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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
+//
+//      http://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 std::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 {
+
+// CUnescape()
+//
+// Unescapes a `source` std::string and copies it into `dest`, rewriting C-style
+// escape sequences (http://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` 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 = absl::CUnescape(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' std::string using C-style escapes sequences
+// (http://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' std::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' std::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' std::string using C-style escape sequences, escaping bytes as
+// hexidecimal sequences, and passing through UTF-8 characters without
+// conversion.
+std::string Utf8SafeCHexEscape(absl::string_view src);
+
+// Base64Unescape()
+//
+// Converts a `src` std::string encoded in Base64 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`.
+bool Base64Unescape(absl::string_view src, std::string* dest);
+
+// WebSafeBase64Unescape(absl::string_view, std::string*)
+//
+// Converts a `src` std::string encoded in Base64 to its binary equivalent, writing
+// it to a `dest` buffer, but using '-' instead of '+', and '_' instead of '/'.
+// If `src` contains invalid characters, `dest` is cleared and returns `false`.
+bool WebSafeBase64Unescape(absl::string_view src, std::string* dest);
+
+// Base64Escape()
+//
+// Encodes a `src` std::string into a `dest` buffer using base64 encoding, with
+// padding characters. This function conforms with RFC 4648 section 4 (base64).
+void Base64Escape(absl::string_view src, std::string* dest);
+
+// WebSafeBase64Escape()
+//
+// Encodes a `src` std::string into a `dest` buffer using uses '-' instead of '+' and
+// '_' instead of '/', and without padding. This function conforms with RFC 4648
+// section 5 (base64url).
+void WebSafeBase64Escape(absl::string_view src, std::string* dest);
+
+// HexStringToBytes()
+//
+// Converts an ASCII hex std::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 std::string, returing a std::string of size
+// `2*from.size()`.
+std::string BytesToHexString(absl::string_view from);
+
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_ESCAPING_H_