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Fully implemented the JSON spec

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This commit is contained in:
Raphael Isemann 2015-01-10 16:49:10 +01:00
parent 222aacc213
commit 5a54e46709
3 changed files with 232 additions and 62 deletions
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246
src/json.cc
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@ -2049,40 +2049,61 @@ std::string json::parser::parseString()
// the result of the parse process
std::string result;
// iterate with pos_ over the whole string
for (; pos_ < buffer_.size(); pos_++) {
// 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) {
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 == '/'
|| currentChar == '\\'
|| currentChar == '"') {
|| currentChar == '"')
{
result += currentChar;
} else {
// All other characters are replaced by their respective special character
if (currentChar == 't') {
result += '\t';
} else if (currentChar == 'b') {
result += '\b';
} else if (currentChar == 'f') {
result += '\f';
} else if (currentChar == 'n') {
result += '\n';
} else if (currentChar == 'r') {
result += '\r';
} else if (currentChar == 'u') {
pos_++;
result += parseUnicodeEscape();
} else {
error("expected one of \\,/,b,f,n,r,t behind backslash.");
}
// TODO implement \uXXXX
}
} else {
if (currentChar == '"') {
else
{
// All other characters are replaced by their respective special character
if (currentChar == 't')
result += '\t';
else if (currentChar == 'b')
result += '\b';
else if (currentChar == 'f')
result += '\f';
else if (currentChar == 'n')
result += '\n';
else if (currentChar == 'r')
result += '\r';
else if (currentChar == '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
// ^
// so we need to go one character back or the parser
// would skip the character we are currently pointing at
// (as the for-loop will drecement pos_ after this iteration).
pos_--;
}
else // user did something like \z and we should report a error
error("expected one of \\,/,b,f,n,r,t,u behind backslash.");
}
}
else
{
if (currentChar == '"')
{
// currentChar is a quote, so we found the end of the string
@ -2093,7 +2114,9 @@ std::string json::parser::parseString()
// bring the result of the parsing process back to the caller
return result;
} else if (currentChar != '\\') {
}
else if (currentChar != '\\')
{
// 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;
@ -2121,34 +2144,74 @@ std::string json::parser::parseString()
error("expected '\"'");
}
std::string json::parser::unicodeToUTF8(unsigned int codepoint) {
// it's just a ASCII compatible codepoint,
// so we just interpret the point as a character
if (codepoint <= 0x7f) {
/*!
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 codepoint
@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)
{
std::string result(2, static_cast<char>(0xc0 | ((codepoint >> 6) & 0x1f)));
result[1] = static_cast<char>(0x80 | (codepoint & 0x3f));
// 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)
{
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));
// 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;
}
else if (codepoint <= 0x1fffff)
// if true, we need maximal four bytes to encode this as UTF-8
else if (codepoint <= 0x10ffff)
{
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));
// 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 {
}
else
{
// Can't be tested without direct access to this private method.
std::string errorMessage = "Invalid codepoint: ";
errorMessage += codepoint;
error(errorMessage);
@ -2156,39 +2219,110 @@ std::string json::parser::unicodeToUTF8(unsigned int codepoint) {
}
/*!
Parses the JSON style unicode escape sequence (\uXXXX).
Parses 4 hexadecimal characters as a number.
@return the utf-8 character the escape sequence escaped
@return the value of the number the hexadecimal characters represent.
@pre An opening quote \p " was read in the main parse function @ref parse.
pos_ is the position after the opening quote.
@pre pos_ is pointing to the first of the 4 hexadecimal characters.
@post The character after the closing quote \p " is the current character @ref
current_. Whitespace is skipped.
@post pos_ is pointing to the character after the 4 hexadecimal characters.
*/
std::string json::parser::parseUnicodeEscape() {
unsigned int json::parser::parse4HexCodepoint()
{
const auto startPos = pos_;
if (pos_ + 3 >= buffer_.size()) {
// 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_++) {
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')) {
|| (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 {
}
else
{
error("Found non-hexadecimal character in unicode escape sequence!");
}
}
pos_--;
// case is safe as 4 hex characters can't present more than 16 bits
return unicodeToUTF8(static_cast<unsigned int>(std::stoul(hexCode, nullptr, 16)));
// 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 final 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);
}
/*!

6
src/json.h
View File

@ -419,8 +419,10 @@ class json
/// parse a quoted string
inline std::string parseString();
/// transforms a unicode codepoint to it's UTF-8 presentation
inline std::string unicodeToUTF8(unsigned int codepoint);
/// parses a unicode escape sequence
inline std::string codepointToUTF8(unsigned int codepoint);
/// parses 4 hex characters that represent a unicode codepoint
inline unsigned int parse4HexCodepoint();
/// parses \uXXXX[\uXXXX] unicode escape characters
inline std::string parseUnicodeEscape();
/// parse a Boolean "true"
inline void parseTrue();

42
test/json_unit.cc
View File

@ -1652,10 +1652,6 @@ TEST_CASE("Parser")
CHECK(json::parse("\"a\\nz\"") == json("a\nz"));
CHECK(json::parse("\"\\n\"") == json("\n"));
// escape unicode characters
CHECK(json::parse("\"\\u002F\"") == json("/"));
CHECK(json::parse("\"\\u00E4\"") == json(u8"\u00E4"));
// escaping senseless stuff
CHECK_THROWS_AS(json::parse("\"\\z\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\ \""), std::invalid_argument);
@ -1665,6 +1661,44 @@ TEST_CASE("Parser")
CHECK_THROWS_AS(json::parse("\""), std::invalid_argument);
}
SECTION("unicode_escaping")
{
// two tests for uppercase and lowercase hex
// normal forward slash in ASCII range
CHECK(json::parse("\"\\u002F\"") == json("/"));
CHECK(json::parse("\"\\u002f\"") == json("/"));
// german a umlaut
CHECK(json::parse("\"\\u00E4\"") == json(u8"\u00E4"));
CHECK(json::parse("\"\\u00e4\"") == json(u8"\u00E4"));
// weird d
CHECK(json::parse("\"\\u0111\"") == json(u8"\u0111"));
// unicode arrow left
CHECK(json::parse("\"\\u2190\"") == json(u8"\u2190"));
// pleasing osiris by testing hieroglyph support
CHECK(json::parse("\"\\uD80C\\uDC60\"") == json(u8"\U00013060"));
CHECK(json::parse("\"\\ud80C\\udc60\"") == json(u8"\U00013060"));
// no hex numbers behind the \u
CHECK_THROWS_AS(json::parse("\"\\uD80v\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uD80 A\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uD8v\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uDv\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uv\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\u\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\u\\u\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"a\\uD80vAz\""), std::invalid_argument);
// missing part of a surrogate pair
CHECK_THROWS_AS(json::parse("\"bla \\uD80C bla\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uD80C bla bla\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"bla bla \\uD80C bla bla\""), std::invalid_argument);
// senseless surrogate pair
CHECK_THROWS_AS(json::parse("\"\\uD80C\\uD80C\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uD80C\\u0000\""), std::invalid_argument);
CHECK_THROWS_AS(json::parse("\"\\uD80C\\uFFFF\""), std::invalid_argument);
}
SECTION("boolean")
{
// accept the exact values