base64.h

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#ifndef BASE64_H
#define BASE64_H
 
#include <vector>
#include <string>
 
class Base64 {
private:
    static unsigned char const PAD = '=';
 
    static unsigned char enc(int c)
    {
        static const unsigned char table[] = {
            0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
            0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
            0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76,
            0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f,
        };
        return table[c & 63];
    }
 
    static unsigned char dec(int c)
    {
        static const unsigned char table[] = {
            0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
            0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
            0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x3e, 0xff, 0xff, 0xff, 0x3f,
            0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
            0xff, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
            0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0xff, 0xff, 0xff, 0xff, 0xff,
            0xff, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
            0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0xff, 0xff, 0xff, 0xff, 0xff,
        };
        return table[c & 127];
    }
public:
    static void encode(char const *src, size_t length, std::vector<char> *out)
    {
        size_t srcpos, dstlen, dstpos;
 
        dstlen = (length + 2) / 3 * 4;
        out->resize(dstlen);
        if (dstlen == 0) {
            return;
        }
        char *dst = &out->at(0);
        dstpos = 0;
        for (srcpos = 0; srcpos < length; srcpos += 3) {
            int v = (unsigned char)src[srcpos] << 16;
            if (srcpos + 1 < length) {
                v |= (unsigned char)src[srcpos + 1] << 8;
                if (srcpos + 2 < length) {
                    v |= (unsigned char)src[srcpos + 2];
                    dst[dstpos + 3] = enc(v);
                } else {
                    dst[dstpos + 3] = PAD;
                }
                dst[dstpos + 2] = enc(v >> 6);
            } else {
                dst[dstpos + 2] = PAD;
                dst[dstpos + 3] = PAD;
            }
            dst[dstpos + 1] = enc(v >> 12);
            dst[dstpos] = enc(v >> 18);
            dstpos += 4;
        }
    }
 
    static void decode(char const *src, size_t length, std::vector<char> *out)
    {
        unsigned char const *begin = (unsigned char const *)src;
        unsigned char const *end = begin + length;
        unsigned char const *ptr = begin;
        out->clear();
        out->reserve(length * 3 / 4);
        int count = 0;
        int bits = 0;
        while (1) {
            if (isspace(*ptr)) {
                ptr++;
            } else {
                unsigned char c = 0xff;
                if (ptr < end && *ptr < 0x80) {
                    c = dec(*ptr);
                }
                if (c < 0x40) {
                    bits = (bits << 6) | c;
                    count++;
                } else {
                    if (count < 4) {
                        bits <<= (4 - count) * 6;
                    }
                    c = 0xff;
                }
                if (count == 4 || c == 0xff) {
                    if (count >= 2) {
                        out->push_back(bits >> 16);
                        if (count >= 3) {
                            out->push_back(bits >> 8);
                            if (count == 4) {
                                out->push_back(bits);
                            }
                        }
                    }
                    count = 0;
                    bits = 0;
                    if (c == 0xff) {
                        break;
                    }
                }
                ptr++;
            }
        }
    }
 
    static std::string _to_s_(std::vector<char> const *vec)
    {
        if (!vec || vec->empty()) return std::string();
        return std::string((char const *)&(*vec)[0], vec->size());
    }
};
 
static inline void base64_encode(char const *src, size_t length, std::vector<char> *out)
{
    Base64::encode(src, length, out);
}
 
static inline void base64_decode(char const *src, size_t length, std::vector<char> *out)
{
    Base64::decode(src, length, out);
}
 
static inline void base64_encode(std::vector<char> const *src, std::vector<char> *out)
{
    Base64::encode(&src->at(0), src->size(), out);
}
 
static inline void base64_decode(std::vector<char> const *src, std::vector<char> *out)
{
    Base64::decode(&src->at(0), src->size(), out);
}
 
static inline void base64_encode(char const *src, std::vector<char> *out)
{
    Base64::encode((char const *)src, strlen(src), out);
}
 
static inline void base64_decode(char const *src, std::vector<char> *out)
{
    Base64::decode((char const *)src, strlen(src), out);
}
 
static inline std::string base64_encode(std::string const &src)
{
    std::vector<char> vec;
    base64_encode((char const *)src.c_str(), src.size(), &vec);
    return Base64::_to_s_(&vec);
}
 
static inline std::string base64_decode(std::string const &src)
{
    std::vector<char> vec;
    base64_decode((char const *)src.c_str(), src.size(), &vec);
    return Base64::_to_s_(&vec);
}
 
#endif