* characters.
 *
 * <p>As there are important reasons, including potential security issues, to handle Unicode
 * correctly if you are considering implementing a new escaper you should favor using UnicodeEscaper
 * wherever possible.
 *
 * <p>A {@code UnicodeEscaper} instance is required to be stateless, and safe when used concurrently
 * by multiple threads.
 *
 * <p>Popular escapers are defined as constants in classes like {@link

  // Escapes nothing
  private static final UnicodeEscaper NOP_ESCAPER =
      new UnicodeEscaper() {
        @Override
        protected char @Nullable [] escape(int c) {
          return null;
        }
      };

  // Escapes everything except [a-zA-Z0-9]
  private static final UnicodeEscaper SIMPLE_ESCAPER =
      new UnicodeEscaper() {
        @Override
        protected char @Nullable [] escape(int cp) {

 * with short strings already known to be free of unpaired surrogates.
 *
 * <p>The two primary implementations of this interface are {@link CharEscaper} and {@link
 * UnicodeEscaper}. They are heavily optimized for performance and greatly simplify the task of
 * implementing new escapers. It is strongly recommended that when implementing a new escaper you

    assertThat(e.escape("******@****.***")).isEqualTo("foo%40bar.com");
  }

  public void testUrlPathSegmentEscaper() {
    UnicodeEscaper e = (UnicodeEscaper) urlPathSegmentEscaper();
    assertPathEscaper(e);
    assertUnescaped(e, '+');
  }

  public void testUrlFragmentEscaper() {
    UnicodeEscaper e = (UnicodeEscaper) urlFragmentEscaper();
    assertUnescaped(e, '+');
    assertUnescaped(e, '/');
    assertUnescaped(e, '?');

    assertThat(e.escape("******@****.***")).isEqualTo("foo%40bar.com");
  }

  public void testUrlPathSegmentEscaper() {
    UnicodeEscaper e = (UnicodeEscaper) urlPathSegmentEscaper();
    assertPathEscaper(e);
    assertUnescaped(e, '+');
  }

  public void testUrlFragmentEscaper() {
    UnicodeEscaper e = (UnicodeEscaper) urlFragmentEscaper();
    assertUnescaped(e, '+');
    assertUnescaped(e, '/');
    assertUnescaped(e, '?');

  }

  // Helper to assert common expected behaviour of uri escapers.
  static void assertBasicUrlEscaper(UnicodeEscaper e) {
    assertBasicUrlEscaperExceptPercent(e);
    // The escape character must always be escaped
    assertEscaping(e, "%25", '%');
  }

  static void assertPathEscaper(UnicodeEscaper e) {
    assertBasicUrlEscaper(e);

    assertUnescaped(e, '!');
    assertUnescaped(e, '\'');

  }

  /** Tests the various ways that the space character can be handled */
  public void testPlusForSpace() {
    UnicodeEscaper basicEscaper = new PercentEscaper("", false);
    UnicodeEscaper plusForSpaceEscaper = new PercentEscaper("", true);
    UnicodeEscaper spaceEscaper = new PercentEscaper(" ", false);

    assertThat(basicEscaper.escape("string with spaces")).isEqualTo("string%20with%20spaces");

  }

  /** Tests the various ways that the space character can be handled */
  public void testPlusForSpace() {
    UnicodeEscaper basicEscaper = new PercentEscaper("", false);
    UnicodeEscaper plusForSpaceEscaper = new PercentEscaper("", true);
    UnicodeEscaper spaceEscaper = new PercentEscaper(" ", false);

    assertThat(basicEscaper.escape("string with spaces")).isEqualTo("string%20with%20spaces");

  }

  // Helper to assert common expected behaviour of uri escapers.
  static void assertBasicUrlEscaper(UnicodeEscaper e) {
    assertBasicUrlEscaperExceptPercent(e);
    // The escape character must always be escaped
    assertEscaping(e, "%25", '%');
  }

  static void assertPathEscaper(UnicodeEscaper e) {
    assertBasicUrlEscaper(e);

    assertUnescaped(e, '!');
    assertUnescaped(e, '\'');

  public void testReplacements() throws IOException {
    // In reality this is not a very sensible escaper to have (if you are only
    // escaping elements from a map you would use a ArrayBasedCharEscaper).
    UnicodeEscaper escaper =
        new ArrayBasedUnicodeEscaper(
            SIMPLE_REPLACEMENTS, Character.MIN_VALUE, Character.MAX_CODE_POINT, null) {
          @Override
          protected char[] escapeUnsafe(int c) {