Re: C++ Deflate (zlib-like) library

From: Domen Vrankar (domen.vrankar_at_[hidden])
Date: 2020-03-11 06:12:17

aOn Tue, Mar 10, 2020 at 5:49 PM Vinnie Falco <vinnie.falco_at_[hidden]>
wrote:

> On Tue, Mar 10, 2020 at 1:31 AM Domen Vrankar <domen.vrankar_at_[hidden]>
> wrote:
> > You compress/decompress in chunks so all you need is a const std::span
> for input and std::span for output and call decompress on a for loop.
>
> You need to know:
>
>     1. how much input was consumed
>     2. how much output was produced
>

Now I understand what you mean. You got me confused as your compress
function wasn't receiving any state (like z_stream in zlib) so I assumed
that you meant to compress the entire buffer in one go.

> > ...input iterator pair/range for input/output...
> > ...std::istream_iterator...
> > ...boost.spirit x3 parser...
> > ...read->decompress->parse/process
> > ...
> > Whit iterators/ranges described above you wouldn't
> > need to return std::size_t so return can be used for
> > error codes instead.
>
> It isn't clear what these things mean without seeing a function
> signature or class declaration.
>

Since you need to hold state I was talking about something like this:

struct Reader // should be implemented for reading from vector, file
stream... some provided as convinience, others user defined so an extension
point
{
    std::span<std::byte> read(); // remains stable untill next call to
read, at that point it is auto consumed
    bool eof();
};

template<typename InReader, typename WriteBuffer>
class Deflate_range
{
public:
    Deflate_range(InReader& in, WriteBuffer& write);

    class Deflate_iterator{...};

    Deflate_iterator begin(); // can be called only once
    Deflate_iterator end();

private:
    InReader& in_;
    WriteBuffer& write_;
    z_stream zs_; // holds the compression/encryption/... state
};

Polymorphic_deflate_range compress(std::istream_iterator<std::byte> begin,
std::istream_iterator<std::byte> end); // it packs iterators into a Reader
(an overload of compress coud also take in streams directly - it's just a
convinience function)

std::istringstream str{"1234567890"};
auto range = compress(std::istream_iterator<std::byte>{str},
std::istream_iterator<std::byte>{});

bool ok = boost::spirit::x3::phrase_parse(range.begin(), range.end(), ...);

I haven't used std::ranges yet so perhaps such a range should be
implemented differently.

Then I got confused by your compress API so size_t my return comment was
just me being confused and reading/replying to mails on my phone...

Hope this clarifies things a bit.

I'm guessing that I could use such thing in my toy game engine - not
certain but perhaps I won't need the whole libarchive functionality
there... To early to say.

Regards,
Domen

>
> Thanks
>