transmission/libtransmission/tr-strbuf.h

329 lines
7.4 KiB
C++

// This file Copyright © 2022 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#pragma once
#include <cstddef>
#include <string_view>
#include <utility>
#include <fmt/format.h>
/**
* A memory buffer which uses a builtin array of N bytes, using heap
* memory only if its string gets too big. Its main use case is building
* temporary strings in stack memory.
*
* It is a convenience wrapper around `fmt::basic_memory_buffer`.
*/
template<typename Char, size_t N>
class tr_strbuf
{
private:
fmt::basic_memory_buffer<Char, N> buffer_;
public:
using value_type = Char;
using const_reference = const Char&;
tr_strbuf()
{
ensure_sz();
}
tr_strbuf(tr_strbuf const& other) = delete;
tr_strbuf& operator=(tr_strbuf const& other) = delete;
tr_strbuf(tr_strbuf&& other)
: buffer_{ std::move(other.buffer_) }
{
ensure_sz();
}
tr_strbuf& operator=(tr_strbuf&& other)
{
buffer_ = std::move(other.buffer_);
ensure_sz();
return *this;
}
template<typename... Args>
explicit tr_strbuf(Args const&... args)
{
append(args...);
}
[[nodiscard]] constexpr auto begin() noexcept
{
return buffer_.begin();
}
[[nodiscard]] constexpr auto end() noexcept
{
return buffer_.end();
}
[[nodiscard]] constexpr auto begin() const noexcept
{
return buffer_.begin();
}
[[nodiscard]] constexpr auto end() const noexcept
{
return buffer_.end();
}
[[nodiscard]] constexpr Char& at(size_t pos) noexcept
{
return buffer_[pos];
}
[[nodiscard]] constexpr Char at(size_t pos) const noexcept
{
return buffer_[pos];
}
[[nodiscard]] constexpr auto size() const noexcept
{
return buffer_.size();
}
[[nodiscard]] constexpr bool empty() const noexcept
{
return size() == 0;
}
[[nodiscard]] constexpr auto* data() noexcept
{
return buffer_.data();
}
[[nodiscard]] constexpr auto const* data() const noexcept
{
return buffer_.data();
}
[[nodiscard]] constexpr auto const* c_str() const noexcept
{
return data();
}
[[nodiscard]] constexpr auto sv() const noexcept
{
return std::basic_string_view<Char>{ data(), size() };
}
template<typename ContiguousRange>
[[nodiscard]] constexpr auto operator==(ContiguousRange const& x) const noexcept
{
return sv() == x;
}
///
[[nodiscard]] constexpr bool ends_with(Char const& x) const noexcept
{
auto const n = size();
return n != 0 && data()[n - 1] == x;
}
template<typename ContiguousRange>
[[nodiscard]] constexpr bool ends_with(ContiguousRange const& x) const noexcept
{
auto const x_len = std::size(x);
auto const len = size();
return len >= x_len && this->sv().substr(len - x_len) == x;
}
[[nodiscard]] constexpr bool ends_with(Char const* x) const noexcept
{
return x != nullptr && ends_with(std::basic_string_view<Char>(x));
}
///
[[nodiscard]] constexpr bool starts_with(Char const& x) const noexcept
{
return !empty() && *data() == x;
}
template<typename ContiguousRange>
[[nodiscard]] constexpr bool starts_with(ContiguousRange const& x) const noexcept
{
auto const x_len = std::size(x);
return size() >= x_len && this->sv().substr(0, x_len) == x;
}
[[nodiscard]] constexpr bool starts_with(Char const* x) const noexcept
{
return x != nullptr && starts_with(std::basic_string_view<Char>(x));
}
///
void clear()
{
buffer_.clear();
ensure_sz();
}
void resize(size_t n)
{
buffer_.resize(n);
ensure_sz();
}
///
void append(Char const& value)
{
buffer_.push_back(value);
ensure_sz();
}
template<typename ContiguousRange>
void append(ContiguousRange const& args)
{
buffer_.append(std::data(args), std::data(args) + std::size(args));
ensure_sz();
}
void append(Char const* sz_value)
{
if (sz_value != nullptr)
{
append(std::basic_string_view<Char>{ sz_value });
}
}
template<typename... Args>
void append(Args const&... args)
{
(append(args), ...);
}
template<typename Arg>
auto& operator+=(Arg const& arg)
{
append(arg);
return *this;
}
///
template<typename... Args>
void assign(Args const&... args)
{
clear();
append(args...);
}
template<typename Arg>
auto& operator=(Arg const& arg)
{
assign(arg);
return *this;
}
void push_back(Char const& value)
{
append(value);
}
///
template<typename... Args>
void join(Char delim, Args const&... args)
{
((append(args), append(delim)), ...);
resize(size() - 1);
}
template<typename ContiguousRange, typename... Args>
void join(ContiguousRange const& delim, Args const&... args)
{
((append(args), append(delim)), ...);
resize(size() - std::size(delim));
}
template<typename... Args>
void join(Char const* sz_delim, Args const&... args)
{
join(std::basic_string_view<Char>{ sz_delim }, args...);
}
[[nodiscard]] constexpr operator std::basic_string_view<Char>() const noexcept
{
return sv();
}
[[nodiscard]] constexpr operator auto() const noexcept
{
return c_str();
}
bool popdir() noexcept
{
std::string_view tr_sys_path_dirname(std::string_view path);
auto const parent = tr_sys_path_dirname(sv());
auto const changed = parent != sv();
if (changed)
{
if (std::data(parent) == std::data(*this))
{
resize(std::size(parent));
}
else
{
assign(parent);
}
}
return changed;
}
private:
/**
* Ensure that the buffer's string is zero-terminated, e.g. for
* external APIs that require `char*` strings.
*
* Note that the added trailing '\0' does not increment `size()`.
* This is to ensure that `strlen(buf.c_str()) == buf.size()`.
*/
void ensure_sz()
{
auto const n = size();
buffer_.reserve(n + 1);
buffer_[n] = '\0';
}
};
template<typename Char, size_t N>
struct fmt::formatter<tr_strbuf<Char, N>> : formatter<std::basic_string_view<Char>, Char>
{
template<typename FormatContext>
constexpr auto format(tr_strbuf<Char, N> const& strbuf, FormatContext& ctx) const
{
return formatter<std::basic_string_view<Char>, Char>::format(strbuf.sv(), ctx);
}
};
/**
* Good for building short-term URLs.
* The initial size is big enough to avoid heap allocs in most cases,
* but that also makes it a poor choice for longer-term storage.
* https://stackoverflow.com/a/417184
*/
using tr_urlbuf = tr_strbuf<char, 2000>;
/**
* Good for building short-term filenames.
* The initial size is big enough to avoid heap allocs in most cases,
* but that also makes it a poor choice for longer-term storage.
* https://stackoverflow.com/a/65174437
*/
using tr_pathbuf = tr_strbuf<char, 4096>;