From c66456a9e5232655bfb60d14b156fbbe326e588f Mon Sep 17 00:00:00 2001
From: kris <kris.kennaway@gmail.com>
Date: Sat, 15 Apr 2017 22:32:26 +0100
Subject: [PATCH] Initial support for reading .dsk images.

For each sector we compute a sha1 hash, and use this to recognie some common sector types (zero, common RWTS sectors)

Also compute the zlib compressibility of the sector as a way of estimating entropy, which might be useful in providing insight into whether it contains e.g. code or data.
---
 src/apple2disk/__init__.py |   0
 src/apple2disk/disk.py     | 118 +++++++++++++++++++++++++++++++++++++
 2 files changed, 118 insertions(+)
 create mode 100644 src/apple2disk/__init__.py
 create mode 100644 src/apple2disk/disk.py

diff --git a/src/apple2disk/__init__.py b/src/apple2disk/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/apple2disk/disk.py b/src/apple2disk/disk.py
new file mode 100644
index 0000000..bbfc712
--- /dev/null
+++ b/src/apple2disk/disk.py
@@ -0,0 +1,118 @@
+import bitstring
+import hashlib
+import os
+import sys
+import zlib
+
+SECTOR_SIZE = 256
+SECTORS_PER_TRACK = 16
+# TODO: support larger disks
+TRACKS_PER_DISK = 35
+
+TRACK_SIZE = SECTORS_PER_TRACK * SECTOR_SIZE
+
+class IOError(Exception):
+    pass
+
+class Disk(object):
+    def __init__(self, name, data):
+        self.name = name
+        self.data = data
+        # TODO: support larger disk sizes
+        assert len(data) == 140 * 1024
+
+        self.hash = hashlib.sha1(data).hexdigest()
+
+        self.sectors = {}
+        for track in xrange(TRACKS_PER_DISK):
+            for sector in xrange(SECTORS_PER_TRACK):
+                self.sectors[(track, sector)] = self._ReadSector(track, sector)
+
+    def _ReadSector(self, track, sector):
+        offset = track * TRACK_SIZE + sector * SECTOR_SIZE
+        if sector >= SECTORS_PER_TRACK or offset > len(self.data):
+            raise IOError("Track $%02x sector $%02x out of bounds" % (track, sector))
+
+        data = bitstring.BitString(self.data[offset:offset + SECTOR_SIZE])
+        return Sector(self, track, sector, data)
+
+    def ReadSector(self, track, sector):
+        try:
+            return self.sectors[(track, sector)]
+        except KeyError:
+            raise IOError("Track $%02x sector $%02x out of bounds" % (track, sector))
+
+    def RWTS(self):
+        return self.sectors[(0,0)]
+
+
+class Sector(object):
+    def __init__(self, disk, track, sector, data):
+        # Reference back to parent disk
+        self.disk = disk
+
+        self.track = track
+        self.sector = sector
+
+        self.data = data
+        self.hash = hashlib.sha1(data.tobytes()).hexdigest()
+
+        # Estimate entropy of disk sector
+        compressed_data = zlib.compress(data.tobytes())
+        self.compress_ratio = len(compressed_data) * 100 / len(data.tobytes())
+
+    KNOWN_HASHES = {
+        'b376885ac8452b6cbf9ced81b1080bfd570d9b91': 'Zero sector',
+        '90e6b1a0689974743cb92ca0b833ff1e683f4a73': 'RWTS (DOS 3.3 August 1980)',
+        '7ab36247fdf62e87f98d2964dd74d6572d17fff0': 'RWTS (DOS 3.3 January 1983)',
+        '16e4c17a85eb321bae784ab716975ddeef6da2c6': 'RWTS (DOS 3.3 System Master)',
+        '822c7450afa01f46bbc828d4d46e01bc08d73198': 'RWTS (ProntoDOS (1982))',
+        '30da15678e0d70e20ecf86bcb2de3fd3874dbd0d': 'RWTS (ProntoDOS (March 1983))',
+        '93d81a812d824d58dedec8f7787e9cfcc7a2d3b3': 'RWTS (Apple Pascal, Fortran)',
+        'adeb3be5c3d9487a76f1917d1c28104a1a6fc72f': 'RWTS (Faster DOS 3.3?)',
+        '4f4aff4e1eb8d806164544b64dc967abd76128a4': 'RWTS (ProDOS?)'
+    }
+
+    def HumanName(self):
+        try:
+            human_name = self.KNOWN_HASHES[self.hash]
+        except KeyError:
+            human_name = "Hash %s (Entropy: %d%%)" % (self.hash, self.compress_ratio)
+        return human_name
+
+    def __str__(self):
+        return "Track $%02x Sector $%02x: %s" % (self.track, self.sector, self.HumanName())
+
+def main():
+    disks = {}
+    for root, dirs, files in os.walk(sys.argv[1]):
+        for f in files:
+            if not f.lower().endswith('.dsk') and not f.lower().endswith('.do'):
+                continue
+
+            print f
+            b = bytearray(open(os.path.join(root, f), 'r').read())
+            try:
+                disk = Disk(f, b)
+                disks[f] = disk
+            except IOError:
+                continue
+            except AssertionError:
+                continue
+
+            for ts, data in sorted(disk.sectors.iteritems()):
+                print data
+
+    # Group disks by hash of RWTS sector
+    rwts_hashes = {}
+    for f, d in disks.iteritems():
+        rwts_hash = d.RWTS().hash
+        rwts_hashes.setdefault(rwts_hash, []).append(f)
+
+    for h, disks in rwts_hashes.iteritems():
+        print h
+        for d in sorted(disks):
+            print "  %s" % d
+
+if __name__ == "__main__":
+    main()