base64プログラム

gistfile1.cpp

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <fstream>
//#include <iostream>
#include <string>
#include <exception>
#include <stdexcept>
#include "scope_exit.hpp"

bool base64decode(char const * const base64, unsigned int const plen, void ** const ret, unsigned int * const psize){
    static char const list[] = {
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 62,  0,  0,  0, 63,
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61,  0,  0,  0,  0,  0,  0,
         0,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
        15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,  0,  0,  0,  0,  0,
         0, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
        41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
         0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    };
    unsigned int const len = plen ? plen : std::strlen(base64);
    if(len & 0x3){
        return false;
    }
    
    bool const haspadding = base64[len - 1] == '=', hastwopadding = base64[len - 2] == '=';
    unsigned int const fulllen = (len >> 2) - haspadding;
    unsigned char *retdata = new(std::nothrow) unsigned char[*psize = fulllen * 3 + (haspadding ? hastwopadding ? 1 : 2 : 0)];
    *ret = retdata;
    unsigned char const *basedata = reinterpret_cast<unsigned char const*>(base64);
    
    for(unsigned int i = fulllen; ~(--i); basedata += 4, retdata += 3){
        unsigned char const ddata[] = {list[basedata[0]], list[basedata[1]], list[basedata[2]], list[basedata[3]]};
        retdata[0] = (ddata[0] << 2) | (ddata[1] >> 4);
        retdata[1] = (ddata[1] << 4) | (ddata[2] >> 2);
        retdata[2] = (ddata[2] << 6) | ddata[3];
    }
    
    if(haspadding){
        if(hastwopadding){
            retdata[0] = (list[basedata[0]] << 2) | (list[basedata[1]] >> 4);
        }else{
            unsigned char const ddata[] = {list[basedata[0]], list[basedata[1]], list[basedata[2]]};
            retdata[0] = (ddata[0] << 2) | (ddata[1] >> 4);
            retdata[1] = (ddata[1] << 4) | (ddata[2] >> 2);
        }
    }
    
    return true;
}

bool base64encode(void const * const data, unsigned int const size, char ** const ret){
    static char const * const list = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    unsigned int const fullsize = size / 3, rest = size % 3;
    unsigned char *retp = new(std::nothrow) unsigned char[(fullsize + (rest ? 1 : 0)) * 4 + 1];
    *ret = reinterpret_cast<char*>(retp);
    unsigned char const *datap = static_cast<unsigned char const*>(data);
    if(retp == NULL){
        return false;
    }
    
    for(unsigned int i = fullsize; ~(--i); datap += 3, retp += 4){
        retp[0] = list[datap[0] >> 2];
        retp[1] = list[(datap[0] & 0x3) << 4 | datap[1] >> 4];
        retp[2] = list[(datap[1] & 0xF) << 2 | datap[2] >> 6];
        retp[3] = list[datap[2] & 0x3F];
    }
    
    switch(rest){
        case 1:{
            retp[0] = list[datap[0] >> 2];
            retp[1] = list[(datap[0] & 0x3) << 4];
            retp[2] = retp[3] = '=';
            retp += 4;
            break;
        }
        
        case 2:{
            retp[0] = list[datap[0] >> 2];
            retp[1] = list[(datap[0] & 0x3) << 4 | datap[1] >> 4];
            retp[2] = list[(datap[1] & 0xF) << 2];
            retp[3] = '=';
            retp += 4;
            break;
        }
    }
    
    retp[0] = '\0';
    
    return true;
}

void base64free(void *base64){
    delete[] static_cast<unsigned char*>(base64);
}

int main(int argc, char **argv){
    try{
        if(argc < 2) throw std::runtime_error("引数が足りません");
        if(argc == 2){
            FILE *file = std::fopen(argv[1], "rb");
            if(!file) throw std::runtime_error("fopenエラー");
            scope_exit{std::fclose(file);};
            
            if(std::fseek(file, 0, SEEK_END)) throw std::runtime_error("fseekエラー1");
            
            long size = std::ftell(file);
            if(size == -1) throw std::runtime_error("ftellエラー");
            
            if(std::fseek(file, 0, SEEK_SET)) throw std::runtime_error("fseekエラー2");
            
            char *data = static_cast<char*>(std::malloc(size * sizeof(char)));
            if(!data) throw std::runtime_error("mallocエラー");
            scope_exit{std::free(data);};
            
            if(!std::fread(data, size, 1, file)) throw std::runtime_error("freadエラー");
            
            char *ret;
            if(!base64encode(data, size, &ret)) throw std::runtime_error("base64encodeエラー");
            scope_exit{base64free(ret);};
            
            std::puts(ret);
        }else if(argc == 3){
            std::ifstream file(argv[1]);
            if(!file) throw std::runtime_error("ifstreamエラー");
            
            FILE *ofile = std::fopen(argv[2], "wb");
            if(!ofile) throw std::runtime_error("fopenエラー");
            
            std::string str;
            std::getline(file, str);
            if(!file) throw std::runtime_error("getlineエラー");
            
            void *p;
            unsigned int size;
            if(!base64decode(str.c_str(), str.length(), &p, &size)) throw std::runtime_error("base64decodeエラー");
            scope_exit{base64free(p);};
            
            if(!std::fwrite(p, size, 1, ofile)) throw std::runtime_error("fwriteエラー");
        }else{
            throw std::runtime_error("引数が多すぎます");
        }
    }catch(std::exception &e){
        std::fprintf(stderr, "Exception is thrown. what:%s\n", e.what());
        return -1;
    }
    return 0;
}