diff --git a/absl/strings/escaping.cc b/absl/strings/escaping.cc
new file mode 100644
index 0000000..0d336e3
--- /dev/null
+++ b/absl/strings/escaping.cc
@@ -0,0 +1,1129 @@
+// 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.
+
+#include "absl/strings/escaping.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <iterator>
+#include <limits>
+#include <string>
+
+#include "absl/base/internal/endian.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/unaligned_access.h"
+#include "absl/strings/internal/char_map.h"
+#include "absl/strings/internal/resize_uninitialized.h"
+#include "absl/strings/internal/utf8.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_join.h"
+#include "absl/strings/string_view.h"
+
+namespace absl {
+namespace {
+
+// Digit conversion.
+constexpr char kHexChar[] = "0123456789abcdef";
+
+constexpr char kHexTable[513] =
+    "000102030405060708090a0b0c0d0e0f"
+    "101112131415161718191a1b1c1d1e1f"
+    "202122232425262728292a2b2c2d2e2f"
+    "303132333435363738393a3b3c3d3e3f"
+    "404142434445464748494a4b4c4d4e4f"
+    "505152535455565758595a5b5c5d5e5f"
+    "606162636465666768696a6b6c6d6e6f"
+    "707172737475767778797a7b7c7d7e7f"
+    "808182838485868788898a8b8c8d8e8f"
+    "909192939495969798999a9b9c9d9e9f"
+    "a0a1a2a3a4a5a6a7a8a9aaabacadaeaf"
+    "b0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
+    "c0c1c2c3c4c5c6c7c8c9cacbcccdcecf"
+    "d0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
+    "e0e1e2e3e4e5e6e7e8e9eaebecedeeef"
+    "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
+
+// These are used for the leave_nulls_escaped argument to CUnescapeInternal().
+constexpr bool kUnescapeNulls = false;
+
+inline bool is_octal_digit(char c) { return ('0' <= c) && (c <= '7'); }
+
+inline int hex_digit_to_int(char c) {
+  static_assert('0' == 0x30 && 'A' == 0x41 && 'a' == 0x61,
+                "Character set must be ASCII.");
+  assert(absl::ascii_isxdigit(c));
+  int x = static_cast<unsigned char>(c);
+  if (x > '9') {
+    x += 9;
+  }
+  return x & 0xf;
+}
+
+inline bool IsSurrogate(char32_t c, absl::string_view src, std::string* error) {
+  if (c >= 0xD800 && c <= 0xDFFF) {
+    if (error) {
+      *error = absl::StrCat("invalid surrogate character (0xD800-DFFF): \\",
+                            src);
+    }
+    return true;
+  }
+  return false;
+}
+
+// ----------------------------------------------------------------------
+// CUnescapeInternal()
+//    Implements both CUnescape() and CUnescapeForNullTerminatedString().
+//
+//    Unescapes C escape sequences and is the reverse of CEscape().
+//
+//    If 'source' is valid, stores the unescaped string and its size in
+//    'dest' and 'dest_len' respectively, and returns true. Otherwise
+//    returns false and optionally stores the error description in
+//    'error'. Set 'error' to nullptr to disable error reporting.
+//
+//    'dest' should point to a buffer that is at least as big as 'source'.
+//    'source' and 'dest' may be the same.
+//
+//     NOTE: any changes to this function must also be reflected in the older
+//     UnescapeCEscapeSequences().
+// ----------------------------------------------------------------------
+bool CUnescapeInternal(absl::string_view source, bool leave_nulls_escaped,
+                       char* dest, ptrdiff_t* dest_len, std::string* error) {
+  char* d = dest;
+  const char* p = source.data();
+  const char* end = p + source.size();
+  const char* last_byte = end - 1;
+
+  // Small optimization for case where source = dest and there's no escaping
+  while (p == d && p < end && *p != '\\') p++, d++;
+
+  while (p < end) {
+    if (*p != '\\') {
+      *d++ = *p++;
+    } else {
+      if (++p > last_byte) {  // skip past the '\\'
+        if (error) *error = "String cannot end with \\";
+        return false;
+      }
+      switch (*p) {
+        case 'a':  *d++ = '\a';  break;
+        case 'b':  *d++ = '\b';  break;
+        case 'f':  *d++ = '\f';  break;
+        case 'n':  *d++ = '\n';  break;
+        case 'r':  *d++ = '\r';  break;
+        case 't':  *d++ = '\t';  break;
+        case 'v':  *d++ = '\v';  break;
+        case '\\': *d++ = '\\';  break;
+        case '?':  *d++ = '\?';  break;    // \?  Who knew?
+        case '\'': *d++ = '\'';  break;
+        case '"':  *d++ = '\"';  break;
+        case '0':
+        case '1':
+        case '2':
+        case '3':
+        case '4':
+        case '5':
+        case '6':
+        case '7': {
+          // octal digit: 1 to 3 digits
+          const char* octal_start = p;
+          unsigned int ch = *p - '0';
+          if (p < last_byte && is_octal_digit(p[1])) ch = ch * 8 + *++p - '0';
+          if (p < last_byte && is_octal_digit(p[1]))
+            ch = ch * 8 + *++p - '0';      // now points at last digit
+          if (ch > 0xff) {
+            if (error) {
+              *error = "Value of \\" +
+                       std::string(octal_start, p + 1 - octal_start) +
+                       " exceeds 0xff";
+            }
+            return false;
+          }
+          if ((ch == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            const ptrdiff_t octal_size = p + 1 - octal_start;
+            *d++ = '\\';
+            memcpy(d, octal_start, octal_size);
+            d += octal_size;
+            break;
+          }
+          *d++ = ch;
+          break;
+        }
+        case 'x':
+        case 'X': {
+          if (p >= last_byte) {
+            if (error) *error = "String cannot end with \\x";
+            return false;
+          } else if (!absl::ascii_isxdigit(p[1])) {
+            if (error) *error = "\\x cannot be followed by a non-hex digit";
+            return false;
+          }
+          unsigned int ch = 0;
+          const char* hex_start = p;
+          while (p < last_byte && absl::ascii_isxdigit(p[1]))
+            // Arbitrarily many hex digits
+            ch = (ch << 4) + hex_digit_to_int(*++p);
+          if (ch > 0xFF) {
+            if (error) {
+              *error = "Value of \\" +
+                       std::string(hex_start, p + 1 - hex_start) +
+                       " exceeds 0xff";
+            }
+            return false;
+          }
+          if ((ch == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            const ptrdiff_t hex_size = p + 1 - hex_start;
+            *d++ = '\\';
+            memcpy(d, hex_start, hex_size);
+            d += hex_size;
+            break;
+          }
+          *d++ = ch;
+          break;
+        }
+        case 'u': {
+          // \uhhhh => convert 4 hex digits to UTF-8
+          char32_t rune = 0;
+          const char* hex_start = p;
+          if (p + 4 >= end) {
+            if (error) {
+              *error = "\\u must be followed by 4 hex digits: \\" +
+                       std::string(hex_start, p + 1 - hex_start);
+            }
+            return false;
+          }
+          for (int i = 0; i < 4; ++i) {
+            // Look one char ahead.
+            if (absl::ascii_isxdigit(p[1])) {
+              rune = (rune << 4) + hex_digit_to_int(*++p);  // Advance p.
+            } else {
+              if (error) {
+                *error = "\\u must be followed by 4 hex digits: \\" +
+                         std::string(hex_start, p + 1 - hex_start);
+              }
+              return false;
+            }
+          }
+          if ((rune == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            *d++ = '\\';
+            memcpy(d, hex_start, 5);  // u0000
+            d += 5;
+            break;
+          }
+          if (IsSurrogate(rune, absl::string_view(hex_start, 5), error)) {
+            return false;
+          }
+          d += strings_internal::EncodeUTF8Char(d, rune);
+          break;
+        }
+        case 'U': {
+          // \Uhhhhhhhh => convert 8 hex digits to UTF-8
+          char32_t rune = 0;
+          const char* hex_start = p;
+          if (p + 8 >= end) {
+            if (error) {
+              *error = "\\U must be followed by 8 hex digits: \\" +
+                       std::string(hex_start, p + 1 - hex_start);
+            }
+            return false;
+          }
+          for (int i = 0; i < 8; ++i) {
+            // Look one char ahead.
+            if (absl::ascii_isxdigit(p[1])) {
+              // Don't change rune until we're sure this
+              // is within the Unicode limit, but do advance p.
+              uint32_t newrune = (rune << 4) + hex_digit_to_int(*++p);
+              if (newrune > 0x10FFFF) {
+                if (error) {
+                  *error = "Value of \\" +
+                           std::string(hex_start, p + 1 - hex_start) +
+                           " exceeds Unicode limit (0x10FFFF)";
+                }
+                return false;
+              } else {
+                rune = newrune;
+              }
+            } else {
+              if (error) {
+                *error = "\\U must be followed by 8 hex digits: \\" +
+                         std::string(hex_start, p + 1 - hex_start);
+              }
+              return false;
+            }
+          }
+          if ((rune == 0) && leave_nulls_escaped) {
+            // Copy the escape sequence for the null character
+            *d++ = '\\';
+            memcpy(d, hex_start, 9);  // U00000000
+            d += 9;
+            break;
+          }
+          if (IsSurrogate(rune, absl::string_view(hex_start, 9), error)) {
+            return false;
+          }
+          d += strings_internal::EncodeUTF8Char(d, rune);
+          break;
+        }
+        default: {
+          if (error) *error = std::string("Unknown escape sequence: \\") + *p;
+          return false;
+        }
+      }
+      p++;                                 // read past letter we escaped
+    }
+  }
+  *dest_len = d - dest;
+  return true;
+}
+
+// ----------------------------------------------------------------------
+// CUnescapeInternal()
+//
+//    Same as above but uses a std::string for output. 'source' and 'dest'
+//    may be the same.
+// ----------------------------------------------------------------------
+bool CUnescapeInternal(absl::string_view source, bool leave_nulls_escaped,
+                       std::string* dest, std::string* error) {
+  strings_internal::STLStringResizeUninitialized(dest, source.size());
+
+  ptrdiff_t dest_size;
+  if (!CUnescapeInternal(source,
+                         leave_nulls_escaped,
+                         &(*dest)[0],
+                         &dest_size,
+                         error)) {
+    return false;
+  }
+  dest->erase(dest_size);
+  return true;
+}
+
+// ----------------------------------------------------------------------
+// CEscape()
+// CHexEscape()
+// Utf8SafeCEscape()
+// Utf8SafeCHexEscape()
+//    Escapes 'src' using C-style escape sequences.  This is useful for
+//    preparing query flags.  The 'Hex' version uses hexadecimal rather than
+//    octal sequences.  The 'Utf8Safe' version does not touch UTF-8 bytes.
+//
+//    Escaped chars: \n, \r, \t, ", ', \, and !absl::ascii_isprint().
+// ----------------------------------------------------------------------
+std::string CEscapeInternal(absl::string_view src, bool use_hex,
+                            bool utf8_safe) {
+  std::string dest;
+  bool last_hex_escape = false;  // true if last output char was \xNN.
+
+  for (unsigned char c : src) {
+    bool is_hex_escape = false;
+    switch (c) {
+      case '\n': dest.append("\\" "n"); break;
+      case '\r': dest.append("\\" "r"); break;
+      case '\t': dest.append("\\" "t"); break;
+      case '\"': dest.append("\\" "\""); break;
+      case '\'': dest.append("\\" "'"); break;
+      case '\\': dest.append("\\" "\\"); break;
+      default:
+        // Note that if we emit \xNN and the src character after that is a hex
+        // digit then that digit must be escaped too to prevent it being
+        // interpreted as part of the character code by C.
+        if ((!utf8_safe || c < 0x80) &&
+            (!absl::ascii_isprint(c) ||
+             (last_hex_escape && absl::ascii_isxdigit(c)))) {
+          if (use_hex) {
+            dest.append("\\" "x");
+            dest.push_back(kHexChar[c / 16]);
+            dest.push_back(kHexChar[c % 16]);
+            is_hex_escape = true;
+          } else {
+            dest.append("\\");
+            dest.push_back(kHexChar[c / 64]);
+            dest.push_back(kHexChar[(c % 64) / 8]);
+            dest.push_back(kHexChar[c % 8]);
+          }
+        } else {
+          dest.push_back(c);
+          break;
+        }
+    }
+    last_hex_escape = is_hex_escape;
+  }
+
+  return dest;
+}
+
+/* clang-format off */
+constexpr char c_escaped_len[256] = {
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 4, 2, 4, 4,  // \t, \n, \r
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1,  // ", '
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // '0'..'9'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // 'A'..'O'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1,  // 'P'..'Z', '\'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  // 'a'..'o'
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4,  // 'p'..'z', DEL
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
+};
+/* clang-format on */
+
+// Calculates the length of the C-style escaped version of 'src'.
+// Assumes that non-printable characters are escaped using octal sequences, and
+// that UTF-8 bytes are not handled specially.
+inline size_t CEscapedLength(absl::string_view src) {
+  size_t escaped_len = 0;
+  for (unsigned char c : src) escaped_len += c_escaped_len[c];
+  return escaped_len;
+}
+
+void CEscapeAndAppendInternal(absl::string_view src, std::string* dest) {
+  size_t escaped_len = CEscapedLength(src);
+  if (escaped_len == src.size()) {
+    dest->append(src.data(), src.size());
+    return;
+  }
+
+  size_t cur_dest_len = dest->size();
+  strings_internal::STLStringResizeUninitialized(dest,
+                                                 cur_dest_len + escaped_len);
+  char* append_ptr = &(*dest)[cur_dest_len];
+
+  for (unsigned char c : src) {
+    int char_len = c_escaped_len[c];
+    if (char_len == 1) {
+      *append_ptr++ = c;
+    } else if (char_len == 2) {
+      switch (c) {
+        case '\n':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 'n';
+          break;
+        case '\r':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 'r';
+          break;
+        case '\t':
+          *append_ptr++ = '\\';
+          *append_ptr++ = 't';
+          break;
+        case '\"':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\"';
+          break;
+        case '\'':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\'';
+          break;
+        case '\\':
+          *append_ptr++ = '\\';
+          *append_ptr++ = '\\';
+          break;
+      }
+    } else {
+      *append_ptr++ = '\\';
+      *append_ptr++ = '0' + c / 64;
+      *append_ptr++ = '0' + (c % 64) / 8;
+      *append_ptr++ = '0' + c % 8;
+    }
+  }
+}
+
+bool Base64UnescapeInternal(const char* src_param, size_t szsrc, char* dest,
+                            size_t szdest, const signed char* unbase64,
+                            size_t* len) {
+  static const char kPad64Equals = '=';
+  static const char kPad64Dot = '.';
+
+  size_t destidx = 0;
+  int decode = 0;
+  int state = 0;
+  unsigned int ch = 0;
+  unsigned int temp = 0;
+
+  // If "char" is signed by default, using *src as an array index results in
+  // accessing negative array elements. Treat the input as a pointer to
+  // unsigned char to avoid this.
+  const unsigned char* src = reinterpret_cast<const unsigned char*>(src_param);
+
+  // The GET_INPUT macro gets the next input character, skipping
+  // over any whitespace, and stopping when we reach the end of the
+  // std::string or when we read any non-data character.  The arguments are
+  // an arbitrary identifier (used as a label for goto) and the number
+  // of data bytes that must remain in the input to avoid aborting the
+  // loop.
+#define GET_INPUT(label, remain)                                \
+  label:                                                        \
+  --szsrc;                                                      \
+  ch = *src++;                                                  \
+  decode = unbase64[ch];                                        \
+  if (decode < 0) {                                             \
+    if (absl::ascii_isspace(ch) && szsrc >= remain) goto label; \
+    state = 4 - remain;                                         \
+    break;                                                      \
+  }
+
+  // if dest is null, we're just checking to see if it's legal input
+  // rather than producing output.  (I suspect this could just be done
+  // with a regexp...).  We duplicate the loop so this test can be
+  // outside it instead of in every iteration.
+
+  if (dest) {
+    // This loop consumes 4 input bytes and produces 3 output bytes
+    // per iteration.  We can't know at the start that there is enough
+    // data left in the std::string for a full iteration, so the loop may
+    // break out in the middle; if so 'state' will be set to the
+    // number of input bytes read.
+
+    while (szsrc >= 4) {
+      // We'll start by optimistically assuming that the next four
+      // bytes of the std::string (src[0..3]) are four good data bytes
+      // (that is, no nulls, whitespace, padding chars, or illegal
+      // chars).  We need to test src[0..2] for nulls individually
+      // before constructing temp to preserve the property that we
+      // never read past a null in the std::string (no matter how long
+      // szsrc claims the std::string is).
+
+      if (!src[0] || !src[1] || !src[2] ||
+          ((temp = ((unsigned(unbase64[src[0]]) << 18) |
+                    (unsigned(unbase64[src[1]]) << 12) |
+                    (unsigned(unbase64[src[2]]) << 6) |
+                    (unsigned(unbase64[src[3]])))) &
+           0x80000000)) {
+        // Iff any of those four characters was bad (null, illegal,
+        // whitespace, padding), then temp's high bit will be set
+        // (because unbase64[] is -1 for all bad characters).
+        //
+        // We'll back up and resort to the slower decoder, which knows
+        // how to handle those cases.
+
+        GET_INPUT(first, 4);
+        temp = decode;
+        GET_INPUT(second, 3);
+        temp = (temp << 6) | decode;
+        GET_INPUT(third, 2);
+        temp = (temp << 6) | decode;
+        GET_INPUT(fourth, 1);
+        temp = (temp << 6) | decode;
+      } else {
+        // We really did have four good data bytes, so advance four
+        // characters in the std::string.
+
+        szsrc -= 4;
+        src += 4;
+      }
+
+      // temp has 24 bits of input, so write that out as three bytes.
+
+      if (destidx + 3 > szdest) return false;
+      dest[destidx + 2] = temp;
+      temp >>= 8;
+      dest[destidx + 1] = temp;
+      temp >>= 8;
+      dest[destidx] = temp;
+      destidx += 3;
+    }
+  } else {
+    while (szsrc >= 4) {
+      if (!src[0] || !src[1] || !src[2] ||
+          ((temp = ((unsigned(unbase64[src[0]]) << 18) |
+                    (unsigned(unbase64[src[1]]) << 12) |
+                    (unsigned(unbase64[src[2]]) << 6) |
+                    (unsigned(unbase64[src[3]])))) &
+           0x80000000)) {
+        GET_INPUT(first_no_dest, 4);
+        GET_INPUT(second_no_dest, 3);
+        GET_INPUT(third_no_dest, 2);
+        GET_INPUT(fourth_no_dest, 1);
+      } else {
+        szsrc -= 4;
+        src += 4;
+      }
+      destidx += 3;
+    }
+  }
+
+#undef GET_INPUT
+
+  // if the loop terminated because we read a bad character, return
+  // now.
+  if (decode < 0 && ch != kPad64Equals && ch != kPad64Dot &&
+      !absl::ascii_isspace(ch))
+    return false;
+
+  if (ch == kPad64Equals || ch == kPad64Dot) {
+    // if we stopped by hitting an '=' or '.', un-read that character -- we'll
+    // look at it again when we count to check for the proper number of
+    // equals signs at the end.
+    ++szsrc;
+    --src;
+  } else {
+    // This loop consumes 1 input byte per iteration.  It's used to
+    // clean up the 0-3 input bytes remaining when the first, faster
+    // loop finishes.  'temp' contains the data from 'state' input
+    // characters read by the first loop.
+    while (szsrc > 0) {
+      --szsrc;
+      ch = *src++;
+      decode = unbase64[ch];
+      if (decode < 0) {
+        if (absl::ascii_isspace(ch)) {
+          continue;
+        } else if (ch == kPad64Equals || ch == kPad64Dot) {
+          // back up one character; we'll read it again when we check
+          // for the correct number of pad characters at the end.
+          ++szsrc;
+          --src;
+          break;
+        } else {
+          return false;
+        }
+      }
+
+      // Each input character gives us six bits of output.
+      temp = (temp << 6) | decode;
+      ++state;
+      if (state == 4) {
+        // If we've accumulated 24 bits of output, write that out as
+        // three bytes.
+        if (dest) {
+          if (destidx + 3 > szdest) return false;
+          dest[destidx + 2] = temp;
+          temp >>= 8;
+          dest[destidx + 1] = temp;
+          temp >>= 8;
+          dest[destidx] = temp;
+        }
+        destidx += 3;
+        state = 0;
+        temp = 0;
+      }
+    }
+  }
+
+  // Process the leftover data contained in 'temp' at the end of the input.
+  int expected_equals = 0;
+  switch (state) {
+    case 0:
+      // Nothing left over; output is a multiple of 3 bytes.
+      break;
+
+    case 1:
+      // Bad input; we have 6 bits left over.
+      return false;
+
+    case 2:
+      // Produce one more output byte from the 12 input bits we have left.
+      if (dest) {
+        if (destidx + 1 > szdest) return false;
+        temp >>= 4;
+        dest[destidx] = temp;
+      }
+      ++destidx;
+      expected_equals = 2;
+      break;
+
+    case 3:
+      // Produce two more output bytes from the 18 input bits we have left.
+      if (dest) {
+        if (destidx + 2 > szdest) return false;
+        temp >>= 2;
+        dest[destidx + 1] = temp;
+        temp >>= 8;
+        dest[destidx] = temp;
+      }
+      destidx += 2;
+      expected_equals = 1;
+      break;
+
+    default:
+      // state should have no other values at this point.
+      ABSL_RAW_LOG(FATAL, "This can't happen; base64 decoder state = %d",
+                   state);
+  }
+
+  // The remainder of the std::string should be all whitespace, mixed with
+  // exactly 0 equals signs, or exactly 'expected_equals' equals
+  // signs.  (Always accepting 0 equals signs is an Abseil extension
+  // not covered in the RFC, as is accepting dot as the pad character.)
+
+  int equals = 0;
+  while (szsrc > 0) {
+    if (*src == kPad64Equals || *src == kPad64Dot)
+      ++equals;
+    else if (!absl::ascii_isspace(*src))
+      return false;
+    --szsrc;
+    ++src;
+  }
+
+  const bool ok = (equals == 0 || equals == expected_equals);
+  if (ok) *len = destidx;
+  return ok;
+}
+
+// The arrays below were generated by the following code
+// #include <sys/time.h>
+// #include <stdlib.h>
+// #include <string.h>
+// main()
+// {
+//   static const char Base64[] =
+//     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+//   char* pos;
+//   int idx, i, j;
+//   printf("    ");
+//   for (i = 0; i < 255; i += 8) {
+//     for (j = i; j < i + 8; j++) {
+//       pos = strchr(Base64, j);
+//       if ((pos == nullptr) || (j == 0))
+//         idx = -1;
+//       else
+//         idx = pos - Base64;
+//       if (idx == -1)
+//         printf(" %2d,     ", idx);
+//       else
+//         printf(" %2d/*%c*/,", idx, j);
+//     }
+//     printf("\n    ");
+//   }
+// }
+//
+// where the value of "Base64[]" was replaced by one of the base-64 conversion
+// tables from the functions below.
+/* clang-format off */
+constexpr signed char kUnBase64[] = {
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      62/*+*/, -1,      -1,      -1,      63/*/ */,
+    52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
+    60/*8*/, 61/*9*/, -1,      -1,      -1,      -1,      -1,      -1,
+    -1,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
+    07/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
+    15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
+    23/*X*/, 24/*Y*/, 25/*Z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
+    33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
+    41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
+    49/*x*/, 50/*y*/, 51/*z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1
+};
+
+constexpr signed char kUnWebSafeBase64[] = {
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      62/*-*/, -1,      -1,
+    52/*0*/, 53/*1*/, 54/*2*/, 55/*3*/, 56/*4*/, 57/*5*/, 58/*6*/, 59/*7*/,
+    60/*8*/, 61/*9*/, -1,      -1,      -1,      -1,      -1,      -1,
+    -1,       0/*A*/,  1/*B*/,  2/*C*/,  3/*D*/,  4/*E*/,  5/*F*/,  6/*G*/,
+    07/*H*/,  8/*I*/,  9/*J*/, 10/*K*/, 11/*L*/, 12/*M*/, 13/*N*/, 14/*O*/,
+    15/*P*/, 16/*Q*/, 17/*R*/, 18/*S*/, 19/*T*/, 20/*U*/, 21/*V*/, 22/*W*/,
+    23/*X*/, 24/*Y*/, 25/*Z*/, -1,      -1,      -1,      -1,      63/*_*/,
+    -1,      26/*a*/, 27/*b*/, 28/*c*/, 29/*d*/, 30/*e*/, 31/*f*/, 32/*g*/,
+    33/*h*/, 34/*i*/, 35/*j*/, 36/*k*/, 37/*l*/, 38/*m*/, 39/*n*/, 40/*o*/,
+    41/*p*/, 42/*q*/, 43/*r*/, 44/*s*/, 45/*t*/, 46/*u*/, 47/*v*/, 48/*w*/,
+    49/*x*/, 50/*y*/, 51/*z*/, -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1,
+    -1,      -1,      -1,      -1,      -1,      -1,      -1,      -1
+};
+/* clang-format on */
+
+size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {
+  // Base64 encodes three bytes of input at a time. If the input is not
+  // divisible by three, we pad as appropriate.
+  //
+  // (from https://tools.ietf.org/html/rfc3548)
+  // Special processing is performed if fewer than 24 bits are available
+  // at the end of the data being encoded.  A full encoding quantum is
+  // always completed at the end of a quantity.  When fewer than 24 input
+  // bits are available in an input group, zero bits are added (on the
+  // right) to form an integral number of 6-bit groups.  Padding at the
+  // end of the data is performed using the '=' character.  Since all base
+  // 64 input is an integral number of octets, only the following cases
+  // can arise:
+
+  // Base64 encodes each three bytes of input into four bytes of output.
+  size_t len = (input_len / 3) * 4;
+
+  if (input_len % 3 == 0) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (1) the final quantum of encoding input is an integral multiple of 24
+    // bits; here, the final unit of encoded output will be an integral
+    // multiple of 4 characters with no "=" padding,
+  } else if (input_len % 3 == 1) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (2) the final quantum of encoding input is exactly 8 bits; here, the
+    // final unit of encoded output will be two characters followed by two
+    // "=" padding characters, or
+    len += 2;
+    if (do_padding) {
+      len += 2;
+    }
+  } else {  // (input_len % 3 == 2)
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (3) the final quantum of encoding input is exactly 16 bits; here, the
+    // final unit of encoded output will be three characters followed by one
+    // "=" padding character.
+    len += 3;
+    if (do_padding) {
+      len += 1;
+    }
+  }
+
+  assert(len >= input_len);  // make sure we didn't overflow
+  return len;
+}
+
+size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
+                            size_t szdest, const char* base64,
+                            bool do_padding) {
+  static const char kPad64 = '=';
+
+  if (szsrc * 4 > szdest * 3) return 0;
+
+  char* cur_dest = dest;
+  const unsigned char* cur_src = src;
+
+  char* const limit_dest = dest + szdest;
+  const unsigned char* const limit_src = src + szsrc;
+
+  // Three bytes of data encodes to four characters of cyphertext.
+  // So we can pump through three-byte chunks atomically.
+  if (szsrc >= 3) {  // "limit_src - 3" is UB if szsrc < 3.
+    while (cur_src < limit_src - 3) {  // While we have >= 32 bits.
+      uint32_t in = absl::big_endian::Load32(cur_src) >> 8;
+
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+
+      cur_dest += 4;
+      cur_src += 3;
+    }
+  }
+  // To save time, we didn't update szdest or szsrc in the loop.  So do it now.
+  szdest = limit_dest - cur_dest;
+  szsrc = limit_src - cur_src;
+
+  /* now deal with the tail (<=3 bytes) */
+  switch (szsrc) {
+    case 0:
+      // Nothing left; nothing more to do.
+      break;
+    case 1: {
+      // One byte left: this encodes to two characters, and (optionally)
+      // two pad characters to round out the four-character cypherblock.
+      if (szdest < 2) return 0;
+      uint32_t in = cur_src[0];
+      cur_dest[0] = base64[in >> 2];
+      in &= 0x3;
+      cur_dest[1] = base64[in << 4];
+      cur_dest += 2;
+      szdest -= 2;
+      if (do_padding) {
+        if (szdest < 2) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest[1] = kPad64;
+        cur_dest += 2;
+        szdest -= 2;
+      }
+      break;
+    }
+    case 2: {
+      // Two bytes left: this encodes to three characters, and (optionally)
+      // one pad character to round out the four-character cypherblock.
+      if (szdest < 3) return 0;
+      uint32_t in = absl::big_endian::Load16(cur_src);
+      cur_dest[0] = base64[in >> 10];
+      in &= 0x3FF;
+      cur_dest[1] = base64[in >> 4];
+      in &= 0x00F;
+      cur_dest[2] = base64[in << 2];
+      cur_dest += 3;
+      szdest -= 3;
+      if (do_padding) {
+        if (szdest < 1) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest += 1;
+        szdest -= 1;
+      }
+      break;
+    }
+    case 3: {
+      // Three bytes left: same as in the big loop above.  We can't do this in
+      // the loop because the loop above always reads 4 bytes, and the fourth
+      // byte is past the end of the input.
+      if (szdest < 4) return 0;
+      uint32_t in = (cur_src[0] << 16) + absl::big_endian::Load16(cur_src + 1);
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+      cur_dest += 4;
+      szdest -= 4;
+      break;
+    }
+    default:
+      // Should not be reached: blocks of 4 bytes are handled
+      // in the while loop before this switch statement.
+      ABSL_RAW_LOG(FATAL, "Logic problem? szsrc = %zu", szsrc);
+      break;
+  }
+  return (cur_dest - dest);
+}
+
+constexpr char kBase64Chars[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+constexpr char kWebSafeBase64Chars[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+template <typename String>
+void Base64EscapeInternal(const unsigned char* src, size_t szsrc, String* dest,
+                          bool do_padding, const char* base64_chars) {
+  const size_t calc_escaped_size =
+      CalculateBase64EscapedLenInternal(szsrc, do_padding);
+  strings_internal::STLStringResizeUninitialized(dest, calc_escaped_size);
+
+  const size_t escaped_len = Base64EscapeInternal(
+      src, szsrc, &(*dest)[0], dest->size(), base64_chars, do_padding);
+  assert(calc_escaped_size == escaped_len);
+  dest->erase(escaped_len);
+}
+
+template <typename String>
+bool Base64UnescapeInternal(const char* src, size_t slen, String* dest,
+                            const signed char* unbase64) {
+  // Determine the size of the output std::string.  Base64 encodes every 3 bytes into
+  // 4 characters.  any leftover chars are added directly for good measure.
+  // This is documented in the base64 RFC: http://tools.ietf.org/html/rfc3548
+  const size_t dest_len = 3 * (slen / 4) + (slen % 4);
+
+  strings_internal::STLStringResizeUninitialized(dest, dest_len);
+
+  // We are getting the destination buffer by getting the beginning of the
+  // std::string and converting it into a char *.
+  size_t len;
+  const bool ok =
+      Base64UnescapeInternal(src, slen, &(*dest)[0], dest_len, unbase64, &len);
+  if (!ok) {
+    dest->clear();
+    return false;
+  }
+
+  // could be shorter if there was padding
+  assert(len <= dest_len);
+  dest->erase(len);
+
+  return true;
+}
+
+/* clang-format off */
+constexpr char kHexValue[256] = {
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  1,  2,  3,  4,  5,  6, 7, 8, 9, 0, 0, 0, 0, 0, 0,  // '0'..'9'
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'A'..'F'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0,  // 'a'..'f'
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+/* clang-format on */
+
+// This is a templated function so that T can be either a char*
+// or a string.  This works because we use the [] operator to access
+// individual characters at a time.
+template <typename T>
+void HexStringToBytesInternal(const char* from, T to, ptrdiff_t num) {
+  for (int i = 0; i < num; i++) {
+    to[i] = (kHexValue[from[i * 2] & 0xFF] << 4) +
+            (kHexValue[from[i * 2 + 1] & 0xFF]);
+  }
+}
+
+// This is a templated function so that T can be either a char* or a
+// std::string.
+template <typename T>
+void BytesToHexStringInternal(const unsigned char* src, T dest, ptrdiff_t num) {
+  auto dest_ptr = &dest[0];
+  for (auto src_ptr = src; src_ptr != (src + num); ++src_ptr, dest_ptr += 2) {
+    const char* hex_p = &kHexTable[*src_ptr * 2];
+    std::copy(hex_p, hex_p + 2, dest_ptr);
+  }
+}
+
+}  // namespace
+
+// ----------------------------------------------------------------------
+// CUnescape()
+//
+// See CUnescapeInternal() for implementation details.
+// ----------------------------------------------------------------------
+bool CUnescape(absl::string_view source, std::string* dest,
+               std::string* error) {
+  return CUnescapeInternal(source, kUnescapeNulls, dest, error);
+}
+
+std::string CEscape(absl::string_view src) {
+  std::string dest;
+  CEscapeAndAppendInternal(src, &dest);
+  return dest;
+}
+
+std::string CHexEscape(absl::string_view src) {
+  return CEscapeInternal(src, true, false);
+}
+
+std::string Utf8SafeCEscape(absl::string_view src) {
+  return CEscapeInternal(src, false, true);
+}
+
+std::string Utf8SafeCHexEscape(absl::string_view src) {
+  return CEscapeInternal(src, true, true);
+}
+
+// ----------------------------------------------------------------------
+// Base64Unescape() - base64 decoder
+// Base64Escape() - base64 encoder
+// WebSafeBase64Unescape() - Google's variation of base64 decoder
+// WebSafeBase64Escape() - Google's variation of base64 encoder
+//
+// Check out
+// http://tools.ietf.org/html/rfc2045 for formal description, but what we
+// care about is that...
+//   Take the encoded stuff in groups of 4 characters and turn each
+//   character into a code 0 to 63 thus:
+//           A-Z map to 0 to 25
+//           a-z map to 26 to 51
+//           0-9 map to 52 to 61
+//           +(- for WebSafe) maps to 62
+//           /(_ for WebSafe) maps to 63
+//   There will be four numbers, all less than 64 which can be represented
+//   by a 6 digit binary number (aaaaaa, bbbbbb, cccccc, dddddd respectively).
+//   Arrange the 6 digit binary numbers into three bytes as such:
+//   aaaaaabb bbbbcccc ccdddddd
+//   Equals signs (one or two) are used at the end of the encoded block to
+//   indicate that the text was not an integer multiple of three bytes long.
+// ----------------------------------------------------------------------
+
+bool Base64Unescape(absl::string_view src, std::string* dest) {
+  return Base64UnescapeInternal(src.data(), src.size(), dest, kUnBase64);
+}
+
+bool WebSafeBase64Unescape(absl::string_view src, std::string* dest) {
+  return Base64UnescapeInternal(src.data(), src.size(), dest, kUnWebSafeBase64);
+}
+
+void Base64Escape(absl::string_view src, std::string* dest) {
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), dest, true, kBase64Chars);
+}
+
+void WebSafeBase64Escape(absl::string_view src, std::string* dest) {
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), dest, false, kWebSafeBase64Chars);
+}
+
+std::string Base64Escape(absl::string_view src) {
+  std::string dest;
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), &dest, true, kBase64Chars);
+  return dest;
+}
+
+std::string WebSafeBase64Escape(absl::string_view src) {
+  std::string dest;
+  Base64EscapeInternal(reinterpret_cast<const unsigned char*>(src.data()),
+                       src.size(), &dest, false, kWebSafeBase64Chars);
+  return dest;
+}
+
+std::string HexStringToBytes(absl::string_view from) {
+  std::string result;
+  const auto num = from.size() / 2;
+  strings_internal::STLStringResizeUninitialized(&result, num);
+  absl::HexStringToBytesInternal<std::string&>(from.data(), result, num);
+  return result;
+}
+
+std::string BytesToHexString(absl::string_view from) {
+  std::string result;
+  strings_internal::STLStringResizeUninitialized(&result, 2 * from.size());
+  absl::BytesToHexStringInternal<std::string&>(
+      reinterpret_cast<const unsigned char*>(from.data()), result, from.size());
+  return result;
+}
+
+}  // namespace absl