1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14
15 #include "pw_base64/base64.h"
16
17 #include <cstdint>
18
19 namespace pw::base64 {
20 namespace {
21
22 // Encoding functions
23 constexpr size_t kEncodedGroupSize = 4;
24 constexpr char kChar62 = '+'; // URL safe encoding uses - instead
25 constexpr char kChar63 = '/'; // URL safe encoding uses _ instead
26 constexpr char kPadding = '=';
27
28 // Table that encodes a 6-bit pattern as a Base64 character
29 constexpr char kEncodeTable[64] = {
30 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
31 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
32 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
33 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
34 '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', kChar62, kChar63};
35
BitGroup0Char(uint8_t byte0)36 constexpr char BitGroup0Char(uint8_t byte0) {
37 return kEncodeTable[(byte0 & 0b11111100) >> 2];
38 }
BitGroup1Char(uint8_t byte0,uint8_t byte1=0)39 constexpr char BitGroup1Char(uint8_t byte0, uint8_t byte1 = 0) {
40 return kEncodeTable[((byte0 & 0b00000011) << 4) |
41 ((byte1 & 0b11110000) >> 4)];
42 }
BitGroup2Char(uint8_t byte1,uint8_t byte2=0)43 constexpr char BitGroup2Char(uint8_t byte1, uint8_t byte2 = 0) {
44 return kEncodeTable[((byte1 & 0b00001111) << 2) |
45 ((byte2 & 0b11000000) >> 6)];
46 }
BitGroup3Char(uint8_t byte2)47 constexpr char BitGroup3Char(uint8_t byte2) {
48 return kEncodeTable[byte2 & 0b00111111];
49 }
50
51 // Decoding functions
52 constexpr char kMinValidChar = '+';
53 constexpr char kMaxValidChar = 'z';
54 constexpr uint8_t kX = 0xff; // Value used for invalid characters
55
56 // Table that decodes a Base64 character to its 6-bit value. Supports the
57 // standard (+/) and URL-safe (-_) alphabets. Starts from the lowest-value valid
58 // character, which is +.
59 constexpr uint8_t kDecodeTable[] = {
60 62, kX, 62, kX, 63, 52, 53, 54, 55, 56, // 0 - 09
61 57, 58, 59, 60, 61, kX, kX, kX, 0, kX, // 10 - 19
62 kX, kX, 0, 1, 2, 3, 4, 5, 6, 7, // 20 - 29
63 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, // 30 - 39
64 18, 19, 20, 21, 22, 23, 24, 25, kX, kX, // 40 - 49
65 kX, kX, 63, kX, 26, 27, 28, 29, 30, 31, // 50 - 59
66 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, // 60 - 69
67 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // 70 - 79
68 };
69
CharToBits(char ch)70 constexpr uint8_t CharToBits(char ch) {
71 return kDecodeTable[ch - kMinValidChar];
72 }
73
Byte0(uint8_t bits0,uint8_t bits1)74 constexpr uint8_t Byte0(uint8_t bits0, uint8_t bits1) {
75 return (bits0 << 2) | ((bits1 & 0b110000) >> 4);
76 }
Byte1(uint8_t bits1,uint8_t bits2)77 constexpr uint8_t Byte1(uint8_t bits1, uint8_t bits2) {
78 return ((bits1 & 0b001111) << 4) | ((bits2 & 0b111100) >> 2);
79 }
Byte2(uint8_t bits2,uint8_t bits3)80 constexpr uint8_t Byte2(uint8_t bits2, uint8_t bits3) {
81 return ((bits2 & 0b000011) << 6) | bits3;
82 }
83
84 } // namespace
85
pw_Base64Encode(const void * binary_data,const size_t binary_size_bytes,char * output)86 extern "C" void pw_Base64Encode(const void* binary_data,
87 const size_t binary_size_bytes,
88 char* output) {
89 const uint8_t* bytes = static_cast<const uint8_t*>(binary_data);
90
91 // Encode groups of 3 source bytes into 4 output characters.
92 size_t remaining = binary_size_bytes;
93 for (; remaining >= 3u; remaining -= 3u, bytes += 3) {
94 *output++ = BitGroup0Char(bytes[0]);
95 *output++ = BitGroup1Char(bytes[0], bytes[1]);
96 *output++ = BitGroup2Char(bytes[1], bytes[2]);
97 *output++ = BitGroup3Char(bytes[2]);
98 }
99
100 // If the source data length isn't a multiple of 3, pad the end with either 1
101 // or 2 '=' characters, to stay Python-compatible.
102 if (remaining > 0u) {
103 *output++ = BitGroup0Char(bytes[0]);
104 if (remaining == 1u) {
105 *output++ = BitGroup1Char(bytes[0]);
106 *output++ = kPadding;
107 } else {
108 *output++ = BitGroup1Char(bytes[0], bytes[1]);
109 *output++ = BitGroup2Char(bytes[1]);
110 }
111 *output++ = kPadding;
112 }
113 }
114
pw_Base64Decode(const char * base64,size_t base64_size_bytes,void * output)115 extern "C" size_t pw_Base64Decode(const char* base64,
116 size_t base64_size_bytes,
117 void* output) {
118 // If too small, can't be valid input, due to likely missing padding
119 if (base64_size_bytes < 4) {
120 return 0;
121 }
122
123 uint8_t* binary = static_cast<uint8_t*>(output);
124 for (size_t ch = 0; ch < base64_size_bytes; ch += kEncodedGroupSize) {
125 const uint8_t char0 = CharToBits(base64[ch + 0]);
126 const uint8_t char1 = CharToBits(base64[ch + 1]);
127 const uint8_t char2 = CharToBits(base64[ch + 2]);
128 const uint8_t char3 = CharToBits(base64[ch + 3]);
129
130 *binary++ = Byte0(char0, char1);
131 *binary++ = Byte1(char1, char2);
132 *binary++ = Byte2(char2, char3);
133 }
134
135 size_t pad = 0;
136 if (base64[base64_size_bytes - 2] == kPadding) {
137 pad = 2;
138 } else if (base64[base64_size_bytes - 1] == kPadding) {
139 pad = 1;
140 }
141
142 return binary - static_cast<uint8_t*>(output) - pad;
143 }
144
pw_Base64IsValid(const char * base64_data,size_t base64_size)145 extern "C" bool pw_Base64IsValid(const char* base64_data, size_t base64_size) {
146 if (base64_size % kEncodedGroupSize != 0) {
147 return false;
148 }
149
150 for (size_t i = 0; i < base64_size; ++i) {
151 if (base64_data[i] < kMinValidChar || base64_data[i] > kMaxValidChar ||
152 CharToBits(base64_data[i]) == kX /* invalid char */) {
153 return false;
154 }
155 }
156 return true;
157 }
158
Encode(std::span<const std::byte> binary,std::span<char> output_buffer)159 size_t Encode(std::span<const std::byte> binary,
160 std::span<char> output_buffer) {
161 const size_t required_size = EncodedSize(binary.size_bytes());
162 if (output_buffer.size_bytes() < required_size) {
163 return 0;
164 }
165 pw_Base64Encode(binary.data(), binary.size_bytes(), output_buffer.data());
166 return required_size;
167 }
168
Decode(std::string_view base64,std::span<std::byte> output_buffer)169 size_t Decode(std::string_view base64, std::span<std::byte> output_buffer) {
170 if (output_buffer.size_bytes() < MaxDecodedSize(base64.size()) ||
171 !IsValid(base64)) {
172 return 0;
173 }
174 return Decode(base64, output_buffer.data());
175 }
176
177 } // namespace pw::base64
178