JsonTokenizer.h

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#ifndef ZSERIO_JSON_TOKENIZER_H_INC
#define ZSERIO_JSON_TOKENIZER_H_INC
 
#include <array>
#include <istream>
#include <memory>
#include <string_view>
 
#include "zserio/Any.h"
#include "zserio/CppRuntimeException.h"
#include "zserio/JsonDecoder.h"
#include "zserio/String.h"
 
namespace zserio
{
 
enum class JsonToken : int8_t
{
    UNKNOWN = -1,
    BEGIN_OF_FILE,
    END_OF_FILE,
    BEGIN_OBJECT,
    END_OBJECT,
    BEGIN_ARRAY,
    END_ARRAY,
    KEY_SEPARATOR,
    ITEM_SEPARATOR,
    VALUE
};
 
class JsonParserException : public CppRuntimeException
{
public:
    using CppRuntimeException::CppRuntimeException;
};
 
CppRuntimeException& operator<<(CppRuntimeException& exception, JsonToken token);
 
template <typename ALLOC = std::allocator<uint8_t>>
class BasicJsonTokenizer
{
public:
    using allocator_type = ALLOC;
 
    BasicJsonTokenizer(std::istream& in, const ALLOC& allocator) :
            m_buffer(),
            m_in(in),
            m_decoder(allocator),
            m_decoderResult(0, allocator),
            m_content(readContent(allocator)),
            m_value(allocator)
    {
        m_token = m_content.empty() ? JsonToken::END_OF_FILE : JsonToken::BEGIN_OF_FILE;
    }
 
    JsonToken next();
 
    JsonToken getToken() const
    {
        return m_token;
    }
 
    const BasicAny<ALLOC>& getValue() const
    {
        return m_value;
    }
 
    size_t getLine() const
    {
        return m_lineNumber;
    }
 
    size_t getColumn() const
    {
        return m_tokenColumnNumber;
    }
 
private:
    BasicString<RebindAlloc<ALLOC, char>> readContent(const ALLOC& allocator);
 
    bool decodeNext();
    bool skipWhitespaces();
 
    template <typename T>
    void setToken(JsonToken token, T&& value);
    void setToken(JsonToken token, BasicAny<ALLOC>&& value);
    void setToken(JsonToken token);
    void setPosition(size_t newPos, size_t newColumnNumber);
    void setTokenValue();
 
    static constexpr size_t BUFFER_SIZE = 64 * 1024;
    std::array<char, BUFFER_SIZE> m_buffer;
 
    std::istream& m_in;
    BasicJsonDecoder<ALLOC> m_decoder;
    typename BasicJsonDecoder<ALLOC>::DecoderResult m_decoderResult;
    BasicString<RebindAlloc<ALLOC, char>> m_content;
    size_t m_lineNumber = 1;
    size_t m_columnNumber = 1;
    size_t m_tokenColumnNumber = 1;
    size_t m_pos = 0;
    JsonToken m_token;
    BasicAny<ALLOC> m_value;
};
 
template <typename ALLOC>
JsonToken BasicJsonTokenizer<ALLOC>::next()
{
    while (!decodeNext())
    {
        BasicString<RebindAlloc<ALLOC, char>> newContent = readContent(m_content.get_allocator());
        if (newContent.empty())
        {
            if (m_token == JsonToken::END_OF_FILE)
            {
                m_tokenColumnNumber = m_columnNumber;
            }
            else
            {
                // stream is finished but last token is not EOF => value must be at the end
                setTokenValue();
            }
 
            return m_token;
        }
 
        m_content = m_content.substr(m_pos) + newContent;
        m_pos = 0;
    }
 
    return m_token;
}
 
template <typename ALLOC>
BasicString<RebindAlloc<ALLOC, char>> BasicJsonTokenizer<ALLOC>::readContent(const ALLOC& allocator)
{
    const size_t count = static_cast<size_t>(m_in.rdbuf()->sgetn(m_buffer.data(), BUFFER_SIZE));
 
    return BasicString<RebindAlloc<ALLOC, char>>(m_buffer.data(), count, allocator);
}
 
template <typename ALLOC>
bool BasicJsonTokenizer<ALLOC>::decodeNext()
{
    if (!skipWhitespaces())
    {
        return false;
    }
 
    m_tokenColumnNumber = m_columnNumber;
 
    const char nextChar = m_content[m_pos];
    switch (nextChar)
    {
    case '{':
        setToken(JsonToken::BEGIN_OBJECT, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    case '}':
        setToken(JsonToken::END_OBJECT, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    case '[':
        setToken(JsonToken::BEGIN_ARRAY, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    case ']':
        setToken(JsonToken::END_ARRAY, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    case ':':
        setToken(JsonToken::KEY_SEPARATOR, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    case ',':
        setToken(JsonToken::ITEM_SEPARATOR, nextChar);
        setPosition(m_pos + 1, m_columnNumber + 1);
        break;
    default:
        m_decoderResult = m_decoder.decodeValue(std::string_view(m_content.data()).substr(m_pos));
        if (m_pos + m_decoderResult.numReadChars >= m_content.size())
        {
            return false; // we are at the end of chunk => read more
        }
 
        setTokenValue();
        break;
    }
 
    return true;
}
 
template <typename ALLOC>
bool BasicJsonTokenizer<ALLOC>::skipWhitespaces()
{
    while (true)
    {
        if (m_pos >= m_content.size())
        {
            setToken(JsonToken::END_OF_FILE);
            return false;
        }
 
        const char nextChar = m_content[m_pos];
        switch (nextChar)
        {
        case ' ':
        case '\t':
            setPosition(m_pos + 1, m_columnNumber + 1);
            break;
        case '\n':
            m_lineNumber++;
            setPosition(m_pos + 1, 1);
            break;
        case '\r':
            if (m_pos + 1 >= m_content.size())
            {
                setToken(JsonToken::END_OF_FILE);
                return false;
            }
            m_lineNumber++;
            setPosition(m_pos + (m_content[m_pos + 1] == '\n' ? 2 : 1), 1);
            break;
        default:
            return true;
        }
    }
}
 
template <typename ALLOC>
template <typename T>
void BasicJsonTokenizer<ALLOC>::setToken(JsonToken token, T&& value)
{
    m_token = token;
    m_value.set(std::forward<T>(value));
}
 
template <typename ALLOC>
void BasicJsonTokenizer<ALLOC>::setToken(JsonToken token, BasicAny<ALLOC>&& value)
{
    m_token = token;
    m_value = std::move(value);
}
 
template <typename ALLOC>
void BasicJsonTokenizer<ALLOC>::setToken(JsonToken token)
{
    m_token = token;
    m_value.reset();
}
 
template <typename ALLOC>
void BasicJsonTokenizer<ALLOC>::setPosition(size_t newPos, size_t newColumnNumber)
{
    m_pos = newPos;
    m_columnNumber = newColumnNumber;
}
 
template <typename ALLOC>
void BasicJsonTokenizer<ALLOC>::setTokenValue()
{
    if (!m_decoderResult.value.hasValue())
    {
        throw JsonParserException("JsonTokenizer:")
                << m_lineNumber << ":" << m_tokenColumnNumber << ": "
                << (m_decoderResult.integerOverflow ? "Value is outside of the 64-bit integer range!"
                                                    : "Unknown token!");
    }
 
    setToken(JsonToken::VALUE, std::move(m_decoderResult.value));
    setPosition(m_pos + m_decoderResult.numReadChars, m_columnNumber + m_decoderResult.numReadChars);
}
 
} // namespace zserio
 
#endif // ZSERIO_JSON_TOKENIZER_H_INC