ZAP: new utility

This strips off Mark Pizzolato trailers from disk container.

extracters/zap.py

@@ -0,0 +1,92 @@
+#!/usr/bin/env python3
+
+"""SIMH disk container trailer stripper
+
+Copyright (C) 2022 by Paul Koning
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+Except as contained in this notice, the names of The Authors shall not be
+used in advertising or otherwise to promote the sale, use or other dealings
+in this Software without prior written authorization from the Authors.
+
+This program strips the "trailer" from Mark Pizzolato's version of SIMH from
+disk container files.
+
+To use it, run the script with the names of the containers to be
+stripped.  Two switches may be included in the argument list; they
+take effect when seen, so typically you will want them at the start of
+the argument list:
+
+-q: don't print any messages
+-f: if a trailer is found, strip it without asking
+
+By default, messages are printed as to whether a trailer is seen or
+not, and if found, the user is prompted whether to strip it.  In that
+prompt, the default answer is "no".
+"""
+
+import sys
+import io
+from zlib import crc32
+
+m1 = 0xffffffff
+force = quiet = False
+
+def zap (fn):
+    with open (fn, "r+b") as f:
+        l = f.seek (0, io.SEEK_END)
+        if l < 8192:
+            if not quiet:
+                print (fn, "is too small to consider")
+            return
+        lastblk = f.seek (-512, io.SEEK_END)
+        if lastblk % 512:
+            if not quiet:
+                print (fn, "is not a multiple of 512 bytes long")
+            return
+        tail = f.read (512)
+        if not tail.startswith (b"simh"):
+            if not quiet:
+                print (fn, "last block does not start with 'simh'")
+            return
+        c1 = crc32 (tail[:508]) & m1
+        c = int.from_bytes (tail[508:], "big")
+        if c1 != c:
+            print (fn, "trailer CRC does not match, {:0>8x} vs. {:0>8x}".format (c, c1))
+            return
+        if force or input ("{} strip trailer? ".format (fn)).lower ().startswith ("y"):
+            f.truncate (lastblk)
+            if not quiet:
+                print ("trailer stripped from", fn)
+        else:
+            if not quiet:
+                print (fn, "not changed")
+            
+if __name__ == "__main__":
+    args = sys.argv[1:]
+    if not args:
+        print ("usage: zap.py [-q] [-f] container ...")
+    for fn in args:
+        if fn == "-q":
+            quiet = True
+            continue
+        if fn == "-f":
+            force = True
+            continue
+        zap (fn)