♻️ re-used existing UTF-8 decoder to simplfy string serialization
This commit is contained in:
Niels Lohmann
parent
afe4571309
commit
7456f1d87b
2 changed files with 307 additions and 691 deletions
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@ -34,6 +34,9 @@ class serializer
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using number_float_t = typename BasicJsonType::number_float_t;
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using number_integer_t = typename BasicJsonType::number_integer_t;
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using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
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static constexpr uint8_t UTF8_ACCEPT = 0;
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static constexpr uint8_t UTF8_REJECT = 1;
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public:
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/*!
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@param[in] s output stream to serialize to
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@ -43,7 +46,8 @@ class serializer
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: o(std::move(s)), loc(std::localeconv()),
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thousands_sep(loc->thousands_sep == nullptr ? '\0' : * (loc->thousands_sep)),
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decimal_point(loc->decimal_point == nullptr ? '\0' : * (loc->decimal_point)),
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indent_char(ichar), indent_string(512, indent_char) {}
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indent_char(ichar), indent_string(512, indent_char)
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{}
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// delete because of pointer members
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serializer(const serializer&) = delete;
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@ -259,171 +263,6 @@ class serializer
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}
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private:
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/*!
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@brief returns the number of expected bytes following in UTF-8 string
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@param[in] u the first byte of a UTF-8 string
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@return the number of expected bytes following
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*/
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static constexpr std::size_t bytes_following(const uint8_t u)
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{
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return ((u <= 127) ? 0
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: ((192 <= u and u <= 223) ? 1
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: ((224 <= u and u <= 239) ? 2
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: ((240 <= u and u <= 247) ? 3 : std::string::npos))));
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}
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/*!
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@brief calculates the extra space to escape a JSON string
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@param[in] s the string to escape
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@param[in] ensure_ascii whether to escape non-ASCII characters with
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\uXXXX sequences
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@return the number of characters required to escape string @a s
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@complexity Linear in the length of string @a s.
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*/
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static std::size_t extra_space(const string_t& s,
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const bool ensure_ascii) noexcept
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{
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std::size_t res = 0;
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for (std::size_t i = 0; i < s.size(); ++i)
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{
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switch (s[i])
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{
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// control characters that can be escaped with a backslash
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case '"':
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case '\\':
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case '\b':
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case '\f':
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case '\n':
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case '\r':
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case '\t':
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{
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// from c (1 byte) to \x (2 bytes)
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res += 1;
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break;
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}
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// control characters that need \uxxxx escaping
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case 0x00:
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case 0x01:
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case 0x02:
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case 0x03:
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case 0x04:
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case 0x05:
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case 0x06:
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case 0x07:
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case 0x0B:
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case 0x0E:
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case 0x0F:
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case 0x10:
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case 0x11:
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case 0x12:
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case 0x13:
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case 0x14:
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case 0x15:
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case 0x16:
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case 0x17:
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case 0x18:
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case 0x19:
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case 0x1A:
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case 0x1B:
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case 0x1C:
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case 0x1D:
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case 0x1E:
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case 0x1F:
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{
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// from c (1 byte) to \uxxxx (6 bytes)
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res += 5;
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break;
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}
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default:
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{
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if (ensure_ascii and (s[i] & 0x80 or s[i] == 0x7F))
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{
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const auto bytes = bytes_following(static_cast<uint8_t>(s[i]));
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// invalid characters will be detected by throw_if_invalid_utf8
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assert (bytes != std::string::npos);
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if (bytes == 3)
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{
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// codepoints that need 4 bytes (i.e., 3 additional
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// bytes) in UTF-8 need a surrogate pair when \u
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// escaping is used: from 4 bytes to \uxxxx\uxxxx
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// (12 bytes)
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res += (12 - bytes - 1);
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}
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else
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{
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// from x bytes to \uxxxx (6 bytes)
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res += (6 - bytes - 1);
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}
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// skip the additional bytes
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i += bytes;
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}
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break;
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}
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}
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}
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return res;
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}
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static void escape_codepoint(int codepoint, string_t& result, std::size_t& pos)
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{
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// expecting a proper codepoint
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assert(0x00 <= codepoint and codepoint <= 0x10FFFF);
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// the last written character was the backslash before the 'u'
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assert(result[pos] == '\\');
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// write the 'u'
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result[++pos] = 'u';
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// convert a number 0..15 to its hex representation (0..f)
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static const std::array<char, 16> hexify =
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{
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{
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'0', '1', '2', '3', '4', '5', '6', '7',
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'8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
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}
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};
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if (codepoint < 0x10000)
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{
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// codepoints U+0000..U+FFFF can be represented as \uxxxx.
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result[++pos] = hexify[(codepoint >> 12) & 0x0F];
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result[++pos] = hexify[(codepoint >> 8) & 0x0F];
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result[++pos] = hexify[(codepoint >> 4) & 0x0F];
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result[++pos] = hexify[codepoint & 0x0F];
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}
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else
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{
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// codepoints U+10000..U+10FFFF need a surrogate pair to be
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// represented as \uxxxx\uxxxx.
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// http://www.unicode.org/faq/utf_bom.html#utf16-4
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codepoint -= 0x10000;
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const int high_surrogate = 0xD800 | ((codepoint >> 10) & 0x3FF);
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const int low_surrogate = 0xDC00 | (codepoint & 0x3FF);
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result[++pos] = hexify[(high_surrogate >> 12) & 0x0F];
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result[++pos] = hexify[(high_surrogate >> 8) & 0x0F];
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result[++pos] = hexify[(high_surrogate >> 4) & 0x0F];
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result[++pos] = hexify[high_surrogate & 0x0F];
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++pos; // backslash is already in output
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result[++pos] = 'u';
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result[++pos] = hexify[(low_surrogate >> 12) & 0x0F];
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result[++pos] = hexify[(low_surrogate >> 8) & 0x0F];
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result[++pos] = hexify[(low_surrogate >> 4) & 0x0F];
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result[++pos] = hexify[low_surrogate & 0x0F];
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}
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++pos;
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}
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/*!
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@brief dump escaped string
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@ -438,145 +277,145 @@ class serializer
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@complexity Linear in the length of string @a s.
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*/
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void dump_escaped(const string_t& s, const bool ensure_ascii) const
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void dump_escaped(const string_t& s, const bool ensure_ascii)
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{
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throw_if_invalid_utf8(s);
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const auto space = extra_space(s, ensure_ascii);
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if (space == 0)
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{
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o->write_characters(s.c_str(), s.size());
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return;
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}
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// create a result string of necessary size
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string_t result(s.size() + space, '\\');
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std::size_t pos = 0;
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uint32_t codepoint;
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uint8_t state = UTF8_ACCEPT;
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std::size_t bytes = 0; // number of bytes written to string_buffer
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for (std::size_t i = 0; i < s.size(); ++i)
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{
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switch (s[i])
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const auto byte = static_cast<uint8_t>(s[i]);
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switch (decode(state, codepoint, byte))
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{
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case '"': // quotation mark (0x22)
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case UTF8_ACCEPT: // decode found a new code point
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{
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result[pos + 1] = '"';
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pos += 2;
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break;
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}
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case '\\': // reverse solidus (0x5C)
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{
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// nothing to change
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pos += 2;
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break;
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}
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case '\b': // backspace (0x08)
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{
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result[pos + 1] = 'b';
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pos += 2;
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break;
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}
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case '\f': // formfeed (0x0C)
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{
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result[pos + 1] = 'f';
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pos += 2;
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break;
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}
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case '\n': // newline (0x0A)
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{
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result[pos + 1] = 'n';
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pos += 2;
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break;
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}
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case '\r': // carriage return (0x0D)
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{
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result[pos + 1] = 'r';
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pos += 2;
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break;
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}
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case '\t': // horizontal tab (0x09)
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{
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result[pos + 1] = 't';
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pos += 2;
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break;
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}
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default:
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{
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// escape control characters (0x00..0x1F) or, if
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// ensure_ascii parameter is used, non-ASCII characters
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if ((0x00 <= s[i] and s[i] <= 0x1F) or
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(ensure_ascii and (s[i] & 0x80 or s[i] == 0x7F)))
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switch (codepoint)
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{
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const auto bytes = bytes_following(static_cast<uint8_t>(s[i]));
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// invalid characters will be detected by throw_if_invalid_utf8
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assert (bytes != std::string::npos);
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// check that the additional bytes are present
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assert(i + bytes < s.size());
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// to use \uxxxx escaping, we first need to calculate
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// the codepoint from the UTF-8 bytes
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int codepoint = 0;
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// bytes is unsigned type:
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assert(bytes <= 3);
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switch (bytes)
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case 0x08: // backspace
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{
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case 0:
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{
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codepoint = s[i] & 0xFF;
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break;
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}
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case 1:
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{
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codepoint = ((s[i] & 0x3F) << 6)
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+ (s[i + 1] & 0x7F);
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break;
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}
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case 2:
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{
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codepoint = ((s[i] & 0x1F) << 12)
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+ ((s[i + 1] & 0x7F) << 6)
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+ (s[i + 2] & 0x7F);
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break;
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}
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case 3:
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{
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codepoint = ((s[i] & 0xF) << 18)
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+ ((s[i + 1] & 0x7F) << 12)
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+ ((s[i + 2] & 0x7F) << 6)
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+ (s[i + 3] & 0x7F);
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break;
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}
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default:
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break; // LCOV_EXCL_LINE
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = 'b';
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break;
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}
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escape_codepoint(codepoint, result, pos);
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i += bytes;
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case 0x09: // horizontal tab
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = 't';
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break;
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}
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case 0x0A: // newline
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = 'n';
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break;
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}
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case 0x0C: // formfeed
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = 'f';
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break;
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}
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case 0x0D: // carriage return
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = 'r';
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break;
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}
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case 0x22: // quotation mark
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = '\"';
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break;
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}
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case 0x5C: // reverse solidus
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{
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string_buffer[bytes++] = '\\';
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string_buffer[bytes++] = '\\';
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break;
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}
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default:
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{
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// escape control characters (0x00..0x1F) or, if
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// ensure_ascii parameter is used, non-ASCII characters
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if ((codepoint <= 0x1F) or (ensure_ascii and (codepoint >= 0x7F)))
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{
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if (codepoint <= 0xFFFF)
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{
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std::snprintf(string_buffer.data() + bytes, 7, "\\u%04x", codepoint);
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bytes += 6;
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}
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else
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{
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std::snprintf(string_buffer.data() + bytes, 13, "\\u%04x\\u%04x",
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(0xD7C0 + (codepoint >> 10)),
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(0xDC00 + (codepoint & 0x3FF)));
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bytes += 12;
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}
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}
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else
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{
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// copy byte to buffer (all previous bytes
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// been copied have in default case above)
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string_buffer[bytes++] = s[i];
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}
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break;
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}
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}
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else
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// write buffer and reset index; there must be 13 bytes
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// left, as this is the maximal number of bytes to be
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// written ("\uxxxx\uxxxx\0") for one code point
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if (string_buffer.size() - bytes < 13)
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{
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// all other characters are added as-is
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result[pos++] = s[i];
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o->write_characters(string_buffer.data(), bytes);
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bytes = 0;
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}
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break;
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}
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case UTF8_REJECT: // decode found invalid UTF-8 byte
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{
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std::stringstream ss;
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ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(byte);
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JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + ss.str()));
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}
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default: // decode found yet incomplete multi-byte code point
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{
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if (not ensure_ascii)
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{
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// code point will not be escaped - copy byte to buffer
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string_buffer[bytes++] = s[i];
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}
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break;
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}
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}
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}
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assert(pos == result.size());
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o->write_characters(result.c_str(), result.size());
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if (JSON_LIKELY(state == UTF8_ACCEPT))
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{
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// write buffer
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if (bytes > 0)
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{
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o->write_characters(string_buffer.data(), bytes);
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}
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}
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else
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{
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// we finish reading, but do not accept: string was incomplete
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std::stringstream ss;
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ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(static_cast<uint8_t>(s.back()));
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JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + ss.str()));
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}
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}
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/*!
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@ -701,15 +540,16 @@ class serializer
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followed.
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@param[in,out] state the state of the decoding
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@param[in,out] codep codepoint (valid only if resulting state is UTF8_ACCEPT)
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@param[in] byte next byte to decode
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@return new state
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@note The function has been edited: a std::array is used and the code
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point is not calculated.
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@note The function has been edited: a std::array is used.
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@copyright Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
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@sa http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
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*/
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static void decode(uint8_t& state, const uint8_t byte)
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static uint8_t decode(uint8_t& state, uint32_t& codep, const uint8_t byte) noexcept
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{
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static const std::array<uint8_t, 400> utf8d =
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{
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@ -732,42 +572,13 @@ class serializer
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};
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const uint8_t type = utf8d[byte];
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codep = (state != UTF8_ACCEPT)
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? (byte & 0x3fu) | (codep << 6)
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: (0xff >> type) & (byte);
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state = utf8d[256u + state * 16u + type];
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}
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/*!
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@brief throw an exception if a string is not UTF-8 encoded
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@param[in] str UTF-8 string to check
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@throw type_error.316 if passed string is not UTF-8 encoded
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@since version 3.0.0
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*/
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static void throw_if_invalid_utf8(const std::string& str)
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{
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// start with state 0 (= accept)
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uint8_t state = 0;
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||||
for (size_t i = 0; i < str.size(); ++i)
|
||||
{
|
||||
const auto byte = static_cast<uint8_t>(str[i]);
|
||||
decode(state, byte);
|
||||
if (state == 1)
|
||||
{
|
||||
// state 1 means reject
|
||||
std::stringstream ss;
|
||||
ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(byte);
|
||||
JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + ss.str()));
|
||||
}
|
||||
}
|
||||
|
||||
if (state != 0)
|
||||
{
|
||||
// we finish reading, but do not accept: string was incomplete
|
||||
std::stringstream ss;
|
||||
ss << std::setw(2) << std::uppercase << std::setfill('0') << std::hex << static_cast<int>(static_cast<uint8_t>(str.back()));
|
||||
JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + ss.str()));
|
||||
}
|
||||
return state;
|
||||
}
|
||||
|
||||
private:
|
||||
|
|
@ -784,9 +595,11 @@ class serializer
|
|||
/// the locale's decimal point character
|
||||
const char decimal_point = '\0';
|
||||
|
||||
/// string buffer
|
||||
std::array<char, 512> string_buffer{{}};
|
||||
|
||||
/// the indentation character
|
||||
const char indent_char;
|
||||
|
||||
/// the indentation string
|
||||
string_t indent_string;
|
||||
};
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue