Utility to strip metadata from NSF2 files.

nsf2_strip.py

#!/usr/bin/env python3
import sys
assert sys.version_info[0] >= 3, "Python 3 required."

#
# nsf2_strip.py
# Brad Smith, 2018-08-25
#
# This strips metadata from NSF2 files.
#

import struct

in_nsf2 = "in.nsf"
out_nsf = "out.nsf"

show_cut = True

def nsf2_strip(nsf2):
    if len(nsf2) < 0x80:
        raise Exception("NSF2 too short for header?")
    nsf = bytearray(nsf2)
    version = nsf[5]
    nsf2_bits = nsf[0x7E]
    if version >= 2 and (nsf2_bits & 0x80) != 0:
        raise Exception("NSF2 metadata is flagged as essential.")
    suffix = nsf[0x7D] | (nsf[0x7E]<<8) | (nsf[0x7F]<<16)
    nsf[0x7D] = 0
    nsf[0x7E] = 0
    nsf[0x7F] = 0
    stripped = 0
    if suffix != 0:
        cut = suffix + 0x80
        if cut > len(nsf):
            raise Exception("NSF2 metadata pointer is past end of file?")
        stripped = len(nsf) - cut
        nsf = nsf[0:cut]
    if show_cut:
        print("%d bytes stripped." % stripped)
    return nsf

print("Reading " + in_nsf2  + "...")
nsf2 = open(in_nsf2,"rb").read()
nsf = nsf2_strip(nsf2)
print("Saving " + out_nsf + "...")
open(out_nsf,"wb").write(nsf)
print ("Done.")