applesingle.py

r"""Routines to decode AppleSingle files
"""
import struct
import sys
try:
    import MacOS
    import Carbon.File
except:
    class MacOS:
        def openrf(path, mode):
            return open(path + '.rsrc', mode)
        openrf = classmethod(openrf)
    class Carbon:
        class File:
            class FSSpec:
                pass
            class FSRef:
                pass
            class Alias:
                pass

# all of the errors in this module are really errors in the input
# so I think it should test positive against ValueError.
class Error(ValueError):
    pass

# File header format: magic, version, unused, number of entries
AS_HEADER_FORMAT="LL16sh"
AS_HEADER_LENGTH=26
# The flag words for AppleSingle
AS_MAGIC=0x00051600
AS_VERSION=0x00020000

# Entry header format: id, offset, length
AS_ENTRY_FORMAT="lll"
AS_ENTRY_LENGTH=12

# The id values
AS_DATAFORK=1
AS_RESOURCEFORK=2
AS_IGNORE=(3,4,5,6,8,9,10,11,12,13,14,15)

class AppleSingle(object):
    datafork = None
    resourcefork = None

    def __init__(self, fileobj, verbose=False):
        header = fileobj.read(AS_HEADER_LENGTH)
        try:
            magic, version, ig, nentry = struct.unpack(AS_HEADER_FORMAT, header)
        except ValueError, arg:
            raise Error, "Unpack header error: %s" % (arg,)
        if verbose:
            print 'Magic:   0x%8.8x' % (magic,)
            print 'Version: 0x%8.8x' % (version,)
            print 'Entries: %d' % (nentry,)
        if magic != AS_MAGIC:
            raise Error, "Unknown AppleSingle magic number 0x%8.8x" % (magic,)
        if version != AS_VERSION:
            raise Error, "Unknown AppleSingle version number 0x%8.8x" % (version,)
        if nentry <= 0:
            raise Error, "AppleSingle file contains no forks"
        headers = [fileobj.read(AS_ENTRY_LENGTH) for i in xrange(nentry)]
        self.forks = []
        for hdr in headers:
            try:
                restype, offset, length = struct.unpack(AS_ENTRY_FORMAT, hdr)
            except ValueError, arg:
                raise Error, "Unpack entry error: %s" % (arg,)
            if verbose:
                print "Fork %d, offset %d, length %d" % (restype, offset, length)
            fileobj.seek(offset)
            data = fileobj.read(length)
            if len(data) != length:
                raise Error, "Short read: expected %d bytes got %d" % (length, len(data))
            self.forks.append((restype, data))
            if restype == AS_DATAFORK:
                self.datafork = data
            elif restype == AS_RESOURCEFORK:
                self.resourcefork = data

    def tofile(self, path, resonly=False):
        outfile = open(path, 'wb')
        data = False
        if resonly:
            if self.resourcefork is None:
                raise Error, "No resource fork found"
            fp = open(path, 'wb')
            fp.write(self.resourcefork)
            fp.close()
        elif (self.resourcefork is None and self.datafork is None):
            raise Error, "No useful forks found"
        else:
            if self.datafork is not None:
                fp = open(path, 'wb')
                fp.write(self.datafork)
                fp.close()
            if self.resourcefork is not None:
                fp = MacOS.openrf(path, '*wb')
                fp.write(self.resourcefork)
                fp.close()

def decode(infile, outpath, resonly=False, verbose=False):
    """decode(infile, outpath [, resonly=False, verbose=False])

    Creates a decoded file from an AppleSingle encoded file.
    If resonly is True, then it will create a regular file at
    outpath containing only the resource fork from infile.
    Otherwise it will create an AppleDouble file at outpath
    with the data and resource forks from infile.  On platforms
    without the MacOS module, it will create inpath and inpath+'.rsrc'
    with the data and resource forks respectively.

    """
    if not hasattr(infile, 'read'):
        if isinstance(infile, Carbon.File.Alias):
            infile = infile.ResolveAlias()[0]
        if isinstance(infile, (Carbon.File.FSSpec, Carbon.File.FSRef)):
            infile = infile.as_pathname()
        infile = open(infile, 'rb')

    as = AppleSingle(infile, verbose=verbose)
    as.tofile(outpath, resonly=resonly)

def _test():
    if len(sys.argv) < 3 or sys.argv[1] == '-r' and len(sys.argv) != 4:
        print 'Usage: applesingle.py [-r] applesinglefile decodedfile'
        sys.exit(1)
    if sys.argv[1] == '-r':
        resonly = True
        del sys.argv[1]
    else:
        resonly = False
    decode(sys.argv[1], sys.argv[2], resonly=resonly)

if __name__ == '__main__':
    _test()