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81 lines
2.5 KiB
C++
81 lines
2.5 KiB
C++
#include "Common/Data/Encoding/Base64.h"
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// TODO: This is a simple but not very efficient implementation.
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std::string Base64Encode(const uint8_t *p, size_t sz) {
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const char digits[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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size_t unpaddedLength = (4 * sz + 2) / 3;
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std::string result;
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result.resize((unpaddedLength + 3) & ~3, '=');
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for (size_t i = 0; i < unpaddedLength; ++i) {
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// This is the index into the original string.
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size_t pos = (i * 3) / 4;
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int8_t off = 2 * ((i * 3) % 4);
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int c = p[pos];
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if (off > 2) {
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c <<= 8;
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off -= 8;
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// Grab more bits from the next character.
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if (pos + 1 < sz) {
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c |= p[pos + 1];
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}
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}
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// Since we take from the big end, off starts at 2 and goes down.
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int8_t shift = 2 - off;
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// Now take the bits at off and encode the character.
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result[i] = digits[(c >> shift) & 0x3F];
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}
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return result;
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}
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std::vector<uint8_t> Base64Decode(const char *s, size_t sz) {
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const uint8_t lookup[256] = {
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255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
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255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
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255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 63, 62, 255, 63,
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// '0' starts here.
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52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 255, 255, 255,
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// 'A' after an invalid.
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255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
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15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 63,
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// 'a' after an invalid.
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255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
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41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255, 255,
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};
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std::vector<uint8_t> result;
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result.reserve(3 * sz / 4);
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for (size_t i = 0; i < sz; i += 4) {
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uint8_t quad[4] = {
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lookup[s[i]],
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i + 1 < sz ? lookup[s[i + 1]] : 255,
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i + 2 < sz ? lookup[s[i + 2]] : 255,
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i + 3 < sz ? lookup[s[i + 3]] : 255,
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};
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// First: ABCDEF GHXXXX XXXXXX XXXXXX. Neither 6-bit value should be invalid.
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result.push_back((quad[0] << 2) | ((quad[1] & 0x30) >> 4));
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// Next: XXXXXX XXABCD EFGHXX XXXXXX. Invalid if quad[2] is invalid.
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if (quad[2] == 255) {
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continue;
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}
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result.push_back(((quad[1] & 0x0F) << 4) | ((quad[2] & 0x3C) >> 2));
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// Last: XXXXXX XXXXXX XXXXAB CDEFGH. Invalid only if quad[3] is.
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if (quad[3] == 255) {
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continue;
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}
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result.push_back(((quad[2] & 0x03) << 6) | (quad[3] & 0x3F));
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}
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return result;
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}
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