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Kotlin core Protocol Buffers library. Protocol Buffers are a way of encoding structured data in an efficient yet extensible format.
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// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package com.google.protobuf;

/**
 * Provide text format escaping of proto instances. These ASCII characters are escaped:
 *
 * ASCII #7   (bell) --> \a
 * ASCII #8   (backspace) --> \b
 * ASCII #9   (horizontal tab) --> \t
 * ASCII #10  (linefeed) --> \n
 * ASCII #11  (vertical tab) --> \v
 * ASCII #13  (carriage return) --> \r
 * ASCII #12  (formfeed) --> \f
 * ASCII #34  (apostrophe) --> \'
 * ASCII #39  (straight double quote) --> \"
 * ASCII #92  (backslash) --> \\
 *
 * Other printable ASCII characters between 32 and 127 inclusive are output as is, unescaped.
 * Other ASCII characters less than 32 and all Unicode characters 128 or greater are
 * first encoded as UTF-8, then each byte is escaped individually as a 3-digit octal escape.
 */
final class TextFormatEscaper {
  private TextFormatEscaper() {}

  private interface ByteSequence {
    int size();

    byte byteAt(int offset);
  }

  /**
   * Backslash escapes bytes in the format used in protocol buffer text format.
   */
  static String escapeBytes(ByteSequence input) {
    final StringBuilder builder = new StringBuilder(input.size());
    for (int i = 0; i < input.size(); i++) {
      byte b = input.byteAt(i);
      switch (b) {
        case 0x07:
          builder.append("\\a");
          break;
        case '\b':
          builder.append("\\b");
          break;
        case '\f':
          builder.append("\\f");
          break;
        case '\n':
          builder.append("\\n");
          break;
        case '\r':
          builder.append("\\r");
          break;
        case '\t':
          builder.append("\\t");
          break;
        case 0x0b:
          builder.append("\\v");
          break;
        case '\\':
          builder.append("\\\\");
          break;
        case '\'':
          builder.append("\\\'");
          break;
        case '"':
          builder.append("\\\"");
          break;
        default:
          // Only ASCII characters between 0x20 (space) and 0x7e (tilde) are
          // printable.  Other byte values must be escaped.
          if (b >= 0x20 && b <= 0x7e) {
            builder.append((char) b);
          } else {
            builder.append('\\');
            builder.append((char) ('0' + ((b >>> 6) & 3)));
            builder.append((char) ('0' + ((b >>> 3) & 7)));
            builder.append((char) ('0' + (b & 7)));
          }
          break;
      }
    }
    return builder.toString();
  }

  /**
   * Backslash escapes bytes in the format used in protocol buffer text format.
   */
  static String escapeBytes(final ByteString input) {
    return escapeBytes(
        new ByteSequence() {
          @Override
          public int size() {
            return input.size();
          }

          @Override
          public byte byteAt(int offset) {
            return input.byteAt(offset);
          }
        });
  }

  /** Like {@link #escapeBytes(ByteString)}, but used for byte array. */
  static String escapeBytes(final byte[] input) {
    return escapeBytes(
        new ByteSequence() {
          @Override
          public int size() {
            return input.length;
          }

          @Override
          public byte byteAt(int offset) {
            return input[offset];
          }
        });
  }

  /**
   * Like {@link #escapeBytes(ByteString)}, but escapes a text string.
   */
  static String escapeText(String input) {
    return escapeBytes(ByteString.copyFromUtf8(input));
  }

  /** Escape double quotes and backslashes in a String for unicode output of a message. */
  static String escapeDoubleQuotesAndBackslashes(String input) {
    return input.replace("\\", "\\\\").replace("\"", "\\\"");
  }
}