如何从备份文件解码MySql Blob？

Question

I got a MySql backup file containing a column like:

CREATE TABLE `person` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`profilepicture` blob,
)

The content of this row profilepicture is encoded in the backup file to some kind of dump, starting (in a text editor) like this:

INSERT INTO `tbox_account_transaction` VALUES (8,'?\?\?0JFIF\0\0\0\0\0\0[...]');                  

How can I decode this from the .sql backup file in c#? It is not Base64, but I do not recognize what else it might be. I don't want to restore the backup.sql file to MySql but instead decode the blob from the backup file.

Answer 1

The bytes you are seeing are almost certainly the initial bytes of a JPEG image. The readable string "JFIF" starting at the fifth byte is the clue (see https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format ).

Many of the other binary bytes are null or else non-printable characters. All the weird \\? or \\0 sequences are the client's best effort at representing these bytes on your text display.

The easiest way to access this data is to restore the dump file to a MySQL instance (even a local one running on a laptop), and then use SQL in your C# code to access the binary contents of the profilepicture blob.

Either save the data from one blob to a .jpg file as @Tommaso Belluzzo suggests, or else just display it directly, if you can. I'm not a C# programmer, but it seems there's a Bitmap class for this (see https://msdn.microsoft.com/en-us/library/8tda2c3c(v=vs.85).aspx ).

It's outside the scope of a Stack Overflow answer to give a tutorial on how to write SQL in a C# application. There are plenty of resources available for that.

Answer 2

That looks like a jpg file header. Try the following ( blob is a String typed variable containing the profilepicture ):

using (MemoryStream stream = new MemoryStream(buffer))
{
    Image image = Image.FromStream(stream, true, true);
    image.Save("C:\\Test.jpg", ImageFormat.Jpeg);
}