Boost gzip how to output compressed string as text

Question

I'm using boost gzip example code here. I am attempting to compress a simple string test and am expecting the compressed string H4sIAAAAAAAACitJLS4BAAx+f9gEAAAA as shown in this online compressor

static std::string compress(const std::string& data)
{
    namespace bio = boost::iostreams;
    std::stringstream compressed;
    std::stringstream origin(data);

    bio::filtering_streambuf<bio::input> out;
    out.push(bio::gzip_compressor(bio::gzip_params(bio::gzip::best_compression)));
    out.push(origin);
    
    bio::copy(out, compressed);
    return compressed.str();
}

int main(int argc, char* argv[]){
    std::cout << compress("text") << std::endl;
    // prints out garabage

    return 0;
}

However when I print out the result of the conversion I get garbage values like +I-. ~

I know that it's a valid conversion because the decompression value returns the correct string. However I need the format of the string to be human readable ie H4sIAAAAAAAACitJLS4BAAx+f9gEAAAA .

How can I modify the code to output human readable text?

Thanks

Motivation

The garbage format is not compatible with my JSON library where I will send the compressed text through.

Answer 1

The example site completely fails to mention they also base64 encode the result:

base64 -d <<< 'H4sIAAAAAAAACitJLS4BAAx+f9gEAAAA' | gunzip -

Prints :

test

---

In short, you need to also do that:

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#include <boost/iostreams/copy.hpp>
#include <boost/iostreams/filter/gzip.hpp>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <iostream>
#include <sstream>

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

std::string decode64(std::string const& val)
{
    using namespace boost::archive::iterators;
    return {
        transform_width<binary_from_base64<std::string::const_iterator>, 8, 6>{
            std::begin(val)},
        {std::end(val)},
    };
}

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

static std::string compress(const std::string& data)
{
    namespace bio = boost::iostreams;
    std::istringstream origin(data);

    bio::filtering_istreambuf in;
    in.push(
        bio::gzip_compressor(bio::gzip_params(bio::gzip::best_compression)));
    in.push(origin);

    std::ostringstream compressed;
    bio::copy(in, compressed);
    return compressed.str();
}

static std::string decompress(const std::string& data)
{
    namespace bio = boost::iostreams;
    std::istringstream compressed(data);

    bio::filtering_istreambuf in;
    in.push(bio::gzip_decompressor());
    in.push(compressed);

    std::ostringstream origin;
    bio::copy(in, origin);
    return origin.str();
}

int main() { 
    auto msg = encode64(compress("test"));
    std::cout << msg << std::endl;
    std::cout << decompress(decode64(msg)) << std::endl;
}

Prints

H4sIAAAAAAAC/ytJLS4BAAx+f9gEAAAA
test