node' from successors (already covered by predecessors,
                          // above)
                          Sets.difference(graph.successors(node), ImmutableSet.of(node)).iterator(),

 *
 * Supported on OpenJDK 9+ via SSLParameters and SSLSocket features.
 *
 * ### Trust Manager Extraction
 *
 * Supported on Android 2.3+ and OpenJDK 7+. There are no public APIs to recover the trust
 * manager that was used to create an [SSLSocketFactory].
 *
 * Not supported by choice on JDK9+ due to access checks.
 *
 * ### Android Cleartext Permit Detection
 *

    @Override
    public Set<K> keySet() {
      /*
       * We can't use StandardKeySet, as NavigableMapTestSuiteBuilder assumes that our keySet is a
       * NavigableSet. We test StandardKeySet in the superclass, so it's still covered.
       */
      return navigableKeySet();
    }

    @Override
    public Collection<V> values() {
      return new StandardValues();
    }

    @Override
    public String toString() {

    assertThrows(IllegalStateException.class, () -> peekingIterator.remove());

    assertEquals(
        "After remove() throws exception, peek should still be ok", "B", peekingIterator.peek());

    /* Should recover to be able to remove() after next(). */
    assertEquals("B", peekingIterator.next());
    peekingIterator.remove();
    assertEquals("Should have removed an element", 2, list.size());

```console
$ bash scripts/test-cov-html.sh
```

</div>

This command generates a directory `./htmlcov/`, if you open the file `./htmlcov/index.html` in your browser, you can explore interactively the regions of code that are covered by the tests, and notice if there is any region missing.

## Docs

First, make sure you set up your environment as described above, that will install all the requirements.

### Docs live

    /**
     * Circuit breaker states
     */
    public enum State {
        CLOSED, // Normal operation
        OPEN, // Failing, requests blocked
        HALF_OPEN // Testing recovery
    }

    private final String name;
    private final AtomicReference<State> state = new AtomicReference<>(State.CLOSED);
    private final AtomicInteger consecutiveFailures = new AtomicInteger(0);