base/json/string_escape.cc

   1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/json/string_escape.h"
   6
   7 #include <string>
   8
   9 #include "base/strings/string_util.h"
  10 #include "base/strings/stringprintf.h"
  11 #include "base/strings/utf_string_conversion_utils.h"
  12 #include "base/strings/utf_string_conversions.h"
  13 #include "base/third_party/icu/icu_utf.h"
  14
  15 namespace base {
  16
  17 namespace {
  18
  19 // Format string for printing a \uXXXX escape sequence.
  20 const char kU16EscapeFormat[] = "\\u%04X";
  21
  22 // The code point to output for an invalid input code unit.
  23 const uint32 kReplacementCodePoint = 0xFFFD;
  24
  25 // Used below in EscapeSpecialCodePoint().
  26 COMPILE_ASSERT('<' == 0x3C, less_than_sign_is_0x3c);
  27
  28 // Try to escape the |code_point| if it is a known special character. If
  29 // successful, returns true and appends the escape sequence to |dest|. This
  30 // isn't required by the spec, but it's more readable by humans.
  31 bool EscapeSpecialCodePoint(uint32 code_point, std::string* dest) {
  32   // WARNING: if you add a new case here, you need to update the reader as well.
  33   // Note: \v is in the reader, but not here since the JSON spec doesn't
  34   // allow it.
  35   switch (code_point) {
  36     case '\b':
  37       dest->append("\\b");
  38       break;
  39     case '\f':
  40       dest->append("\\f");
  41       break;
  42     case '\n':
  43       dest->append("\\n");
  44       break;
  45     case '\r':
  46       dest->append("\\r");
  47       break;
  48     case '\t':
  49       dest->append("\\t");
  50       break;
  51     case '\\':
  52       dest->append("\\\\");
  53       break;
  54     case '"':
  55       dest->append("\\\"");
  56       break;
  57     // Escape < to prevent script execution; escaping > is not necessary and
  58     // not doing so save a few bytes.
  59     case '<':
  60       dest->append("\\u003C");
  61       break;
  62     default:
  63       return false;
  64   }
  65   return true;
  66 }
  67
  68 template <typename S>
  69 bool EscapeJSONStringImpl(const S& str, bool put_in_quotes, std::string* dest) {
  70   bool did_replacement = false;
  71
  72   if (put_in_quotes)
  73     dest->push_back('"');
  74
  75   // Casting is necessary because ICU uses int32. Try and do so safely.
  76   CHECK_LE(str.length(), static_cast<size_t>(kint32max));
  77   const int32 length = static_cast<int32>(str.length());
  78
  79   for (int32 i = 0; i < length; ++i) {
  80     uint32 code_point;
  81     if (!ReadUnicodeCharacter(str.data(), length, &i, &code_point)) {
  82       code_point = kReplacementCodePoint;
  83       did_replacement = true;
  84     }
  85
  86     if (EscapeSpecialCodePoint(code_point, dest))
  87       continue;
  88
  89     // Escape non-printing characters.
  90     if (code_point < 32)
  91       base::StringAppendF(dest, kU16EscapeFormat, code_point);
  92     else
  93       WriteUnicodeCharacter(code_point, dest);
  94   }
  95
  96   if (put_in_quotes)
  97     dest->push_back('"');
  98
  99   return !did_replacement;
 100 }
 101
 102 }  // namespace
 103
 104 bool EscapeJSONString(const StringPiece& str,
 105                       bool put_in_quotes,
 106                       std::string* dest) {
 107   return EscapeJSONStringImpl(str, put_in_quotes, dest);
 108 }
 109
 110 bool EscapeJSONString(const StringPiece16& str,
 111                       bool put_in_quotes,
 112                       std::string* dest) {
 113   return EscapeJSONStringImpl(str, put_in_quotes, dest);
 114 }
 115
 116 std::string GetQuotedJSONString(const StringPiece& str) {
 117   std::string dest;
 118   bool ok = EscapeJSONStringImpl(str, true, &dest);
 119   DCHECK(ok);
 120   return dest;
 121 }
 122
 123 std::string GetQuotedJSONString(const StringPiece16& str) {
 124   std::string dest;
 125   bool ok = EscapeJSONStringImpl(str, true, &dest);
 126   DCHECK(ok);
 127   return dest;
 128 }
 129
 130 std::string EscapeBytesAsInvalidJSONString(const StringPiece& str,
 131                                            bool put_in_quotes) {
 132   std::string dest;
 133
 134   if (put_in_quotes)
 135     dest.push_back('"');
 136
 137   for (StringPiece::const_iterator it = str.begin(); it != str.end(); ++it) {
 138     ToUnsigned<StringPiece::value_type>::Unsigned c = *it;
 139     if (EscapeSpecialCodePoint(c, &dest))
 140       continue;
 141
 142     if (c < 32 || c > 126)
 143       base::StringAppendF(&dest, kU16EscapeFormat, c);
 144     else
 145       dest.push_back(*it);
 146   }
 147
 148   if (put_in_quotes)
 149     dest.push_back('"');
 150
 151   return dest;
 152 }
 153
 154 }  // namespace base