Question

I am trying to extract a byte string in .NET from a SQL Server database and convert it to an image. My Code looks something like this

Dim strqry As String = "SELECT preview FROM dbo.AmazonS3FilePreview WHERE fileKey ='" + incomingKey + "'"
    Dim myComm As SqlCommand = New SqlCommand(strqry, myConn)
    Dim resultReader As SqlDataReader = myComm.ExecuteReader
    Dim previewBytes As Byte() = Nothing
    While resultReader.Read()
        previewBytes = DirectCast(resultReader.Item("preview"), Byte())
    End While
    If Not previewBytes Is Nothing Then
        Dim ms As MemoryStream = New MemoryStream(previewBytes)
        Response.ContentType = "image/jpeg"
        Response.OutputStream.Write(ms.GetBuffer, 0, ms.GetBuffer.Length)
        Response.AddHeader("Content-Disposition", "attachment;filename=" + incomingKey)
    End If

However on the line Response.OutputStream.Write(ms.GetBuffer, 0, ms.GetBuffer.Length) I get an error saying UnauthorizedAccessException: MemoryStream's internal buffer cannot be accessed. I can definitely read regular char columns in the database, why are there issues with reading bytes?

Answer 1

You don’t need to use GetBuffer, and anyway you shouldn’t (it’s the internal buffer, which is larger than the actual data, so its length is meaningless). Actually, you don’t need a MemoryStream at all, since you already have the bytes. You can do it like this:

    Response.ContentType = "image/jpeg"
    Response.OutputStream.Write(previewBytes, 0, previewBytes.Length)