mirror of https://github.com/oxen-io/oxen-mq.git
374 lines
16 KiB
C++
374 lines
16 KiB
C++
// Copyright (c) 2019-2021, The Oxen Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#pragma once
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#include <string>
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#include <string_view>
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#include <array>
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#include <iterator>
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#include <cassert>
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#include "byte_type.h"
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namespace oxenmq {
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namespace detail {
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/// Compile-time generated lookup tables for base64 conversion.
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struct b64_table {
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// Store the 0-63 decoded value of every possible char; all the chars that aren't valid are set
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// to 0. (If you don't trust your data, check it with is_base64 first, which uses these 0's
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// to detect invalid characters -- which is why we want a full 256 element array).
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char from_b64_lut[256];
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// Store the encoded character of every 0-63 (6 bit) value.
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char to_b64_lut[64];
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// constexpr constructor that fills out the above (and should do it at compile time for any half
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// decent compiler).
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constexpr b64_table() noexcept : from_b64_lut{}, to_b64_lut{} {
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for (unsigned char c = 0; c < 26; c++) {
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from_b64_lut[(unsigned char)('A' + c)] = 0 + c;
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to_b64_lut[ (unsigned char)( 0 + c)] = 'A' + c;
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}
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for (unsigned char c = 0; c < 26; c++) {
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from_b64_lut[(unsigned char)('a' + c)] = 26 + c;
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to_b64_lut[ (unsigned char)(26 + c)] = 'a' + c;
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}
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for (unsigned char c = 0; c < 10; c++) {
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from_b64_lut[(unsigned char)('0' + c)] = 52 + c;
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to_b64_lut[ (unsigned char)(52 + c)] = '0' + c;
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}
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to_b64_lut[62] = '+'; from_b64_lut[(unsigned char) '+'] = 62;
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to_b64_lut[63] = '/'; from_b64_lut[(unsigned char) '/'] = 63;
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}
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// Convert a b64 encoded character into a 0-63 value
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constexpr char from_b64(unsigned char c) const noexcept { return from_b64_lut[c]; }
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// Convert a 0-31 value into a b64 encoded character
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constexpr char to_b64(unsigned char b) const noexcept { return to_b64_lut[b]; }
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} constexpr b64_lut;
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// This main point of this static assert is to force the compiler to compile-time build the constexpr tables.
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static_assert(b64_lut.from_b64('/') == 63 && b64_lut.from_b64('7') == 59 && b64_lut.to_b64(38) == 'm', "");
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} // namespace detail
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/// Returns the number of characters required to encode a base64 string from the given number of bytes.
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inline constexpr size_t to_base64_size(size_t byte_size, bool padded = true) {
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return padded
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? (byte_size + 2) / 3 * 4 // bytes*4/3, rounded up to the next multiple of 4
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: (byte_size * 4 + 2) / 3; // ⌈bytes*4/3⌉
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}
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/// Returns the (maximum) number of bytes required to decode a base64 string of the given size.
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/// Note that this may overallocate by 1-2 bytes if the size includes 1-2 padding chars.
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inline constexpr size_t from_base64_size(size_t b64_size) {
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return b64_size * 3 / 4; // == ⌊bits/8⌋; floor because we ignore trailing "impossible" bits (see below)
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}
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/// Iterable object for on-the-fly base64 encoding. Used internally, but also particularly useful
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/// when converting from one encoding to another.
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template <typename InputIt>
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struct base64_encoder final {
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private:
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InputIt _it, _end;
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static_assert(sizeof(decltype(*_it)) == 1, "base64_encoder requires chars/bytes input iterator");
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// How much padding (at most) we can add at the end
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int padding;
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// Number of bits held in r; will always be >= 6 until we are at the end.
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int bits{_it != _end ? 8 : 0};
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// Holds bits of data we've already read, which might belong to current or next chars
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uint_fast16_t r{bits ? static_cast<unsigned char>(*_it) : (unsigned char)0};
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public:
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using iterator_category = std::input_iterator_tag;
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using difference_type = std::ptrdiff_t;
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using value_type = char;
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using reference = value_type;
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using pointer = void;
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base64_encoder(InputIt begin, InputIt end, bool padded = true)
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: _it{std::move(begin)}, _end{std::move(end)}, padding{padded} {}
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base64_encoder end() { return {_end, _end, false}; }
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bool operator==(const base64_encoder& i) { return _it == i._it && bits == i.bits && padding == i.padding; }
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bool operator!=(const base64_encoder& i) { return !(*this == i); }
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base64_encoder& operator++() {
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if (bits == 0) {
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padding--;
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return *this;
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}
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assert(bits >= 6);
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// Discard the most significant 6 bits
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bits -= 6;
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r &= (1 << bits) - 1;
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// If we end up with less than 6 significant bits then try to pull another 8 bits:
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if (bits < 6 && _it != _end) {
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if (++_it != _end) {
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r = (r << 8) | static_cast<unsigned char>(*_it);
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bits += 8;
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} else if (bits > 0) {
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// No more input bytes, so shift `r` to put the bits we have into the most
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// significant bit position for the final character, and figure out how many padding
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// bytes we want to append. E.g. if we have "11" we want
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// the last character to be encoded "110000".
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if (padding) {
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// padding should be:
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// 3n+0 input => 4n output, no padding, handled below
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// 3n+1 input => 4n+2 output + 2 padding; we'll land here with 2 trailing bits
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// 3n+2 input => 4n+3 output + 1 padding; we'll land here with 4 trailing bits
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padding = 3 - bits / 2;
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}
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r <<= (6 - bits);
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bits = 6;
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} else {
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padding = 0; // No excess bits, so input was a multiple of 3 and thus no padding
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}
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}
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return *this;
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}
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base64_encoder operator++(int) { base64_encoder copy{*this}; ++*this; return copy; }
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char operator*() {
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if (bits == 0 && padding)
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return '=';
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// Right-shift off the excess bits we aren't accessing yet
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return detail::b64_lut.to_b64(r >> (bits - 6));
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}
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};
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/// Converts bytes into a base64 encoded character sequence, writing them starting at `out`.
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/// Returns the final value of out (i.e. the iterator positioned just after the last written base64
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/// character).
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template <typename InputIt, typename OutputIt>
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OutputIt to_base64(InputIt begin, InputIt end, OutputIt out, bool padded = true) {
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static_assert(sizeof(decltype(*begin)) == 1, "to_base64 requires chars/bytes");
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auto it = base64_encoder{begin, end, padded};
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return std::copy(it, it.end(), out);
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}
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/// Creates and returns a base64 string from an iterator pair of a character sequence. The
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/// resulting string will have '=' padding, if appropriate.
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template <typename It>
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std::string to_base64(It begin, It end) {
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std::string base64;
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if constexpr (std::is_base_of_v<std::random_access_iterator_tag, typename std::iterator_traits<It>::iterator_category>) {
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using std::distance;
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base64.reserve(to_base64_size(distance(begin, end)));
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}
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to_base64(begin, end, std::back_inserter(base64));
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return base64;
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}
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/// Creates and returns a base64 string from an iterator pair of a character sequence. The
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/// resulting string will not be padded.
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template <typename It>
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std::string to_base64_unpadded(It begin, It end) {
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std::string base64;
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if constexpr (std::is_base_of_v<std::random_access_iterator_tag, typename std::iterator_traits<It>::iterator_category>) {
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using std::distance;
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base64.reserve(to_base64_size(distance(begin, end), false));
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}
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to_base64(begin, end, std::back_inserter(base64), false);
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return base64;
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}
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/// Creates a base64 string from an iterable, std::string-like object. The string will have '='
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/// padding, if appropriate.
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template <typename CharT>
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std::string to_base64(std::basic_string_view<CharT> s) { return to_base64(s.begin(), s.end()); }
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inline std::string to_base64(std::string_view s) { return to_base64<>(s); }
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/// Creates a base64 string from an iterable, std::string-like object. The string will not be
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/// padded.
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template <typename CharT>
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std::string to_base64_unpadded(std::basic_string_view<CharT> s) { return to_base64_unpadded(s.begin(), s.end()); }
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inline std::string to_base64_unpadded(std::string_view s) { return to_base64_unpadded<>(s); }
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/// Returns true if the range is a base64 encoded value; we allow (but do not require) '=' padding,
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/// but only at the end, only 1 or 2, and only if it pads out the total to a multiple of 4.
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/// Otherwise the string must contain only valid base64 characters, and must not have a length of
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/// 4n+1 (because that cannot be produced by base64 encoding).
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template <typename It>
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constexpr bool is_base64(It begin, It end) {
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static_assert(sizeof(decltype(*begin)) == 1, "is_base64 requires chars/bytes");
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using std::distance;
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using std::prev;
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size_t count = 0;
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constexpr bool random = std::is_base_of_v<std::random_access_iterator_tag, typename std::iterator_traits<It>::iterator_category>;
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if constexpr (random) {
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count = distance(begin, end) % 4;
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if (count == 1)
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return false;
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}
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// Allow 1 or 2 padding chars *if* they pad it to a multiple of 4.
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if (begin != end && distance(begin, end) % 4 == 0) {
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auto last = prev(end);
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if (static_cast<unsigned char>(*last) == '=')
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end = last--;
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if (static_cast<unsigned char>(*last) == '=')
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end = last;
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}
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for (; begin != end; ++begin) {
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auto c = static_cast<unsigned char>(*begin);
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if (detail::b64_lut.from_b64(c) == 0 && c != 'A')
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return false;
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if constexpr (!random)
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count++;
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}
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if constexpr (!random)
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if (count % 4 == 1) // base64 encoding will produce 4n, 4n+2, 4n+3, but never 4n+1
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return false;
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return true;
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}
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/// Returns true if the string-like value is a base64 encoded value
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template <typename CharT>
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constexpr bool is_base64(std::basic_string_view<CharT> s) { return is_base64(s.begin(), s.end()); }
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constexpr bool is_base64(std::string_view s) { return is_base64(s.begin(), s.end()); }
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/// Iterable object for on-the-fly base64 decoding. Used internally, but also particularly useful
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/// when converting from one encoding to another. The input range must be a valid base64 encoded
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/// string (with or without padding).
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///
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/// Note that we ignore "padding" bits without requiring that they actually be 0. For instance, the
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/// bytes "\ff\ff" are ideally encoded as "//8=" (16 bits of 1s + 2 padding 0 bits, then a full
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/// 6-bit padding char). We don't, however, require that the padding bits be 0. That is, "///=",
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/// "//9=", "//+=", etc. will all decode to the same \ff\ff output string.
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template <typename InputIt>
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struct base64_decoder final {
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private:
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InputIt _it, _end;
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static_assert(sizeof(decltype(*_it)) == 1, "base64_decoder requires chars/bytes input iterator");
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uint_fast16_t in = 0;
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int bits = 0; // number of bits loaded into `in`; will be in [8, 12] until we hit the end
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public:
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using iterator_category = std::input_iterator_tag;
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using difference_type = std::ptrdiff_t;
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using value_type = char;
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using reference = value_type;
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using pointer = void;
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base64_decoder(InputIt begin, InputIt end) : _it{std::move(begin)}, _end{std::move(end)} {
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if (_it != _end)
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load_byte();
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}
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base64_decoder end() { return {_end, _end}; }
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bool operator==(const base64_decoder& i) { return _it == i._it; }
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bool operator!=(const base64_decoder& i) { return _it != i._it; }
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base64_decoder& operator++() {
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// Discard 8 most significant bits
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bits -= 8;
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in &= (1 << bits) - 1;
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if (++_it != _end)
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load_byte();
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return *this;
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}
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base64_decoder operator++(int) { base64_decoder copy{*this}; ++*this; return copy; }
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char operator*() {
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return in >> (bits - 8);
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}
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private:
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void load_in() {
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// We hit padding trying to read enough for a full byte, so we're done. (And since you were
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// already supposed to have checked validity with is_base64, the padding can only be at the
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// end).
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auto c = static_cast<unsigned char>(*_it);
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if (c == '=') {
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_it = _end;
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bits = 0;
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return;
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}
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in = in << 6
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| detail::b64_lut.from_b64(c);
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bits += 6;
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}
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void load_byte() {
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load_in();
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if (bits && bits < 8 && ++_it != _end)
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load_in();
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// If we hit the _end iterator above then we hit the end of the input (or hit padding) with
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// fewer than 8 bits accumulated to make a full byte. For a properly encoded base64 string
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// this should only be possible with 0, 2, or 4 bits of all 0s; these are essentially
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// "padding" bits (e.g. encoding 2 byte (16 bits) requires 3 b64 chars (18 bits), where
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// only the first 16 bits are significant). Ideally any padding bits should be 0, but we
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// don't check that and rather just ignore them.
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}
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};
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/// Converts a sequence of base64 digits to bytes. Undefined behaviour if any characters are not
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/// valid base64 alphabet characters. It is permitted for the input and output ranges to overlap as
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/// long as `out` is no later than `begin`. Trailing padding characters are permitted but not
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/// required. Returns the final value of out (that is, the iterator positioned just after the
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/// last written character).
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///
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/// It is possible to provide "impossible" base64 encoded values; for example "YWJja" which has 30
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/// bits of data even though a base64 encoded byte string should have 24 (4 chars) or 36 (6 chars)
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/// bits for a 3- and 4-byte input, respectively. We ignore any such "impossible" bits, and
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/// similarly ignore impossible bits in the bit "overhang"; that means "YWJjZA==" (the proper
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/// encoding of "abcd") and "YWJjZB", "YWJjZC", ..., "YWJjZP" all decode to the same "abcd" value:
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/// the last 4 bits of the last character are essentially considered padding.
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template <typename InputIt, typename OutputIt>
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OutputIt from_base64(InputIt begin, InputIt end, OutputIt out) {
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static_assert(sizeof(decltype(*begin)) == 1, "from_base64 requires chars/bytes");
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base64_decoder it{begin, end};
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auto bend = it.end();
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while (it != bend)
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*out++ = static_cast<detail::byte_type_t<OutputIt>>(*it++);
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return out;
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}
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/// Converts base64 digits from a iterator pair of characters into a std::string of bytes.
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/// Undefined behaviour if any characters are not valid base64 characters.
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template <typename It>
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std::string from_base64(It begin, It end) {
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std::string bytes;
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if constexpr (std::is_base_of_v<std::random_access_iterator_tag, typename std::iterator_traits<It>::iterator_category>) {
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using std::distance;
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bytes.reserve(from_base64_size(distance(begin, end)));
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}
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from_base64(begin, end, std::back_inserter(bytes));
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return bytes;
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}
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/// Converts base64 digits from a std::string-like object into a std::string of bytes. Undefined
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/// behaviour if any characters are not valid base64 characters.
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template <typename CharT>
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std::string from_base64(std::basic_string_view<CharT> s) { return from_base64(s.begin(), s.end()); }
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inline std::string from_base64(std::string_view s) { return from_base64<>(s); }
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}
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