boost_beast/include/beast/static_string.hpp

//------------------------------------------------------------------------------
/*
    This file is part of Beast: https://github.com/vinniefalco/Beast
    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

#ifndef BEAST_WEBSOCKET_STATIC_STRING_HPP
#define BEAST_WEBSOCKET_STATIC_STRING_HPP

#include <algorithm>
#include <array>
#include <cstdint>
#include <iterator>
#include <stdexcept>
#include <string>

namespace beast {
namespace websocket {

/** A string with a fixed-size storage area.

    `static_string` objects behave like `std::string` except that
    the storage is not dynamically allocated but rather fixed in
    size.

    These strings offer performance advantages when a protocol
    imposes a natural small upper limit on the size of a value.

    @note The stored string is always null-terminated.
*/
template<
    std::size_t N,
    class CharT = char,
    class Traits = std::char_traits<CharT>>
class static_string
{
    template<std::size_t, class, class>
    friend class static_string;

    std::size_t n_;
    std::array<CharT, N+1> s_;

public:
    using traits_type = Traits;
    using value_type = typename Traits::char_type;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;
    using pointer = value_type*;
    using reference = value_type&;
    using const_pointer = value_type const*;
    using const_reference = value_type const&;
    using iterator = value_type*;
    using const_iterator = value_type const*;
    using reverse_iterator =
        std::reverse_iterator<iterator>;
    using const_reverse_iterator =
        std::reverse_iterator<const_iterator>;

    /** Default constructor.

        The string is initially empty, and null terminated.
    */
    static_string();

    /// Copy constructor.
    static_string(static_string const& s);

    /// Copy constructor.
    template<std::size_t M>
    static_string(static_string<M, CharT, Traits> const& s);

    /// Copy assignment.
    static_string&
    operator=(static_string const& s);

    /// Copy assignment.
    template<std::size_t M>
    static_string&
    operator=(static_string<M, CharT, Traits> const& s);

    /// Construct from string literal.
    template<std::size_t M>
    static_string(const CharT (&s)[M]);

    /// Assign from string literal.
    template<std::size_t M>
    static_string& operator=(const CharT (&s)[M]);

    /// Access specified character with bounds checking.
    reference
    at(size_type pos);

    /// Access specified character with bounds checking.
    const_reference
    at(size_type pos) const;

    /// Access specified character.
    reference
    operator[](size_type pos)
    {
        return s_[pos];
    }

    /// Access specified character.
    const_reference
    operator[](size_type pos) const
    {
        return s_[pos];
    }

    /// Accesses the first character.
    CharT&
    front()
    {
        return s_[0];
    }

    /// Accesses the first character.
    CharT const&
    front() const
    {
        return s_[0];
    }

    /// Accesses the last character.
    CharT&
    back()
    {
        return s_[n_-1];
    }

    /// Accesses the last character.
    CharT const&
    back() const
    {
        return s_[n_-1];
    }

    /// Returns a pointer to the first character of a string.
    CharT*
    data()
    {
        return &s_[0];
    }

    /// Returns a pointer to the first character of a string.
    CharT const*
    data() const
    {
        return &s_[0];
    }

    /// Returns a non-modifiable standard C character array version of the string.
    CharT const*
    c_str() const
    {
        return &s_[0];
    }

    /// Returns an iterator to the beginning.
    iterator
    begin()
    {
        return &s_[0];
    }

    /// Returns an iterator to the beginning.
    const_iterator
    begin() const
    {
        return &s_[0];
    }

    /// Returns an iterator to the beginning.
    const_iterator
    cbegin() const
    {
        return &s_[0];
    }

    /// Returns an iterator to the end.
    iterator
    end()
    {
        return &s_[n_];
    }

    /// Returns an iterator to the end.
    const_iterator
    end() const
    {
        return &s_[n_];
    }

    /// Returns an iterator to the end.
    const_iterator
    cend() const
    {
        return &s_[n_];
    }

    /// Returns a reverse iterator to the beginning.
    reverse_iterator
    rbegin()
    {
        return reverse_iterator{end()};
    }

    /// Returns a reverse iterator to the beginning.
    const_reverse_iterator
    rbegin() const
    {
        return const_reverse_iterator{cend()};
    }

    /// Returns a reverse iterator to the beginning.
    const_reverse_iterator
    crbegin() const
    {
        return const_reverse_iterator{cend()};
    }

    /// Returns a reverse iterator to the end.
    reverse_iterator
    rend()
    {
        return reverse_iterator{begin()};
    }

    /// Returns a reverse iterator to the end.
    const_reverse_iterator
    rend() const
    {
        return const_reverse_iterator{cbegin()};
    }

    /// Returns a reverse iterator to the end.
    const_reverse_iterator
    crend() const
    {
        return const_reverse_iterator{cbegin()};
    }

    /// Returns `true` if the string is empty.
    bool
    empty() const
    {
        return n_ == 0;
    }

    /// Returns the number of characters, excluding the null terminator.
    size_type
    size() const
    {
        return n_;
    }

    /// Returns the maximum number of characters that can be stored, excluding the null terminator.
    size_type constexpr
    max_size() const
    {
        return N;
    }

    /// Returns the number of characters that can be held in currently allocated storage.
    size_type
    capacity() const
    {
        return N;
    }
    
    /// Reduces memory usage by freeing unused memory.
    void
    shrink_to_fit()
    {
        // no-op
    }

    /// Clears the contents.
    void
    clear()
    {
        resize(0);
    }

    /** Changes the number of characters stored.

        @note No value-initialization is performed.
    */
    void
    resize(std::size_t n);

    /** Changes the number of characters stored.

        If the resulting string is larger, the new
        characters are initialized to the value of `c`.
    */
    void
    resize(std::size_t n, CharT c);

    /// Compare two character sequences.
    template<std::size_t M>
    int compare(static_string<M, CharT, Traits> const& rhs) const;

    /// Return the characters as a `basic_string`.
    std::basic_string<CharT, Traits>
    to_string() const
    {
        return std::basic_string<
            CharT, Traits>{&s_[0], n_};
    }

private:
    void
    assign(CharT const* s);
};

template<std::size_t N, class CharT, class Traits>
static_string<N, CharT, Traits>::
static_string()
    : n_(0)
{
    s_[0] = 0;
}

template<std::size_t N, class CharT, class Traits>
static_string<N, CharT, Traits>::
static_string(static_string const& s)
    : n_(s.n_)
{
    Traits::copy(&s_[0], &s.s_[0], n_ + 1);
}

template<std::size_t N, class CharT, class Traits>
template<std::size_t M>
static_string<N, CharT, Traits>::
static_string(static_string<M, CharT, Traits> const& s)
{
    if(s.size() > N)
        throw std::length_error("static_string overflow");
    n_ = s.size();
    Traits::copy(&s_[0], &s.s_[0], n_ + 1);
}

template<std::size_t N, class CharT, class Traits>
auto
static_string<N, CharT, Traits>::
operator=(static_string const& s) ->
    static_string&
{
    n_ = s.n_;
    Traits::copy(&s_[0], &s.s_[0], n_ + 1);
    return *this;
}

template<std::size_t N, class CharT, class Traits>
template<std::size_t M>
auto
static_string<N, CharT, Traits>::
operator=(static_string<M, CharT, Traits> const& s) ->
    static_string&
{
    if(s.size() > N)
        throw std::length_error("static_string overflow");
    n_ = s.size();
    Traits::copy(&s_[0], &s.s_[0], n_ + 1);
    return *this;
}

template<std::size_t N, class CharT, class Traits>
template<std::size_t M>
static_string<N, CharT, Traits>::
static_string(const CharT (&s)[M])
    : n_(M-1)
{
    static_assert(M-1 <= N,
        "static_string overflow");
    Traits::copy(&s_[0], &s[0], M);
}

template<std::size_t N, class CharT, class Traits>
template<std::size_t M>
auto
static_string<N, CharT, Traits>::
operator=(const CharT (&s)[M]) ->
    static_string&
{
    static_assert(M-1 <= N,
        "static_string overflow");
    n_ = M-1;
    std::copy(&s[0], &s[M], &s_[0]);
    return *this;
}

template<std::size_t N, class CharT, class Traits>
auto
static_string<N, CharT, Traits>::
at(size_type pos) ->
    reference
{
    if(pos >= n_)
        throw std::out_of_range("static_string::at");
    return s_[pos];
}

template<std::size_t N, class CharT, class Traits>
auto
static_string<N, CharT, Traits>::
at(size_type pos) const ->
    const_reference
{
    if(pos >= n_)
        throw std::out_of_range("static_string::at");
    return s_[pos];
}

template<std::size_t N, class CharT, class Traits>
void
static_string<N, CharT, Traits>::
resize(std::size_t n)
{
    if(n > N)
        throw std::length_error("static_string overflow");
    n_ = n;
    s_[n_] = 0;
}

template<std::size_t N, class CharT, class Traits>
void
static_string<N, CharT, Traits>::
resize(std::size_t n, CharT c)
{
    if(n > N)
        throw std::length_error("static_string overflow");
    if(n > n_)
        Traits::assign(&s_[n_], n - n_, c);
    n_ = n;
    s_[n_] = 0;
}

template<std::size_t N, class CharT, class Traits>
template<std::size_t M>
int
static_string<N, CharT, Traits>::
compare(static_string<M, CharT, Traits> const& rhs) const
{
    if(size() < rhs.size())
    {
        auto const v = Traits::compare(
            data(), rhs.data(), size());
        if(v == 0)
            return -1;
        return v;
    }
    else if(size() > rhs.size())
    {
        auto const v = Traits::compare(
            data(), rhs.data(), rhs.size());
        if(v == 0)
            return 1;
        return v;
    }
    return Traits::compare(data(), rhs.data(), size());
}

template<std::size_t N, class CharT, class Traits>
void
static_string<N, CharT, Traits>::
assign(CharT const* s)
{
    auto const n = Traits::length(s);
    if(n > N)
        throw std::out_of_range("too large");
    n_ = n;
    Traits::copy(&s_[0], s, n_ + 1);
}

namespace detail {

template<std::size_t N, std::size_t M, class CharT, class Traits>
int compare(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    if(lhs.size() < M-1)
    {
        auto const v = Traits::compare(
            lhs.data(), &s[0], lhs.size());
        if(v == 0)
            return -1;
        return v;
    }
    else if(lhs.size() > M-1)
    {
        auto const v = Traits::compare(
            lhs.data(), &s[0], M-1);
        if(v == 0)
            return 1;
        return v;
    }
    return Traits::compare(lhs.data(), &s[0], lhs.size());
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
int compare(
    const CharT (&s)[M],
    static_string<N, CharT, Traits> const& rhs)
{
    if(M-1 < rhs.size())
    {
        auto const v = Traits::compare(
            &s[0], rhs.data(), M-1);
        if(v == 0)
            return -1;
        return v;
    }
    else if(M-1 > rhs.size())
    {
        auto const v = Traits::compare(
            &s[0], rhs.data(), rhs.size());
        if(v == 0)
            return 1;
        return v;
    }
    return Traits::compare(&s[0], rhs.data(), M-1);
}

} // detail

#if ! GENERATING_DOCS

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator==(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) == 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator!=(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) != 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator<(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) < 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator<=(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) <= 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator>(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) > 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator>=(
    static_string<N, CharT, Traits> const& lhs,
    static_string<M, CharT, Traits> const& rhs)
{
    return lhs.compare(rhs) >= 0;
}

//---

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator==(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) == 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator==(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) == 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator!=(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) != 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator!=(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) != 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator<(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) < 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator<(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) < 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator<=(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) <= 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator<=(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) <= 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator>(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) > 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator>(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) > 0;
}

template<std::size_t N, std::size_t M, class CharT, class Traits>
bool operator>=(
    const CharT (&s)[N],
    static_string<M, CharT, Traits> const& rhs)
{
    return detail::compare(s, rhs) >= 0;
}

template<std::size_t N, class CharT, class Traits, std::size_t M>
bool operator>=(
    static_string<N, CharT, Traits> const& lhs,
    const CharT (&s)[M])
{
    return detail::compare(lhs, s) >= 0;
}

#endif

} // websocket
} // beast

#endif