src/base64/base64.cpp

#include <iostream>
#include <fstream>
#include <vector>
#include <string>

// Base64编码表
static const std::string base64_chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

// 检查字符是否是base64字符
static inline bool is_base64(unsigned char c) {
    return (isalnum(c) || (c == '+') || (c == '/'));
}

// 将二进制数据转换为base64字符串
std::string base64_encode(std::string pth_img) {

    // 打开二进制文件
    std::ifstream file(pth_img, std::ios::binary);
    if (!file) {
        std::cerr << "无法打开文件: " << pth_img << std::endl;
    }

    // 读取文件内容到vector
    const std::vector<unsigned char> data(
        (std::istreambuf_iterator<char>(file)),
        (std::istreambuf_iterator<char>())
    );

    std::string ret;
    int i = 0;
    int j = 0;
    unsigned char char_array_3[3];
    unsigned char char_array_4[4];
    int data_size = data.size();

    while (data_size--) {
        char_array_3[i++] = data[j++];
        if (i == 3) {
            char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
            char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
            char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
            char_array_4[3] = char_array_3[2] & 0x3f;

            for (i = 0; i < 4; i++)
                ret += base64_chars[char_array_4[i]];
            i = 0;
        }
    }

    if (i) {
        for (j = i; j < 3; j++)
            char_array_3[j] = '\0';

        char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
        char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
        char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
        char_array_4[3] = char_array_3[2] & 0x3f;

        for (j = 0; j < i + 1; j++)
            ret += base64_chars[char_array_4[j]];

        while (i++ < 3)
            ret += '=';
    }

    return ret;
}

// 将base64字符串转换回二进制数据
std::vector<unsigned char> base64_decode(const std::string& input) {

    const std::string BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    std::vector<int> decode_table(256, -1);
    for (int i = 0; i < 64; i++)
        decode_table[BASE64_CHARS[i]] = i; // 构建解码表[6,8](@ref)

    std::vector<unsigned char> decoded;
    int val = 0, bits = -8; // val:24位缓冲区, bits:当前有效位数
    for (unsigned char c : input) {
        if (c == '=') break;               // 遇填充符终止
        if (decode_table[c] == -1) continue; // 跳过非法字符

        val = (val << 6) + decode_table[c]; // 合并6位数据[6](@ref)
        bits += 6;
        if (bits >= 0) {                   // 每凑够8位输出1字节
            decoded.push_back((val >> bits) & 0xFF);
            bits -= 8;
        }
    }
    return decoded;
}
// std::vector<unsigned char> binary_data = base64_decode(base64_data);
    // std::ofstream out_file(output_file, std::ios::binary);
    // out_file.write(reinterpret_cast<const char*>(binary_data.data()), binary_data.size());
    // out_file.close();