### [Fast Fallback](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback/)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

  // The number of elements in the replacement array.
  private final int replacementsLength;
  // The first code point in the safe range.
  private final int safeMin;
  // The last code point in the safe range.
  private final int safeMax;

  // Cropped values used in the fast path range checks.
  private final char safeMinChar;
  private final char safeMaxChar;

  /**

  // The number of elements in the replacement array.
  private final int replacementsLength;
  // The first code point in the safe range.
  private final int safeMin;
  // The last code point in the safe range.
  private final int safeMax;

  // Cropped values used in the fast path range checks.
  private final char safeMinChar;
  private final char safeMaxChar;

  /**

---
name: Bug report
about: A reproducible problem
title: ''
labels: bug
assignees: ''

---

Good bug reports include a failing test! Writing a test helps you to isolate and describe the problem, and it helps us to fix it fast. Bug reports without a failing test or reproduction steps are likely to be closed.

Here’s an example test to get you started.

        plusIsSpace = plusIsSpace,
        unicodeAllowed = unicodeAllowed,
        charset = charset,
      )
      return out.readUtf8()
    }
    i += Character.charCount(codePoint)
  }

  // Fast path: no characters in [pos..limit) required encoding.
  return substring(pos, limit)
}

internal fun Buffer.writePercentDecoded(
  encoded: String,
  pos: Int,
  limit: Int,
  plusIsSpace: Boolean,

   * the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
   * documentation.
   */
  public void add(Runnable runnable, Executor executor) {
    // Fail fast on a null. We throw NPE here because the contract of Executor states that it throws
    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");

    // Don't use checkState(), because we don't want the overhead of generating the error message
    // unless it's actually going to be used; validate() is called for all set method calls, so it
    // needs to be fast.
    // (We could instead generate the message once, when the set is created, but zero is better.)
    if (!validator.get()) {
      throw new IllegalStateException(errorMessage.get());
    }
  }

import org.jspecify.annotations.NullUnmarked;

/**
 * Android-incompatible tests for {@link FileBackedOutputStream}.
 *
 * @author Chris Nokleberg
 */
@AndroidIncompatible // Finalization probably just doesn't happen fast enough?
@NullUnmarked
public class FileBackedOutputStreamAndroidIncompatibleTest extends IoTestCase {

  public void testFinalizeDeletesFile() throws Exception {
    byte[] data = newPreFilledByteArray(100);

          // TODO: Fix tests not to call this directly and make it throw an error.
          return null;
        }
      };

  /**
   * Returns a builder for creating simple, fast escapers. A builder instance can be reused and each
   * escaper that is created will be a snapshot of the current builder state. Builders are not
   * thread safe.
   *
   * <p>The initial state of the builder is such that:

   * the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
   * documentation.
   */
  public void add(Runnable runnable, Executor executor) {
    // Fail fast on a null. We throw NPE here because the contract of Executor states that it throws
    // NPE on null listener, so we propagate that contract up into the add method as well.
    checkNotNull(runnable, "Runnable was null.");