c++ - How do I encode a string to base64 using only boost?

Question

I'm trying to quickly encode a simple ASCII string to base64 (Basic HTTP Authentication using boost::asio) and not paste in any new code code or use any libraries beyond boost.

Simple signature would look like: string Base64Encode(const string& text);

Again I realize the algorithm is easy and there are many libraries/examples doing this but I'm looking for a clean boost example. I found boost serialization but no clear examples there or from Google. http://www.boost.org/doc/libs/1_46_1/libs/serialization/doc/dataflow.html

Is this possible without adding the actual base64 algorithm explicitly to my code?

Answer 1

Here is my solution. It uses the same basic technique as the other solutions on this page, but solves the problem of the padding in what I feel is a more elegant way. This solution also makes use of C++11.

I think that most of the code is self explanatory. The bit of math in the encode function calculates the number of '=' characters we need to add. The modulo 3 of val.size() the remainder, but what we really want is the difference between val.size() and the next number divisible by three. Since we have the remainder we can just subtract the remainder from 3, but that leaves 3 in the case that we want 0, so we have to modulo 3 one more time.

#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 == '';
    });
}

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, '=');
}