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// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#include "pw_base64/base64.h"
#include <cstdint>
namespace pw::base64 {
namespace {
// Encoding functions
constexpr size_t kEncodedGroupSize = 4;
constexpr char kChar62 = '+'; // URL safe encoding uses - instead
constexpr char kChar63 = '/'; // URL safe encoding uses _ instead
constexpr char kPadding = '=';
// Table that encodes a 6-bit pattern as a Base64 character
constexpr char encode_bits[64] = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', kChar62, kChar63};
constexpr char BitGroup0Char(uint8_t byte0) {
return encode_bits[(byte0 & 0b11111100) >> 2];
}
constexpr char BitGroup1Char(uint8_t byte0, uint8_t byte1 = 0) {
return encode_bits[((byte0 & 0b00000011) << 4) | ((byte1 & 0b11110000) >> 4)];
}
constexpr char BitGroup2Char(uint8_t byte1, uint8_t byte2 = 0) {
return encode_bits[((byte1 & 0b00001111) << 2) | ((byte2 & 0b11000000) >> 6)];
}
constexpr char BitGroup3Char(uint8_t byte2) {
return encode_bits[byte2 & 0b00111111];
}
// Decoding functions
constexpr char kMinValidChar = '+';
constexpr char kMaxValidChar = 'z';
constexpr uint8_t kX = 0xff; // Value used for invalid characters
// Table that decodes a Base64 character to its 6-bit value. Supports the
// standard (+/) and URL-safe (-_) alphabets. Starts from the lowest-value valid
// character, which is +.
constexpr uint8_t decode_char[] = {
62, kX, 62, kX, 63, 52, 53, 54, 55, 56, // 0 - 09
57, 58, 59, 60, 61, kX, kX, kX, 0, kX, // 10 - 19
kX, kX, 0, 1, 2, 3, 4, 5, 6, 7, // 20 - 29
8, 9, 10, 11, 12, 13, 14, 15, 16, 17, // 30 - 39
18, 19, 20, 21, 22, 23, 24, 25, kX, kX, // 40 - 49
kX, kX, 63, kX, 26, 27, 28, 29, 30, 31, // 50 - 59
32, 33, 34, 35, 36, 37, 38, 39, 40, 41, // 60 - 69
42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // 70 - 79
};
constexpr uint8_t CharToBits(char ch) {
return decode_char[ch - kMinValidChar];
}
constexpr uint8_t Byte0(uint8_t bits0, uint8_t bits1) {
return (bits0 << 2) | ((bits1 & 0b110000) >> 4);
}
constexpr uint8_t Byte1(uint8_t bits1, uint8_t bits2) {
return ((bits1 & 0b001111) << 4) | ((bits2 & 0b111100) >> 2);
}
constexpr uint8_t Byte2(uint8_t bits2, uint8_t bits3) {
return ((bits2 & 0b000011) << 6) | bits3;
}
} // namespace
extern "C" void pw_Base64Encode(const void* binary_data,
const size_t binary_size_bytes,
char* output) {
const uint8_t* bytes = static_cast<const uint8_t*>(binary_data);
// Encode groups of 3 source bytes into 4 output characters.
size_t remaining = binary_size_bytes;
for (; remaining >= 3u; remaining -= 3u, bytes += 3) {
*output++ = BitGroup0Char(bytes[0]);
*output++ = BitGroup1Char(bytes[0], bytes[1]);
*output++ = BitGroup2Char(bytes[1], bytes[2]);
*output++ = BitGroup3Char(bytes[2]);
}
// If the source data length isn't a multiple of 3, pad the end with either 1
// or 2 '=' characters, to stay Python-compatible.
if (remaining > 0u) {
*output++ = BitGroup0Char(bytes[0]);
if (remaining == 1u) {
*output++ = BitGroup1Char(bytes[0]);
*output++ = kPadding;
} else {
*output++ = BitGroup1Char(bytes[0], bytes[1]);
*output++ = BitGroup2Char(bytes[1]);
}
*output++ = kPadding;
}
}
extern "C" size_t pw_Base64Decode(const char* base64,
size_t base64_size_bytes,
void* output) {
// If too small, can't be valid input, due to likely missing padding
if (base64_size_bytes < 4) {
return 0;
}
uint8_t* binary = static_cast<uint8_t*>(output);
for (size_t ch = 0; ch < base64_size_bytes; ch += kEncodedGroupSize) {
const uint8_t char0 = CharToBits(base64[ch + 0]);
const uint8_t char1 = CharToBits(base64[ch + 1]);
const uint8_t char2 = CharToBits(base64[ch + 2]);
const uint8_t char3 = CharToBits(base64[ch + 3]);
*binary++ = Byte0(char0, char1);
*binary++ = Byte1(char1, char2);
*binary++ = Byte2(char2, char3);
}
size_t pad = 0;
if (base64[base64_size_bytes - 2] == kPadding) {
pad = 2;
} else if (base64[base64_size_bytes - 1] == kPadding) {
pad = 1;
}
return binary - static_cast<uint8_t*>(output) - pad;
}
extern "C" bool pw_Base64IsValid(const char* base64_data, size_t base64_size) {
if (base64_size % kEncodedGroupSize != 0) {
return false;
}
for (size_t i = 0; i < base64_size; ++i) {
if (base64_data[i] < kMinValidChar || base64_data[i] > kMaxValidChar ||
CharToBits(base64_data[i]) == kX /* invalid char */) {
return false;
}
}
return true;
}
size_t Encode(std::span<const std::byte> binary,
std::span<char> output_buffer) {
const size_t required_size = EncodedSize(binary.size_bytes());
if (output_buffer.size_bytes() < required_size) {
return 0;
}
pw_Base64Encode(binary.data(), binary.size_bytes(), output_buffer.data());
return required_size;
}
size_t Decode(std::string_view base64, std::span<std::byte> output_buffer) {
if (output_buffer.size_bytes() < MaxDecodedSize(base64.size()) ||
!IsValid(base64)) {
return 0;
}
return Decode(base64, output_buffer.data());
}
} // namespace pw::base64