base64/base64.cpp at master · marcoaurelima/base64 · GitHub

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// ***************************************** //
//       AUTOR: Marco Aurélio Lima           //
//      GITHUB: github.com/marcoaurelima     //
// ***************************************** //
#include "base64.h"

using UCHAR = unsigned char;
std::string charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

std::string base64encoder(const std::string& input)
{
    std::stringstream output;

    for(size_t i=0;i<input.size()/3;++i)
    {
        UCHAR byte_0 = (input[(3*i)+0] & 0xFC) >> 2;
        UCHAR byte_1 = (input[(3*i)+0] & 0x03) << 4;
        UCHAR byte_2 = (input[(3*i)+1] & 0xF0) >> 4;
        UCHAR byte_3 = (input[(3*i)+1] & 0x0F) << 2;
        UCHAR byte_4 = (input[(3*i)+2] & 0xC0) >> 6;
        UCHAR byte_5 = (input[(3*i)+2] & 0x3F) >> 0;

        output << charset[byte_0] << charset[byte_1 + byte_2]
               << charset[byte_3 + byte_4] << charset[byte_5];
    }

    if(input.size()%3 == 1)
    {
        UCHAR byte_0 = (input[input.size()-1] & 0xFC) >> 2;
        UCHAR byte_1 = (input[input.size()-1] & 0x03) << 4;
        UCHAR byte_2 = '=';
        UCHAR byte_3 = '=';
        output << charset[byte_0] << charset[byte_1] << byte_2 << byte_3;
    } else
    if(input.size()%3 == 2)
    {
        UCHAR byte_0 = (input[input.size()-2] & 0xFC) >> 2;
        UCHAR byte_1 = (input[input.size()-2] & 0x03) << 4;
        UCHAR byte_2 = (input[input.size()-1] & 0xF0) >> 4;
        UCHAR byte_3 = (input[input.size()-1] & 0x0F) << 2;
        UCHAR byte_4 = '=';
        output << charset[byte_0] << charset[byte_1 + byte_2]
               << charset[byte_3] << byte_4;
    }

  return output.str();
}

bool isBase64String(const std::string& input)
{
    for(size_t i=0;i<input.size();++i)
    {
        if(charset.find(input[i]) == std::string::npos)
        {
            return false;
        }
    }
    return true;
}

std::string base64decoder(const std::string& input)
{
    if(!isBase64String(input)){ return ""; }

    std::stringstream output;

    for(size_t i=0;i<input.size()/4;++i)
    {
        size_t index_0 = charset.find(input[(4*i)+0]);
        size_t index_1 = charset.find(input[(4*i)+1]);
        size_t index_2 = charset.find(input[(4*i)+2]);
        size_t index_3 = charset.find(input[(4*i)+3]);

        UCHAR byte_0 = (index_0 & 0x3F) << 2;
        UCHAR byte_1 = (index_1 & 0x30) >> 4;
        UCHAR byte_2 = (index_1 & 0x0F) << 4;
        UCHAR byte_3 = (index_2 & 0x3C) >> 2;
        UCHAR byte_4 = (index_2 & 0x03) << 6;
        UCHAR byte_5 = (index_3 & 0x3F) >> 0;

        output << (char)(byte_0 + byte_1) << (char)(byte_2 + byte_3)
               << (char)(byte_4 + byte_5);
    }

    std::string out = output.str();

    // Remover sobras
    for(size_t i=input.size()-1; i>=input.size()-2; i--)
    {
        if(input[i] == '='){ out.pop_back();}
    }

    return out;
}