Tar-like module?

Drew Csillag drew_csillag at geocities.com
Fri Dec 21 15:20:01 CET 2001


On Thu, Dec 20, 2001 at 09:24:07PM -0500, Scott Fenton wrote:
> This may be an idiotic question, but is there a module
> to read tar files in python? I googled around and 
> couldn't find anything, and the Python Std Library docs
> didn't have anything. Any help would be nice.

As far as I know there isn't, but I've written the following module
which I've been using.

This (or something like it) should probably be in the standard library as
this question comes up often enough.  Guido...Hint... Hint...

Cheers,
Drew

"""Module for reading tar files"""
import string
import struct

def _checksum(ck, contents):
    sum = 0L
    for i in contents:
        sum += 0xFFL & ord(i)
        
    for i in contents[148:156]:  #treat checksum bytes as spaces
        sum -= 0xFFL & ord(i)
        sum += ord(' ')

    return sum == ck

def _cvtnulloctal(f, k=None):
    zi = f.find('\0')
    if zi > -1:
        f = f[:zi]
    try:
        return string.atoi(f, 8)
    except:
        return 0

def _tarstr(f):
    zi = f.find('\0')
    if zi > -1:
        f = f[:zi]
    return f

def _tf(name, *args):
    print name

def readTar(fileObj, tarEater=_tf):
    """Read through the contents of a tar archive

    fileObj is a file (or file-like) object
    tarEater is a callable object which takes the following arguments:
        name, contents, size, mode, uid, gid, mtime
        typeflag, linkname, uname, gname, devmaj, devmin
    """
    while 1:
        header = fileObj.read(512)
        if len(header) != 512:
            raise EOFError, 'Unexpected end of tar stream'

        (name, mode, uid, gid, size, mtime, cksum, typeflag,
         linkname, ustar_p, ustar_vsn, uname, gname, devmaj,
         devmin, prefix) = struct.unpack(
            '100s8s8s8s12s12s8s1s100s6s6s32s32s8s8s155s', header[:504])

        name, linkname, uname, gname, prefix = map(_tarstr, (
            name, linkname, uname, gname, prefix))

        mode, uid, gid, size, mtime, cksum, devmaj, devmin = map(
            _cvtnulloctal, (mode, uid, gid, size, mtime, cksum, devmaj,
                            devmin))
        if name:
            try:  
                typeflag = {
                    '': 'regular',
                    '0': 'regular',
                    '\0': 'regular',
                    '1': 'link',
                    '2': 'symbolic link',
                    '3': 'character special',
                    '4': 'block special',
                    '5': 'directory',
                    '6': 'fifo',
                    '7': 'reserved',
                    }[typeflag]
            except:
                raise KeyError, 'unknown file type in tar %X <%s> ' % (ord(typeflag), name)
            
        blocks_to_read = size / 512
        if size - (blocks_to_read * 512):
            blocks_to_read += 1
        contents = fileObj.read(blocks_to_read * 512)
        contents = contents[:size]

        if prefix:
            name = prefix + name 
        if name:
            ecount = 0
        else:
            ecount += 1
        if ecount == 2:
            break
        
        if name: #null name fields are normal in tar files, so have to check
            #here you would do whatever you wanted with the information
            #in: name, linkname, uname, gname, mode, uid,gid,size,mtime,devmaj
            #devmin, contents
            if not _checksum(cksum, header):
                raise ValueError, "checksum error -- %s" % name

            tarEater(name, contents, size, mode, uid, gid, mtime, 
                     typeflag, linkname, uname, gname, devmaj, devmin)
            
             

if __name__ == '__main__':
    import sys
    if sys.argv[1][-2:] == 'gz':
	import gzip
        readTar(gzip.GzipFile(sys.argv[1]))
    else:
        readTar(open(sys.argv[1]))
    




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