boost base64编码

方案一

#include <boost/archive/iterators/base64_from_binary.hpp>
#include <boost/archive/iterators/binary_from_base64.hpp>
#include <boost/archive/iterators/transform_width.hpp>

bool Base64Encode(const std::string& input, std::string& output) {
    typedef boost::archive::iterators::base64_from_binary<boost::archive::iterators::transform_width<std::string::const_iterator, 6, 8> > Base64EncodeIterator;
    std::stringstream result;
    std::copy(Base64EncodeIterator(input.begin()), Base64EncodeIterator(input.end()), std::ostream_iterator<char>(result));
    size_t equal_count = (3 - input.length() % 3) % 3;
    for (size_t i = 0; i < equal_count; i++) {
        result.put('=');
    }
    output = result.str();
    return output.empty() == false;
}

bool Base64Decode(const std::string& input, std::string& output) {
    typedef boost::archive::iterators::transform_width<boost::archive::iterators::binary_from_base64<std::string::const_iterator>, 8, 6> Base64DecodeIterator;
    std::stringstream result;
    try {
        std::copy(Base64DecodeIterator(input.begin()), Base64DecodeIterator(input.end()), std::ostream_iterator<char>(result));
    }
    catch (...) {
        return false;
    }
    output = result.str();
    return output.empty() == false;
}

方案一有问题，在使用Base64Decode解码的时候，如果输入源的末尾有“=”补位符，那么output的字符串的长度是不对的，不是实际字符串的长度，比实际的字符串长度要长（就是包含补位符的input的字符串应算出来的解码长度）。

方案二

#include <boost/archive/iterators/binary_from_base64.hpp>
#include <boost/archive/iterators/base64_from_binary.hpp>
#include <boost/archive/iterators/transform_width.hpp>
#include <boost/algorithm/string.hpp>

std::string decode64(const std::string &val) {
    using namespace boost::archive::iterators;
    using It = transform_width<binary_from_base64<std::string::const_iterator>, 8, 6>;
    return boost::algorithm::trim_right_copy_if(std::string(It(std::begin(val)), It(std::end(val))), [](char c) {
        return c == '\0';
    });
}

std::string encode64(const std::string &val) {
    using namespace boost::archive::iterators;
    using It = base64_from_binary<transform_width<std::string::const_iterator, 6, 8>>;
    auto tmp = std::string(It(std::begin(val)), It(std::end(val)));
    return tmp.append((3 - val.size() % 3) % 3, '=');
}

方案二没有方案一的那个问题。