From 96e063057d1d5ee037fb4a014e32cb5d88177b60 Mon Sep 17 00:00:00 2001
From: Elliot Nunn <elliotnunn@me.com>
Date: Tue, 23 Jun 2020 13:46:45 +0800
Subject: [PATCH] "Professionalise" greggybits

---
 bin/greggybits             | 11 +++++++----
 macresources/greggybits.py | 10 ++++++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/bin/greggybits b/bin/greggybits
index dede560..c3e1c1c 100755
--- a/bin/greggybits
+++ b/bin/greggybits
@@ -67,7 +67,7 @@ if __name__ == '__main__':
     args = parser.parse_args()
 
     for el in args.path:
-        from macresources.greggybits import pack, unpack
+        from macresources.greggybits import pack, unpack, WrongFormatError
 
         with open(el, 'r+b') as f:
             already_compressed = (f.read(4) == b'\xA8\x9Fer')
@@ -82,11 +82,14 @@ if __name__ == '__main__':
                     if args.debug: debug_round_trip(el, data)
                 else:
                     if args.debug: debug_round_trip(el, data)
-                    data = unpack(data)
+                    try:
+                        data = unpack(data)
+                    except WrongFormatError:
+                        continue
 
                 f.seek(0)
                 f.write(data)
                 f.truncate()
-            except ValueError:
+            except:
+                print(el)
                 raise
-                print('some kind of error')
diff --git a/macresources/greggybits.py b/macresources/greggybits.py
index 9f789b2..05edc86 100644
--- a/macresources/greggybits.py
+++ b/macresources/greggybits.py
@@ -21,6 +21,11 @@
 
 import struct
 
+
+class WrongFormatError(ValueError):
+    pass
+
+
 # predefined lookup table of the most frequent words
 TABLE = (
     0x0000, 0x0008, 0x4EBA, 0x206E, 0x4E75, 0x000C, 0x0004, 0x7000,
@@ -61,12 +66,17 @@ TABLE_DICT = {word: idx for (idx, word) in enumerate(TABLE)}
 
 
 def unpack(src, _calculate_slop=False):
+    if len(src) < 18: raise WrongFormatError
+
     dst = bytearray()
 
     pos = 0
     magic, hdrLen, vers, iscmp, unpackSize, _dcmp, _slop, tabSize, comprFlags = struct.unpack_from(">LHBBLHHBB", src, pos)
     pos += 18
 
+    if magic != 0xA89F6572 or hdrLen != 18 or vers != 9 or iscmp != 1 or _dcmp != 2:
+        raise WrongFormatError
+
     hasDynamicTab = comprFlags & 1
     isBitmapped   = comprFlags & 2