ClickHouse/dbms/include/DB/IO/ReadHelpers.h

#pragma once

#include <cmath>
#include <cstring>
#include <limits>
#include <algorithm>

#include <type_traits>

#include <common/Common.h>
#include <common/DateLUT.h>

#include <common/LocalDate.h>
#include <common/LocalDateTime.h>

#include <common/exp10.h>

#include <DB/Core/Types.h>
#include <DB/Core/StringRef.h>
#include <DB/Common/Exception.h>
#include <DB/Common/StringUtils.h>
#include <DB/Common/Arena.h>

#include <DB/IO/ReadBuffer.h>
#include <DB/IO/ReadBufferFromMemory.h>
#include <DB/IO/VarInt.h>
#include <city.h>

#define DEFAULT_MAX_STRING_SIZE 0x00FFFFFFULL


namespace DB
{

namespace ErrorCodes
{
    extern const int CANNOT_PARSE_DATE;
    extern const int CANNOT_PARSE_DATETIME;
    extern const int CANNOT_READ_ARRAY_FROM_TEXT;
}

/// Helper functions for formatted input.

inline char parseEscapeSequence(char c)
{
    switch(c)
    {
        case 'a':
            return '\a';
        case 'b':
            return '\b';
        case 'f':
            return '\f';
        case 'n':
            return '\n';
        case 'r':
            return '\r';
        case 't':
            return '\t';
        case 'v':
            return '\v';
        case '0':
            return '\0';
        default:
            return c;
    }
}

inline char unhex(char c)
{
    switch (c)
    {
        case '0' ... '9':
            return c - '0';
        case 'a' ... 'f':
            return c - 'a' + 10;
        case 'A' ... 'F':
            return c - 'A' + 10;
        default:
            return 0;
    }
}


/// These functions are located in VarInt.h
/// inline void throwReadAfterEOF()


inline void readChar(char & x, ReadBuffer & buf)
{
    if (!buf.eof())
    {
        x = *buf.position();
        ++buf.position();
    }
    else
        throwReadAfterEOF();
}


/// Read POD-type in native format
template <typename T>
inline void readPODBinary(T & x, ReadBuffer & buf)
{
    buf.readStrict(reinterpret_cast<char *>(&x), sizeof(x));
}

template <typename T>
inline void readIntBinary(T & x, ReadBuffer & buf)
{
    readPODBinary(x, buf);
}

template <typename T>
inline void readFloatBinary(T & x, ReadBuffer & buf)
{
    readPODBinary(x, buf);
}


inline void readStringBinary(std::string & s, ReadBuffer & buf, size_t MAX_STRING_SIZE = DEFAULT_MAX_STRING_SIZE)
{
    size_t size = 0;
    readVarUInt(size, buf);

    if (size > MAX_STRING_SIZE)
        throw Poco::Exception("Too large string size.");

    s.resize(size);
    buf.readStrict(&s[0], size);
}


inline StringRef readStringBinaryInto(Arena & arena, ReadBuffer & buf)
{
    size_t size = 0;
    readVarUInt(size, buf);

    char * data = arena.alloc(size);
    buf.readStrict(data, size);

    return StringRef(data, size);
}


template <typename T>
void readVectorBinary(std::vector<T> & v, ReadBuffer & buf, size_t MAX_VECTOR_SIZE = DEFAULT_MAX_STRING_SIZE)
{
    size_t size = 0;
    readVarUInt(size, buf);

    if (size > MAX_VECTOR_SIZE)
        throw Poco::Exception("Too large vector size.");

    v.resize(size);
    for (size_t i = 0; i < size; ++i)
        readBinary(v[i], buf);
}


void assertString(const char * s, ReadBuffer & buf);
void assertEOF(ReadBuffer & buf);
void assertChar(char symbol, ReadBuffer & buf);

inline void assertString(const String & s, ReadBuffer & buf)
{
    assertString(s.c_str(), buf);
}

bool checkString(const char * s, ReadBuffer & buf);
inline bool checkString(const String & s, ReadBuffer & buf)
{
    return checkString(s.c_str(), buf);
}

inline bool checkChar(char c, ReadBuffer & buf)
{
    if (buf.eof() || *buf.position() != c)
        return false;
    ++buf.position();
    return true;
}

bool checkStringCaseInsensitive(const char * s, ReadBuffer & buf);
inline bool checkStringCaseInsensitive(const String & s, ReadBuffer & buf)
{
    return checkStringCaseInsensitive(s.c_str(), buf);
}

void assertStringCaseInsensitive(const char * s, ReadBuffer & buf);
inline void assertStringCaseInsensitive(const String & s, ReadBuffer & buf)
{
    return assertStringCaseInsensitive(s.c_str(), buf);
}

/** Check that next character in buf matches first character of s.
  * If true, then check all characters in s and throw exception if it doesn't match.
  * If false, then return false, and leave position in buffer unchanged.
  */
bool checkStringByFirstCharacterAndAssertTheRest(const char * s, ReadBuffer & buf);
bool checkStringByFirstCharacterAndAssertTheRestCaseInsensitive(const char * s, ReadBuffer & buf);

inline bool checkStringByFirstCharacterAndAssertTheRest(const String & s, ReadBuffer & buf)
{
    return checkStringByFirstCharacterAndAssertTheRest(s.c_str(), buf);
}

inline bool checkStringByFirstCharacterAndAssertTheRestCaseInsensitive(const String & s, ReadBuffer & buf)
{
    return checkStringByFirstCharacterAndAssertTheRestCaseInsensitive(s.c_str(), buf);
}


inline void readBoolText(bool & x, ReadBuffer & buf)
{
    char tmp = '0';
    readChar(tmp, buf);
    x = tmp != '0';
}

template <typename T, typename ReturnType = void>
ReturnType readIntTextImpl(T & x, ReadBuffer & buf)
{
    static constexpr bool throw_exception = std::is_same<ReturnType, void>::value;

    bool negative = false;
    x = 0;
    if (buf.eof())
    {
        if (throw_exception)
            throwReadAfterEOF();
        else
            return ReturnType(false);
    }

    while (!buf.eof())
    {
        switch (*buf.position())
        {
            case '+':
                break;
            case '-':
                if (std::is_signed<T>::value)
                    negative = true;
                else
                    return ReturnType(false);
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                x *= 10;
                x += *buf.position() - '0';
                break;
            default:
                if (negative)
                    x = -x;
                return ReturnType(true);
        }
        ++buf.position();
    }
    if (negative)
        x = -x;

    return ReturnType(true);
}

template <typename T>
void readIntText(T & x, ReadBuffer & buf)
{
    readIntTextImpl<T, void>(x, buf);
}

template <typename T>
bool tryReadIntText(T & x, ReadBuffer & buf)
{
    return readIntTextImpl<T, bool>(x, buf);
}

/** More efficient variant (about 1.5 times on real dataset).
  * Differs in following:
  * - for numbers starting with zero, parsed only zero;
  * - symbol '+' before number is not supported;
  * - symbols :;<=>? are parsed as some numbers.
  */
template <typename T, bool throw_on_error = true>
void readIntTextUnsafe(T & x, ReadBuffer & buf)
{
    bool negative = false;
    x = 0;

    auto on_error = []
    {
        if (throw_on_error)
            throwReadAfterEOF();
    };

    if (unlikely(buf.eof()))
        return on_error();

    if (std::is_signed<T>::value && *buf.position() == '-')
    {
        ++buf.position();
        negative = true;
        if (unlikely(buf.eof()))
            return on_error();
    }

    if (*buf.position() == '0')                    /// There are many zeros in real datasets.
    {
        ++buf.position();
        return;
    }

    while (!buf.eof())
    {
        if ((*buf.position() & 0xF0) == 0x30)    /// It makes sense to have this condition inside loop.
        {
            x *= 10;
            x += *buf.position() & 0x0F;
            ++buf.position();
        }
        else
            break;
    }

    if (std::is_signed<T>::value && negative)
        x = -x;
}

template<typename T>
void tryReadIntTextUnsafe(T & x, ReadBuffer & buf)
{
    return readIntTextUnsafe<T, false>(x, buf);
}


template <bool throw_exception, class ExcepFun, class NoExcepFun, class... Args>
bool exceptionPolicySelector(ExcepFun && excep_f, NoExcepFun && no_excep_f, Args &&... args)
{
    if (throw_exception)
    {
        excep_f(std::forward<Args>(args)...);
        return true;
    }
    else
        return no_excep_f(std::forward<Args>(args)...);
};


/// Returns true, iff parsed.
bool parseInfinity(ReadBuffer & buf);
bool parseNaN(ReadBuffer & buf);

void assertInfinity(ReadBuffer & buf);
void assertNaN(ReadBuffer & buf);


/// Rough: not exactly nearest machine representable number is returned.
/// Some garbage may be successfully parsed, examples: '.' parsed as 0; 123Inf parsed as inf.
template <typename T, typename ReturnType, char point_symbol = '.'>
ReturnType readFloatTextImpl(T & x, ReadBuffer & buf)
{
    static constexpr bool throw_exception = std::is_same<ReturnType, void>::value;

    bool negative = false;
    x = 0;
    bool after_point = false;
    double power_of_ten = 1;

    if (buf.eof())
    {
        if (throw_exception)
            throwReadAfterEOF();
        else
            return ReturnType(false);
    }

    while (!buf.eof())
    {
        switch (*buf.position())
        {
            case '+':
                break;
            case '-':
                negative = true;
                break;
            case point_symbol:
                after_point = true;
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                if (after_point)
                {
                    power_of_ten /= 10;
                    x += (*buf.position() - '0') * power_of_ten;
                }
                else
                {
                    x *= 10;
                    x += *buf.position() - '0';
                }
                break;
            case 'e':
            case 'E':
            {
                ++buf.position();
                Int32 exponent = 0;
                bool res = exceptionPolicySelector<throw_exception>(readIntText<Int32>, tryReadIntText<Int32>, exponent, buf);
                if (res)
                {
                    x *= exp10(exponent);
                    if (negative)
                        x = -x;
                }
                return ReturnType(res);
            }

            case 'i':
            case 'I':
            {
                bool res = exceptionPolicySelector<throw_exception>(assertInfinity, parseInfinity, buf);
                if (res)
                {
                    x = std::numeric_limits<T>::infinity();
                    if (negative)
                        x = -x;
                }
                return ReturnType(res);
            }

            case 'n':
            case 'N':
            {
                bool res = exceptionPolicySelector<throw_exception>(assertNaN, parseNaN, buf);
                if (res)
                {
                    x = std::numeric_limits<T>::quiet_NaN();
                    if (negative)
                        x = -x;
                }
                return ReturnType(res);
            }

            default:
            {
                if (negative)
                    x = -x;
                return ReturnType(true);
            }
        }
        ++buf.position();
    }

    if (negative)
        x = -x;

    return ReturnType(true);
}

template <class T>
inline bool tryReadFloatText(T & x, ReadBuffer & buf)
{
    return readFloatTextImpl<T, bool>(x, buf);
}

template <class T>
inline void readFloatText(T & x, ReadBuffer & buf)
{
    readFloatTextImpl<T, void>(x, buf);
}

/// rough; all until '\n' or '\t'
void readString(String & s, ReadBuffer & buf);

void readEscapedString(String & s, ReadBuffer & buf);

void readQuotedString(String & s, ReadBuffer & buf);

void readDoubleQuotedString(String & s, ReadBuffer & buf);

void readJSONString(String & s, ReadBuffer & buf);

void readBackQuotedString(String & s, ReadBuffer & buf);

void readStringUntilEOF(String & s, ReadBuffer & buf);


/** Read string in CSV format.
  * Parsing rules:
  * - string could be placed in quotes; quotes could be single: ' or double: ";
  * - or string could be unquoted - this is determined by first character;
  * - if string is unquoted, then it is read until next delimiter,
  *   either until end of line (CR or LF),
  *   or until end of stream;
  *   but spaces and tabs at begin and end of unquoted string are consumed but ignored (note that this behaviour differs from RFC).
  * - if string is in quotes, then it will be read until closing quote,
  *   but sequences of two consecutive quotes are parsed as single quote inside string;
  */
void readCSVString(String & s, ReadBuffer & buf, const char delimiter = ',');


/// Read and append result to array of characters.
template <typename Vector>
void readStringInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readEscapedStringInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readQuotedStringInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readDoubleQuotedStringInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readBackQuotedStringInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readStringUntilEOFInto(Vector & s, ReadBuffer & buf);

template <typename Vector>
void readCSVStringInto(Vector & s, ReadBuffer & buf, const char delimiter = ',');

template <typename Vector>
void readJSONStringInto(Vector & s, ReadBuffer & buf);

/// This could be used as template parameter for functions above, if you want to just skip data.
struct NullSink
{
    void append(const char *, size_t) {};
    void push_back(char) {};
};


/// In YYYY-MM-DD format
inline void readDateText(DayNum_t & date, ReadBuffer & buf)
{
    char s[10];
    size_t size = buf.read(s, 10);
    if (10 != size)
    {
        s[size] = 0;
        throw Exception(std::string("Cannot parse date ") + s, ErrorCodes::CANNOT_PARSE_DATE);
    }

    UInt16 year = (s[0] - '0') * 1000 + (s[1] - '0') * 100 + (s[2] - '0') * 10 + (s[3] - '0');
    UInt8 month = (s[5] - '0') * 10 + (s[6] - '0');
    UInt8 day = (s[8] - '0') * 10 + (s[9] - '0');

    date = DateLUT::instance().makeDayNum(year, month, day);
}

inline void readDateText(LocalDate & date, ReadBuffer & buf)
{
    char s[10];
    size_t size = buf.read(s, 10);
    if (10 != size)
    {
        s[size] = 0;
        throw Exception(std::string("Cannot parse date ") + s, ErrorCodes::CANNOT_PARSE_DATE);
    }

    date.year((s[0] - '0') * 1000 + (s[1] - '0') * 100 + (s[2] - '0') * 10 + (s[3] - '0'));
    date.month((s[5] - '0') * 10 + (s[6] - '0'));
    date.day((s[8] - '0') * 10 + (s[9] - '0'));
}


template <typename T>
inline T parse(const char * data, size_t size);


void readDateTimeTextFallback(time_t & datetime, ReadBuffer & buf, const DateLUTImpl & date_lut);

/** In YYYY-MM-DD hh:mm:ss format, according to current time zone.
  * As an exception, also supported parsing of unix timestamp in form of decimal number.
  */
inline void readDateTimeText(time_t & datetime, ReadBuffer & buf, const DateLUTImpl & date_lut = DateLUT::instance())
{
    /** Read 10 characters, that could represent unix timestamp.
      * Only unix timestamp of 5-10 characters is supported.
      * Then look at 5th charater. If it is a number - treat whole as unix timestamp.
      * If it is not a number - then parse datetime in YYYY-MM-DD hh:mm:ss format.
      */

    /// Optimistic path, when whole value are in buffer.
    const char * s = buf.position();
    if (s + 19 < buf.buffer().end())
    {
        if (s[4] < '0' || s[4] > '9')
        {
            UInt16 year = (s[0] - '0') * 1000 + (s[1] - '0') * 100 + (s[2] - '0') * 10 + (s[3] - '0');
            UInt8 month = (s[5] - '0') * 10 + (s[6] - '0');
            UInt8 day = (s[8] - '0') * 10 + (s[9] - '0');

            UInt8 hour = (s[11] - '0') * 10 + (s[12] - '0');
            UInt8 minute = (s[14] - '0') * 10 + (s[15] - '0');
            UInt8 second = (s[17] - '0') * 10 + (s[18] - '0');

            if (unlikely(year == 0))
                datetime = 0;
            else
                datetime = date_lut.makeDateTime(year, month, day, hour, minute, second);

            buf.position() += 19;
        }
        else
            /// Why not readIntTextUnsafe? Because for needs of AdFox, parsing of unix timestamp with leading zeros is supported: 000...NNNN.
            readIntText(datetime, buf);
    }
    else
        readDateTimeTextFallback(datetime, buf, date_lut);
}

inline void readDateTimeText(LocalDateTime & datetime, ReadBuffer & buf)
{
    char s[19];
    size_t size = buf.read(s, 19);
    if (19 != size)
    {
        s[size] = 0;
        throw Exception(std::string("Cannot parse datetime ") + s, ErrorCodes::CANNOT_PARSE_DATETIME);
    }

    datetime.year((s[0] - '0') * 1000 + (s[1] - '0') * 100 + (s[2] - '0') * 10 + (s[3] - '0'));
    datetime.month((s[5] - '0') * 10 + (s[6] - '0'));
    datetime.day((s[8] - '0') * 10 + (s[9] - '0'));

    datetime.hour((s[11] - '0') * 10 + (s[12] - '0'));
    datetime.minute((s[14] - '0') * 10 + (s[15] - '0'));
    datetime.second((s[17] - '0') * 10 + (s[18] - '0'));
}


/// Generic methods to read value in native binary format.
template <typename T>
inline typename std::enable_if<std::is_arithmetic<T>::value, void>::type
readBinary(T & x, ReadBuffer & buf) { readPODBinary(x, buf); }

inline void readBinary(String & x,     ReadBuffer & buf) { readStringBinary(x, buf); }
inline void readBinary(uint128 & x,    ReadBuffer & buf) { readPODBinary(x, buf); }
inline void readBinary(LocalDate & x,     ReadBuffer & buf)     { readPODBinary(x, buf); }
inline void readBinary(LocalDateTime & x, ReadBuffer & buf) { readPODBinary(x, buf); }


/// Generic methods to read value in text tab-separated format.
template <typename T>
inline typename std::enable_if<std::is_integral<T>::value, void>::type
readText(T & x, ReadBuffer & buf) { readIntText(x, buf); }

template <typename T>
inline typename std::enable_if<std::is_floating_point<T>::value, void>::type
readText(T & x, ReadBuffer & buf) { readFloatText(x, buf); }

inline void readText(bool & x,         ReadBuffer & buf) { readBoolText(x, buf); }
inline void readText(String & x,     ReadBuffer & buf) { readEscapedString(x, buf); }
inline void readText(LocalDate & x,     ReadBuffer & buf) { readDateText(x, buf); }
inline void readText(LocalDateTime & x, ReadBuffer & buf) { readDateTimeText(x, buf); }


/// Generic methods to read value in text format,
///  possibly in single quotes (only for data types that use quotes in VALUES format of INSERT statement in SQL).
template <typename T>
inline typename std::enable_if<std::is_arithmetic<T>::value, void>::type
readQuoted(T & x, ReadBuffer & buf) { readText(x, buf); }

inline void readQuoted(String & x,     ReadBuffer & buf) { readQuotedString(x, buf); }

inline void readQuoted(LocalDate & x, ReadBuffer & buf)
{
    assertChar('\'', buf);
    readDateText(x, buf);
    assertChar('\'', buf);
}

inline void readQuoted(LocalDateTime & x, ReadBuffer & buf)
{
    assertChar('\'', buf);
    readDateTimeText(x, buf);
    assertChar('\'', buf);
}


/// Same as above, but in double quotes.
template <typename T>
inline typename std::enable_if<std::is_arithmetic<T>::value, void>::type
readDoubleQuoted(T & x, ReadBuffer & buf) { readText(x, buf); }

inline void readDoubleQuoted(String & x,     ReadBuffer & buf) { readDoubleQuotedString(x, buf); }

inline void readDoubleQuoted(LocalDate & x, ReadBuffer & buf)
{
    assertChar('"', buf);
    readDateText(x, buf);
    assertChar('"', buf);
}

inline void readDoubleQuoted(LocalDateTime & x, ReadBuffer & buf)
{
    assertChar('"', buf);
    readDateTimeText(x, buf);
    assertChar('"', buf);
}


/// CSV, for numbers, dates, datetimes: quotes are optional, no special escaping rules.
template <typename T>
inline void readCSVSimple(T & x, ReadBuffer & buf)
{
    if (buf.eof())
        throwReadAfterEOF();

    char maybe_quote = *buf.position();

    if (maybe_quote == '\'' || maybe_quote == '\"')
        ++buf.position();

    readText(x, buf);

    if (maybe_quote == '\'' || maybe_quote == '\"')
        assertChar(maybe_quote, buf);
}

template <typename T>
inline typename std::enable_if<std::is_arithmetic<T>::value, void>::type
readCSV(T & x, ReadBuffer & buf) { readCSVSimple(x, buf); }

inline void readCSV(String & x, ReadBuffer & buf, const char delimiter = ',') { readCSVString(x, buf, delimiter); }
inline void readCSV(LocalDate & x,     ReadBuffer & buf) { readCSVSimple(x, buf); }
inline void readCSV(LocalDateTime & x, ReadBuffer & buf) { readCSVSimple(x, buf); }


template <typename T>
void readBinary(std::vector<T> & x, ReadBuffer & buf)
{
    size_t size = 0;
    readVarUInt(size, buf);

    if (size > DEFAULT_MAX_STRING_SIZE)
        throw Poco::Exception("Too large vector size.");

    x.resize(size);
    for (size_t i = 0; i < size; ++i)
        readBinary(x[i], buf);
}

template <typename T>
void readQuoted(std::vector<T> & x, ReadBuffer & buf)
{
    bool first = true;
    assertChar('[', buf);
    while (!buf.eof() && *buf.position() != ']')
    {
        if (!first)
        {
            if (*buf.position() == ',')
                ++buf.position();
            else
                throw Exception("Cannot read array from text", ErrorCodes::CANNOT_READ_ARRAY_FROM_TEXT);
        }

        first = false;

        x.push_back(T());
        readQuoted(x.back(), buf);
    }
    assertChar(']', buf);
}

template <typename T>
void readDoubleQuoted(std::vector<T> & x, ReadBuffer & buf)
{
    bool first = true;
    assertChar('[', buf);
    while (!buf.eof() && *buf.position() != ']')
    {
        if (!first)
        {
            if (*buf.position() == ',')
                ++buf.position();
            else
                throw Exception("Cannot read array from text", ErrorCodes::CANNOT_READ_ARRAY_FROM_TEXT);
        }

        first = false;

        x.push_back(T());
        readDoubleQuoted(x.back(), buf);
    }
    assertChar(']', buf);
}

template <typename T>
void readText(std::vector<T> & x, ReadBuffer & buf)
{
    readQuoted(x, buf);
}


/// Skip whitespace characters.
inline void skipWhitespaceIfAny(ReadBuffer & buf)
{
    while (!buf.eof() && isWhitespaceASCII(*buf.position()))
        ++buf.position();
}

/// Skips json value. If the value contains objects (i.e. {...} sequence), an exception will be thrown.
void skipJSONFieldPlain(ReadBuffer & buf, const StringRef & name_of_filed);


/** Read serialized exception.
  * During serialization/deserialization some information is lost
  * (type is cut to base class, 'message' replaced by 'displayText', and stack trace is appended to 'message')
  * Some additional message could be appended to exception (example: you could add information about from where it was received).
  */
void readException(Exception & e, ReadBuffer & buf, const String & additional_message = "");
void readAndThrowException(ReadBuffer & buf, const String & additional_message = "");


/** Helper function for implementation.
  */
template <typename T>
static inline const char * tryReadIntText(T & x, const char * pos, const char * end)
{
    bool negative = false;
    x = 0;
    if (pos >= end)
        return pos;

    while (pos < end)
    {
        switch (*pos)
        {
            case '+':
                break;
            case '-':
                if (std::is_signed<T>::value)
                    negative = true;
                else
                    return pos;
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                x *= 10;
                x += *pos - '0';
                break;
            default:
                if (negative)
                    x = -x;
                return pos;
        }
        ++pos;
    }
    if (negative)
        x = -x;
    return pos;
}


/// Convenient methods for reading something from string in text format.
template <typename T>
inline T parse(const char * data, size_t size)
{
    T res;
    ReadBufferFromMemory buf(data, size);
    readText(res, buf);
    return res;
}

template <typename T>
inline T parse(const char * data)
{
    return parse<T>(data, strlen(data));
}

template <typename T>
inline T parse(const String & s)
{
    return parse<T>(s.data(), s.size());
}


/** Skip UTF-8 BOM if it is under cursor.
  * As BOM is usually located at start of stream, and buffer size is usually larger than three bytes,
  *  the function expects, that all three bytes of BOM is fully in buffer (otherwise it don't skip anything).
  */
inline void skipBOMIfExists(ReadBuffer & buf)
{
    if (!buf.eof()
        && buf.position() + 3 < buf.buffer().end()
        && buf.position()[0] == '\xEF'
        && buf.position()[1] == '\xBB'
        && buf.position()[2] == '\xBF')
    {
        buf.position() += 3;
    }
}


/// Skip to next character after next \n. If no \n in stream, skip to end.
void skipToNextLineOrEOF(ReadBuffer & buf);

/// Skip to next character after next unescaped \n. If no \n in stream, skip to end. Does not throw on invalid escape sequences.
void skipToUnescapedNextLineOrEOF(ReadBuffer & buf);

}