Export Blob to File, what extension?

ta5

Hi
I want to export the files stored in myTable.myBlob to separate files, from a batch.
The problem is the extension. How can I give the correct file extension to the created files? It could be bmp, jpg etc., so I don't know.
Thx in advance
Thomas

lynge

Hi Thomas

Most files got magic numbers - a few bytes in the beginning identifying the type of the contents.
See https://en.wikipedia.org/wiki/Magic_number_(programming)

rocatis

Store the extension in a separate field when you populate the BLOB.

ta5

Hi experts
Thx for your answers. Because there are already data existing, I'll opt for the "Magic Numbers"!
Regards
Thomas

Marijn

I have some working code which does this. I'll post it here if I can still find it.

Marijn

What about this? This code can probably be improved in many ways, but it does the job for images and should get you going.

PROCEDURE GetFileType@1000000005(BlobRef@1000000000 : Record 99008535) : Text[3];
VAR
NVInStream@1000000005 : InStream;
MyChar@1000000004 : Char;
MyString@1000000003 : Text[10];
i@1000000002 : Integer;
Extention@1000000001 : Text[3];
BEGIN
//**
// Function to resolve file extension from the blob contents..
//*

BlobRef.Blob.CREATEINSTREAM(NVInStream);

FOR i := 1 TO 10 DO BEGIN
NVInStream.READ(MyChar, 1);
MyString += FORMAT(MyChar);
END;

IF COPYSTR(MyString, 7, 4) = 'JFIF' THEN
Extention := 'jpg'
ELSE IF COPYSTR(MyString, 2, 3) = 'PNG' THEN
Extention := 'png'
ELSE IF COPYSTR(MyString, 1, 3) = 'GIF' THEN
Extention := 'gif'
ELSE IF COPYSTR(MyString, 1, 2) = 'BM' THEN
Extention := 'bmp'
ELSE
ERROR('unresolved');

EXIT(Extention);
END;

ta5

Hi Marijn
Thx for the code. I'll give it a try!
Regards
Thomas