Earlier quoted context omitted.
Of course, but I would still strongly advise against this. If you really cannot avoid implementing something like this, you should inspect the 7-Zip code in order to be 100% sure that the magic number detection in your filter is identical (or matches a superset) to the one from 7-Zip.
> you should inspect the 7-Zip code in order to be 100% sure that the magic number detection in your filter is identical (or matches a superset) to the one from 7-Zip CPP/7zip/Archive/Rar/RarHandler.cpp: #define SIGNATURE { 0x52 , 0x61, 0x72, 0x21, 0x1a, 0x07, 0x00 } CPP/7zip/UI/Common/OpenArchive.cpp: const Byte kRarHeader[] = { 0x52 , 0x61, 0x72, 0x21, 0x1a, 0x07, 0x00 }; CPP/7zip/Archive/Rar/Rar5Handler.cpp: #defi…
You missed my point. It is trivial to find out what the magic number is. What is more important though: How exactly is the magic number matched? From what you have written, one might be tempted to simply check whether a file begins with this magic number. And this would be wrong. If you take a look at the matching in CPP/7zip/Archive/Rar/RarHandler.cpp:
Byte marker[NHeader::kMarkerSize];
RINOK(ReadStream_FALSE(stream, marker, NHeader::kMarkerSize));
if (memcmp(marker, kMarker, NHeader::kMarkerSize) == 0)
m_Position += NHeader::kMarkerSize;
else
{
if (searchHeaderSizeLimit && *searchHeaderSizeLimit == 0)
return S_FALSE;
RINOK(stream->Seek(m_StreamStartPosition, STREAM_SEEK_SET, NULL));
RINOK(FindSignatureInStream(stream, kMarker, NHeader::kMarkerSize,
searchHeaderSizeLimit, arcStartPos));
m_Position = arcStartPos + NHeader::kMarkerSize;
RINOK(stream->Seek(m_Position, STREAM_SEEK_SET, NULL));
}