base64.hpp

#pragma once

namespace base64 {

static const std::string base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                        "abcdefghijklmnopqrstuvwxyz"
                                        "0123456789+/";
static inline bool is_base64( unsigned char c ) {
    return ( isalnum( c ) || ( c == '+' ) || ( c == '/' ) );
}

std::string encode( unsigned char const* bytes_to_encode, size_t in_len ) {
    std::string ret;
    size_t i = 0, j = 0;
    unsigned char char_array_3[ 3 ], char_array_4[ 4 ];
    while( in_len-- ) {
        char_array_3[ i++ ] = *( bytes_to_encode++ );
        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;
}

std::string decode( std::string const& encoded_string ) {
    size_t in_len = encoded_string.size();
    size_t i = 0, j = 0, in_ = 0;
    unsigned char char_array_4[ 4 ], char_array_3[ 3 ];
    std::string ret;
    while( in_len-- && ( encoded_string[ in_ ] != '=' ) && is_base64( encoded_string[ in_ ] ) ) {
        char_array_4[ i++ ] = encoded_string[ in_ ];
        in_++;
        if( i == 4 ) {
            for( i = 0; i < 4; i++ )
                char_array_4[ i ] = base64_chars.find( char_array_4[ i ] );
            char_array_3[ 0 ] = ( char_array_4[ 0 ] << 2 ) + ( ( char_array_4[ 1 ] & 0x30 ) >> 4 );
            char_array_3[ 1 ] = ( ( char_array_4[ 1 ] & 0xf ) << 4 ) + ( ( char_array_4[ 2 ] & 0x3c ) >> 2 );
            char_array_3[ 2 ] = ( ( char_array_4[ 2 ] & 0x3 ) << 6 ) + char_array_4[ 3 ];
            for( i = 0; ( i < 3 ); i++ )
                ret += char_array_3[ i ];
            i = 0;
        }
    }
    if( i ) {
        for( j = i; j < 4; j++ )
            char_array_4[ j ] = 0;
        for( j = 0; j < 4; j++ )
            char_array_4[ j ] = base64_chars.find( char_array_4[ j ] );
        char_array_3[ 0 ] = ( char_array_4[ 0 ] << 2 ) + ( ( char_array_4[ 1 ] & 0x30 ) >> 4 );
        char_array_3[ 1 ] = ( ( char_array_4[ 1 ] & 0xf ) << 4 ) + ( ( char_array_4[ 2 ] & 0x3c ) >> 2 );
        char_array_3[ 2 ] = ( ( char_array_4[ 2 ] & 0x3 ) << 6 ) + char_array_4[ 3 ];
        for( j = 0; ( j < i - 1 ); j++ )
            ret += char_array_3[ j ];
    }
    return ret;
}
}  // namespace base64