private unsafe Stream GetBitmapStream(ReadOnlySpan <byte> rawData)
{
try
{
short signature = MemoryMarshal.Read <short>(rawData);
if (signature != 0x1c15)
{
return(null);
}
// The data is in the form of OBJECTHEADER. It's an encoded format that Access uses to push imagesinto the DB.
OBJECTHEADER pHeader = MemoryMarshal.Read <OBJECTHEADER>(rawData);
// pHeader.signature will always be 0x1c15.
// "PBrush" should be the 6 chars after position 12 as well.
if (rawData.Length <= pHeader.headersize + 18 ||
!rawData.Slice(pHeader.headersize + 12, 6).SequenceEqual(PBrush))
{
return(null);
}
// We can safely trust that we've got a bitmap.
// The start of our bitmap data in the rawdata is always 78.
return(new MemoryStream(rawData.Slice(78).ToArray()));
}
catch (OutOfMemoryException) // This exception may be caused by creating a new MemoryStream.
{
}
catch (ArgumentOutOfRangeException) // This exception may get thrown by MemoryMarshal when input array size is less than the size of the output type.
{
}
return(null);
}
private unsafe Stream GetBitmapStream(byte[] rawData)
{
Debug.Assert(rawData != null, "rawData is null.");
fixed(byte *pByte = rawData)
{
IntPtr addr = (IntPtr)pByte;
if (addr == IntPtr.Zero)
{
return(null);
}
//
// This will be pHeader.signature, but we try to
// do this first so we avoid building the structure when we shouldn't
//
if (Marshal.ReadInt16(addr) != 0x1c15)
{
return(null);
}
//
// The data is one of these OBJECTHEADER dudes. It's an encoded format that Access uses to push images
// into the DB. It's not particularly documented, here is a KB:
//
// http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q175261
//
OBJECTHEADER pHeader = (OBJECTHEADER)Marshal.PtrToStructure(addr, typeof(OBJECTHEADER));
//
// "PBrush" should be the 6 chars after position 12 as well.
//
string strPBrush = System.Text.Encoding.ASCII.GetString(rawData, pHeader.headersize + 12, 6);
if (strPBrush != "PBrush")
{
return(null);
}
// OK, now we can safely trust that we've got a bitmap.
byte[] searchArray = System.Text.Encoding.ASCII.GetBytes("BM");
//
// Search for "BMP" in the data which is the start of our bitmap data...
//
// 18 is from (12+6) above.
//
for (int i = pHeader.headersize + 18; i < pHeader.headersize + 510; i++)
{
if (searchArray[0] == pByte[i] &&
searchArray[1] == pByte[i + 1])
{
//
// found the bitmap data.
//
return(new MemoryStream(rawData, i, rawData.Length - i));
}
}
}
return(null);
}
