How to determine if data is valid tar file without a file?

Question

My upload form expects a tar file and I want to check whether the uploaded data is valid. The tarfile module supports is_tarfile(), but expects a filename - I don't want to waste resources writing the file to disk just to check if it is valid.

Is there a way to check the data is a valid tar file without writing to disk, using standard Python libraries?

Answer 1

Say your uploaded data is contained in string data.

from tarfile import TarFile, TarError
from StringIO import StringIO

sio = StringIO(data)
try:
    tf = TarFile(fileobj=sio)
    # process the file....
except TarError:
    print "Not a tar file"

There are additional complexities such as handling different tar file formats and compression. More info is available in the tarfile documentation.