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#include "base64.hh"
#include <cstddef>
#include <cstdint>
#include <optional>
#include <span>
#include <string>
#include <string_view>
#include <vector>
namespace base64 {
namespace {
std::string_view kAlphabet(
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/");
[[nodiscard]]
inline char encode(uint8_t c) {
return kAlphabet[c];
}
[[nodiscard]]
inline uint8_t decode(char c) {
if (c >= 'A' && c <= 'Z') {
return c - 'A';
}
if (c >= 'a' && c <= 'z') {
return 26 + (c - 'a');
}
if (c >= '0' && c <= '9') {
return 52 + (c - '0');
}
if (c == '+')
return 62;
if (c == '/')
return 63;
return 255;
}
} // namespace
std::string encode(std::span<uint8_t const> data) {
std::string ret;
encode(data, ret);
return ret;
}
void encode(std::span<uint8_t const> in, std::string& out) {
out.reserve((in.size() * 4 + 3) / 3);
size_t const leftover = in.size() % 3;
size_t const end = in.size() - leftover;
size_t i = 0;
for (; i < end; i += 3) {
out.push_back(encode(in[i] >> 2));
out.push_back(encode(((in[i] & 0x03) << 4) | (in[i + 1] >> 4)));
out.push_back(encode(((in[i + 1] & 0x0f) << 2) | (in[i + 2] >> 6)));
out.push_back(encode(in[i + 2] & 0x3f));
}
switch (leftover) { // NOLINT(bugprone-switch-missing-default-case)
case 0:
return;
case 1:
out.push_back(encode(in[i] >> 2));
out.push_back(encode((in[i] & 0x03) << 4));
out.push_back('=');
break;
case 2:
out.push_back(encode(in[i] >> 2));
out.push_back(encode(((in[i] & 0x03) << 4) | (in[i + 1] >> 4)));
out.push_back(encode((in[i + 1] & 0x0f) << 2));
break;
}
out.push_back('=');
}
std::optional<std::vector<uint8_t>> decode(std::string_view value) {
std::vector<uint8_t> ret;
if (decode(value, ret))
return ret;
return std::nullopt;
}
bool decode(std::string_view in, std::vector<uint8_t>& out) {
if (in.size() % 4)
return false;
if (in.empty())
return true;
size_t pad;
if (in.back() == '=') {
if (in[in.size() - 2] == '=') {
pad = 2;
} else {
pad = 1;
}
} else {
pad = 0;
}
size_t const end = in.size() - (pad ? 4 : 0);
size_t i = 0;
for (; i < end; i += 4) {
auto v1 = decode(in[i]);
auto v2 = decode(in[i + 1]);
auto v3 = decode(in[i + 2]);
auto v4 = decode(in[i + 3]);
if (v1 == 255 || v2 == 255 || v3 == 255 || v4 == 255)
return false;
out.push_back((v1 << 2) | (v2 >> 4));
out.push_back(((v2 & 0xf) << 4) | (v3 >> 2));
out.push_back(((v3 & 0x3) << 6) | v4);
}
switch (pad) { // NOLINT(bugprone-switch-missing-default-case)
case 0:
break;
case 1: {
auto v1 = decode(in[i]);
auto v2 = decode(in[i + 1]);
auto v3 = decode(in[i + 2]);
if (v1 == 255 || v2 == 255 || v3 == 255)
return false;
out.push_back((v1 << 2) | (v2 >> 4));
out.push_back(((v2 & 0xf) << 4) | (v3 >> 2));
break;
}
case 2: {
auto v1 = decode(in[i]);
auto v2 = decode(in[i + 1]);
if (v1 == 255 || v2 == 255)
return false;
out.push_back((v1 << 2) | (v2 >> 4));
break;
}
}
return true;
}
} // namespace base64
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