private unsafe Stream GetBitmapStream(byte[] rawData)
{
try
{
try
{
fixed(byte *numRef = rawData)
{
IntPtr ptr = (IntPtr)numRef;
if (ptr == IntPtr.Zero)
{
return(null);
}
if ((rawData.Length <= sizeof(SafeNativeMethods.OBJECTHEADER)) || (Marshal.ReadInt16(ptr) != 0x1c15))
{
return(null);
}
SafeNativeMethods.OBJECTHEADER objectheader = (SafeNativeMethods.OBJECTHEADER)Marshal.PtrToStructure(ptr, typeof(SafeNativeMethods.OBJECTHEADER));
if (rawData.Length <= (objectheader.headersize + 0x12))
{
return(null);
}
if (Encoding.ASCII.GetString(rawData, objectheader.headersize + 12, 6) != "PBrush")
{
return(null);
}
byte[] bytes = Encoding.ASCII.GetBytes("BM");
for (int i = objectheader.headersize + 0x12; (i < (objectheader.headersize + 510)) && ((i + 1) < rawData.Length); i++)
{
if ((bytes[0] == numRef[i]) && (bytes[1] == numRef[i + 1]))
{
return(new MemoryStream(rawData, i, rawData.Length - i));
}
}
}
}
finally
{
numRef = null;
}
}
catch (OutOfMemoryException)
{
}
catch (ArgumentException)
{
}
return(null);
}
private unsafe Stream GetBitmapStream(byte[] rawData)
{
Debug.Assert(rawData != null, "rawData is null.");
try
{
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 (rawData.Length <= sizeof(SafeNativeMethods.OBJECTHEADER) || 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, but I found a KB:
//
// http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q175261
//
SafeNativeMethods.OBJECTHEADER pHeader = (SafeNativeMethods.OBJECTHEADER)Marshal.PtrToStructure(addr, typeof(SafeNativeMethods.OBJECTHEADER));
// "PBrush" should be the 6 chars after position 12 as well.
//
if (rawData.Length <= pHeader.headersize + 18)
{
return(null);
}
string strPBrush = System.Text.Encoding.ASCII.GetString(rawData, pHeader.headersize + 12, 6);
if (strPBrush != "PBrush")
{
return(null);
}
// okay, now we can safely trust that we've got a bitmap.
byte[] searchArray = System.Text.Encoding.ASCII.GetBytes("BM");
// search for "BM" 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 + 1 < rawData.Length; i++)
{
if (searchArray[0] == pByte[i] &&
searchArray[1] == pByte[i + 1])
{
// found the bitmap data.
//
return(new MemoryStream(rawData, i, rawData.Length - i));
}
}
}
}
catch (OutOfMemoryException) // this exception may be caused by creating a new MemoryStream
{
}
catch (ArgumentException) // may be caused by Marshal.PtrToStructure
{
}
// nevermind...
return(null);
}