return null;
        }
        return tryParseInt(s);
    }

    private static Integer tryParseInt(String s) {
        // for performance, check digits instead of relying later on catching NumberFormatException
        if (!isDigits(s)) {
            return null;
        }

        try {
            long longValue = Long.parseLong(s);
            if (longValue > Integer.MAX_VALUE) {

  public void testCatching() throws Exception {
    FluentFuture<?> f =
        FluentFuture.from(immediateFailedFuture(new CustomRuntimeException()))
            .catching(
                Throwable.class,
                new Function<Throwable, Class<?>>() {
                  @Override
                  public Class<?> apply(Throwable input) {
                    return input.getClass();

/// tip

You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

///

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.
* Assign that result to the parameter in your *path operation function*.

```mermaid
graph TB

   * in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked exception
   * types your try block can throw when calling an overload of this method so as to avoid losing
   * the original exception type.
   *
   * <p>This method always throws, and as such should be called as {@code throw closer.rethrow(e);}

   */
  private static void assertCrc(int expectedCrc, byte[] data) {
    int actualCrc = Hashing.crc32c().hashBytes(data).asInt();
    assertEquals(
        String.format("expected: %08x, actual: %08x", expectedCrc, actualCrc),
        expectedCrc,
        actualCrc);
    int actualCrcHasher = Hashing.crc32c().newHasher().putBytes(data).hash().asInt();
    assertEquals(

	// The returned value can no longer be modified once returned.
	// Should be set before calling Get().
	updateFn func(ctx context.Context) (T, error)

	// ttl for a cached value.
	ttl time.Duration

	opts Opts

	// Once can be used to initialize values for lazy initialization.
	// Should be set before calling Get().
	Once sync.Once

	// Managed values.
	val          atomic.Pointer[T]

    parts.nextPart()!!
    val partMno = parts.nextPart()!!
    assertThat(partMno.body.readUtf8()).isEqualTo("mnop")

    assertThat(parts.nextPart()).isNull()
  }

  @Test fun `cannot read part after calling nextPart`() {
    val multipart =
      """
      |--simple boundary
      |
      |abcd
      |efgh
      |ijkl
      |--simple boundary
      |
      |mnop
      |--simple boundary--

import okio.Options
import okio.Source
import okio.Timeout
import okio.buffer

/**
 * Reads a stream of [RFC 2046][rfc_2046] multipart body parts. Callers read parts one-at-a-time
 * until [nextPart] returns null. After calling [nextPart] any preceding parts should not be read.
 *
 * Typical use loops over the parts in sequence:
 *
 * ```kotlin
 * val response: Response = call.execute()
 * val multipartReader = MultipartReader(response.body!!)

import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * A set multimap which forwards all its method calls to another set multimap. Subclasses should
 * override one or more methods to modify the behavior of the backing multimap as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code

type Checker struct {
	c io.Closer
	r io.Reader
	h hash.Hash

	want []byte
}

// NewChecker ensures that content with the specified length is read from rc.
// Calling Close on this will close upstream.
func NewChecker(rc io.ReadCloser, h hash.Hash, wantSum []byte, length int64) *Checker {
	return &Checker{c: rc, r: ioutil.HardLimitReader(rc, length), h: h, want: wantSum}
}