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 //
 // Copyright 2017 The Abseil Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
 // -----------------------------------------------------------------------------
 // File: escaping.h
 // -----------------------------------------------------------------------------
 //
 // This header file contains string utilities involved in escaping and
 // unescaping strings in various ways.
 
 #ifndef ABSL_STRINGS_ESCAPING_H_
 #define ABSL_STRINGS_ESCAPING_H_
 
 #include <cstddef>
 #include <string>
 #include <vector>
 
 #include "absl/base/macros.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
 // CUnescape()
 //
 // Unescapes a `source` string and copies it into `dest`, rewriting C-style
 // escape sequences (https://en.cppreference.com/w/cpp/language/escape) into
 // their proper code point equivalents, returning `true` if successful.
 //
 // The following unescape sequences can be handled:
 //
 //   * ASCII escape sequences ('\n','\r','\\', etc.) to their ASCII equivalents
 //   * Octal escape sequences ('\nnn') to byte nnn. The unescaped value must
 //     resolve to a single byte or an error will occur. E.g. values greater than
 //     0xff will produce an error.
 //   * Hexadecimal escape sequences ('\xnn') to byte nn. While an arbitrary
 //     number of following digits are allowed, the unescaped value must resolve
 //     to a single byte or an error will occur. E.g. '\x0045' is equivalent to
 //     '\x45', but '\x1234' will produce an error.
 //   * Unicode escape sequences ('\unnnn' for exactly four hex digits or
 //     '\Unnnnnnnn' for exactly eight hex digits, which will be encoded in
 //     UTF-8. (E.g., `\u2019` unescapes to the three bytes 0xE2, 0x80, and
 //     0x99).
 //
 // If any errors are encountered, this function returns `false`, leaving the
 // `dest` output parameter in an unspecified state, and stores the first
 // encountered error in `error`. To disable error reporting, set `error` to
 // `nullptr` or use the overload with no error reporting below.
 //
 // Example:
 //
 //   std::string s = "foo\\rbar\\nbaz\\t";
 //   std::string unescaped_s;
 //   if (!absl::CUnescape(s, &unescaped_s) {
 //     ...
 //   }
 //   EXPECT_EQ(unescaped_s, "foo\rbar\nbaz\t");
 bool CUnescape(absl::string_view source, std::string* dest, std::string* error);
 
 // Overload of `CUnescape()` with no error reporting.
 inline bool CUnescape(absl::string_view source, std::string* dest) {
   return CUnescape(source, dest, nullptr);
 }
 
 // CEscape()
 //
 // Escapes a 'src' string using C-style escapes sequences
 // (https://en.cppreference.com/w/cpp/language/escape), escaping other
 // non-printable/non-whitespace bytes as octal sequences (e.g. "\377").
 //
 // Example:
 //
 //   std::string s = "foo\rbar\tbaz\010\011\012\013\014\x0d\n";
 //   std::string escaped_s = absl::CEscape(s);
 //   EXPECT_EQ(escaped_s, "foo\\rbar\\tbaz\\010\\t\\n\\013\\014\\r\\n");
 std::string CEscape(absl::string_view src);
 
 // CHexEscape()
 //
 // Escapes a 'src' string using C-style escape sequences, escaping
 // other non-printable/non-whitespace bytes as hexadecimal sequences (e.g.
 // "\xFF").
 //
 // Example:
 //
 //   std::string s = "foo\rbar\tbaz\010\011\012\013\014\x0d\n";
 //   std::string escaped_s = absl::CHexEscape(s);
 //   EXPECT_EQ(escaped_s, "foo\\rbar\\tbaz\\x08\\t\\n\\x0b\\x0c\\r\\n");
 std::string CHexEscape(absl::string_view src);
 
 // Utf8SafeCEscape()
 //
 // Escapes a 'src' string using C-style escape sequences, escaping bytes as
 // octal sequences, and passing through UTF-8 characters without conversion.
 // I.e., when encountering any bytes with their high bit set, this function
 // will not escape those values, whether or not they are valid UTF-8.
 std::string Utf8SafeCEscape(absl::string_view src);
 
 // Utf8SafeCHexEscape()
 //
 // Escapes a 'src' string using C-style escape sequences, escaping bytes as
 // hexadecimal sequences, and passing through UTF-8 characters without
 // conversion.
 std::string Utf8SafeCHexEscape(absl::string_view src);
 
 // Base64Escape()
 //
 // Encodes a `src` string into a base64-encoded 'dest' string with padding
 // characters. This function conforms with RFC 4648 section 4 (base64) and RFC
 // 2045.
 void Base64Escape(absl::string_view src, std::string* dest);
 std::string Base64Escape(absl::string_view src);
 
 // WebSafeBase64Escape()
 //
 // Encodes a `src` string into a base64 string, like Base64Escape() does, but
 // outputs '-' instead of '+' and '_' instead of '/', and does not pad 'dest'.
 // This function conforms with RFC 4648 section 5 (base64url).
 void WebSafeBase64Escape(absl::string_view src, std::string* dest);
 std::string WebSafeBase64Escape(absl::string_view src);
 
 // Base64Unescape()
 //
 // Converts a `src` string encoded in Base64 (RFC 4648 section 4) to its binary
 // equivalent, writing it to a `dest` buffer, returning `true` on success. If
 // `src` contains invalid characters, `dest` is cleared and returns `false`.
 // If padding is included (note that `Base64Escape()` does produce it), it must
 // be correct. In the padding, '=' and '.' are treated identically.
 bool Base64Unescape(absl::string_view src, std::string* dest);
 
 // WebSafeBase64Unescape()
 //
 // Converts a `src` string encoded in "web safe" Base64 (RFC 4648 section 5) to
 // its binary equivalent, writing it to a `dest` buffer. If `src` contains
 // invalid characters, `dest` is cleared and returns `false`. If padding is
 // included (note that `WebSafeBase64Escape()` does not produce it), it must be
 // correct. In the padding, '=' and '.' are treated identically.
 bool WebSafeBase64Unescape(absl::string_view src, std::string* dest);
 
 // HexStringToBytes()
 //
 // Converts an ASCII hex string into bytes, returning binary data of length
 // `from.size()/2`.
 std::string HexStringToBytes(absl::string_view from);
 
 // BytesToHexString()
 //
 // Converts binary data into an ASCII text string, returning a string of size
 // `2*from.size()`.
 std::string BytesToHexString(absl::string_view from);
 
 ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_STRINGS_ESCAPING_H_

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