#### Internal API changes

The `okhttp3.internal` package is not a published API and we change it frequently without warning.
Depending on code in this package is bad and will cause you problems with any upgrade! But the 4.x
will be particularly painful to naughty developers that import from this package! We changed a lot
to take advantage of sweet Kotlin features.

#### Credentials.basic()

    connection takes more than 10 seconds to complete, you’ll need to adjust
    the timeouts manually.

 *  **OkHttp now rejects request headers that contain invalid characters.** This
    includes potential security problems (newline characters) as well as simple
    non-ASCII characters (including international characters and emoji).

 *  **Call canceling is more reliable.**  We had a bug where a socket being

    }

    @Override
    public Optional<Long> sizeIfKnown() {
      if (!(sources instanceof Collection)) {
        // Infinite Iterables can cause problems here. Of course, it's true that most of the other
        // methods on this class also have potential problems with infinite  Iterables. But unlike
        // those, this method can cause issues even if the user is dealing with a (finite) slice()

 * corresponding entries will be dropped from the cache. If an error occurs while writing a cache
 * value, the edit will fail silently. Callers should handle other problems by catching
 * `IOException` and responding appropriately.
 *
 * @constructor Create a cache which will reside in [directory]. This cache is lazily initialized on
 *     first access and will be created if it does not exist.

  /**
   * Handles cases of updates involving initialization, resizing, creating new Cells, and/or
   * contention. See above for explanation. This method suffers the usual non-modularity problems of
   * optimistic retry code, relying on rechecked sets of reads.
   *
   * @param x the value
   * @param hc the hash code holder
   * @param wasUncontended false if CAS failed before call
   */

   * {@code [1]} and {@code [1, 1]}).
   */
  // Note: 90% of the time we don't add type parameters or wildcards that serve only to "tweak" the
  // desired return type. However, *nested* generics introduce a special class of problems that we
  // think tip it over into being worthwhile.
  public static <T extends @Nullable Object, S extends T> Comparator<Iterable<S>> lexicographical(
      Comparator<T> comparator) {

      }
    }

    /*
     * TODO(cpovirk): `return (V) removedValue` once our checker permits that.
     *
     * (We promoted a class of warnings into errors because sometimes they indicate real problems.
     * But now we need to "undo" some instance of spurious errors, as discussed in
     * https://github.com/jspecify/checker-framework/issues/8.)
     */
    return removedValue == null ? null : (V) removedValue;
  }

        annotations = new ArrayList<>();
        for (Annotation a : classOrMethod.getDeclaredAnnotations()) {
          /*
           * We avoid reflecting on NullMarked because its @Target(..., MODULE) causes problems
           * under JDK 8.
           */
          if (!(a instanceof NullMarked)
              && a.annotationType().isAnnotationPresent(TesterAnnotation.class)) {
            annotations.add(a);
          }

      Class<?> cls;
      try {
        cls = classInfo.load();
      } catch (NoClassDefFoundError e) {
        // In case there were linking problems, this is probably not a class we care to test anyway.
        logger.log(Level.SEVERE, "Cannot load class " + classInfo + ", skipping...", e);
        continue;
      }
      if (!cls.isInterface()) {

    ```

### Timeouts ([.kt][ConfigureTimeoutsKotlin], [.java][ConfigureTimeoutsJava])

Use timeouts to fail a call when its peer is unreachable. Network partitions can be due to client connectivity problems, server availability problems, or anything between. OkHttp supports connect, write, read, and full call timeouts.

=== ":material-language-kotlin: Kotlin"
    ```kotlin
      private val client: OkHttpClient = OkHttpClient.Builder()