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Merge pull request #22 from Teemperor/unicode_escaping

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Unicode escaping
This commit is contained in:
Niels 2015-01-11 15:08:13 +01:00
commit 6533b33387
9 changed files with 329 additions and 8 deletions
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222
src/json.cc
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@ -2096,23 +2096,30 @@ std::string json::parser::parseString()
// the result of the parse process
std::string result;
// iterate with pos_ over the whole string
// iterate with pos_ over the whole input until we found the end and return
// or we exit via error()
for (; pos_ < buffer_.size(); pos_++)
{
char currentChar = buffer_[pos_];
// uneven amount of backslashes means the user wants to escape something
if (!evenAmountOfBackslashes)
{
// uneven amount of backslashes means the user wants to escape
// something so we know there is a case such as '\X' or '\\\X' but
// we don't know yet what X is.
// at this point in the code, the currentChar has the value of X.
// slash, backslash and quote are copied as is
if (currentChar == '/' or currentChar == '\\' or currentChar == '"')
if ( currentChar == '/'
|| currentChar == '\\'
|| currentChar == '"')
{
result += currentChar;
}
else
{
// all other characters are replaced by their respective
// special character
// all other characters are replaced by their respective special
// character
switch (currentChar)
{
case 't':
@ -2140,12 +2147,26 @@ std::string json::parser::parseString()
result += '\r';
break;
}
case 'u':
{
// \uXXXX[\uXXXX] is used for escaping unicode, which
// has it's own subroutine.
result += parseUnicodeEscape();
// the parsing process has brought us one step behind
// the unicode escape sequence:
// \uXXXX
// ^
// we need to go one character back or the parser would
// skip the character we are currently pointing at as
// the for-loop will decrement pos_ after this iteration
pos_--;
break;
}
default:
{
error("expected one of \\, /, b, f, n, r, t behind backslash.");
error("expected one of \\, /, b, f, n, r, t, u behind backslash.");
}
}
// TODO implement \uXXXX
}
}
else
@ -2164,7 +2185,7 @@ std::string json::parser::parseString()
}
else if (currentChar != '\\')
{
// All non-backslash characters are added to the end of the
// all non-backslash characters are added to the end of the
// result string. The only backslashes we want in the result
// are the ones that are escaped (which happens above).
result += currentChar;
@ -2192,6 +2213,191 @@ std::string json::parser::parseString()
error("expected '\"'");
}
/*!
Turns a code point into it's UTF-8 representation.
You should only pass numbers < 0x10ffff into this function
(everything else is a invalid code point).
@return the UTF-8 representation of the given code point
@pre This method isn't accessing the members of the parser
@post This method isn't accessing the members of the parser
*/
std::string json::parser::codePointToUTF8(unsigned int codePoint)
{
// this method contains a lot of bit manipulations to
// build the bytes for UTF-8.
// the '(... >> S) & 0xHH'-patterns are used to retrieve
// certain bits from the code points.
// all static casts in this method have boundary checks
// we initialize all strings with their final length
// (e.g. 1 to 4 bytes) to save the reallocations.
if (codePoint <= 0x7f)
{
// it's just a ASCII compatible codePoint,
// so we just interpret the point as a character
// and return ASCII
return std::string(1, static_cast<char>(codePoint));
}
// if true, we need two bytes to encode this as UTF-8
else if (codePoint <= 0x7ff)
{
// the 0xC0 enables the two most significant two bits
// to make this a two-byte UTF-8 character.
std::string result(2, static_cast<char>(0xC0 | ((codePoint >> 6) & 0x1F)));
result[1] = static_cast<char>(0x80 | (codePoint & 0x3F));
return result;
}
// if true, now we need three bytes to encode this as UTF-8
else if (codePoint <= 0xffff)
{
// the 0xE0 enables the three most significant two bits
// to make this a three-byte UTF-8 character.
std::string result(3, static_cast<char>(0xE0 | ((codePoint >> 12) & 0x0F)));
result[1] = static_cast<char>(0x80 | ((codePoint >> 6) & 0x3F));
result[2] = static_cast<char>(0x80 | (codePoint & 0x3F));
return result;
}
// if true, we need maximal four bytes to encode this as UTF-8
else if (codePoint <= 0x10ffff)
{
// the 0xE0 enables the four most significant two bits
// to make this a three-byte UTF-8 character.
std::string result(4, static_cast<char>(0xF0 | ((codePoint >> 18) & 0x07)));
result[1] = static_cast<char>(0x80 | ((codePoint >> 12) & 0x3F));
result[2] = static_cast<char>(0x80 | ((codePoint >> 6) & 0x3F));
result[3] = static_cast<char>(0x80 | (codePoint & 0x3F));
return result;
}
else
{
// Can't be tested without direct access to this private method.
std::string errorMessage = "Invalid codePoint: ";
errorMessage += codePoint;
error(errorMessage);
}
}
/*!
Parses 4 hexadecimal characters as a number.
@return the value of the number the hexadecimal characters represent.
@pre pos_ is pointing to the first of the 4 hexadecimal characters.
@post pos_ is pointing to the character after the 4 hexadecimal characters.
*/
unsigned int json::parser::parse4HexCodePoint()
{
const auto startPos = pos_;
// check if the remaining buffer is long enough to even hold 4 characters
if (pos_ + 3 >= buffer_.size())
{
error("Got end of input while parsing unicode escape sequence \\uXXXX");
}
// make a string that can hold the pair
std::string hexCode(4, ' ');
for(; pos_ < startPos + 4; pos_++)
{
// no boundary check here as we already checked above
char currentChar = buffer_[pos_];
// check if we have a hexadecimal character
if ( (currentChar >= '0' && currentChar <= '9')
|| (currentChar >= 'a' && currentChar <= 'f')
|| (currentChar >= 'A' && currentChar <= 'F'))
{
// all is well, we have valid hexadecimal chars
// so we copy that char into our string
hexCode[pos_ - startPos] = currentChar;
}
else
{
error("Found non-hexadecimal character in unicode escape sequence!");
}
}
// the cast is safe as 4 hex characters can't present more than 16 bits
// the input to stoul was checked to contain only hexadecimal characters
// (see above)
return static_cast<unsigned int>(std::stoul(hexCode, nullptr, 16));
}
/*!
Parses the unicode escape codes as defined in the ECMA-404.
The escape sequence has two forms:
1. \uXXXX
2. \uXXXX\uYYYY
where X and Y are a hexadecimal character (a-zA-Z0-9).
Form 1 just contains the unicode code point in the hexadecimal number XXXX.
Form 2 is encoding a UTF-16 surrogate pair. The high surrogate is XXXX, the low
surrogate is YYYY.
@return the UTF-8 character this unicode escape sequence escaped.
@pre pos_ is pointing at at the 'u' behind the first backslash.
@post pos_ is pointing at the character behind the last X (or Y in form 2).
*/
std::string json::parser::parseUnicodeEscape()
{
// jump to the first hex value
pos_++;
// parse the hex first hex values
unsigned int firstCodePoint = parse4HexCodePoint();
if (firstCodePoint >= 0xD800 && firstCodePoint <= 0xDBFF)
{
// we found invalid code points, which means we either have a malformed
// input or we found a high surrogate.
// we can only find out by seeing if the next character also wants to
// encode a unicode character (so, we have the \uXXXX\uXXXX case here).
// jump behind the next \u
pos_ += 2;
// try to parse the next hex values.
// the method does boundary checking for us, so no need to do that here
unsigned secondCodePoint = parse4HexCodePoint();
// ok, we have a low surrogate, check if it is a valid one
if (secondCodePoint >= 0xDC00 && secondCodePoint <= 0xDFFF)
{
// calculate the code point from the pair according to the spec
unsigned int finalCodePoint =
// high surrogate occupies the most significant 22 bits
(firstCodePoint << 10)
// low surrogate occupies the least significant 15 bits
+ secondCodePoint
// there is still the 0xD800, 0xDC00 and 0x10000 noise in
// the result
// so we have to substract with:
// (0xD800 << 10) + DC00 - 0x10000 = 0x35FDC00
- 0x35FDC00;
// we transform the calculated point into UTF-8
return codePointToUTF8(finalCodePoint);
}
else
error("missing low surrogate");
}
// We have Form 1, so we just interpret the XXXX as a code point
return codePointToUTF8(firstCodePoint);
}
/*!
This function is called in case a \p "t" is read in the main parse function
@ref parse. In the standard, the \p "true" token is the only candidate, so the

6
src/json.h
View file

@ -421,6 +421,12 @@ class json
inline void error(const std::string&) __attribute__((noreturn));
/// parse a quoted string
inline std::string parseString();
/// transforms a unicode codepoint to it's UTF-8 presentation
std::string codePointToUTF8(unsigned int codePoint);
/// parses 4 hex characters that represent a unicode code point
inline unsigned int parse4HexCodePoint();
/// parses \uXXXX[\uXXXX] unicode escape characters
inline std::string parseUnicodeEscape();
/// parse a Boolean "true"
inline void parseTrue();
/// parse a Boolean "false"