OggAudioFileFormat fails to load content

[Atsushi Eno]

I have been trying choc these days for some audio code. I noticed that AudioReader from OggAudioFileFormat<supportWriting> cannot read file at all in my app. It is probably IF the input is seekable.

I think I figured out why. In choc_AudioFileFormat_Ogg.h (line 59558 at 24556f4, cannot put permalink as the file is too large):

        bool fillCache (uint64_t frameIndex)
        {
            if (ov_pcm_tell (std::addressof (oggfile)) != static_cast<int64_t> (frameIndex))
                if (! ov_pcm_seek (std::addressof (oggfile), static_cast<int64_t> (frameIndex)))
                    return false;

It returns false when ov_pcm_seek() returns 0, but this function returns 0 for SUCCESS. Therefore, it never succeeds when our code reaches there.

Partial repro code:

class SeekableByteBuffer : public std::streambuf {
public:
    SeekableByteBuffer(uint8_t* data, std::size_t size) {
        setg(reinterpret_cast<char*>(data), reinterpret_cast<char*>(data), reinterpret_cast<char*>(data) + size);
    }

    std::streampos seekoff(std::streamoff off, std::ios_base::seekdir dir, std::ios_base::openmode which) override {
        if (dir == std::ios_base::cur) {
            gbump(static_cast<int>(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();
    }
};

void repro(uint8_t *data, int dataLength, const char *filename) {
    choc::audio::OggAudioFileFormat<false> format{};

    if (format.filenameSuffixMatches(filename)) {
        SeekableByteBuffer buffer(data, dataLength);
        auto stream = std::make_shared<std::istream>(&buffer);
        auto reader = format.createReader(stream);
        reader->loadFileContent();
    }
}

[Julian Storer]

Thanks for the great bug report!
I can't really figure out what your stream class was supposed to be doing, and it seemed to behave oddly when I tried it, but I added a simpler test that seemed to be triggering the same bug, and fixed it, so it should be fine now. Let me know if you still have any problems with it

[Atsushi Eno]

Oops, yes the streambuf hack would be odd. I hoped to use std::basic_spanstream with span alternative in choc, but it requires C++23 (of course). So I resorted to some hacky workaround. The fix worked. Thanks!