fill buffer with data not from file but of a known format

[lain3d]

Just as a test I've done this:

struct membuf : std::streambuf
{
    membuf(char* begin, char* end) {
        this->setg(begin, begin, end);
    }
};

class FileFactory final : public alure::FileIOFactory {
private:
    membuf buf;
public:
    FileFactory(membuf &bufin) : buf(bufin)
    {
        std::cout << "hello" << std::endl;
    }

    alure::UniquePtr<std::istream> openFile(const alure::String &name) noexcept override
    {
        auto stream = alure::MakeUnique<std::istream>(&buf);
        if (stream->fail()) {
            std::cout << "failed" << std::endl;
        }
        return std::move(stream); 
    }
};

In my main function I have:
membuf sbuf(existing_buff, existing_buff + sz);
alure::FileIOFactory::set(alure::MakeUnique<FileFactory>(sbuf));

When I run my test I get:
Failed to rewind file for the next decoder factory

This is just a test, I was planning to pass in a map of id,buf in the constructor to the factory if I got this to work.

[kcat]

This doesn't look like proper use of the file IO factory. Each given filename needs to return a unique file/istream handle for the named file, rather than one membuf for all files. Your custom istream handle type also needs to implement seeking, or else the decoders will have problems.

[McSinyx]

I think OP's final goal is to have an istream created from the factory from each ID, which is analogous to file handling. @lain3d: Here is a quite informative article on properly deriving std::streambuf.

[lain3d]

@McSinyx I'm now using the std::streambuf for that example + this seekoff:

membuf::pos_type membuf::seekoff(off_type off,
                 std::ios_base::seekdir dir,
                 std::ios_base::openmode which = std::ios_base::in) {
    if (dir == std::ios_base::cur)
        gbump(off);
    else if (dir == std::ios_base::end)
        setg(eback(), egptr() + off, egptr());
    else if (dir == std::ios_base::beg)
        setg(eback(), eback() + off, egptr());
    return gptr() - eback();
}

Unfortunately when I'm creating the object it looks like the underlying std::basic_streambuf is not updated..? So I'm still having the same problem as before.

[lain3d]

After I implemented membuf::seekpos it's getting further but for some reason not decoding the frame properly..

But if I instead use the file the audio plays fine.

[kcat]

FWIW, this is what I use to create a std::istream that reads from a memory buffer instead of a file on disk:
https://github.com/kcat/openal-soft/blob/openal-soft-1.20.1/alc/hrtf.cpp#L111...L178

Your factory's openFile method would just need to create an idstream using the appropriate start and end data pointers.

[lain3d]

Hell yeah, got it working thanks to that.. I needed to have

this->setg(const_cast<char_type*>(begin_), const_cast<char_type*>(begin_),
         const_cast<char_type*>(end_)); 

in my constructor (I took it out earlier because the example from the above link did not have setg).. Thanks. :)