Extract file from upload using POST get rid of header/footer

[Mike Doty]

How do you extract the file from an upload using POST?
Here is the start of the uploaded file, approximately.
The file is 548440 bytes.
The footer is simulated below
Content-length shows 548652.

-----------------------------7d91b51f14003a
Content-Disposition: form-data; name="userfile"; filename="\test\test.exe"
Content-Type: application/octet-stream
 
MZôõ` ÿÿH:  ~        
.
.
.
 
Footer looks like this:
-----------------------------7d91b51f14003a--

[Tom Hanlin]

There's an example of encoding file attachments in the PowerBASIC Gazette, number 33. Your headers there don't show what the encoding type is but, if it's the common Base64, you'll just need to reverse the Base64 encoding. The MZ suggests it may just be raw binary data, which would make it simple. MZ is the identifier at the start of an .EXE file.

[Jeff Blakeney]

In the header of the POST command, there will be a line that will tell you if the message has been MIME enocded and there will be a "boundary" string defined. In your case it is "7d91b51f14003a". Each section of the message will be enclosed between these strings:

-----------------------------7d91b51f14003a
-----------------------------7d91b51f14003a--

All you need to do is get the remainder of the message after the line that has "-----------------------------" + BoundaryString and then extract all the data up to the line that has "-----------------------------" + BoundaryString + "--". There will be another header in this section followed by CRLFCRLF. You can check those headers for more information. In your case, the Content-Type is set to application/octet-stream which is just a fancy way of saying 8 bit binary data.

The following code should pull out the actual binary data:

sBoundary = "7d91b51f14003a" ' set this from the boundary string in the POST header

sBoundaryStart = $CRLF + "-----------------------------" + sBoundary + $CRLF
sBoundaryEnd   = $CRLF + "-----------------------------" + sBoundary + "--" + $CRLF

' sMessage contains the original POST data
sData = REMAIN$(sMessage, sBoundaryStart)
sData = EXTRACT$(sData, sBoundaryEnd)
' insert code here to check the Content-Type if it might change
sData = REMAIN$(sData, $CRLF + $CRLF)
' insert code here to process the data if it isn't just 8 bit binary data

If the POST header says that it is a multi-part message, you may need to loop through each of the sections enclosed in the start and end boundary strings.

[Mike Doty]

That was it, thanks much!