Merge "FLACExtractor: Fix sniffer to allow STREAMINFO only metadata"

bool SniffFLAC(DataSourceHelper *source, float *confidence)

{

    // first 4 is the signature word

    // second 4 is the sizeof STREAMINFO

    // 042 is the mandatory STREAMINFO

    // no need to read rest of the header, as a premature EOF will be caught later

    uint8_t header[4+4];

    if (source->readAt(0, header, sizeof(header)) != sizeof(header)

            || memcmp("fLaC\0\0\0\042", header, 4+4))

    {

    // FLAC header.

    // https://xiph.org/flac/format.html#stream

    //

    // Note: content stored big endian.

    // byte offset  bit size  content

    // 0            32        fLaC

    // 4            8         metadata type STREAMINFO (0) (note: OR with 0x80 if last metadata)

    // 5            24        size of metadata, for STREAMINFO (0x22).

    // Android is LE, so express header as little endian int64 constant.

    constexpr int64_t flacHeader = (0x22LL << 56) | 'CaLf';

    constexpr int64_t flacHeader2 = flacHeader | (0x80LL << 32); // alternate form (last metadata)

    int64_t header;

    if (source->readAt(0, &header, sizeof(header)) != sizeof(header)

            || (header != flacHeader && header != flacHeader2)) {

        return false;

    }