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Copy pathbase64.cpp
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89 lines (80 loc) · 3.2 KB
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/* Copyright (C) 2026 Sebastiano Merlino; SPDX-License-Identifier: LGPL-2.1-or-later */
#include <httpserver/detail/base64.hpp>
#include <string>
#include <vector>
namespace httpserver::detail {
void encode_quantum(std::string& out, std::uint32_t bits) {
out.push_back(k_base64_alphabet[(bits >> 18) & 0x3f]);
out.push_back(k_base64_alphabet[(bits >> 12) & 0x3f]);
out.push_back(k_base64_alphabet[(bits >> 6) & 0x3f]);
out.push_back(k_base64_alphabet[bits & 0x3f]);
}
std::string base64_encode(std::span<const std::byte> input) {
std::string out;
out.reserve((input.size() / 3 + 1) * 4);
std::size_t i = 0;
while (i + 3 <= input.size()) {
encode_quantum(out, (octet(input[i]) << 16) | (octet(input[i + 1]) << 8) | octet(input[i + 2]));
i += 3;
}
const std::size_t rest = input.size() - i;
if (rest == 1) {
const std::uint32_t bits = octet(input[i]) << 16;
out.push_back(k_base64_alphabet[(bits >> 18) & 0x3f]);
out.push_back(k_base64_alphabet[(bits >> 12) & 0x3f]);
out.append("==");
} else if (rest == 2) {
const std::uint32_t bits = (octet(input[i]) << 16) | (octet(input[i + 1]) << 8);
out.push_back(k_base64_alphabet[(bits >> 18) & 0x3f]);
out.push_back(k_base64_alphabet[(bits >> 12) & 0x3f]);
out.push_back(k_base64_alphabet[(bits >> 6) & 0x3f]);
out.push_back('=');
}
return out;
}
int base64_value(const char c) noexcept {
const std::size_t pos = k_base64_alphabet.find(c);
return pos == std::string_view::npos ? -1 : static_cast<int>(pos);
}
std::size_t base64_padding(std::string_view input) noexcept {
if (input.empty() || input.back() != '=') return 0;
if (input.size() >= 2 && input[input.size() - 2] == '=') return 2;
return 1;
}
void decode_quantum(std::vector<std::byte>& out, std::uint32_t bits) {
out.push_back(static_cast<std::byte>((bits >> 16) & 0xff));
out.push_back(static_cast<std::byte>((bits >> 8) & 0xff));
out.push_back(static_cast<std::byte>(bits & 0xff));
}
bool decode_final_quantum(std::vector<std::byte>& out, std::uint32_t bits, int count) {
if (count == 2) {
if ((bits & 0xf) != 0) return false;
out.push_back(static_cast<std::byte>(bits >> 4));
} else if (count == 3) {
if ((bits & 0x3) != 0) return false;
out.push_back(static_cast<std::byte>(bits >> 10));
out.push_back(static_cast<std::byte>((bits >> 2) & 0xff));
}
return true;
}
std::optional<std::vector<std::byte>> base64_decode(std::string_view input) {
if (input.size() % 4 != 0) return std::nullopt;
const std::size_t pad = base64_padding(input);
std::vector<std::byte> out;
out.reserve(input.size() / 4 * 3);
std::uint32_t bits = 0;
int count = 0;
for (std::size_t i = 0; i < input.size() - pad; ++i) {
const int value = base64_value(input[i]);
if (value < 0) return std::nullopt;
bits = (bits << 6) | static_cast<std::uint32_t>(value);
if (++count == 4) {
decode_quantum(out, bits);
bits = 0;
count = 0;
}
}
if (!decode_final_quantum(out, bits, count)) return std::nullopt;
return out;
}
} // namespace httpserver::detail