static SRes Xz_ReadBackward(CXzStream *p, ILookInStream *stream, Int64 *startOffset, ISzAllocPtr alloc)
{
UInt64 indexSize;
Byte buf[XZ_STREAM_FOOTER_SIZE];
UInt64 pos = *startOffset;
if ((pos & 3) != 0 || pos < XZ_STREAM_FOOTER_SIZE)
return SZ_ERROR_NO_ARCHIVE;
pos -= XZ_STREAM_FOOTER_SIZE;
RINOK(LookInStream_SeekRead_ForArc(stream, pos, buf, XZ_STREAM_FOOTER_SIZE));
if (!XZ_FOOTER_SIG_CHECK(buf + 10))
{
UInt32 total = 0;
pos += XZ_STREAM_FOOTER_SIZE;
for (;;)
{
size_t i;
#define TEMP_BUF_SIZE (1 << 10)
Byte temp[TEMP_BUF_SIZE];
i = (pos > TEMP_BUF_SIZE) ? TEMP_BUF_SIZE : (size_t)pos;
pos -= i;
RINOK(LookInStream_SeekRead_ForArc(stream, pos, temp, i));
total += (UInt32)i;
for (; i != 0; i--)
if (temp[i - 1] != 0)
break;
if (i != 0)
{
if ((i & 3) != 0)
return SZ_ERROR_NO_ARCHIVE;
pos += i;
break;
}
if (pos < XZ_STREAM_FOOTER_SIZE || total > (1 << 16))
return SZ_ERROR_NO_ARCHIVE;
}
if (pos < XZ_STREAM_FOOTER_SIZE)
return SZ_ERROR_NO_ARCHIVE;
pos -= XZ_STREAM_FOOTER_SIZE;
RINOK(LookInStream_SeekRead_ForArc(stream, pos, buf, XZ_STREAM_FOOTER_SIZE));
if (!XZ_FOOTER_SIG_CHECK(buf + 10))
return SZ_ERROR_NO_ARCHIVE;
}
p->flags = (CXzStreamFlags)GetBe16(buf + 8);
if (!XzFlags_IsSupported(p->flags))
return SZ_ERROR_UNSUPPORTED;
if (GetUi32(buf) != CrcCalc(buf + 4, 6))
return SZ_ERROR_ARCHIVE;
indexSize = ((UInt64)GetUi32(buf + 4) + 1) << 2;
if (pos < indexSize)
return SZ_ERROR_ARCHIVE;
pos -= indexSize;
RINOK(LookInStream_SeekTo(stream, pos));
RINOK(Xz_ReadIndex(p, stream, indexSize, alloc));
{
UInt64 totalSize = Xz_GetPackSize(p);
if (totalSize == XZ_SIZE_OVERFLOW
|| totalSize >= ((UInt64)1 << 63)
|| pos < totalSize + XZ_STREAM_HEADER_SIZE)
return SZ_ERROR_ARCHIVE;
pos -= (totalSize + XZ_STREAM_HEADER_SIZE);
RINOK(LookInStream_SeekTo(stream, pos));
*startOffset = pos;
}
{
CXzStreamFlags headerFlags;
CSecToRead secToRead;
SecToRead_CreateVTable(&secToRead);
secToRead.realStream = stream;
RINOK(Xz_ReadHeader(&headerFlags, &secToRead.vt));
return (p->flags == headerFlags) ? SZ_OK : SZ_ERROR_ARCHIVE;
}
}
static SRes Xz_ReadBackward(CXzStream *p, ILookInStream *stream, Int64 *startOffset, ISzAlloc *alloc)
{
UInt64 indexSize;
Byte buf[XZ_STREAM_FOOTER_SIZE];
if ((*startOffset & 3) != 0 || *startOffset < XZ_STREAM_FOOTER_SIZE)
return SZ_ERROR_NO_ARCHIVE;
*startOffset = -XZ_STREAM_FOOTER_SIZE;
RINOK(SeekFromCur(stream, startOffset));
RINOK(LookInStream_Read2(stream, buf, XZ_STREAM_FOOTER_SIZE, SZ_ERROR_NO_ARCHIVE));
if (memcmp(buf + 10, XZ_FOOTER_SIG, XZ_FOOTER_SIG_SIZE) != 0)
{
UInt32 total = 0;
*startOffset += XZ_STREAM_FOOTER_SIZE;
for (;;)
{
size_t i;
#define TEMP_BUF_SIZE (1 << 10)
Byte tempBuf[TEMP_BUF_SIZE];
if (*startOffset < XZ_STREAM_FOOTER_SIZE || total > (1 << 16))
return SZ_ERROR_NO_ARCHIVE;
i = (*startOffset > TEMP_BUF_SIZE) ? TEMP_BUF_SIZE : (size_t)*startOffset;
total += (UInt32)i;
*startOffset = -(Int64)i;
RINOK(SeekFromCur(stream, startOffset));
RINOK(LookInStream_Read2(stream, tempBuf, i, SZ_ERROR_NO_ARCHIVE));
for (; i != 0; i--)
if (tempBuf[i - 1] != 0)
break;
if (i != 0)
{
if ((i & 3) != 0)
return SZ_ERROR_NO_ARCHIVE;
*startOffset += i;
break;
}
}
if (*startOffset < XZ_STREAM_FOOTER_SIZE)
return SZ_ERROR_NO_ARCHIVE;
*startOffset -= XZ_STREAM_FOOTER_SIZE;
RINOK(stream->Seek(stream, startOffset, SZ_SEEK_SET));
RINOK(LookInStream_Read2(stream, buf, XZ_STREAM_FOOTER_SIZE, SZ_ERROR_NO_ARCHIVE));
if (memcmp(buf + 10, XZ_FOOTER_SIG, XZ_FOOTER_SIG_SIZE) != 0)
return SZ_ERROR_NO_ARCHIVE;
}
p->flags = (CXzStreamFlags)GetBe16(buf + 8);
if (!XzFlags_IsSupported(p->flags))
return SZ_ERROR_UNSUPPORTED;
if (GetUi32(buf) != CrcCalc(buf + 4, 6))
return SZ_ERROR_ARCHIVE;
indexSize = ((UInt64)GetUi32(buf + 4) + 1) << 2;
*startOffset = -(Int64)(indexSize + XZ_STREAM_FOOTER_SIZE);
RINOK(SeekFromCur(stream, startOffset));
RINOK(Xz_ReadIndex(p, stream, indexSize, alloc));
{
UInt64 totalSize = Xz_GetPackSize(p);
UInt64 sum = XZ_STREAM_HEADER_SIZE + totalSize + indexSize;
if (totalSize == XZ_SIZE_OVERFLOW ||
sum >= ((UInt64)1 << 63) ||
totalSize >= ((UInt64)1 << 63))
return SZ_ERROR_ARCHIVE;
*startOffset = -(Int64)sum;
RINOK(SeekFromCur(stream, startOffset));
}
{
CXzStreamFlags headerFlags;
CSecToRead secToRead;
SecToRead_CreateVTable(&secToRead);
secToRead.realStream = stream;
RINOK(Xz_ReadHeader(&headerFlags, &secToRead.s));
return (p->flags == headerFlags) ? SZ_OK : SZ_ERROR_ARCHIVE;
}
}
